BK virus was first discovered in a kidney transplant recipient who presented with a ureteral stricture in 1971. In 1993 was the first definitive biopsy proven case of BKVAN was described. BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family . The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region. Epidemiology The seroprevalence rates of over 90% by 4 years of age . The primary routes for virus transmission are: from mucosal contact including the oral, gastrointestinal, and respiratory tract. After a primary viremia, the BK virus settled in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection. In post-transplant patient, viral replication mostly occurs in the first year because of the high immunosuppression drugs doses. Viral replication is associated with the following risk factors: 1. Intensity of immunosuppression. 2. Recipient characteristics: older age, diabetes , and specific HLA-C alleles 3.The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement. 4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant . Clinical manifestations : 1- Viuria ; up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia but sensitive marker to progression to BKVAN. 2- Viremia is present in 10–30 percent of recipients in the first six months post-transplantation and in 5–10 percent of recipients thereafter. Viremia is a better predictor of progression to BKVAN in comparison to viruria . 3- BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities. Mostly occurs within the first post-transplant year due to attenuated cellular immunity, with the highest incidence in the first 2–6 months being periods . 4- Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis. 5- There are reports of a possible link between the BK virus and genitourinary (GU) malignancies. Screening and Diagnosis:
The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 month. 1- Urine BK PCR: Urine BK PCR is not a recommended screening test because if positive, it requires confirmation with plasma PCR. Around fifty percent of patients with viruria will not develop viremia. 2- Plasma BK PCR: The World Health Organization (WHO) established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL in 2016.
The genotype I (Dunlop) strain is currently utilized as the reference sequence against which primers and probes are designed for various assays. A viral load > or equal to 10,000 is diagnostic. 3- Urine cytology : This will reveal the characteristic BK virus-infected cells called decoy cells due to their similarity to renal carcinoma cells. These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin . They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin. Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN. 4- Donor-Derived Cell-Free DNA (dd-cfDNA) : A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN. It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN .
5-Transplant Kidney Biopsy:
1- Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen.
6- Histology : The histologically, tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intra-nuclear inclusions. Viral cytopathic changes may also include granular nuclear inclusions Viral cytopathic changes may also include granular nuclear inclusions and clumps of intra-nuclear virion particles.
Treatment :
A- Immune suppression reduction:
1- Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. Monitor creatinine and viral load every 2 weeks.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
B- IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression (balancing with risk of rejection). The rationale for use is the presence of BK-neutralizing antibodies in IVIG preparations C- Quinolones: Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia . D- Cidofovir: A nucleotide analog of cytosine has demonstrated activity against Polyomaviridae in-vitro . Studies have shown no benefit with cidofovir use. Cidofovir is associated with proteinuria, proximal tubular dysfunction, and kidney disease . 4. Leflunomide: A prodrug that converts to an active metabolite, A77 1726, which has demonstrated both immunosuppressive and anti-viral properties . While there was initial enthusiasm for its use in BK virus infection based on a case series, a pharmaco-dynamic and prospective open-label study showed no benefit . Another metabolite, FK778, did not demonstrate efficacy in a phase 2, proof-of-concept, randomized, open-label, parallel-group, 6-month study in kidney transplant patients when compared with a reduction in immunosuppression . Kidney Re-Transplantation Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success. Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation. Allograft survival in patients who re-transplanted is 98% and 94% at 1 and 3 years, respectively .
BKvirus infection is still one of the most frequent clinical problems that transplant doctors confront.Increased surveillance procedures have sped up disease detection and lessened its severity. In terms of diagnosis and treatment, it can also be confusing. The only effective treatment is to reduce immunosuppression, which may lead to rejection in the end. It can be accompanied by histologic characteristics resembling rejection. Furthermore, no antiviral is now known to be helpful in the removal of the infection. However, there is hope that innovative treatments could deliver the efficacy that the transplant community has yet to achieve.
BK virus-associated nephropathy (BKVAN) is a significant cause of graft loss in kidney transplant recipients.
BK viremia (BKV) occurs in up to 30% of kidney transplant recipients, despite advancements in immunosuppression.
This review provides an extensive overview of BKVAN, including viral epidemiology, pathogenesis, screening, diagnosis, clinical manifestations, and treatment strategies.
History of the BK Virus:
BK virus was first discovered in a kidney transplant recipient in 1971, and the first confirmed case of BKVAN was reported in 1993.
The increasing incidence of BK viremia may be attributed to improved testing methods and more potent immunosuppression.
Graft loss rates due to BKVAN have decreased to under 15% in the last two decades.
Virology:
BK virus is a small, non-enveloped, double-stranded DNA virus belonging to the Polyomaviridae family.
The virus consists of three regions: the early coding region, the non-coding control region, and the late coding region.
Mutations in the non-coding control region affect viral replication and tropism, while the late coding region codes for structural proteins and the agnoprotein.
Epidemiology:
BK virus infection is widespread in the general population, with seroprevalence rates of over 90% by age 4.
The primary routes of transmission are through mucosal contact, such as the oral, gastrointestinal, and respiratory tract.
BK viremia occurs in kidney transplant recipients via reactivation of latent infection or transmission from the donor kidney.
Risk factors for BK viral replication include intensity of immunosuppression, recipient characteristics, donor-recipient interface, and donor-related factors.
Cellular Immune Response and Pathogenesis:
Cellular immune response plays a crucial role in mitigating and clearing BK viremia, with CD4 and CD8 cells involved in the process.
T cell responses are elicited by BK viral proteins and are associated with the resolution of BKVAN.
BKVAN typically occurs after sustained viremia, resulting in renal function decline and urinary abnormalities.
Clinical Manifestations and Complications:
In addition to BKVAN, the BK virus can cause ureteral stenosis, hemorrhagic cystitis, and possibly be linked to genitourinary malignancies.
The occurrence of malignancies in transplant recipients may be attributed to lowered cellular immunity and reduced tumor surveillance.
Screening and Diagnosis:
BK viremia screening protocols are recommended in the first post-transplant year, with monthly screenings for the initial six months and then every three months.
Plasma BK PCR is the preferred screening method due to its higher positive predictive value compared to urine BK PCR.
Urine cytology and the presence of PV-Haufen can aid in the diagnosis of BKVAN.
Donor-derived cell-free DNA (dd-cfDNA) has shown potential as a noninvasive test to assess the progression of BKV to BKVAN.
Transplant kidney biopsy remains the gold standard for diagnosing BVAN and assessing the severity of viral involvement and other pathologies.
Summary of the article : -The article discusses in detail the BK virus in context of renal transplantation regarding the virology, replication and risk factors, presentation, and finally the management. -Risk factors include immunosuppression, elderly individuals, white race, HLA –ABO mismatch and ureteric insults. -Presentation varies from asymptomatic picture to BK nephropathy, ureteric stenosis or hemorrhagic cystitis. -Management starts by proper diagnosis through plasma PCR of the virus+ renal biopsy with evidence of viral inclusions. -Treatment mainly entails reduction of IS; reduction of antimetabolites by 50% and complete cessation if no proper response, reduction of CNI’s. -No strong evidence of antivirals against -IVIG may have a role especially in the setting of rejection and BKVN.
This article is about BK virus infection in kidney transplant recipients. The different aspects related to this infection, along with the necessary screening practices and the diagnostic and therapeutic challenges posed. This review extensively covers viral epidemiology, pathogenesis, screening and diagnostic methods, clinical manifestations and recommended treatment strategies.
Discussion
BKV infection is an important cause of graft loss in renal transplant recipients. The history of the virus goes back to 1971 when it was discovered in a kidney transplant recipient presenting with ureteral stricture.
BK virus is a small non enveloped icosahedral closed circular double stranded DNA virus that is a member of the polyomaviridae family. The viral genome is of 3 regions – the early coding region of the large T and small t antigens, the non coding control region, and the late coding region.
The T antigen binds to p53 and Rb protein, taking control of cell cycle and leading to persistent infection. The non coding parts of the virus assist in pathogenesis of the virus. Mutations in the non coding region lead to replication of the virus.
BK virus infection is seen as primary infection in childhood, below the age of 4 years. Transmission routes of the virus include mucosal contact – oral, gastrointestinal, and respiratory tract. Viral replication is linked with risk factors such as :
intensive immunosuppression
recipient characteristics such as old age, diabetes, specific HLA C alleles.
donor recipient interface factors such as ABo incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of transplanted kidney, ureteral stent placement, seropositive donor with negative recipient.
Donor associated factors such as reduced immune response to BKV, BK viruria prior to transplant.
Clinical manifestations in these patients may not be prominent in all cases. Many patients are asymptomatic. The sequence of the infection in the patient includes viruira, viremia, and BKVAN.
Investigations includes plasma BK PCR, urine cytology, and transplant kidney biopsy. Urine PCR is not recommended for screening since it always required confirmation with plasma PCR and lack of specificity. It is also more expensive.
Transplant kidney biopsy is gold standard for diagnosis. The following characteristics on biopsy will form part of definitive diagnosis of BKVAN :
characteristic cytopathic changes such as tubular epithelial cells with enlarged hyper chromatic nuclei and “ground glass” intranuclear inclusions.
positive immunohistochemistry tests using antibodies directing against BKV or against cross reacting SV40 large T antigen.
Treatment involves reduction in immunosuppression, monitoring of serum creatinine and serial plasma BK PCRR levels. IVIG, quinolone, cidofovir, and leflunomide are other therapies that are part of the treatment regimen for these patients.
Conclusion
BK virus infection and BKVAN can lead to graft loss in transplant patients. Heightened surveillance protocols are needed for early detection and effective treatment in order to mitigate severe disease. Further studies are need sot hat novel therapeutics can be used to increase treatment efficacy and prevent rejection.
Review BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review. Introduction:
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
Rates of BK viremia (BKV) is up to 30% of kidney transplant recipients. History of the BK Virus:
Discovered in patient with ureteral stenosis.
early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported .The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% . Virology BK virus:
Is a small, non-enveloped, icosahedral, double-stranded DNA virus and member of the Polyomaviridae family?
The genome of the virus consists of three regions: The early coding region:
Of the large T and small t antigens (large and small tumor antigen), T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection. The non-coding control region, contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
Mutations in the non-coding control regions result in permit replication in other cell types (permissively), cell tropism, and altered rates of replication .These mutations correlate with high BK virus loads in kidney transplant recipients with clinically significant viral replication And the late coding region code for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). The agnoprotein .The agnoprotein is responsible for the assembly of viral capsids and the release of virions from cells.
VP-1 is the major structural protein that engages with cellular receptors and has significant genetic heterogeneity.
Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases. Epidemiology: Prevalence:
Seroprevalence rates of over 90% by 4 years of age. Routes for transmission:
Mucosal contact including the oral, gastrointestinal, and respiratory tract.
After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelium cells resulting in lifelong latent/persistent infection. Risk factors for viral replication is associated with the following:
1- Intensity of immunosuppression
2– Recipient characteristics: older age, diabetes, and specific HLA-C alleles. 3-the donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus ,ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN. Cellular Immune Response and Pathogenesis:
Virus maintains persistent infection after initial childhood infection this latent infection can become active with reduced potency of cellular immunity.
Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss. Clinical Manifestations:
Asymptomatic.
In kidney transplant patient: Viruria: up to 50% of patients in the first year of transplantation, with most cases not progressing to Viremia.
Viremia:
Present in 10–30 percent of recipients in the first six months post transplantation and in 5–10 percent of recipients thereafter. BKVAN:
Manifesting as a decline in renal function with or without urinary abnormality.
Majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence.
Other manifestations of the BK virus include:
Ureteral stenosis and hemorrhagic cystitis—albeit rare in Renal transplant more in HSCT. Screening and Diagnosis:
KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months. Urine BK PCR:
Is not a recommended low specificity and cost—if positive, it always requires confirmation with plasma PCR and nearly fifty percent of patients with viruria will not develop viremia? Plasma BK PCR:
Is the preferred method, higher positive predictive value of plasma BK levels?
A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL Urine Cytology: Decoy cells, these are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. “Owl eye” inclusions, multinucleation, or clumped chromatin. Although decoy cells are high false-positive rates and low positive predictive values. Haufen:
Has extremely high positive and negative predictive values for BK nephropathy, respectively. Donor-Derived Cell-Free DNA (dd-cfDNA):
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVA.
Transplant Kidney Biopsy: Kidney allograft biopsy:
Aid not only in diagnosis, but also in assessing the severity of viral involvement and the presence of other ongoing pathologies.
The following pathologic features:
1. Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN);
Although, it does not distinguish between BKV and JC virus. Histology:
Due to focal nature of infection two biopsy cores containing renal cortex and medulla are recommended. Virus: Enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions
Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles. Tubular cells: lyse and slough from the basement membrane into the tubular lumens.
Then tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.
More proximal portions of the nephron, including the parietal epithelial cells lining Bowman′s capsule, may also become involved. Other test on biopsy sample:
Currently, it is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen.
Quantitative PCR for PV can also be performed on tissue samples.
PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of TUBULES.
A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN.
Treatment:
Mainstay is IS reduction.
1-Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies:
Include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin. A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir.
Intravenous immunoglobulin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended. Kidney Retransplantation:
Extensive evidence of success
Failed transplant or native nephrectomy is not recommended.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
There was no significant difference in the rates of acute rejection or patient survival at one year. Conclusions:
BK virus infection continues to be one of the most common clinical issues.
It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection.
There is no anti-viral currently known to be of benefit in the clearance of the virus.
Introduction:
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in
kidney transplant recipients, anda risk factor for graft loss.
Increasing efficacious immunosuppression leads to increasing BK viremia, other viruses, and opportunistic infections. Epidemiology:
In transplant cases, viral replication is associated with the following risk factors;
The intensity of immunosuppression.
Recipient characteristics; (Age, DM, and specific HLA-C alleles).
The D/R interface; (serostatus, ABO incompatibility, HLA MM, DGF, rejection, ischemia, and ureteral stent placement).
Donor-related factors (reduce the immune response to BK virus, and BK viruria prior to transplantation)
Clinical manifestation:
1) Viruria, up to 50% of recipients in the 1st year of transplantation.
2) Viremia may be asymptomatic, present in 5-10% of recipients in the 1st 6 months post-Tx, a predictor of BKVAN.
3) BKVAN, after sustained progressive viremia, is associated with reduced graft function, manifested by ureteral stenosis, and hemorrhagic cystitis, with controversial oncogenic properties of BKV.
4) There is a possible link between BKV and genitourinary malignancy. Screening and diagnosis:
The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
KDIGO and AST-IDCOP; recommend monthly screening for the 1st 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BK PCR: not recommended screening test.
Plasma BK PCR.
Urine cytology: characteristic decoy cells, (but similar to renal cell carcinoma), considered as a marker of PV replication, also there are owl eye inclusions.
Donor-derived cell-free DNA: higher dd-cfDNA levels associated with higher BK viral loads, biopsy diagnosed BKVAN, as well as histologic changes meeting Banff criteria for t-cell mediated rejection, and it may be used as a useful noninvasive test for progression of BKV to BKVAN.
Graft biopsy: the gold standard for the diagnosis of BKVAN, assesses the severity of the disease, and a definitive diagnosis based on characteristic cytopathic changes and positive immunohistochemistry.
Histology: tubular epithelial cells, with enlarged hyperchromatic nuclei and ground glass intranuclear inclusion, clumps of virion particles.
Treatment:
The reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.by stepwise approach:
1) Reduce the antimetabolite by half and keep the CNI dose and prednisolone.
2) Complete cessation of antimetabolite if viremia and viral load persist.
3) Reduce CNI dose if viral load persists over 4 weeks after complete cessation of antimetabolite with target truth level of (4-6 ng/ml for TAC, and 50-100 ng/l for CyA).
4) IVIG; in case of nonresponse to a maximum reduction of IS.
5) Quinolones; have anti-viral properties.
6) Cidofovir; has no benefit with the risk of graft dysfunction.
7) Leflunomide; an active metabolite exhibits immunosuppressive and anti-viral properties. Kidney Re-Transplantation:
Patients with graft loss due to BKVAN should be considered for re-transplantation
given its extensive evidence of success.
Nephrectomy of failed graft or native kidney is not recommended prior to re-transplantation.
BK polyomavirus (BKPyV) is a small DNA virus that establishes lifelong infection in the renal tubular and uroepithelial cells of most of the world’s population
Epidemiology-
BK polyomavirus (BKPyV) is a ubiquitous virus with a worldwide seroprevalence of approximately 80 to 90 percent Primary infection is typically acquired during childhood, possibly via fecal-oral or respiratory transmission . Following primary infection, the virus establishes lifelong infection in renal tubular and uroepithelial cells.
Viruria and viremia-Viruria is the earliest manifestation of BKPyV infection in kidney transplant recipients, affecting approximately one-quarter to one-third of patients during the first year following transplantation For most, viruria is asymptomatic, detected only by screening, and does not progress to viremia While viruria is a sensitive marker for progression to BKPyV-associated nephropathy (BKPyVAN), it is nonspecific . Viremia may follow viruria in a few weeks and occurs most frequently in those with high urine viral loads and sustained viruria. Viremia is detected in 10 to 30 percent of recipients in the first six months posttransplantation and in 5 to 10 percent of recipients thereafter. As with viruria, viremia is typically asymptomatic. However, viremia has a greater predictive value than viruria for progression to BKPyVAN.
Risk factors for viral replication –
The intensity of immunosuppression (particularly suppression of cellular immunity) appears to be a dominant risk factor for BKPyV replication and disease. Several studies have suggested that certain drugs (particularly tacrolimus) may be associated with an increased relative risk Other important risk factors include high risk serostatus (ie, kidney transplant from a BKPyV-.seropositive donor to a seronegative recipient) impaired immune response to BKPyV and donor BKPyV viruria prior to transplant. The last two factors suggest that the donor is an important source of transmission .
Other risk factors associated with an increased risk of BKPyVAN or disease severity include older age, ureteral stent placement, ABO incompatibility rejection or ischemia of the transplanted kidney , delayed graft function HLA mismatch specific HLA-C alleles , BKPyV polymorphisms , and transplantation from an HCV-positive donor .
Recipient HLA-B51 positivity and the presence of polycystic kidney disease,have been shown to be protective factors against the development of BKVAN.
Clinical Picture of BK virus infection-
BK polyomavirus (BKPyV) replication typically develops in stages: viruria followed by viremia and then, if viral replication persists, nephropathy can ensue. Asymptomatic viruria, viremia, and/or a slow progressive rise in serum creatinine are typically the only indicators of BKPyVAN. The incidence of BKPyVAN is highest in the first two to six months posttransplant. While the majority of cases occur in the first posttransplant year, BKPyVAN can occur years after transplantation. . Without resolution of infection, progressive kidney allograft dysfunction and graft loss can ensue over a period of months . Within the allograft, early infection triggers interstitial inflammation, which then progresses to fibrosis and tubular injury. Accordingly, urinalysis may reveal pyuria, hematuria, and/or cellular casts consisting of renal tubular cells and inflammatory cells, or may be normal.
Other manifestation-ureteral stenosis and In bone marrow transplant recipients, BKV can lead to hemorrhagic cystitis.
Posttransplant screening —
Screening and preemptive reduction in immunosuppression for patients with clinically significant BKPyV viremia prevent progression to BKPyVAN in the majority of patients. Screening should be done with Plasma PCR Monthly for the first six months following transplant, then every three months until 18 months posttransplant,
Testing methods-
Plasma quantitative PCR —
Quantification of plasma BKPyV DNA by real-time polymerase chain reaction (PCR) is the preferred screening test for BKPyVAN at most transplant centers The detection of BKPyV viremia by plasma quantitative PCR is both highly sensitive (100 percent) and specific (88 percent) for the diagnosis of BKPyVAN and has a higher positive predictive value for BKPyVAN than the detection of viruria by urine quantitative PCR or urine cytology (50 to 60 percent versus 40 and 29 percent, respectively)
Urine quantitative PCR-
patients who are found to have viruria require confirmation with quantitative plasma PCR, since approximately one-half of patients with BKPyV viruria will not develop viremia or BKPyVAN. As such, the cost effectiveness of this approach has been questioned
Urine cytology in BK virus nephropathy-
Cytologic examination of the urine, which may reveal BKPyV-infected cells, Decoy cells,is infrequently used to screen for BKPyVAN.These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin . They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin. Decoy cell are less sensitive and specific for the diagnosis of BKPyVAN compared with plasma quantitative PCR.Negative-staining electron microscopy of the urine of patients with BKPyVAN often reveals the presence of cast-like, three-dimensional polyomavirus aggregates, termed Haufen .he detection of Haufen in voided urine had a sensitivity, specificity, negative predictive value, and positive predictive value for biopsy-proven BKPyVAN of greater than 95 percent
Donor-Derived Cell-Free DNA (dd-cfDNA)
A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN.
Kidney allograft biopsy-
Because biopsy is invasive and sampling error can occur, a presumptive diagnosis is often made based upon the presence of significant viremia (plasma BKPyV viral load ≥10,000 copies/mL).
A definitive diagnosis of BKPyVAN requires the following findings on kidney biopsy
Characteristic cytopathic changes. plus
Positive immunohistochemistry tests using antibodies directed specifically against BKPyV or against the cross-reacting SV40 large T antigen.
In BKVN, light microscopy examinations would show the following:
(1) basophilic intranuclear viral inclusions without a surrounding halo ; (2) anisonucleosis, hyperchromasia, and chromatin clumping of infected cells; (3) areas of tubular damage showing interstitial mononuclear or polymorphonuclear cell infiltrates (4)tubular injury in the form of tubular cell apoptosis, desquamation, and flattened epithelial liningand (5) tubulitis with lymphocyte invasion to the basement membrane of the tubular epithelium
Distinguishing BKPyVAN from rejection-
BKPyVAN is generally distinguished from rejection by the presence of BKPyV inclusions and immunohistologic or in situ hybridization evidence of virally infected cells, which are usually tubular epithelial cells, rather than podocytes or endothelial cells .It is important to correlate the histologic findings with PCR evidence of viremia. Establishing a diagnosis of concomitant T cell-mediated rejection in a biopsy that has BKPyVAN is difficult since both the histologic features and transcriptional profiles of these two disorders are similar. In general, the presence of extensive tubulitis in areas remote from the viral cytopathic changes suggests that acute rejection is present, in addition to BKPyVAN. The combined presence of endarteritis, fibrinoid vascular necrosis, glomerulitis, and C4d deposits along peritubular capillaries is conclusive evidence of concurrent rejection
Treatment-
Since there are no specific antiviral therapies for BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN), the cornerstone of management is to decrease immunosuppressive medications .In patients who are on a triple immunosuppression therapy consisting of a calcineurin inhibitor , an antimetabolite and prednisone, we initially reduce the dose of the antimetabolite by 50 percent. If the BKPyV viral load does not decrease within two to four weeks, we completely discontinue the antimetabolite. If there is still no decrease in viral load after another two weeks, we decrease the dose of the calcineurin inhibitor by 25 to 50 percent, targeting a whole blood tacrolimus trough level of 4 to 6 ng/mL or a whole blood cyclosporine trough level of 60 to 100 ng/mL
Adjunctive therapies –Several agents have been shown to have in vitro anti-BKPyV activity. However, we do not routinely use any of these agents for the treatment of BKPyV infection, given that the efficacy of these agents has not been established and use of these therapies has not been clearly shown to be superior to reduction in immunosuppression alone
Increasing efficacious immunosuppression leads to increasing BK viremia, other viruses, and opportunistic infections.
Epidemiology In transplant cases, viral replication is associated with the following risk factors;
The intensity of immunosuppression.
Recipient characteristics; (Age, DM, and specific HLA-C alleles).
The D/R interface; (serostatus, ABO incompatibility, HLA MM, DGF, rejection, ischemia, and ureteral stent placement).
Donor-related factors (reduce the immune response to BK virus, and BK viruria prior to transplantation).
Clinical manifestation
Viruria, up to 50% of recipients in the 1st year of transplantation.
Viremia may be asymptomatic, present in 5-10% of recipients in the 1st 6 months post-Tx, a predictor of BKVAN.
BKVAN, after sustained progressive viremia, is associated with reduced graft function, manifested by ureteral stenosis, and hemorrhagic cystitis, with controversial oncogenic properties of BKV.
There is a possible link between BKV and genitourinary malignancy.
Screening and diagnosis
KDIGO and AST-IDCOP; recommend monthly screening for the 1st 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BK PCR; not recommended screening test.
Plasma BK PCR.
urine cytology; characteristic decoy cells, (but similar to renal cell carcinoma), considered as a marker of PV replication, also there are owl eye inclusions.
Donor-derived cell-free DNA; higher dd-cfDNA levels associated with higher BK viral loads, biopsy diagnosed BKVAN, as well as histologic changes meeting Banff criteria for t-cell mediated rejection, and it may be used as a useful noninvasive test for progression of BKV to BKVAN.
Graft biopsy; the gold standard for the diagnosis of BKVAN, assesses the severity of the disease, and a definitive diagnosis based on characteristic cytopathic changes and positive immunohistochemistry.
Histology; tubular epithelial cells, with enlarged hyperchromatic nuclei and ground glass intranuclear inclusion, clumps of virion particles.
Treatment stepwise approach;
Reduce the antimetabolite by half and keep the CNI dose and prednisolone.
Complete cessation of antimetabolite if viremia and viral load persist.
Reduce CNI dose if viral load persists over 4 weeks after complete cessation of antimetabolite with target truth level of (4-6 ng/ml for TAC, and 50-100 ng/l for CyA).
IVIG; in case of nonresponse to a maximum reduction of IS.
Quinolones; have anti-viral properties.
Cidofovir; has no benefit with the risk of graft dysfunction.
Leflunomide; an active metabolite exhibit immunosuppressive and anti-viral properties.
Upcoming therapeutic trial
IgG1; binds the viral capsid protein VP1.
Adoptively transferred posoleuccel (ALVR105) multi-virus-specific T Cells in kidney transplant recipients.
Kidney re-transplantation
Re-transplantation after graft loss due to BKVAN can be provided with extensive evidence of success.
Nephrectomy of failed graft or native kidney is not recommended prior to re-transplantation.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review.
1. Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in
kidney transplant recipients.
The potent immunosuppression lead to high rates of BK viremia (BKV) in about 30% of kidney
transplant recipients.
its discovered in 1971, but till now there is no effective treatment or prophylaxis .
This review provides an extensive overview of viral epidemiology, pathogenesis, screening, and
diagnostic methods. 2. History of the BK Virus:
BK virus was first discovered in Sudanese a kidney transplant recipient presented with a
ureteral stricture in 1971 .
During the period of its early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported .
The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% within the last 2 decades .
Virolology:
BK virus belongs to a family of polyomavirus family, small ds-DNA virus, categorized into four groups with different activity .
The genome consists of three region.
1. Large T, small t antigen (bind to p53, protein Rb and lead to persistant infection.
2. Non-coding control region (it causes replication, and enhance elements and modulate transcription ).
3. Late coding region (codes for agnoprotein responsible for assembly of viral capsids VP-1 and release of virion, and viral capsid protein.
Epidemiology:
The prevalence rates is about 90% by 4 years of age
transmission route : fecooral – through mucosal contact ( oral, gastrointestinal, and respiratory tract)
post a primary infection , the BK virus infect the kidney and uroepithelial cells lead to lifelong latent/persistent infection.
Frequently occur in first year , the time of most immunosuppression state.
infection occurs in kidney transplant either by reactivation of latent infection or transmission of new infection from the donor.
Viruria and viremia are occur in about 30% and 12% of kidney transplant recipients, respectively.
Viremia occur in 50% of viruric patient , BKVAN occur in 50% of viremic patient.
Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology. Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age , diabetes, and specific HLA-C alleles .
3. The donor–recipient interface.
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant [
Cellular Immune Response and Pathogenesis:
Control of BK viremia are dependent competent cellular immune response- of both CD4 and CD8 cells type .
The shorter time needed (<1 month) to appear anti-BK T cell response associated with the clearance of viremia, while recipient who develop BKVAN need a median period of 5 months to achieve cellular immunity toward the virus.
The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium.
Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways .
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
clinical manifestation :
1- Usually asymptomatic .
2- Stepwise progression involves : Viruria then viremia and then BKVAN.
3- Usually present in the first year post kidney transplant time of potent immunosuppression.
4- Urine BK viral loads is not standard practice in diagnosis of BKVAN but is assign of disease progression.
5- Viremia is asymptomatic but it is a useful tool for progression to BKVAN
6- BKVAN usually manifests as graft dysfunction.
7- Ureteral stenosis mau occur.
8- Hemorrhagic cystitis is rare complication commonly occur in in hematopoietic stem cell transplants patients.
9- Genitourinary (GU) malignancies – data is not conclusive .
Screening and Diagnosis:
1- Urine BK virus PCR .
2- plasma BK virus PCR .
3- Urine cytology: decoy cell.
4- Donor-Derived Cell-Free DNA (dd-cfDNA).
Treatment :
Stepwise approach to reduce immunosssuppression:
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin
inhibitor and/or prednisone. With serial plasma BK PCR levels from the same laboratory every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus
and 50–100 ng/L for cyclosporine).
Other adjunctive therapies utilized to treat BK virus infection :
1. IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression. It is benefit still not ctear. It is only viable adjunctive therapy
2. Quinolones: Studies not prove its efficacy as prophylaxis or treatment .
3. Cidofovir: Studies shows negative results with wide range of side effect.
4. Leflunomide: Some study showed no benefit.
9. Kidney Re-Transplantation: – Patients with graft loss due to BKVAN should be considered for re-transplantation
given its extensive evidence of success .
-Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
Introduction BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. The advancement in effective IS therapy increased the rate BK viremia in up to 30% of kidney transplant recipients.
History of the BK virus Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN. The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL. The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
Virology Small double-stranded DNA virus and member of the Polyomaviridae family – It has 4 different genotypes ( I- IV) – The genome of the virus consists of three regions; the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
Epidemiology
BKV is ubiquitous – 90% seroprevalence by 5 years age
Transmission through respiratory and faeco-oral route – remains latent in the kidney and urothelial cells
BKV infection post renal transplant can be due to reactivation of latent infection or transmission from the donor kidney
Chronology of infection course –
– Viruria precedes viremia by 4-6 weeks, and BKVAN by 6-10 weeks
– urine BK viral load > 8 log10 copies/mL predict the onset of viremia
– plasma BK viral load > 4 log10 copies/mL are associated with higher rates BKVAN
– plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN (SV40-IHC and inflammatory infiltrates) Risk factors –
Intense immunosuppression is most important risk factor – highest incidence of BKV infection during early post-transplant period
Older age, diabetes, specific HLA-C alleles recipients
Donor-related factors – reduced immune response to BKV, BK viruria prior to transplant
Donor-recipient interface – BKV serostatus D+/R-, ABO-incompatible and HLA mismatch, DGF, Rejection or ischaemia of the graft kidney, ureteral stent placement.
PCKD and positive LA-B51 – protective factors
Cellular immune response:
· Cellular immune response (both CD4 & CD8) is important in mitigation and clearance of BK viremia
o IFN-gamma activity (indicate cellular immune response) is associated with the resolution of BKVAN
o Shorter time (<1month) to develop anti-BK-T cell response a/w better viremia clearance, while longer median time (>5months) is seen in patients who develop BKVAN.
o CD8-based cellular responses correlated with lower BK viral loads in blood and urine
o BK-directed cytokine signatures from CD4 cells have demonstrated similar results
· Various Studies are being conducted to assess these assays, which could be utilized to predict the clearance of BKV and also to identify patients at risk for progression. Pathogenesis:
Latent infection in Kidney and Urothelium is reactivated in immunosuppressed state.
Viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways – cause tubular damage (atrophy), interstitial fibrosis and progressive nephron loss. Clinical manifestations:
· mostly asymptomatic
· Viruria is most common (30-50%) and earliest manifestation of BKV
· Although it is a sensitive marker for progression of infection, Urine BK viral loads is not standard practice in transplant, because viruria can occur in pregnancy, older age and other immunosuppressive states.
· Plasma Viral load (Viremia) is a better predictor of progression to BKVAN
· BKVAN is manifested as decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia
· ureteral stenosis is a rare complication
· hemorrhagic cystitis commonly seen in HSCT recipients
Screening and diagnosis:
· Urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value, thus screening for BK viremia is the preferred method.
· Urine PCR for BKV is not recommended as a screening test – (low specificity, cost)
· Plasma BKV PCR (viremia) is a better predictor of progression to BKVAN
– KDIGO and American society (AST-IDCOP) recommend screening monthly for first 6 months, then 3-monthly for 18 months (total 2 years).
· Urine cytology – “decoy cells” are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by condensed rim of chromatin
o marker of polyomavirus replication but do not necessarily indicate PVN
· Polyomavirus-Haufen in urine sample via negative staining EM
o correlates well with disease severity with a high positive and negative predictive value.
· donor-derived cell-free DNA (dd-cfDNA) – higher levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR
– dd-cfDNA can be used as noninvasive test to assess progression to BKVAN
Renal Allograft Biopsy is the gold standard for diagnosis of BKVAN, assessment of severity and any other pathology (Rejection)
· Due to medullary tropism and chances of missing focal lesions (30%) – 2 biopsy cores including medulla are recommended.
– repeat biopsy can be considered if clinical suspicions is high
· Histopathologic features of BKVAN – cytopathic changes and positive IHC (using antibodies directed against BKV or SV40 large T antigen)
– Tubular epithelial cells with enlarged, hyperchromatic nuclei and ground glass intranuclear inclusions
· Positive SV40 staining is100% specific for PVN
· Diagnosis can be made if the plasma BK viral load is >10,000 copies/mL
Tubular injury (epithelial flattening, tubular atrophy), tubulitis, interstitial inflammation and fibrosis (IF/TA) is also seen in AMR / Chronic Rejection, which may coexist with BKVAN.
· Features of vascular injury (glomerulitis, peritubular capillary C4d staining) in presence of DSA can distinguish towards ABMR, whereas high BK viral load can be indicative of BKVAN.
Treatment
mainstay of management for BK viremia and BKVAN is reduction in immunosuppression
– currently, there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy
– reduce antimetabolite dose by half, monitor serum creatinine and plasma BK PCR every two weeks
– if BK viral loads remain at similar levels or increase, withdraw the antimetabolite completely
– if BK viral loads do not reduce in 4 weeks despite stopping the antimetabolite, reduce the CNI dose targeting trough levels of 4-6ng/mL for tacrolimus and 50-100ng/L for cyclosporine
– kidney transplant recipients on tacrolimus-based regimens have lower rates of rejection and higher eGFRs on 5-year follow up data
– other adjunctive therapies used to treat BKV infection include: – cidofovir, fluoroquinolones, IVIG, leflunomide
– there was no difference in graft outcomes when reduction in immunosuppression was combined with leflunomide or cidofovir compared with reduction in immunosuppression alone
– IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended
– there are upcoming therapeutic trials involving modified T cells and monoclonal antibodies Kidney re-transplantation
– kidney re-transplantation can be considered in patients with graft loss due to BKVAN
– failed transplant or native kidney nephrectomy is not recommended
– viral clearance should be confirmed prior to re-transplantation
– consider lower immunosuppression without triggering rejection
– graft survival following re-transplantation is 98% and 94% at 1- and 3-years respectively
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Summarize this article
Introduction: Potent immunosuppression has come up with high incidence of BKV infection – (viremia 30%) and morbidity like BKV associated nephropathy (5-10%) and graft loss in significant number of renal transplant recipients.
Overview of viral epidemiology, pathogenesis, screening, and diagnostic methods, clinical manifestations and recommended treatment strategies are discussed. History of BK virus: 1971 – Virus discovered in a kidney transplant recipient with ureteral stricture 1993 – First case of BKVAN (biopsy-proven) was described High incidence of viremia being reported due to strong immunosuppression use and better testing facility. Incidence of graft loss reduced significantly (<15% from 50%) by early recognition and better management of BKVAN Virology: · Family – Polyoma viridae · Small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus · 3 regions of viral genome – early coding region is for large T and small t (tumor) antigens Epidemiology: BKV is ubiquitous – 90% seroprevalence by 5 years age Transmission through respiratory and faeco-oral route – remains latent in the kidney and urothelial cells BKV infection post renal transplant can be due to reactivation of latent infection or transmission from the donor kidney Chronology of infection course – – Viruria precedes viremia by 4-6 weeks, and BKVAN by 6-10 weeks – urine BK viral load > 8 log10 copies/mL predict the onset of viremia – plasma BK viral load > 4 log10 copies/mL are associated with higher rates BKVAN – plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN (SV40-IHC and inflammatory infiltrates) Risk factors –
Intense immunosuppression is most important risk factor – highest incidence of BKV infection during early post-transplant period
Older age, diabetes, specific HLA-C alleles recipients
Donor-related factors – reduced immune response to BKV, BK viruria prior to transplant
Donor-recipient interface – BKV serostatus D+/R-, ABO-incompatible and HLA mismatch, DGF, Rejection or ischaemia of the graft kidney, ureteral stent placement.
PCKD and positive LA-B51 – protective factors
Cellular immune response: · Cellular immune response (both CD4 & CD8) is important in mitigation and clearance of BK viremia
o IFN-gamma activity (indicate cellular immune response) is associated with the resolution of BKVAN
o Shorter time (<1month) to develop anti-BK-T cell response a/w better viremia clearance, while longer median time (>5months) is seen in patients who develop BKVAN.
o CD8-based cellular responses correlated with lower BK viral loads in blood and urine
o BK-directed cytokine signatures from CD4 cells have demonstrated similar results
· Various Studies are being conducted to assess these assays, which could be utilized to predict the clearance of BKV and also to identify patients at risk for progression. Pathogenesis: Latent infection in Kidney and Urothelium is reactivated in immunosuppressed state.
Viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways – cause tubular damage (atrophy), interstitial fibrosis and progressive nephron loss. Clinical manifestations: · mostly asymptomatic · Viruria is most common (30-50%) and earliest manifestation of BKV
· Although it is a sensitive marker for progression of infection, Urine BK viral loads is not standard practice in transplant, because viruria can occur in pregnancy, older age and other immunosuppressive states. · Plasma Viral load (Viremia) is a better predictor of progression to BKVAN · BKVAN is manifested as decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia · ureteral stenosis is a rare complication · hemorrhagic cystitis commonly seen in HSCT recipients Screening and diagnosis: · Urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value, thus screening for BK viremia is the preferred method. · Urine PCR for BKV is not recommended as a screening test – (low specificity, cost)
· Plasma BKV PCR (viremia) is a better predictor of progression to BKVAN – KDIGO and American society (AST-IDCOP) recommend screening monthly for first 6 months, then 3-monthly for 18 months (total 2 years). · Urine cytology – “decoy cells” are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by condensed rim of chromatin o marker of polyomavirus replication but do not necessarily indicate PVN · Polyomavirus-Haufen in urine sample via negative staining EM o correlates well with disease severity with a high positive and negative predictive value. · donor-derived cell-free DNA (dd-cfDNA) – higher levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR – dd-cfDNA can be used as noninvasive test to assess progression to BKVAN Renal Allograft Biopsy is the gold standard for diagnosis of BKVAN, assessment of severity and any other pathology (Rejection) · Due to medullary tropism and chances of missing focal lesions (30%) – 2 biopsy cores including medulla are recommended. – repeat biopsy can be considered if clinical suspicions is high · Histopathologic features of BKVAN – cytopathic changes and positive IHC (using antibodies directed against BKV or SV40 large T antigen) – Tubular epithelial cells with enlarged, hyperchromatic nuclei and ground glass intranuclear inclusions · Positive SV40 staining is100% specific for PVN · Diagnosis can be made if the plasma BK viral load is >10,000 copies/mL Tubular injury (epithelial flattening, tubular atrophy), tubulitis, interstitial inflammation and fibrosis (IF/TA) is also seen in AMR / Chronic Rejection, which may coexist with BKVAN. · Features of vascular injury (glomerulitis, peritubular capillary C4d staining) in presence of DSA can distinguish towards ABMR, whereas high BK viral load can be indicative of BKVAN. Treatment: – there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy – mainstay of treatment is reduction of immunosuppression – reduce MMF by half – monitor serum creatinine and plasma BK PCR every two weeks – Increased or static viral load indicates complete withdrawal of antimetabolite – BK viral loads not reduce in 4 weeks despite stopping antimetabolite à reduce CNI dose targeting lower trough level (Tac C0 of 4-6ng/mL; CsA C2 level 50-100ng/L) Adjunctive therapies used to treat BKV infection – cidofovir, IVIG, leflunomide · No difference in graft outcomes by IS reduction combined with leflunomide or cidofovir has been reported, compared to IS reduction alone. · IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended · upcoming therapeutic trials involving modified T cells and monoclonal antibodies have shown promising results in isolated case reports / small case series. Kidney re-transplantation · can be considered in patients with graft loss due to BKVAN · failed transplant or native kidney nephrectomy is not recommended · viral clearance should be confirmed prior to re-transplantation · consider lower immunosuppression without triggering rejection · graft survival of 98% @ 1year, 94% @3-years has been reported Conclusions: · BKV infection remains a major concern after transplant (heavy immunosuppression) · Strict surveillance protocols have led to early detection and mitigation of severe disease · Histologic findings may be similar to acute rejection, which may coexist with BKN · Reduction in immunosuppression can be helpful for BKV infection and prevention of BKVAN, but may precipitate Rejection · No antiviral therapy has been effective in clearance of BKV · Novel therapeutic agents has shown positive results in case reports or small series, are being evaluated in large scale in Upcoming Therapeutic Trials: 1. MAU868 – human monoclonal antibody (IgG1): – (ClinicalTrials.gov identifier: NCT04294472). 2. adoptively transferred posoleuccel (ALVR105) multi-virus-specific T Cells in kidney transplant recipients: – (ClinicalTrials.gov identifier: NCT04605484).
1. Please summarize this article; Introduction; The strong immunosuppression revolution has improved graft survival but also accompanied by high rates of BKVN in up-to 30% of kidney transplant recipients. History of BK virus; In 1971 BKV was discovered when a patient was investigated for ureteral structure, and biopsy proven case was diagnosed by 1993. It’s still not clear that increasing incidence of viremia is secondary to strong immunosuppression or better availability of testing. Early recognition has decreased the incidence of graft loss by 15%, otherwise, it was 50 to 100% in early period. Virolology; BK virus belongs to a family of polyomavirus family, small double-stranded non-enveloped DNA virus, categorized into four groups with different virulence. The genome consists of three region. 1. Large T, small t antigen (bind to p53, protein Rb and persistant infection. 2. Non-coding control region (it causes replication, and enhance elements and modulate transcription, if mutated will causes cell tropism and altered rate of replication). 3. Late coding region (codes for agnoprotein responsible for assembly of viral capsids VP-1 and release of virion, and viral capsid protein. Epidemiology; . 90% seropositive by 4 years. . Become dormant in urothelial and kidney tissue. . Its main routes of transmission are via mucosal rout. . Usually reactivation and sever infection occurs after strong immunosuppression post-transplantation. . The incidence of viruria 30%, viremia 12% in renal transplants. . Usually a patient develops viruria there is 50% possibility of developing viremia and Nephropathy within 2 to 6 weeks. . Viriuria and urine viral load >8-10 log/ml, . While plasma viral load >4 log/ml associated with BKVAN, . Viral load >6 log shows sever disease. Based on recent data 1-10% of renal transplant recipient develop BKVAN. Risk factors; . Immunosuppression dose, incidence of viremia highest in early post-transplantation, with tacrolimus has higher risk. . Recipient factors like, diabetes, older age, and HLA C alleles. . Donor recipient interface, D+/R-, ABO incompatible, HLA mismatch, Delayed graft function, AMR. Increased ischemia time. . Donor related factors; carrier for BKV (viruria) Protective factors; Factors like the cause of renal failure ADPKD, recipient with HLA-B51 positivity. Cellular Immune Response and Pathogenesis;
CD4, CD8 has crucial role in clearance of BK viremia. The patients with BK viremia required required 5 months to eliminate virus, however, after initial infection the virus remain dormant in urinary epithelial cells. On exposure due to strong immunosuppression, ischemia, injury to epithelial cells causes activation of different cascades and destruction characterized by IFTA and progressive nephron loss. Clinical manifestation; The classic sequence of infection viruria, viremia, and BKVAN. The most common and earlest manifestation is 50% viruria, without symptoms, although, viremia is a sensitive marker and better predictor of progression to BKVAN in comparison to viruria. Other manifestation are uretral stenosis and heamurrhegis cystitis. Reports associated GI malignancy with BKV. Screening and Diagnosis. With higher predictive value of plasma BKV level is better predictor. KDIGO and AST-IDCOP guidelines recommends monthly screening for first six months post-transplantation and every three months for next 18 months. Urine cytology, decoy cell (polyomavirus-Haufen) has high positive and negative predictive value. Donor derived cell free DNA (dd-cfDNA); could be useful noninvasive test to assess for progressive BKV to BKVAN. Biopsy findings; This is gold standard for diagnosis and severity ofBKVAN. . Findings; Simian virus (SV40), 100% specific but does not distinguish between BKV and JC virus but can differentiate between adenovirus infection.. Infected tubular cells shows enlarged, hyperchromatic nuclei with ground glass and intranuclear inclusions, and clumps. Initial tubulitis then they progress to IFTA. Treatment; Stepwise Immunosuppression dose modification, first, antimetabolite, CIN, and last corticosteroids. Monitor viral load if persist then complete withdrawal of antimetabolites. Next step minimize level of CIN tac 4-6ng/l, while, CaS 50-100ng/l. Adjunctive treatment quinolones, cidofovir, leflonmide, IVIG. There few trails in progress. Re-transplantation; allograft survival 98%, 94% at 1 and 3 year respectively. Should be done with lower immunosuppression regime. There was no difference in rates of AMR or survival at one year. Conclusion; There is no such antiviral available to benefit.
BK virus was first discovered in a kidney transplant recipient who presented with a ureteral stricture in 1971
BKVAN frequently resulted in graft loss with rates of 50–100% reported
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family
Epidemiology
The seroprevalence rates of over 90% by 4 years of age
The primary routes for transmission: mucosal contact including the oral, gastrointestinal, and respiratory tract.
After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
Since cellular immunity is most suppressed in the first post-transplant year as a result of induction therapy, viral replication can frequently ensue during this period.
Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
Viruria and viremia are detected in approximately 30% and 12% of kidney transplant recipients, respectively.
After the onset of viruria, nearly 50% of kidney transplant recipients develop viremia during a period of 2–6 weeks, with a similar proportion of viremic patients developing BKVAN in the aforementioned time period.
Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology
Risk factors:
Intensity of immunosuppression:
This is considered as the most significant factor associated with BK viral replication
tacrolimus may portend a higher risk of BK virus infection
Recipient characteristics: older age , diabetes, and specific HLA-C alleles
The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement
Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN
Cellular Immune Response and Pathogenesis
The mitigation and clearance of BK viremia are dependent on a robust cellular immune response—with both CD4 and CD8 cells playing a crucial role in this process
The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus.
The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium.
Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens).
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
Clinical Manifestations
Most clinically significant infections associated with the BK virus lack any systemic symptoms.
The classic sequence of infections in kidney transplant recipients is viruria, viremia, and BKVAN.
The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia.
Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter.
BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
The vast majority of BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence
Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis.
Screening and Diagnosis
Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in these protocols.
Guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
Plasma BK PCR
BK viral loads are measured by polymerase chain reaction (PCR)—a fluorescent probe BK-specific sequence, and the number of amplicons produced is compared with a standard curve generated with serial dilutions of a known concentration of BK DNA
Urine cytology
The characteristic BK virus-infected cells that present on cytologic examination of urine are called 0decoy cells due to their similarity to renal carcinoma cells. These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin.
The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively.
Donor-Derived Cell-Free DNA (dd-cfDNA)
It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
Transplant kidney biopsy
Gold standard for diagnosis of BAVN.
Since BK is tropic for the medulla, it is necessary that the biopsy core has medulla present to decrease the likelihood of a sampling error
The following pathologic features should be present for a definitive diagnosis of BKVAN
1. Characteristic cytopathic changes
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN)
A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
Given that BK mostly affects the medulla and is associated with focal disease, diagnosis via a kidney biopsy is estimated to be missed in nearly 30% of cases
If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain.
To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended.
Currently, it is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen
The SV40 IHC stain detects the large T antigen expressed by all polyoma viruses pathogenic in humans (SV, JC, and BK).
This stain can highlight cells in the early stages of infection, before viral cytopathic changes may be detectable on routine stains.
Differential with acute rejection
Tubular injury, tubulitis, and interstitial inflammation are key histologic findings
The presence of these findings in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection.
A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach histologic classes of definitive PVN are defined by the morphologic degree of intrarenal pvl (polyomavirus replication/load level) and Banff ci scores (interstitial fibrosis).
The scoring of pvl is on the basis of the extent of virally induced tubular changes, while a tubule with intranuclear viral inclusion bodies (type 1 or 2) and/or a positive IHC reaction for SV40-T antigen in one or more cells per tubular cross-section is considered “a positive tubule”.
The overall percentage of positive tubular cross-sections is estimated in the entire biopsy sample (all available cores, cortex, and medulla).
Treatment
A reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN. There is no therapeutic agent available to treat this virus-associated disease
The following is a stepwise approach for the reduction in immunosuppression
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir
Other drugs
IVIG
Quinolones
Cidofovir
Leflunomide
Kidney Re-Transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success
Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
● BKVAN is an important cause of graft loss in kidney transplant recipients.
● The genome of the virus consists of
three regions— (large T and small T tumor antigen), the non-coding control region, and the late coding region.
● The T antigen has a propensity to bind to p53 and protein Rb
● The non-coding region contains the origin of replication and enhancer elements that can modulate transcription. ● Mutations in the non-coding control regions result in permit replication in other cell types (permissivity), cell tropism, and altered rates of replication
● The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Ir responsible for the release of virion from cells
● antibodies against one serotype does not result in durable protection against other types
● VP-3 leads to depletion of (ATP) and cell death
● BKV seroprevalence rates of over 90% by 4 years of age
● The transmission is from mucosal contact including the oral, gastrointestinal, and respiratory tract.
● After a primary viremia, BKV latent in the kidney and uroepithelial cells
● viral replication can ensue in the first year after transplantation
● BKV infection occurs in kidney recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
● Stages of infection ( viruria, viremia, and allograft nephropathy )
● Viruria and viremia are detected in kidney recipients by 30% and 12%
● 50% of kidney recipients develop viremia and BKVAN after viruria during 2–6 weeks
● 1–10% of kidney recipients develop BKVAN
● Urine BK viral loads > 10^8 c/mL predict the onset of viremia, while plasma BK viral loads >10^4 c/mL are associated with higher rates of BKVAN and loads>10^6 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates
● Risk factors for Viral replication :
1. Intensity of immunosuppression
2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles
3. The donor–recipient interface: D+/R- , ABO incompatibility, HLA mismatch , DGF, rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
● Protective factors against BKVAN
☆ Recipient HLA-B51 positivity due to highly immunogenic cytotoxic T cells
☆ presence of PCKD
Cellular Immune Response and Pathogenesis
● The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus
● Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissue
● Viral replication activate pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
● BKVAN is associated with increased expression of messenger RNAs (mRNAs), expressed in T cell-mediated rejection (TCMR) then interstitial fibrosis and tubular atrophy
● BKVAN manifesting as a decline in renal function with or without urinary abnormalities.
● Ureteral stenosis and hemorrhagic cystitis are mostly seen in HSCT patients
● There are an association between BK virus and development of urothelial malignancies in transplant recipients
Screening and Diagnosis
● Guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for
the next 18 months
● Urine BK PCR is not a recommended screening test
● Plasma BK PCR it’s sensitivity differs upon BKV genotypes
● Urine Cytology
☆ Decoy cells are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin
☆ “owl eye” inclusions, multinucleation, or clumped chromatin.
☆ polyomavirus-Haufen which is cast-like PV aggregates which has high BK nephropathy and correlates well with disease severity
● A higher dd-cfDNA levels were associated with higher BK viral loads so it may be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant Kidney Biopsy
● The gold standard for diagnosis of BVAN
● Biopsy must include medulla to decrease a sampling error
● Diagnosis via a kidney biopsy missed in 30% of cases
● The features present for a definitive diagnosis of BKVAN :
☆ Positive SV40 staining
☆ Tubular epithelial cell with a “ground glass” nuclear inclusion
☆ Plasma cell-rich infiltrate or injury found primarily in the medulla
Treatment
● A reduction of immunosuppression
☆ 50% reduction of antimetabolite and continuing the same doses of CNi/pred
☆ Cessation of anti-metabolite if viral loads continue to be at similar levels or increase
☆ If viral loads do not reduce over 4 weeks reduce CNi trough goals if viral loads do not
reduce over 4 weeks
☆ Other therapies include quinolones, cidofovir, leflunomide, and (IVIG).
Upcoming Therapeutic Trials
1. A human monoclonal antibody binds VP1 which is responsible for binding to the surface of host cells
2. Multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia
Kidney Re-Transplantation
● Consideration for lower IS should be balanced with the risk of rejection.
● Allograft survival 98% and 94% at 1 and 3 years
● There was no significant difference in the rates of acute rejection or patient survival at one year
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Summarise this article
Introduction
– with the advent of more efficacious and potent immunosuppression, BKVAN has an important cause of graft loss among kidney transplant recipients given the high rates of BK viremia
History of BK virus
– 1st discovered in 1971 in a kidney transplant recipient who presented with a ureteral stricture
– the 1st definitive biopsy-proven case of BKVAN was described in 1983
– there has been a significant reduction in the cases of associated graft loss, this is attributable to a better understanding of the management of BKVAN
Virology
– BKV is a small non-enveloped double stranded DNA virus belonging to the polyomaviridae family
Epidemiology
– BKV infection is ubiquitous in the general population
– modes of transmission of the virus are due to mucosal contact through oral, respiratory and gastrointestinal tracts
– following primary viremia, the BKV becomes latent in the kidney and uroepithelial cells
– in kidney transplant recipients, BKV infection can occur as a result of reactivation of a latent infection or as transmission of a new infection from the donor kidney
– the chronological stages include viruria (precedes viremia by 2-6 weeks), viremia (precedes BKVAN by 2-6 weeks) and BKVAN
– urine BK viral load > 8 log 10 copies/mL predict the onset of viremia
– plasma BK viral load > 4 log 10 copies/mL are associated with higher rates of biopsy-proven BKVAN
– plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN pathology measured by SV40 IHC and associated with inflammatory infiltrates
– Risk factors for BKV replication include: –
intensity of immunosuppression – incidence of BKV viremia is highest in the early post-transplant period due to the heavy immunosuppression
recipient characteristics e.g., older age, diabetes, specific HLA-C alleles
donor-related factors i.e., reduced immune response to BKV, BK viruria prior to transplant
donor-recipient interface i.e., D+/ R- BKV serostatus, ABO incompatibility, HLA mismatch, DGF, rejection or ischaemia of the graft kidney, ureteral stent placement
– presence of polycystic kidney disease and recipient LA-B51 positivity have been shown to be protective factors against the development of BKVAN
Cellular immune response and pathogenesis
– a robust cellular immune response plays a key role in the mitigation and clearance of BK viremia
– sites of latency following primary infection include: –
other sites like prostate, testes, cervix, vulva, seminiferous tubules, hematolymphoid tissues (tonsils, peripheral blood mononuclear cells)
– the latent infection becomes reactivated in states of immunosuppression
– BKV replication and its cytopathic effect result in damage to the tubular epithelium
– the final stage is characterized by interstitial fibrosis and tubular atrophy which are associated with progressive nephron loss
– mRNAs are increasingly expressed in BKVAN as well as TCMR making it difficult to differentiate these two entities
Clinical manifestations
– most BKV infections lack systemic symptoms
– the classic sequence of infections involves viruria, viremia and BKVAN
– viruria is the most common and earliest manifestation of BKV
– viruria can occur in pregnancy, older patients, other immunosuppressive states outside transplantation hence checking of urine BK viral loads is not standard practice
– compared to viruria, viremia is a better predictor of progression to BKVAN
– BKVAN manifests as a decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia
– other manifestations of BKV infection include ureteral stenosis and hemorrhagic cystitis commonly seen in HSCT recipients
– role of BKV in carcinogenesis remains controversial although there is a possible link between BKV and genitourinary malignancies
Screening and diagnosis
– urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value
– KDIGO recommends monthly screening for the 1st six months then every 3 months for the next 18 months
o urine BK PCR: – is not recommended as a screening test given its low specificity and cost since if positive, it will still require confirmation with plasma BK PCR and also ~50% of the patients with viruria may not develop viremia
o plasma BK PCR: – viremia is a better predictor of progression to BKVAN
o urine cytology: – decoy cells are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin; they resemble renal carcinoma cells; decoy cells are a marker of polyomavirus replication but do not necessarily indicate PVN
– urine samples can be screened for polyomavirus-Haufen via negative staining EM
– amount of PV-Haufen shed correlates well with disease severity
– presence of PV-Haufen has a high positive predictive value while a negative PV-Haufen has a high negative predictive value
o donor-derived cell-free DNA (dd-cfDNA): – higher dd-cfDNA levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR therefore dd-cfDNA can be used as a useful noninvasive test to assess progression of BKV to BKVAN
o transplant kidney biopsy: – it is the gold standard for BKVAN diagnosis; it helps in diagnosis as well as assessing the severity of BKV involvement and presence of other ongoing pathologies
– BKV has tropism for the medulla therefore to avoid sampling error the two biopsy cores containing the renal cortex and medulla are recommended
– the diagnosis is missed in ~30% of the kidney biopsy cases given the focal nature of the disease; a repeat biopsy can be considered in such cases if the clinical suspicions remain
– pathologic features in keeping with a definitive diagnosis of BKVAN include characteristic cytopathic changes and positive IHC tests using antibodies directed against BKV or SV40 large T antigen
– a positive SV40 staining has ~100% specificity for PVN but does not differentiate between BKV and JCV
– SV40 staining helps differentiate PVN from other viral nephropathies e.g., adenovirus
– a presumptive diagnosis can be made if the plasma BKV viral load is >10,000 copies/mL
o histology: – findings include
tubular epithelial cells with enlarged, hyperchromatic nuclei and ground glass intranuclear inclusions
tubular cell injury i.e., tubulitis and interstitial inflammation which may result in interstitial fibrosis and tubular atrophy
– histologic similarities do exist between PVN and acute rejection (AR) i.e., tubular injury, tubulitis, interstitial inflammation
– the two entities (PVN and AR) can co-exist creating a treatment dilemma
– distinguishing characteristics include: – features of vascular injury (i.e., glomerulitis, endarteritis, arterial fibrinoid necrosis, peritubular capillary C4d staining), presence of DSA, BKV viral load
Treatment
– mainstay of management for BK viremia and BKVAN is reduction in immunosuppression
– currently, there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy
– reduce antimetabolite dose by half, monitor serum creatinine and plasma BK PCR every two weeks
– if BK viral loads remain at similar levels or increase, withdraw the antimetabolite completely
– if BK viral loads do not reduce in 4 weeks despite stopping the antimetabolite, reduce the CNI dose targeting trough levels of 4-6ng/mL for tacrolimus and 50-100ng/L for cyclosporine
– kidney transplant recipients on tacrolimus-based regimens have lower rates of rejection and higher eGFRs on 5-year follow up data
– other adjunctive therapies used to treat BKV infection include: – cidofovir, fluoroquinolones, IVIG, leflunomide
– there was no difference in graft outcomes when reduction in immunosuppression was combined with leflunomide or cidofovir compared with reduction in immunosuppression alone
– IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended
– there are upcoming therapeutic trials involving modified T cells and monoclonal antibodies
Kidney re-transplantation
– kidney re-transplantation can be considered in patients with graft loss due to BKVAN
– failed transplant or native kidney nephrectomy is not recommended
– viral clearance should be confirmed prior to re-transplantation
– consider lower immunosuppression without triggering rejection
– graft survival following re-transplantation is 98% and 94% at 1- and 3-years respectively
Conclusions
– BKV infection remains a major clinical concern however strict surveillance protocols have led to early detection and mitigation of severe disease
– BKV infection can be associated with histologic findings similar to acute rejection
– reduction in immunosuppression can by itself result in rejection
– currently there is no antiviral therapy directed towards clearance of BKV
– however, there are novel therapeutic agents being evaluated
BKV NEPHROPATHY IN KIDNEY TRANSPLANTS;A STATE OF THE ART REVIEW.
INTRODUCTION.
-Good post transplant outcomes from adequate immunosuppression has led to increased BKVAN with viremia being seen in up to 30% post transplant.
-We are yet to get adequate tx for BK infection.
HX OF BK VIRUS.
-Discovered in 1971 in pt with ureteral stricture post transplant.1st BKVAN proven biopsy seen in 1993.
-Initially had graft loss of 50-100%,this has decreased to < 15% in last two decades.
VIROLOGY.
-BK is a non enveloped ,icosahedral shaped double stranded DNA virus.
-Gene has an early, non coding and late region. Early has T and t antigens with the former binding to p53 and protein RB while the later codes for VP1.VP2 and VP3 viral caspid proteins.
EPIDEMIOLOGY.
-Prevalence of 90% in general population by 4 yrs.
-Stages of infection ; Viruria,viremia and nephropathy.
-After viruria,50% KTR will have viremia in 2-/ time.
-Transmission routes ; Oral, GIT and resp tract.
-Plasma VL>4 log 10 are associated with more risk of BKVAN.
RISK FACTORS.
-These include ;
Immunosuppressive meds- More incidences immediately post transplant,Tac > CYC,MTOR >CNI
Recipient xtics -Old age,DM,HLA C alleles.
Donor ; recipient interphase – D+/R+ pair, ABO incompatibility, DGF,HLA Mismatch ,Rejection or ischemia of graft, ureteral stent.
CELLULAR IMMUNE RESPONSE AND PATHOGENESIS.
-T cell mediated immunity ;CD4 and CD8 cells key in clearing BK infection. Increased interferon gamma is a good pointer yo BK specific cellular response.
-Post childhood infection, BK maintains latency in renal epithelium, prostate, testes, seminiferous tubules, cervix, vulva and lymphoid tissues ,with reduced immunity, the infection flares up and pt becomes symptomatic.
CLINICAL MANIFESTATION.
-Stepwise ; Viruria, viremia then nephropathy. Viruria occurs in up to 50% in 1st 1 yr post transplant.
-Viremia is a better marker of those at risk of BKVAN. Viremia may present as increase in creatinine +/- urinary anomalies.
-Others; Ureteral stenosis, hemorrhagic cystitis.
-Rare ; GU malignancies.
SCREENING AND DIAGNOSIS.
-BK viremia screening is the preferred modality.
Urine BK PCR – not sensitive for screeening,if +VE,confirm with plasma PCR.
Plasma BK PCR – varied genotypes may give different results. Sensitive as a screening tool, monitoring treatment and also to determine those at risk of BKVAN. High VL associated with more risk of nephropathy.
Urine cytology – Decoy cells ar a marker of polyomavirus replication but do nit necessarily indicate nephropathy. Has low PPV and high NPV. Haufen cells have both high PPV and NPV.
Donor derived cell free DNA – The higher the dd-cfDNA, the higher the VL and risk of nephropathy, Can assess progression of BKV to nephropathy.
Graft biopsy -Gold standard to dx BKVAN. biopsy core should have medulla to decrease false negative. Can be missed in up to 30%,Features ; cytopathic changes and +VE IHC- SV40 staining.
Histology -x2 biopsy cores with cortex + medulla recommended to increase diagnostic yield. All histology should be stained for SV40 where features of nephropathy are absent.C4d staining is more sensitive for acute rejection than nephropathy.
Presumptive dx ;VL > 10000 Copies/ml.
TREATMENT.
RIS is mainstay of treatment.
Decrease antimetabolite by 50% and maintain CNI + Steroid dose while monitoring graft function and BK PCR every fortnight.
Stop antimetabolite if no change in VL.
Decrease CNI and aim for 4-6ng/ml for Tac AND 50-100ng/l for CYC if no change in VL despite stopping the antimetabolite.
2.Other therapies;
IVIG – Has BK neutralizing antibodies and can be used if no change with RIS.
Quinolones – No efficacy seen post transplant despite having antiviral properties.
Cidofovir – Has high nephrotoxicity SE with little efficacy being reported from studies. Also associated with proteinuria and proximal tubular dysfunction.
Leflunomide -No outright benefit in BK infected pts when compared to RIS.
3.Future therapeutic trials.
Human IgG1
Adoptive transferred posoleuccel
KIDNEY RE-TRANSPLANTATION.
-Successful post graft dysfunction from BKVAN.
-Graft/Native nephrectomy not recommended.
-Careful dosing of immunosuppression to avert rejection to be adhered to.
-Graft survival post transplant 98% and 94% at 1 yr and 3 yrs respectively.
Please summarise this article.
-BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
-BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family .
– The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
– The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
-After a primary viremia, the BK virus establishes refuge in the kidney
and uroepithelial cells resulting in lifelong latent/persistent infection.
-Cellular immunity is suppressed in the first post-transplant year, viral replication can frequently ensue during this period.
-The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy .
-Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression: This is considered as the most significant factor associated with BK viral replication.
2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles .
3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
-Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
-HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients .
– Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine.
-Most clinically significant infections associated with the BK virus lack any systemic symptoms.
-BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities
-Other manifestations of the BK virus include ureteral stenosis, hemorrhagic cystitis and genitourinary (GU) malignancies.
-Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in screening protocols .
-KDIGO) and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for
the next 18 months .
-Urine BK PCR is not a recommended screening test because if positive, it always requires confirmation with plasma PCR and nearly 50% of patients with viruria will not develop viremia .
-Plasma BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference. This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN.
-Cytologic examination of urine may show decoy cells which are
tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin .
-Urine samples may be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . It has extremely high positive and negative predictive values for BK nephropathy.
– BK is tropic the medulla, so the biopsy core medulla must be present .
The following pathologic features should be present for a definitive diagnosis of BKVAN :
1. Characteristic cytopathic changes .
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. Positive SV40 staining is useful as it is associated with a specificity of almost 100% for PVN; although, it does not distinguish between BKV and JCV.
– If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is
recommended if clinical suspicions remain.
-To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended .
– A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
-It is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen .
-The SV40 IHC stain detects the large T antigen expressed by all polyoma viruses pathogenic in humans (SV, JC, and BK).
– PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
-A reduction in the intensity of immunosuppression is principle for the treatment of BK viremia and BKVAN. There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
-Protocols for a reduction in immunosuppression:
1.Reduce dose of antimetabolite by 50% while continuing on the same doses of CNI and/or prednisone.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce CNI trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
Upcoming Therapeutic Trials
Given the lack of therapies available for the treatment of BK infection, the two following
trials involving modified T cells and monoclonal antibodies are currently underway:
1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868—a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1, which is responsible for binding to the surface of host cells (ClinicalTrials.gov identifier: NCT04294472).
2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia(ClinicalTrials.gov identifier: NCT04605484)
-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success .
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Please summarise this article 1. Introduction and history :
BK virus-associated nephropathy (BKVAN) is found to be an important cause of graft loss in kidney transplant recipients especially with emergent of efficacious immunosuppression that lead to increase risk BK viremia (BKV) in up to 30% of kidney transplant recipients . It was first discovered in 1971, in a Kidney transplant recipient present with ureteric stricture. The first definitive biopsy proven case of BKVAN was described in 1993 . Early on , BKVAN frequently resulted in graft loss with rates of 50–100% reported, but the last 2 decades increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% .
Virology :
BK virus is a member of the Polyomaviridae family, it is a small ,icosahedral, closed circular, non-enveloped,double-stranded DNA virus. Its genome is consists of three regions:
The early coding region of the large T and small t antigens
-The non-coding control regions: Are significant contributors to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
The late coding region:The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3)
Epidemiology:
BK virus infection has seroprevalence rates of over 90% by 4 years of age which is considered significantly ubiquitous in the general population. Routes of transmission are : oral, gastrointestinal, and respiratory tract. After a primary viremia, the BK virus migrates to the kidney and uroepithelial cells and stays dormant resulting in lifelong latent/persistent infection.
During the period of intensive immunosuppression especially in the first year post kidney transplant the virus may cause significant infection when reactivated ,start with urine shedding of the virus (viruria) followed by viremia, and allograft nephropathy . After the onset of viruria, nearly 50% of kidney transplant recipients develop viremia during a period of 2–6 weeks, with a similar proportion of viremic patients developing BKVAN in the previously mentioned time period . Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates .
Risk factors of BKV replications is increased by : : 1. Intensity of immunosuppression, which is the most significant factor . 2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles 3. The donor–recipient interface: ( D+ve ,R-ve) , ABO incompatibility, , HLA mismatch , delayed graft function , ischemia or rejection of the transplanted kidney and ureteral stent placement . 4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
*Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis :
Both CD4 and CD8 cells playing a crucial role in the clearance of BK viremia . The presence of ELISPOT measured IFN-gamma activity, indicative of a BK-directed cellular immune response, is associated with the resolution of BKVAN. Vigorous CD8-based cellular responses were found to be correlated with lower BK viral loads in urine and blood while high viral loads and the continued presence of the virus were associated with a weak response.
BK-directed cytokine signatures from CD4 cells have demonstrated similar results. , The BKV remains dormant after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium; the activity of the virus is correlated with immunity of the host which if suppressed viral replication and its cytopathic effect will take place .
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), which are also expressed in T cell-mediated rejection (TCMR) leading to difficulty in distinguishing between BKVAN and TCMR different entities . The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss .
clinical manifestation :
Commonly asymptomatic
Viruria is the earliest manifestation followed by viremia and BKVAN.
Usually present in the first year post kidney transplant
Urine BK viral loads is not standard practice despite it being a sensitive marker for progression to BKVAN,especially in compromised cellular immunity (other than transplant recipients) .
-*Viremia is also asymptomatic but if present it is a better predictor of progression to BKVAN in comparison to viruria . -*BKVAN usually manifests as a symptomatic decline in renal function with or without urinary abnormalities. -* Ureteral stenosis is the first discovered presentation of BKV. -*Hemorrhagic cystitis is rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants. T -* Genitourinary (GU) malignancies There are accumulating reports that there may be an association of the BK virus with the development of urothelial malignancies in transplant recipients .
Screening and Diagnosis Kidney Disease Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months .
1. Urine BK PCR Urine BK PCR is not a recommended screening test; it is less specific and requires confirmation with plasma PCR and nearly 50% of patients with viruria will not develop viremia .
2. Plasma BK PCR BK viral loads are measured by polymerase chain reaction .
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I) . This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN. Therefore, rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads.
-*Urine Cytology: The characteristic BK virus-infected tubular epithelial cells are called decoy cells due to their similarity to renal carcinoma cells. They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin. Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN.
polyomavirus-Haufen are cast-like PV aggregates found in urine , via negative staining electron microscopy ,it has extremely high positive and negative predictive values for BK nephropathy, respectively. Additionally, the amount of PV-Haufen shed correlates well with disease severity .
-*Donor-Derived Cell-Free DNA (dd-cfDNA):
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. So it may be a useful noninvasive test to assess the progression of BKV to BKVAN .
-*Transplant kidney biopsy :
Kidney allograft biopsy is the gold standard for the diagnosis of BVAN, it confirms the diagnosis and assesses the severity of viral involvement and the presence of other ongoing pathologies. A biopsy should be adequate and contain medullary tissue.
For a definitive diagnosis of BKVAN The following pathologic features should be present : 1. Characteristic cytopathic changes . 2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. . -Diagnosis via a kidney biopsy is estimated to be missed in nearly 30% of cases so if the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain.
-* Histology :
_ The histologic findings include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions . _ Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles, usually in the distal nephron or medulla.
_As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen . _ Tubular cell injury , tubulitis and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.
-* Presence of tubular injury, tubulitis, and interstitial inflammation in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection .
Treatment :
A reduction in immunosuppression is the main therapeutic intervention in the treatment of BK viremia and BKVAN.
There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral load .
Protocols :
1.*Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone and monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks . 2.* complete cessation of anti-metabolite if viral loads continue to be at similar levels or increase . 3. * Reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies with antiviral activities :
*- IVIG:The rationale for use is the presence of BK-neutralizing antibodies in IVIG preparations. It is utilized in the setting of non-response to a maximal reduction in immunosuppression .Data from five observational studies have demonstrated a reduction in BK viral loads; however, other antiviral agents were administered at the same time as well . 2. Quinolones: is failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia
3. Cidofovir: limited by nephrotoxicity 4. Leflunomide: It demonstrated both immunosuppressive and anti-viral properties but has not proved efficacy in BKVN.
*Upcoming Therapeutic Trials :
1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868—a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1, which is responsible for binding to the surface of host cells (ClinicalTrials.gov identifier: NCT04294472).
2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia (ClinicalTrials.gov identifier: NCT04605484).
Kidney Re-Transplantation ; -Patients with graft loss due to BKVAN should be considered for re-transplantation . -Nephrectomy of failed transplant or native of is not recommended -Confirmation of viral clearance should be made prior to transplantation. -Consideration for lower immunosuppression should be balanced with the risk of rejection. -Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively. -In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group. – There was no significant difference in the rates of acute rejection or patient survival at one year.
BKPyV is the most common viral infection encountered post kidney transplantation with increasing mortality and morbidity. Epidemiology:
BKPyV is extensively prevalent in population, attracted early in life mainly through GIT, feco-oral rout. It’s characterized by prolonged period of latency in uroepithelium and renal interstitial cells after a period of viremia.
The virus is a double DNA virus consist of early coding larg T antigen TAg and small t antigen tAg, middle non-coding segment and late coding segment.
Immune suppression post transplantation is triggering the reactivation of dormant virus.
It was resulting in a 50-100% allograft loss earlier after the discovery of BKPyV.
currently its associated with 13 % allograft loss owing to increasing understanding and recognition of the virus. Consequences of reactivation
owing to suppression of cellular immunity post tansplantation there is reactivation of dormant virus or transferred virus with allograft,
The infection features 3 consequative stages, Viruria, Viremia and BKPN.
Viruria was detected in 30% and viremia in 12 % of patient post transplantation.
After developing viruria , 50% mount viremia in 2-6 weeks. 50% of viremic patient will ultimately develop BKPN.
Urine BK viral load of 8 log predict viremia.
Plasma viral load of 4 log predict BKPN.
Plasma viral load of 6 log is correlated with extensive BKPN with heavy infiltration detected by SV40 finding.
Treatment Plan:
In view of strong association of immune suppression with development of BKPyV infection, main strategy is to reduce immune suppressant medications, primarily by reducing and then stopping antimetabolytes .
second step is to reduce by half the doses of CNi ,
if no improvement then try medications:
Cedofovir, quinolones and recently leflunamide. However, with debatable effects.
IVIG is the most effective therapy in treating BKPN.
· BKV infection leads to BKN with subsequent graft loss.
· The prevalence increased among kidney transplant recipients after the introduction of potent immunosuppressive therapy (TAC and MMF).
· BK is DNA virus with 3 parts: early coding region for large and small tumor antigen (T and t), none coding part and late coding part.
· Primary infection occurs early in life and remains dormant in the kidney. Reactivation occurs in kidney transplant recipients after immunosuppression.
· Infection has 3 stages: viuria, viremia and BK nphropathy.
· Risk factors as old diabetic recipients, with prolonged cols ischemia time, and DGF, HLA and ABO incompatibility, serostatus prior to transplantation (D+/R-), use of strong immunosuppression as tacrolimus and MMF, treatment of repeated attacks of rejection, presence of ureteral stent.
· Screening for BKV infection:
o By blood PCR (more sensitive than urine PCR). Monthly screening during 1st 6 months then every 3months for 18 months is indicated for early detection of viremia and for reduction of immunosuppression prior to development of BKN (preemptive therapy)
o Urine PCR not recommended as it is not specific or correlated to pathology proven BKN, and needs further confirmation by blood PCR if it is positive.
o Decoy cells in urine:similar to renal carcinoma cells. These are
o tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed chromatin. it is a marker of PV replication, but not necessarily indicate PVN. Some studies have shown high false-positive rates and low positive predictive values, high PPV.
o Allograft biopsy remains the golden standard for diagnosis of BKN, however, negative biopsy in 30 % of cases due to focal and medullary affection.
o A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load >10,000 copies/mL.
o If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions is present.
· Treatment of BKV infection: reduction of immunosuppression (IS) is the main line of treatment.
o Reduction of IS; decrease dose of MMF to 50 % and follow up PCR after 2 weeks …if constant or increasing stop MMF completely.
o FU PCR after further 2 weeks, if no decrease in viral load try to decrease CNI dose.
o Additional IVIG, leflunamide, cidofovir can be used.
o Adoptive T cell immunotherapy can be used in resistant cases to reduction of IS (for fear of rejection with marked decrease in IS).
o For failing grafts: retransplantation is indicated after complete clearance of viremia, no clear recommendations to perform nephrectomy for either the native kidney or for the failing graft.
Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review: Introduction:
BK virus leading to nephropathy and it’s responsible for allograft kidney loss post transplant due to use of immunosuppressive therapy and it’s account 30% in kidney transplant cases. History of the BK Virus:
It’s first discovery in 1971 in case of ureteric stricture. In 1993 the first biopsy done prove presence of BK virus nephropathy. Virology:
It’s one of the Polyomaviridae family, it’s small closed circle non evolved double strand DNA. It’s consist of 3 regions ( first is consist of small t antigen and large T antigen); second non coding region and third coding region. Epidemiology:
Risk factors for replication of virus:
Intensity of immunosuppression
Old age of recipient / DM
Sero positive of donor and seronegative of recipient
ABO incompatible
HLA mismatch
Delay graft function and previous rejection.
Clinical manifestations:
Patients may asymptomatic; Viremia is present in 10–30 percent of recipients in the first six months post- transplantation and in 5–10 % of recipients. Viremia is a better predictor of progression to BKV in comparison to viruria. it’s also may lead to ureteral stenosis and hemorrhagic cystitis. Screening and Diagnosis:
Urine and plasma BK virus PCR
Urine culture for presence decoy cell.
Donor-Derived Cell-Free DNA (dd-cfDNA) Renal graft biopsy:
Presence of BK virus features is diagnostic for BK nephropathy and tubular cell enlargement and hyperchromatic nuclei and “ground glass” intra nuclear inclusion. With progress of infection tubulitis and interstitial inflam- into the tubular lumens (Figure 3). As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell. Treatment:
Reducing of immunosuppressive therapy to half especially anti metabolite to half (cellcept), and continuous prednisolone and calcinurine inhibitors; if viral load continues will stop cellcept but if viremia continues will reduce calcinurine inhibitors to half but not more than 4 weeks. Treat BK virus infection by quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG). Kidney Re-Transplantation:
BKV can lead to graft loss and allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years. Transplant kidney and native nephrectomy not recommended.
Summary of the article BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review BKV; virology and history 1. BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family. 2. BKV was first discovered in1971in a Sudanese KTR presented with ureteral stricture.The first definitive biopsy- proven case of BKVAN was described in 1993. 3. Based on the most recent registry data, 1–10% of kidney transplant recipients develop BKVAN. 4. BKV has a viremia rate of up to 30% in kidney transplant recipients.BKVAN frequently resulted in graft loss with rates of 50–100% reported. BKV;Epidemiology
1. BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
2. The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
3. Viruria and viremia are detected in approximately 30% and 12% of kidney transplant recipients, respectively.
4. After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
5. Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN.
6. BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates Risk factors for BKV replication:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3. The donor–recipient interface: The high-risk serostatus of D+/R-, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
5. Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis
1. Both CD4 and CD8 cells are playing a crucial role in cellular immune response against BKV.Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine.
2. Sites of latent infection include:
a) kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium.
b) Other sites: prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
3. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens).
4. BKVAN is associated with increased expression of various major groups of messenger RNAs.These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities.
5. The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
BKV infection; Clinical Manifestations
1. The classic sequence of infections in KTRs is viruria, viremia, and BKVAN.
2. The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation. The presence of sustained viruria may progress to viremia, which is asymptomatic initially.
3. BKVAN usually occurs after a period of sustained progressively worsening viremia.
a) The vast majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence.
b) Manifesting as a decline in renal function with or without urinary abnormalities.
4. Ureteral stenosis and hemorrhagic cystitis: albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants.
5. Urothelial malignancies in transplant recipients.
BKV infection; Screening and Diagnosis
1. The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
2. Urine BK PCR :not a recommended screening test given issues related to specificity and cost. It always requires confirmation with plasma PCR.
a) Plasma BK PCR has a higher positive predictive value of plasma BK levels. plasma BK viral load ≥10,000 copies/mL is a presumptive diagnosis for BKVN.
3. Urine Cytology:
a) for BK virus-infected cells (decoy cells), may exhibit “owl eye” inclusions, multi- nucleation, or clumped chromatin.
b) for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy.The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively. The amount of PV-Haufen shed correlates well with disease severity.
4. Donor-Derived Cell-Free DNA (dd-cfDNA) in association with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN.
5. Transplant Kidney Biopsy is the gold standard for the diagnosis of BVAN.
b) Characteristic cytopathic changes.
c) Positive immune-histochemistry tests(SV40).
BKV infection; Treatment
a) Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
b) If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
c) The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
d) Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
e) Upcoming Therapeutic Trials;
a) a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1.
b) adoptively transferred posoleuccel, multivirus-specific T Cells.
Kidney Re-Transplantation
1. Confirmation of viral clearance should be made prior to transplantation.
2. Consideration for lower immunosuppression should be balanced with the risk of rejection.
3. Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
4. Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines.
5. Five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group. There was no significant difference in the rates of acute rejection or patient survival at one year.
#The objective:
*To give overview on (BKV) epidemiology, pathogenesis, screening, diagnostic methods, as well as to discuss the clinical manifestations and recommended treatment strategies.
#Introduction:
*(BKVAN) is an important cause of graft loss in kidney transplant recipients. # Virology:
*BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
*The genome of the virus consists of three region
1)Early coding region of the large T and small t antigens.
2)Non-coding control region.
3)Late coding region.
*The T antigen has ability to bind to p53 and protein Rb, resulting in persistent infection.
* The non-coding control regions are for pathogenesis of the virus and can modulate transcription.
*Mutations in the non-coding control regions result in permit replication in other cell types cell tropism, and altered rates of replication.
*The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1,
VP-2, and VP-3).
# Epidemiology
*BK virus infection could be considered ubiquitous in the general population, with
seroprevalence rates of over 90% by 4 years of age.
*In the first post-transplant year the CMI suppressed due to induction therapy, which result in viral replication.
*Clinically significant infection occurs in KTR via reactivation of latent infection or transmission of new infection from the donor kidney.
*The infection occurs in the following chronological stages:
1)Viruria in 30%
2)Viremia in 12%
3)Allograft nephropathy.
# The risk factors for viral replication:
1. Intensity of immunosuppression ( most important facror):
The incidence of BK viremia is highest in the early post-transplant period.
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3.The donor–recipient interface:
The high-risk serostatus (D+/R-), ABO incompatibility, HLA mismatch, DGF, rejection or ischemia, and ureteral stent placement.
4. Donor-related factors:
Reduced immune response to BK virus and BK viruria prior to transplant.
*Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
# Cellular Immune Response and Pathogenesis:
*The clearance of BK viremia is dependent on a robust cellular immune response with both CD4 and CD8 cells playing a crucial role in this process.
*Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine, while high viral loads and the continued presence of the virus were associated with a weak response.
*BK-directed cytokine signatures from CD4 cells have demonstrated similar results, providing further evidence that a concerted effort from components of the cellular immune system is vital for tempering the virus
# Clinical Manifestations:
*Most BK virus infection lack of any systemic symptoms.
*The classic sequence of infections in KTR is viruria, viremia, and BKVAN.
*The most common and earliest manifestation of BKV is viruria (50%) in the first year of transplantation, with most cases not progressing to viremia.
*Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter it is a better predictor of progression to BKVAN in comparison to viruria.
*BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
*Ureteral stenosis and hemorrhagic cystitis
# Screening and Diagnosis:
* The (KDIGO) and (AST-IDCOP) guidelines recommend monthly screening for the first 6 months PKT every 3 months for the next 18 months.
** Urine BK PCR:
Not a recommended screening test given issues related to specificity and cost.
**Plasma BK PCR:
* Assay results are influenced by variations in DNA extraction techniques, sample type/source, primer and probe sequences.
*The (WHO) establishing an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL.
*BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference, this could lead to the non-detection of rarer genotypes.
** Urine Cytology:
*To detect the decoy cells which are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. Some studies have shown high false-positive rates and low positive predictive values when attempting to use the presence of decoy cells to
screen for PVN in transplant patients.
*To detect the presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively.
**Donor-Derived Cell-Free DNA (dd-cfDNA)
It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for TCR.
**Transplant Kidney Biopsy
*Is the gold standard for the diagnosis of BVAN.
*The pathologic features should be present for a definitive diagnosis of
BKVAN:
1. Characteristic cytopathic changes .
2. Positive immunohistochemistry tests using antibodies directed specifically against
BKV or against the cross-reacting SV40 large T antigen.
# Treatment:
*A reduction in the intensity of immunosuppression is cornerstone, with following steps:
1. Reduce antimetabolite by half while continuing on the same doses of CNI and/or prednisone.
( monitor serum creatinine and plasma BK PCR every 2 weeks).
2. If viral loads still at the same levels or increase, stop anti-metabolite.
3. Reduce CNI trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
*Other adjunctive therapies utilized to treat BK virus infection
1. IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression. It is benefit still not ctear.
2. Quinolones:
Studies failed to show the efficacy as prophylaxis or treatment for BK viremia
3. Cidofovir:
Studies have shown no benefit, associated with proteinuria, proximal tubular dysfunction,
and kidney disease.
4. Leflunomide:
Some study showed no benefit.
# Kidney Re-Transplantation
*Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
*Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and
3 years, respectively.
*Re-transplantation for graft failure due to other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
*There was no significant difference in the rates of AR or patient survival at one year.
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipient.
The rate of BK viremia (BKV) is as high as30% of kidney transplant recipients
History of BK virus:
BK virus was first discovered in a kidney transplant recipient in 1971.
The first definitive biopsy proven case of BKVAN was described in 1993.
BKVN was associated with graft loss in 15% of cases in the last 2 decades
Virology:
A small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
The genome of the virus consists of three regions: the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
Epidemiology:
The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
After primary infection, it remains dormant in kidney and uroepithelial cells for life.
After renal transplantation:
1. Viruria is detected in 30 % of cases, of which 50% develops viraemia
within 2-6 weeks.
2. Viraemia is detected in 12 %
3. BKVN develops in 1-10% of cases.
Risk factors:
1- Severity of IS: more with high level of IS. Less with m-TOR inhibitors.
2- Recipient factors: old age, DM.
3- Donor-recipient interface: D+/R-, Abo incompatibility, HLA-mismatch, delayed graft function, acute rejection, stent placement
4- Donor-related factors:reduced immune response to BKV, previous infection. Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective against BKV infection Clinical manifestations:\
Most infections are asymptomatic
The classic consequence is viruria, viraemia and BKVN
Viruira: 50% of cases develop in the first year after transplantation.
Viremia is present in 10–30 % of recipients in the first six months post-transplantation and in 5–10 % of recipients thereafter.
Viremia is a better predictor of progression to BKVAN in comparison to viruria.
BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
Other consequences: ureteral stenosis and hemorrhagic cystitis
Screening and diagnosis:
KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
1- Urine BKPCR: is not a recommended screening test for low specificity and cost.
2– Plasma BKV level is the preferred method because of high positive predictive value. It is higly sensitive for genotype I and with low sensitivity for other genotypes.
3- Urine cytology: To detect viral infected cells (decoy cells).These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. Highly sensitive but low specific with 100% negative predictive value.
4- Donor-Derived Cell-Free DNA (dd-cfDNA): Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for
T-cell-mediated rejection. 5- Kidney biopsy:
The gold standard for diagnosis of BKVN.
As the infection affect the medulla, diagnosis could be missed in 30% of cases and two biopsies including cortex and medulla are recommended.
Pathological features for diagnosis:
A- Cytopathic changes (histological)
The histologic findings of this process include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions.
May also include granular nuclear inclusions and “clumps” of intranuclear virion particles.
As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cells may be seen.
It may result in tubular atrophy and interstitial fibrosis.
B- Positive immune-histochemistery test:
Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN); although, it does not distinguish between BKV and JC virus (JCV)
C- Electron microscopy: PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify sample
AR and PVN can co-occur, creating a treatment dilemma.
In both cases, tubular injury, tubulitis, and interstitial inflammation are key histologic findings.
The presence of these findings in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection.
A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN.
Features of vascular injury such as endarteritis, arterial fibrinoid necrosis, glomerulitis, or peritubular capillary C4d staining are more consistent with acute rejection than PVN.
Treatment:
There is no therapeutic agent available to treat this virus-associated disease.
The following is a stepwise approach for management:
1- Reduce dose of antimetabolite by half while continuing on the same doses of
calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine
and serial plasma BK PCR level every 2 weeks in the interim.
2- If viral loads continue to be at similar levels or increase, proceed with complete
cessation of anti-metabolite.
3- The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for
tacrolimus and 50–100 ng/L for cyclosporine.
The 5-year follow-up data of patients with BK viremia and BKVAN, kidney transplant recipients maintained on tacrolimus-based regimes had lower rates of rejection and a higher eGFR.
Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir.
IVIG: The rationale for use is the presence of BK-neutralizing antibodies in IVIG preparations. Data from five observational studies have demonstrated a reduction in BK viral loads; however, other anti-viral agents were administered at the same time as well.
Quinolones: randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viraemia
Cidofovir: Studies have shown no benefit with cidofovir use with associated nephropathy.
Leflunomide: the drug and its active metabolite have immunosuppression and anti-viral effect. prospective open-label study showed no benefit.
Kidney re-transplantation:
Patients with graft loss due to BKVN should be considered for re-transplantation given its extensive evidence of success.
Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family .
The genome of the virus consists of three regions;
1-The early coding region of the large T and small t antigens (large and small tumor antigen).
The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection.
2-The non-coding control region.
Are a significant contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription. Mutations in the non-coding control regions result in permit replication in other cell types (permissivity), cell tropism, and altered rates of replication .
3- The late coding region.
for the agnoprotein and viral capsid proteins (VP-1,VP-2, and VP-3).
Epidemiology;
———————————
BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age .
The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract. After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
The infection occurs in the following chronological stage ;
———— ——————— ————–
1-viruria
Viruria is detected in approximately 30% kidney transplant recipients.
2-viremia
viremia is detected in approximately 12% of kidney transplant recipients .
Viral replication is associated with the following risk factors:
———————————————————————–
1-Intensity of immunosuppression .
2-Recipient characteristics: older age , diabetes , and specific HLA-C alleles .
3-The donor–recipient interface:
a-The high-risk serostatus of donor positive and recipient negative for BK virus .
b-ABO incompatibility.
c-HLA mismatch .
d-delayed graft function .
e-rejection or ischemia of the transplanted kidney .
f- ureteral stent placement .
4- Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
The protective factors;
——————————————————-
1-Recipient HLA-B51 positivity .
2- The presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis;
——————————————————————–
1-The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium . Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
2-The latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
3-Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways.
4- BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
5-These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities .
6-The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss .
Clinical Manifestations; ———————————————– 1- The classic sequence of infections in kidney transplant recipients is viruria, viremia, and BKVAN.
2-The most common and earliest manifestation of BKV is viruria
occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia .
3- Viremia is present in 10–30 percent of recipients in the first six months post- transplantation and in 5–10 percent of recipients thereafter .
4- BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities. The vast majority of BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence .
5- Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis—albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants. There are reports of a possible link between the BK virus and genitourinary (GU) malignancies, especially given its protracted infection in epithelia of the GU tract.
Screening and Diagnosis ; ——————————————————— 1- Urine BK PCR;
Urine BK PCR is not a recommended screening test given issues related to specificity and cost—if positive, it always requires confirmation with plasma PCR and nearly fifty percent of patients with viruria will not develop viremia .
2- Plasma BK PCR;
BK viral loads are measured by polymerase chain reaction (PCR)—a fluorescent probe BK-specific sequence, and the number of amplicons produced is compared with a standard curve generated with serial dilutions of a known concentration of BK DNA .
3- Urine Cytology;
A-The characteristic BK virus-infected cells that present on cytologic examination of urine are called ′decoy cells′ due to their similarity to renal carcinoma cells.
Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN.
B-Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively. Additionally, the amount of PV-Haufen shed correlates well with disease severity .
4- Donor-Derived Cell-Free DNA (dd-cfDNA);
It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful
noninvasive test to assess for progression of BKV to BKVAN .
5- Transplant Kidney Biopsy;
Kidney allograft biopsy continues to be the gold standard for the diagnosis of BVAN.
A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL. Given that BK mostly affects the medulla and is associated with focal disease, diagnosis via a kidney biopsy is estimated to be missed in nearly 30%
of cases . If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain.
The following pathologic features should be present for a definitive diagnosis of BKVAN :
1- Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen.
Histology; ————————————————–
The histologic findings of this process include;
1-Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions .
In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla.
As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen .
More proximal portions of the nephron, including the parietal epithelial cells lining Bowman′s capsule, may also become involved. The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis .
2-Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles.
Limitations of the histological diagnosis ;
—————————————————————-
Histologic confirmation of the presence of polyoma virus can prove difficult.
1-The random and focal nature of the infection can result in false negatives if uninvolved parenchyma is sampled .
2- The histologic similarities it shares with acute rejection (AR).
How to maximize the likelihood of identifying the histolgic diagnostic features;
—————————————————————————————————
1-Two biopsy cores containing renal cortex and medulla are recommended .
2-To aid in the detection of PV within biopsies, ancillary tests such as immunohistochemical (IHC) stains or in situ hybridization (ISH) can be performed.
Currently, it is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen .
3- Quantitative PCR for PV can also be performed on tissue samples . However, given the high frequency of latent PV virus infection, interpretation of these results requires caution.
4-PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
The histological differentiation between PVN and acute rejection (AR);
———————————————————————————————
1-AR and PVN can co-occur, creating a treatment dilemma . In both cases, tubular injury, tubulitis, and interstitial inflammation are key histologic findings .
2-The presence of these findings in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection.
3-A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN. However, plasma cell-rich infiltrates are not PV specific and can be seen in TCMR .
4- Features of vascular injury such as endarteritis, arterial fibrinoid necrosis, glomerulitis, or peritubular capillary C4d staining are more consistent with acute rejection than PVN .
