Nosocomial BK Polyomavirus Infection Causing Hemorrhagic Cystitis Among Patients With Hematological Malignancies After Hematopoietic Stem Cell Transplantation

BK polyomavirus (BKPyV) is recognized as a pathogen that causes diseases such as hemorrhagic cystitis and nephritis after allogeneic hematopoietic stem cell transplantation (HSCT) or renal transplantation. BKPyV‐associated disease is thought to occur through reactivation under immunosuppression. However, the possibility of its nosocomial transmission and the clinical significance of such transmission have not been elucidated. During a 6‐month period, nine adult patients (median age: 47 years) who had hematological disorders and who were treated with HSCT (n = 7) or chemotherapy (n = 2) in a single hematology department developed hemorrhagic cystitis due to BKPyV infection. The polymerase chain reaction products of BKPyV DNA obtained from each patient were sequenced. Of the nine patients, six had subtype I, 2 had subtype IV, and 1 had subtype II or III. In the alignment of sequences, four and two of the six subtype I strains were completely homologous (100%). These results strongly suggest that BKPyV has the potential to cause nosocomial infection within a medical facility, especially among recipients of HSCT. Further studies are clearly warranted to elucidate the route(s) of BKPyV transmission in order to establish optimal infection control.     

Banff Initiative for Quality Assurance in Transplantation (BIFQUIT): Reproducibility of C4d Immunohistochemistry in Kidney Allografts

Detection of C4d is crucial for diagnosing antibody‐mediated‐rejection. We conducted a multicenter trial to assess the reproducibility for C4d immunohistochemistry on paraffin tissue. Unstained slides from a tissue microarray (TMA) comprising 44 kidney allograft specimens representing a full analytical spectrum for C4d were distributed to 73 institutions. Participants stained TMA slides using local protocols and evaluated their slides following the Banff C4d schema. Local staining details and evaluation scores were collected online. Stained slides were returned for centralized panel re‐evaluation. Kappa statistics were used to determine reproducibility. Poor interinstitutional reproducibility was observed (kappa 0.17), which was equally due to limitations in interobserver (kappa 0.44) and interlaboratory reproducibility (kappa 0.46). Depending on the cut‐off, reproducibility could be improved by omitting C4d grading and only considering ± calls. Heat‐induced epitope recovery (pH 6–7, 20–30 min, citrate buffer) with polyclonal antibody incubation (<1:80, >40 min) appeared as best practice. The BIFQUIT trial results indicated that C4d staining on paraffin sections varies considerably between laboratories. Refinement of the current Banff C4d scoring schema and harmonization of tissue processing and staining protocols is necessary to achieve acceptable reproducibility.     

BK Polyomavirus Genomic Integration and Large T Antigen Expression: Evolving Paradigms in Human Oncogenesis

Human polyomaviruses are ubiquitous, with primary infections that typically occur during childhood and subsequent latency that may last a lifetime. Polyomavirus‐mediated disease has been described in immunocompromised patients; its relationship to oncogenesis is poorly understood. We present deep sequencing data from a high‐grade BK virus–associated tumor expressing large T antigen. The carcinoma arose in a kidney allograft 6 years after transplantation. We identified a novel genotype 1a BK polyomavirus, called Chapel Hill BK polyomavirus 2 (CH‐2), that was integrated into the BRE gene in chromosome 2 of tumor cells. At the chromosomal integration site, viral break points were found, disrupting late BK gene sequences encoding capsid proteins VP1 and VP2/3. Immunohistochemistry and in situ hybridization studies demonstrated that the integrated BK virus was replication incompetent. We propose that the BK virus CH‐2 was integrated into the human genome as a concatemer, resulting in alterations of feedback loops and overexpression of large T antigen. Collectively, these findings support the emerging understanding that viral integration is a nearly ubiquitous feature in polyomavirus‐associated malignancy and that unregulated large T antigen expression drives a proliferative state that is conducive to oncogenesis. Based on the current observations, we present an updated model of polyomavirus‐mediated oncogenesis.     

