Source and Relevance of the BK Polyomavirus Genotype for Infection After Kidney Transplantation

The Second International Consensus Guidelines on the Management of BK Polyomavirus in Kidney Transplantation

BK polyomavirus (BKPyV) remains a significant challenge after kidney transplantation. International experts reviewed current evidence and updated recommendations according to Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). Risk factors for BKPyV-DNAemia and biopsy-proven BKPyV-nephropathy include recipient older age, male sex, donor BKPyV-viruria, BKPyV-seropositive donor/-seronegative recipient, tacrolimus, acute rejection, and higher steroid exposure. To facilitate early intervention with limited allograft damage, all kidney transplant recipients should be screened monthly for plasma BKPyV-DNAemia loads until month 9, then every 3 mo until 2 y posttransplant (3 y for children). In resource-limited settings, urine cytology screening at similar time points can exclude BKPyV-nephropathy, and testing for plasma BKPyV-DNAemia when decoy cells are detectable. For patients with BKPyV-DNAemia loads persisting >1000 copies/mL, or exceeding 10 000 copies/mL (or equivalent), or with biopsy-proven BKPyV-nephropathy, immunosuppression should be reduced according to predefined steps targeting antiproliferative drugs, calcineurin inhibitors, or both. In adults without graft dysfunction, kidney allograft biopsy is not required unless the immunological risk is high. For children with persisting BKPyV-DNAemia, allograft biopsy may be considered even without graft dysfunction. Allograft biopsies should be interpreted in the context of all clinical and laboratory findings, including plasma BKPyV-DNAemia. Immunohistochemistry is preferred for diagnosing biopsy-proven BKPyV-nephropathy. Routine screening using the proposed strategies is cost-effective, improves clinical outcomes and quality of life. Kidney retransplantation subsequent to BKPyV-nephropathy is feasible in otherwise eligible recipients if BKPyV-DNAemia is undetectable; routine graft nephrectomy is not recommended. Current studies do not support the usage of leflunomide, cidofovir, quinolones, or IVIGs. Patients considered for experimental treatments (antivirals, vaccines, neutralizing antibodies, and adoptive T cells) should be enrolled in clinical trials.

The risk factors associated with post-transplantation BKPyV nephropathy and BKPyV DNAemia: a prospective study in kidney transplant recipients

BACKGROUND

BK polyomavirus (BKPyV) infection after kidney transplantation can lead to serious complications such as BKPyV-associated nephropathy (BKPyVAN) and graft loss. The aim of this study was to investigate the incidence of BKPyVAN after implementing a BKPyV screening program, to map the distribution of BKPyV genotypes and subtypes in the Uppsala-Örebro region and to identify host and viral risk factors for clinically significant events.

METHODS

This single-center prospective cohort study included kidney transplant patients aged ≥ 18 years at the Uppsala University Hospital in Sweden between 2016 and 2018. BKPyV DNA was analyzed in plasma and urine every 3 months until 18 months after transplantation. Also genotype and subtype were determined. A logistic regression model was used to analyze selected risk factors including recipient sex and age, AB0 incompatibility and rejection treatment prior to BKPyVAN or high-level BKPyV DNAemia.

RESULTS

In total, 205 patients were included. Of these, 151 (73.7%) followed the screening protocol with 6 plasma samples, while184 (89.8%) were sampled at least 5 times. Ten (4.9%) patients developed biopsy confirmed BKPyVAN and 33 (16.1%) patients met criteria for high-level BKPyV DNAemia. Male sex (OR 2.85, p = 0.025) and age (OR 1.03 per year, p = 0.020) were identified as significant risk factors for developing BKPyVAN or high-level BKPyV DNAemia. BKPyVAN was associated with increased viral load at 3 months post transplantation (82,000 vs. < 400 copies/mL; p = 0.0029) and with transient, high-level DNAemia (n = 7 (27%); p < 0.0001). The most common genotypes were subtype Ib2 (n = 50 (65.8%)) and IVc2 (n = 20 (26.3%)).

CONCLUSIONS

Male sex and increasing age are related to an increased risk of BKPyVAN or high-level BKPyV DNAemia. BKPyVAN is associated with transient, high-level DNAemia but no differences related to viral genotype were detected.