5-In cases of histologic overlap, a diagnosis of concomitant PVN and AR should be considered. In these instances, the histologic findings should be correlated with the clinical history and results of additional laboratory studies, such as BK viral load and the presence of donor-specific antibodies (DSA).
The histological grading ;
—————————————
1-The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
2-As per this system, histologic classes of definitive PVN are defined by the morphologic degree of intrarenal pvl (polyomavirus replication/load level) and Banff ci scores (interstitial fibrosis).
3-The scoring of pvl is on the basis of the extent of virally induced tubular changes, while a tubule with intranuclear viral inclusion bodies (type 1 or 2) and/or a positive IHC reaction for SV40-T antigen in one or more cells per tubular cross-section is considered “a positive tubule”.
The overall percentage of positive tubular cross-sections is estimated in the entire biopsy sample (all available cores, cortex, and medulla). The pvl score is calculated based on the extent of virally induced changes identified on H&E or via SV40 IHC staining.
Scores for pvl are calculated as follows:
pvl1: ≤1% of all tubules/ducts with viral replication.
pvl2: >1 to ≤10% of all tubules/ducts with viral replication.
pvl3: >10% of all tubules/ducts with viral replication.
Treatment ;
1-A reduction in the intensity of immunosuppression ;
———————————————————————–
is the overarching principle for the treatment of BK viremia and BKVAN.
The following is a stepwise approach for the reduction in immunosuppression in the setting of BK viremia and BKVAN based on trials in adult and pediatric kidney transplant
recipients :
A-Reduce dose of anti metabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay
variability) every 2 weeks in the interim.
B. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
C. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
2-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
————————————————————————————————-
1. IVIG:
It is utilized in the setting of non-response to a maximal reduction in immunosuppression (balancing with risk of rejection).
2. Quinolones:
Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia .
3. Cidofovir:
A nucleotide analog of cytosine has demonstrated activity against Poly- omaviridae in-vitro . Studies have shown no benefit with cidofovir use, notwithstanding that a significant risk of kidney dysfunction was noted.
4. Leflunomide:
A pro drug that converts to an active metabolite, which has demonstrated both immunosuppressive and anti-viral properties . While there was initial enthusiasm for its use in BK virus infection based on a case series,a pharmacodynamic and prospective open-label study showed no benefit .
Upcoming Therapeutic Trials
————————————————
Given the lack of therapies available for the treatment of BK infection, the two following trials involving modified T cells and monoclonal antibodies are currently underway.
Kidney Re-Transplantation;
——————————————————
1-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success .
2- Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
3- Consideration for lower immunosuppression should be balanced with the risk of rejection.
4-Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively .
5-In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
6- There was no significant difference in the rates of acute rejection or patient survival at one year .
Introduction
BK virus-associated nephropathy (BKVAN) can lead to graft loss in kidney transplant recipients. A higher incidence of BK viremia has been noted with more efficient immune suppression after kidney transplantation. The aim of this review was to provide information on BK virus – history, epidemiology, virology, cellular response, pathogenesis, screening methods, diagnosis and the appropriate treatment strategies.
History of BK virus
In 1971, a kidney transplant recipient presented with a ureteral stricture which helped us discover BK virus. The first definitive biopsy proved BKVAN in 1993. Initially, BKVAN led to a 50-100% risk of graft loss. Better management has reduced this to approximately 15%.
Virology
BK virus belongs to the Polyomaviridae family. It is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus. The genome consists of three regions:
The early coding region
The late coding region
The non-coding region
Epidemiology
BK virus infection is quite prevalent in the general population, approximately 90%. It is transmitted via mucosal contact (oral, gastrointestinal, respiratory tract). After the primary infection, the virus remains in the kidney and uroepithelial cells, leading to a persistent latent infection. During the first year after transplantation, the induction therapy for immune suppression suppresses the cellular immunity. This may result in viral replication, reactivation of latent infection or new infection from the donor kidney. The infections occurs as viruria, viremia then allograft nephropathy. The risk factors of viral replication include:
The intensity of immune suppression in the first year post transplantation
The characteristics of the transplant recipient
Older age of patients, diabetes, specific HLA-C alleles pose a higher risk
The donor-recipient interface
Donor positive/recipient negative, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the graft, ureteral stent placement are considered high risk
Donor-related interface
Reduced immune response to BK virus, BK viruria before the transplant are considered high risk.
Cellular immune response and pathogenesis
Cellular response is required for the mitigation and clearance of BK virus. The presence of IFN-gamma activity is indicative of BK-directed cellular immune response, and therefore is associated with the resolution of BKVAN. IFN-gamma activity can be quantified using ELISPOT (enzyme-linked immunosorbent spot). Also, vigorous CD8-based cellular response correlated with lower BK viral loads in blood and urine. The latent infection takes refuge in the kidney, mainly the parietal epithelium of the Bowman’s capsule, renal tubular epithelium and transitional epithelium. Other sites of the latent infection include prostate, testes, seminiferous tubules, cervix, vulva and hematolymphoid tissues. Damage to the tubular epithelium is due to the continuous viral replication and its cytopathic effect with inflammation. The final stage of destruction is characterized by interstitial fibrosis, tubular atrophy and hence loss of nephrons.
Clinical manifestations
Most clinically significant BK virus infections lack any systemic symptoms. The sequence of infections in kidney transplant recipients is viruria, viremia and BKVAN. Other manifestations include ureteral stenosis and hemorrhagic cystitis. There are reports of a possible link between BK virus and genitourinary malignancies. Screening and diagnosisScreening of BK virus is now used due to the high incidence rate of the infection.
Urine BK PCR
Not a recommended screening test, as it has low specificity and high costs.
Plasma BK PCR
It has inter-assay variability due to variations in DNA extraction techniques, sample type/source, primer and probe sequences and the strain of BK DNA. Also, rare genotypes are often not detected.
Urine cytology
On cytologic examination of urine, the BK virus-infected cells are called ‘decoy cells’ as they are similar to renal carcinoma cells. The cells are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed ring of chromatin. They may also include ‘owl eye’ inclusions, multi-nucleation or clumped chromatin.
Donor-derived cell-free DNA (dd-cfDNA)
A recent study demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BKVAN and histologic changes associated with T-cell-mediated rejection. These findings validate that dd-cfDNA may be useful investigation to assess the progression of BKV to BKVAN.
Transplant kidney biopsy
Kidney allograft biopsy is the gold standard for the diagnosis of BKVAN. It also assesses the severity of viral involvement and the presence of other pathologies. The biopsy core should contain the medulla, as BK is usually found in the medulla. A definitive diagnosis requires the following pathologic features:
Characteristic cytopathic changes
Positive immunohistochemistry tests using antibodies specifically against BK virus.
Histology
In the genitourinary tract, the virus targets the urothelial and renal tubular cells. The histologic findings include tubular epithelial cells with enlarged, hyperchromatic nuclei and ‘ground glass’ intra-nuclear inclusions. Viral cytopathic changes may also include granular nuclear inclusions and ‘clumps’ of intranuclear virion particles.
In the early stages, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla. These cells will eventually lyse and slough from the basement membrane into the tubular lumens. As the infection progresses, tubulitis and interstitial inflammation may be seen. The proximal parts of the nephron may also be involved. The tubular cell injury, tubulitis and interstitial inflammation may lead to tubular atrophy and interstitial fibrosis.
The random and focal nature of the infection may lead to false negatives, especially if the uninvolved parenchyma is sampled. Therefore, two biopsy cores containing the renal cortex and medulla are recommended.
The Simian Virus 40 (SV40) ICH stain can be performed to highlight cells in the early stages of infection and may also help to differentiate PVN from other viral nephropathies. PV can also be identified using electron microscopy.
Acute rejection has histologic similarities to PVN – tubular injury, tubulitis and interstitial inflammation. Features of vascular injury such as endarteritis, arterial fibrinoid necrosis, glomerulitis or peritubular capillary C4d staining are more consistent with acute rejection than PVN.
Treatment Immunosuppression Reduction:
Treatment of BK viremia and BKVAN begins with a reduction in immune suppression:
Reduce the dose of antimetabolite by half, continue the same dose of CNI and prednisone, while monitoring serum creatinine and plasma BK PCR levels.
If viral loads continue to be similar or increase, the antimetabolite needs to be stopped.
The next step is to reduce the CNI, if the viral load do not reduce after 4 weeks of stopping the antimetabolite.
Other adjunctive therapies used to treat BK virus infection include: IVIG
It is used when there is no response to a reduction in immune suppression. IVIG contains BK-neutralizing antibodies in its preparation. Quinolones
In vitro, quinolones demonstrated anti-viral properties. However, randomized trials have failed to show its efficacy as prophylaxis in the treatment for BK viremia. Cidofovir
It is a nucleotide analog of cytosine. It has also demonstrated anti-viral properties in vitro. Unfortunately, studies have shown no benefit with cidofovir use. Its use has also been associated with kidney dysfunction: proteinuria, proximal tubular dysfunction and kidney disease. Leflunomide
It is a prodrug that converts to an active metabolite, which has demonstrated immunosuppressive and anti-viral properties. A pharmacodynamics and prospective open-label study has shown no benefit of the medication.
Kidney Re-transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation. Consideration for using lower doses of immune suppression should be balanced with the risk of rejection. It has been shown that patients who undergo re-transplantation have an allograft survival rate of 98% at 1 year post transplantation and 94% at three years.
Conclusion
BK virus infection post kidney transplantation is a common clinical issue. Increasing the surveillance for the infection has led to understanding its true prevalence and aids in reducing progression to severe disease. There is no antiviral treatment for the BK virus. The main treatment consists of reducing the immunosuppression which has to be balanced with risk of acute rejection. However, there is hope as several trials are underway to ascertain the appropriate treatment regime.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
Please summarise this article. Introduction: BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. The efficacious immunosuppression has been accompanied by high rates of BK viremia (BKV) in up to 30% of kidney transplant recipients. No effective prophylaxis or treatment for (BKVAN) described yet. History of the BK Virus: First described in 1971 in a transplanted patient with ureteral stricture, but proven tissue biopsy diagnosis was in 1993. The increasing incidence of BK viremia over the subsequent years was as a result of: the increasing availability of reliable testing methods. a consequence of more potent immunosuppression regimes. Graft loss occurs in 50-100% of patients with (BKVAN), this rates decreased by better understanding the virus and the role of immunosuppression modification. Virology: A small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family. The genome of the virus consists of three regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region. T antigen binds to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection. The non-coding control regions are a reason for virus enhancement and replication that can modulate transcription. The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3), that are responsible for the assembly of viral capsids, the release of virion from cells, and the classification of viral genotypes I to VI (by VP-1). VP-3 leads to activation of the adenosine diphosphate-ribose polymerase, resulting in depletion of adenosine triphosphate (ATP) and cell death. Epidemiology: 90% of population at age of 4 years are seropositive for BKV. Transmitted through the mucous membranes oral, gastrointestinal, and respiratory tract. Lifelong latent/persistent infection colonize the kidneys and uroepithelial cells. The infection occurs in the following chronological stages—viruria 30%, viremia 20%, and allograft nephropathy. Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates. Recipient HLA-B51, and the presence of polycystic kidney disease are protective of BKVAN. Risk factors: 1. Intensity of immunosuppression: 2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles. 3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement. 4. Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant. Cellular Immune Response and Pathogenesis: The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus. Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine, and BK-directed cytokine signatures from CD4 cells have demonstrated similar results. The virus maintains persistent infection in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, transitional epithelium, prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils). The mRNAs expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities. The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss. Clinical Manifestations: Mostly asymptomatic, viruria occurs in 50% of patients within the first year of transplantation, may progress to viremia in 10-30% of patients in the first 6 months, decreasing to 5-10% thereafter. Ureteral stenosis and hemorrhagic cystitis, and urethral malignancies. Screening and Diagnosis: Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method. The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months. Urine BKV PCR: NOT recommended for screening, as 50% of viruria will not develop viremia, with low specificity. Plasma BKV PCR: Factors that affect the accuracy of the test are, the sample size, source, primer and probe sequences, and BK strain DNA, BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I). This could lead to the non-detection of rarer genotypes. Urine Cytology: decoy cells, are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin, they do not necessarily indicate BKVN, can be found in other viral infection as well as tumor cells, but its of high negative predictive values for PKVN. polyomavirus-Haufen, cast-like PV aggregates, has a high positive predictive value, and high NPV for BKVN, and correlate with disease severity. Donor-Derived Cell-Free DNA (dd-cfDNA): higher levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection, so it helps in assessing progression of the disease, but not diagnosis. Transplant kidney biopsy: is the gold standard for diagnosis of BKVN, and other etiologies, with two cores, medulla sampling to decrease error results. Pathological features are: 1. Characteristic cytopathic changes: focal medullary lesions. 2. Positive histoimmunochemistry, antibodies against SV40 large T antigen, with 100% specificity, but distinguish between BKV and JCV. A kidney biopsy is missing in nearly 30% of cases, so repeat biopsy is recommended if clinical suspicions remains with high serum BKV PCR> 10,000 copies/ml. Histology: 1. Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusion, “clumps” of intranuclear virion particles. 2. Tubulitis and interstitial inflammation with a prominent plasma cell components. 3. IFTA. However; team discussion of the biopsy and BKV viral load and DSA results, with clinical history to distinguish between BKV and acute rejection is mandatory as the treatment is opposite. Treatment: Reduction of immunosuppression (IS) is the mainstay treatment, protocols as follow: 1. Reduce dose of antimetabolite by 50%, continuing on the same doses of calcineurin inhibitor and/or prednisone, with every 2 weeks monitor serum creatinine and plasma BK PCR levels. 2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite. 3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine). IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression. Quinolones: data showed failure in BKV prophylaxis, not used in treatment. Cidofovir: Studies have showed no benefit from its use, with nephrotoxicity. Leflunomide: data showed no effect in treatment. Upcoming Therapeutics in trials are a human monoclonal antibody (IgG1), and adoptive immunotherapy. Kidney Re-Transplantation: Re-transplantation should be done, after viral clearance by PCR, with Allograft survival of 98% and 94% at 1 and 3 years which is much better than that for other causes of graft failure (91% and 84% respectively). Conclusions: BKV is a common challenge faced in kidney transplantation, the only treatment is IS reduction, there is ongoing promising therapeutics in clinical trials. Retransplantation should be offered for those treated patients with absent viral load with an excellent graft survival.
Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. History of the BK Virus
BK virus was first discovered in a kidney transplant recipient in 1971. Virology
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and a member of the Polyomaviridae family.
It consists of three regions: the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region. VP-1 is the major structural protein that engages with cellular receptors and VP-2 and VP-3 act as nuclear location signals.
Epidemiology BK virus infection is ubiquitous in the general population, with seroprevalence rates of over 90%. In kidney transplant recipients, Viruria, viremia, and allograft nephropathy are detected.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression is the most significant factor associated with BK viral replication, with the incidence of BK viremia highest in the early post-transplant period. Recipient characteristics: older age, diabetes, and specific HLA-C alleles
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3. Donor-recipient interface is at high-risk for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia, and ureteral stent placement.
4. HLA-B51 positivity and polycystic kidney disease are protective factors against BKVAN, resulting in a fivefold reduction in its occurrence. Cellular Immune Response and Pathogenesis
T-cell responses are essential for BK viremia mitigation and clearance, quantified with ELISPOT and tetramer staining.
ELISPOT-measured IFN-gamma activity is associated with BKVAN resolution, with shorter time interval (<1 month) and longer duration of anti-BK T cell response.
BKVAN maintains persistent infection in the kidney epithelium and can become active with reduced cellular immunity after immunosuppression.
It is associated with increased expression of various mRNAs, including CD8, perforin, interferon-γ, and CXCR3, which may explain common clinical and pathological features in BKVAN and TCMR.
Clinical Manifestations:
Viruria is the most common manifestation of BKV in kidney transplant recipients, with most cases not progressing to viremia.
Viremia is a better predictor of progression to BKVAN than viruria.
BKVAN usually occurs after a period of worsening viremia, with the first 2-6 months being the highest incidence. There are reports of a possible link between the BK virus and genitourinary (GU) malignancies, but its causative role in humans is controversial.
Screening and Diagnosis
Screening for BK viremia is the primary technique used in transplant centers due to its positive predictive value.
KDIGO and AST-IDCOP guidelines recommend monthly screening for BKVAN. a. Urine BK PCR
Urine BK PCR is not recommended due to specificity and cost. b. Plasma BK PCR
The WHO established an international standard to standardize viral load values among different laboratory assays, but there is still variability due to DNA extraction techniques and amplicon size.
Genotypes of the BK virus detected by PCR assays can be less sensitive for variant strains, leading to the non-detection of rarer genotypes. Rare genotypes should be considered in the event of lower viral loads.
c. Urine Cytology
Urine can be examined for Decoy cells, polyomavirus-Haufen, and cast-like PV aggregates which have high positive and negative predictive values for BK nephropathy. d. Donor-Derived Cell-Free DNA (dd-cfDNA):
dd-cfDNA may be a useful noninvasive test to distinguish asymptomatic BKV from BKVAN. e. Transplant Kidney Biopsy
Considered the gold standard for the diagnosis of BVAN, as BK is tropic for the medulla, reducing sampling error.
The following pathologic features should be present for a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes.
2. Positive SV40 staining is useful for identifying BKV and PVN, but does not distinguish between JCV.
Diagnosis of BKVAN is likely to be missed in 30% of cases, with repeat biopsy recommended if clinical suspicions remain. f. Histology
Identifying the histologic features of polyomavirus infection on renal biopsy is essential for the diagnosis of “definitive” BKVAN.
Viral cytopathic changes may include enlarged, hyperchromatic nuclei, granular nuclear inclusions, and intranuclear virion particles. As the infection progresses, tubulitis and interstitial inflammation may occur, resulting in tubular atrophy and fibrosis.
Treatment
A reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
A stepwise approach for reducing immunosuppression in BK viremia and BKVAN based on trials in adult and pediatric kidney transplant recipients.
1. Reduce the dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. Monitor serum creatinine and BK PCR levels every 2 weeks to reduce inter-assay variability.
2. Complete cessation of anti-metabolite if viral loads increase.
3. The next step is to reduce calcineurin-inhibitor through goals if viral loads do not reduce.
Adjunctive therapies such as quinolones, cidofovir, leflunomide, and intravenous immunoglobulin are the only viable adjunctive therapies for BK virus infection, while other agents are not recommended. Upcoming Therapeutic Trials
Given the lack of therapies available for the treatment of BK infection, the two follow- ing trials involving modified T cells and monoclonal antibodies are currently underway:
1. A human monoclonal antibody (IgG1) that binds the viral capsid protein
2. Adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients Kidney Re-Transplantation
Re-transplantation is recommended for patients with graft loss due to BKVAN, but confirmation of viral clearance should be made prior to transplantation. Conclusions
BK virus infection is a common clinical issue for transplant providers, with increased surveillance protocols leading to expedient detection and mitigation of severe disease.
Novel therapeutics may bring efficacy, but no anti-viral is currently known to be of benefit.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Introduction
· The genome of the virus consists of three regions, the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
· BKV has 3 viral capsid proteins (VP-1, VP-2, and VP-3).
· VP-1 has significant genetic heterogeneity—this recognition has led to the classification of viral genotypes I to VI.
· Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases.
· Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
· The infection occurs first as viruria, then viremia, and finally allograft nephropathy.
· Urine BK viral loads >8 log10 c/mL predict the onset of viremia.
· Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN.
· Loads above 6 log10 c/mL are predictive of extensive BKVN pathology.
Cellular Immune Response and Pathogenesis: · Clearance of BK viremia is dependent cellular immune response—with both CD4 and CD8 cells implicated in this process. · Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect. · Continued inflammation leads to the activation of pro-fibrotic pathways. · The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy. Clinical Manifestations · Most clinically significant infections associated with the BK are asymptomatic. · The most common is viruria. · Viremia is a better predictor of progression to BKVAN in comparison to viruria. · The first 2–6 months are the periods of highest incidence of BAKVAN. · Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis (rare in kidney transplant recipients). · There are reports of a possible link between the BK virus and genitourinary malignancies. Screening and Diagnosis · There are standard screening protocols. · Screening for BK viremia is the preferred method. · The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 month. 1. Plasma BK PCR: · The results are expressed as international units/mL. 2. Urine Cytology · For decoy cells. · Decoy cells do not necessarily indicate PVKN. · Urine samples may also be screened for the presence of cast-like PV aggregates, called polyoma virus- Haufen in electron microscopy. 3. dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN 4. Transplant kidney biopsy: · Kidney allograft biopsy is the gold standard diagnosis for BKVN. · The following pathologic features should be present for a definitive diagnosis of BKVAN: A. Characteristic cytopathic changes. B. Positive immunohistochemistry tests against BKV or against SV40 large T antigen. It has a specifity of almost 100%.for PVN. 6. Histology · Viral cytopathic changes: include tubular epithelial cells with enlarged, hyperchromatic nuclei and “groundglass” intranuclear inclusions. · As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen. · The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis. · To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended. · immunohistochemical stains (SV40) or in situ hybridization can be performed. · EM: The presence of 40 nm viral particles within the nuclei of tubular cells. Histology of BKV and AR: · There are histological similarities between BKVN and AR. · Reaching a correct diagnosis is clinically important. · In rare cases BKVN and AR can occur together. · In both cases, tubular injury, tubulitis, and interstitial inflammation are key histologic findings. · The presence of above mentioned findings in the absence of morphologic or immunohistochemical evidence of PV infection should permit consideration of ACR. · If the changes are confined only to the medulla, this should raise concerns of BKVN. · If there is histologic overlap, the diagnosis of both condition should be made. Treatment: · A reduction of immunosuppression is the principle for the treatment of BK viremia and BKVAN. 9. There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads. Stepwise approach for the reduction in immunosuppression in the setting of BKVN based on clinical trials: 1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. 2. If viral loads continue to be the same levels or increased, proceed with complete cessation of anti-metabolite. 3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine). Other adjunctive therapies: 1. Quinolones, cidofovir: Studies have shown no benefit with their use. 2. Leflonamide: an open-label study showed no benefit with its use. 3. IVIG: Data from five observational studies have demonstrated a reduction in BK viral loads; however, other anti-viral agents were administered at the same time as well. Upcoming Therapeutic Trials 1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868. 2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) in kidney transplant recipients with either high or low levels of BK viremia
BK virus maintains a latent infection in humans, which can reactivate in the setting of a dysfunctional cellular immune response and is frequently encountered in kidney transplant recipients. With BK virus infection there is higher risk of graft loss. Virology BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family Its genome has three regions – The early coding region of the large T and small t antigens The non-coding control region The late coding region. Epidemiology The seroprevalence rates of over 90% by 4 years of age. Transmission by mucosal contact including the oral, gastrointestinal, and respiratory tract Viral replication can frequently ensues in first year post transplant The chronological stages—viruria, viremia, and allograft nephropathy 1–10% of kidney transplant recipients develop BKVAN Risk Factor of BKV infection Intensity of immunosuppression Recipient characteristics: older age, diabetes, and specific HLA-C alleles The donor–recipient interface- The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney and ureteral stent placement Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant HLA-B51 positivity and the presence of polycystic kidney disease has protective effect against BKV Clinical Presentation Viruria It occurrs in up to 50% of patients in the first year of transplantation Viremia Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter BKVAN It manifests as a decline in renal function with or without urinary abnormalities BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence Hemorrhagic cystitis Ureteric stricture Diagnosis Urine BK PCR– it always requires confirmation with plasma PCR Plasma BK PCR– BK viral loads are measured by polymerase chain reaction (PCR) Urine Cytology– Decoy cells are typical. Donor-Derived Cell-Free DNA (dd-cfDNA)– association of dd-cfDNA with plasma BK viral loads Transplant kidney biopsy– Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear Treatment Decrease Immune suppression- Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite Next step is reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite . IVIG Quinolones Cidofovir Leflunomide Kidney Re-Transplantation Re transplantation should be considered. Failed transplant or native nephrectomy is not recommended. Consideration for lower immunosuppression should be balanced with the risk of rejection. Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
The successful advent of increasingly efficacious immunosup- pression has been accompanied by high rates of BK viremia (BKV) in up to 30% of kidney transplant recipients .
During the period of its early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported .
Viral replication is associated with the following risk factors .
Intensity of immunosuppression: This is considered as the most significant factor associated with BK viral replication .
Recipient characteristics: older age , diabetes , and specific HLA-C alleles.
The donor–recipient interface ,ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement .
Donor-related factors: reduced immune response to BK virus , and BK viruria prior to transplant .
Most clinically significant infections associated with the BK virus lack any systemic symptoms
The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia .
Viremia is present in 10–30 percent of recipients in the first six months post- transplantation and in 5–10 percent of recipients thereafter .
The vast majority of BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence . Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis .
Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in these protocols .
PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/μL for the variant strain compared with 10 copies/μL for genotype I) .
Kidney allograft biopsy continues to be the gold standard for the diagnosis of BVAN .
A reduction in the intensity of immunosuppression is the overarching principle for the tretment.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review. History of the BK Virus.
First case was discovered in post kidney transplant recipient presented with ureteric obstruction from Sudan but published first time on 1991, it was increasing due to highly discovered newly immunosuppression drugs as well as the highly sensitive tests for diagnosis, it is now associated with graft loss 15% within the last 2 decades. Virology.
A small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family, The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection. The classification of viral genotypes I to VI. Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases. It is notable that the generation of antibodies against one serotype does not result in durable protection against other types. Epidemiology.
Seroprevalence rates of over 90% by 4 years of age . The primary routes for transmission of the virus are from mucosal contact and after a primary viremia, the BK virus establishes refuge in the kidney and uroepithelium cells resulting in lifelong latent/persistent infection which reactivates in immunocompromised patient and lead to infection that occurs in the following chronological stages—viruria, viremia, and allograft nephropathy.
This correlates with the clinical observation that urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates. Viral replication is associated with the following risk factors:
A-Intensity of immunosuppression.
B-Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
C-Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
D-The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney, and ureteral stent placement. Clinical Manifestations.
The presence of sustained viruria may progress to viremia, which is asymptomatic initially. Viremia is present in 10–30 percent of recipients in the first six months post-transplantation and in 5–10 percent later on. Viremia is a better predictor of progression to BKVAN in comparison to viruria, BKVAN usually manifesting as a decline in renal function with or without urinary abnormalities, and other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis. Screening and Diagnosis.
Guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
1-Urine BK PCR is not a recommended screening test given issues related to specificity and nearly fifty percent of patients with viruria will not develop viremia.
2-Plasma BK PCR is sensitive and used mainly to confirm BK Viruria and used for screening.
3-Urine cytology: The characteristic BK virus-infected cells that present on cytological examination of urine are called (decoy cells) and the absence of decoy cells in urine cytology screens had high negative predictive values for PVN.
4-Donor-Derived Cell-Free DNA (dd-cfDNA): higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
5-Transplant Kidney Biopsy: is considered the gold standard for diagnosis BKVN. The histologic findings of this process include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions, overlap, a diagnosis of concomitant PVN and AR should be considered. In these instances, the histologic findings should be correlated with the clinical history and results of additional laboratory studies, such as BK viral load and the presence of donor-specific antibodies (DSA). Treatment.
A-Reduction of immunosuppreive medications.
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
B-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG). A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or Cidofovir. Kidney Re-Transplantation.
Failed transplant or native nephrectomy is not recommended, confirm BKV PCR negativity. Conclusion:
BK virus is one of the most common viral infection post kidney transplant which occurred mainly first year post ktx and screening is important every month for 6 months by BKV PCR and kidney biopsy is the gold standard of diagnosis, reduction of immunosuppreive medications is the cornerstone of treatment with or without adjuvant therapy.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review Summary of this article:
Introduction.
BK virus-associated nephropathy (BKVAN) is one of the major causes of kidney graft loss post-transplant, Rate of viremia (BKV) in kidney transplant recipients is 30% , Initially discovered in a kidney transplant recipient with ureteric stricture in 1971. But First biopsy proven case of BKVAN was diagnosed in 1993. With Graft loss of <15% now a days (in early days it was 50–100%)
BK virus is a small, non-enveloped, closed circular, double-stranded DNA virus of Polyomaviridae family.
The genome of the virus consists of three regions:
1. Early coding region=> of large T & small t antigens (responsible for binding of the virus to host cell an leading to infection persistent).
2. Non-coding control region => responsible of virus pathogenesis
3. Late coding region=> codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Sero – type 1 if present it indicate clinically significant disease
Epidemiology:
BKV Prevalence is > 90% at age 4 years.
BKV infection frequently occurs in first post-transplant year due to intensive suppression of cellular immunity.
Recently, 1–10% of kidney transplant recipients develop BKVAN.
BKV mode of transmission through oral, gastroenterology and respiratory tract.
BKV infection occurs as viruria, viremia and graft nephropathy.
50% of patients develop viremia over 2-6 weeks After viremia,
Urine viral load >8 log10c/ml predict onset of viremia, plasma viral load > 4 log10 c/ml associated with high rate of biopsy proven BKVN and viral load > 6 log10 cml predict extensive BKVN. Risk factors 1.Immunosuppression (the most important). Tacrolimus is having higher risk than cyclosporine, Also, mTORi may be associated with lower risk.
2.Recipient-related factors like olde rage, DM, and specific HLA-C allele 3.Donor-related factors like reduced immune response to BK virus and presence of BK viruria prior to transplant.
4.donor–recipient factors like high-risk cases of D + and R – status for BK virus, ABO incompatibility, HLA mismatches, DGF, and rejection or ischemia of the transplanted kidney. Cellular Immune Response and Pathogenesis Clearance of BK viremia dependents on activation of cellular immune response (both CD4 and CD8 cells) by viral antigens is crucial for BKV infection control, BK capsid proteins, large T antigen, and non-structural proteins all stimulates a T cell response.
Latent infection maintained mainly in kidney epithelial cells, & in lower frequency in prostate, testes, seminiferous tubules, cervix, vulva, & hematolymphoid tissues, can become active with reduced cellular immunity in immunosuppression states. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways, Progressive destruction leads to interstitial fibrosis & tubular atrophy and progressive nephron loss. This leads to Chronic injury to transplanted kidney.
Clinical manifestation:
Most of cases are asymptomatic.
Classical pathway of infection viruria then viremia and BKVAN.
Viremia is present in 10–30 percent of recipients in the first six months post transplantation and in 5–10 percent of recipients thereafter.
Viremia is better than viuria in predicting progression to BKVAN.
BKVAN is more prevalent in 2-6 months post transplantation may be due to immunosuppressive burden presented with elevation of kidney function with or without urine analysis abnormalities.
It may present with ureteric stenosis or hemorrhagic cystitis.
Screening & diagnosis:
BKV urine PCR has low specificity so not used for screening.
Plasma BKV viral load is the preferred method for screening due to its high positive predictive value.
Due to high prevalence early post-transplant, KDIGO & AST-IDCOP guidelines recommend monthly screening for first 6 months every 3 months for next 18 months.
Cause of assay variation, World Health Organization (WHO) addressed this by establishing an international standard to standardize viral load values among different laboratories assays.
Urine cytology: for detection of decoy cell: it has low positive predictive value as screening tool.
Donor-Derived Cell-Free DNA (dd-cf DNA): data suggest that it may be good test indicating the progression of BKV to BKNAN
Biopsy of transplanted kidney: still the gold standard for evaluation of BKVAN it is necessary that the biopsy sample to contain medulla to avoid false negative results.
Distinguishing between BKVN & acute rejection is challenging.
Histological classification of biopsy proven PVN into 3 classes (Banff classification).
Treatment:
1. Reduction of IS.
2. adjuvant therapy:
1- Cidofovir: Nucleoside analog IV: 0.25–1.0 mg/Kg at 1–3 weeks Used in refractory cases; studies showed no benefit, additionally , Nephrotoxicity is the most serious adverse effect
2- Intravenous immunoglobulin (IVIG): Immunoglobulin preparation with high titers of neutralizing antibodies to BK virus Can be used as an adjunct to other measures in refractory cases with uncertain study results
3.leflunomide: a pharmacodynamic and prospective open-label study showed no benefit 4- Levofloxacin:Fluoroquinolones; Antiviral, inhibit helicase activity of large T antigen Levofloxacin failed to show benefit in randomized controlled trials.
Kidney re-transplantation:
Graft Loss 2/2 BKVN Should Be Considered For Re-Transplantation.
Graft Nephrectomy Is Not Recommended.
Consider Lower Immunosuppression That Should Be Balance with Risk Of Acute Rejection.
Graft Survival in Re-Transplant Is 98% & 94% At 1 & 3 Year.
No Significant Difference in Rate Of Acute Rejection Or Patient Survival At 1 Year.
Conclusions: BK virus infection is one of the most common manifestations in transplant recipients and close surveillance is needed to prevent severe disease. Immunosuppression reduction is the only viable strategy in infected cases but may lead to rejection. Currently, there is no role for any anti-viral therapy, no benefit from adjuvant therapy, upcoming therapeutic trials may be of benefit. Level of evidence: This is a narrative review thus level V.
I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review Introduction;
-BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
-The successful advent of increasingly efficacious immunosuppression has been accompanied by high rates of BK viremia (BKV) in up to 30% of kidney transplant recipients. History of the BK Virus;
-BK virus was first discovered in a kidney transplant recipient who presented with a ureteral stricture in 1971.
-However, it was only in 1993 that the first definitive biopsy proven case of BKVAN was described.
-During the period of its early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported. Virology;
-BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
-The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region. Epidemiology;
-BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
-The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
-After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection. Risk Factors; 1-Intensity of immunosuppression:
This is considered as the most significant factor associated with BK viral replication. 2-Recipient characteristics:
older age , diabetes , and specific HLA-C alleles. 3-The donor–recipient interface:
-The high-risk serostatus of donor positive and recipient negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement. 4-Donor-related factors:
-Immune response to BK virus and BK viruria prior to transplant. Clinical Manifestations;
-The classic sequence of infections in kidney transplant recipients is viruria, viremia, and BKVAN.
-The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia.
-The presence of sustained viruria may progress to viremia, which is asymptomatic initially.
-Viremia is present in 10–30 % of recipients in the first six months post transplantation and in 5–10 % of recipients thereafter.
-Viremia is a better predictor of progression to BKVAN in comparison to viruria.
-BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
-Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis. Screening and Diagnosis;
-The high incidence of BK viremia in the first post-transplant year has led to the development of standard screening protocols by transplant centers.
-Screening for BK viremia is the preferred method utilized in these protocols.
-(KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
-Urine BK PCR / Plasma BK PCR / Urine Cytology / Donor-Derived Cell-Free DNA (dd-cfDNA) / Transplant Kidney Biopsy.
-The characteristic BK virus-infected cells that present on cytologic examination of urine are called decoy cells. –Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN.
-In the genitourinary tract, these viruses target urothelial and renal tubular cells, resulting in virion production and subsequent cellular destruction.
-The histologic findings of this process include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions. Treatment;
-Areduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
-There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
-Multiple protocols have been developed for a reduction in immunosuppressions.
1-Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
-It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2-If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3-The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
-It is pertinent to note that based on the 5-year follow-up data of patients with BK viremia and BKVAN, kidney transplant recipients maintained on tacrolimus-based regimes had lower rates of rejection and a higher estimated glomerular filtration rate (eGFR).
-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG). Kidney Re-Transplantation;
-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
-Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
-Allograft survival in patients who receive re-transplantation is 98% at 1 year and 94% at 3 years.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
☆ BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review ________________________________ ¤ This review provided an extensive overview of viral epidemiology, pathogenesis, screening, and diagnostic methods. In addition, it discussed clinical manifestations and recommended treatment strategies. ◇ Introduction ▪︎BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. Since its discovery in 1971, an effective prophylaxis or therapy is yet to be devised, with unmitigated disease frequently resulting in allograft loss.
◇ Virology ▪︎BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNAvirus and member of the Polyomaviridae family. ▪︎The genome of the virus consists of
3 regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
◇ Epidemiology ▪︎The primary routes for transmission of the virus are from mucosal contact including the oral, GIT & RT. ▪︎After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
▪︎Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney. ▪︎The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy. ▪︎Viral replication is associated with the following risk factors: 1. Intensity of immunosuppression. 2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles 3. The donor–recipient interface: The high-risk serostatus of donor positive & recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement. 4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant. ▪︎Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
◇ Cellular Immune Response ▪︎The clearance of BK viremia are dependent on a robust cellular IR (both CD4 and CD8 cells). ▪︎Latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
◇ Clinical Manifestations 1. Mostly a symptomatic. 2. The classic sequence of infections is viruria, viremia, and BKVAN. ▪︎The presence of sustained viruria may progress to viremia, which is asymptomatic initially. ▪︎Viremia is a better predictor of progression to BKVAN in comparison to viruria. ▪︎ BKVAN is manifested as a decline in renal function with or without urinary abnormalities. ▪︎The vast majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence. ▪︎Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis. ▪︎There are reports of a possible link between the BK virus and genitourinary (GU) malignancies.
◇ Screening and Diagnosis ▪︎Screening for BK viremia is the preferred method. ▪︎Fastidious screening and preemptive reduction in IS for established BK viremia have been demonstrated to mitigate progression to BKVAN. ▪︎The KDIGO & AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months. ▪︎Urine BK PCR: is not a recommended screening test ▪︎Plasma BK PCR:rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads.
▪︎Urine Cytology: a. May show the characteristic decoy cells(although they are a marker of PV replication, they do not necessarily indicate PVN). b. Polyomavirus-Haufen, via negative staining EM. ▪︎Donor-Derived Cell-Free DNA (dd-cfDNA): higher levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. ▪︎Transplant kidney biopsy and Histology: Is the gold standard for the diagnosis of “definitive” BKVAN. -The characteristic findings include tubular epithelial cells with enlarged, hyper- chromatic nuclei and “ground glass” intranuclear inclusions. – Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles. – In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla. Eventually, these cells lyse and slough from the basement membrane into the tubular lumens.
– When infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen. More proximal portions of the nephron, including the parietal epithelial cells lining Bowmans capsule, may also become involved.
◇ Treatment ▪︎A reduction in the intensity of IS is the overarching principle for the treatment of BK viremia and BKVAN. ▪︎There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
◇ Stepwise approach for the reduction in immunosuppression in BK viraemia and BKVAN: 1. Reduce dose of antimetabolite by half while continuing on the same doses of CNI and/or prednisone and monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks in the interim. 2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite. 3.Reduce CNI trough if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite. ▪︎Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).The later is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
◇ Kidney Re-Transplantation Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
◇ Conclusion ▪︎BK virus infection continues to be one of the most common clinical issues encountered by transplant providers. It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection. ▪︎There is no anti-viral currently known to be of benefit in the clearance of the virus.
BKVirus Associated Nephropathy ( BKVAN) is an important cause of graft loss in renal transplant recipients.
in 1971,BKV had been discovered in renal transplant recipient but the first biopsy-proven BKVN was in 1993.
Earlier the incidence of graft loss due to BKVN was 50-100%, but in the last 2 decades it has been reduced to <15%
Virology:
BK virus is a small, non-enveloped, icosahedral, closed circular, ds DNA virus and member of the Polyomaviridae family
Virus structure consist of 3 regions:
1. Early coding region of large T & small t antigens (responsible for binding of the virus to host cell an leading to infection persistent). 2. Non coding control region( responsible of virus pathogenesis, 3. The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Sero type 1 if present it indicate clinical significant disease Epidemiology:
BKV Prevalence is >90% at age 4 years
BKV infection frequently occurs in first post transplant year due to intensive suppression of cellular immunity.
Recently , 1–10% of kidney transplant recipients develop BKVAN
BKV mode of transmission through oral, gastroenterology, & respiratory tract.
BKV infection occurs as viruria, viremia & graft nephropathy.
50% of patients develop viremia over 2-6 weeks After viruria,.
Urine viral load >8log10c/ml predict onset of viremia, plasma viral load>4log10 c/ml associated with high rate of biopsy proven BKVN & viral load>6log10 cml predict extensive BKVN.
Risk factors of viral activation:
1. Intensity of immunosuppression 2. Recipient factors: old age, DM, specific HLA allels. 3. Both The donor–recipient related risk: The high-risk serostatus of donor D+R-, delayed graft function rejection or cold ischemic time , and ureteral stent placement . 4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant. 5. Of note Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN due to the presence of highly immunogenic cytotoxic T cells Pathogenesis:
Activation of Cellular immunity (CD8 & CD4) by viral antigens is crucial for BKV infection control.
Latent infection maintained mainly in kidney epithelial cells, & in lower frequency in prostate, testes, seminiferous tubules, cervix, vulva, & hematolymphoid tissues.
In SOT, BKV activation can cause damage through viral replication ( cytopathic effect) & inflammation as cellular immunity is impaired .
Classical pathway of infection vururia then viremia and BKVAN.
Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter
Viremia is better than viuria in predicting progression to BKVAN
BKVAN is more prevelant in 2-6 months posttransplantation may be due to immunosuppressive burden presented with elevation of kidney function with or without urine analysis abnormalities
It may present with ureteric stenosis or hemorrhagic cystitis
Screening & diagnosis:
BKV urine PCR has low specificity so not used for screening
Plasma BKV viral load is the preferred method for screening due to its high positive predictive value
Due to high prevalence early post transplant, KDIGO & AST-IDCOP guidelines recommend monthly screening for first 6 months the every 3 months for next 18 months.
Cause of assay variation , World Health Organization (WHO) addressed this by establishing an international standard to standardize viral load values among different laboratory assays
Urine cytology : for detection of decoy cell : it has low positive predictive value as screening tool
Donor-Derived Cell-Free DNA (dd-cfDNA): data suggest that it may be good test indicating the progression of BKV to BKNAN
Biopsy of transplanted kidney : still the gold standard for evaluation of BKVAN it is necessary that the biopsy sample to contain medulla to avoid false negative results
Distinguishing between BKVN & acute rejection is challenging.
Histological classification of biopsy proven PVN into 3 classes (Banff classification).
Treatment. 1. reduction of immunosuppression 2. adjuvant therapy \ 1- Cidofovir: Nucleoside analog IV: 0.25–1.0 mg/Kg at 1–3 weeks Used in refractory cases;studies showed no benefit , additionally , Nephrotoxicity is the most serious adverse effect 3- Intravenous immunoglobulin (IVIG): Immunoglobulin preparation with high titers of neutralizing antibodies to BK virus Can be used as an adjunct to other measures in refractory cases with uncertain study results 3. luflonamide : a pharmacodynamic and prospective open-label study showed no benefit · 4- Levofloxacin: Fluoroquinolones; Antiviral, inhibit helicase activity of large T antigen Levofloxacin failed to show benefit in randomized controlled trials. upcoming trials: 1. human monoclonal antibodies(IgG1) bind to VP1 (MAU868). 2. adoptive transfered posoleuccel (ALVR105) Kidney re-transplantation.
Graft loss due to BKVN should be considered for re-transplantation.
graft nephrectomy is not recommended.
Consider lower immunosuppression that should be balance with risk of acute rejection.
Graft survival in re-transplant is 98% & 94% at 1 & 3 year.
No significant difference in rate of acute rejection or patient survival at 1 year.
Conclusion
· 1- BKV infection one of the most common post-transplant clinical issue · 2- surveillance protocols has led to early detection and avoidance of advanced disease · 3- reduction of IS is the mainstay of treatment · 4- no benefit from adjuvant therapy · 5- upcoming therapeutic trials may be of benefit
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.
Please summarise this article Introduction
BK virus-associated nephropathy (BKVAN) is one of the major cause of graft losspost transplant Rate of viremia (BKV) in kidney transplant recipients is 30% (efficacious immunosuppression). Initially discovered in a kidney transplant recipient with ureteric stricture in 1971. But First biopsy proven case of BKVAN was diagnosed in 1993. With Graft loss of <15% now a days (in early days it was 50–100%)
BK virus is a small, non-enveloped, closed circular, double-stranded DNA virus of Polyomaviridae family. The genome of the virus consists of three regions:
1. Early coding region
2. Non-coding control region
3. Late coding region
Epidemiology
In 90% of general population antibodies are detectable to BKV by 4 years of age. The common routes for transmission are oral, gastrointestinal, and respiratory tract. After a primary viremia, it mainly persists in the kidneys and urinary tract in a latent form for rest bof the life. In affected patients the Infection is either reactivation or transmission of new infection from the donor kidney. In the Chronological stages infection go through—viruria only then viremia, and finally allograft nephropathy. Viruria in 30% and viremia in12% of kidney transplant recipients is common finding. After viruria, half of the patient develop viremia in next 2–6 weeks, with 50% of viremic patients developing BKVAN.
In Urine, high BK viral loads >8 log10 c/mL can predict subsequent viremia. But Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN
Risk factors
1.Immunosuppression (the most important). Tacrolimus is having higher risk than cyclosporine. Also, mTORi may be associated with lower risk.
2.Recipient-related factors like olde rage, DM, and specific HLA-C allele
3.Donor-related factors like reduced immune response to BK virus and presence of BK viruria prior to transplant.
4.donor–recipient factors like high-risk cases of D positive and R negative status for BK virus, ABO incompatibility, HLA mismatches, DGF, and rejection or ischemia of the transplanted kidney.
Cellular Immune Response and Pathogenesis
Clearance of BK viremia dependents on good cellular immune response (both CD4 and CD8 cells). BK capsid proteins, large T antigen, and non-structural proteins all stimulates a T cell response.
Latent infection can become active with reduced cellular immunity in immunosuppression states. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways. This leads to Chronic injury to transplanted kidney.
Clinical Manifestations
Often asymptomatic. The earliest manifestation of BKV is viruria only (50%) in the first year of transplantation. Urine BK viral loads is not sustainable but if Sustained viruria occurs it may progress to viremia in 10–30 % of recipients in the first 6 months post transplantation and in 5–10 % of recipients thereafter Viremia is a better predictor of progression to BKVAN in comparison to viruria. BKVAN occurs in the first post-transplant year (highest incidence is 2-6 months)
Other manifestations of the BK virus are ureteral stenosis and hemorrhagic cystitis with rare possiblity of genitourinary (GU) malignancies, which might be an association.
Screening and Diagnosis
The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months Urine BK PCR
· Not recommended because it always requires confirmation by plasma PCR
· 50% of patients with viruria will not develop viremia Plasma BK PCR
· WHO established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL. BK PCR can be 4 times less sensitive for variants strains Urine Cytology
· BK virus-infected cells in urine are called decoy cells. They are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. although High false-positive rates and low positive predictive values is case in presence of decoy call in urine but absence of decoy cells in urine cytology screens has high NPV for PVN Donor-Derived Cell-Free DNA (dd-cfDNA) May be a useful noninvasive test to assess for progression of BKV to BKVAN
Good tool to distinguish asymptomatic BKV from BKVAN. Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
Transplant kidney biopsy
· The gold standard for the diagnosis of BVAN, severity of viral involvement and other pathology and for a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes
2. Positive immunohistochemistry tests (using antibodies directed against BKV or against the cross-reacting SV40 large T antigen. Specificity of SV40 is 100 but not distinguish between BKV and JCV Histology:
· The histologic findings of this include ground glass”intranuclear inclusions
· Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles
· As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
· More proximal portions of the nephron, including the parietal epithelial cells lining Bowmans capsule, may also become involved
· The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis
· Two biopsy cores containing renal cortex and medulla are recommended
· Simian Virus 40 (SV40) IHC stain is recommended in all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN
· There are several grading systems for evaluation of PKN (use viral cytopathic effect, injury, and atrophy for classification)
Treatment
Reduction of of immunosuppression is the main treatment of BK viremia and BKVAN Approach for reduction:
Reduce dose of antimetabolite by 50% and continue with same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR levels every 2 weeks. Complete cessation of anti-metabolite if viral loads continue to be at similar levels or increasing, Third options reduce CNIs to the lowest trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine) Other adjunctive therapies:
1. IVIG:
2. Quinolones
3. Cidofovir
4. Leflunomide
Although Cidofovair, Ciprofloxacin and Leflunamide have not been proven in any trial yet.