BK Polyomavirus Infection and Renourinary Tumorigenesis

BK polyomavirus (BKPyV) infection represents a major problem in transplantation, particularly for renal recipients developing polyomavirus‐associated nephropathy (PyVAN). The possibility that BKPyV may also be oncogenic is not routinely considered. Twenty high‐grade renourinary tumors expressing polyomavirus large T antigen in the entirety of the neoplasm in 19 cases, including the metastases in six, have been reported in transplant recipients with a history of PyVAN or evidence of BKPyV infection. Morphological and phenotypical features consistent with inactivation of the tumor suppressors pRB and p53 were found in the bladder tumors, suggesting a carcinogenesis mechanism involving the BKPyV large tumor oncoprotein/antigen. The pathogenesis of these tumors is unclear, but given the generally long interval between transplantation and tumor development, the risk for neoplasms after BKPyV infections may well be multifactorial. Other elements potentially implicated include exposure to additional exogenous carcinogens, further viral mutations, and cell genomic instability secondary to viral integration, as occurs with the Merkel cell PyV–associated carcinoma. The still scarce but increasingly reported association between longstanding PyVAN and renourinary neoplasms requires a concerted effort from the transplant community to better understand, diagnose, and treat the putative association between the BKPyV and these neoplasms.     

The 2018 Banff Working Group classification of definitive polyomavirus nephropathy: A multicenter validation study in the modern era

Polyomavirus nephropathy (PVN) remained inadequately classified until 2018 when the Banff Working Group published a new 3-tier morphologic classification scheme derived from in-depth statistical analysis of a large multinational patient cohort. Here we report a multicenter “modern-era” validation study that included 99 patients with definitive PVN transplanted post January 1, 2009 and followed the original 2018 study design. Results validate the PVN classification, that is, the 3 PVN disease classes predicted clinical presentation, allograft function, and outcome independent of therapeutic intervention. PVN class 1 compared to classes 2 and 3 was diagnosed earlier (16.9 weeks posttransplant [median], P = .004), and showed significantly better function at 24 months postindex biopsy (serum creatinine 1.75 mg/dl, geometric mean, vs class 2: P = .037, vs class 3: P = .013). Class 1 presented during long-term follow-up with a low graft failure rate: 5% class 1, vs 30% class 2, vs 50% class 3 (P = .009). Persistent PVN was associated with an increased risk for graft failure (and functional decline in class 2 at 24 months postdiagnosis; serum creatinine with persistence: 2.48 mg/dL vs 1.65 with clearance, geometric means, P = .018). In conclusion, we validate the 2018 Banff Working Group PVN classification that provides significant clinical information and enhances comparative data analysis.     

Banff Histopathological Consensus Criteria for Preimplantation Kidney Biopsies

The Banff working group on preimplantation biopsy was established to develop consensus criteria (best practice guidelines) for the interpretation of preimplantation kidney biopsies. Digitally scanned slides were used (i) to evaluate interobserver variability of histopathologic findings, comparing frozen sections with formalin‐fixed, paraffin‐embedded tissue of wedge and needle core biopsies, and (ii) to correlate consensus histopathologic findings with graft outcome in a cohort of biopsies from international medical centers. Intraclass correlations (ICCs) and univariable and multivariable statistical analyses were performed. Good to fair reproducibility was observed in semiquantitative scores for percentage of glomerulosclerosis, arterial intimal fibrosis and interstitial fibrosis on frozen wedge biopsies. Evaluation of frozen wedge and core biopsies was comparable for number of glomeruli, but needle biopsies showed worse ICCs for glomerulosclerosis, interstitial fibrosis and tubular atrophy. A consensus evaluation form is provided to help standardize the reporting of histopathologic lesions in donor biopsies. It should be recognized that histologic parameters may not correlate with graft outcome in studies based on organs deemed to be acceptable after careful clinical assessment. Significant limitations remain in the assessment of implantation biopsies.     

