Allogeneic CD4 T Cells Sustain Effective BK Polyomavirus-Specific CD8 T Cell Response in Kidney Transplant Recipients.

Introduction: BK polyomavirus-associated nephropathy (BKPyVAN) is a significant complication in kidney transplant recipients (KTRs), associated with a higher level of plasmatic BK polyomavirus (BKPyV) replication and leading to poor graft survival. Methods: We prospectively followed-up with 100 KTRs with various degrees of BKPyV reactivation (no BKPyV reactivation, BKPyV-DNAuria, BKPyV-DNAemia, and biopsy-proven BKPyVAN [bp-BKPyVAN], 25 patients per group) and evaluated BKPyV-specific T cell functionality and phenotype. Results: We demonstrate that bp-BKPyVAN is associated with a loss of BKPyV-specific T cell proliferation, cytokine secretion, and cytotoxic capacities. This severe functional impairment is associated with an overexpression of lymphocyte inhibitory receptors (programmed cell death 1 [PD1], cytotoxic T lymphocyte-associated protein 4, T cell immunoreceptor with Ig and ITIM domains, and T cell immunoglobulin and mucin domain-containing-3), highlighting an exhausted-like phenotype of BKPyV-specific CD4 and CD8 T cells in bp-BKPyVAN. This T cell dysfunction is associated with low class II donor-recipient human leukocyte antigen (HLA) divergence. In contrast, in the context of higher class II donor-recipient HLA (D/R-HLA) divergence, allogeneic CD4 T cells can provide help that sustains BKPyV-specific CD8 T cell responses. In vitro, allogeneic HLA-mismatched CD4 T cells rescue BKPyV-specific CD8 T cell responses. Conclusion: Our findings suggest that in KTRs, allogeneic CD4 T cells can help to maintain an effective BKPyV-specific CD8 T cell response that better controls BKPyV replication in the kidney allograft and may protect against BKPyVAN.

Risk factors and outcome of BK polyomavirus infection in pediatric kidney transplantation.

BACKGROUND: BK polyomavirus (BKV) infection is a critical complication hindering graft survival after kidney transplantation. We aimed to investigate the risk factors and outcome of BKV infection in pediatric kidney transplantation. METHODS: The clinical and follow-up data of pediatric kidney transplant recipients at the Children's Hospital of Fudan University from Jan 2015 to June 2023 were retrospectively analyzed. RESULTS: A total of 217 patients were included in the study with mean follow-up time of 24.3 ± 19.9 months. The mean age at transplantation was 9.7 ± 4.2 years. The patient survival rate and graft survival rate were 98.2% and 96.8%, respectively. Twenty-nine patients (13.4%) developed BKV infection, which was detected at 5.8 ± 3.2 months after transplantation. Among these 29 patients with BKV infection, 8 patients (3.6%) developed BKV nephropathy (BKVN), which was diagnosed at 8.3 ± 2.9 months after transplantation, and 2 patients developed graft failure eventually. Compared with the non-BKV infection group (eGFR 76.7 ± 26.1 mL/min/1.73 m2) and BKV infection without BKVN group (eGFR 85.2 ± 23.8 mL/min/1.73 m2), BKVN group had lowest eGFR during follow-up (33.5 ± 11.0 ml/min/1.73 m2, P < 0.001). Younger age at transplant (OR 0.850, 95%CI 0.762-0.948, P = 0.005), CAKUT disease of primary etiology (OR 2.890, 95%CI 1.200-6.961, P = 0.018), and CMV negative recipient serostatus before transplantation (OR 3.698, 95%CI 1.583-8.640, P = 0.003) were independent risk factors for BKV infection. CONCLUSIONS: Incidence of BKV infection is quite high within 12 months after pediatric kidney transplantation and children with BKVN have poor graft function. Younger age at transplant, CAKUT disease, and CMV negative recipient serostatus before transplantation increase the risk of BKV infection after kidney transplantation.

Nonclinical and clinical characterization of MAU868, a novel human-derived monoclonal neutralizing antibody targeting BK polyomavirus VP1.