Upcoming Therapeutic Trials (modified T cells and monoclonal antibodies) Kidney Re-Transplantation
If transplant fails thyen it is an option but nephrectomy of failed kidney is not recommended. Viral clearance prior to transplantation should be the Goal. They should be exposed to Lower immunosuppression.
Conclusions
· BK virus infection is one of the most common manifestations in transplant recipients and close surveillance is needed to prevent severe disease. Immunosuppression reduction is the only viable strategy in infected cases but may lead to rejection. Currently, there is no role for any anti-viral therapy.
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article. One may have to discontinue MMF for some time. I would not wait for watching the effect of MMF reduction
BKVAN is an important cause of graft loss in KTX patients.
The advent of efficacious IS medications was accompanied by high rates of BKV viremia 1/3 of KTX recipients.
Virology
BKV is a small, closed circular, ds DNA (a member of the Polyomaviridae family).
Its genome consists of:
the early coding region of the large T & small t antigens
the non-coding control region
the late coding region.
Epidemiology
Seroprevalence >90% by 4 years of age.
Transmission: from mucosal contact (oral, GIT, & respiratory tract).
Latent/persistent infection in the kidney & uroepithelial cells.
Clinically infection occurs in KTX recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
Viruria & viremia are seen in 30% 7 12% of KTX recipients, respectively.
BKVAN develop in 1–10% of KTX recipients.
Risk factors for viral replication:
Intensity of IS
Recipient factors: older age, DM, & specific HLA-C alleles.
The donor–recipient interface: (D+/R-) serostatus, ABO incompatibility, HLA mm, DGF, rejection or ischemia of the graft, & ureteral stent placement.
Donor-related factors: reduced immune response to BK virus & BK viruria prior to TX.
Protective factors against the development of BKVAN:
Recipient HLA-B51 positivity (associated with the presence of highly immunogenic cytotoxic T cells)
Presence of polycystic kidney disease
Pathogenesis
A strong cellular immune response is needed for the mitigation & clearance of BK viremia, & both CD4 & CD8 cells are essential for this process.
T cell responses to the BK proteins can be measured using tetramer labeling & ELISPOT technology.
Clinical Manifestations
Viruria: occurs in 50% of patients 1styear of TX; mostly not progressing to viremia.
Viremia: in 10–30 % of recipients in the 1stsix months & in 5–10 & thereafter. It is a better predictor of progression to BKVAN in comparison to viruria.
BKVAN: manifests as a decline in renal function with or without urinary abnormalities. The majority of cases occurs within the 1stpost-TX year (attenuated cellular immunity).
Ureteral stenosis
Hemorrhagic cystitis (rare in KTX; mostly in HSCT).
Genitourinary malignancies (a possible link).
Screening and Diagnosis
Urine BK PCR: not a recommended screening (specificity& cost issues)
Plasma BK PCR: viral load is the preferred method.
Urine Cytology:
decoy cells are tubular epithelial or urothelial cells with nuclear viral inclusions.
Haufen (PV aggregates seen via negative staining EM)
Donor-Derived Cell-Free DNA (dd-cfDNA): higher levels are linked to higher BK viral loads & biopsy-diagnosed BVAN.
Transplant Kidney Biopsy:
Gold standard for the diagnosis of BVAN.
Pathologic features for a definitive diagnosis of BKVAN:
Characteristic cytopathic changes
Positive IHC tests using BKV antibodies or cross-reacting SV40 large T antigen antibodies.
Treatment
Reduction in the intensity of IS is the mainstay.
There is no therapeutic agent available to treat BKVAN.
Adjunctive therapies used:
Quinolones
Cidofovir
Leflunomide
IVIG: is probably the only viable adjunctive therapy.
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
====================================================================
Please summarise this article
1. Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients, with no effective prophylaxis or therapy.
BK virus is a latent infection that has a propensity for reactivation in kidney transplant recipients, making it a diagnostic and therapeutic challenge.
==================================================================== 2. History of the BK Virus
BK virus was first discovered in a kidney transplant recipient in 1971, but it was only in 1993 that the first definitive biopsy proven case of BKVAN was described.
Since then, recognition and nuanced management have resulted in a reduction in graft loss to under 15%.
Virology BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus with three regions.
The non-coding control regions of the T antigen are a major contributor to the pathogenesis of BK virus, leading to high BK virus loads in kidney transplant recipients with clinically significant viral replication.
VP-1, VP-2, and VP-3 are responsible for the assembly of viral capsids and the release of virions from cells, with VP-1 being the predominant genotype and implicated in most clinically significant viral diseases.
BK virus infection is widespread in the general population, with seroprevalence rates of over 90% by 4 years of age.
Viruria, viremia, and allograft nephropathy are common in kidney transplant recipients, with 50% developing BKVAN in 2-6 weeks.
BK viral loads >8 log10 c/mL predict onset of viremia, higher rates of biopsy-proven BKVAN, and extensive BKVN pathology.
Viral replication is associated with the following risk factors:-
1. Intensity of immunosuppression: Immunosuppression is the most significant factor associated with BK viral replication, with the incidence of BK viremia highest in the early post-transplant period.
2. Recipient characteristics: Older age, diabetes, and specific HLA-C alleles.
3.The donor–recipient interface is a high-risk serostatus of BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection, and stent placement.
4.Donor-related factors reduce immune response to BK virus and BK viruria prior to transplant.
Recipient HLA-B51 positivity and polycystic kidney disease are protective factors against BKVAN.
==================================================================== 5. Cellular Immune Response and Pathogenesis
The mitigation and clearance of BK viremia is dependent on a robust cellular immune response, with both CD4 and CD8 cells playing a crucial role.
ELISPOT measured IFN-gamma activity, which is associated with the resolution of BKVAN. CD8-based responses correlated with lower BK viral loads in blood and urine, while high viral loads and the continued presence of the virus were associated with a weak response.
Various studies are being conducted to predict the clearance of the BK virus and identify patients at high risk for progression.
BKVAN maintains persistent infection in kidney epithelium, other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues.
It is associated with increased expression of various mRNAs, including CD8, perforin, interferon-γ, and CXCR3, which may explain common clinical and pathological features in BKVAN and TCMR.
Viruria is the most common and earliest manifestation of BKV in kidney transplant recipients, with most cases not progressing to viremia.
Viremia is a better predictor of progression to BKVAN than viruria.
BKVAN usually occurs after a period of worsening viremia, with the first 2-6 months being the highest incidence.
There are reports of a possible link between the BK virus and genitourinary (GU) malignancies, but its causative role in malignancies in humans is controversial.
The high incidence of BK viremia in the first post-transplant year has led to the development of standard screening protocols.
Fastidious screening and preemptive reduction in immunosuppression are recommended to mitigate progression.
7.1. Urine BK PCR
Urine BK PCR is not a recommended screening test due to specificity and cost, but nearly 50% of patients with viruria will not develop viremia.
7.2. Plasma BK PCR
BK viral loads are measured by polymerase chain reaction (PCR) and are influenced by variations in DNA extraction techniques, sample type/source, primer and probe sequences, and BK strain DNA.
WHO established an international standard to standardize viral load values, but there is still variability due to PCR primer design and amplicon size.
The genotypes of the BK virus detected by PCR assays warrant special discussion due to discordance due to subtype-associated polymorphisms and BK PCR being four times less sensitive for variant strains.
Rare genotypes should be considered in the event of lower viral loads.
7.3. Urine Cytology
Decoy cells are BK virus-infected cells that present on cytologic examination of urine, but they do not necessarily indicate PVN.
Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, which have high positive and negative predictive values for BK nephropathy.
7.4. Donor-Derived Cell-Free DNA (dd-cfDNA)
dd-cfDNA may be a useful noninvasive test to assess progression of BKV to BKVAN.
7.5. Transplant Kidney Biopsy
Kidney allograft biopsy is the gold standard for diagnosis of BVAN, with medulla present to reduce sampling error.
Pathologic features such as cytopathic changes and positive immunohistochemistry tests should be present for a definitive diagnosis of BKVAN. A presumptive diagnosis is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
A repeat biopsy is recommended if clinical suspicions remain.
7.6. Histology
Identifying the histologic features of polyoma virusinfection on renal biopsy is the gold standard for diagnosis of “definitive” BKVAN.
Viral cytopathic changes may include enlarged, hyperchromatic nuclei and “ground glass” intranu-clear inclusions.
As the infection progresses, tubulitis and interstitial inflammation may occur, resulting in tubular atrophy and interstial fibrosis.
Histologic confirmation of the presence of polyoma virus (PVN) can be difficult due to its random and focal nature.
To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended and ancillary tests such as immunohistochemical (IHC) stains or in situ hybridization (ISH) can be performed.
Quantitative PCR for PV can also be performed on tissue samples, but interpretation of these results requires caution.
Finally, PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
PVN and acute rejection (AR) share many similarities, making diagnosis difficult.
In rare cases, AR and PVN can co-occur, with tubular injury, tubulitis, and interstitial inflammation being key histologic findings.
In cases of histologic overlap, a diagnosis of concomitant PVN and AR should be considered.
The histologic findings should be correlated with the clinical history and results of additional laboratory studies, such as BK viral load and the presence of donor-specific antibodies (DSA).
A review of the biopsy and discussions with the clinical team may also prove insightful.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that uses morphologic evidence of PV infection and interstitial fibrosis to classify samples.
It is based on the morphologic degree of intrarenal pvl (polyomavirus replication/load level) and Banff ci scores (interstitial fibrosis).
The overall percentage of positive tubular cross-sections is estimated in the entire biopsy sample.
Treatment of BK viremia and BKVAN requires a reduction in the intensity of immunosuppression, with multiple protocols developed to reduce viral loads.
Multiple protocols have been developed to reduce immunosuppression in BK viremia and BKVAN based on trials in adult and pediatric kidney transplant recipients.
1-Reduce dose of antimetabolite by half while continuing on the same doses of cal-
cineurin inhibitor and/or prednisone.
Monitor serum creatinine and BK PCR levels every 2 weeks to reduce inte assay variability.
2- Complete cessation of anti-metabolite if viral loads increase.
3- The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks. Adjunctive therapies include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin, with IVIG being the only viable option.
The discussion of this aspect
IVIG is used to reduce BK viral loads, balancing risk of rejection.
Quinolones failed to show efficacy as prophylaxis in post-transplant period or treatment for BK viremia.
Cidofovir has been associated with proteinuria, proximal tubular dysfunction, and kidney disease.
Leflunomide has both immunosuppressive and anti-viral properties, but FK778 did not demonstrate efficacy in kidney transplant patients.
Two trials involving modified T cells and monoclonal antibodies are underway to assess the safety, pharmacokinetics, and efficacy of MAU868 and ALVR105 in BK infection.
BK virus infection is a common clinical issue for transplant providers, with increased surveillance protocols leading to expedient detection and mitigation of severe disease.
Novel therapeutics may bring efficacy, but no anti-viral currently known to be of benefit.
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
Summary Virology.
BK virus is a small non-enveloped double stranded DNA of the polyomaviridae family.
The genome has three regions; the non-coding region contains the origin of replication thus a significant contributor to its pathogenesis. Mutations here permit replication.
There are six viral genotypes with serotype I the most predominant and associated with most clinically significant disease.
Formation of antibodies against one serotype doesn’t confer protection against other serotypes.
Epidemiology.
The general population has seroprevalence rates of 90% by 4 years of age.
Routes of transmission for primary infection: mucosal contact in the oral, GIT and respiratory tract.
Then remains latent in the kidney and uroepithelial leading to lifelong infection.
Kidney transplant recipient infection could be due to reactivation of the latent infection or new infection from donor kidney.
First year post transplant associated with increased immunosuppression hence leading to most viral replication occurring in this period.
Risk factors
1. Intensity of immunosuppression.
Most significant factor.
BK viremia is highest in the early post transplant period due to the high immunosuppression.
2.Recipient factors
Include older age, DM, specific HLA C alleles.
3.Donor-recipient interface
Include D+/R- for BK virus, ABO incompatibility, HLA mismatch, DGF rejection, placement of a ureteral stent.
4.Donor factors
BK viruria prior to transplant, reduced immune response to BK virus.
Pathogenesis
Both CD4 and CD8 T cells play crucial role in clearance of BK viremia.
After primary infection the virus remains latent in kidneys mostly in the parietal epithelium, tubular epithelium and transitional epithelium.
Other organs that it can remain latent include: prostate, testes, vulva, cervix and seminiferous tubules.
Latent infection is reactivated with reduced cellular immunity due to introduction of immunosuppression.
Leading to damage of the tubular epithelium due to the viral replication and its cytopathic changes.
Further inflammation leads to activation of pro-fibrotic pathways.
BKVAN has expression of several messenger RNA that are similar to those seen in T cell mediated rejection, could explain why both have common clinical and pathological features.
Clinical manifestation.
Chronological stages of the infection are: viruria, viremia and allograft nephropathy. Viruria: Most common and earliest manifestation. Viremia: Persistent viruria may progress to viremia. Better predictor to BKVAN than viruria. BKVAN: Occurs after a period of prolonged and worsening viremia. Manifest as declining renal function ± urinary abnormalities. First 2-6 months post transplant associated with highest incidence.
Other manifestations: Ureteral stenosis, hemorrhagic cystitis.
BKV and malignancies: Controversy may be more of an association than causation. BKV infection occurs in the setting of lowered cellular immunity; hence reduced tumour surveillance thus a risk of development of malignancy.
Screening and diagnosis. Urine BKV PCR:
Not a recommended screening tool due to low specificity- half of the patients with viruria will not develop viremia.
Requires confirmation with plasma PCR. Plasma BK PCR:
Has a high PPV for BKVAN.
Assays are influenced by DNA extraction techniques, sample/ source, primer and probe sequence, BK strain DNA used for standard curve genotype variance. Urine cytology:
Decoy cells are characteristic BK infected cells present on the cytologic examination of urine. They are tubular epithelium or urothelial cells with ground glass nuclear inclusion surrounded with chromatin.
They are a marker of viral replication but don’t necessarily indicate BKVAN. Donor derived Cell Free DNA (ddcfDNA):
High ddcfDNA is associated with high BK viral loads, biopsy proven BKVAN, and histologic features meeting Banff criteria for T cell mediated rejection.
Thus may be used to asses progression to BKVAN non-invasively. Histology:
Gold standard for definitive diagnosis.
Requires 2 cores (cortex and medulla) to increase diagnostic yield.
Histologic findings: tubular epithelial cells with enlarged hyper-chromatic nuclei and ground glass intranuclear inclusions.
Viral cytopathic changes: granular nuclear inclusions, clumps of intranuclear vision particles.
Tubular injury, tubulitis, and interstitial inflammation are histological findings common in BKVAN and TCMR. IHC/ISH:
Done on the biopsy to aid detection of BKV.
SV40 IHC stain detects large T cell antigens expressed on all polyomaviruses. Detects early stages of infection before detectable on routine stains.
Interpretation requires caution due to latency of the BKV.
Treatment Reduced immunosuppression is the principal of treatment.
Stepwise approach of reduction:
Reduce antimetabolite by half while maintaining same dose of CNI/steroids. Monitor Scr and plasma PCR every 2 weeks.
Withdraw antimetabolite- when viral loads increase or remain the same level.
Reduce CNI trough levels (TAC 4-6ng/ml, cyclosporine 50-100ng/ml)- If viral loads do not reduce after 4 weeks of withdrawal of antimetabolite.
Other treatments: IVIG: Utilised in the setting of non-response after maximal reduction in immunosuppression. Quinolones: Studies have failed to show efficacy in prophylaxis. Cidofovir: Studies have not shown any benefit. Nephrotoxic. Leflunomide: Prospective open label study failed to show benefit.
Re-transplantation.
Confirmation of viral clearance prior to transplantation.
Nephrectomy of native or failed graft not recommended.
Lower immunosuppression with a balance to prevent rejection.
Level of evidence: This is a narrative review thus level V.
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
BKVN is an important cause of graft loss in renal transplant recipients.
Viremia occur in 30% of recipients.
BKV discovered in 1971 in renal transplant recipient presented with ureteric stenosis, & first biopsy-proven BKVN was in 1993.
Previously graft loss due to BKVN was 50-100%, but it reduced to <15% in last 2 decades.
Virology:
BKV is a dsDNA virus, & member of polyomaviridae family.
Virus genome consist of 3 regions:
Early coding region of large T & small t antigens (responsible of infection persistent).
Non coding control region( responsible of virus pathogenesis, mutation of non coding control region associated with high BKV viral load in kidney transplant recipients with clinical significant viral replication.
Epidemiology:
>90% of children at age 4 years are seropostive to BKV.
BKV transmission through oral, gastroenterology, & respiratory tract.
Lifelong latent/persistent infection due to dormant virus in kidney & uroepithelial cells.
BKV infection frequently occur in first post transplant year due to intensive suppression of cellular immunity.
Most BKV infections are due to activation or new infection through infected allograft.
BKV infection occur as viruria, viremia & graft nephropathy.
After viruria, 50% of patients develop viremia over 2-6 weeks.
Urine viral load >8log10c/ml predict onset of viremia, plasma viral load>4log10 c/ml associated with high rate of biopsy proven BKVN & viral load>6log10 cml predict extensive BKVN.
Risk factors of viral activation:
Intensity of immunosuppression
Recipient factors: old age, DM, specific HLA allels.
BK virus-associated nephropathy has been one of the causes of allograft loss particularly with a breakthrough in the advent of more potent immunosuppression for kidney transplantation. In addition, the availability of standard prophylaxis or treatment of the BKVAN has not been ascertained despite the discovery of the virus in 1971. Although, the rate of kidney allograft loss has reduced from it the previous level of between 50-100% to now around 15% partly because of the ability to make a definitive diagnosis through kidney tissue for histology.
The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection
Epidemiology
BK virus prevalence is about 90% at age years
The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection
Routes of the virus are from the oral, gastrointestinal, and respiratory tract.
After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection
Suppression of cellular immunity after transplantation could reactivate the dormant virus in the recipient or from the donor organ
BKV follows the pattern of viruria, viremia, and allograft nephropathy
About 1 -10% of kidney transplant recipients will develop BKVAN
Viral replication is associated with the following factors
Intensity of immunosuppression
Recipient characteristics, like older age, DM, and specific HLA C allele
viruria – 50% of recipients in first-year post-KTP
viremia – 10-30% in recipients in the first 6 months after post-KTP
BKVAN – occurs after a sustained period of viremia
Screening and Diagnosis
Urine BK PCR always requires plasma BK PCR
Plasma BK PCR
Urine cytology
Donor-derived cell-free DNA, a high level is associated with high viral load and BKVAN
Transplant kidney biopsy for histology
Treatment
Reduce the dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other suggested tried forms of treatment
IVIG
Leflunomide
Cidofovir
Quinolones
And other drugs still on RCT
Kidney retransplantation
Another kidney transplantation can be carried out following a loss of a previous graft to BKVAN. This must be carried out after complete clearance of the virus from the system. Nephrectomy of the native kidney is not necessary
Conclusion
Among the challenges encountered following kidney transplantation is the BKVAN which could lead to allograft loss if not detected early by regular surveillance screening and reduction of immunosuppression if viral load is persistently high. Unfortunately, there is no viable antiviral agent against the virus, but a few kinds of research are ongoing for the discovery of a potent antiviral agent.
Introduction Kidney transplant recipients are at risk of graft loss because of BK virus-associated nephropathy. Up to 30% of kidney transplant recipients have BK viremia due to more effective immunosuppressives. Since its discovery in 1971, no effective prophylactic or treatment has been found, resulting in allograft loss. This comprehensive study covers viral epidemiology, etiology, screening, and diagnosis.
Virology The Polyomaviridae virus BK has small, non-enveloped, icosahedral, closed-circular, double-stranded DNA. The virus genome has three regions: the early coding region of the big T and small T antigens (large and small tumor antigens), the non-coding regulatory region, and the late coding section.
Epidemiology By age 4, 90% of people have BK virus infection. The virus spreads through oral, gastrointestinal, and respiratory mucosa. BK virus hides in kidney and uroepithelial cells after primary viremia, causing lifelong latent/persistent infection. Induction therapy suppresses cellular immunity in the first year post-transplant, allowing virus multiplication. Kidney transplant recipients can contract clinically severe infections from donor kidneys or reactivate dormant infections. Viruria, viremia, and allograft nephropathy occur in order.
Cellular Immune Response and Pathogenesis A strong cellular immune response—including CD4 and CD8 cells—is needed to reduce and eradicate BK viremia. ELISPOT and tetramer labeling quantify T cell responses to BK capsid proteins, big T antigen, and non-structural proteins. BKVAN resolves with ELISPOT-measured IFN-gamma activity, indicating a BK-directed cellular immune response. BKVAN increases CD8, perforin, interferon-, and CXCR3 mRNA expression. BKVAN and TCMR have clinical and pathological symptoms, making them difficult to identify. These mRNAs are also expressed in TCMR. Interstitial fibrosis and tubular atrophy cause nephron loss in the final stage.
Clinical Manifestations Most BK virus infections are asymptomatic. Kidney transplant recipients typically develop viruria, viremia, and BKVAN. Viruria, the most prevalent BKV symptom, occurs in up to 50% of transplant recipients in the first year. Most cases do not proceed to viremia. Sustained viruria can cause asymptomatic viremia. 10–30% of recipients have viremia in the first six months after transplantation and 5–10% thereafter. Viremia predicts BKVAN better than viruria. After prolonged, worsening viremia, BKVAN causes renal function decrease with or without urine problems. Given attenuated cellular immunity, BKVAN is most common in the first 2–6 months after transplantation.
Screening/Diagnosis Transplant facilities have established screening processes due to the high frequency of BK viremia in the first year post-transplant. Screening for BK viremia is preferable over urine BK viral loads because it has better positive predictive value.
Treatment Immunosuppression reduction is the primary treatment for BK viremia and BKVAN. Strategy for reduction: Reduce the antimetabolite dose by 50% while maintaining the same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR values every two weeks from the same laboratory. Complete termination of anti-metabolite treatment if virus loads remain stable or increase. Reduce CNIs trough objectives if viral loads do not decrease within 4 weeks despite discontinuation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/mL for cyclosporine). Alternatives treatment include IVIG, Cidofovir, leflunamide and others.
Retransplantation
Offered the significant success data, patients who experienced graft loss as a result of BKVAN should be given consideration for a second transplant. Given the paucity of guidelines based on data to support this approach, failed transplants or native nephrectomy are not advised, and viral clearance should be confirmed before transplantation. The risk of rejection should be considered against consideration for less immunosuppression.
Introduction within the last 2 decades The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss from 50–100% to under 15%
Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis—albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants
cellular immunity is most suppressed in the first post-transplant year as a result of induction therapy, viral replication during this period. via reactivation of latent infection or transmission of new infection from the donor kidney.
The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy
Viruria and viremia are detected in approximately 30% and 12% of kidney transplant recipients, respectively
The checking of urine BK viral loads is not standard practice despite it being a sensitive marker for progression to BKVAN
Viremia is a better predictor of progression to BKVAN in comparison to viruria
extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates
Viral replication risk factors:
1. Intensity of immunosuppression: tacrolimus may a higher risk of BK virus infection than cyclosporine while (mTOR) inhibitors may be associated with lower risk
the presence of BK viremia reflects a higher level of immunosuppression and its occurrence with or without BKVAN is in the setting of all maintenance immunosuppressive agents/combinations
2. Recipient characteristics: older age -diabetes and specific HLA-C alleles
3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus– ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney, and ureteral stent placement
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN. HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients
Latent infection
The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss
Screening and Diagnosis
(KDIGO) and (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BK PCR is not a recommended screening test
Plasma BK PCR BK viral loads
The genotype I strain is currently utilized as the reference sequence
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I)
Urine Cytology The characteristic BK virus-infected cells that present on cytologic examination of urine are called decoy cells
. Some studies have shown high false-positive rates and low positive predictive values However, some of these studies also found the absence of decoy cells in urine cytology screens had high negative predictive values for PVN.
Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively.
Donor-Derived Cell-Free DNA (dd-cfDNA)
A recent study demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant Kidney Biopsy
the gold standard for the diagnosis of BVAN. assessing the severity of viral involvement and the presence of other ongoing pathologies. Since BK is tropic for the medulla, it is necessary that the biopsy core has medulla present to decrease the likelihood of a sampling error
TREATMENT
Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
monitor serum creatinine and serial plasma BK PCR levels every 2 weeks If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine). It is noted that based on the 5-year follow-up data of patients with BK viremia and BKVAN, kidney transplant recipients maintained on tacrolimus-based regimes had lower rates of rejection and a higher estimated glomerular filtration rate (eGFR)
. Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir
Intravenous immunoglobulin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
Kidney Re-Transplantation
confirmation of viral clearance should be made prior to transplantation.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival is 98% and 94% at 1 and 3 years,
five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
there was no significant difference in the rates of acute rejection or patient survival at one year
Introduction
BK virus-associated nephropathy is a significant etiology of graft loss in kidney transplant recipients BKV history
It was first noticed in 1971 in a kidney transplant recipient with ureteral stricture
BKVAN was implicated to cause graft loss in 50–100% of cases at that time . Virology
BKV is a double-stranded DNA virus of Polyomaviridae family.
The genome is made of 3 regions consisting of
· early coding region of the large T and small t antigens , which binds to p53 and protein Rb, leading to start and persistence of infection
· the non-coding control region harbouring the replication origin and modulate transcription it’s mutation enhance viral replication.
· the late coding region codes for the agnoprotein and viral capsid proteins (VP-1,
VP-2, and VP-3) .Antibodies produced against one serotype does not lead to durable protection against other types .
Epidemiology
BKV infection is common in general population ,route of transmission include oral gastrointestinal, and respiratory tract then it can be latent in the kidney and uroepithelium life long.
Infection in kidney transplant recipients occurs either by reactivation of latent infection or transmission of denovo infection from the donor kidney enhanced by the immunocompromised state ,infection starts in the forum of viruria, viremia, and allograft nephropathy.
Urine BK viral loads >8 log10 c/mL indicates viremia onset
plasma BK viral loads >4 log10 c/mL indicates biopsy-proven BKVAN high rate
levels much higher than 6 log10 c/mL signifies extensive BKVN pathology measured by SV40 immunohistochemistry.
Risk factors
· Immunosuppression intensity which is the most important factor for viral replication
· Recipient character includes older age , diabetes , and specific HLA-C alleles
· The donor–recipient interface involving donor positive and recipient
negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft
function , graft rejection and ureteral stent placement .
· Donor factors: reduced immune response to BK virus and BK viruria before transplant
Polycystic kidney disease and HLA-B51 positivity of the recipient are protective factors
Cellular Immune Response and Pathogenesis
Anti-BK T cell response developpment short time interval correlates with viremia resolution, while cases whom suffer BKVAN need a median period of 5 months to develop cellular immunity against the virus .
These data can be used to predict the clearance of the BK virus and notice risky cases for progression of the virus-associated disease.
The virus remains latent in kidney epithelium particularly in the parietal epithelium of the Bowman’s capsule,renal tubular epithelium, and transitional epithelium, prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues.
Immunosuppression can enhance this latent virus to progress to active disease.
Differentiating between BKVN and TCMR can be difficult sometimes because both are associated with increased expression of various groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
Clinical picture
The most common and earliest presentation is viruria occurring in the first year of transplantation, without progression to viremia in most cases.
Urine BK viral loads are sensitive but non specific .
Viruria can progress to viremia in the first 6 months post transplantation, which is asymptomatic but predicts BKVN progression.
BKVN can be manifested by reduced renal function, ureteral stenosis and haemorrhagic cystitis that is more common in HSCT.
BK virus association with the development of urothelial malignancies in transplant recipients is under further study .
Screening and diagnosing
Screening for BK viremia in the first year post transplant is the standard screening method.
KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months Urine BKV
Is non specific , costy ,and need to be verified by plasma PCR Plasma BK PCR
Precise viral loads measurement is difficult due to inter-assay variability , WHO introduced an international standard to standardize viral load values among different laboratories meanwhile some variabilities exist due to PCR primer design DNA extraction techniques variation also rare genotypes can be missed due to low viral load. Urine cytology
Decoy cells are characteristic BKV infected cells harbouring owl eye inclusion in urine cytology mimicking renal cell carcinoma cells but decoy cell presence doesnot necessary indicate PVN.
Polyomavirus-Haufen screening in urine harbours high positive and negative predictive values for
BK nephropathy. Donor-Derived Cell-Free DNA (dd-cfDNA)
dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN and histologic features in accordance with Banff criteria of T-cell-mediated rejection ,which can be indicative of progression to BKVAN. Renal graft biopsy
It is the gold standard for diagnosis with particular considerations including multiple core biopsies and involving the medulla .
Pathological findings include;
· Characteristic cytopathic changes including tubular epithelial cells affection with ground glass” intranuclear inclusions, these cells can slough from basement membrane into the tubular lumen and spread infection leading to tubulitis and interstitial inflammation ending in tubular atrophy and interstitial fibrosis
· positive immunohistochemistry tests using Ab against BKV or cross reacting with SV40 large T Ag
BKVAN diagnosis is likely with plasma BK viral load ≥10,000 copies/mL
The focal ,random nature ,medullda involvement can increase missing risk to 30%
PV can be detected on electron microscopy as well
Differentiation between AR and PVN can be challenging ,eventually both can be present at the same time ,therefore the existence of the common histological features in the absence of immunohistochemical evidence render AR more likely .
Several grading systems were proposed including viral cytopathic effect, injury, and atrophy to classify cases.
Banff score incorporates the degree of morphologic evidence of PV infection and interstitial fibrosis
to classify biopsies.
Treatment
Reduction of immunosuppression is the main core of therapy
It can be implicated by halving antimetabolite dose and maintain CNI and/or prednisone dose along with monitoring serum creatinine and serial plasma BK PCR levels from the same lab every 2 weeks .
If viral loads remain the same or increase anti-metabolite can be stopped afterwards CNI trough goals can be decreased if viral loads do not reduce over 4 weeks.
Other therapies include IVIG
It is the only viable adjunctive therapy. Quinolones
As a prophylaxis in the immediate post-transplant period or as treatment for BK viremia ,quinolones were not effective Cidofovir
It’s major limitation is it’s nephrotoxic effect Leflunamide
Harbouring immunosuppressive and anti-viral properties ,did not show efficacy for BKV therapy in studies . Therapeutic trials
Modified T cells and monoclonal antibodies as a therapeutic option for BK infection are under study
Kidney Re-Transplantation
After BKVAN can be considered after confirmation of viral clearance
Allograft survival in re-transplantation cases is 98% at 1 year and 94% at 3 years.
5-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
Conclusions
BK virus infection is a common clinical disease faced by transplant providers with it’s challenging diagnosis due to similar histological findings with AR.
Screening improved the detection and lessened disease severity
Immunosuppression reduction is the only option for therapy till now
New therapeutic modalities are under trial.
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
The successful advent of increasingly efficacious immunosuppression has been accompanied by high rates of BK viremia(BKV) in up to 30% of kidney transplant recipients
Virology
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
The genome of the virus consists of three regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
The non-coding control region are a significant contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
Mutations in the non-coding control region result in permit replication in other cell types, cell tropism, and altered rates of replication.
BK virus loads in kidney transplant recipients with clinically significant viral replication
The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3).
VP-3leads to activation of the adenosine diphosphate-ribose polymerase, resulting in depletion of adenosine triphosphate” target=”_blank”
Epidemiology
BK viral infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
After the onset of viruria, nearly 50% of kidney transplant recipients develop viremia during a period of 2–6 weeks, with a similar proportion of viremic patients developing BKVAN in the aforementioned time period .
Intensity of immunosuppression: This is considered as the most significant factor associated with BK viral replication.
This is based on the finding that the incidence of BK viremia is highest in the early post-transplant period given the magnitude of immunosuppression.
It is pertinent to note the presence of BK viremia reflects a higher level of immunosuppression and its occurrence with or without BKVAN is in the setting of all maintenance immunosuppressive agents/combinations.
The donor-recipient interface
The high-risk serostatus of donor positive and recipient negative for BK virus .
ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease.
Have been shown to be protective factors against the development of BKVAN.
HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients.
Celluluar immune response and pathogenesis
The mitigation and clearance of BK viremia are dependent on a robust cellular immune response—with both CD4 and CD8 cells playing a crucial role in this process.
The presence of ELISPOT measured IFN-gamma activity, indicative of a BK-directed cellular immune response, is associated with the resolution of BKVAN.
The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus .
Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues.
This latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
BKVAN is associated with increased expression of various major groups of messenger RNAs, including CD8, perforin, interferon-γ, and CXCR3.
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
Clinical manifestations
Most clinically significant infections associated with the BK virus lack any systemic symptoms.
The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia.
The checking of urine BK viral loads is not standard practice despite it being a sensitive marker for progression to BKVAN.
This is because of the nonspecific nature of viruria occurring without any risk of progression in pregnant women, Viruses 2022, 14, 1616 4 of 18 older patients, and those with compromised cellular immunity.
There are accumulating reports that there may be an association of the BK virus with the development of urothelial malignancies in transplant recipients, a possibility of confounding exists since patients who develop BKVAN have lowered cellular immunity, and as a result of reduced tumor surveillance are at risk of development of malignancies
Screening and diagnosis
The high incidence of BK viremia in the first post-transplant year has led to the development of standard screening protocols by transplant centers.
Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in these protocols.
Fastidious screening and preemptive reduction in immunosuppression for established.
BK viremia have been demonstrated to mitigate progression to BKVAN.
The. Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and every 3 months for the 18 months.
Plasma BK PCR
BK viral loads are measured by polymerase chain reaction (PCR)—a fluorescent probe. BK-specific sequence, and the number of amplicons produced is compared with a standard curve generated with serial dilutions of a known concentration of BK DNA.
Assay results are influenced by variations in DNA extraction techniques, sample type/source, primer and probe sequences, and BK strain DNA used for standard-curve BK virus genotype variance and discordant BK viremia PCR assay results.
While there has been improvement in the reporting of BK PCR values since the introduction of this international standard in 2016, there continues to be variability among laboratories attributed to PCR primer design DNA extraction techniques and amplicon size.
The genotype I (Dunlop) strain is currently utilized as the reference sequence against which primers and probes are designed for various assays.
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference.
This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN.
Rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads Urine cytology
The characteristic BK virus -infected cells that present on cytologic examination of urine are called ′decoy cells′ due to their similarity to renal carcinoma cells
Some studies have shown high false-positive rates and low positive predictive values when attempting to use the presence of decoy cell to screen for PVN in transplant patients.
Some of these studies found the absence of decoy cell in urine cytology screens had high negative predictive values for PVN.
The amount of PV-Haufen shed correlates well with disease severity. Donor derived cell free DNA
A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from.
BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
Transplant kidney biopsy
Kidney allograft biopsy continues to be the gold standard for the diagnosis of BVAN.
It aids, in diagnosis, and in assessing the severity of viral involvement and the presence of other ongoing pathologies.
Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN); it does not distinguish between BKV and JC virus.
If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain
Histology
Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN.
The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
Treatment
A reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
The following is a stepwise approach for the reduction in immunosuppression in the setting of BK viremia and BKVAN based on trials in adult and pediatric kidney transplant recipients.
The step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobin.
Intravenous immunoglobin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
Quinolones
Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia.
While there was initial enthusiasm for its use in BK virus infection based on a case series, a pharmacodynamic and prospective open-label study showed no benefit.
Another metabolite, FK778, did not demonstrate efficacy in a phase 2, proof-of-concept, randomized, open-label, parallel-group, 6-month study in kidney transplant patients when compared with a reduction in immunosuppression.
Kidney re-transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and.
In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group. Findings
There was no significant difference in the rates of acute rejection or patient survival at one year.
Conclusion
BK virus infection continues to be one of the most common clinical issues encountered by transplant providers.
Heightened surveillance protocols have led to expedient detection and have mitigated severe disease.
It can be a conundrum from a diagnostic and therapeutic standpoint.
It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection.
There is no anti-viral currently known to be of benefit in the clearance of the virus.
There is, promise that novel therapeutics may bring efficacy that continues to elude the transplant community
Introduction
· BK virus-associated nephropathy (BKVAN) is an important cause of graft loss
· Rate of BK viremia (BKV) in kidney transplant recipients is 30% (efficacious immunosuppression)
· First discovered in a kidney transplant recipient with ureteric stricture in 1971
· First biopsy proven case of BKVAN in 1993
· Graft loss now <15% (early was 50–100%)
· BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus (Polyomaviridae family)
The genome of the virus consists of three regions:
1. the early coding region of the large T and small t antigens (large and small tumor antigen)
2. the non-coding control region
3. the late coding region
Aim of the study (level V):
Discuss the history of the virus, virology, epidemiology, cellular response, pathogenesis, methods of screening and diagnosis, treatment strategies, upcoming therapeutics, and re-transplantation
Epidemiology
· 90% of the general population has a detectable antibody to BKV by 4 years of age
· Routes for transmission include oral, gastrointestinal, and respiratory tract
· After a primary viremia, BKV largely persists in the kidneys and urinary tract in a latent form
· Infection is either via reactivation of latent infection or transmission of new infection from the donor kidney
· Chronological stages of infection—viruria, viremia, and allograft nephropathy
· Viruria and viremia in 30% and 12% of kidney transplant recipients, respectively
· After viruria, 50% develop viremia during a period of 2–6 weeks, with 50% of viremic patients develop BKVAN in the same time
· Urine BK viral loads >8 log10 c/mL predict the onset of viremia
· Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads above 6 log10 c/mL are predictive of extensive BKVN pathology
Risk factors
1. Intensity of immunosuppression (the most important). Tacrolimus may portend a higher risk than cyclosporine. (mTORi) may be associated with lower risk. It reflects a higher level of immunosuppression
2. Recipient-related factors (olderage, diabetes, and specificHLA-Callele)
3. Donor-related factors (reduced immune response to BK virus [48,52] and BK viruria prior to transplant)
4. donor–recipient factors (The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, DGF, rejection or ischemia of the transplanted kidneY, and ureteral stent placement)
Cellular Immune Response and Pathogenesis
*Clearance of BK viremia is dependent on arobust cellular immune response (both CD4 and CD8 cells)
*BK capsid proteins, large T antigen, and non-structural proteins elicit T cell responses
*Latent infection after initial childhood infection in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium
*Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils)
*Latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression
*Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways
Clinical Manifestations
· Usually no systemic symptoms
· The earliest manifestation of BKV is viruria (50%) in the first year of transplantation, with most cases not progressing to viremia
· Urine BK viral loads is not standard practice
· Sustained viruria may progress to viremia
· Viremia occurs in 10–30 % of recipients in the first 6 months post transplantation and in 5–10 % of recipients thereafter
· Viremia is a better predictor of progression to BKVAN in comparison to viruria
· BKVAN usually manifesting as a decline in renal function with or without urinary abnormalities
· BKVAN occurs mostly in the first post-transplant year (highest incidence is 2-6 months)
· Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis (rare and mostly in patients with hematopoietic stem cell transplants
· Possible link between the BK virus and genitourinary (GU) malignancies
Screening and Diagnosis
Screening for BK viremia is the preferred method
The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BK PCR
· Not recommended for screening (low specificity and cost)
· If positive, it always requires confirmation with plasma PCR
· 50% of patients with viruria will not develop viremia
Plasma BK PCR
· Inter-assay variability makes the accurate measurement of viral loads difficult (WHO established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL)
· BK PCR assayscanbefourtimeslesssensitiveforvariantstrainswhenusinggenotypeIasareference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I)
Urine Cytology
· BK virus-infected cells on cytologic examination of urine are called decoy cells due to their similarity to renal carcinoma cells
· They are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin
· They may exhibit “owl eye” inclusions, multinucleation, or clumped chromatin
· They are a marker of PV replication, but they do not necessarily indicate PVN
· High false-positive rates and low positive predictive values
· Absence of decoy cells in urine cytology screens has high NPV for PVN
· Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy (high positive and negative predictive values for BK nephropathy for presence or absence of PV-Haufen , respectively
Donor-Derived Cell-Free DNA (dd-cfDNA)
· To distinguish asymptomatic BKV from BKVAN
· Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection
· May be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant kidney biopsy
· The gold standard for the diagnosis of BVAN
· For diagnosis, severity of viral involvement and other pathology
· To decrease sample error, sample should include medulla
· For a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes
2. Positive immunohistochemistry tests (using antibodies directed against BKV or against the cross-reacting SV40 large T antigen. Specificity of SV40 is 100 but not distinguish between BKV and JCV
Histology:
· The histologic findings of this include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass”intranuclear inclusions
· Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles
· In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla
· Eventually, these cells lyse and slough from the basement membrane into the tubular lumens
· As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
· More proximal portions of the nephron, including the parietal epithelial cells lining Bowman0s capsule, may also become involved
· The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis
· Two biopsy cores containing renal cortex and medulla are recommended
· Simian Virus 40 (SV40) IHC stain is recommended in all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN
· There are several grading systems for evaluation of PKN (use viral cytopathic effect, injury, and atrophy for classification)
Treatment
Reduction of of immunosuppression is the main treatment of BK viremia and BKVAN
Approach for reduction:
1. Reduce dose of antimetabolite by 50% and continuing on the same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks
2. Complete cessation of anti-metabolite if viral loads continue to be at similar levels or increase
3. Reduce CNIs trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine)
Other adjunctive therapies:
No difference in graft outcomes when reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir
1. IVIG: probably the only viable adjunctive therapy
2. Quinolones
3. Cidofovir
4. Leflunomide
2, 3, and 4 are not recommended
Upcoming Therapeutic Trials (modified T cells and monoclonal antibodies)
Kidney Re-Transplantation
· Failed transplant or native nephrectomy is not recommended
· Viral clearance prior to transplantation
· Lower immunosuppression before transplantation (balanced with the risk of rejection)
· Allograft survival is 98% and 94% at 1 and 3 years, respectively
Conclusions
· BK virus infection is one of the most common clinical issues faced by transplant recipients
· Surveillance alleviates severe disease
· Immunosuppression reduction is the only viable treatment strategy, which may lead to rejection
· Currently, there is no anti-viral known to be of benefit in the clearance of the virus
· Novel therapy is promising
Kidney transplant patients often lose grafts because of BK virus-associated nephropathy (BKVAN). Up to 30% of kidney transplant patients have BK viremia (BKV) due to more effective immunosuppression.
Epidemiology:
By 4 years old, 90% of people have a BK virus infection. The virus spreads via oral, gastrointestinal, and respiratory mucosa. The BK virus hides in kidney and uroepithelial cells after initial viremia, causing lifelong latent/persistent infection.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression:
2-Age, diabetes, and HLA-C alleles
3. Donor–recipient interface: high-risk serostatus includes donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, kidney rejection or ischemia, and ureteral stent implantation.
4. Donor-related factors: decreased immunological response to BK virus and BK viruria before transplant, and Polycystic kidney disease and HLA-B51 positivity.
Cellular Immunity and Pathogenesis:
A strong cellular immune response—including CD4 and CD8 cells—is needed to reduce and eradicate BK viremia. ELISPOT and tetramer labeling quantify T cell responses to BK capsid proteins, big T antigens, and non-structural proteins.
ELISPOT-measured IFN-gamma activity, which indicates a BK-directed cellular immune response, resolves BKVAN.
Symptoms:
Most BK virus infections are asymptomatic. Kidney transplant patients often develop viruria, viremia, and BKVAN. In the first year after transplantation, up to 50% of patients have viruria, which rarely progresses to viremia. Urine BK virus loads, a sensitive indicator for BKVAN development, are seldom checked.
After prolonged, worsening viremia, BKVAN causes the renal function to decrease with or without urine problems. Given reduced cellular immunity, the first 2–6 months post-transplant are the most common for BKVAN. Ureteral stenosis and hemorrhagic cystitis are BK virus symptoms.
Screening and Diagnosis:
Urine BK-PCR
Given its specificity and expense, urine BK PCR is not a suggested screening test. If positive, it always needs plasma PCR confirmation, and almost 50% of patients with viruria will not develop viremia.
Plasma BK PCR
uses a fluorescent probe with a BK-specific sequence and a standard curve to assess BK virus loads. DNA extraction methods, sample type/source, primer and probe sequences, and BK strain DNA utilized for standard-curve BK virus genotype variance and discordant BK viremia PCR assays affect test findings.
Urine Cytology:
Due to their resemblance to renal cancer cells, BK virus-infected urine cells are dubbed decoy cells. These tubular epithelial or urothelial cells have condensed chromatin around ground-glass nuclear inclusions.
DD(dd-cfDNA):
dd-cfDNA was examined in relation to plasma BK virus levels and biopsy results to investigate whether it may identify asymptomatic BKV from BKVAN. Greater dd-cfDNA levels were related to higher BK virus loads, biopsy-diagnosed BVAN, and histologic alterations fulfilling Banff’s criteria for T-cell-mediated rejection. These early data suggest that dd-cfDNA may be a noninvasive diagnostic for BKV to BKVAN development.
Histopathological features:
Positive IHC tests for SV40 antigen: The stain may highlight cells in the early stages of infection, before viral cytopathic alterations may be evident on conventional stains. -The stain can also highlight cells in the later stages of infection.
A positive SV40 staining is almost unambiguous evidence of BKV infection.
Treatment:
BK viremia and BKVAN are treated by reducing immunosuppression. This virus-associated illness has no treatment, and several medicines fail to reduce viral levels. Multiple immunosuppression-reduction strategies have been proposed, but their efficacy has yet to be tested.
Based on research in adult and juvenile kidney transplant patients, BK viremia and BKVAN immunosuppression may be reduced progressively :
1. Halve antimetabolite dosage while maintaining calcineurin inhibitor and/or prednisone levels. To minimize inter-assay variability, serum creatinine and serial plasma BK PCR levels must be monitored every two weeks from the same lab.
2. Stop antimetabolite if virus loads remain high.
3. Reduce calcineurin-inhibitor trough objectives if viral loads do not decrease after 4 weeks despite stopping anti-metabolites (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
IVIG, BK-neutralizing antibodies, and other adjuvant therapies lower the BKV burden.
Quinolones; anti-viral, significant chance of resistant bacterial infection
Cidofovir is nephrotoxic; leflunomide is immunosuppressive and antiviral.
Kidney Re-Transplant:
Given its success rate, BKVAN patients who lose grafts may consider re-transplantation. Given the dearth of evidence-based guidance, failed transplants or native nephrectomies should be avoided. Before transplantation, virus clearance should be confirmed. balance decreased immunosuppression with rejection risk.
1. Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in KTRs. The advancement in effective IS therapy increased the rate BK viremia in up to 30% of KTRs.