BK polyomavirus: latency, reactivation, diseases and tumorigenesis

The identification of the first human polyomavirus BK (BKV) has been over half century, The previous epidemiological and phylogenetic studies suggest that BKV prevailed and co-evolved with humans, leading to high seroprevalence all over the world. In general, BKV stays latent and symptomless reactivation in healthy individuals. BKV has been mainly interlinked with BKV-associated nephropathy (BKVAN) in kidney-transplant recipients and hemorrhagic cystitis (HC) in hematopoietic stem cell transplant recipients (HSCTRs). However, the mechanisms underlying BKV latency and reactivation are not fully understood and lack of extensive debate. As Merkel cell polyomavirus (MCV) was identified as a pathogenic agent of malignant cutaneous cancer Merkel cell carcinoma (MCC) since 2008, linking BKV to tumorigenesis of urologic tumors raised concerns in the scientific community. In this review, we mainly focus on advances of mechanisms of BKV latency and reactivation, and BKV-associated diseases or tumorigenesis with systematical review of formerly published papers following the PRISMA guidelines. The potential tumorigenesis of BKV in two major types of cancers, head and neck cancer and urologic cancer, was systematically updated and discussed in depth. Besides, BKV may also play an infectious role contributing to HIV-associated salivary gland disease (HIVSGD) presentation. As more evidence indicates the key role of BKV in potential tumorigenesis, it is important to pay more attention on its etiology and pathogenicity in vitro and in vivo.

Stepwise Reduction of Mycophenolate Mofetil with Conversion to Everolimus for the Treatment of Active BKV in Kidney Transplant Recipients: A Single-Center Experience in Vietnam

Background: No specific antiviral drug can effectively treat BKV reactivation after kidney transplantation. Thus, we evaluated stepwise-reduced immunosuppression to treat BKV reactivation. Methods: 341 kidney-transplant recipients were monitored for BKV infection (BKV-viremia, BKV-viruria). Positive samples with a significant virus load were nested PCR-genotyped in the VP1 region. In 97/211 patients presenting BKV viremia ≥104 copies/mL and/or BKV viruria ≥107 copies/mL, or BKV-nephropathy immunosuppression (i.e., mycophenolate mofetil [MMF]) was reduced by 50%. If viral load did not decrease within 28 days, MMF dose was further reduced by 25%, although calcineurin-inhibitor (CNI) therapy remained unchanged. If BKV viral load did not decrease within another 28 days, MMF was withdrawn and replaced by everolimus combined with reduced CNIs. Results: Only 41/97 BKV (+) cases completed the 6-month follow-up. Among these, 29 (71%) were in the BKV-I group and 12 (29%) were in BKV-IV. BKV viruria and BKV viremia were significantly decreased from 9.32 to 6.09 log10 copies/mL, and from 3.59 to 2.45 log10 copies/mL (p < 0.001 and p = 0.024, respectively). 11/32 (34.4%) patients were cleared of BKV viremia; 2/32 (6.3%) patients were cleared of BKV in both serum and urine, and 9/9 (100%) only had BKV viruria but did not develop BKV viremia. eGFR remained stable. No patient with BKV-related nephropathy had graft loss. There was a significant inverse relationship between changes in eGFR and serum BKV load (r = −0.314, p = 0.04). Conclusions: This stepwise immunosuppressive strategy proved effective at reducing BKV viral load in kidney transplant recipients that had high BKV loads in serum and/or urine. Renal function remained stable without rejection.

Polyomavirus BK Genome Comparison Shows High Genetic Diversity in Kidney Transplant Recipients Three Months after Transplantation

BK polyomavirus (BKPyV) is a human DNA virus generally divided into twelve subgroups based on the genetic diversity of Viral Protein 1 (VP1). BKPyV can cause polyomavirus-associated nephropathy (PVAN) after kidney transplantation. Detection of BKPyV DNA in blood (viremia) is a source of concern and increase in plasma viral load is associated with a higher risk of developing PVAN. In this work, we looked for possible associations of specific BKPyV genetic features with higher plasma viral load in kidney transplant patients. We analyzed BKPyV complete genome in three-month samples from kidney recipients who developed viremia during their follow-up period. BKPyV sequences were obtained by next-generation sequencing and were de novo assembled using the new BKAnaLite pipeline. Based on the data from 72 patients, we identified 24 viral groups with unique amino acid sequences: three in the VP1 subgroup IVc2, six in Ib1, ten in Ib2, one in Ia, and four in II. In none of the groups did the mean plasma viral load reach a statistically significant difference from the overall mean observed at three months after transplantation. Further investigation is needed to better understand the link between the newly described BKPyV genetic variants and pathogenicity in kidney transplant recipients.

