Reducing calcineurin inhibitor first for treating BK polyomavirus replication after kidney transplantation: long-term outcomes

Challenges and opportunities in research on BK virus infection after renal transplantation

Renal transplantation is one of the primary approaches for curing end-stage kidney disease. With advancements in immunosuppressive agents, the short-term and long-term survival rates of transplanted kidneys have significantly improved. However, infections associated with potent immunosuppression have remained a persistent challenge. Among them, BK virus (BKV) reactivation following renal transplantation leading to BK virus-associated nephropathy (BKVAN) is a major cause of graft dysfunction. However, we still face significant challenges in understanding the pathogenesis, prevention, diagnosis, and treatment of BKVAN. These challenges include: 1. The mechanism of BKV reactivation under immunosuppressive conditions has not been well elucidated, leading to difficulties in breakthroughs in clinical research on prevention, diagnosis, and treatment. 2. Lack of proper identification of high-risk individuals, and effective personalized clinical management strategies. 3.Lack of early and sensitive diagnostic markers. 4. Lack of direct and effective treatment options due to the absence of specific antiviral drugs. The purpose of this review is to summarize the current status and cutting-edge advancements in BKV-related research, providing new methods and perspectives to address future research challenges.

Risk of cellular or antibody-mediated rejection in pediatric kidney transplant recipients with BK polyomavirus replication-an international CERTAIN registry study

BACKGROUND

In kidney transplant recipients (KTR), BK polyomavirus-associated nephropathy (BKPyVAN) is a major cause of graft loss. To facilitate the clearance of BKPyV-DNAemia, reduction of immunosuppression is currently the treatment of choice but may increase the risk of graft rejection.

METHODS

This international CERTAIN study was designed to determine the risk of alloimmune response and graft dysfunction associated with immunosuppression reduction for BKPyV treatment in 195 pediatric KTR.

RESULTS

BKPyV-DNAemia was associated with a more than twofold increased risk of late T cell-mediated rejection (TCMR) (HR 2.22, p = 0.024), of de novo donor-specific HLA antibodies (dnDSA) and/or antibody-mediated rejection (ABMR) (HR 2.64, p = 0.002), and of graft function deterioration (HR 2.73, p = 0.001). Additional independent risk factors for dnDSA/ABMR development were a higher HLA mismatch (HR 2.72, p = 0.006) and re-transplantation (HR 6.40, p = 0.000). Other independent predictors of graft function deterioration were TCMR (HR 3.98, p = 0.003), higher donor age (HR 1.03, p = 0.020), and re-transplantation (HR 3.56, p = 0.013).

CONCLUSIONS

These data indicate that reduction of immunosuppression for BKPyV-DNAemia management is associated with increased alloimmune response in pediatric KTR. Therefore, regular dnDSA screening and close monitoring of graft function in case of BKPyV-DNAemia followed by subsequent reduction of immunosuppressive therapy are recommended.

The simultaneous presence of active BK, Epstein Barr, and human cytomegalovirus infection and their correlation by host factors in patients suspected of kidney transplant rejection

AIMS

This study aims to evaluate the presence of EBV, HCMV, and BKV genomic sequences in the plasma samples (active infection/viremia) of kidney transplant recipients suspected of rejection and to investigate host and risk factors related to the activation of these viruses in these patients.

METHODS

In this cross-sectional single-center study, plasma samples were collected from 98 suspected kidney transplant rejection patients at Labafinejad Hospital, Tehran, Iran, between December 2022 and June 2023. Quantitative real-time PCR assays for HCMV, EBV, and BK were performed using GeneProof Real-time PCR kits. ROC curve analysis was used to determine the viral load cutoff point for each virus.