Reactivation of BK polyomavirus (BKPyV) can cause significant kidney and bladder disease in immunocompromised patients. There are currently no effective, BKPyV-specific therapies. MAU868 is a novel, human immunoglobulin (Ig) G1 monoclonal antibody that binds the major capsid protein, VP1, of BKPyV with picomolar affinity, neutralizes infection by the 4 major BKPyV genotypes (EC50 ranging from 0.009-0.093 µg/mL; EC90 ranging from 0.102-4.160 µg/mL), and has comparable activity against variants with highly prevalent VP1 polymorphisms. No resistance-associated variants were identified in long-term selection studies, indicating a high in vitro barrier-to-resistance. The high-resolution crystal structure of MAU868 in complex with VP1 pentamer identified 3 key contact residues in VP1 (Y169, R170, and K172). A first-in-human study was conducted to assess the safety, tolerability, and pharmacokinetics of MAU868 following intravenous and subcutaneous administration to healthy adults in a randomized, placebo-controlled, double-blinded, single ascending dose design. MAU868 was safe and well-tolerated. All adverse events were grade 1 and resolved. The pharmacokinetics of MAU868 was typical of a human IgG, with dose-proportional systemic exposure and an elimination half-life ranging between 23 and 30 days. These results demonstrate the potential of MAU868 as a first-in-class therapeutic agent for the treatment or prevention of BKPyV disease.

BK polyomavirus infection: more than 50 years and still a threat to kidney transplant recipients.

BK polyomavirus (BKPyV) is a ubiquitous human polyomavirus and a major infection after kidney transplantation, primarily due to immunosuppression. BKPyV reactivation can manifest as viruria in 30%-40%, viremia in 10%-20%, and BK polyomavirus-associated nephropathy (BKPyVAN) in 1%-10% of recipients. BKPyVAN is an important cause of kidney graft failure. Although the first case of BKPyV was identified in 1971, progress in its management has been limited. Specifically, there is no safe and effective antiviral agent or vaccine to treat or prevent the infection. Even in the current era, the mainstay approach to BKPyV is a reduction in immunosuppression, which is also limited by safety (risk of de novo donor specific antibody and rejection) and efficacy (graft failure). However, recently BKPyV has been getting more attention in the field, and some new treatment strategies including the utilization of viral-specific T-cell therapy are emerging. Given all these challenges, the primary focus of this article is complications associated with BKPyV, as well as strategies to mitigate negative outcomes.

Possible association between polyomaviruses and gastrointestinal complications: a narrative review.

Polyomaviruses are a group of small, double-stranded DNA viruses that are known to be associated with the development of certain human diseases, but there is evidence that these viruses might be associated with gastrointestinal (GI) cancers. Several polyomaviruses have been identified, such as JC polyomavirus (JCPyV), BK polyomavirus (BKPyV) and recently Merkel cell polyomavirus (MCPyV). Although the direct effects of polyomaviruses on transformation of human cells and cancer development are not clearly recognized, their association with certain human diseases including GI cancers has been proposed through several molecular and epidemiological studies. For example, JCPyV and BKPyV have been linked to colorectal cancer, as there is growing evidence of finding viral genomes in cancerous tissues. Nevertheless, the major role of JCPyV, BKPyV and MCPyV in colorectal cancer progression is still under extensive investigation, and further surveys is required to establish a conclusive cause-and-effect relationship. Understanding the role of these viruses in cancer development has significant implications for diagnosis, treatment, and prevention strategies. It seems that proving a causal link between polyomaviruses and GI cancers might provide a novel path for targeted therapies or design and development of specific therapeutic vaccines. In addition, performing research on the possible link can provide insights into the underlying molecular mechanisms of carcinogenesis, potentially leading to the identification of novel biomarkers. This review focuses on polyomaviruses, in particular a recently discovered polyomavirus, MCPyV, and their possible link with human gastrointestinal disorders.

BK Polyomavirus in Pediatric Renal Transplantation-What We Know and What We Do Not.