Genomic Mutations of BK Polyomavirus in Patients after Kidney Transplantation: A Cross-Sectional Study in Vietnam

Objectives: The purpose of this study was to identify the SNP sites and determine the BKV genotype circulating in kidney-transplant Vietnamese recipients based on the VP1 gene region. Methods: 344 samples were collected from post-kidney-transplant recipients at the 103 Vietnam Military Hospital to investigate the number of BKV infections. Positive samples with a sufficient virus concentration were analyzed by nested PCR in the VP1 region, sequencing detected genotyping and single-nucleotide polymorphism. Results: BKV infection was determined in 214 patients (62.2%), of whom 11 (5.1%) were diagnosed with BKV-associated nephropathy. Among the 90 BKV-I strains sequenced, 89 (98.88%) were strains of I/b-1 and 1 (1.12%) was strain I/b-2. The 60 BKV-IV strains had a greater diversity of subgroups, including 40% IV/a-1, 1.66% IV/a-2, 56.68% IV/c-1, and 1.16% IV/c-2. Additionally, of 11 cases diagnosed with BKVN, seven belonged to subgroup I/b-1 (63.6%) and four to subgroup IV/c-1 (36.4%). Moreover, 22 specific SNPs that were genotype I or IV were determined in this Vietnamese population. Specifically, at position 1745, for the Vietnamese BKV-IV strains, the SNP position (A→G) appeared in 57/60 samples (95%). This causes transformation of the amino acid N→S. This SNP site can enable detection of genotype IV in Vietnam. It represents a unique evolution pattern and mutation that has not been found in other international strains. Conclusion: The BKV-I genotype was more common than BKV-IV; however, mutations that occur on the VP1 typing region of BKV-IV strains were more frequent than in BKV-I strains.

Torque teno virus loads after kidney transplantation predict allograft rejection but not viral infection

The main challenge of immunosuppressive therapy after solid organ transplantation is to create a new immunological balance that prevents organ rejection and does not promote opportunistic infection. Torque teno virus (TTV), a ubiquitous and non-pathogenic single-stranded DNA virus, has been proposed as a marker of functional immunity in immunocompromised patients. Here we investigate whether TTV loads predict the risk of common viral infection and allograft rejection in kidney transplantation recipients. In a retrospective cohort of 389 kidney transplantation recipients, individual TTV loads in were measured by qPCR in consecutive plasma samples during one year follow-up. The endpoints were allograft rejection, BK polyomavirus (BKPyV) viremia and cytomegalovirus (CMV) viremia. Repeated TTV measurements and rejection and infection survival data were analysed in a joint model. During follow-up, TTV DNA detection in the transplant recipients increased from 85 to 100%. The median viral load increased to 10⁷ genome copies/ml within three months after transplantation. Rejection, BKPyV viremia and CMV viremia occurred in 23%, 27% and 17% of the patients, respectively. With every 10-fold TTV load-increase, the risk of rejection decreased considerably (HR: 0.74, CI 95%: 0.71-0.76), while the risk of BKPyV and CMV viremia remained the same (HR: 1.03, CI 95%: 1.03-1.04 and HR: 1.01, CI 95%: 1.01-1.01). In conclusion, TTV load kinetics predict allograft rejection in kidney transplantation recipients, but not the BKPyV and CMV infection. The potential use of TTV load levels as a guide for optimal immunosuppressive drug dosage to prevent allograft rejection deserves further validation.

Non-permissive human conventional CD1c+ dendritic cells enable trans-infection of human primary renal tubular epithelial cells and protect BK polyomavirus from neutralization

The BK polyomavirus (BKPyV) is a ubiquitous human virus that persists in the renourinary epithelium. Immunosuppression can lead to BKPyV reactivation in the first year post-transplantation in kidney transplant recipients (KTRs) and hematopoietic stem cell transplant recipients. In KTRs, persistent DNAemia has been correlated to the occurrence of polyomavirus-associated nephropathy (PVAN) that can lead to graft loss if not properly controlled. Based on recent observations that conventional dendritic cells (cDCs) specifically infiltrate PVAN lesions, we hypothesized that those cells could play a role in BKPyV infection. We first demonstrated that monocyte-derived dendritic cells (MDDCs), an in vitro model for mDCs, captured BKPyV particles through an unconventional GRAF-1 endocytic pathway. Neither BKPyV particles nor BKPyV-infected cells were shown to activate MDDCs. Endocytosed virions were efficiently transmitted to permissive cells and protected from the antibody-mediated neutralization. Finally, we demonstrated that freshly isolated CD1c⁺ mDCs from the blood and kidney parenchyma behaved similarly to MDDCs thus extending our results to cells of clinical relevance. This study sheds light on a potential unprecedented CD1c⁺ mDC involvement in the BKPyV infection as a promoter of viral spreading.