BK Virus Nephropathy: Histological Evolution by Sequential Pathology

Reactivation of BK virus in renal allografts causes a destructive chronic infection. This single‐center retrospective cohort study describes the evolution of BK virus allograft nephropathy (BKVAN) from 63 kidneys (from 61 patients) using sequential histopathology (454 biopsies, averaging 7.8 ± 2.6 per kidney) followed for 60.1 mo. Uninfected protocol biopsies formulated time‐matched control Banff scores (n = 975). Interstitial inflammation occurred in 73% at diagnosis, correlating with viral histopathology (r = 0.413, p = 0.008) and amplifying early injury with accelerated interstitial fibrosis and tubular atrophy (IF/TA, p = 0.017) by 3 mo. Prodromal simian virus 40 large T antigen (SV40T)–negative inflammation with viremia preceded the histological diagnosis in 23.8%. Persistent subacute injury from viral cytopathic effect was associated with acute tubular necrosis and ongoing interstitial inflammation, culminating in IF/TA in 86.9%. Overall, cellular interstitial infiltration mitigated the intensity of subsequent tubular injury, SV40T, and tissue viral load, assessed by sequential paired histology (p < 0.001). Graft loss was predicted by high‐level viremia (hazard ratio [HR] 4.996, 95% CI 2.19–11.396, p < 0.001), deceased donor (HR 3.201, 95% CI 1.149–8.915, p = 0.026), and late acute rejection (HR 3.124, 95% CI 1.037–9.413, p = 0.043). Transplant failure occurred in 38.1%, with uncontrolled infection (58.3%) and SV40T‐negative chronic rejection (41.7%) causing losses. BKVAN is characterized by subacute virus‐induced tubular injury, inflammation, and progressive nephron destruction. Effective antiviral therapy remains an unmet clinical need.     

Pretransplantation Donor–Recipient Pair Seroreactivity Against BK Polyomavirus Predicts Viremia and Nephropathy After Kidney Transplantation

Kidney transplant donors are not currently implicated in predicting BK polyomavirus (BKPyV) infection in kidney transplant recipients. It has been postulated, however, that BKPyV infection originates from the kidney allograft. Because BKPyV seroreactivity correlates with BKPyV replication and thus might mirror the infectious load, we investigated whether BKPyV seroreactivity of the donor predicts viremia and BKPyV‐associated nephropathy (BKPyVAN) in the recipient. In a retrospective cohort of 407 living kidney donor–recipient pairs, pretransplantation donor and recipient sera were tested for BKPyV IgG levels and correlated with the occurrence of recipient BKPyV viremia and BKPyVAN within 1 year after transplantation. Donor BKPyV IgG level was strongly associated with BKPyV viremia and BKPyVAN (p < 0.001), whereas recipient BKPyV seroreactivity showed a nonsignificant inverse trend. Pairing of high–BKPyV‐seroreactive donors with low‐seroreactive recipients resulted in a 10‐fold increased risk of BKPyV viremia (hazard ratio 10.1, 95% CI 3.5–29.0, p < 0.001). In multivariate analysis, donor BKPyV seroreactivity was the strongest pretransplantation factor associated with viremia (p < 0.001) and BKPyVAN (p = 0.007). The proportional relationship between donor BKPyV seroreactivity and recipient infection suggests that donor BKPyV seroreactivity reflects the infectious load of the kidney allograft and calls for the use of pretransplantation BKPyV serological testing of (potential) donors and recipients.     

Treatment for presumed BK polyomavirus nephropathy and risk of urinary tract cancers among kidney transplant recipients in the United States

Recent case series describe detection of BK polyomavirus (BKV) in urinary tract cancers in kidney transplant recipients, suggesting that BKV could contribute to the development of these cancers. We assessed risk for urinary tract cancers in kidney recipients with or without treatment for presumed BKV nephropathy (tBKVN) using data from the United States Transplant Cancer Match Study (2003‐2013). Among 55 697 included recipients, 2015 (3.6%) were reported with tBKVN. Relative to the general population, incidence was similarly elevated (approximately 4.5‐fold) for kidney cancer in recipients with or without tBKVN, and incidence was not increased in either group for prostate cancer. In contrast, for invasive bladder cancer, incidence was more strongly elevated in recipients with versus without tBKVN (standardized incidence ratios 4.5 vs. 1.7; N = 48 cases), corresponding to an incidence rate ratio (IRR) of 2.9 (95% confidence interval [CI] 1.0‐8.2), adjusted for sex, age, transplant year, and use of polyclonal antibody induction. As a result, recipients with tBKVN had borderline increased incidence for all urothelial cancers combined (renal pelvis, ureter, and bladder cancers: adjusted IRR 2.2, 95% CI 0.9‐5.4; N = 89 cases). Together with reports describing BKV detection in tumor tissues, these results support an association between BKV and urothelial carcinogenesis among kidney transplant recipients.     