BK polyomavirus (BKPyV) is still a real threat in the management of kidney transplantation. Immunosuppressive treatment disrupts the equilibrium between virus replication and immune response, and uncontrolled BKPyV replication leads to nephropathy (BKPyV nephropathy). The first evidence of BKPyV reactivation in transplant recipients is the detection of viral shedding in urine, which appears in 20% to 60% of patients, followed by BKPyV viremia in 10-20% of kidney transplant recipients. BKPyV nephropathy eventually occurs in 1-10% of this population, mainly within the first 2 years post-transplantation, causing graft loss in about half of those patients. Few data exist regarding the pediatric population and we focus on them. In this paper, we review the existing diagnostic methods and summarize the evidence on the role of BKPyV humoral and cellular immunity in modulating the clinical course of BKPyV infection and as potential predictors of the outcome. We look at the known risk factors for BKPyV nephropathy in the immunosuppressed patient. Finally, we propose a sensible clinical attitude in order to screen and manage BKPyV infection in kidney transplant children.

Management strategies for common viral infections in pediatric renal transplant recipients.

Viral infections have been considered as a major cause of morbidity and mortality after kidney transplantation in pediatric cohort. Children are at high risk of acquiring virus-related complications due to immunological immaturity and the enhanced alloreactivity risk that led to maintenance of high immunosuppressive regimes. Hence, prevention, early detection, and prompt treatment of such infe ctions are of paramount importance. Among all viral infections, herpes viruses (herpes simplex virus, varicella zoster virus, Epstein-Barr virus, cytomegalovirus), hepatitis B and C viruses, BK polyomavirus, and respiratory viruses (respiratory syncytial virus, parainfluenza virus, influenza virus and adenovirus) are common in kidney transplant recipients. These viruses can cause systemic disease or allograft dysfunction affecting the clinical outcome. Recent advances in tech nology and antiviral therapy have improved management strategies in screening, monitoring, adoption of prophylactic or preemptive therapy and precise trea tment in the immunocompromised host, with significant impact on the outcome. This review discusses the etiology, screening and monitoring, diagnosis, pre vention, and treatment of common viral infections in pediatric renal transplant recipients.

Uncommon BK polyomaviruses detected in allogeneic hematopoietic cell transplant recipients.

The role of viral diversity in the pathogenesis of BK polyomavirus (BKPyV)-associated disease is poorly understood. Here, we report near full-length BKPyV genome sequences from two allogeneic hematopoietic cell transplant recipients infected with BKPyV genotype II, which is uncommon in the USA.

Cell-Free Mitochondrial DNA: An Upcoming Non-Invasive Tool for Diagnosis of BK Polyomavirus-Associated Nephropathy.

Mitochondria are essential organelles that possess their own DNA. Mitochondrial dysfunction has been revealed in many kidney diseases, including BK polyomavirus-associated nephropathy (BKPyVAN). In this study, we introduce an innovative approach for non-invasive monitoring of mitochondrial impairment through urinary donor-derived cell-free mitochondrial DNA (ddcfmtDNA), addressing the crucial challenge of BKPyVAN diagnosis. Urinary samples were collected at the time of biopsy from a total of 60 kidney transplant recipients, comprising 12 with stable function, 22 with T cell-mediated rejection, and 21 with biopsy-proven BKPyVAN. Our findings reveal that the ddcfmtDNA-to-ddcfDNA ratio exhibits superior capability in distinguishing BKPyVAN from other conditions, with a cutoff value of 4.96% (area under curve = 0.933; sensitivity: 71.4%; and specificity: 97.1%). Notably, an elevation of ddcfmtDNA levels is associated with mitochondrial damage, as visualized through electron microscopy. These results underscore the promise of non-invasive monitoring for detecting subtle mitochondrial damage and its potential utility in BKPyVAN diagnosis. Further investigations are required to advance this field of research.

Diagnosing Polyomavirus Nephropathy without a Biopsy: Validation of the Urinary PyV-Haufen-Test in a Proof-of-Concept Study including Uromodulin Knock-out-Mice.