2. History of the BK Virus
-It was first discovered in a KTRs who presented with a ureteral stricture in 1971
-It was reported that it resulted in graft loss with rates of 50–100%, this rate reduced to 15 % in the last 2 decades.
3. Virology
– Small double-stranded DNA virus and member of the Polyomaviridae family
– It has 4 different genotypes ( I- IV)
– The genome of the virus consists of three regions; the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
4. Epidemiology
– Highly prevalentin general population with seroprevalence rates of over 90% by 4 years of age. – Routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory.
– After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection
– The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy.
– Viruria, viremia and BKVAN occurred in 30% , 12% and 1-10 % of KTRs, respectively Risk factors for viral replication: -Intensity of immunosuppression : the most significant factor –Recipient characteristics: older age, diabetes, and specific HLA-C alleles. -The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement. -Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
5. Cellular Immune Response and Pathogenesis; – The virus clearance is dependent on cellular immune response with both CD4 and CD8 cells.
– Currently, various studies are being conducted to assess different assays could be utilized to predict the viral clearance and identify those who might progress to BKVAN.
– After primary infection virus remain latent in the body mainly in kidneys, urogenital epithelium and hematolymphoid tissues.
– In KTRs; latent virus become actively replicated once potency of cellular immunity is reduced by IS.
– Viral exert cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways that progress to IFTA and nephron loss.
– The clinical and pathological features in BKVAN and TCMR are similar as BKVAN increase expression of different mRNAs which also increased in TCMR.
6. Clinical Manifestations: – Mostly have no systemic symptoms.
– Viruria, occur in 50% (the most common and earliest manifestation of BKV )
– Viremia which is a symptomatic initially , occurred after viuria, it is a better predictor of progression to BKVAN in comparison to viruria.
– BKVAN usually occurs after a period of sustained progressively worsening viremia, manifest as a decline in renal function with or without urinary abnormalities.
– Other manifestations: ureteral stenosis and hemorrhagic cystitis, a possible link with genitourinary
(GU) malignancies.
7. Screening and Diagnosis
KDIGO) and AST-IDCOP guidelines recommend; monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BK PCR:
It isnot a recommended screening test, 50% of patient will not develop viuria, need blood PCR confirmation.
Plasma BK PCR;
Inter-assay variability.
The genotype I strain is used as the reference sequence for designed for various assays
It can be four times less sensitive for variant strains.
Urine Cytology :
Characteristic of infected cells on cytologic examination of are called decoy cells, marker of PV replication, they do not necessarily indicate PVN. It has a high NPV.
Donor-Derived Cell-Free DNA (dd-cfDNA)
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection
Transplant Kidney Biopsy
The gold standard for diagnosis of BVAN.
Tow Core biopsy should include medulla to decrease the risk of sampling error it might be missed in 30%.
It is used to assess the severity and the presence of other pathology.
Histopathological features for a definitive diagnosis of BKVAN
*Characteristic cytopathic changes:
– Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions.
– Granular nuclear inclusions and inclusions and “clumps” of intranuclear.
– Tubulitis and interstitial inflammation with a prominent plasma cell component
– May result in tubular atrophy and interstitial fibrosis
* Positive IHC tests SV40 antigen:
-The stain can highlight cells in the early stages of infection, before viral cytopathic changes may be detectable on routine stains
-Positive SV40 staining is almost 100 specific for BKV.
– Help differentiate PVN from other viral nephropathies.
The diagnosis of PVN is difficult due to the histologic similarities shares with acute rejection (AR), and they can occur together, creating a treatment dilemma.
Several grading systems for the evaluation and reporting of PKN, including AST and Banff Working group. These systems use features such as viral cytopathic effect, injury, and atrophy to classify cases.
8.Treatment.
– There is No definitive therapeutic agent available.
-Reduction in the intensity of IS is the mainstay for the treatment with different protocols available.
*Stepwise approach for the reduction in immunosuppression BKv/ BVAN:
-Reduce dose of antimetabolite by 50% while continuing on the same doses of CNI and/or prednisone.
-Monitor; creatinine, BK PCR levels every 2 weeks.
– Discontinuation of of anti-metabolite, if PCR did not improve or increases.
– If no improvement in viral load 4 weeks after stopping antimetabolites, reduce CNI trough goals
(4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine)
– Other adjunctive therapies utilized to treat BK virus infection include:
– IVIG; BK-neutralizing antibodies, reduce BKV load.
– Quinolones; anti-viral properties, high risk for resistant bacterial infection
– Cidofovir; nephrotoxic – Leflunomid; both immunosuppressive and anti-viral properties.
Upcoming Therapeutic Trials:
– Human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1.
– Multivirus-specific T Cells therapy 9. Kidney Re-Transplantation – Re-transplantation should be considered for any patient lost graft with BKAN.
– Graft or native nephrectomy is not recommended.
– Consider lower immunosuppression should be balanced with the risk of rejection.
– Allograft survival in retrasplantation is excellent 94%, 5-year death-censored graft survival 91%.
Conclusion:
BKV is one of the most common clinical issues in KTRs. Viral surveillance and early detection and treatment have mitigated severe disease. Reduction in immunosuppression is the only treatment strategy, which may itself increase risk of rejection. Upcoming therapeutic agents are showing promising results.
It is first identified early in 1971 as a cause of ureteric stricture post transplantation, in 1993 the first case of BK nephropathy discovered, at that time graft loss occur in 50-100 % of cases (now reduced to 15%)
BK polyomavirus is a small, double stranded, non-enveloped DNA virus. Serotype 1 in the most common. Its genome encodes for 6 viral proteins, 2 early, 1 none coding and 3 late proteins.
The early proteins include large (T) and small tumor antigen (t); the large T antigen is responsible for immortalization of the infected cells and subsequent latent infection.
Infection is usually acquired in childhood, through either feco-oral or respiratory route, it infects renal tubules and uroepithelium of most of people ( around 90% of people are infected worldwide by the age of 4 ) and infection remain lifelong
In immune-competent individuals the infection is usually benign and asymptomatic.
In immune-compromised renal transplant recipients, infection can be acquired either due to reactivation of latent infection or newly transmitted from the donor kidney, infection is either subclinical or it may become symptomatic causing BK nephropathy with subsequent graft dysfunction and probable graft loss
BK infection has a stereotypical pattern, starting by viruria (occurring in 30% of transplant recipients), then viremia (occurring in 12% of transplant recipients) and lastly nephropathy (occurring in 1-10% of transplant recipients)
Risk factors for viremia
A- The intensity of immunosuppression
Typically viremia occur in the early period of transplantation.
It is more common in cases of ABO and HLA mismatches due to aggressive immunosuppression used
It is more common also in patients with frequent rejection episodes and patients with DGF
No specific drug is linked to infection but tacrolimus may be associated with more infection than cyclosporine due to synergy between tacrolimus and MMF , and m TOR may be assocuiaetd with lower incidence of infection.
B- Donor factors
BK serostatus, such as transplanting kidney from BK + donor to BK – recipient
The presence of donor viruria before transplantation
C- Recipient factors
Older age
Male sex
The use of ureteric stent as a prophylaxis of ureteric leak
Damage of transplanted kidney related to Ischemia or rejection
Some factors may be associated with lower incidence of BK viremia including HLA B 51 positivity and PCKD
Clinical presentation of BK virus
Most of cases are asymptomatic
Graft dysfunction (BK nephropathy) in the form of increase in the serum creatinine associated with pyuria, hematuria and/or cellular casts
Ureteritis and ureteric stenosis secondary to BKV infection is uncommon but some studies reported association
Rarely presents with hemorrhagic cystitis
Debatable and unclear association with genitourinary malignancies
Screening of BK virus
Urine PCR is not recommended due to high cost and low specificity for BK nephropathy
Decoy cells has low positive predictive value but high negative predictive value for nephropathy
Blood PCR is the best method for screening since it correlate well with BK nephropathy, but it is less sensitive in detefction of strains other than serotype 1
Screening is recommended monthly in the first 6 months then /3 months for 2 years post transplantation then annually for 5 years.
Blood test (PCR ) should be done in the setting of graft dysfunction or if viruria or decoy cells detected
Diagnosis
A- Viruria (urine PCR, urine decoy cells)
Sensitive but nonspecific (most of patients are asymptomatic and do not progress to BK nephropathy), 50 % may progress to viremia within weeks to months
Present in around half of the patients by the first year of transplantation
May be replaced by decoy cells (cheaper) which represents renal tubular or uroepithelial cells containing intranucelar viral inclusions and reflects higher urinary viral load.
Both low positive predictive value for progression to nephropathy
Detection of viruria is an indication for doing PCR blood
B- Viremia (PCR )
Sensitive and more specific than urinary PCR
Present in 10-30% of renal traplant recipietn in the first 6 months and in 5-10% later on
Level > 1000 copies/ml are considered positive, positive predictive value for progression to nephropathy is 50% within 1-2 weeks
Level > 10000 copies/ml has a very high positive predictive value of nephropathy and some recommend settling the diagnosis of BK nephropathy at this level of viremia without biopsy
Sustained viremia and higher viral load are associated with higher incidence of progression to nephropathy
The presence of viremia is an indication for reduction of immunosuppression
C- BK nephropathy
Occur mostly in the first year after transplantation especially between 2–6 months after transplantation
Presents by graft dysfunction (increase in serum creatinine associated with pyuria, hematuria and/or cellular casts), the diagnosis is confirmed by renal biopsy.
It may be misdiagnosed as cellular rejection since biopsy can mimic ACR, and the main diagnostic difference is the detection of the virus or viral antigen by IHC.
In conclusion around half of patients with viruria can progress to viremia and around half of patients with viremia can progress to BK nephropathy
Renal biopsy for BK nephropathy
Renal biopsy is indicated in case of graft dysfunction associated with viral load is >1000 (BK viremia)
Patient with viral load> 10000 copies/ml, diagnosis of BK nephropathy is settled and renal biopsy can be done only if rejection is expected.
Renal biopsy can be done immediately if the diagnosis is uncertain or there is suspicion of rejection or it may be delayed for 2-4 weeks (after reduction of immunosuppression) if no improvement in graft function or if there is suspicion of superadded rejection (rise of kidney function again after resolution of viremia).
At least 2 biopsy cores should be taken since the injury is usually focal, and medulla should be included since BK virus is more likely to be present in the medulla and around 1/3 of cases are missed with one core
The diagnosis requires the presence of the following:
A- Characteristic cytopathy (not specific) including
Intranuclear basophilic viral inclusions without surrounding hallo, best seen by EM, DD : CMV which is associated with cytoplasmic inclusions
First reduce MMF by 50%, if no response stop MMF, if no response reduce CNI dose (keeping trough for tacrolimus 4-6, and for cyclosporine 50-100)
Monitor viral load (plasma PCR) /2-4 weeks, clearance of viremia precedes viruria by weeks to months so monitoring of viruria has no clinical implication in follow up
Monitor renal functions/2-4 weeks (especially in patients with graft dysfunction)
Several agents were tried in the treatment of BK nephropathy due to their in vitro anti-BKPyV activity, including IVIG, leflunomide, cidofovir, and quinolone. All these are not routinely recommended as there is no clear evidence of their superiority on reduction of immunosuppression alone
Re-transplantation after graft failure due to BK nephropathy
Kidney Re-Transplantation is feasible with excellent graft survival at 1(98%) and 3 years (94%) after transplantation
Viral clearance should be confirmed before transplantation
Native or graft nephrectomy is not recommended
Consider HLL and ABO compatible transplantation, in order to avoid aggressive immunosuppression
BK virus associated nephropathy (BKAN) is one of the major leading causes of allograft dysfunction and loss in kidney transplantation (KT).
BKVN is associated with heavy immune suppression
Discovered in 1971 in a KT recipient diagnosed with ureteric stenosis
It is small, non-eveloped, icosahedral , DNA virus and a member of polyomaviride family. BKV genome composed of 3 regions; early coding region for large T and small t (tumour antigen), non-coding region, and late coding region
Epidemiology:
Prevalence is 90% by the age of 4 years
Transmission is mainly through mucosal contact; e.g oral, GIT & respiratory
Stages of infection are viruria, viremia,and allograft nephropathy in chronological order with the following prevalence 30%, 30%, 12% respectively.
Risk factors:
Heavy immune suppression is the major risk factor rather than the type of immune suppression
Patient profile e.g older age, diabetes, specific HLA-C alleles
The donor-recipient interface; D+/R- status, ABO/HLA incompatibilty, DGF, rejection, prolonged cold ischemia time, and ureteric stent.
Donor related factors; decrease immune response to BKV, the presence of viruria before transplantation
HLA-B51+ve recipients; are protected against BKVAN due highly immunogenic cytotoxic T cells
Polycytic kidney disease patients: are protected as well against BKVAN
Cellular immune response:
The presence of intact immune system including both humoral and cellular immunity are essential for the process of viral clearance.
Clinical features:
Asymptomatic
Viruria in 50% of KT recipient in the first year after transplantation (early sign) and mostly with no progression to viremia
Sustained viruria may lead to viremia in 10 to 30% in the first six months after transplantation. Later on it is 5 to 10%.
Sustained progressive viremia may lead to BKVAN(usually within the first 2 to 6 months),which is a form of allograft dysfunction with or without urinary abnormalilites.
ureteric stenosis
Hemorrhagic cystitis in bone marrow transplantation
Genitourinary malignancies ?
Screening and diagnosis:
The recommendation is monthly screening for the first 6 months after transplantation, then every 3 months for 2 years (KGIGO & AST-IDCOP)
How ?
Urine PCR; not recommended due specificity and half of patients will not progress to viremia
Plasma BKV PCR; May be problematic due variabilities, dis concordance among assays and defection of rare BKV genotype
Urine cytology; decoy cells = BKV virus-infected tubular epithelial cells, ground glass nuclear inclusions surrounded by a condensed rim of chromatin. They may exhibit “owel eye” inclusion, multinucleated, or clumped chromatin. It may not necessarily suggest BKVN. Urine electron microscopy may show a cast-like aggregates of polyomavirus which is known a Haufen bodies.
Donor-drived cell-free DNA (dd-cfDNA); dd-cfDNA may be useful non-invasive method to evaluate for progression of BKV to BKVAN. Higher levels of dd-cfDNA correlated with higher levels of BKVviremia and histologic diagnosis of BKVAN.
Biopsy; definitive diagnoses is histolologic changes of inflammation, tubular atrophy and fibrosis + immune histo-chmenistry of SV 40. You can missed one third of cases due to focal disease and involvement of the medulla rather than the cortex. Bann grading of BKV nephritis are; grade 1(minimal viral replication in < 1% of the biopsy with < 25% fibrosis), grade 3 (marked viral replication > 10% with > 25% fibrosis, grade 2 any thing between grade 1 and grade 3
Treatment: the key thing is to reduce immune-suppression
Decrease anti-metabolite by 50%; if no response hold it completely.
If no reduction in BKV viral load after 4 weeks of stoppage of anti-metabolite, consider reducing CNIs trough level e.g 4 to 6 ng/ml for tacrolimus and 50 to 100 ng/ml for cyclosporine.
Other adjunct therapies are quinolones, cidofovir, leflunomide, IVIG but more RCTs are needed to confirm their routine use in this condition and some are on the pipelines.
Re-transplantation:
Is a viable options for patients with allograft loss due BKVAN
Confirm viral clearance before transplantation
Balance between the lower immune suppression and risk of rejection
Outcomes are comparable to a patients with graft loss due to other causes
Conclusion:
BKVAN is an important cause of allograft loss
Over immune suppression is the major risk factor
Screening and surveillance is the key to prevent of BKVAN
No specific treatment ,only reduction of immune-suppression
Re-transplantation is possible option after allograft loss due to BKVAN
BK virus was first discovered in a kidney transplant recipient who presented with a ureteral stricture in 1971. In 1993 was the first definitive biopsy proven case of BKVAN was described.
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family . The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small
tumor antigen), the non-coding control region, and the late coding region.
Epidemiology
The seroprevalence rates of over 90% by 4 years of age .
The primary routes for virus transmission are:
from mucosal contact including the oral, gastrointestinal, and
respiratory tract. After a primary viremia, the BK virus settled in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection. In post-transplant patient, viral replication mostly occurs in the first year because of the high immunosuppression drugs doses.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age, diabetes , and specific HLA-C alleles
3.The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement.
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
Clinical manifestations :
1- Viuria ; up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia but sensitive marker to progression to BKVAN.
2- Viremia is present in 10–30 percent of recipients in the first six months post-transplantation and in 5–10 percent of recipients thereafter. Viremia is a better predictor of progression to BKVAN in comparison to viruria .
3- BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities. Mostly occurs within the first post-transplant year due to attenuated cellular immunity, with the highest incidence in the first 2–6 months being periods .
4- Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis.
5- There are reports of a possible link between the BK virus and genitourinary (GU) malignancies.
Screening and Diagnosis:
The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 month.
1- Urine BK PCR:
Urine BK PCR is not a recommended screening test because if positive, it requires confirmation with plasma PCR. Around fifty
percent of patients with viruria will not develop viremia.
2- Plasma BK PCR:
The World Health Organization (WHO) established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL in 2016.
The genotype I (Dunlop) strain is currently utilized as the reference sequence against which primers and probes are designed for various assays. A viral load > or equal to 10,000 is diagnostic.
3- Urine cytology :
This will reveal the characteristic BK virus-infected cells called decoy cells due to their similarity to renal carcinoma cells. These are
tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin . They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin. Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN.
4- Donor-Derived Cell-Free DNA (dd-cfDNA) :
A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN. It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN .
5-Transplant Kidney Biopsy:
1- Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen.
6- Histology :
The histologically, tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intra-nuclear inclusions. Viral cytopathic changes may also include granular nuclear inclusions Viral cytopathic changes may also include granular nuclear inclusions and clumps of intra-nuclear virion particles.
Treatment :
A- Immune suppression reduction:
1- Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. Monitor creatinine and viral load every 2 weeks.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
B- IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression (balancing with risk of rejection). The rationale for use is the presence of BK-neutralizing antibodies in IVIG preparations
C- Quinolones: Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia .
D- Cidofovir: A nucleotide analog of cytosine has demonstrated activity against Polyomaviridae in-vitro . Studies have shown no benefit with cidofovir use. Cidofovir is associated with proteinuria, proximal tubular dysfunction, and kidney disease .
4. Leflunomide: A prodrug that converts to an active metabolite, A77 1726, which has demonstrated both immunosuppressive and anti-viral properties . While there was initial enthusiasm for its use in BK virus infection based on a case series, a pharmaco-dynamic and prospective open-label study showed no benefit . Another metabolite, FK778, did not demonstrate efficacy in a phase 2, proof-of-concept, randomized, open-label, parallel-group, 6-month study in kidney transplant patients
when compared with a reduction in immunosuppression .
Kidney Re-Transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
Allograft survival in patients who re-transplanted is 98% and 94% at 1 and 3 years, respectively .
BKvirus infection is still one of the most frequent clinical problems that transplant doctors confront. Increased surveillance procedures have sped up disease detection and lessened its severity. In terms of diagnosis and treatment, it can also be confusing. The only effective treatment is to reduce immunosuppression, which may lead to rejection in the end. It can be accompanied by histologic characteristics resembling rejection. Furthermore, no antiviral is now known to be helpful in the removal of the infection. However, there is hope that innovative treatments could deliver the efficacy that the transplant community has yet to achieve.
Introduction:
History of the BK Virus:
Virology:
Epidemiology:
Cellular Immune Response and Pathogenesis:
Clinical Manifestations and Complications:
Screening and Diagnosis:
Summary of the article :
-The article discusses in detail the BK virus in context of renal transplantation regarding the virology, replication and risk factors, presentation, and finally the management.
-Risk factors include immunosuppression, elderly individuals, white race, HLA –ABO mismatch and ureteric insults.
-Presentation varies from asymptomatic picture to BK nephropathy, ureteric stenosis or hemorrhagic cystitis.
-Management starts by proper diagnosis through plasma PCR of the virus+ renal biopsy with evidence of viral inclusions.
-Treatment mainly entails reduction of IS; reduction of antimetabolites by 50% and complete cessation if no proper response, reduction of CNI’s.
-No strong evidence of antivirals against
-IVIG may have a role especially in the setting of rejection and BKVN.
Summary
Introduction
This article is about BK virus infection in kidney transplant recipients. The different aspects related to this infection, along with the necessary screening practices and the diagnostic and therapeutic challenges posed. This review extensively covers viral epidemiology, pathogenesis, screening and diagnostic methods, clinical manifestations and recommended treatment strategies.
Discussion
BKV infection is an important cause of graft loss in renal transplant recipients. The history of the virus goes back to 1971 when it was discovered in a kidney transplant recipient presenting with ureteral stricture.
BK virus is a small non enveloped icosahedral closed circular double stranded DNA virus that is a member of the polyomaviridae family. The viral genome is of 3 regions – the early coding region of the large T and small t antigens, the non coding control region, and the late coding region.
The T antigen binds to p53 and Rb protein, taking control of cell cycle and leading to persistent infection. The non coding parts of the virus assist in pathogenesis of the virus. Mutations in the non coding region lead to replication of the virus.
BK virus infection is seen as primary infection in childhood, below the age of 4 years. Transmission routes of the virus include mucosal contact – oral, gastrointestinal, and respiratory tract. Viral replication is linked with risk factors such as :
Clinical manifestations in these patients may not be prominent in all cases. Many patients are asymptomatic. The sequence of the infection in the patient includes viruira, viremia, and BKVAN.
Investigations includes plasma BK PCR, urine cytology, and transplant kidney biopsy. Urine PCR is not recommended for screening since it always required confirmation with plasma PCR and lack of specificity. It is also more expensive.
Transplant kidney biopsy is gold standard for diagnosis. The following characteristics on biopsy will form part of definitive diagnosis of BKVAN :
Treatment involves reduction in immunosuppression, monitoring of serum creatinine and serial plasma BK PCRR levels. IVIG, quinolone, cidofovir, and leflunomide are other therapies that are part of the treatment regimen for these patients.
Conclusion
BK virus infection and BKVAN can lead to graft loss in transplant patients. Heightened surveillance protocols are needed for early detection and effective treatment in order to mitigate severe disease. Further studies are need sot hat novel therapeutics can be used to increase treatment efficacy and prevent rejection.
Review BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review.
Introduction:
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
Rates of BK viremia (BKV) is up to 30% of kidney transplant recipients.
History of the BK Virus:
Discovered in patient with ureteral stenosis.
early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported .The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% .
Virology BK virus:
Is a small, non-enveloped, icosahedral, double-stranded DNA virus and member of the Polyomaviridae family?
The genome of the virus consists of three regions:
The early coding region:
Of the large T and small t antigens (large and small tumor antigen), T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection.
The non-coding control region, contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
Mutations in the non-coding control regions result in permit replication in other cell types (permissively), cell tropism, and altered rates of replication .These mutations correlate with high BK virus loads in kidney transplant recipients with clinically significant viral replication
And the late coding region code for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). The agnoprotein .The agnoprotein is responsible for the assembly of viral capsids and the release of virions from cells.
VP-1 is the major structural protein that engages with cellular receptors and has significant genetic heterogeneity.
Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases.
Epidemiology:
Prevalence:
Seroprevalence rates of over 90% by 4 years of age.
Routes for transmission:
Mucosal contact including the oral, gastrointestinal, and respiratory tract.
After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelium cells resulting in lifelong latent/persistent infection.
Risk factors for viral replication is associated with the following:
1- Intensity of immunosuppression
2– Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3-the donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus ,ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis:
Virus maintains persistent infection after initial childhood infection this latent infection can become active with reduced potency of cellular immunity.
Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
Clinical Manifestations:
Asymptomatic.
In kidney transplant patient:
Viruria: up to 50% of patients in the first year of transplantation, with most cases not progressing to Viremia.
Viremia:
Present in 10–30 percent of recipients in the first six months post transplantation and in 5–10 percent of recipients thereafter.
BKVAN:
Manifesting as a decline in renal function with or without urinary abnormality.
Majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence.
Other manifestations of the BK virus include:
Ureteral stenosis and hemorrhagic cystitis—albeit rare in Renal transplant more in HSCT.
Screening and Diagnosis:
KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BK PCR:
Is not a recommended low specificity and cost—if positive, it always requires confirmation with plasma PCR and nearly fifty percent of patients with viruria will not develop viremia?
Plasma BK PCR:
Is the preferred method, higher positive predictive value of plasma BK levels?
A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL
Urine Cytology:
Decoy cells, these are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. “Owl eye” inclusions, multinucleation, or clumped chromatin. Although decoy cells are high false-positive rates and low positive predictive values.
Haufen:
Has extremely high positive and negative predictive values for BK nephropathy, respectively.
Donor-Derived Cell-Free DNA (dd-cfDNA):
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVA.
Transplant Kidney Biopsy:
Kidney allograft biopsy:
Aid not only in diagnosis, but also in assessing the severity of viral involvement and the presence of other ongoing pathologies.
The following pathologic features:
1. Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN);
Although, it does not distinguish between BKV and JC virus.
Histology:
Due to focal nature of infection two biopsy cores containing renal cortex and medulla are recommended.
Virus: Enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions
Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles.
Tubular cells: lyse and slough from the basement membrane into the tubular lumens.
Then tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.
More proximal portions of the nephron, including the parietal epithelial cells lining Bowman′s capsule, may also become involved.
Other test on biopsy sample:
Currently, it is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen.
Quantitative PCR for PV can also be performed on tissue samples.
PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of TUBULES.
A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN.
Treatment:
Mainstay is IS reduction.
1-Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies:
Include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin. A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir.
Intravenous immunoglobulin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
Kidney Retransplantation:
Extensive evidence of success
Failed transplant or native nephrectomy is not recommended.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
There was no significant difference in the rates of acute rejection or patient survival at one year.
Conclusions:
BK virus infection continues to be one of the most common clinical issues.
It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection.
There is no anti-viral currently known to be of benefit in the clearance of the virus.
Introduction:
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in
kidney transplant recipients, and a risk factor for graft loss.
Increasing efficacious immunosuppression leads to increasing BK viremia, other viruses, and opportunistic infections.
Epidemiology:
In transplant cases, viral replication is associated with the following risk factors;
Clinical manifestation:
1) Viruria, up to 50% of recipients in the 1st year of transplantation.
2) Viremia may be asymptomatic, present in 5-10% of recipients in the 1st 6 months post-Tx, a predictor of BKVAN.
3) BKVAN, after sustained progressive viremia, is associated with reduced graft function, manifested by ureteral stenosis, and hemorrhagic cystitis, with controversial oncogenic properties of BKV.
4) There is a possible link between BKV and genitourinary malignancy.
Screening and diagnosis:
Treatment:
The reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.by stepwise approach:
1) Reduce the antimetabolite by half and keep the CNI dose and prednisolone.
2) Complete cessation of antimetabolite if viremia and viral load persist.
3) Reduce CNI dose if viral load persists over 4 weeks after complete cessation of antimetabolite with target truth level of (4-6 ng/ml for TAC, and 50-100 ng/l for CyA).
4) IVIG; in case of nonresponse to a maximum reduction of IS.
5) Quinolones; have anti-viral properties.
6) Cidofovir; has no benefit with the risk of graft dysfunction.
7) Leflunomide; an active metabolite exhibits immunosuppressive and anti-viral properties.
Kidney Re-Transplantation:
Patients with graft loss due to BKVAN should be considered for re-transplantation
given its extensive evidence of success.
Nephrectomy of failed graft or native kidney is not recommended prior to re-transplantation.
BK polyomavirus (BKPyV) is a small DNA virus that establishes lifelong infection in the renal tubular and uroepithelial cells of most of the world’s population
Epidemiology-
BK polyomavirus (BKPyV) is a ubiquitous virus with a worldwide seroprevalence of approximately 80 to 90 percent Primary infection is typically acquired during childhood, possibly via fecal-oral or respiratory transmission . Following primary infection, the virus establishes lifelong infection in renal tubular and uroepithelial cells.
Viruria and viremia-Viruria is the earliest manifestation of BKPyV infection in kidney transplant recipients, affecting approximately one-quarter to one-third of patients during the first year following transplantation For most, viruria is asymptomatic, detected only by screening, and does not progress to viremia While viruria is a sensitive marker for progression to BKPyV-associated nephropathy (BKPyVAN), it is nonspecific . Viremia may follow viruria in a few weeks and occurs most frequently in those with high urine viral loads and sustained viruria. Viremia is detected in 10 to 30 percent of recipients in the first six months posttransplantation and in 5 to 10 percent of recipients thereafter. As with viruria, viremia is typically asymptomatic. However, viremia has a greater predictive value than viruria for progression to BKPyVAN.
Risk factors for viral replication –
The intensity of immunosuppression (particularly suppression of cellular immunity) appears to be a dominant risk factor for BKPyV replication and disease. Several studies have suggested that certain drugs (particularly tacrolimus) may be associated with an increased relative risk Other important risk factors include high risk serostatus (ie, kidney transplant from a BKPyV-.seropositive donor to a seronegative recipient) impaired immune response to BKPyV and donor BKPyV viruria prior to transplant. The last two factors suggest that the donor is an important source of transmission .
Other risk factors associated with an increased risk of BKPyVAN or disease severity include older age, ureteral stent placement, ABO incompatibility rejection or ischemia of the transplanted kidney , delayed graft function HLA mismatch specific HLA-C alleles , BKPyV polymorphisms , and transplantation from an HCV-positive donor .
Recipient HLA-B51 positivity and the presence of polycystic kidney disease,have been shown to be protective factors against the development of BKVAN.
Clinical Picture of BK virus infection-
BK polyomavirus (BKPyV) replication typically develops in stages: viruria followed by viremia and then, if viral replication persists, nephropathy can ensue. Asymptomatic viruria, viremia, and/or a slow progressive rise in serum creatinine are typically the only indicators of BKPyVAN. The incidence of BKPyVAN is highest in the first two to six months posttransplant. While the majority of cases occur in the first posttransplant year, BKPyVAN can occur years after transplantation. . Without resolution of infection, progressive kidney allograft dysfunction and graft loss can ensue over a period of months . Within the allograft, early infection triggers interstitial inflammation, which then progresses to fibrosis and tubular injury. Accordingly, urinalysis may reveal pyuria, hematuria, and/or cellular casts consisting of renal tubular cells and inflammatory cells, or may be normal.
Other manifestation-ureteral stenosis and In bone marrow transplant recipients, BKV can lead to hemorrhagic cystitis.
Posttransplant screening —
Screening and preemptive reduction in immunosuppression for patients with clinically significant BKPyV viremia prevent progression to BKPyVAN in the majority of patients. Screening should be done with Plasma PCR Monthly for the first six months following transplant, then every three months until 18 months posttransplant,
Testing methods-
Plasma quantitative PCR —
Quantification of plasma BKPyV DNA by real-time polymerase chain reaction (PCR) is the preferred screening test for BKPyVAN at most transplant centers The detection of BKPyV viremia by plasma quantitative PCR is both highly sensitive (100 percent) and specific (88 percent) for the diagnosis of BKPyVAN and has a higher positive predictive value for BKPyVAN than the detection of viruria by urine quantitative PCR or urine cytology (50 to 60 percent versus 40 and 29 percent, respectively)
Urine quantitative PCR-
patients who are found to have viruria require confirmation with quantitative plasma PCR, since approximately one-half of patients with BKPyV viruria will not develop viremia or BKPyVAN. As such, the cost effectiveness of this approach has been questioned
Urine cytology in BK virus nephropathy-
Cytologic examination of the urine, which may reveal BKPyV-infected cells, Decoy cells,is infrequently used to screen for BKPyVAN.These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin . They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin. Decoy cell are less sensitive and specific for the diagnosis of BKPyVAN compared with plasma quantitative PCR.Negative-staining electron microscopy of the urine of patients with BKPyVAN often reveals the presence of cast-like, three-dimensional polyomavirus aggregates, termed Haufen .he detection of Haufen in voided urine had a sensitivity, specificity, negative predictive value, and positive predictive value for biopsy-proven BKPyVAN of greater than 95 percent
Donor-Derived Cell-Free DNA (dd-cfDNA)
A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN.
Kidney allograft biopsy-
Because biopsy is invasive and sampling error can occur, a presumptive diagnosis is often made based upon the presence of significant viremia (plasma BKPyV viral load ≥10,000 copies/mL).
A definitive diagnosis of BKPyVAN requires the following findings on kidney biopsy
Characteristic cytopathic changes.
plus
Positive immunohistochemistry tests using antibodies directed specifically against BKPyV or against the cross-reacting SV40 large T antigen.
In BKVN, light microscopy examinations would show the following:
(1) basophilic intranuclear viral inclusions without a surrounding halo ; (2) anisonucleosis, hyperchromasia, and chromatin clumping of infected cells; (3) areas of tubular damage showing interstitial mononuclear or polymorphonuclear cell infiltrates (4)tubular injury in the form of tubular cell apoptosis, desquamation, and flattened epithelial liningand (5) tubulitis with lymphocyte invasion to the basement membrane of the tubular epithelium
Distinguishing BKPyVAN from rejection-
BKPyVAN is generally distinguished from rejection by the presence of BKPyV inclusions and immunohistologic or in situ hybridization evidence of virally infected cells, which are usually tubular epithelial cells, rather than podocytes or endothelial cells .It is important to correlate the histologic findings with PCR evidence of viremia. Establishing a diagnosis of concomitant T cell-mediated rejection in a biopsy that has BKPyVAN is difficult since both the histologic features and transcriptional profiles of these two disorders are similar. In general, the presence of extensive tubulitis in areas remote from the viral cytopathic changes suggests that acute rejection is present, in addition to BKPyVAN. The combined presence of endarteritis, fibrinoid vascular necrosis, glomerulitis, and C4d deposits along peritubular capillaries is conclusive evidence of concurrent rejection
Treatment-
Since there are no specific antiviral therapies for BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN), the cornerstone of management is to decrease immunosuppressive medications .In patients who are on a triple immunosuppression therapy consisting of a calcineurin inhibitor , an antimetabolite and prednisone, we initially reduce the dose of the antimetabolite by 50 percent. If the BKPyV viral load does not decrease within two to four weeks, we completely discontinue the antimetabolite. If there is still no decrease in viral load after another two weeks, we decrease the dose of the calcineurin inhibitor by 25 to 50 percent, targeting a whole blood tacrolimus trough level of 4 to 6 ng/mL or a whole blood cyclosporine trough level of 60 to 100 ng/mL
Adjunctive therapies –Several agents have been shown to have in vitro anti-BKPyV activity. However, we do not routinely use any of these agents for the treatment of BKPyV infection, given that the efficacy of these agents has not been established and use of these therapies has not been clearly shown to be superior to reduction in immunosuppression alone
BK virus in kidney transplantation
Introduction
Epidemiology
In transplant cases, viral replication is associated with the following risk factors;
Clinical manifestation
Screening and diagnosis
Treatment
stepwise approach;
Upcoming therapeutic trial
Kidney re-transplantation
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review.
1. Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in
kidney transplant recipients.
The potent immunosuppression lead to high rates of BK viremia (BKV) in about 30% of kidney
transplant recipients.
its discovered in 1971, but till now there is no effective treatment or prophylaxis .
This review provides an extensive overview of viral epidemiology, pathogenesis, screening, and
diagnostic methods.
2. History of the BK Virus:
BK virus was first discovered in Sudanese a kidney transplant recipient presented with a
ureteral stricture in 1971 .
During the period of its early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported .
The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% within the last 2 decades .
Virolology:
BK virus belongs to a family of polyomavirus family, small ds-DNA virus, categorized into four groups with different activity .
The genome consists of three region.
1. Large T, small t antigen (bind to p53, protein Rb and lead to persistant infection.
2. Non-coding control region (it causes replication, and enhance elements and modulate transcription ).
3. Late coding region (codes for agnoprotein responsible for assembly of viral capsids VP-1 and release of virion, and viral capsid protein.
Epidemiology:
The prevalence rates is about 90% by 4 years of age
transmission route : fecooral – through mucosal contact ( oral, gastrointestinal, and respiratory tract)
post a primary infection , the BK virus infect the kidney and uroepithelial cells lead to lifelong latent/persistent infection.
Frequently occur in first year , the time of most immunosuppression state.
infection occurs in kidney transplant either by reactivation of latent infection or transmission of new infection from the donor.
Viruria and viremia are occur in about 30% and 12% of kidney transplant recipients, respectively.
Viremia occur in 50% of viruric patient , BKVAN occur in 50% of viremic patient.
Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age , diabetes, and specific HLA-C alleles .
3. The donor–recipient interface.
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant [
Cellular Immune Response and Pathogenesis:
Control of BK viremia are dependent competent cellular immune response- of both CD4 and CD8 cells type .
The shorter time needed (<1 month) to appear anti-BK T cell response associated with the clearance of viremia, while recipient who develop BKVAN need a median period of 5 months to achieve cellular immunity toward the virus.
The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium.
Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways .
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
clinical manifestation :
1- Usually asymptomatic .
2- Stepwise progression involves : Viruria then viremia and then BKVAN.
3- Usually present in the first year post kidney transplant time of potent immunosuppression.
4- Urine BK viral loads is not standard practice in diagnosis of BKVAN but is assign of disease progression.
5- Viremia is asymptomatic but it is a useful tool for progression to BKVAN
6- BKVAN usually manifests as graft dysfunction.
7- Ureteral stenosis mau occur.
8- Hemorrhagic cystitis is rare complication commonly occur in in hematopoietic stem cell transplants patients.
9- Genitourinary (GU) malignancies – data is not conclusive .
Screening and Diagnosis:
1- Urine BK virus PCR .
2- plasma BK virus PCR .
3- Urine cytology: decoy cell.
4- Donor-Derived Cell-Free DNA (dd-cfDNA).
Treatment :
Stepwise approach to reduce immunosssuppression:
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin
inhibitor and/or prednisone. With serial plasma BK PCR levels from the same laboratory every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus
and 50–100 ng/L for cyclosporine).
Other adjunctive therapies utilized to treat BK virus infection :
1. IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression. It is benefit still not ctear. It is only viable adjunctive therapy
2. Quinolones: Studies not prove its efficacy as prophylaxis or treatment .
3. Cidofovir: Studies shows negative results with wide range of side effect.
4. Leflunomide: Some study showed no benefit.
9. Kidney Re-Transplantation:
– Patients with graft loss due to BKVAN should be considered for re-transplantation
given its extensive evidence of success .
-Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. The advancement in effective IS therapy increased the rate BK viremia in up to 30% of kidney transplant recipients.
History of the BK virus
Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN.
The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
Virology
Small double-stranded DNA virus and member of the Polyomaviridae family
– It has 4 different genotypes ( I- IV)
– The genome of the virus consists of three regions; the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
Epidemiology
BKV is ubiquitous – 90% seroprevalence by 5 years age
Transmission through respiratory and faeco-oral route – remains latent in the kidney and urothelial cells
BKV infection post renal transplant can be due to reactivation of latent infection or transmission from the donor kidney
Chronology of infection course –
– Viruria precedes viremia by 4-6 weeks, and BKVAN by 6-10 weeks
– urine BK viral load > 8 log10 copies/mL predict the onset of viremia
– plasma BK viral load > 4 log10 copies/mL are associated with higher rates BKVAN
– plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN (SV40-IHC and inflammatory infiltrates)
Risk factors –
Cellular immune response:
· Cellular immune response (both CD4 & CD8) is important in mitigation and clearance of BK viremia
o IFN-gamma activity (indicate cellular immune response) is associated with the resolution of BKVAN
o Shorter time (<1month) to develop anti-BK-T cell response a/w better viremia clearance, while longer median time (>5months) is seen in patients who develop BKVAN.
o CD8-based cellular responses correlated with lower BK viral loads in blood and urine
o BK-directed cytokine signatures from CD4 cells have demonstrated similar results
· Various Studies are being conducted to assess these assays, which could be utilized to predict the clearance of BKV and also to identify patients at risk for progression.
Pathogenesis:
Latent infection in Kidney and Urothelium is reactivated in immunosuppressed state.
Viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways – cause tubular damage (atrophy), interstitial fibrosis and progressive nephron loss.
Clinical manifestations:
· mostly asymptomatic
· Viruria is most common (30-50%) and earliest manifestation of BKV
· Although it is a sensitive marker for progression of infection, Urine BK viral loads is not standard practice in transplant, because viruria can occur in pregnancy, older age and other immunosuppressive states.
· Plasma Viral load (Viremia) is a better predictor of progression to BKVAN
· BKVAN is manifested as decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia
· ureteral stenosis is a rare complication
· hemorrhagic cystitis commonly seen in HSCT recipients
Screening and diagnosis:
· Urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value, thus screening for BK viremia is the preferred method.
· Urine PCR for BKV is not recommended as a screening test – (low specificity, cost)
· Plasma BKV PCR (viremia) is a better predictor of progression to BKVAN
– KDIGO and American society (AST-IDCOP) recommend screening monthly for first 6 months, then 3-monthly for 18 months (total 2 years).
· Urine cytology – “decoy cells” are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by condensed rim of chromatin
o marker of polyomavirus replication but do not necessarily indicate PVN
· Polyomavirus-Haufen in urine sample via negative staining EM
o correlates well with disease severity with a high positive and negative predictive value.
· donor-derived cell-free DNA (dd-cfDNA) – higher levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR
– dd-cfDNA can be used as noninvasive test to assess progression to BKVAN
Renal Allograft Biopsy is the gold standard for diagnosis of BKVAN, assessment of severity and any other pathology (Rejection)
· Due to medullary tropism and chances of missing focal lesions (30%) – 2 biopsy cores including medulla are recommended.
– repeat biopsy can be considered if clinical suspicions is high
· Histopathologic features of BKVAN – cytopathic changes and positive IHC (using antibodies directed against BKV or SV40 large T antigen)
– Tubular epithelial cells with enlarged, hyperchromatic nuclei and ground glass intranuclear inclusions
· Positive SV40 staining is100% specific for PVN
· Diagnosis can be made if the plasma BK viral load is >10,000 copies/mL
Tubular injury (epithelial flattening, tubular atrophy), tubulitis, interstitial inflammation and fibrosis (IF/TA) is also seen in AMR / Chronic Rejection, which may coexist with BKVAN.
· Features of vascular injury (glomerulitis, peritubular capillary C4d staining) in presence of DSA can distinguish towards ABMR, whereas high BK viral load can be indicative of BKVAN.
Treatment
mainstay of management for BK viremia and BKVAN is reduction in immunosuppression
– currently, there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy
– reduce antimetabolite dose by half, monitor serum creatinine and plasma BK PCR every two weeks
– if BK viral loads remain at similar levels or increase, withdraw the antimetabolite completely
– if BK viral loads do not reduce in 4 weeks despite stopping the antimetabolite, reduce the CNI dose targeting trough levels of 4-6ng/mL for tacrolimus and 50-100ng/L for cyclosporine
– kidney transplant recipients on tacrolimus-based regimens have lower rates of rejection and higher eGFRs on 5-year follow up data
– other adjunctive therapies used to treat BKV infection include: – cidofovir, fluoroquinolones, IVIG, leflunomide
– there was no difference in graft outcomes when reduction in immunosuppression was combined with leflunomide or cidofovir compared with reduction in immunosuppression alone
– IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended
– there are upcoming therapeutic trials involving modified T cells and monoclonal antibodies
Kidney re-transplantation
– kidney re-transplantation can be considered in patients with graft loss due to BKVAN
– failed transplant or native kidney nephrectomy is not recommended
– viral clearance should be confirmed prior to re-transplantation
– consider lower immunosuppression without triggering rejection
– graft survival following re-transplantation is 98% and 94% at 1- and 3-years respectively
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Summarize this article
Introduction:
Potent immunosuppression has come up with high incidence of BKV infection – (viremia 30%) and morbidity like BKV associated nephropathy (5-10%) and graft loss in significant number of renal transplant recipients.
Overview of viral epidemiology, pathogenesis, screening, and diagnostic methods, clinical manifestations and recommended treatment strategies are discussed.
History of BK virus:
1971 – Virus discovered in a kidney transplant recipient with ureteral stricture
1993 – First case of BKVAN (biopsy-proven) was described
High incidence of viremia being reported due to strong immunosuppression use and better testing facility.
Incidence of graft loss reduced significantly (<15% from 50%) by early recognition and better management of BKVAN
Virology:
· Family – Polyoma viridae
· Small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus
· 3 regions of viral genome – early coding region is for large T and small t (tumor) antigens
Epidemiology:
BKV is ubiquitous – 90% seroprevalence by 5 years age
Transmission through respiratory and faeco-oral route – remains latent in the kidney and urothelial cells
BKV infection post renal transplant can be due to reactivation of latent infection or transmission from the donor kidney
Chronology of infection course –
– Viruria precedes viremia by 4-6 weeks, and BKVAN by 6-10 weeks
– urine BK viral load > 8 log10 copies/mL predict the onset of viremia
– plasma BK viral load > 4 log10 copies/mL are associated with higher rates BKVAN
– plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN (SV40-IHC and inflammatory infiltrates)
Risk factors –
Cellular immune response:
· Cellular immune response (both CD4 & CD8) is important in mitigation and clearance of BK viremia
o IFN-gamma activity (indicate cellular immune response) is associated with the resolution of BKVAN
o Shorter time (<1month) to develop anti-BK-T cell response a/w better viremia clearance, while longer median time (>5months) is seen in patients who develop BKVAN.
o CD8-based cellular responses correlated with lower BK viral loads in blood and urine
o BK-directed cytokine signatures from CD4 cells have demonstrated similar results
· Various Studies are being conducted to assess these assays, which could be utilized to predict the clearance of BKV and also to identify patients at risk for progression.
Pathogenesis:
Latent infection in Kidney and Urothelium is reactivated in immunosuppressed state.
Viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways – cause tubular damage (atrophy), interstitial fibrosis and progressive nephron loss.
Clinical manifestations:
· mostly asymptomatic
· Viruria is most common (30-50%) and earliest manifestation of BKV
· Although it is a sensitive marker for progression of infection, Urine BK viral loads is not standard practice in transplant, because viruria can occur in pregnancy, older age and other immunosuppressive states.
· Plasma Viral load (Viremia) is a better predictor of progression to BKVAN
· BKVAN is manifested as decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia
· ureteral stenosis is a rare complication
· hemorrhagic cystitis commonly seen in HSCT recipients
Screening and diagnosis:
· Urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value, thus screening for BK viremia is the preferred method.
· Urine PCR for BKV is not recommended as a screening test – (low specificity, cost)
· Plasma BKV PCR (viremia) is a better predictor of progression to BKVAN
– KDIGO and American society (AST-IDCOP) recommend screening monthly for first 6 months, then 3-monthly for 18 months (total 2 years).
· Urine cytology – “decoy cells” are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by condensed rim of chromatin
o marker of polyomavirus replication but do not necessarily indicate PVN
· Polyomavirus-Haufen in urine sample via negative staining EM
o correlates well with disease severity with a high positive and negative predictive value.
· donor-derived cell-free DNA (dd-cfDNA) – higher levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR
– dd-cfDNA can be used as noninvasive test to assess progression to BKVAN
Renal Allograft Biopsy is the gold standard for diagnosis of BKVAN, assessment of severity and any other pathology (Rejection)
· Due to medullary tropism and chances of missing focal lesions (30%) – 2 biopsy cores including medulla are recommended.