Kidney allograft biopsy findings after COVID-19

COVID-19 has been associated with acute kidney injury and published reports of native kidney biopsies have reported diverse pathologies. Case series directed specifically to kidney allograft biopsy findings in the setting of COVID-19 are lacking. We evaluated 18 kidney transplant recipients who were infected with SARS-CoV-2 and underwent allograft biopsy. Patients had a median age of 55 years, six were female, and five were Black. Fifteen patients developed COVID-19 pneumonia, of which five required mechanical ventilation. Notably, five of 11 (45%) biopsies obtained within 1 month of positive SARS-CoV-2 PCR showed acute rejection (four with arteritis, three of which were not associated with reduced immunosuppression). The remaining six biopsies revealed podocytopathy (n = 2, collapsing glomerulopathy and lupus podocytopathy), acute tubular injury (n = 2), infarction (n = 1), and transplant glomerulopathy (n = 1). Biopsies performed >1 month after positive SARS-CoV-2 PCR revealed collapsing glomerulopathy (n = 1), acute tubular injury (n = 1), and nonspecific histologic findings (n = 5). No direct viral infection of the kidney allograft was detected by immunohistochemistry, in situ hybridization, or electron microscopy. On follow-up, two patients died and most patients showed persistent allograft dysfunction. In conclusion, we demonstrate diverse causes of kidney allograft dysfunction after COVID-19, the most common being acute rejection with arteritis.     

The Loss of BKV‐specific Immunity From Pretransplantation to Posttransplantation Identifies Kidney Transplant Recipients at Increased Risk of BKV Replication

Quantification of BKV‐load and BKV‐specific immunity have been evaluated to monitor BKV‐replication and outcomes in kidney transplant recipients (KTRs) with BKV‐infection. However, it remains crucial to better understand how immune markers can predict the risk for later infection. We studied all KTRs between 2008 and 2011. Twenty‐four KTRs were diagnosed with BKV‐replication and a control group of 127 KTRs was used for comparison. Samples were collected before at +1, +2, and +3 months posttransplantation. BKV‐specific and alloreactive T cells were measured using an interferon‐γ Elispot assay. The extent of immunosuppression was quantified by lymphocyte subpopulations and interferon‐gamma levels. KTRs with a loss of BKV‐specific T cells directed to Large T‐antigen from pretransplantation to posttransplantation were at increased risk of BKV‐replication (p < 0.001). In contrast, KTRs with stable/rising BKV‐specific T cells were more likely not to develop BKV‐replication (p < 0.05). KTRs developing BKV‐replication showed significantly lower CD3+, CD4+, CD8+ T cells and interferon‐γ levels posttransplantation, but significantly higher alloreactive T cells (p < 0.05). Monitoring pretransplant and posttransplant BKV‐specific T cells is suggested a sensitive marker to identify KTRs at increased risk of BKV‐replication. Increased susceptibility to immunosuppression predisposes KTRs to a loss of protective BKV‐specific immunity that results in impaired virus control and BKV‐replication.     

Transplantation of kidneys from hepatitis C–infected donors to hepatitis C–negative recipients: Single center experience

Our aim was to evaluate the safety of transplanting kidneys from HCV‐infected donors in HCV‐uninfected recipients. Data collected from 53 recipients in a single center, observational study included donor and recipient characteristics, liver and kidney graft function, new infections and de novo donor‐specific antibodies and renal histology. Treatment with a direct‐acting antiviral regimen was initiated when HCV RNA was detected. The mean ± SD age of recipients was 53 ± 11 years, 34% were female, 19% and 79% of recipients were white and African American, respectively. The median and interquartile range (IQR) time between transplant and treatment initiation was 76 (IQR: 68‐88) days. All 53 recipients became viremic (genotype: 1a [N = 34], 1b [N = 1], 2 [N = 3], and 3 [N = 15]). The majority (81%) of recipients did not experience clinically significant increases (>3 times higher than upper limit of the normal value) in aminotransferase levels and their HCV RNA levels were in the 5 to 6 log range. One patient developed fibrosing cholestatic hepatitis with complete resolution. All recipients completed antiviral treatment and 100% were HCV RNA–negative and achieved 12‐week sustained virologic response. The estimated GFRs at end of treatment and 12‐week posttreatment were 67 ± 21 mL/min/1.73 m² and 67 ± 17 mL/min/1.73 m², respectively. Four recipients developed acute rejection. Kidney transplantation from HCV‐infected donors to HCV‐negative recipients should be considered in all eligible patients.     