BACKGROUND: Polyomavirus nephropathy (PyVN) leads to kidney transplant dysfunction and loss. Since a definitive diagnosis requires an invasive kidney biopsy, a timely diagnosis is often hampered. In this clinical dilemma the PyV-haufen-test, centering around the detection of three-dimensional PyV aggregates in the urine, might provide crucial diagnostic information. METHODS: A multistep experimental design. Hypothesis: PyV-haufen form within the kidneys under high concentrations of uromodulin, a kidney specific protein; PyV-haufen are kidney-specific-disease-markers. RESULTS: Investigative step A showed colocalization of uromodulin with aggregated PyV (i) in ten kidneys with PyVN by immunohistochemistry, (ii) in urine samples containing PyV-haufen by electron microscopy/immunogold labeling (n = 3), and (iii) in urine samples containing PyV-haufen by immunoprecipitation assays (n = 4). Investigative step B: In in-vitro experiments only high uromodulin concentrations of ≥ 1.25 mg/mL aggregated PyV, as is expected to occur within injured nephrons. In contrast, in voided urine samples (n = 59) uromodulin concentrations were below aggregation concentrations (1.2 -19.6 µg/mL). Investigative step C: 0/11 (0%) uromodulin KO-/- mice with histologic signs of PyVN showed urinary PyV-haufen shedding compared to 10/14 (71%) WT+/+ mice. CONCLUSION: PyV-haufen form within kidneys under high uromodulin concentrations. Thus, PyV-haufen detected in the urine are specific biomarkers for intra-renal disease, i.e. definitive PyVN.

Safety and efficacy of a reduced frequency viral monitoring strategy for Epstein-Barr virus, cytomegalovirus, and BK polyomavirus post-kidney transplant: A quality assurance initiative.

BACKGROUND: There is variability in recommended viral monitoring protocols after kidney transplant. In response to increased demand for laboratory testing during the COVID-19 pandemic, the Transplant Manitoba Adult Kidney Program updated its monitoring protocols for cytomegalovirus (CMV), Epstein-Barr virus (EBV), and BK polyomavirus (BKV) to a reduced frequency. METHODS: This single-center nested case-control study evaluated 252 adult kidney transplant recipients transplanted from 2015 to 2021, with the updated protocols effective on March 19th 2020. Cases included recipients transplanted after the protocol update who developed CMV, EBV, and BKV DNAemia and were matched to controls with DNAemia transplanted prior to the protocol update. The primary outcome was the difference in maximum DNA load titers between cases and matched controls. Secondary outcomes included time to initial DNAemia detection and DNAemia clearance. Safety outcomes of tissue-invasive viral disease were described. RESULTS: There were 216 recipients transplanted preupdate and 36 recipients postupdate. There was no difference between cases and controls in maximum or first DNA load titers for EBV, CMV, or BKV. Cases experienced earlier EBV DNAemia detection (26 (IQR 8, 32) vs. 434 (IQR 96, 1184) days, p = .005). Median follow-up was significantly longer for recipients transplanted preupdate (4.3 vs. 1.3 years, p < .0001). After adjusting for follow-up time, there was no difference in DNAemia clearance or tissue-invasive viral disease. CONCLUSION: Our findings suggest that reduced frequency viral monitoring protocols may be safe and cost-effective. This quality assurance initiative should be extended to detect longer-term and tissue-invasive disease outcomes.

Impact of BK Polyomavirus NCCR variations in post kidney transplant outcomes.

The human BK Polyomavirus (BKPyV) is a DNA virus that is prevalent in 80 % of the population. Infection with this virus may begin in childhood, followed by asymptomatic persistence in the urinary tract. However, in immunocompromised individuals, especially kidney transplant recipients (KTRs), heightened replication of BKPyV can lead to severe complications. The genome of this virus is divided into three parts; the early and late region, and the non-coding control region (NCCR). Mutations in the NCCR can change the archetype strain to the rearranged strain, and NCCR rearrangements play a significant in virus pathogenesis. Interestingly, diverse types of NCCR block rearrangement result in significant differences in conversion potential and host cell viability in the infected cells. A correlation has been detected between increased viral replication potential and pathogenesis in BKPyV-infected KTRs with specific NCCR rearrangements. The objective of this review study was to examine the disease-causing and clinical consequences of variations in the NCCR in BKPyV-infected KTRs such as virus-associated nephropathy (BKPyVAN).