Dr Sylvia Gardner first discovered the BK polyomavirus (BKPyV) in the urine of a kidney-transplant recipient in 1970. In the 1990’s, the widespread use of potent immunosuppressive drugs such as tacrolimus, sirolimus or mycophenolate mofetil led to the emergence of BKPyV nephropathy. Recently, various studies reported a specific influx of myeloid dendritic cells (mDCs) in the renal tissue of kidney-transplant patients who were diagnosed with a BKPyV nephropathy. MDCs are immune cells both residing in tissues and migrating to other organs or compartments like the blood when changes in their environment occur. Their main functions are the detection of danger signals such as pathogens or tumors and the processing of antigens to prime naïve specific effectors of the adaptive immune response. Although anti-BKPyV cellular immune responses have been investigated in post-transplant recipients as well as healthy individuals, supporting an active role of mDCs little is known about how mDCs and BKPyV interact with each other. Our study provides the basis to understand the role played by mDCs in virus capture through an unprecedented endocytic mechanism and possibly in viral protection from neutralization by specific antibodies. Moreover, we showed that mDCs are unable to sense BKPyV particles or BKPyV-infected dying cells as a danger signal, supporting the view that other DC subsets might act as the true antigen presenting cells that promote the adaptive immune response against BKPyV infection.

The Role of HLA and KIR Immunogenetics in BK Virus Infection after Kidney Transplantation

BK virus (BKV) is a polyomavirus with high seroprevalence in the general population with an unremarkable clinical presentation in healthy people, but a potential for causing serious complications in immunosuppressed transplanted patients. Reactivation or primary infection in kidney allograft recipients may lead to allograft dysfunction and subsequent loss. Currently, there is no widely accepted specific treatment for BKV infection and reduction of immunosuppressive therapy is the mainstay therapy. Given this and the sequential appearance of viruria-viremia-nephropathy, screening and early detection are of utmost importance. There are numerous risk factors associated with BKV infection including genetic factors, among them human leukocyte antigens (HLA) and killer cell immunoglobulin-like receptors (KIR) alleles have been shown to be the strongest so far. Identification of patients at risk for BKV infection would be useful in prevention or early action to reduce morbidity and progression to frank nephropathy. Assessment of risk involving HLA ligands and KIR genotyping of recipients in the pre-transplant or early post-transplant period might be useful in clinical practice. This review summarizes current knowledge of the association between HLA, KIR and BKV infection and potential future directions of research, which might lead to optimal utilization of these genetic markers.

Clinical Efficacy of Intravenous Immunoglobulin for BK Polyomavirus-Associated Nephropathy After Living Kidney Transplantation

Purpose

BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) is one of the most difficult infections to be treated after kidney transplantation. Although patients with BKPyVAN usually received a reduction of immunosuppressive agents, the majority of these patients undergo the loss of the graft kidney without any effective treatment afterward. Therefore, development of more effective therapy for BKPyVAN is eagerly expected.

Patients and Methods

Among patients who underwent a kidney transplantation between January 2016 and April 2019 at our hospital, there were five cases of BKPyVAN. After the initial diagnosis, all patients discontinued administration of mycophenolate mofetil (MMF), which was not enough to diminish decoy cells in urine cytology test. Therefore, all patients received additional intravenous immunoglobulin (IVIG) (100 mg/kg/day) therapy for five days and were evaluated for the therapeutic effect of IVIG with immunohistochemical examination using re-biopsy samples of the graft kidney.

Results

After IVIG therapy, 2 cases showed negative decoy cells in urine and 3 cases showed a drastic decrease of plasma BK virus load. Importantly, simian virus (SV) 40 large T antigens diminished after IVIG administration in all cases, which degraded polyomavirus nephropathy classification.

Conclusion

Although it is difficult to treat BKPyVAN after kidney transplant, IVIG therapy was considered to a promising treatment to improve severity of BKPyVAN especially in cases that dose reduction of immunosuppressive agents was ineffective.