Intravenous immunoglobulin as a preventive strategy against BK virus viremia and BKV-associated nephropathy in kidney transplant recipients—Results from a proof-of-concept study

BK virus (BKV) replication occurs frequently in kidney transplant recipients (KTR), potentially leading to BKV-associated nephropathy (BKVAN) and graft loss. Patients with high titers of BKV-neutralizing antibodies (NAbs) are protected against BKV replication, and intravenous immunoglobulin (IVIg) infusion can increase NAb titers. We investigated whether early IVIg administration prevents BKV replication in patients with low NAb titers (<4 log₁₀ against the BKV-specific genotype). Based on NAb titers on the day of transplantation, KTR followed in the Strasbourg University Hospital (n = 174) were retrospectively divided into the following 3 risk categories for BKV replication: (1) patients with low NAb titers (“high-risk”) who received IVIg for the first 3 posttransplant months (n = 44), (2) patients with low NAb titers (“high-risk”) who did not undergo IVIg treatment (n = 41), and (3) patients with high NAb titers (“low-risk”) who did not receive IVIg (n = 89). At 12 posttransplant months, the incidence of BKV viremia in the high-risk group treated with IVIg (6.8%) was similar to that observed in the low-risk group (10.1%) and markedly lower than that of the untreated high-risk group (36.6%; P < .001). Similar results were observed with regard to BKVAN. We conclude that IVIg may be a valuable strategy for preventing BKV replication.     

Histological Evolution of BK Virus–Associated Nephropathy: Importance of Integrating Clinical and Pathological Findings

Long‐term clinicopathological studies of BK‐associated nephropathy (PyVAN) are not available. We studied 206 biopsies (71 patients), followed 3.09 ± 1.46 years after immunosuppression reduction. The biopsy features (% immunostain for PyV large T ag + staining and inflammation ± acute rejection) were correlated with viral load dynamics and serum creatinine to define the clinicopathological status (PyVCPS). Incidence of acute rejection was 28% in the second biopsy and 50% subsequently (25% mixed T cell–mediated allograft rejection (TCMR) + antibody‐mediated allograft rejection (AMR); rejection overall affected 38% of patients (>50% AMR). Graft loss was 15.4% (0.8–5.3 years after PyVAN); 76% had complete viral clearance (mean 28 weeks). The only predictors of graft loss were acute rejection (TCMR p = 0.008, any type p = 0.07), and increased “t” and “ci” in the second biopsy (p = 0.006 and 0.048). Higher peak viremia correlated with poorer viral clearance (p = 0.002). Presumptive and proven PyVAN had similar presentation, evolution, and outcome. Late PyVAN (>2 years, 9.8%) justifies BK viremia evaluation at any point with graft dysfunction and/or biopsy evaluation. This study describes the histological evolution of PyVAN and corresponding clinicopathological correlations. Although the pathological features overall reflect the viral and immunological interactions, the PyVAN course remains difficult to predict based on any single feature. Appropriate clinical management requires repeat biopsies and determination of the PyVCPS at relevant time points, for corresponding personalized immunosuppression adjustment.     