– repeat biopsy can be considered if clinical suspicions is high
· Histopathologic features of BKVAN – cytopathic changes and positive IHC (using antibodies directed against BKV or SV40 large T antigen)
– Tubular epithelial cells with enlarged, hyperchromatic nuclei and ground glass intranuclear inclusions
· Positive SV40 staining is100% specific for PVN
· Diagnosis can be made if the plasma BK viral load is >10,000 copies/mL
Tubular injury (epithelial flattening, tubular atrophy), tubulitis, interstitial inflammation and fibrosis (IF/TA) is also seen in AMR / Chronic Rejection, which may coexist with BKVAN.
· Features of vascular injury (glomerulitis, peritubular capillary C4d staining) in presence of DSA can distinguish towards ABMR, whereas high BK viral load can be indicative of BKVAN.
Treatment:
– there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy
– mainstay of treatment is reduction of immunosuppression
– reduce MMF by half
– monitor serum creatinine and plasma BK PCR every two weeks
– Increased or static viral load indicates complete withdrawal of antimetabolite
– BK viral loads not reduce in 4 weeks despite stopping antimetabolite à reduce CNI dose targeting lower trough level (Tac C0 of 4-6ng/mL; CsA C2 level 50-100ng/L)
Adjunctive therapies used to treat BKV infection – cidofovir, IVIG, leflunomide
· No difference in graft outcomes by IS reduction combined with leflunomide or cidofovir has been reported, compared to IS reduction alone.
· IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended
· upcoming therapeutic trials involving modified T cells and monoclonal antibodies have shown promising results in isolated case reports / small case series.
Kidney re-transplantation
· can be considered in patients with graft loss due to BKVAN
· failed transplant or native kidney nephrectomy is not recommended
· viral clearance should be confirmed prior to re-transplantation
· consider lower immunosuppression without triggering rejection
· graft survival of 98% @ 1year, 94% @3-years has been reported
Conclusions:
· BKV infection remains a major concern after transplant (heavy immunosuppression)
· Strict surveillance protocols have led to early detection and mitigation of severe disease
· Histologic findings may be similar to acute rejection, which may coexist with BKN
· Reduction in immunosuppression can be helpful for BKV infection and prevention of BKVAN, but may precipitate Rejection
· No antiviral therapy has been effective in clearance of BKV
· Novel therapeutic agents has shown positive results in case reports or small series, are being evaluated in large scale in Upcoming Therapeutic Trials:
1. MAU868 – human monoclonal antibody (IgG1):
– (ClinicalTrials.gov identifier: NCT04294472).
2. adoptively transferred posoleuccel (ALVR105) multi-virus-specific T Cells in kidney transplant recipients:
– (ClinicalTrials.gov identifier: NCT04605484).
1. Please summarize this article;
Introduction;
The strong immunosuppression revolution has improved graft survival but also accompanied by high rates of BKVN in up-to 30% of kidney transplant recipients.
History of BK virus;
In 1971 BKV was discovered when a patient was investigated for ureteral structure, and biopsy proven case was diagnosed by 1993.
It’s still not clear that increasing incidence of viremia is secondary to strong immunosuppression or better availability of testing.
Early recognition has decreased the incidence of graft loss by 15%, otherwise, it was 50 to 100% in early period.
Virolology;
BK virus belongs to a family of polyomavirus family, small double-stranded non-enveloped DNA virus, categorized into four groups with different virulence.
The genome consists of three region.
1. Large T, small t antigen (bind to p53, protein Rb and persistant infection.
2. Non-coding control region (it causes replication, and enhance elements and modulate transcription, if mutated will causes cell tropism and altered rate of replication).
3. Late coding region (codes for agnoprotein responsible for assembly of viral capsids VP-1 and release of virion, and viral capsid protein.
Epidemiology;
. 90% seropositive by 4 years.
. Become dormant in urothelial and kidney tissue.
. Its main routes of transmission are via mucosal rout.
. Usually reactivation and sever infection occurs after strong immunosuppression post-transplantation.
. The incidence of viruria 30%, viremia 12% in renal transplants.
. Usually a patient develops viruria there is 50% possibility of developing viremia and Nephropathy within 2 to 6 weeks.
. Viriuria and urine viral load >8-10 log/ml,
. While plasma viral load >4 log/ml associated with BKVAN,
. Viral load >6 log shows sever disease.
Based on recent data 1-10% of renal transplant recipient develop BKVAN.
Risk factors;
. Immunosuppression dose, incidence of viremia highest in early post-transplantation, with tacrolimus has higher risk.
. Recipient factors like, diabetes, older age, and HLA C alleles.
. Donor recipient interface,
D+/R-,
ABO incompatible,
HLA mismatch,
Delayed graft function, AMR. Increased ischemia time.
. Donor related factors; carrier for BKV (viruria)
Protective factors;
Factors like the cause of renal failure ADPKD, recipient with HLA-B51 positivity.
Cellular Immune Response and Pathogenesis;
CD4, CD8 has crucial role in clearance of BK viremia.
The patients with BK viremia required required 5 months to eliminate virus, however, after initial infection the virus remain dormant in urinary epithelial cells. On exposure due to strong immunosuppression, ischemia, injury to epithelial cells causes activation of different cascades and destruction characterized by IFTA and progressive nephron loss.
Clinical manifestation;
The classic sequence of infection viruria, viremia, and BKVAN.
The most common and earlest manifestation is 50% viruria, without symptoms, although, viremia is a sensitive marker and better predictor of progression to BKVAN in comparison to viruria.
Other manifestation are uretral stenosis and heamurrhegis cystitis.
Reports associated GI malignancy with BKV.
Screening and Diagnosis.
With higher predictive value of plasma BKV level is better predictor.
KDIGO and AST-IDCOP guidelines recommends monthly screening for first six months post-transplantation and every three months for next 18 months.
Urine cytology, decoy cell (polyomavirus-Haufen) has high positive and negative predictive value.
Donor derived cell free DNA (dd-cfDNA); could be useful noninvasive test to assess for progressive BKV to BKVAN.
Biopsy findings;
This is gold standard for diagnosis and severity ofBKVAN.
. Findings; Simian virus (SV40), 100% specific but does not distinguish between BKV and JC virus but can differentiate between adenovirus infection..
Infected tubular cells shows enlarged, hyperchromatic nuclei with ground glass and intranuclear inclusions, and clumps.
Initial tubulitis then they progress to IFTA.
Treatment;
Stepwise Immunosuppression dose modification, first, antimetabolite, CIN, and last corticosteroids.
Monitor viral load if persist then complete withdrawal of antimetabolites.
Next step minimize level of CIN tac 4-6ng/l, while, CaS 50-100ng/l.
Adjunctive treatment quinolones, cidofovir, leflonmide, IVIG.
There few trails in progress.
Re-transplantation; allograft survival 98%, 94% at 1 and 3 year respectively. Should be done with lower immunosuppression regime. There was no difference in rates of AMR or survival at one year.
Conclusion;
There is no such antiviral available to benefit.
History of the BK Virus
Epidemiology
Risk factors:
Cellular Immune Response and Pathogenesis
Clinical Manifestations
Screening and Diagnosis
Treatment
Kidney Re-Transplantation
Introduction
● BKVAN is an important cause of graft loss in kidney transplant recipients.
● The genome of the virus consists of
three regions— (large T and small T tumor antigen), the non-coding control region, and the late coding region.
● The T antigen has a propensity to bind to p53 and protein Rb
● The non-coding region contains the origin of replication and enhancer elements that can modulate transcription. ● Mutations in the non-coding control regions result in permit replication in other cell types (permissivity), cell tropism, and altered rates of replication
● The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Ir responsible for the release of virion from cells
● antibodies against one serotype does not result in durable protection against other types
● VP-3 leads to depletion of (ATP) and cell death
● BKV seroprevalence rates of over 90% by 4 years of age
● The transmission is from mucosal contact including the oral, gastrointestinal, and respiratory tract.
● After a primary viremia, BKV latent in the kidney and uroepithelial cells
● viral replication can ensue in the first year after transplantation
● BKV infection occurs in kidney recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
● Stages of infection ( viruria, viremia, and allograft nephropathy )
● Viruria and viremia are detected in kidney recipients by 30% and 12%
● 50% of kidney recipients develop viremia and BKVAN after viruria during 2–6 weeks
● 1–10% of kidney recipients develop BKVAN
● Urine BK viral loads > 10^8 c/mL predict the onset of viremia, while plasma BK viral loads >10^4 c/mL are associated with higher rates of BKVAN and loads>10^6 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates
● Risk factors for Viral replication :
1. Intensity of immunosuppression
2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles
3. The donor–recipient interface: D+/R- , ABO incompatibility, HLA mismatch , DGF, rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
● Protective factors against BKVAN
☆ Recipient HLA-B51 positivity due to highly immunogenic cytotoxic T cells
☆ presence of PCKD
Cellular Immune Response and Pathogenesis
● The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus
● Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissue
● Viral replication activate pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
● BKVAN is associated with increased expression of messenger RNAs (mRNAs), expressed in T cell-mediated rejection (TCMR) then interstitial fibrosis and tubular atrophy
● BKVAN manifesting as a decline in renal function with or without urinary abnormalities.
● Ureteral stenosis and hemorrhagic cystitis are mostly seen in HSCT patients
● There are an association between BK virus and development of urothelial malignancies in transplant recipients
Screening and Diagnosis
● Guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for
the next 18 months
● Urine BK PCR is not a recommended screening test
● Plasma BK PCR it’s sensitivity differs upon BKV genotypes
● Urine Cytology
☆ Decoy cells are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin
☆ “owl eye” inclusions, multinucleation, or clumped chromatin.
☆ polyomavirus-Haufen which is cast-like PV aggregates which has high BK nephropathy and correlates well with disease severity
● A higher dd-cfDNA levels were associated with higher BK viral loads so it may be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant Kidney Biopsy
● The gold standard for diagnosis of BVAN
● Biopsy must include medulla to decrease a sampling error
● Diagnosis via a kidney biopsy missed in 30% of cases
● The features present for a definitive diagnosis of BKVAN :
☆ Positive SV40 staining
☆ Tubular epithelial cell with a “ground glass” nuclear inclusion
☆ Plasma cell-rich infiltrate or injury found primarily in the medulla
Treatment
● A reduction of immunosuppression
☆ 50% reduction of antimetabolite and continuing the same doses of CNi/pred
☆ Cessation of anti-metabolite if viral loads continue to be at similar levels or increase
☆ If viral loads do not reduce over 4 weeks reduce CNi trough goals if viral loads do not
reduce over 4 weeks
☆ Other therapies include quinolones, cidofovir, leflunomide, and (IVIG).
Upcoming Therapeutic Trials
1. A human monoclonal antibody binds VP1 which is responsible for binding to the surface of host cells
2. Multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia
Kidney Re-Transplantation
● Consideration for lower IS should be balanced with the risk of rejection.
● Allograft survival 98% and 94% at 1 and 3 years
● There was no significant difference in the rates of acute rejection or patient survival at one year
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Summarise this article
Introduction
– with the advent of more efficacious and potent immunosuppression, BKVAN has an important cause of graft loss among kidney transplant recipients given the high rates of BK viremia
History of BK virus
– 1st discovered in 1971 in a kidney transplant recipient who presented with a ureteral stricture
– the 1st definitive biopsy-proven case of BKVAN was described in 1983
– there has been a significant reduction in the cases of associated graft loss, this is attributable to a better understanding of the management of BKVAN
Virology
– BKV is a small non-enveloped double stranded DNA virus belonging to the polyomaviridae family
Epidemiology
– BKV infection is ubiquitous in the general population
– modes of transmission of the virus are due to mucosal contact through oral, respiratory and gastrointestinal tracts
– following primary viremia, the BKV becomes latent in the kidney and uroepithelial cells
– in kidney transplant recipients, BKV infection can occur as a result of reactivation of a latent infection or as transmission of a new infection from the donor kidney
– the chronological stages include viruria (precedes viremia by 2-6 weeks), viremia (precedes BKVAN by 2-6 weeks) and BKVAN
– urine BK viral load > 8 log 10 copies/mL predict the onset of viremia
– plasma BK viral load > 4 log 10 copies/mL are associated with higher rates of biopsy-proven BKVAN
– plasma BK viral load > 6 log 10 copies/mL are predictive of extensive BKVAN pathology measured by SV40 IHC and associated with inflammatory infiltrates
– Risk factors for BKV replication include: –
– presence of polycystic kidney disease and recipient LA-B51 positivity have been shown to be protective factors against the development of BKVAN
Cellular immune response and pathogenesis
– a robust cellular immune response plays a key role in the mitigation and clearance of BK viremia
– sites of latency following primary infection include: –
– the latent infection becomes reactivated in states of immunosuppression
– BKV replication and its cytopathic effect result in damage to the tubular epithelium
– the final stage is characterized by interstitial fibrosis and tubular atrophy which are associated with progressive nephron loss
– mRNAs are increasingly expressed in BKVAN as well as TCMR making it difficult to differentiate these two entities
Clinical manifestations
– most BKV infections lack systemic symptoms
– the classic sequence of infections involves viruria, viremia and BKVAN
– viruria is the most common and earliest manifestation of BKV
– viruria can occur in pregnancy, older patients, other immunosuppressive states outside transplantation hence checking of urine BK viral loads is not standard practice
– compared to viruria, viremia is a better predictor of progression to BKVAN
– BKVAN manifests as a decline in kidney function ± urinary abnormalities following a period of sustained progressively worsening viremia
– other manifestations of BKV infection include ureteral stenosis and hemorrhagic cystitis commonly seen in HSCT recipients
– role of BKV in carcinogenesis remains controversial although there is a possible link between BKV and genitourinary malignancies
Screening and diagnosis
– urine BK viral load has low specificity while plasma BK viral load has a higher positive predictive value
– KDIGO recommends monthly screening for the 1st six months then every 3 months for the next 18 months
o urine BK PCR: – is not recommended as a screening test given its low specificity and cost since if positive, it will still require confirmation with plasma BK PCR and also ~50% of the patients with viruria may not develop viremia
o plasma BK PCR: – viremia is a better predictor of progression to BKVAN
o urine cytology: – decoy cells are BKV-infected tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin; they resemble renal carcinoma cells; decoy cells are a marker of polyomavirus replication but do not necessarily indicate PVN
– urine samples can be screened for polyomavirus-Haufen via negative staining EM
– amount of PV-Haufen shed correlates well with disease severity
– presence of PV-Haufen has a high positive predictive value while a negative PV-Haufen has a high negative predictive value
o donor-derived cell-free DNA (dd-cfDNA): – higher dd-cfDNA levels are associated with higher BKV viral loads, biopsy-proven BKVAN and histologic changes meeting the Banff criteria for TCMR therefore dd-cfDNA can be used as a useful noninvasive test to assess progression of BKV to BKVAN
o transplant kidney biopsy: – it is the gold standard for BKVAN diagnosis; it helps in diagnosis as well as assessing the severity of BKV involvement and presence of other ongoing pathologies
– BKV has tropism for the medulla therefore to avoid sampling error the two biopsy cores containing the renal cortex and medulla are recommended
– the diagnosis is missed in ~30% of the kidney biopsy cases given the focal nature of the disease; a repeat biopsy can be considered in such cases if the clinical suspicions remain
– pathologic features in keeping with a definitive diagnosis of BKVAN include characteristic cytopathic changes and positive IHC tests using antibodies directed against BKV or SV40 large T antigen
– a positive SV40 staining has ~100% specificity for PVN but does not differentiate between BKV and JCV
– SV40 staining helps differentiate PVN from other viral nephropathies e.g., adenovirus
– a presumptive diagnosis can be made if the plasma BKV viral load is >10,000 copies/mL
o histology: – findings include
– histologic similarities do exist between PVN and acute rejection (AR) i.e., tubular injury, tubulitis, interstitial inflammation
– the two entities (PVN and AR) can co-exist creating a treatment dilemma
– distinguishing characteristics include: – features of vascular injury (i.e., glomerulitis, endarteritis, arterial fibrinoid necrosis, peritubular capillary C4d staining), presence of DSA, BKV viral load
Treatment
– mainstay of management for BK viremia and BKVAN is reduction in immunosuppression
– currently, there is no therapeutic agent directed against BKV-associated disease, many agents lack conclusive efficacy
– reduce antimetabolite dose by half, monitor serum creatinine and plasma BK PCR every two weeks
– if BK viral loads remain at similar levels or increase, withdraw the antimetabolite completely
– if BK viral loads do not reduce in 4 weeks despite stopping the antimetabolite, reduce the CNI dose targeting trough levels of 4-6ng/mL for tacrolimus and 50-100ng/L for cyclosporine
– kidney transplant recipients on tacrolimus-based regimens have lower rates of rejection and higher eGFRs on 5-year follow up data
– other adjunctive therapies used to treat BKV infection include: – cidofovir, fluoroquinolones, IVIG, leflunomide
– there was no difference in graft outcomes when reduction in immunosuppression was combined with leflunomide or cidofovir compared with reduction in immunosuppression alone
– IVIG might be the only viable adjunctive therapy, the use of the other agents is not recommended
– there are upcoming therapeutic trials involving modified T cells and monoclonal antibodies
Kidney re-transplantation
– kidney re-transplantation can be considered in patients with graft loss due to BKVAN
– failed transplant or native kidney nephrectomy is not recommended
– viral clearance should be confirmed prior to re-transplantation
– consider lower immunosuppression without triggering rejection
– graft survival following re-transplantation is 98% and 94% at 1- and 3-years respectively
Conclusions
– BKV infection remains a major clinical concern however strict surveillance protocols have led to early detection and mitigation of severe disease
– BKV infection can be associated with histologic findings similar to acute rejection
– reduction in immunosuppression can by itself result in rejection
– currently there is no antiviral therapy directed towards clearance of BKV
– however, there are novel therapeutic agents being evaluated
BKV NEPHROPATHY IN KIDNEY TRANSPLANTS;A STATE OF THE ART REVIEW.
INTRODUCTION.
-Good post transplant outcomes from adequate immunosuppression has led to increased BKVAN with viremia being seen in up to 30% post transplant.
-We are yet to get adequate tx for BK infection.
HX OF BK VIRUS.
-Discovered in 1971 in pt with ureteral stricture post transplant.1st BKVAN proven biopsy seen in 1993.
-Initially had graft loss of 50-100%,this has decreased to < 15% in last two decades.
VIROLOGY.
-BK is a non enveloped ,icosahedral shaped double stranded DNA virus.
-Gene has an early, non coding and late region. Early has T and t antigens with the former binding to p53 and protein RB while the later codes for VP1.VP2 and VP3 viral caspid proteins.
EPIDEMIOLOGY.
-Prevalence of 90% in general population by 4 yrs.
-Stages of infection ; Viruria,viremia and nephropathy.
-After viruria,50% KTR will have viremia in 2-/ time.
-Transmission routes ; Oral, GIT and resp tract.
-Plasma VL>4 log 10 are associated with more risk of BKVAN.
RISK FACTORS.
-These include ;
CELLULAR IMMUNE RESPONSE AND PATHOGENESIS.
-T cell mediated immunity ;CD4 and CD8 cells key in clearing BK infection. Increased interferon gamma is a good pointer yo BK specific cellular response.
-Post childhood infection, BK maintains latency in renal epithelium, prostate, testes, seminiferous tubules, cervix, vulva and lymphoid tissues ,with reduced immunity, the infection flares up and pt becomes symptomatic.
CLINICAL MANIFESTATION.
-Stepwise ; Viruria, viremia then nephropathy. Viruria occurs in up to 50% in 1st 1 yr post transplant.
-Viremia is a better marker of those at risk of BKVAN. Viremia may present as increase in creatinine +/- urinary anomalies.
-Others; Ureteral stenosis, hemorrhagic cystitis.
-Rare ; GU malignancies.
SCREENING AND DIAGNOSIS.
-BK viremia screening is the preferred modality.
Presumptive dx ;VL > 10000 Copies/ml.
TREATMENT.
2.Other therapies;
3.Future therapeutic trials.
KIDNEY RE-TRANSPLANTATION.
-Successful post graft dysfunction from BKVAN.
-Graft/Native nephrectomy not recommended.
-Careful dosing of immunosuppression to avert rejection to be adhered to.
-Graft survival post transplant 98% and 94% at 1 yr and 3 yrs respectively.
Please summarise this article.
-BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
-BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family .
– The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
– The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
-After a primary viremia, the BK virus establishes refuge in the kidney
and uroepithelial cells resulting in lifelong latent/persistent infection.
-Cellular immunity is suppressed in the first post-transplant year, viral replication can frequently ensue during this period.
-The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy .
-Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression: This is considered as the most significant factor associated with BK viral replication.
2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles .
3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
-Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
-HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients .
– Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine.
-Most clinically significant infections associated with the BK virus lack any systemic symptoms.
-BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities
-Other manifestations of the BK virus include ureteral stenosis, hemorrhagic cystitis and genitourinary (GU) malignancies.
-Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in screening protocols .
-KDIGO) and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for
the next 18 months .
-Urine BK PCR is not a recommended screening test because if positive, it always requires confirmation with plasma PCR and nearly 50% of patients with viruria will not develop viremia .
-Plasma BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference. This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN.
-Cytologic examination of urine may show decoy cells which are
tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin .
-Urine samples may be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . It has extremely high positive and negative predictive values for BK nephropathy.
– BK is tropic the medulla, so the biopsy core medulla must be present .
The following pathologic features should be present for a definitive diagnosis of BKVAN :
1. Characteristic cytopathic changes .
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. Positive SV40 staining is useful as it is associated with a specificity of almost 100% for PVN; although, it does not distinguish between BKV and JCV.
– If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is
recommended if clinical suspicions remain.
-To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended .
– A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
-It is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen .
-The SV40 IHC stain detects the large T antigen expressed by all polyoma viruses pathogenic in humans (SV, JC, and BK).
– PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
-A reduction in the intensity of immunosuppression is principle for the treatment of BK viremia and BKVAN. There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
-Protocols for a reduction in immunosuppression:
1.Reduce dose of antimetabolite by 50% while continuing on the same doses of CNI and/or prednisone.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce CNI trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
Upcoming Therapeutic Trials
Given the lack of therapies available for the treatment of BK infection, the two following
trials involving modified T cells and monoclonal antibodies are currently underway:
1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868—a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1, which is responsible for binding to the surface of host cells (ClinicalTrials.gov identifier: NCT04294472).
2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia(ClinicalTrials.gov identifier: NCT04605484)
-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success .
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Please summarise this article
1. Introduction and history :
BK virus-associated nephropathy (BKVAN) is found to be an important cause of graft loss in kidney transplant recipients especially with emergent of efficacious immunosuppression that lead to increase risk BK viremia (BKV) in up to 30% of kidney transplant recipients . It was first discovered in 1971, in a Kidney transplant recipient present with ureteric stricture. The first definitive biopsy proven case of BKVAN was described in 1993 .
Early on , BKVAN frequently resulted in graft loss with rates of 50–100% reported, but the last 2 decades increasing recognition and nuanced management have now resulted in a reduction in associated graft loss to under 15% .
Virology :
BK virus is a member of the Polyomaviridae family, it is a small ,icosahedral, closed circular, non-enveloped,double-stranded DNA virus.
Its genome is consists of three regions:
-The non-coding control regions: Are significant contributors to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
Epidemiology:
BK virus infection has seroprevalence rates of over 90% by 4 years of age which is considered significantly ubiquitous in the general population.
Routes of transmission are : oral, gastrointestinal, and respiratory tract.
After a primary viremia, the BK virus migrates to the kidney and uroepithelial cells and stays dormant resulting in lifelong latent/persistent infection.
During the period of intensive immunosuppression especially in the first year post kidney transplant the virus may cause significant infection when reactivated ,start with urine shedding of the virus (viruria) followed by viremia, and allograft nephropathy . After the onset of viruria, nearly 50% of kidney transplant recipients develop viremia during a period of 2–6 weeks, with a similar proportion of viremic patients developing BKVAN in the previously mentioned time period . Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates .
Risk factors of BKV replications is increased by :
:
1. Intensity of immunosuppression, which is the most significant factor .
2. Recipient characteristics: older age , diabetes , and specific HLA-C alleles
3. The donor–recipient interface: ( D+ve ,R-ve) , ABO incompatibility, , HLA mismatch , delayed graft function , ischemia or rejection of the transplanted kidney and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
*Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis :
Both CD4 and CD8 cells playing a crucial role in the clearance of BK viremia . The presence of ELISPOT measured IFN-gamma activity, indicative of a BK-directed cellular immune response, is associated with the resolution of BKVAN. Vigorous CD8-based cellular responses were found to be correlated with lower BK viral loads in urine and blood while high viral loads and the continued presence of the virus were associated with a weak response.
BK-directed cytokine signatures from CD4 cells have demonstrated similar results. ,
The BKV remains dormant after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium; the activity of the virus is correlated with immunity of the host which if suppressed viral replication and its cytopathic effect will take place .
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), which are also expressed in T cell-mediated rejection (TCMR) leading to difficulty in distinguishing between BKVAN and TCMR different entities . The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss .
clinical manifestation :
-*Viremia is also asymptomatic but if present it is a better predictor of progression to BKVAN in comparison to viruria .
-*BKVAN usually manifests as a symptomatic decline in renal function with or without urinary abnormalities.
-* Ureteral stenosis is the first discovered presentation of BKV.
-*Hemorrhagic cystitis is rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants. T
-* Genitourinary (GU) malignancies There are accumulating reports that there may be an association of the BK virus with the development of urothelial malignancies in transplant recipients .
Screening and Diagnosis
Kidney Disease Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months .
1. Urine BK PCR Urine BK PCR is not a recommended screening test; it is less specific and requires confirmation with plasma PCR and nearly 50% of patients with viruria will not develop viremia .
2. Plasma BK PCR BK viral loads are measured by polymerase chain reaction .
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I) . This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN. Therefore, rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads.
-*Urine Cytology: The characteristic BK virus-infected tubular epithelial cells are called decoy cells due to their similarity to renal carcinoma cells. They may also exhibit “owl eye” inclusions, multinucleation, or clumped chromatin.
Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN.
-*Donor-Derived Cell-Free DNA (dd-cfDNA):
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. So it may be a useful noninvasive test to assess the progression of BKV to BKVAN .
-*Transplant kidney biopsy :
Kidney allograft biopsy is the gold standard for the diagnosis of BVAN, it confirms the diagnosis and assesses the severity of viral involvement and the presence of other ongoing pathologies. A biopsy should be adequate and contain medullary tissue.
For a definitive diagnosis of BKVAN The following pathologic features should be present :
1. Characteristic cytopathic changes .
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen. .
-Diagnosis via a kidney biopsy is estimated to be missed in nearly 30% of cases so if the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain.
-* Histology :
_ The histologic findings include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions .
_ Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles, usually in the distal nephron or medulla.
_As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen .
_ Tubular cell injury , tubulitis and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.
-* Presence of tubular injury, tubulitis, and interstitial inflammation in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection .
Treatment :
Protocols :
1.*Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone and monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks .
2.* complete cessation of anti-metabolite if viral loads continue to be at similar levels or increase .
3. * Reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
*- IVIG:The rationale for use is the presence of BK-neutralizing antibodies in IVIG preparations. It is utilized in the setting of non-response to a maximal reduction in immunosuppression .Data from five observational studies have demonstrated a reduction in BK viral loads; however, other antiviral agents were administered at the same time as well .
2. Quinolones: is failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia
3. Cidofovir: limited by nephrotoxicity
4. Leflunomide: It demonstrated both immunosuppressive and anti-viral properties but has not proved efficacy in BKVN.
*Upcoming Therapeutic Trials :
1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868—a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1, which is responsible for binding to the surface of host cells (ClinicalTrials.gov identifier: NCT04294472).
2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients with either high or low levels of BK viremia (ClinicalTrials.gov identifier: NCT04605484).
Kidney Re-Transplantation ;
-Patients with graft loss due to BKVAN should be considered for re-transplantation .
-Nephrectomy of failed transplant or native of is not recommended
-Confirmation of viral clearance should be made prior to transplantation.
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
-Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
-In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
– There was no significant difference in the rates of acute rejection or patient survival at one year.
BKPyV is the most common viral infection encountered post kidney transplantation with increasing mortality and morbidity.
Epidemiology:
BKPyV is extensively prevalent in population, attracted early in life mainly through GIT, feco-oral rout. It’s characterized by prolonged period of latency in uroepithelium and renal interstitial cells after a period of viremia.
The virus is a double DNA virus consist of early coding larg T antigen TAg and small t antigen tAg, middle non-coding segment and late coding segment.
Immune suppression post transplantation is triggering the reactivation of dormant virus.
It was resulting in a 50-100% allograft loss earlier after the discovery of BKPyV.
currently its associated with 13 % allograft loss owing to increasing understanding and recognition of the virus.
Consequences of reactivation
owing to suppression of cellular immunity post tansplantation there is reactivation of dormant virus or transferred virus with allograft,
The infection features 3 consequative stages, Viruria, Viremia and BKPN.
Viruria was detected in 30% and viremia in 12 % of patient post transplantation.
After developing viruria , 50% mount viremia in 2-6 weeks. 50% of viremic patient will ultimately develop BKPN.
Urine BK viral load of 8 log predict viremia.
Plasma viral load of 4 log predict BKPN.
Plasma viral load of 6 log is correlated with extensive BKPN with heavy infiltration detected by SV40 finding.
Treatment Plan:
In view of strong association of immune suppression with development of BKPyV infection, main strategy is to reduce immune suppressant medications, primarily by reducing and then stopping antimetabolytes .
second step is to reduce by half the doses of CNi ,
if no improvement then try medications:
Cedofovir, quinolones and recently leflunamide. However, with debatable effects.
IVIG is the most effective therapy in treating BKPN.
Summary
· BKV infection leads to BKN with subsequent graft loss.
· The prevalence increased among kidney transplant recipients after the introduction of potent immunosuppressive therapy (TAC and MMF).
· BK is DNA virus with 3 parts: early coding region for large and small tumor antigen (T and t), none coding part and late coding part.
· Primary infection occurs early in life and remains dormant in the kidney. Reactivation occurs in kidney transplant recipients after immunosuppression.
· Infection has 3 stages: viuria, viremia and BK nphropathy.
· Risk factors as old diabetic recipients, with prolonged cols ischemia time, and DGF, HLA and ABO incompatibility, serostatus prior to transplantation (D+/R-), use of strong immunosuppression as tacrolimus and MMF, treatment of repeated attacks of rejection, presence of ureteral stent.
· Screening for BKV infection:
o By blood PCR (more sensitive than urine PCR). Monthly screening during 1st 6 months then every 3months for 18 months is indicated for early detection of viremia and for reduction of immunosuppression prior to development of BKN (preemptive therapy)
o Urine PCR not recommended as it is not specific or correlated to pathology proven BKN, and needs further confirmation by blood PCR if it is positive.
o Decoy cells in urine: similar to renal carcinoma cells. These are
o tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed chromatin. it is a marker of PV replication, but not necessarily indicate PVN. Some studies have shown high false-positive rates and low positive predictive values, high PPV.
o Allograft biopsy remains the golden standard for diagnosis of BKN, however, negative biopsy in 30 % of cases due to focal and medullary affection.
o A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load >10,000 copies/mL.
o If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions is present.
· Treatment of BKV infection: reduction of immunosuppression (IS) is the main line of treatment.
o Reduction of IS; decrease dose of MMF to 50 % and follow up PCR after 2 weeks …if constant or increasing stop MMF completely.
o FU PCR after further 2 weeks, if no decrease in viral load try to decrease CNI dose.
o Additional IVIG, leflunamide, cidofovir can be used.
o Adoptive T cell immunotherapy can be used in resistant cases to reduction of IS (for fear of rejection with marked decrease in IS).
o For failing grafts: retransplantation is indicated after complete clearance of viremia, no clear recommendations to perform nephrectomy for either the native kidney or for the failing graft.
Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review:
Introduction:
BK virus leading to nephropathy and it’s responsible for allograft kidney loss post transplant due to use of immunosuppressive therapy and it’s account 30% in kidney transplant cases.
History of the BK Virus:
It’s first discovery in 1971 in case of ureteric stricture. In 1993 the first biopsy done prove presence of BK virus nephropathy.
Virology:
It’s one of the Polyomaviridae family, it’s small closed circle non evolved double strand DNA. It’s consist of 3 regions ( first is consist of small t antigen and large T antigen); second non coding region and third coding region.
Epidemiology:
Risk factors for replication of virus:
Clinical manifestations:
Patients may asymptomatic; Viremia is present in 10–30 percent of recipients in the first six months post- transplantation and in 5–10 % of recipients. Viremia is a better predictor of progression to BKV in comparison to viruria. it’s also may lead to ureteral stenosis and hemorrhagic cystitis.
Screening and Diagnosis:
Urine and plasma BK virus PCR
Urine culture for presence decoy cell.
Donor-Derived Cell-Free DNA (dd-cfDNA)
Renal graft biopsy:
Presence of BK virus features is diagnostic for BK nephropathy and tubular cell enlargement and hyperchromatic nuclei and “ground glass” intra nuclear inclusion. With progress of infection tubulitis and interstitial inflam- into the tubular lumens (Figure 3). As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell.
Treatment:
Reducing of immunosuppressive therapy to half especially anti metabolite to half (cellcept), and continuous prednisolone and calcinurine inhibitors; if viral load continues will stop cellcept but if viremia continues will reduce calcinurine inhibitors to half but not more than 4 weeks. Treat BK virus infection by quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
Kidney Re-Transplantation:
BKV can lead to graft loss and allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years. Transplant kidney and native nephrectomy not recommended.
Summary of the article
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
BKV; virology and history
1. BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
2. BKV was first discovered in1971in a Sudanese KTR presented with ureteral stricture. The first definitive biopsy- proven case of BKVAN was described in 1993.
3. Based on the most recent registry data, 1–10% of kidney transplant recipients develop BKVAN.
4. BKV has a viremia rate of up to 30% in kidney transplant recipients. BKVAN frequently resulted in graft loss with rates of 50–100% reported.
BKV;Epidemiology
1. BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
2. The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
3. Viruria and viremia are detected in approximately 30% and 12% of kidney transplant recipients, respectively.
4. After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
5. Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN.
6. BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates
Risk factors for BKV replication:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3. The donor–recipient interface: The high-risk serostatus of D+/R-, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
5. Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis
1. Both CD4 and CD8 cells are playing a crucial role in cellular immune response against BKV.Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine.
2. Sites of latent infection include:
a) kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium.
b) Other sites: prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
3. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens).
4. BKVAN is associated with increased expression of various major groups of messenger RNAs.These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities.
5. The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
BKV infection; Clinical Manifestations
1. The classic sequence of infections in KTRs is viruria, viremia, and BKVAN.
2. The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation. The presence of sustained viruria may progress to viremia, which is asymptomatic initially.
3. BKVAN usually occurs after a period of sustained progressively worsening viremia.
a) The vast majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence.
b) Manifesting as a decline in renal function with or without urinary abnormalities.
4. Ureteral stenosis and hemorrhagic cystitis: albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants.
5. Urothelial malignancies in transplant recipients.
BKV infection; Screening and Diagnosis
1. The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
2. Urine BK PCR :not a recommended screening test given issues related to specificity and cost. It always requires confirmation with plasma PCR.
a) Plasma BK PCR has a higher positive predictive value of plasma BK levels. plasma BK viral load ≥10,000 copies/mL is a presumptive diagnosis for BKVN.
3. Urine Cytology:
a) for BK virus-infected cells (decoy cells), may exhibit “owl eye” inclusions, multi- nucleation, or clumped chromatin.
b) for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy.The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively. The amount of PV-Haufen shed correlates well with disease severity.
4. Donor-Derived Cell-Free DNA (dd-cfDNA) in association with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from BKVAN.
5. Transplant Kidney Biopsy is the gold standard for the diagnosis of BVAN.
b) Characteristic cytopathic changes.
c) Positive immune-histochemistry tests(SV40).
BKV infection; Treatment
a) Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
b) If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
c) The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
d) Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
e) Upcoming Therapeutic Trials;
a) a human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1.
b) adoptively transferred posoleuccel, multivirus-specific T Cells.
Kidney Re-Transplantation
1. Confirmation of viral clearance should be made prior to transplantation.
2. Consideration for lower immunosuppression should be balanced with the risk of rejection.
3. Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively.
4. Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines.
5. Five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
There was no significant difference in the rates of acute rejection or patient survival at one year.
Please summarise this article.
#The objective:
*To give overview on (BKV) epidemiology, pathogenesis, screening, diagnostic methods, as well as to discuss the clinical manifestations and recommended treatment strategies.
#Introduction:
*(BKVAN) is an important cause of graft loss in kidney transplant recipients.
# Virology:
*BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
*The genome of the virus consists of three region
1)Early coding region of the large T and small t antigens.
2)Non-coding control region.
3)Late coding region.
*The T antigen has ability to bind to p53 and protein Rb, resulting in persistent infection.
* The non-coding control regions are for pathogenesis of the virus and can modulate transcription.
*Mutations in the non-coding control regions result in permit replication in other cell types cell tropism, and altered rates of replication.
*The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1,
VP-2, and VP-3).
# Epidemiology
*BK virus infection could be considered ubiquitous in the general population, with
seroprevalence rates of over 90% by 4 years of age.
*In the first post-transplant year the CMI suppressed due to induction therapy, which result in viral replication.
*Clinically significant infection occurs in KTR via reactivation of latent infection or transmission of new infection from the donor kidney.
*The infection occurs in the following chronological stages:
1)Viruria in 30%
2)Viremia in 12%
3)Allograft nephropathy.
# The risk factors for viral replication:
1. Intensity of immunosuppression ( most important facror):
The incidence of BK viremia is highest in the early post-transplant period.
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3.The donor–recipient interface:
The high-risk serostatus (D+/R-), ABO incompatibility, HLA mismatch, DGF, rejection or ischemia, and ureteral stent placement.
4. Donor-related factors:
Reduced immune response to BK virus and BK viruria prior to transplant.
*Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
# Cellular Immune Response and Pathogenesis:
*The clearance of BK viremia is dependent on a robust cellular immune response with both CD4 and CD8 cells playing a crucial role in this process.
*Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine, while high viral loads and the continued presence of the virus were associated with a weak response.
*BK-directed cytokine signatures from CD4 cells have demonstrated similar results, providing further evidence that a concerted effort from components of the cellular immune system is vital for tempering the virus
# Clinical Manifestations:
*Most BK virus infection lack of any systemic symptoms.
*The classic sequence of infections in KTR is viruria, viremia, and BKVAN.
*The most common and earliest manifestation of BKV is viruria (50%) in the first year of transplantation, with most cases not progressing to viremia.
*Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter it is a better predictor of progression to BKVAN in comparison to viruria.
*BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
*Ureteral stenosis and hemorrhagic cystitis
# Screening and Diagnosis:
* The (KDIGO) and (AST-IDCOP) guidelines recommend monthly screening for the first 6 months PKT every 3 months for the next 18 months.
** Urine BK PCR:
Not a recommended screening test given issues related to specificity and cost.
**Plasma BK PCR:
* Assay results are influenced by variations in DNA extraction techniques, sample type/source, primer and probe sequences.
*The (WHO) establishing an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL.
*BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference, this could lead to the non-detection of rarer genotypes.
** Urine Cytology:
*To detect the decoy cells which are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. Some studies have shown high false-positive rates and low positive predictive values when attempting to use the presence of decoy cells to
screen for PVN in transplant patients.
*To detect the presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively.
**Donor-Derived Cell-Free DNA (dd-cfDNA)
It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for TCR.
**Transplant Kidney Biopsy
*Is the gold standard for the diagnosis of BVAN.
*The pathologic features should be present for a definitive diagnosis of
BKVAN:
1. Characteristic cytopathic changes .
2. Positive immunohistochemistry tests using antibodies directed specifically against
BKV or against the cross-reacting SV40 large T antigen.
# Treatment:
*A reduction in the intensity of immunosuppression is cornerstone, with following steps:
1. Reduce antimetabolite by half while continuing on the same doses of CNI and/or prednisone.
( monitor serum creatinine and plasma BK PCR every 2 weeks).
2. If viral loads still at the same levels or increase, stop anti-metabolite.
3. Reduce CNI trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
*Other adjunctive therapies utilized to treat BK virus infection
1. IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression. It is benefit still not ctear.
2. Quinolones:
Studies failed to show the efficacy as prophylaxis or treatment for BK viremia
3. Cidofovir:
Studies have shown no benefit, associated with proteinuria, proximal tubular dysfunction,
and kidney disease.
4. Leflunomide:
Some study showed no benefit.
# Kidney Re-Transplantation
*Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
*Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and
3 years, respectively.
*Re-transplantation for graft failure due to other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
*There was no significant difference in the rates of AR or patient survival at one year.
Introduction:
History of BK virus:
Virology:
Epidemiology:
1. Viruria is detected in 30 % of cases, of which 50% develops viraemia
within 2-6 weeks.
2. Viraemia is detected in 12 %
3. BKVN develops in 1-10% of cases.
Risk factors:
1- Severity of IS: more with high level of IS. Less with m-TOR inhibitors.
2- Recipient factors: old age, DM.
3- Donor-recipient interface: D+/R-, Abo incompatibility, HLA-mismatch, delayed graft function, acute rejection, stent placement
4- Donor-related factors:reduced immune response to BKV, previous infection.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective against BKV infection
Clinical manifestations:\
Screening and diagnosis:
1- Urine BKPCR: is not a recommended screening test for low specificity and cost.
2– Plasma BKV level is the preferred method because of high positive predictive value. It is higly sensitive for genotype I and with low sensitivity for other genotypes.
3- Urine cytology: To detect viral infected cells (decoy cells).These are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. Highly sensitive but low specific with 100% negative predictive value.
4- Donor-Derived Cell-Free DNA (dd-cfDNA): Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for
T-cell-mediated rejection.
5- Kidney biopsy:
Pathological features for diagnosis:
A- Cytopathic changes (histological)
B- Positive immune-histochemistery test:
C- Electron microscopy: PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
Treatment:
1- Reduce dose of antimetabolite by half while continuing on the same doses of
calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine
and serial plasma BK PCR level every 2 weeks in the interim.
2- If viral loads continue to be at similar levels or increase, proceed with complete
cessation of anti-metabolite.
3- The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not
reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for
tacrolimus and 50–100 ng/L for cyclosporine.
Kidney re-transplantation:
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
Virology;
—————————
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family .
The genome of the virus consists of three regions;
1-The early coding region of the large T and small t antigens (large and small tumor antigen).
The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection.
2-The non-coding control region.
Are a significant contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription. Mutations in the non-coding control regions result in permit replication in other cell types (permissivity), cell tropism, and altered rates of replication .
3- The late coding region.
for the agnoprotein and viral capsid proteins (VP-1,VP-2, and VP-3).
Epidemiology;
———————————
BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age .
The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract. After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
The infection occurs in the following chronological stage ;
———— ——————— ————–
1-viruria
Viruria is detected in approximately 30% kidney transplant recipients.
2-viremia
viremia is detected in approximately 12% of kidney transplant recipients .
3- allograft nephropathy .
1–10% of kidney transplant recipients develop BKVAN .
Viral replication is associated with the following risk factors:
———————————————————————–
1-Intensity of immunosuppression .
2-Recipient characteristics: older age , diabetes , and specific HLA-C alleles .
3-The donor–recipient interface:
a-The high-risk serostatus of donor positive and recipient negative for BK virus .
b-ABO incompatibility.
c-HLA mismatch .
d-delayed graft function .
e-rejection or ischemia of the transplanted kidney .
f- ureteral stent placement .
4- Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant .
The protective factors;
——————————————————-
1-Recipient HLA-B51 positivity .
2- The presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
Cellular Immune Response and Pathogenesis;
——————————————————————–
1-The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium . Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
2-The latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
3-Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways.
4- BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
5-These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities .
6-The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss .
Clinical Manifestations;
———————————————–
1- The classic sequence of infections in kidney transplant recipients is viruria, viremia, and BKVAN.
2-The most common and earliest manifestation of BKV is viruria
occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia .
3- Viremia is present in 10–30 percent of recipients in the first six months post- transplantation and in 5–10 percent of recipients thereafter .
4- BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities. The vast majority of BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence .
5- Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis—albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants. There are reports of a possible link between the BK virus and genitourinary (GU) malignancies, especially given its protracted infection in epithelia of the GU tract.
Screening and Diagnosis ;
———————————————————
1- Urine BK PCR;
Urine BK PCR is not a recommended screening test given issues related to specificity and cost—if positive, it always requires confirmation with plasma PCR and nearly fifty percent of patients with viruria will not develop viremia .
2- Plasma BK PCR;
BK viral loads are measured by polymerase chain reaction (PCR)—a fluorescent probe BK-specific sequence, and the number of amplicons produced is compared with a standard curve generated with serial dilutions of a known concentration of BK DNA .
3- Urine Cytology;
A-The characteristic BK virus-infected cells that present on cytologic examination of urine are called ′decoy cells′ due to their similarity to renal carcinoma cells.
Although decoy cells are a marker of PV replication, they do not necessarily indicate PVN.
B-Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively. Additionally, the amount of PV-Haufen shed correlates well with disease severity .
4- Donor-Derived Cell-Free DNA (dd-cfDNA);
It demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These preliminary findings show that dd-cfDNA may be a useful
noninvasive test to assess for progression of BKV to BKVAN .
5- Transplant Kidney Biopsy;
Kidney allograft biopsy continues to be the gold standard for the diagnosis of BVAN.
A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL. Given that BK mostly affects the medulla and is associated with focal disease, diagnosis via a kidney biopsy is estimated to be missed in nearly 30%
of cases . If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain.
The following pathologic features should be present for a definitive diagnosis of BKVAN :
1- Characteristic cytopathic changes.
2. Positive immunohistochemistry tests using antibodies directed specifically against BKV or against the cross-reacting SV40 large T antigen.
Histology;
————————————————–
The histologic findings of this process include;
1-Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions .
In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla.
As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen .
More proximal portions of the nephron, including the parietal epithelial cells lining Bowman′s capsule, may also become involved. The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis .
2-Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles.
Limitations of the histological diagnosis ;
—————————————————————-
Histologic confirmation of the presence of polyoma virus can prove difficult.
1-The random and focal nature of the infection can result in false negatives if uninvolved parenchyma is sampled .
2- The histologic similarities it shares with acute rejection (AR).
How to maximize the likelihood of identifying the histolgic diagnostic features;
—————————————————————————————————
1-Two biopsy cores containing renal cortex and medulla are recommended .
2-To aid in the detection of PV within biopsies, ancillary tests such as immunohistochemical (IHC) stains or in situ hybridization (ISH) can be performed.
Currently, it is recommended that the Simian Virus 40 (SV40) IHC stain be performed on all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN are seen .
3- Quantitative PCR for PV can also be performed on tissue samples . However, given the high frequency of latent PV virus infection, interpretation of these results requires caution.
4-PV can be identified on electron microscopy by the presence of 40 nm paracrystalline viral particles within the nuclei of tubular cells.
The histological differentiation between PVN and acute rejection (AR);
———————————————————————————————
1-AR and PVN can co-occur, creating a treatment dilemma . In both cases, tubular injury, tubulitis, and interstitial inflammation are key histologic findings .