Establishment of COS-BK cells persistently infected with archetype BK polyomavirus.

BK polyomavirus (BKPyV) was the first human polyomavirus to be isolated from an immunosuppressed kidney transplant recipient in 1971. BKPyV reactivation causes BKPyV-associated nephropathy and hemorrhagic cystitis. However, the mechanisms underlying BKPyV replication remain unclear. In the present study, we performed the long-term cultivation of COS-7 cells transfected with archetype KOM-5 DNA, which were designated as COS-BK cells. BKPyV derived from COS-BK cells was characterized by analyzing the amount of the virus based on hemagglutination, viral replication, and the production of viral protein 1 (VP1). Immunostaining showed that VP1-positive cells accounted for a small percentage of COS-BK cells. The nucleotide sequences encompassing the origin of the DNA replication of BKPyV derived from COS-BK cells were generated from KOM-5 by the deletion of an 8-bp sequence, which did not involve T antigen binding sites. BKPyV replicated most efficiently in COS-BK cells in DMEM containing 2% fetal bovine serum. These results indicate that COS-BK cells are a suitable culture system for studying the persistent infection of archetype BKPyV.

Impact of BK polyomavirus viremia on the outcomes of allogeneic hematopoietic stem cell transplantation.

Although it is known that BK polyomavirus (BKPyV) causes hemorrhagic cystitis (HC) after allogeneic hematopoietic stem cell transplantation (HSCT), the clinical significance of BKPyV viremia has not been fully evaluated. We retrospectively analyzed the results of quantitative polymerase chain reaction (PCR) evaluations for detecting BKPyV in the whole blood samples of patients undergoing allogeneic HSCT during the period from January 2010 to June 2020 at a single institute, Tokyo Medical and Dental University. BKPyV was detected in the blood of 28 of the 107 evaluated patients, and the cumulative incidence of was 27.9% (95%CI: 20.2-37.9%). HC due to BKPyV developed in four of the 28 patients with BKPyV viremia (14.3%) and in two of the 79 patients without it (2.5%; P < 0.05). BKPyV viremia itself did not affect the patients' post-transplant estimated glomerular filtration rate (eGFR), but BKPyV viremia with a high viral load was significantly associated with decreased eGFR values (P < 0.05). BKPyV viremia was also associated with significantly lower progression-free survival at 3 years (35.1% [95%CI: 17.8-53.1%] vs. 60.4% [95%CI: 48.4-70.5], P < 0.05). Our findings demonstrated that BKPyV viremia was associated with onset of HC, an early decline of renal function, and poorer survival after allogeneic HSCT. Further studies are needed to test these results and elucidate the mechanisms of renal dysfunction associated with BKPyV viremia.

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.

A multicenter prospective study to define the natural history of BK viral infections in kidney transplantation.

BACKGROUND: BK polyomavirus (BKV) can cause permanent loss of allograft function due to BKV-associated nephropathy (BKVN) in kidney transplant recipients. Besides immunosuppression reduction, there are no consistently effective interventions for BKV infection. Study purpose was to define natural history of BKV infection, identify risk factors for BKV reactivation and BKVN in kidney transplant recipients, and inform the design/conduct of future clinical trials of BKV-targeted therapeutics. METHODS: We conducted a multicenter prospective observational study of incident kidney transplant recipients at six U.S. transplant centers. Participants were monitored every 4 weeks for BKV reactivation and followed for up to 24 months post-transplant. We used regression models (logistic, survival, mixed models) to study relationships between BK viremia/BKVN, clinical characteristics, and allograft function. RESULTS: We enrolled 335 participants. Fifty-eight (17%) developed BK viremia, 6 (2%) developed biopsy-proven BKVN, and 29 (9%) developed suspected/presumed BKVN (defined as BKV viral load > 10,000 copies/mL without biopsy). Male donor sex was associated with lower odds for BK viremia, whereas recipient Black race was associated with two-fold increased odds for BK viremia. Recipient female sex was associated with more rapid clearance of BK viremia. Persistent BK viremia/BKVN was associated with poorer allograft function by 24 months post-transplant. CONCLUSIONS: We identified multiple donor and recipient demographic factors associated with risk for BKV infection and poorer allograft function by 24 months post-transplant. This may help design future clinical trials of therapies to prevent or mitigate the deleterious impact of BKV reactivation on kidney transplant outcomes.