Short‐term outcomes of deceased donor renal transplants of HCV uninfected recipients from HCV seropositive nonviremic donors and viremic donors in the era of direct‐acting antivirals

The United States opioid use epidemic over the past decade has coincided with an increase in hepatitis C virus  (HCV) positive donors. Using propensity score matching, and the Organ Procurement Transplant Network data files from January 2015 to June 2019, we analyzed the short‐term outcomes of adult deceased donor kidney transplants of HCV uninfected recipients with two distinct groups of HCV positive donors (HCV seropositive, nonviremic n = 352 and viremic n = 196) compared to those performed using HCV uninfected donors (n = 36 934). Compared to the reference group, the transplants performed using HCV seropositive, nonviremic and viremic donors experienced a lower proportion of delayed graft function (35.2 vs 18.9%; P < .001 [HCV seropositive, nonviremic donors] and 36.2 vs 16.8% ;  P < .001[HCV viremic donors]). The recipients of HCV viremic donors had better allograft function at 6 months posttransplant (eGFR [54.1 vs 68.3 mL/min/1.73 m2; P = .004]. Furthermore, there was no statistical difference in the overall graft failure risk at 12 months posttransplant by propensity score matched multivariable Cox proportional analysis (HR =  0.60, 95% CI  0.23 to  1.29 [HCV seropositive, nonviremic donors] and HR =  0.85, 95% CI 0.25 to  2.96 [HCV viremic donors]). Further studies are required to determine the long‐term outcomes of these transplants and address unanswered questions regarding the use of HCV viremic donors.     

Efficacy and Safety of Sofosbuvir‐Based Antiviral Therapy to Treat Hepatitis C Virus Infection After Kidney Transplantation

There is no approved therapy for hepatitis C virus (HCV) infection after kidney transplantation, and no data regarding the use of new‐generation direct antiviral agents (DAAs) have been published so far. The aims of this pilot study were to assess the efficacy and safety of an interferon‐free sofosbuvir‐based regimen to treat chronic HCV infection in kidney transplant recipients. Twenty‐five kidney transplant recipients with chronic HCV infection were given, for 12 (n = 19) or 24 weeks (n = 6), sofosbuvir plus ribavirin (n = 3); sofosbuvir plus daclatasvir (n = 4); sofosbuvir plus simeprevir, with (n = 1) or without ribavirin (n = 6); sofosbuvir plus ledipasvir, with (n = 1) or without ribavirin (n = 9); and sofosbuvir plus pegylated‐interferon plus ribavirin (n = 1). A rapid virological response, defined by undetectable viremia at week 4 after starting DAA therapy, was observed in 22 of the 25 patients (88%). At the end of therapy, HCV RNA was undetectable in all patients. At 4 and 12 weeks after completing DAA therapy, all had a sustained virological response. The tolerance to anti‐HCV therapy was excellent and no adverse event was observed. A significant decrease in calcineurin inhibitor levels was observed after HCV clearance. New‐generation oral DAAs are efficient and safe to treat HCV infection after kidney transplantation.     

BK Polyomavirus‐Specific 9mer CD8 T Cell Responses Correlate With Clearance of BK Viremia in Kidney Transplant Recipients: First Report From the Swiss Transplant Cohort Study

BK polyomavirus (BKPyV) causes premature kidney transplant (KT) failure in 1–15% of patients. Because antivirals are lacking, most programs screen for BKPyV‐viremia and, if positive, reduce immunosuppression. To evaluate the relationship of viremia and BKPyV‐specific immunity, we examined prospectively cryopreserved plasma and peripheral blood mononuclear cells at the time of transplantation (T0) and at 6 mo (T6) and 12 mo (T12) after transplant from 28 viremic KT patients and 68 nonviremic controls matched for the transplantation period. BKPyV IgG seroprevalence was comparable between cases (89.3%) and controls (91.2%; p = 0.8635), but cases had lower antibody levels (p = 0.022) at T0. Antibody levels increased at T6 and T12 but were not correlated with viremia clearance. BKPyV‐specific T cell responses to pools of overlapping 15mers (15mer peptide pool [15mP]) or immunodominant CD8 9mers (9mer peptide pool [9mP]) from the early viral gene region were not different between cases and controls at T0; however, clearance of viremia was associated with stronger 9mP responses at T6 (p = 0.042) and T12 (p = 0.048), whereas 15mP responses were not informative (T6 p = 0.359; T12 p = 0.856). BKPyV‐specific T cells could be expanded in vitro from all patients after transplant, permitting identification of 78 immunodominant 9mer epitopes including 50 new ones across different HLA class I. Thus, 9mP‐responses may be a novel marker of reconstituting CD8 T cell function that warrants further study as a complement of plasma BKPyV loads for guiding immunosuppression reduction.