Early fulminant BK polyomavirus-associated nephropathy in two kidney transplant patients with low neutralizing antibody titers receiving allografts from the same donor

BACKGROUND

BK Polyomavirus (BKPyV) causes premature graft failure in 1 to 15% of kidney transplant (KT) recipients. High-level BKPyV-viruria and BKPyV-DNAemia precede polyomavirus-associated nephropathy (PyVAN), and guide clinical management decisions. In most cases, BKPyV appears to come from the donor kidney, but data from biopsy-proven PyVAN cases are lacking. Here, we report the early fulminant course of biopsy-proven PyVAN in two male KT recipients in their sixties, receiving kidneys from the same deceased male donor.

CASE PRESENTATIONS

Both recipients received intravenous basiliximab induction, and maintenance therapy consisting of tacrolimus (trough levels 3-7 ng/mL from time of engraftment), mycophenolate mofetil 750 mg bid, and prednisolone. At 4 weeks post-transplant, renal function was satisfactory with serum creatinine concentrations of 106 and 72 μmol/L in recipient #1 and recipient #2, respectively. Plasma BKPyV-DNAemia was first investigated at 5 and 8 weeks post-transplant being 8.58 × 104 and 1.12 × 106 copies/mL in recipient #1 and recipient #2, respectively. Renal function declined and biopsy-proven PyVAN was diagnosed in both recipients at 12 weeks post-transplant. Mycophenolate mofetil levels were reduced from 750 mg to 250 mg bid while tacrolimus levels were kept below 5 ng/mL. Recipient #2 cleared BKPyV-DNAemia at 5.5 months post-transplant, while recipient #1 had persistent BKPyV-DNAemia of 1.07 × 105 copies/mL at the last follow-up 52 weeks post-transplant. DNA sequencing of viral DNA from early plasma samples revealed apparently identical viruses in both recipients, belonging to genotype Ib-2 with archetype non-coding control region. Retrospective serological work-up, demonstrated that the donor had high BKPyV-IgG-virus-like particle ELISA activity and a high BKPyV-genotype I neutralizing antibody titer, whereas both KT recipients only had low neutralizing antibody titers pre-transplantation. By 20 weeks post-transplant, the neutralizing antibody titer had increased by > 1000-fold in both recipients, but only recipient #2 cleared BKPyV-DNAemia.

CONCLUSIONS

Low titers of genotype-specific neutralizing antibodies in recipients pre-transplant, may identify patients at high risk for early fulminant donor-derived BKPyV-DNAemia and PyVAN, but development of high neutralizing antibody titers may not be sufficient for clearance.

Human BK and JC polyomaviruses: Molecular insights and prevalence in Asia

Polyomaviridae family consists of small circular dsDNA viruses. Out of the 14 human polyomaviruses described so far, BKPyV and JCPyV have been studied extensively since their discovery in 1971. Reportedly, both BKPyV and JCPyV are widely distributed across the globe with the frequency of 80-90 % in different populations. The primary infection of these viruses is usually asymptomatic and latent which is activated as a consequence of immunosuppression. Activated BKPyV and JCPyV viruses lead to the development of BK Virus Associated Nephropathy and Progressive Multifocal Leukoencephalopathy, respectively. Immense progress has been made during the last few decades regarding the molecular understanding of polyomaviruses. Epidemiology of polyomaviruses has also been studied extensively. However, most of the epidemiological studies have focused on European and American populations. Therefore, limited data is available regarding the geographical distribution of these potentially oncogenic viruses in Asian countries. In this article, we have presented a compendium of latest advances in the molecular understanding of polyomaviruses and their pathobiology. We also present a comprehensive review of published literature regarding the epidemiology and prevalence of BKPyV and JCPyV in Asian regions. For this purpose, a thorough search of available online resources was performed. As a result, we retrieved 24 studies for BKPyV and 22 studies for JCPyV, that describe their prevalence in Asia. These studies unanimously report high occurrence of both BKPyV and JCPyV in Asian populations. The available data from these studies was categorized into two groups: on the basis of prevalence (low, medium and high) and disease development (healthy and diseased). Altogether, Korean population hasbeen evidenced to possess highest frequency of BKPyV (66.7 %), while JCPyV was found to be most prevalent in Taiwan (88 %). Due to high and ubiquitous distribution of these viruses, frequent studies are required to develop a better understanding regarding the epidemiology and pathobiology of these viruses in Asia.