2-The presence of these findings in the absence of morphologic or immunohistochemical evidence of PV infection should warrant consideration of acute cellular rejection.
3-A plasma cell-rich infiltrate or injury found primarily in the medulla should raise concern for PVN. However, plasma cell-rich infiltrates are not PV specific and can be seen in TCMR .
4- Features of vascular injury such as endarteritis, arterial fibrinoid necrosis, glomerulitis, or peritubular capillary C4d staining are more consistent with acute rejection than PVN .
5-In cases of histologic overlap, a diagnosis of concomitant PVN and AR should be considered. In these instances, the histologic findings should be correlated with the clinical history and results of additional laboratory studies, such as BK viral load and the presence of donor-specific antibodies (DSA).
The histological grading ;
—————————————
1-The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
2-As per this system, histologic classes of definitive PVN are defined by the morphologic degree of intrarenal pvl (polyomavirus replication/load level) and Banff ci scores (interstitial fibrosis).
3-The scoring of pvl is on the basis of the extent of virally induced tubular changes, while a tubule with intranuclear viral inclusion bodies (type 1 or 2) and/or a positive IHC reaction for SV40-T antigen in one or more cells per tubular cross-section is considered “a positive tubule”.
The overall percentage of positive tubular cross-sections is estimated in the entire biopsy sample (all available cores, cortex, and medulla). The pvl score is calculated based on the extent of virally induced changes identified on H&E or via SV40 IHC staining.
Scores for pvl are calculated as follows:
pvl1: ≤1% of all tubules/ducts with viral replication.
pvl2: >1 to ≤10% of all tubules/ducts with viral replication.
pvl3: >10% of all tubules/ducts with viral replication.
Treatment ;
1-A reduction in the intensity of immunosuppression ;
———————————————————————–
is the overarching principle for the treatment of BK viremia and BKVAN.
The following is a stepwise approach for the reduction in immunosuppression in the setting of BK viremia and BKVAN based on trials in adult and pediatric kidney transplant
recipients :
A-Reduce dose of anti metabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay
variability) every 2 weeks in the interim.
B. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
C. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
2-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
————————————————————————————————-
1. IVIG:
It is utilized in the setting of non-response to a maximal reduction in immunosuppression (balancing with risk of rejection).
2. Quinolones:
Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia .
3. Cidofovir:
A nucleotide analog of cytosine has demonstrated activity against Poly- omaviridae in-vitro . Studies have shown no benefit with cidofovir use, notwithstanding that a significant risk of kidney dysfunction was noted.
4. Leflunomide:
A pro drug that converts to an active metabolite, which has demonstrated both immunosuppressive and anti-viral properties . While there was initial enthusiasm for its use in BK virus infection based on a case series,a pharmacodynamic and prospective open-label study showed no benefit .
Upcoming Therapeutic Trials
————————————————
Given the lack of therapies available for the treatment of BK infection, the two following trials involving modified T cells and monoclonal antibodies are currently underway.
Kidney Re-Transplantation;
——————————————————
1-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success .
2- Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
3- Consideration for lower immunosuppression should be balanced with the risk of rejection.
4-Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years, respectively .
5-In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
6- There was no significant difference in the rates of acute rejection or patient survival at one year .
Even though you have used headings and numbered your contents, it is not easy to read. I wish you could type sub-headings as underline or in bold.
Introduction
BK virus-associated nephropathy (BKVAN) can lead to graft loss in kidney transplant recipients. A higher incidence of BK viremia has been noted with more efficient immune suppression after kidney transplantation. The aim of this review was to provide information on BK virus – history, epidemiology, virology, cellular response, pathogenesis, screening methods, diagnosis and the appropriate treatment strategies.
History of BK virus
In 1971, a kidney transplant recipient presented with a ureteral stricture which helped us discover BK virus. The first definitive biopsy proved BKVAN in 1993. Initially, BKVAN led to a 50-100% risk of graft loss. Better management has reduced this to approximately 15%.
Virology
BK virus belongs to the Polyomaviridae family. It is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus. The genome consists of three regions:
Epidemiology
BK virus infection is quite prevalent in the general population, approximately 90%. It is transmitted via mucosal contact (oral, gastrointestinal, respiratory tract). After the primary infection, the virus remains in the kidney and uroepithelial cells, leading to a persistent latent infection. During the first year after transplantation, the induction therapy for immune suppression suppresses the cellular immunity. This may result in viral replication, reactivation of latent infection or new infection from the donor kidney. The infections occurs as viruria, viremia then allograft nephropathy. The risk factors of viral replication include:
Cellular immune response and pathogenesis
Cellular response is required for the mitigation and clearance of BK virus. The presence of IFN-gamma activity is indicative of BK-directed cellular immune response, and therefore is associated with the resolution of BKVAN. IFN-gamma activity can be quantified using ELISPOT (enzyme-linked immunosorbent spot). Also, vigorous CD8-based cellular response correlated with lower BK viral loads in blood and urine. The latent infection takes refuge in the kidney, mainly the parietal epithelium of the Bowman’s capsule, renal tubular epithelium and transitional epithelium. Other sites of the latent infection include prostate, testes, seminiferous tubules, cervix, vulva and hematolymphoid tissues. Damage to the tubular epithelium is due to the continuous viral replication and its cytopathic effect with inflammation. The final stage of destruction is characterized by interstitial fibrosis, tubular atrophy and hence loss of nephrons.
Clinical manifestations
Most clinically significant BK virus infections lack any systemic symptoms. The sequence of infections in kidney transplant recipients is viruria, viremia and BKVAN. Other manifestations include ureteral stenosis and hemorrhagic cystitis. There are reports of a possible link between BK virus and genitourinary malignancies.
Screening and diagnosisScreening of BK virus is now used due to the high incidence rate of the infection.
Urine BK PCR
Not a recommended screening test, as it has low specificity and high costs.
Plasma BK PCR
It has inter-assay variability due to variations in DNA extraction techniques, sample type/source, primer and probe sequences and the strain of BK DNA. Also, rare genotypes are often not detected.
Urine cytology
On cytologic examination of urine, the BK virus-infected cells are called ‘decoy cells’ as they are similar to renal carcinoma cells. The cells are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed ring of chromatin. They may also include ‘owl eye’ inclusions, multi-nucleation or clumped chromatin.
Donor-derived cell-free DNA (dd-cfDNA)
A recent study demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BKVAN and histologic changes associated with T-cell-mediated rejection. These findings validate that dd-cfDNA may be useful investigation to assess the progression of BKV to BKVAN.
Transplant kidney biopsy
Kidney allograft biopsy is the gold standard for the diagnosis of BKVAN. It also assesses the severity of viral involvement and the presence of other pathologies. The biopsy core should contain the medulla, as BK is usually found in the medulla. A definitive diagnosis requires the following pathologic features:
Characteristic cytopathic changes
Positive immunohistochemistry tests using antibodies specifically against BK virus.
Histology
In the genitourinary tract, the virus targets the urothelial and renal tubular cells. The histologic findings include tubular epithelial cells with enlarged, hyperchromatic nuclei and ‘ground glass’ intra-nuclear inclusions. Viral cytopathic changes may also include granular nuclear inclusions and ‘clumps’ of intranuclear virion particles.
In the early stages, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla. These cells will eventually lyse and slough from the basement membrane into the tubular lumens. As the infection progresses, tubulitis and interstitial inflammation may be seen. The proximal parts of the nephron may also be involved. The tubular cell injury, tubulitis and interstitial inflammation may lead to tubular atrophy and interstitial fibrosis.
The random and focal nature of the infection may lead to false negatives, especially if the uninvolved parenchyma is sampled. Therefore, two biopsy cores containing the renal cortex and medulla are recommended.
The Simian Virus 40 (SV40) ICH stain can be performed to highlight cells in the early stages of infection and may also help to differentiate PVN from other viral nephropathies. PV can also be identified using electron microscopy.
Acute rejection has histologic similarities to PVN – tubular injury, tubulitis and interstitial inflammation. Features of vascular injury such as endarteritis, arterial fibrinoid necrosis, glomerulitis or peritubular capillary C4d staining are more consistent with acute rejection than PVN.
Treatment
Immunosuppression Reduction:
Treatment of BK viremia and BKVAN begins with a reduction in immune suppression:
Reduce the dose of antimetabolite by half, continue the same dose of CNI and prednisone, while monitoring serum creatinine and plasma BK PCR levels.
If viral loads continue to be similar or increase, the antimetabolite needs to be stopped.
The next step is to reduce the CNI, if the viral load do not reduce after 4 weeks of stopping the antimetabolite.
Other adjunctive therapies used to treat BK virus infection include:
IVIG
It is used when there is no response to a reduction in immune suppression. IVIG contains BK-neutralizing antibodies in its preparation.
Quinolones
In vitro, quinolones demonstrated anti-viral properties. However, randomized trials have failed to show its efficacy as prophylaxis in the treatment for BK viremia.
Cidofovir
It is a nucleotide analog of cytosine. It has also demonstrated anti-viral properties in vitro. Unfortunately, studies have shown no benefit with cidofovir use. Its use has also been associated with kidney dysfunction: proteinuria, proximal tubular dysfunction and kidney disease.
Leflunomide
It is a prodrug that converts to an active metabolite, which has demonstrated immunosuppressive and anti-viral properties. A pharmacodynamics and prospective open-label study has shown no benefit of the medication.
Kidney Re-transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation. Consideration for using lower doses of immune suppression should be balanced with the risk of rejection. It has been shown that patients who undergo re-transplantation have an allograft survival rate of 98% at 1 year post transplantation and 94% at three years.
Conclusion
BK virus infection post kidney transplantation is a common clinical issue. Increasing the surveillance for the infection has led to understanding its true prevalence and aids in reducing progression to severe disease. There is no antiviral treatment for the BK virus. The main treatment consists of reducing the immunosuppression which has to be balanced with risk of acute rejection. However, there is hope as several trials are underway to ascertain the appropriate treatment regime.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
Please summarise this article.
Introduction:
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. The efficacious immunosuppression has been accompanied by high rates of BK viremia (BKV) in up to 30% of kidney transplant recipients.
No effective prophylaxis or treatment for (BKVAN) described yet.
History of the BK Virus:
First described in 1971 in a transplanted patient with ureteral stricture, but proven tissue biopsy diagnosis was in 1993.
The increasing incidence of BK viremia over the subsequent years was as a result of:
the increasing availability of reliable testing methods.
a consequence of more potent immunosuppression regimes.
Graft loss occurs in 50-100% of patients with (BKVAN), this rates decreased by better understanding the virus and the role of immunosuppression modification.
Virology:
A small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
The genome of the virus consists of three regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
T antigen binds to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection.
The non-coding control regions are a reason for virus enhancement and replication that can modulate transcription.
The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3), that are responsible for the assembly of viral capsids, the release of virion from cells, and the classification of viral genotypes I to VI (by VP-1).
VP-3 leads to activation of the adenosine diphosphate-ribose polymerase, resulting in depletion of adenosine triphosphate (ATP) and cell death.
Epidemiology:
90% of population at age of 4 years are seropositive for BKV.
Transmitted through the mucous membranes oral, gastrointestinal, and respiratory tract.
Lifelong latent/persistent infection colonize the kidneys and uroepithelial cells.
The infection occurs in the following chronological stages—viruria 30%, viremia 20%, and allograft nephropathy.
Urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates.
Recipient HLA-B51, and the presence of polycystic kidney disease are protective of BKVAN.
Risk factors:
1. Intensity of immunosuppression:
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
4. Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant.
Cellular Immune Response and Pathogenesis:
The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus.
Vigorous CD8-based cellular responses correlated with lower BK viral loads in blood and urine, and BK-directed cytokine signatures from CD4 cells have demonstrated similar results.
The virus maintains persistent infection in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, transitional epithelium, prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
The mRNAs expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities.
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
Clinical Manifestations:
Mostly asymptomatic, viruria occurs in 50% of patients within the first year of transplantation, may progress to viremia in 10-30% of patients in the first 6 months, decreasing to 5-10% thereafter.
Ureteral stenosis and hemorrhagic cystitis, and urethral malignancies.
Screening and Diagnosis:
Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method.
The Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BKV PCR: NOT recommended for screening, as 50% of viruria will not develop viremia, with low specificity.
Plasma BKV PCR: Factors that affect the accuracy of the test are, the sample size, source, primer and probe sequences, and BK strain DNA, BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I). This could lead to the non-detection of rarer genotypes.
Urine Cytology: decoy cells, are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin, they do not necessarily indicate BKVN, can be found in other viral infection as well as tumor cells, but its of high negative predictive values for PKVN.
polyomavirus-Haufen, cast-like PV aggregates, has a high positive predictive value, and high NPV for BKVN, and correlate with disease severity.
Donor-Derived Cell-Free DNA (dd-cfDNA): higher levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection, so it helps in assessing progression of the disease, but not diagnosis.
Transplant kidney biopsy: is the gold standard for diagnosis of BKVN, and other etiologies, with two cores, medulla sampling to decrease error results.
Pathological features are:
1. Characteristic cytopathic changes: focal medullary lesions.
2. Positive histoimmunochemistry, antibodies against SV40 large T antigen, with 100% specificity, but distinguish between BKV and JCV.
A kidney biopsy is missing in nearly 30% of cases, so repeat biopsy is recommended if clinical suspicions remains with high serum BKV PCR> 10,000 copies/ml.
Histology:
1. Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusion, “clumps” of intranuclear virion particles.
2. Tubulitis and interstitial inflammation with a prominent plasma cell components.
3. IFTA.
However; team discussion of the biopsy and BKV viral load and DSA results, with clinical history to distinguish between BKV and acute rejection is mandatory as the treatment is opposite.
Treatment:
Reduction of immunosuppression (IS) is the mainstay treatment, protocols as follow:
1. Reduce dose of antimetabolite by 50%, continuing on the same doses of calcineurin inhibitor and/or prednisone, with every 2 weeks monitor serum creatinine and plasma BK PCR levels.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
IVIG: It is utilized in the setting of non-response to a maximal reduction in immunosuppression.
Quinolones: data showed failure in BKV prophylaxis, not used in treatment.
Cidofovir: Studies have showed no benefit from its use, with nephrotoxicity.
Leflunomide: data showed no effect in treatment.
Upcoming Therapeutics in trials are a human monoclonal antibody (IgG1), and adoptive immunotherapy.
Kidney Re-Transplantation:
Re-transplantation should be done, after viral clearance by PCR, with Allograft survival of 98% and 94% at 1 and 3 years which is much better than that for other causes of graft failure (91% and 84% respectively).
Conclusions:
BKV is a common challenge faced in kidney transplantation, the only treatment is IS reduction, there is ongoing promising therapeutics in clinical trials.
Retransplantation should be offered for those treated patients with absent viral load with an excellent graft survival.
I note that reducing immunosuppression is the key step.I agree with your summary of this article.I agree with your analysis.
Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
History of the BK Virus
BK virus was first discovered in a kidney transplant recipient in 1971.
Virology
Epidemiology
BK virus infection is ubiquitous in the general population, with seroprevalence rates of over 90%. In kidney transplant recipients, Viruria, viremia, and allograft nephropathy are detected.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression is the most significant factor associated with BK viral replication, with the incidence of BK viremia highest in the early post-transplant period. Recipient characteristics: older age, diabetes, and specific HLA-C alleles
2. Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
3. Donor-recipient interface is at high-risk for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia, and ureteral stent placement.
4. HLA-B51 positivity and polycystic kidney disease are protective factors against BKVAN, resulting in a fivefold reduction in its occurrence.
Cellular Immune Response and Pathogenesis
Clinical Manifestations:
Screening and Diagnosis
Screening for BK viremia is the primary technique used in transplant centers due to its positive predictive value.
KDIGO and AST-IDCOP guidelines recommend monthly screening for BKVAN.
a. Urine BK PCR
Urine BK PCR is not recommended due to specificity and cost.
b. Plasma BK PCR
c. Urine Cytology
Urine can be examined for Decoy cells, polyomavirus-Haufen, and cast-like PV aggregates which have high positive and negative predictive values for BK nephropathy.
d. Donor-Derived Cell-Free DNA (dd-cfDNA):
dd-cfDNA may be a useful noninvasive test to distinguish asymptomatic BKV from BKVAN.
e. Transplant Kidney Biopsy
Considered the gold standard for the diagnosis of BVAN, as BK is tropic for the medulla, reducing sampling error.
The following pathologic features should be present for a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes.
2. Positive SV40 staining is useful for identifying BKV and PVN, but does not distinguish between JCV.
Diagnosis of BKVAN is likely to be missed in 30% of cases, with repeat biopsy recommended if clinical suspicions remain.
f. Histology
Treatment
A reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
A stepwise approach for reducing immunosuppression in BK viremia and BKVAN based on trials in adult and pediatric kidney transplant recipients.
1. Reduce the dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. Monitor serum creatinine and BK PCR levels every 2 weeks to reduce inter-assay variability.
2. Complete cessation of anti-metabolite if viral loads increase.
3. The next step is to reduce calcineurin-inhibitor through goals if viral loads do not reduce.
Adjunctive therapies such as quinolones, cidofovir, leflunomide, and intravenous immunoglobulin are the only viable adjunctive therapies for BK virus infection, while other agents are not recommended.
Upcoming Therapeutic Trials
Given the lack of therapies available for the treatment of BK infection, the two follow- ing trials involving modified T cells and monoclonal antibodies are currently underway:
1. A human monoclonal antibody (IgG1) that binds the viral capsid protein
2. Adoptively transferred posoleuccel (ALVR105) multivirus-specific T Cells in kidney transplant recipients
Kidney Re-Transplantation
Re-transplantation is recommended for patients with graft loss due to BKVAN, but confirmation of viral clearance should be made prior to transplantation.
Conclusions
I agree with you that none of the drugs mentioned have any conclusive proof of their efficacy in BKV
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Introduction
· The genome of the virus consists of three regions, the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
· BKV has 3 viral capsid proteins (VP-1, VP-2, and VP-3).
· VP-1 has significant genetic heterogeneity—this recognition has led to the classification of viral genotypes I to VI.
· Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases.
· Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
· 1–10%of kidney transplant recipients develop BKVAN.
· The infection occurs first as viruria, then viremia, and finally allograft nephropathy.
· Urine BK viral loads >8 log10 c/mL predict the onset of viremia.
· Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN.
· Loads above 6 log10 c/mL are predictive of extensive BKVN pathology.
Cellular Immune Response and Pathogenesis:
· Clearance of BK viremia is dependent cellular immune response—with both CD4 and CD8 cells implicated in this process.
· Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect.
· Continued inflammation leads to the activation of pro-fibrotic pathways.
· The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy.
Clinical Manifestations
· Most clinically significant infections associated with the BK are asymptomatic.
· The most common is viruria.
· Viremia is a better predictor of progression to BKVAN in comparison to viruria.
· The first 2–6 months are the periods of highest incidence of BAKVAN.
· Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis (rare in kidney transplant recipients).
· There are reports of a possible link between the BK virus and genitourinary malignancies.
Screening and Diagnosis
· There are standard screening protocols.
· Screening for BK viremia is the preferred method.
· The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 month.
1. Plasma BK PCR:
· The results are expressed as international units/mL.
2. Urine Cytology
· For decoy cells.
· Decoy cells do not necessarily indicate PVKN.
· Urine samples may also be screened for the presence of cast-like PV aggregates, called polyoma virus- Haufen in electron microscopy.
3. dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN
4. Transplant kidney biopsy:
· Kidney allograft biopsy is the gold standard diagnosis for BKVN.
· The following pathologic features should be present for a definitive diagnosis of BKVAN:
A. Characteristic cytopathic changes.
B. Positive immunohistochemistry tests against BKV or against SV40 large T antigen. It has a specifity of almost 100%.for PVN.
6. Histology
· Viral cytopathic changes: include tubular epithelial cells with enlarged, hyperchromatic nuclei and “groundglass” intranuclear inclusions.
· As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen.
· The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.
· To maximize the likelihood of identifying diagnostic features, two biopsy cores containing renal cortex and medulla are recommended.
· immunohistochemical stains (SV40) or in situ hybridization can be performed.
· EM: The presence of 40 nm viral particles within the nuclei of tubular cells.
Histology of BKV and AR:
· There are histological similarities between BKVN and AR.
· Reaching a correct diagnosis is clinically important.
· In rare cases BKVN and AR can occur together.
· In both cases, tubular injury, tubulitis, and interstitial inflammation are key histologic findings.
· The presence of above mentioned findings in the absence of morphologic or immunohistochemical evidence of PV infection should permit consideration of ACR.
· If the changes are confined only to the medulla, this should raise concerns of BKVN.
· If there is histologic overlap, the diagnosis of both condition should be made.
Treatment:
· A reduction of immunosuppression is the principle for the treatment of BK viremia and BKVAN.
9. There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
Stepwise approach for the reduction in immunosuppression in the setting of BKVN based on clinical trials:
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
2. If viral loads continue to be the same levels or increased, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies:
1. Quinolones, cidofovir: Studies have shown no benefit with their use.
2. Leflonamide: an open-label study showed no benefit with its use.
3. IVIG: Data from five observational studies have demonstrated a reduction in BK viral loads; however, other anti-viral agents were administered at the same time as well.
Upcoming Therapeutic Trials
1. A randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics, and efficacy of MAU868.
2. A phase 2 multicenter, randomized, double-blind, study of the safety, tolerability, and effectiveness of adoptively transferred posoleuccel (ALVR105) in kidney transplant recipients with either high or low levels of BK viremia
I note that reducing immunosuppression is the key step. None of the drugs mentioned have any conclusive proof of their efficacy in BKV
Article Summary
Introduction
BK virus maintains a latent infection in humans, which can reactivate in the setting of a dysfunctional cellular immune response and is frequently encountered in kidney transplant recipients. With BK virus infection there is higher risk of graft loss.
Virology
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family
Its genome has three regions –
The early coding region of the large T and small t antigens
The non-coding control region
The late coding region.
Epidemiology
The seroprevalence rates of over 90% by 4 years of age.
Transmission by mucosal contact including the oral, gastrointestinal, and respiratory tract
Viral replication can frequently ensues in first year post transplant
The chronological stages—viruria, viremia, and allograft nephropathy
1–10% of kidney transplant recipients develop BKVAN
Risk Factor of BKV infection
Intensity of immunosuppression
Recipient characteristics: older age, diabetes, and specific HLA-C alleles
The donor–recipient interface- The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney and ureteral stent placement
Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
HLA-B51 positivity and the presence of polycystic kidney disease has protective effect against BKV
Clinical Presentation
Viruria
It occurrs in up to 50% of patients in the first year of transplantation
Viremia
Viremia is present in 10–30 percent of recipients in the first six months posttransplantation and in 5–10 percent of recipients thereafter
BKVAN
It manifests as a decline in renal function with or without urinary abnormalities
BKVAN occurs within the first post-transplant year given attenuated cellular immunity, with the first 2–6 months being periods of highest incidence
Hemorrhagic cystitis
Ureteric stricture
Diagnosis
Urine BK PCR– it always requires confirmation with plasma PCR
Plasma BK PCR– BK viral loads are measured by polymerase chain reaction (PCR)
Urine Cytology– Decoy cells are typical.
Donor-Derived Cell-Free DNA (dd-cfDNA)– association of dd-cfDNA with plasma BK viral loads
Transplant kidney biopsy– Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear
Treatment
Decrease Immune suppression- Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone
If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite
Next step is reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite .
IVIG
Quinolones
Cidofovir
Leflunomide
Kidney Re-Transplantation
Re transplantation should be considered. Failed transplant or native nephrectomy is not recommended. Consideration for lower immunosuppression should be balanced with the risk of rejection. Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and 3 years
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation.
None of the drugs mentioned have any conclusive proof of their efficacy in BKV
Thank you Prof
Even though you have numbered your contents, it is not easy to read. I wish you could type headings and sub-headings as underline or in bold.
BK Virus Nephropathy in Kidney Transplantation:
A State-of-the-Art Review.
History of the BK Virus.
First case was discovered in post kidney transplant recipient presented with ureteric obstruction from Sudan but published first time on 1991, it was increasing due to highly discovered newly immunosuppression drugs as well as the highly sensitive tests for diagnosis, it is now associated with graft loss 15% within the last 2 decades.
Virology.
A small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family, The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection. The classification of viral genotypes I to VI. Serotype I has been the predominant genotype and is implicated in most clinically significant viral diseases. It is notable that the generation of antibodies against one serotype does not result in durable protection against other types.
Epidemiology.
Seroprevalence rates of over 90% by 4 years of age . The primary routes for transmission of the virus are from mucosal contact and after a primary viremia, the BK virus establishes refuge in the kidney and uroepithelium cells resulting in lifelong latent/persistent infection which reactivates in immunocompromised patient and lead to infection that occurs in the following chronological stages—viruria, viremia, and allograft nephropathy.
This correlates with the clinical observation that urine BK viral loads >8 log10 c/mL predict the onset of viremia, while plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads peaking above 6 log10 c/mL are predictive of extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates.
Viral replication is associated with the following risk factors:
A-Intensity of immunosuppression.
B-Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
C-Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
D-The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function , rejection or ischemia of the transplanted kidney, and ureteral stent placement.
Clinical Manifestations.
The presence of sustained viruria may progress to viremia, which is asymptomatic initially. Viremia is present in 10–30 percent of recipients in the first six months post-transplantation and in 5–10 percent later on. Viremia is a better predictor of progression to BKVAN in comparison to viruria, BKVAN usually manifesting as a decline in renal function with or without urinary abnormalities, and other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis.
Screening and Diagnosis.
Guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
1-Urine BK PCR is not a recommended screening test given issues related to specificity and nearly fifty percent of patients with viruria will not develop viremia.
2-Plasma BK PCR is sensitive and used mainly to confirm BK Viruria and used for screening.
3-Urine cytology: The characteristic BK virus-infected cells that present on cytological examination of urine are called (decoy cells) and the absence of decoy cells in urine cytology screens had high negative predictive values for PVN.
4-Donor-Derived Cell-Free DNA (dd-cfDNA): higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
5-Transplant Kidney Biopsy: is considered the gold standard for diagnosis BKVN. The histologic findings of this process include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions, overlap, a diagnosis of concomitant PVN and AR should be considered. In these instances, the histologic findings should be correlated with the clinical history and results of additional laboratory studies, such as BK viral load and the presence of donor-specific antibodies (DSA).
Treatment.
A-Reduction of immunosuppreive medications.
1. Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone. It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3. The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
B-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG). A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or Cidofovir.
Kidney Re-Transplantation.
Failed transplant or native nephrectomy is not recommended, confirm BKV PCR negativity.
Conclusion:
BK virus is one of the most common viral infection post kidney transplant which occurred mainly first year post ktx and screening is important every month for 6 months by BKV PCR and kidney biopsy is the gold standard of diagnosis, reduction of immunosuppreive medications is the cornerstone of treatment with or without adjuvant therapy.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Summary of this article:
Introduction.
BK virus-associated nephropathy (BKVAN) is one of the major causes of kidney graft loss post-transplant, Rate of viremia (BKV) in kidney transplant recipients is 30% , Initially discovered in a kidney transplant recipient with ureteric stricture in 1971. But First biopsy proven case of BKVAN was diagnosed in 1993. With Graft loss of <15% now a days (in early days it was 50–100%)
BK virus is a small, non-enveloped, closed circular, double-stranded DNA virus of Polyomaviridae family.
The genome of the virus consists of three regions:
1. Early coding region=> of large T & small t antigens (responsible for binding of the virus to host cell an leading to infection persistent).
2. Non-coding control region => responsible of virus pathogenesis
3. Late coding region=> codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Sero – type 1 if present it indicate clinically significant disease
Epidemiology:
BKV Prevalence is > 90% at age 4 years.
BKV infection frequently occurs in first post-transplant year due to intensive suppression of cellular immunity.
Recently, 1–10% of kidney transplant recipients develop BKVAN.
BKV mode of transmission through oral, gastroenterology and respiratory tract.
BKV infection occurs as viruria, viremia and graft nephropathy.
50% of patients develop viremia over 2-6 weeks After viremia,
Urine viral load >8 log10c/ml predict onset of viremia, plasma viral load > 4 log10 c/ml associated with high rate of biopsy proven BKVN and viral load > 6 log10 cml predict extensive BKVN.
Risk factors
1.Immunosuppression (the most important). Tacrolimus is having higher risk than cyclosporine, Also, mTORi may be associated with lower risk.
2.Recipient-related factors like olde rage, DM, and specific HLA-C allele
3.Donor-related factors like reduced immune response to BK virus and presence of BK viruria prior to transplant.
4.donor–recipient factors like high-risk cases of D + and R – status for BK virus, ABO incompatibility, HLA mismatches, DGF, and rejection or ischemia of the transplanted kidney.
Cellular Immune Response and Pathogenesis
Clearance of BK viremia dependents on activation of cellular immune response (both CD4 and CD8 cells) by viral antigens is crucial for BKV infection control, BK capsid proteins, large T antigen, and non-structural proteins all stimulates a T cell response.
Latent infection maintained mainly in kidney epithelial cells, & in lower frequency in prostate, testes, seminiferous tubules, cervix, vulva, & hematolymphoid tissues, can become active with reduced cellular immunity in immunosuppression states. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways, Progressive destruction leads to interstitial fibrosis & tubular atrophy and progressive nephron loss. This leads to Chronic injury to transplanted kidney.
Clinical manifestation:
Most of cases are asymptomatic.
Classical pathway of infection viruria then viremia and BKVAN.
Viremia is present in 10–30 percent of recipients in the first six months post transplantation and in 5–10 percent of recipients thereafter.
Viremia is better than viuria in predicting progression to BKVAN.
BKVAN is more prevalent in 2-6 months post transplantation may be due to immunosuppressive burden presented with elevation of kidney function with or without urine analysis abnormalities.
It may present with ureteric stenosis or hemorrhagic cystitis.
Screening & diagnosis:
BKV urine PCR has low specificity so not used for screening.
Plasma BKV viral load is the preferred method for screening due to its high positive predictive value.
Due to high prevalence early post-transplant, KDIGO & AST-IDCOP guidelines recommend monthly screening for first 6 months every 3 months for next 18 months.
Cause of assay variation, World Health Organization (WHO) addressed this by establishing an international standard to standardize viral load values among different laboratories assays.
Urine cytology: for detection of decoy cell: it has low positive predictive value as screening tool.
Donor-Derived Cell-Free DNA (dd-cf DNA): data suggest that it may be good test indicating the progression of BKV to BKNAN
Biopsy of transplanted kidney: still the gold standard for evaluation of BKVAN it is necessary that the biopsy sample to contain medulla to avoid false negative results.
Distinguishing between BKVN & acute rejection is challenging.
Histological classification of biopsy proven PVN into 3 classes (Banff classification).
Treatment:
1. Reduction of IS.
2. adjuvant therapy:
1- Cidofovir: Nucleoside analog IV: 0.25–1.0 mg/Kg at 1–3 weeks Used in refractory cases; studies showed no benefit, additionally , Nephrotoxicity is the most serious adverse effect
2- Intravenous immunoglobulin (IVIG): Immunoglobulin preparation with high titers of neutralizing antibodies to BK virus Can be used as an adjunct to other measures in refractory cases with uncertain study results
3. leflunomide: a pharmacodynamic and prospective open-label study showed no benefit
4- Levofloxacin: Fluoroquinolones; Antiviral, inhibit helicase activity of large T antigen Levofloxacin failed to show benefit in randomized controlled trials.
Kidney re-transplantation:
Graft Loss 2/2 BKVN Should Be Considered For Re-Transplantation.
Graft Nephrectomy Is Not Recommended.
Consider Lower Immunosuppression That Should Be Balance with Risk Of Acute Rejection.
Graft Survival in Re-Transplant Is 98% & 94% At 1 & 3 Year.
No Significant Difference in Rate Of Acute Rejection Or Patient Survival At 1 Year.
Conclusions:
BK virus infection is one of the most common manifestations in transplant recipients and close surveillance is needed to prevent severe disease. Immunosuppression reduction is the only viable strategy in infected cases but may lead to rejection. Currently, there is no role for any anti-viral therapy, no benefit from adjuvant therapy, upcoming therapeutic trials may be of benefit.
Level of evidence: This is a narrative review thus level V.
I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
Introduction;
-BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
-The successful advent of increasingly efficacious immunosuppression has been accompanied by high rates of BK viremia (BKV) in up to 30% of kidney transplant recipients.
History of the BK Virus;
-BK virus was first discovered in a kidney transplant recipient who presented with a ureteral stricture in 1971.
-However, it was only in 1993 that the first definitive biopsy proven case of BKVAN was described.
-During the period of its early description, BKVAN frequently resulted in graft loss with rates of 50–100% reported.
Virology;
-BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
-The genome of the virus consists of three regions—the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
Epidemiology;
-BK virus infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
-The primary routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory tract.
-After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
Risk Factors;
1-Intensity of immunosuppression:
This is considered as the most significant factor associated with BK viral replication.
2-Recipient characteristics:
older age , diabetes , and specific HLA-C alleles.
3-The donor–recipient interface:
-The high-risk serostatus of donor positive and recipient negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney , and ureteral stent placement.
4-Donor-related factors:
-Immune response to BK virus and BK viruria prior to transplant.
Clinical Manifestations;
-The classic sequence of infections in kidney transplant recipients is viruria, viremia, and BKVAN.
-The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia.
-The presence of sustained viruria may progress to viremia, which is asymptomatic initially.
-Viremia is present in 10–30 % of recipients in the first six months post transplantation and in 5–10 % of recipients thereafter.
-Viremia is a better predictor of progression to BKVAN in comparison to viruria.
-BKVAN usually occurs after a period of sustained progressively worsening viremia, manifesting as a decline in renal function with or without urinary abnormalities.
-Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis.
Screening and Diagnosis;
-The high incidence of BK viremia in the first post-transplant year has led to the development of standard screening protocols by transplant centers.
-Screening for BK viremia is the preferred method utilized in these protocols.
-(KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
-Urine BK PCR / Plasma BK PCR / Urine Cytology / Donor-Derived Cell-Free DNA (dd-cfDNA) / Transplant Kidney Biopsy.
-The characteristic BK virus-infected cells that present on cytologic examination of urine are called decoy cells.
–Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN.
-In the genitourinary tract, these viruses target urothelial and renal tubular cells, resulting in virion production and subsequent cellular destruction.
-The histologic findings of this process include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions.
Treatment;
-Areduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
-There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
-Multiple protocols have been developed for a reduction in immunosuppressions.
1-Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
-It is imperative to monitor serum creatinine and serial plasma BK PCR levels from the same laboratory (to reduce inter-assay variability) every 2 weeks in the interim.
2-If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3-The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
-It is pertinent to note that based on the 5-year follow-up data of patients with BK viremia and BKVAN, kidney transplant recipients maintained on tacrolimus-based regimes had lower rates of rejection and a higher estimated glomerular filtration rate (eGFR).
-Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
Kidney Re-Transplantation;
-Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
-Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
-Consideration for lower immunosuppression should be balanced with the risk of rejection.
-Allograft survival in patients who receive re-transplantation is 98% at 1 year and 94% at 3 years.
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation.
None of the drugs mentioned have any conclusive proof of their efficacy in BKV
☆ BK Virus Nephropathy in Kidney Transplantation:
A State-of-the-Art Review
________________________________
¤ This review provided an extensive overview of viral epidemiology, pathogenesis, screening, and diagnostic methods. In addition, it discussed clinical manifestations and recommended treatment strategies.
◇ Introduction
▪︎BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients. Since its discovery in 1971, an effective prophylaxis or therapy is yet to be devised, with unmitigated disease frequently resulting in allograft loss.
◇ Virology
▪︎BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNAvirus and member of the Polyomaviridae family.
▪︎The genome of the virus consists of
3 regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
◇ Epidemiology
▪︎The primary routes for transmission of the virus are from mucosal contact including the oral, GIT & RT.
▪︎After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection.
▪︎Clinically significant infection occurs in kidney transplant recipients via reactivation of latent infection or transmission of new infection from the donor kidney.
▪︎The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy.
▪︎Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression.
2. Recipient characteristics: older age,
diabetes, and specific HLA-C alleles
3. The donor–recipient interface: The high-risk serostatus of donor positive & recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
4. Donor-related factors: reduced immune response to BK virus and BK viruria
prior to transplant.
▪︎Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN.
◇ Cellular Immune Response
▪︎The clearance of BK viremia are dependent on a robust cellular IR (both CD4 and CD8 cells).
▪︎Latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
◇ Clinical Manifestations
1. Mostly a symptomatic.
2. The classic sequence of infections is viruria, viremia, and BKVAN.
▪︎The presence of sustained viruria may progress to viremia, which is asymptomatic initially.
▪︎Viremia is a better predictor of progression to BKVAN in comparison to viruria.
▪︎ BKVAN is manifested as a decline in renal function with or without urinary abnormalities.
▪︎The vast majority of BKVAN occurs within the first post-transplant year, with the first 2–6 months being periods of highest incidence.
▪︎Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis.
▪︎There are reports of a possible link between the BK virus and genitourinary (GU) malignancies.
◇ Screening and Diagnosis
▪︎Screening for BK viremia is the preferred method.
▪︎Fastidious screening and preemptive reduction in IS for established BK viremia have been demonstrated to mitigate progression to BKVAN.
▪︎The KDIGO & AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
▪︎Urine BK PCR: is not a recommended screening test
▪︎Plasma BK PCR: rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads.
▪︎Urine Cytology:
a. May show the characteristic decoy cells (although they are a marker of PV
replication, they do not necessarily indicate PVN).
b. Polyomavirus-Haufen, via negative staining EM.
▪︎Donor-Derived Cell-Free DNA (dd-cfDNA): higher levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
▪︎Transplant kidney biopsy and Histology:
Is the gold standard for the diagnosis of “definitive” BKVAN.
-The characteristic findings include tubular epithelial cells with enlarged, hyper- chromatic nuclei and “ground glass” intranuclear inclusions.
– Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles.
– In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla. Eventually, these cells lyse and slough from the basement membrane into the tubular lumens.
– When infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen. More proximal portions of the nephron, including the parietal epithelial cells lining Bowmans capsule, may also become involved.
◇ Treatment
▪︎A reduction in the intensity of IS is the overarching principle for the treatment of BK viremia and BKVAN.
▪︎There is no therapeutic agent available to treat this virus-associated disease, with many agents lacking conclusive efficacy in the reduction in viral loads.
◇ Stepwise approach for the reduction in immunosuppression in BK viraemia and BKVAN:
1. Reduce dose of antimetabolite by half while continuing on the same doses of CNI and/or prednisone and monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks in the interim.
2. If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
3.Reduce CNI trough if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite.
▪︎Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).The later is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
◇ Kidney Re-Transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
◇ Conclusion
▪︎BK virus infection continues to be one of the most common clinical issues encountered by transplant providers. It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection.
▪︎There is no anti-viral currently known to be of benefit in the clearance of the virus.
I note that reducing immunosuppression is the key step.
Introduction:
Virology:
1. Early coding region of large T & small t antigens (responsible for binding of the virus to host cell an leading to infection persistent).
2. Non coding control region( responsible of virus pathogenesis,
3. The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3). Sero type 1 if present it indicate clinical significant disease
Epidemiology:
1. Intensity of immunosuppression
2. Recipient factors: old age, DM, specific HLA allels.
3. Both The donor–recipient related risk: The high-risk serostatus of donor D+R-, delayed graft function rejection or cold ischemic time , and ureteral stent placement .
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
5. Of note Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN due to the presence of highly immunogenic cytotoxic T cells
Pathogenesis:
Clinical manifestation:
Screening & diagnosis:
Treatment.
1. reduction of immunosuppression
2. adjuvant therapy \
1- Cidofovir: Nucleoside analog IV: 0.25–1.0 mg/Kg at 1–3 weeks Used in refractory cases;studies showed no benefit , additionally , Nephrotoxicity is the most serious adverse effect
3- Intravenous immunoglobulin (IVIG): Immunoglobulin preparation with high titers of neutralizing antibodies to BK virus Can be used as an adjunct to other measures in refractory cases with uncertain study results
3. luflonamide : a pharmacodynamic and prospective open-label study showed no benefit
· 4- Levofloxacin: Fluoroquinolones; Antiviral, inhibit helicase activity of large T antigen Levofloxacin failed to show benefit in randomized controlled trials.
upcoming trials:
1. human monoclonal antibodies(IgG1) bind to VP1 (MAU868).
2. adoptive transfered posoleuccel (ALVR105)
Kidney re-transplantation.
· 1- BKV infection one of the most common post-transplant clinical issue
· 2- surveillance protocols has led to early detection and avoidance of advanced disease
· 3- reduction of IS is the mainstay of treatment
· 4- no benefit from adjuvant therapy
· 5- upcoming therapeutic trials may be of benefit
I note that reducing immunosuppression is the key step. I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.
Please summarise this article
Introduction
BK virus-associated nephropathy (BKVAN) is one of the major cause of graft losspost transplant Rate of viremia (BKV) in kidney transplant recipients is 30% (efficacious immunosuppression). Initially discovered in a kidney transplant recipient with ureteric stricture in 1971. But First biopsy proven case of BKVAN was diagnosed in 1993. With Graft loss of <15% now a days (in early days it was 50–100%)
BK virus is a small, non-enveloped, closed circular, double-stranded DNA virus of Polyomaviridae family.
The genome of the virus consists of three regions:
1. Early coding region
2. Non-coding control region
3. Late coding region
Epidemiology
In 90% of general population antibodies are detectable to BKV by 4 years of age. The common routes for transmission are oral, gastrointestinal, and respiratory tract. After a primary viremia, it mainly persists in the kidneys and urinary tract in a latent form for rest bof the life. In affected patients the Infection is either reactivation or transmission of new infection from the donor kidney. In the Chronological stages infection go through—viruria only then viremia, and finally allograft nephropathy. Viruria in 30% and viremia in12% of kidney transplant recipients is common finding. After viruria, half of the patient develop viremia in next 2–6 weeks, with 50% of viremic patients developing BKVAN.
In Urine, high BK viral loads >8 log10 c/mL can predict subsequent viremia. But Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN
Risk factors
1.Immunosuppression (the most important). Tacrolimus is having higher risk than cyclosporine. Also, mTORi may be associated with lower risk.
2.Recipient-related factors like olde rage, DM, and specific HLA-C allele
3.Donor-related factors like reduced immune response to BK virus and presence of BK viruria prior to transplant.
4.donor–recipient factors like high-risk cases of D positive and R negative status for BK virus, ABO incompatibility, HLA mismatches, DGF, and rejection or ischemia of the transplanted kidney.
Cellular Immune Response and Pathogenesis
Clearance of BK viremia dependents on good cellular immune response (both CD4 and CD8 cells). BK capsid proteins, large T antigen, and non-structural proteins all stimulates a T cell response.
Latent infection can become active with reduced cellular immunity in immunosuppression states. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways. This leads to Chronic injury to transplanted kidney.
Clinical Manifestations
Often asymptomatic. The earliest manifestation of BKV is viruria only (50%) in the first year of transplantation. Urine BK viral loads is not sustainable but if Sustained viruria occurs it may progress to viremia in 10–30 % of recipients in the first 6 months post transplantation and in 5–10 % of recipients thereafter Viremia is a better predictor of progression to BKVAN in comparison to viruria. BKVAN occurs in the first post-transplant year (highest incidence is 2-6 months)
Other manifestations of the BK virus are ureteral stenosis and hemorrhagic cystitis with rare possiblity of genitourinary (GU) malignancies, which might be an association.
Screening and Diagnosis
The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BK PCR
· Not recommended because it always requires confirmation by plasma PCR
· 50% of patients with viruria will not develop viremia
Plasma BK PCR
· WHO established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL. BK PCR can be 4 times less sensitive for variants strains
Urine Cytology
· BK virus-infected cells in urine are called decoy cells. They are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin. although High false-positive rates and low positive predictive values is case in presence of decoy call in urine but absence of decoy cells in urine cytology screens has high NPV for PVN
Donor-Derived Cell-Free DNA (dd-cfDNA)
May be a useful noninvasive test to assess for progression of BKV to BKVAN
Good tool to distinguish asymptomatic BKV from BKVAN. Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
Transplant kidney biopsy
· The gold standard for the diagnosis of BVAN, severity of viral involvement and other pathology and for a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes
2. Positive immunohistochemistry tests (using antibodies directed against BKV or against the cross-reacting SV40 large T antigen. Specificity of SV40 is 100 but not distinguish between BKV and JCV
Histology:
· The histologic findings of this include ground glass”intranuclear inclusions
· Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles
· As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
· More proximal portions of the nephron, including the parietal epithelial cells lining Bowmans capsule, may also become involved
· The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis
· Two biopsy cores containing renal cortex and medulla are recommended
· Simian Virus 40 (SV40) IHC stain is recommended in all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN
· There are several grading systems for evaluation of PKN (use viral cytopathic effect, injury, and atrophy for classification)
Treatment
Reduction of of immunosuppression is the main treatment of BK viremia and BKVAN
Approach for reduction:
Reduce dose of antimetabolite by 50% and continue with same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR levels every 2 weeks. Complete cessation of anti-metabolite if viral loads continue to be at similar levels or increasing, Third options reduce CNIs to the lowest trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine)
Other adjunctive therapies:
1. IVIG:
2. Quinolones
3. Cidofovir
4. Leflunomide
Although Cidofovair, Ciprofloxacin and Leflunamide have not been proven in any trial yet.
Upcoming Therapeutic Trials (modified T cells and monoclonal antibodies)
Kidney Re-Transplantation
If transplant fails thyen it is an option but nephrectomy of failed kidney is not recommended. Viral clearance prior to transplantation should be the Goal. They should be exposed to Lower immunosuppression.
Conclusions
· BK virus infection is one of the most common manifestations in transplant recipients and close surveillance is needed to prevent severe disease. Immunosuppression reduction is the only viable strategy in infected cases but may lead to rejection. Currently, there is no role for any anti-viral therapy.
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.
One may have to discontinue MMF for some time. I would not wait for watching the effect of MMF reduction
1. Please summarise this article.
Introduction
Virology
Epidemiology
Risk factors for viral replication:
Protective factors against the development of BKVAN:
Pathogenesis
Clinical Manifestations
Screening and Diagnosis
Treatment
I do not agree that IVIG has any conclusive role in BKV
IV. BK Virus Nephropathy in Kidney Transplantation: A State-of-the-Art Review
====================================================================
Please summarise this article
1. Introduction
====================================================================
2. History of the BK Virus
====================================================================
3. Virology
====================================================================
4. Epidemiology
Viral replication is associated with the following risk factors:-
====================================================================
5. Cellular Immune Response and Pathogenesis
====================================================================
6. Clinical Manifestations
====================================================================
7. Screening and Diagnosis
7.1. Urine BK PCR
7.2. Plasma BK PCR
7.3. Urine Cytology
7.4. Donor-Derived Cell-Free DNA (dd-cfDNA)
7.5. Transplant Kidney Biopsy
7.6. Histology
====================================================================
8. Treatment
1-Reduce dose of antimetabolite by half while continuing on the same doses of cal-
2- Complete cessation of anti-metabolite if viral loads increase.
3- The next step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks. Adjunctive therapies include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin, with IVIG being the only viable option.
The discussion of this aspect
====================================================================
Upcoming Therapeutic Trials
====================================================================
9. Kidney Re-Transplantation
====================================================================
10. Conclusions
=================================================================
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
Many thanks Prof.Sharma
Summary
Virology.