High-throughput drug screen identifies calcium and calmodulin inhibitors that reduce JCPyV infection.

JC polyomavirus (JCPyV) is a nonenveloped, double-stranded DNA virus that infects the majority of the population. Immunocompetent individuals harbor infection in their kidneys, while severe immunosuppression can result in JCPyV spread to the brain, causing the neurodegenerative disease progressive multifocal leukoencephalopathy (PML). Due to a lack of approved therapies to treat JCPyV and PML, the disease results in rapid deterioration, and is often fatal. In order to identify potential antiviral treatments for JCPyV, a high-throughput, large-scale drug screen was performed using the National Institutes of Health Clinical Collection (NCC). Drugs from the NCC were tested for inhibitory effects on JCPyV infection, and drugs from various classes that reduced JCPyV infection were identified, including receptor agonists and antagonists, calcium signaling modulators, and enzyme inhibitors. Given the role of calcium signaling in viral infection including Merkel cell polyomavirus and simian virus 40 polyomavirus (SV40), calcium signaling inhibitors were further explored for the capacity to impact JCPyV infection. Calcium and calmodulin inhibitors trifluoperazine (TFP), W-7, tetrandrine, and nifedipine reduced JCPyV infection, and TFP specifically reduced viral internalization. Additionally, TFP and W-7 reduced infection by BK polyomavirus, SV40, and SARS-CoV-2. These results highlight specific inhibitors, some FDA-approved, for the possible treatment and prevention of JCPyV and several other viruses, and further illuminate the calcium and calmodulin pathway as a potential target for antiviral drug development.

Acute Kidney Injury and BK Polyomavirus in Urine Sediment Cells.

Polyomaviruses are widespread, with BK viruses being most common in humans who require immunosuppression due to allotransplantation. Infection with BK polyomavirus (BKV) may manifest as BK virus-associated nephropathy and hemorrhagic cystitis. Established diagnostic methods include the detection of polyomavirus in urine and blood by PCR and in tissue biopsies via immunohistochemistry. In this study, 79 patients with pathological renal retention parameters and acute kidney injury (AKI) were screened for BK polyomavirus replication by RNA extraction, reverse transcription, and virus-specific qPCR in urine sediment cells. A short fragment of the VP2 coding region was the target of qPCR amplification; patients with (n = 31) and without (n = 48) a history of renal transplantation were included. Urine sediment cell immunofluorescence staining for VP1 BK polyomavirus protein was performed using confocal microscopy. In 22 patients with acute renal injury, urinary sediment cells from 11 participants with kidney transplantation (KTX) and from 11 non-kidney transplanted patients (nonKTX) were positive for BK virus replication. BK virus copies were found more frequently in patients with AKI stage III (n = 14). Higher copy numbers were detected in KTX patients having experienced BK polyoma-nephropathy (BKPyVAN) in the past or diagnosed recently by histology (5.6 × 109-3.1 × 1010). One patient developed BK viremia following delayed graft function (DGF) with BK virus-positive urine sediment. In nonKTX patients with BK copies, decoy cells were absent; however, positive staining of cells was found with epithelial morphology. Decoy cells were only found in KTX patients with BKPyVAN. In AKI, damage to the tubular epithelium itself may render the epithelial cells more permissive for polyoma replication. This non-invasive diagnostic approach to assess BK polyomavirus replication in urine sediment cells has the potential to identify KTX patients at risk for viremia and BKPyVAN during AKI. This method might serve as a valuable screening tool for close monitoring and tailored immunosuppression decisions.