BK virus is a small non-enveloped double stranded DNA of the polyomaviridae family.
The genome has three regions; the non-coding region contains the origin of replication thus a significant contributor to its pathogenesis. Mutations here permit replication.
There are six viral genotypes with serotype I the most predominant and associated with most clinically significant disease.
Formation of antibodies against one serotype doesn’t confer protection against other serotypes.
Epidemiology.
The general population has seroprevalence rates of 90% by 4 years of age.
Routes of transmission for primary infection: mucosal contact in the oral, GIT and respiratory tract.
Then remains latent in the kidney and uroepithelial leading to lifelong infection.
Kidney transplant recipient infection could be due to reactivation of the latent infection or new infection from donor kidney.
First year post transplant associated with increased immunosuppression hence leading to most viral replication occurring in this period.
Risk factors
Most significant factor.
BK viremia is highest in the early post transplant period due to the high immunosuppression.
Include older age, DM, specific HLA C alleles.
Include D+/R- for BK virus, ABO incompatibility, HLA mismatch, DGF rejection, placement of a ureteral stent.
BK viruria prior to transplant, reduced immune response to BK virus.
Pathogenesis
Both CD4 and CD8 T cells play crucial role in clearance of BK viremia.
After primary infection the virus remains latent in kidneys mostly in the parietal epithelium, tubular epithelium and transitional epithelium.
Other organs that it can remain latent include: prostate, testes, vulva, cervix and seminiferous tubules.
Latent infection is reactivated with reduced cellular immunity due to introduction of immunosuppression.
Leading to damage of the tubular epithelium due to the viral replication and its cytopathic changes.
Further inflammation leads to activation of pro-fibrotic pathways.
BKVAN has expression of several messenger RNA that are similar to those seen in T cell mediated rejection, could explain why both have common clinical and pathological features.
Clinical manifestation.
Chronological stages of the infection are: viruria, viremia and allograft nephropathy.
Viruria: Most common and earliest manifestation.
Viremia: Persistent viruria may progress to viremia. Better predictor to BKVAN than viruria.
BKVAN: Occurs after a period of prolonged and worsening viremia. Manifest as declining renal function ± urinary abnormalities. First 2-6 months post transplant associated with highest incidence.
Other manifestations: Ureteral stenosis, hemorrhagic cystitis.
BKV and malignancies: Controversy may be more of an association than causation. BKV infection occurs in the setting of lowered cellular immunity; hence reduced tumour surveillance thus a risk of development of malignancy.
Screening and diagnosis.
Urine BKV PCR:
Not a recommended screening tool due to low specificity- half of the patients with viruria will not develop viremia.
Requires confirmation with plasma PCR.
Plasma BK PCR:
Has a high PPV for BKVAN.
Assays are influenced by DNA extraction techniques, sample/ source, primer and probe sequence, BK strain DNA used for standard curve genotype variance.
Urine cytology:
Decoy cells are characteristic BK infected cells present on the cytologic examination of urine. They are tubular epithelium or urothelial cells with ground glass nuclear inclusion surrounded with chromatin.
They are a marker of viral replication but don’t necessarily indicate BKVAN.
Donor derived Cell Free DNA (ddcfDNA):
High ddcfDNA is associated with high BK viral loads, biopsy proven BKVAN, and histologic features meeting Banff criteria for T cell mediated rejection.
Thus may be used to asses progression to BKVAN non-invasively.
Histology:
Gold standard for definitive diagnosis.
Requires 2 cores (cortex and medulla) to increase diagnostic yield.
Histologic findings: tubular epithelial cells with enlarged hyper-chromatic nuclei and ground glass intranuclear inclusions.
Viral cytopathic changes: granular nuclear inclusions, clumps of intranuclear vision particles.
Tubular injury, tubulitis, and interstitial inflammation are histological findings common in BKVAN and TCMR.
IHC/ISH:
Done on the biopsy to aid detection of BKV.
SV40 IHC stain detects large T cell antigens expressed on all polyomaviruses. Detects early stages of infection before detectable on routine stains.
Interpretation requires caution due to latency of the BKV.
Treatment
Reduced immunosuppression is the principal of treatment.
Stepwise approach of reduction:
Other treatments:
IVIG: Utilised in the setting of non-response after maximal reduction in immunosuppression.
Quinolones: Studies have failed to show efficacy in prophylaxis.
Cidofovir: Studies have not shown any benefit. Nephrotoxic.
Leflunomide: Prospective open label study failed to show benefit.
Re-transplantation.
Confirmation of viral clearance prior to transplantation.
Nephrectomy of native or failed graft not recommended.
Lower immunosuppression with a balance to prevent rejection.
Level of evidence: This is a narrative review thus level V.
I appreciate your steps when considering retransplantation. I agree with your analysis of strengths and limitations, and summary of this article.I agree with your analysis of the level of evidence this article provides.
Introduction:
Virology:
Epidemiology:
Cellular immunity & pathogenesis:
Clinical manifestation:
Screening & diagnosis:
Treatment.
Kidney re-transplantation.
I like your summary of this article
SUMMARY
Introduction
BK virus-associated nephropathy has been one of the causes of allograft loss particularly with a breakthrough in the advent of more potent immunosuppression for kidney transplantation. In addition, the availability of standard prophylaxis or treatment of the BKVAN has not been ascertained despite the discovery of the virus in 1971. Although, the rate of kidney allograft loss has reduced from it the previous level of between 50-100% to now around 15% partly because of the ability to make a definitive diagnosis through kidney tissue for histology.
The T antigen has a propensity to bind to p53 and protein Rb, resulting in the commencement of its cell cycle in host cells and subsequent persistent infection
Epidemiology
Viral replication is associated with the following factors
Clinical manifestation
Screening and Diagnosis
Treatment
Other suggested tried forms of treatment
Kidney retransplantation
Another kidney transplantation can be carried out following a loss of a previous graft to BKVAN. This must be carried out after complete clearance of the virus from the system. Nephrectomy of the native kidney is not necessary
Conclusion
Among the challenges encountered following kidney transplantation is the BKVAN which could lead to allograft loss if not detected early by regular surveillance screening and reduction of immunosuppression if viral load is persistently high. Unfortunately, there is no viable antiviral agent against the virus, but a few kinds of research are ongoing for the discovery of a potent antiviral agent.
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Introduction
Kidney transplant recipients are at risk of graft loss because of BK virus-associated nephropathy. Up to 30% of kidney transplant recipients have BK viremia due to more effective immunosuppressives. Since its discovery in 1971, no effective prophylactic or treatment has been found, resulting in allograft loss. This comprehensive study covers viral epidemiology, etiology, screening, and diagnosis.
Virology
The Polyomaviridae virus BK has small, non-enveloped, icosahedral, closed-circular, double-stranded DNA. The virus genome has three regions: the early coding region of the big T and small T antigens (large and small tumor antigens), the non-coding regulatory region, and the late coding section.
Epidemiology
By age 4, 90% of people have BK virus infection. The virus spreads through oral, gastrointestinal, and respiratory mucosa. BK virus hides in kidney and uroepithelial cells after primary viremia, causing lifelong latent/persistent infection.
Induction therapy suppresses cellular immunity in the first year post-transplant, allowing virus multiplication.
Kidney transplant recipients can contract clinically severe infections from donor kidneys or reactivate dormant infections. Viruria, viremia, and allograft nephropathy occur in order.
Cellular Immune Response and Pathogenesis
A strong cellular immune response—including CD4 and CD8 cells—is needed to reduce and eradicate BK viremia. ELISPOT and tetramer labeling quantify T cell responses to BK capsid proteins, big T antigen, and non-structural proteins. BKVAN resolves with ELISPOT-measured IFN-gamma activity, indicating a BK-directed cellular immune response.
BKVAN increases CD8, perforin, interferon-, and CXCR3 mRNA expression. BKVAN and TCMR have clinical and pathological symptoms, making them difficult to identify. These mRNAs are also expressed in TCMR. Interstitial fibrosis and tubular atrophy cause nephron loss in the final stage.
Clinical Manifestations
Most BK virus infections are asymptomatic. Kidney transplant recipients typically develop viruria, viremia, and BKVAN. Viruria, the most prevalent BKV symptom, occurs in up to 50% of transplant recipients in the first year. Most cases do not proceed to viremia.
Sustained viruria can cause asymptomatic viremia. 10–30% of recipients have viremia in the first six months after transplantation and 5–10% thereafter. Viremia predicts BKVAN better than viruria.
After prolonged, worsening viremia, BKVAN causes renal function decrease with or without urine problems. Given attenuated cellular immunity, BKVAN is most common in the first 2–6 months after transplantation.
Screening/Diagnosis
Transplant facilities have established screening processes due to the high frequency of BK viremia in the first year post-transplant. Screening for BK viremia is preferable over urine BK viral loads because it has better positive predictive value.
Treatment
Immunosuppression reduction is the primary treatment for BK viremia and BKVAN.
Strategy for reduction:
Reduce the antimetabolite dose by 50% while maintaining the same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR values every two weeks from the same laboratory. Complete termination of anti-metabolite treatment if virus loads remain stable or increase.
Reduce CNIs trough objectives if viral loads do not decrease within 4 weeks despite discontinuation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/mL for cyclosporine).
Alternatives treatment include IVIG, Cidofovir, leflunamide and others.
Retransplantation
Offered the significant success data, patients who experienced graft loss as a result of BKVAN should be given consideration for a second transplant. Given the paucity of guidelines based on data to support this approach, failed transplants or native nephrectomy are not advised, and viral clearance should be confirmed before transplantation. The risk of rejection should be considered against consideration for less immunosuppression.
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Introduction
within the last 2 decades The ensuing increasing recognition and nuanced management have now resulted in a reduction in associated graft loss from 50–100% to under 15%
Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis—albeit rare in kidney transplant recipients and mostly seen in patients with hematopoietic stem cell transplants
cellular immunity is most suppressed in the first post-transplant year as a result of induction therapy, viral replication during this period. via reactivation of latent infection or transmission of new infection from the donor kidney.
The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy
Viruria and viremia are detected in approximately 30% and 12% of kidney transplant recipients, respectively
The checking of urine BK viral loads is not standard practice despite it being a sensitive marker for progression to BKVAN
Viremia is a better predictor of progression to BKVAN in comparison to viruria
extensive BKVN pathology measured by SV40 immunohistochemistry and associated inflammatory infiltrates
Viral replication risk factors:
1. Intensity of immunosuppression: tacrolimus may a higher risk of BK virus infection than cyclosporine while (mTOR) inhibitors may be associated with lower risk
the presence of BK viremia reflects a higher level of immunosuppression and its occurrence with or without BKVAN is in the setting of all maintenance immunosuppressive agents/combinations
2. Recipient characteristics: older age -diabetes and specific HLA-C alleles
3. The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus– ABO incompatibility, HLA mismatch , delayed graft function , rejection or ischemia of the transplanted kidney, and ureteral stent placement
4. Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant
.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease have been shown to be protective factors against the development of BKVAN. HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients
Latent infection
The virus maintains persistent infection after initial childhood infection and maintains refuge in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils).
latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression. Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways (transforming growth factor β, matrix metalloproteinase-2, matrix metalloproteinase-9, and matrix collagens)
BKVAN is also associated with increased expression of various major groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
These mRNAs are also expressed in T cell-mediated rejection (TCMR) and could explain common clinical and pathological features in BKVAN and TCMR with associated difficulty in distinguishing the two entities
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss
Screening and Diagnosis
(KDIGO) and (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BK PCR is not a recommended screening test
Plasma BK PCR BK viral loads
The genotype I strain is currently utilized as the reference sequence
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I)
Urine Cytology The characteristic BK virus-infected cells that present on cytologic examination of urine are called decoy cells
. Some studies have shown high false-positive rates and low positive predictive values However, some of these studies also found the absence of decoy cells in urine cytology screens had high negative predictive values for PVN.
Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy . The presence or absence of PV-Haufen has extremely high positive and negative predictive values for BK nephropathy, respectively.
Donor-Derived Cell-Free DNA (dd-cfDNA)
A recent study demonstrated that higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection. These findings show that dd-cfDNA may be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant Kidney Biopsy
the gold standard for the diagnosis of BVAN. assessing the severity of viral involvement and the presence of other ongoing pathologies. Since BK is tropic for the medulla, it is necessary that the biopsy core has medulla present to decrease the likelihood of a sampling error
TREATMENT
Reduce dose of antimetabolite by half while continuing on the same doses of calcineurin inhibitor and/or prednisone.
monitor serum creatinine and serial plasma BK PCR levels every 2 weeks If viral loads continue to be at similar levels or increase, proceed with complete cessation of anti-metabolite.
reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine). It is noted that based on the 5-year follow-up data of patients with BK viremia and BKVAN, kidney transplant recipients maintained on tacrolimus-based regimes had lower rates of rejection and a higher estimated glomerular filtration rate (eGFR)
. Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobulin (IVIG).
A meta-analysis has demonstrated that there is no difference in graft outcomes when the strategy of reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir
Intravenous immunoglobulin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
Kidney Re-Transplantation
confirmation of viral clearance should be made prior to transplantation.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival is 98% and 94% at 1 and 3 years,
five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
there was no significant difference in the rates of acute rejection or patient survival at one year
.
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Introduction
BK virus-associated nephropathy is a significant etiology of graft loss in kidney transplant recipients
BKV history
It was first noticed in 1971 in a kidney transplant recipient with ureteral stricture
BKVAN was implicated to cause graft loss in 50–100% of cases at that time .
Virology
BKV is a double-stranded DNA virus of Polyomaviridae family.
The genome is made of 3 regions consisting of
· early coding region of the large T and small t antigens , which binds to p53 and protein Rb, leading to start and persistence of infection
· the non-coding control region harbouring the replication origin and modulate transcription it’s mutation enhance viral replication.
· the late coding region codes for the agnoprotein and viral capsid proteins (VP-1,
VP-2, and VP-3) .Antibodies produced against one serotype does not lead to durable protection against other types .
Epidemiology
BKV infection is common in general population ,route of transmission include oral gastrointestinal, and respiratory tract then it can be latent in the kidney and uroepithelium life long.
Infection in kidney transplant recipients occurs either by reactivation of latent infection or transmission of denovo infection from the donor kidney enhanced by the immunocompromised state ,infection starts in the forum of viruria, viremia, and allograft nephropathy.
Urine BK viral loads >8 log10 c/mL indicates viremia onset
plasma BK viral loads >4 log10 c/mL indicates biopsy-proven BKVAN high rate
levels much higher than 6 log10 c/mL signifies extensive BKVN pathology measured by SV40 immunohistochemistry.
Risk factors
· Immunosuppression intensity which is the most important factor for viral replication
· Recipient character includes older age , diabetes , and specific HLA-C alleles
· The donor–recipient interface involving donor positive and recipient
negative for BK virus , ABO incompatibility, HLA mismatch , delayed graft
function , graft rejection and ureteral stent placement .
· Donor factors: reduced immune response to BK virus and BK viruria before transplant
Polycystic kidney disease and HLA-B51 positivity of the recipient are protective factors
Cellular Immune Response and Pathogenesis
Anti-BK T cell response developpment short time interval correlates with viremia resolution, while cases whom suffer BKVAN need a median period of 5 months to develop cellular immunity against the virus .
These data can be used to predict the clearance of the BK virus and notice risky cases for progression of the virus-associated disease.
The virus remains latent in kidney epithelium particularly in the parietal epithelium of the Bowman’s capsule,renal tubular epithelium, and transitional epithelium, prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues.
Immunosuppression can enhance this latent virus to progress to active disease.
Differentiating between BKVN and TCMR can be difficult sometimes because both are associated with increased expression of various groups of messenger RNAs (mRNAs), including CD8, perforin, interferon-γ, and CXCR3.
Clinical picture
The most common and earliest presentation is viruria occurring in the first year of transplantation, without progression to viremia in most cases.
Urine BK viral loads are sensitive but non specific .
Viruria can progress to viremia in the first 6 months post transplantation, which is asymptomatic but predicts BKVN progression.
BKVN can be manifested by reduced renal function, ureteral stenosis and haemorrhagic cystitis that is more common in HSCT.
BK virus association with the development of urothelial malignancies in transplant recipients is under further study .
Screening and diagnosing
Screening for BK viremia in the first year post transplant is the standard screening method.
KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BKV
Is non specific , costy ,and need to be verified by plasma PCR
Plasma BK PCR
Precise viral loads measurement is difficult due to inter-assay variability , WHO introduced an international standard to standardize viral load values among different laboratories meanwhile some variabilities exist due to PCR primer design DNA extraction techniques variation also rare genotypes can be missed due to low viral load.
Urine cytology
Decoy cells are characteristic BKV infected cells harbouring owl eye inclusion in urine cytology mimicking renal cell carcinoma cells but decoy cell presence doesnot necessary indicate PVN.
Polyomavirus-Haufen screening in urine harbours high positive and negative predictive values for
BK nephropathy.
Donor-Derived Cell-Free DNA (dd-cfDNA)
dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN and histologic features in accordance with Banff criteria of T-cell-mediated rejection ,which can be indicative of progression to BKVAN.
Renal graft biopsy
It is the gold standard for diagnosis with particular considerations including multiple core biopsies and involving the medulla .
Pathological findings include;
· Characteristic cytopathic changes including tubular epithelial cells affection with ground glass” intranuclear inclusions, these cells can slough from basement membrane into the tubular lumen and spread infection leading to tubulitis and interstitial inflammation ending in tubular atrophy and interstitial fibrosis
· positive immunohistochemistry tests using Ab against BKV or cross reacting with SV40 large T Ag
BKVAN diagnosis is likely with plasma BK viral load ≥10,000 copies/mL
The focal ,random nature ,medullda involvement can increase missing risk to 30%
PV can be detected on electron microscopy as well
Differentiation between AR and PVN can be challenging ,eventually both can be present at the same time ,therefore the existence of the common histological features in the absence of immunohistochemical evidence render AR more likely .
Several grading systems were proposed including viral cytopathic effect, injury, and atrophy to classify cases.
Banff score incorporates the degree of morphologic evidence of PV infection and interstitial fibrosis
to classify biopsies.
Treatment
Reduction of immunosuppression is the main core of therapy
It can be implicated by halving antimetabolite dose and maintain CNI and/or prednisone dose along with monitoring serum creatinine and serial plasma BK PCR levels from the same lab every 2 weeks .
If viral loads remain the same or increase anti-metabolite can be stopped afterwards CNI trough goals can be decreased if viral loads do not reduce over 4 weeks.
Other therapies include
IVIG
It is the only viable adjunctive therapy.
Quinolones
As a prophylaxis in the immediate post-transplant period or as treatment for BK viremia ,quinolones were not effective
Cidofovir
It’s major limitation is it’s nephrotoxic effect
Leflunamide
Harbouring immunosuppressive and anti-viral properties ,did not show efficacy for BKV therapy in studies .
Therapeutic trials
Modified T cells and monoclonal antibodies as a therapeutic option for BK infection are under study
Kidney Re-Transplantation
After BKVAN can be considered after confirmation of viral clearance
Allograft survival in re-transplantation cases is 98% at 1 year and 94% at 3 years.
5-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
Conclusions
BK virus infection is a common clinical disease faced by transplant providers with it’s challenging diagnosis due to similar histological findings with AR.
Screening improved the detection and lessened disease severity
Immunosuppression reduction is the only option for therapy till now
New therapeutic modalities are under trial.
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Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in kidney transplant recipients.
The successful advent of increasingly efficacious immunosuppression has been accompanied by high rates of BK viremia(BKV) in up to 30% of kidney transplant recipients
Virology
BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus and member of the Polyomaviridae family.
The genome of the virus consists of three regions—the early coding region of the large T and small t antigens, the non-coding control region, and the late coding region.
The non-coding control region are a significant contributor to the pathogenesis of the virus since it contains the origin of replication and enhancer elements that can modulate transcription.
Mutations in the non-coding control region result in permit replication in other cell types, cell tropism, and altered rates of replication.
BK virus loads in kidney transplant recipients with clinically significant viral replication
The late-coding region codes for the agnoprotein and viral capsid proteins (VP-1, VP-2, and VP-3).
VP-3leads to activation of the adenosine diphosphate-ribose polymerase, resulting in depletion of adenosine triphosphate” target=”_blank”
Epidemiology
BK viral infection could be considered ubiquitous in the general population, with seroprevalence rates of over 90% by 4 years of age.
After the onset of viruria, nearly 50% of kidney transplant recipients develop viremia during a period of 2–6 weeks, with a similar proportion of viremic patients developing BKVAN in the aforementioned time period .
Intensity of immunosuppression: This is considered as the most significant factor associated with BK viral replication.
This is based on the finding that the incidence of BK viremia is highest in the early post-transplant period given the magnitude of immunosuppression.
It is pertinent to note the presence of BK viremia reflects a higher level of immunosuppression and its occurrence with or without BKVAN is in the setting of all maintenance immunosuppressive agents/combinations.
The donor-recipient interface
The high-risk serostatus of donor positive and recipient negative for BK virus .
ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
Donor-related factors: reduced immune response to BK virus, and BK viruria prior to transplant.
Recipient HLA-B51 positivity and the presence of polycystic kidney disease.
Have been shown to be protective factors against the development of BKVAN.
HLA-B51 positivity is associated with the presence of highly immunogenic cytotoxic T cells, which may explain the fivefold reduction in the occurrence of BKVAN in these patients.
Celluluar immune response and pathogenesis
The mitigation and clearance of BK viremia are dependent on a robust cellular immune response—with both CD4 and CD8 cells playing a crucial role in this process.
The presence of ELISPOT measured IFN-gamma activity, indicative of a BK-directed cellular immune response, is associated with the resolution of BKVAN.
The shorter time interval (<1 month) to develop anti-BK T cell response correlates with the clearance of viremia, while patients who develop BKVAN required a median period of 5 months to develop cellular immunity against the virus .
Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues.
This latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression.
BKVAN is associated with increased expression of various major groups of messenger RNAs, including CD8, perforin, interferon-γ, and CXCR3.
The final stage of destruction is characterized by interstitial fibrosis and tubular atrophy, with associated progressive nephron loss.
Clinical manifestations
Most clinically significant infections associated with the BK virus lack any systemic symptoms.
The most common and earliest manifestation of BKV is viruria occurring in up to 50% of patients in the first year of transplantation, with most cases not progressing to viremia.
The checking of urine BK viral loads is not standard practice despite it being a sensitive marker for progression to BKVAN.
This is because of the nonspecific nature of viruria occurring without any risk of progression in pregnant women, Viruses 2022, 14, 1616 4 of 18 older patients, and those with compromised cellular immunity.
There are accumulating reports that there may be an association of the BK virus with the development of urothelial malignancies in transplant recipients, a possibility of confounding exists since patients who develop BKVAN have lowered cellular immunity, and as a result of reduced tumor surveillance are at risk of development of malignancies
Screening and diagnosis
The high incidence of BK viremia in the first post-transplant year has led to the development of standard screening protocols by transplant centers.
Given the low specificity of urine BK viral loads, and higher positive predictive value of plasma BK levels, screening for BK viremia is the preferred method utilized in these protocols.
Fastidious screening and preemptive reduction in immunosuppression for established.
BK viremia have been demonstrated to mitigate progression to BKVAN.
The. Kidney Disease: Improving Global Outcomes (KDIGO) and American Society of Transplantation Infectious Diseases Community of Practice (AST-IDCOP) guidelines recommend monthly screening for the first 6 months post-transplantation and every 3 months for the 18 months.
Plasma BK PCR
BK viral loads are measured by polymerase chain reaction (PCR)—a fluorescent probe. BK-specific sequence, and the number of amplicons produced is compared with a standard curve generated with serial dilutions of a known concentration of BK DNA.
Assay results are influenced by variations in DNA extraction techniques, sample type/source, primer and probe sequences, and BK strain DNA used for standard-curve BK virus genotype variance and discordant BK viremia PCR assay results.
While there has been improvement in the reporting of BK PCR values since the introduction of this international standard in 2016, there continues to be variability among laboratories attributed to PCR primer design DNA extraction techniques and amplicon size.
The genotype I (Dunlop) strain is currently utilized as the reference sequence against which primers and probes are designed for various assays.
BK PCR assays can be four times less sensitive for variant strains when using genotype I as a reference.
This could lead to the non-detection of rarer genotypes, which are being recognized to be more cytopathic and more frequently associated with BKVAN.
Rare genotypes should be considered in the event that BKVAN is co-existent with lower viral loads
Urine cytology
The characteristic BK virus -infected cells that present on cytologic examination of urine are called ′decoy cells′ due to their similarity to renal carcinoma cells
Some studies have shown high false-positive rates and low positive predictive values when attempting to use the presence of decoy cell to screen for PVN in transplant patients.
Some of these studies found the absence of decoy cell in urine cytology screens had high negative predictive values for PVN.
The amount of PV-Haufen shed correlates well with disease severity.
Donor derived cell free DNA
A recent study evaluated the association of dd-cfDNA with plasma BK viral loads and biopsy findings to determine if dd-cfDNA can distinguish asymptomatic BKV from.
BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection.
Transplant kidney biopsy
Kidney allograft biopsy continues to be the gold standard for the diagnosis of BVAN.
It aids, in diagnosis, and in assessing the severity of viral involvement and the presence of other ongoing pathologies.
Positive SV40 staining is useful as it is associated with a specificity of almost 100 percent for polyomavirus nephropathy (PVN); it does not distinguish between BKV and JC virus.
If the initial biopsy is not confirmatory for BKVAN, a repeat biopsy is recommended if clinical suspicions remain
Histology
Identifying the histologic features of polyoma virus infection on renal biopsy is currently the gold standard for the diagnosis of “definitive” BKVAN.
The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis.A presumptive diagnosis of BKVAN is considered in the setting of plasma BK viral load ≥10,000 copies/mL.
The Banff Working Group on Polyomavirus Nephropathy Classification System is a three-tier scoring approach that incorporates the extent of morphologic evidence of PV infection and interstitial fibrosis to classify samples.
Treatment
A reduction in the intensity of immunosuppression is the overarching principle for the treatment of BK viremia and BKVAN.
The following is a stepwise approach for the reduction in immunosuppression in the setting of BK viremia and BKVAN based on trials in adult and pediatric kidney transplant recipients.
The step is to reduce calcineurin-inhibitor trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
Other adjunctive therapies utilized to treat BK virus infection include quinolones, cidofovir, leflunomide, and intravenous immunoglobin.
Intravenous immunoglobin is probably the only viable adjunctive therapy, while the use of the other aforementioned agents is not recommended.
Quinolones
Despite demonstrating anti-viral properties in vitro, randomized trials failed to show efficacy as prophylaxis in the immediate post-transplant period or treatment for BK viremia.
While there was initial enthusiasm for its use in BK virus infection based on a case series, a pharmacodynamic and prospective open-label study showed no benefit.
Another metabolite, FK778, did not demonstrate efficacy in a phase 2, proof-of-concept, randomized, open-label, parallel-group, 6-month study in kidney transplant patients when compared with a reduction in immunosuppression.
Kidney re-transplantation
Patients with graft loss due to BKVAN should be considered for re-transplantation given its extensive evidence of success.
Failed transplant or native nephrectomy is not recommended given the lack of evidence-based guidelines to substantiate this practice and confirmation of viral clearance should be made prior to transplantation.
Consideration for lower immunosuppression should be balanced with the risk of rejection.
Allograft survival in patients who receive re-transplantation is 98% and 94% at 1 and.
In comparison to re-transplanted patients for graft failure from other causes, five-year death-censored graft survival rates were 91% for the BKVAN group and 84% for the non-BKVAN group.
Findings
There was no significant difference in the rates of acute rejection or patient survival at one year.
Conclusion
BK virus infection continues to be one of the most common clinical issues encountered by transplant providers.
Heightened surveillance protocols have led to expedient detection and have mitigated severe disease.
It can be a conundrum from a diagnostic and therapeutic standpoint.
It can be associated with histologic features akin to rejection, with a reduction in immunosuppression being the only viable treatment strategy, which may itself culminate in rejection.
There is no anti-viral currently known to be of benefit in the clearance of the virus.
There is, promise that novel therapeutics may bring efficacy that continues to elude the transplant community
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Please summarise this article
Introduction
· BK virus-associated nephropathy (BKVAN) is an important cause of graft loss
· Rate of BK viremia (BKV) in kidney transplant recipients is 30% (efficacious immunosuppression)
· First discovered in a kidney transplant recipient with ureteric stricture in 1971
· First biopsy proven case of BKVAN in 1993
· Graft loss now <15% (early was 50–100%)
· BK virus is a small, non-enveloped, icosahedral, closed circular, double-stranded DNA virus (Polyomaviridae family)
The genome of the virus consists of three regions:
1. the early coding region of the large T and small t antigens (large and small tumor antigen)
2. the non-coding control region
3. the late coding region
Aim of the study (level V):
Discuss the history of the virus, virology, epidemiology, cellular response, pathogenesis, methods of screening and diagnosis, treatment strategies, upcoming therapeutics, and re-transplantation
Epidemiology
· 90% of the general population has a detectable antibody to BKV by 4 years of age
· Routes for transmission include oral, gastrointestinal, and respiratory tract
· After a primary viremia, BKV largely persists in the kidneys and urinary tract in a latent form
· Infection is either via reactivation of latent infection or transmission of new infection from the donor kidney
· Chronological stages of infection—viruria, viremia, and allograft nephropathy
· Viruria and viremia in 30% and 12% of kidney transplant recipients, respectively
· After viruria, 50% develop viremia during a period of 2–6 weeks, with 50% of viremic patients develop BKVAN in the same time
· Urine BK viral loads >8 log10 c/mL predict the onset of viremia
· Plasma BK viral loads >4 log10 c/mL are associated with higher rates of biopsy-proven BKVAN and loads above 6 log10 c/mL are predictive of extensive BKVN pathology
Risk factors
1. Intensity of immunosuppression (the most important). Tacrolimus may portend a higher risk than cyclosporine. (mTORi) may be associated with lower risk. It reflects a higher level of immunosuppression
2. Recipient-related factors (olderage, diabetes, and specificHLA-Callele)
3. Donor-related factors (reduced immune response to BK virus [48,52] and BK viruria prior to transplant)
4. donor–recipient factors (The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, DGF, rejection or ischemia of the transplanted kidneY, and ureteral stent placement)
Cellular Immune Response and Pathogenesis
*Clearance of BK viremia is dependent on arobust cellular immune response (both CD4 and CD8 cells)
*BK capsid proteins, large T antigen, and non-structural proteins elicit T cell responses
*Latent infection after initial childhood infection in kidney epithelium, mostly in the parietal epithelium of the Bowman’s capsule, renal tubular epithelium, and transitional epithelium
*Other sites of latent infection include prostate, testes, seminiferous tubules, cervix, vulva, and hematolymphoid tissues (peripheral blood mononuclear cells, and tonsils)
*Latent infection can become active with reduced potency of cellular immunity after the introduction of immunosuppression
*Damage to tubular epithelium results from the ensuing viral replication and its cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways
Clinical Manifestations
· Usually no systemic symptoms
· The earliest manifestation of BKV is viruria (50%) in the first year of transplantation, with most cases not progressing to viremia
· Urine BK viral loads is not standard practice
· Sustained viruria may progress to viremia
· Viremia occurs in 10–30 % of recipients in the first 6 months post transplantation and in 5–10 % of recipients thereafter
· Viremia is a better predictor of progression to BKVAN in comparison to viruria
· BKVAN usually manifesting as a decline in renal function with or without urinary abnormalities
· BKVAN occurs mostly in the first post-transplant year (highest incidence is 2-6 months)
· Other manifestations of the BK virus include ureteral stenosis and hemorrhagic cystitis (rare and mostly in patients with hematopoietic stem cell transplants
· Possible link between the BK virus and genitourinary (GU) malignancies
Screening and Diagnosis
Screening for BK viremia is the preferred method
The KDIGO and AST-IDCOP guidelines recommend monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months
Urine BK PCR
· Not recommended for screening (low specificity and cost)
· If positive, it always requires confirmation with plasma PCR
· 50% of patients with viruria will not develop viremia
Plasma BK PCR
· Inter-assay variability makes the accurate measurement of viral loads difficult (WHO established an international standard to standardize viral load values among different laboratory assays when results are expressed as international units/mL)
· BK PCR assayscanbefourtimeslesssensitiveforvariantstrainswhenusinggenotypeIasareference (limit of detection of 10,000 copies/µL for the variant strain compared with 10 copies/µL for genotype I)
Urine Cytology
· BK virus-infected cells on cytologic examination of urine are called decoy cells due to their similarity to renal carcinoma cells
· They are tubular epithelial or urothelial cells with ground-glass nuclear inclusions surrounded by a condensed rim of chromatin
· They may exhibit “owl eye” inclusions, multinucleation, or clumped chromatin
· They are a marker of PV replication, but they do not necessarily indicate PVN
· High false-positive rates and low positive predictive values
· Absence of decoy cells in urine cytology screens has high NPV for PVN
· Urine samples may also be screened for the presence of cast-like PV aggregates, called polyomavirus-Haufen, via negative staining electron microscopy (high positive and negative predictive values for BK nephropathy for presence or absence of PV-Haufen , respectively
Donor-Derived Cell-Free DNA (dd-cfDNA)
· To distinguish asymptomatic BKV from BKVAN
· Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection
· May be a useful noninvasive test to assess for progression of BKV to BKVAN
Transplant kidney biopsy
· The gold standard for the diagnosis of BVAN
· For diagnosis, severity of viral involvement and other pathology
· To decrease sample error, sample should include medulla
· For a definitive diagnosis of BKVAN:
1. Characteristic cytopathic changes
2. Positive immunohistochemistry tests (using antibodies directed against BKV or against the cross-reacting SV40 large T antigen. Specificity of SV40 is 100 but not distinguish between BKV and JCV
Histology:
· The histologic findings of this include tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass”intranuclear inclusions
· Viral cytopathic changes may also include granular nuclear inclusions and “clumps” of intranuclear virion particles
· In the early stages of infection, only rare tubular cells with viral cytopathic changes may be seen, usually in the distal nephron or medulla
· Eventually, these cells lyse and slough from the basement membrane into the tubular lumens
· As the infection progresses, tubulitis and interstitial inflammation with a prominent plasma cell component may be seen
· More proximal portions of the nephron, including the parietal epithelial cells lining Bowman0s capsule, may also become involved
· The tubular cell injury, tubulitis, and interstitial inflammation may result in tubular atrophy and interstitial fibrosis
· Two biopsy cores containing renal cortex and medulla are recommended
· Simian Virus 40 (SV40) IHC stain is recommended in all transplant biopsies where PVN is suspected clinically, but no definitive features of PVN
· There are several grading systems for evaluation of PKN (use viral cytopathic effect, injury, and atrophy for classification)
Treatment
Reduction of of immunosuppression is the main treatment of BK viremia and BKVAN
Approach for reduction:
1. Reduce dose of antimetabolite by 50% and continuing on the same doses of CNIs and/or prednisone. Monitor serum creatinine and serial plasma BK PCR levels from the same laboratory every 2 weeks
2. Complete cessation of anti-metabolite if viral loads continue to be at similar levels or increase
3. Reduce CNIs trough goals if viral loads do not reduce over 4 weeks despite cessation of anti-metabolite (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine)
Other adjunctive therapies:
No difference in graft outcomes when reduction in immunosuppression is compared with a combination of immunosuppression with leflunomide or cidofovir
1. IVIG: probably the only viable adjunctive therapy
2. Quinolones
3. Cidofovir
4. Leflunomide
2, 3, and 4 are not recommended
Upcoming Therapeutic Trials (modified T cells and monoclonal antibodies)
Kidney Re-Transplantation
· Failed transplant or native nephrectomy is not recommended
· Viral clearance prior to transplantation
· Lower immunosuppression before transplantation (balanced with the risk of rejection)
· Allograft survival is 98% and 94% at 1 and 3 years, respectively
Conclusions
· BK virus infection is one of the most common clinical issues faced by transplant recipients
· Surveillance alleviates severe disease
· Immunosuppression reduction is the only viable treatment strategy, which may lead to rejection
· Currently, there is no anti-viral known to be of benefit in the clearance of the virus
· Novel therapy is promising
I like your detailed summary of this article
Thank you prof
Introduction:
Kidney transplant patients often lose grafts because of BK virus-associated nephropathy (BKVAN). Up to 30% of kidney transplant patients have BK viremia (BKV) due to more effective immunosuppression.
Epidemiology:
By 4 years old, 90% of people have a BK virus infection. The virus spreads via oral, gastrointestinal, and respiratory mucosa. The BK virus hides in kidney and uroepithelial cells after initial viremia, causing lifelong latent/persistent infection.
Viral replication is associated with the following risk factors:
1. Intensity of immunosuppression:
2-Age, diabetes, and HLA-C alleles
3. Donor–recipient interface: high-risk serostatus includes donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, kidney rejection or ischemia, and ureteral stent implantation.
4. Donor-related factors: decreased immunological response to BK virus and BK viruria before transplant, and Polycystic kidney disease and HLA-B51 positivity.
Cellular Immunity and Pathogenesis:
A strong cellular immune response—including CD4 and CD8 cells—is needed to reduce and eradicate BK viremia. ELISPOT and tetramer labeling quantify T cell responses to BK capsid proteins, big T antigens, and non-structural proteins.
ELISPOT-measured IFN-gamma activity, which indicates a BK-directed cellular immune response, resolves BKVAN.
Symptoms:
Most BK virus infections are asymptomatic. Kidney transplant patients often develop viruria, viremia, and BKVAN. In the first year after transplantation, up to 50% of patients have viruria, which rarely progresses to viremia. Urine BK virus loads, a sensitive indicator for BKVAN development, are seldom checked.
After prolonged, worsening viremia, BKVAN causes the renal function to decrease with or without urine problems. Given reduced cellular immunity, the first 2–6 months post-transplant are the most common for BKVAN. Ureteral stenosis and hemorrhagic cystitis are BK virus symptoms.
Screening and Diagnosis:
Urine BK-PCR
Plasma BK PCR
Urine Cytology:
DD(dd-cfDNA):
Histopathological features:
Positive IHC tests for SV40 antigen: The stain may highlight cells in the early stages of infection, before viral cytopathic alterations may be evident on conventional stains. -The stain can also highlight cells in the later stages of infection.
A positive SV40 staining is almost unambiguous evidence of BKV infection.
Treatment:
BK viremia and BKVAN are treated by reducing immunosuppression. This virus-associated illness has no treatment, and several medicines fail to reduce viral levels. Multiple immunosuppression-reduction strategies have been proposed, but their efficacy has yet to be tested.
Based on research in adult and juvenile kidney transplant patients, BK viremia and BKVAN immunosuppression may be reduced progressively :
1. Halve antimetabolite dosage while maintaining calcineurin inhibitor and/or prednisone levels. To minimize inter-assay variability, serum creatinine and serial plasma BK PCR levels must be monitored every two weeks from the same lab.
2. Stop antimetabolite if virus loads remain high.
3. Reduce calcineurin-inhibitor trough objectives if viral loads do not decrease after 4 weeks despite stopping anti-metabolites (4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine).
IVIG, BK-neutralizing antibodies, and other adjuvant therapies lower the BKV burden.
Quinolones; anti-viral, significant chance of resistant bacterial infection
Cidofovir is nephrotoxic; leflunomide is immunosuppressive and antiviral.
Kidney Re-Transplant:
Given its success rate, BKVAN patients who lose grafts may consider re-transplantation. Given the dearth of evidence-based guidance, failed transplants or native nephrectomies should be avoided. Before transplantation, virus clearance should be confirmed. balance decreased immunosuppression with rejection risk.
I like your detailed summary of this article
1. Introduction
BK virus-associated nephropathy (BKVAN) is an important cause of graft loss in KTRs. The advancement in effective IS therapy increased the rate BK viremia in up to 30% of KTRs.
2. History of the BK Virus
-It was first discovered in a KTRs who presented with a ureteral stricture in 1971
-It was reported that it resulted in graft loss with rates of 50–100%, this rate reduced to 15 % in the last 2 decades.
3. Virology
– Small double-stranded DNA virus and member of the Polyomaviridae family
– It has 4 different genotypes ( I- IV)
– The genome of the virus consists of three regions; the early coding region of the large T and small t antigens (large and small tumor antigen), the non-coding control region, and the late coding region.
4. Epidemiology
– Highly prevalent in general population with seroprevalence rates of over 90% by 4 years of age.
– Routes for transmission of the virus are from mucosal contact including the oral, gastrointestinal, and respiratory.
– After a primary viremia, the BK virus establishes refuge in the kidney and uroepithelial cells resulting in lifelong latent/persistent infection
– The infection occurs in the following chronological stages—viruria, viremia, and allograft nephropathy.
– Viruria, viremia and BKVAN occurred in 30% , 12% and 1-10 % of KTRs, respectively
Risk factors for viral replication:
-Intensity of immunosuppression : the most significant factor
– Recipient characteristics: older age, diabetes, and specific HLA-C alleles.
-The donor–recipient interface: The high-risk serostatus of donor positive and recipient negative for BK virus, ABO incompatibility, HLA mismatch, delayed graft function, rejection or ischemia of the transplanted kidney, and ureteral stent placement.
-Donor-related factors: reduced immune response to BK virus and BK viruria prior to transplant.
5. Cellular Immune Response and Pathogenesis;
– The virus clearance is dependent on cellular immune response with both CD4 and CD8 cells.
– Currently, various studies are being conducted to assess different assays could be utilized to predict the viral clearance and identify those who might progress to BKVAN.
– After primary infection virus remain latent in the body mainly in kidneys, urogenital epithelium and hematolymphoid tissues.
– In KTRs; latent virus become actively replicated once potency of cellular immunity is reduced by IS.
– Viral exert cytopathic effect, with continued inflammation leading to the activation of pro-fibrotic pathways that progress to IFTA and nephron loss.
– The clinical and pathological features in BKVAN and TCMR are similar as BKVAN increase expression of different mRNAs which also increased in TCMR.
6. Clinical Manifestations:
– Mostly have no systemic symptoms.
– Viruria, occur in 50% (the most common and earliest manifestation of BKV )
– Viremia which is a symptomatic initially , occurred after viuria, it is a better predictor of progression to BKVAN in comparison to viruria.
– BKVAN usually occurs after a period of sustained progressively worsening viremia, manifest as a decline in renal function with or without urinary abnormalities.
– Other manifestations: ureteral stenosis and hemorrhagic cystitis, a possible link with genitourinary
(GU) malignancies.
7. Screening and Diagnosis
KDIGO) and AST-IDCOP guidelines recommend; monthly screening for the first 6 months post-transplantation and then every 3 months for the next 18 months.
Urine BK PCR:
It is not a recommended screening test, 50% of patient will not develop viuria, need blood PCR confirmation.
Plasma BK PCR;
Inter-assay variability.
The genotype I strain is used as the reference sequence for designed for various assays
It can be four times less sensitive for variant strains.
Urine Cytology :
Characteristic of infected cells on cytologic examination of are called decoy cells, marker of PV replication, they do not necessarily indicate PVN. It has a high NPV.
Donor-Derived Cell-Free DNA (dd-cfDNA)
Higher dd-cfDNA levels were associated with higher BK viral loads, biopsy-diagnosed BVAN, as well histologic changes meeting Banff criteria for T-cell-mediated rejection
Transplant Kidney Biopsy
The gold standard for diagnosis of BVAN.
Tow Core biopsy should include medulla to decrease the risk of sampling error it might be missed in 30%.
It is used to assess the severity and the presence of other pathology.
Histopathological features for a definitive diagnosis of BKVAN
*Characteristic cytopathic changes:
– Tubular epithelial cells with enlarged, hyperchromatic nuclei and “ground glass” intranuclear inclusions.
– Granular nuclear inclusions and inclusions and “clumps” of intranuclear.
– Tubulitis and interstitial inflammation with a prominent plasma cell component
– May result in tubular atrophy and interstitial fibrosis
* Positive IHC tests SV40 antigen:
-The stain can highlight cells in the early stages of infection, before viral cytopathic changes may be detectable on routine stains
-Positive SV40 staining is almost 100 specific for BKV.
– Help differentiate PVN from other viral nephropathies.
The diagnosis of PVN is difficult due to the histologic similarities shares with acute rejection (AR), and they can occur together, creating a treatment dilemma.
Several grading systems for the evaluation and reporting of PKN, including AST and Banff Working group. These systems use features such as viral cytopathic effect, injury, and atrophy to classify cases.
8.Treatment.
– There is No definitive therapeutic agent available.
-Reduction in the intensity of IS is the mainstay for the treatment with different protocols available.
*Stepwise approach for the reduction in immunosuppression BKv/ BVAN:
-Reduce dose of antimetabolite by 50% while continuing on the same doses of CNI and/or prednisone.
-Monitor; creatinine, BK PCR levels every 2 weeks.
– Discontinuation of of anti-metabolite, if PCR did not improve or increases.
– If no improvement in viral load 4 weeks after stopping antimetabolites, reduce CNI trough goals
(4–6 ng/mL for tacrolimus and 50–100 ng/L for cyclosporine)
– Other adjunctive therapies utilized to treat BK virus infection include:
– IVIG; BK-neutralizing antibodies, reduce BKV load.
– Quinolones; anti-viral properties, high risk for resistant bacterial infection
– Cidofovir; nephrotoxic
– Leflunomid; both immunosuppressive and anti-viral properties.
Upcoming Therapeutic Trials:
– Human monoclonal antibody (IgG1) that binds the viral capsid protein, VP1.
– Multivirus-specific T Cells therapy
9. Kidney Re-Transplantation
– Re-transplantation should be considered for any patient lost graft with BKAN.
– Graft or native nephrectomy is not recommended.
– Consider lower immunosuppression should be balanced with the risk of rejection.
– Allograft survival in retrasplantation is excellent 94%, 5-year death-censored graft survival 91%.
Conclusion:
BKV is one of the most common clinical issues in KTRs. Viral surveillance and early detection and treatment have mitigated severe disease. Reduction in immunosuppression is the only treatment strategy, which may itself increase risk of rejection. Upcoming therapeutic agents are showing promising results.
Level of evidence: 5 narrative review.
I agree with your analysis of level of evidence and summary of this article
Introduction
Risk factors for viremia
A- The intensity of immunosuppression
B- Donor factors
C- Recipient factors
Some factors may be associated with lower incidence of BK viremia including HLA B 51 positivity and PCKD
Clinical presentation of BK virus
Screening of BK virus
Diagnosis
A- Viruria (urine PCR, urine decoy cells)
B- Viremia (PCR )
C- BK nephropathy
Renal biopsy for BK nephropathy
The diagnosis requires the presence of the following:
A- Characteristic cytopathy (not specific) including
And
B- Positive IHC test for SV40 antigen
BK nephropathy is classified into 3 classes
NB : pvl 1 (tubulitis <1%), pvl 2( tubulitis 1-10%), pvl 3 (tubulitis > 10%)
Treatment
Re-transplantation after graft failure due to BK nephropathy
I like your detailed summary of this article
Introduction:
Epidemiology:
Risk factors:
Cellular immune response:
Clinical features:
Screening and diagnosis:
How ?
Treatment: the key thing is to reduce immune-suppression
Re-transplantation:
Conclusion:
I like your summary of this article
Any reply?
Yes prof, here we go