FINDINGS

HCMV active viremia was detected in 18 (18.36%) recipients, EBV active viremia in 7 (7.14%), and BKV active viremia in 5 (5.10%). ROC results indicated viral load cutoff points of 778, 661, and 457 points for HCMV, EBV, and BKV, respectively. The duration of time after transplantation significantly differed between active viremia and no viremia groups (120.5 vs. 46 months, P = 0.014). In the BKV active viremia group, the increase in creatinine compared to baseline creatinine was significantly higher than in the no viremia group (2.7 vs. 0.8, P = 0.017). The odds ratio of HCMV active viremia in patients taking tacrolimus was 2.84 times higher, and the odds of HCMV active viremia in patients taking antithymocyte globulin was 3.01 times higher than in patients not taking these drugs.

CONCLUSION

Rapid and timely diagnosis of viral active infections in kidney transplant patients is crucial for effective disease management and implementation of appropriate treatment strategies. Identifying potential risk factors, including host and treatment-related factors that influence transplantation, can facilitate the development of suitable preventive strategies.

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.

BK polyomavirus DNAemia, allograft rejection, and de novo donor-specific antibodies after lowering target tacrolimus levels in pediatric kidney transplant recipients

BACKGROUND

BK polyomavirus (BKV) DNAemia is a challenging infectious complication after kidney transplant (KT). Reduction of immunosuppression is the mainstay of management, and tacrolimus is often the first immunosuppressive medication adjusted upon the diagnosis of BKV DNAemia. This study aimed to evaluate the impact of a new institutional protocol with lower target tacrolimus levels on BKV DNAemia, allograft rejection, and de novo donor-specific antibodies (dnDSA) among pediatric KT recipients.

METHODS

We conducted a retrospective chart review of all KT episodes between January 2013 and December 2018. The new protocol with lower target tacrolimus levels was implemented in March 2015. One hundred twenty-seven patients were included in primary analysis. All patients received induction with basiliximab and methylprednisolone and were maintained on a steroid-based immunosuppressive regimen.

RESULTS

In the post-intervention cohort, cumulative incidence of BKV DNAemia at 100 days (13.4% vs. 17.8%, p = .605) and 18 months post-KT (34.1% vs. 26.7%, p = .504) was not significantly different from the pre-intervention cohort. Biopsy-proven rejection rate did not change. However, we observed a trend toward earlier development of dnDSA in the post-intervention cohort using the Kaplan-Meier survival analysis (log-rank p = .06). Younger recipient age at the time of transplant was found to slightly increase the risk of BKV DNAemia (OR: 1.09, 95% CI [1.01, 1.16], p = .024). There was an association between BKV DNAemia and biopsy-proven rejection of any type (adjustedOR: 2.77, 95% CI [1.26, 6.23], p = .012), especially acute T-cell-mediated rejection grade 1A and above (adjustedOR: 2.95, 95% CI [1.06, 8.30], p = .037), after adjusted for recipient age at the time of transplant.

CONCLUSIONS

Targeting lower tacrolimus levels did not decrease the incidence of BKV DNAemia within 100 days or 18 months post-KT, nor did it increase the risk of biopsy-proven rejection among pediatric KT recipients in our center. However, there was a trend toward earlier development of dnDSA, which may portend worse long-term graft outcome post-KT. Our findings highlight the need for individualized immunosuppressive regimens based on immunologic and infectious risk factors and the importance of implementing innovative biomarkers to guide therapy and improve outcomes.

A comparative analysis of clinical outcomes between conversion to mTOR inhibitor and calcineurin inhibitor reduction in managing BK viremia among kidney transplant patients

BK virus-associated nephropathy (BKVAN) exerts a substantial impact on allograft survival, however, the absence of robust clinical evidence regarding treatment protocols adds to the complexity of managing this condition. This study aimed to compare the two treatment approaches. The study population consisted of patients who underwent kidney transplantation between January 2016 and June 2020 at two tertiary hospitals in Korea. Patients diagnosed with BK viremia were evaluated based on their initial viral load and the treatment methods. The 'Reduction group' involved dose reduction of tacrolimus while the 'Conversion group' included tacrolimus discontinuation and conversion to sirolimus. A total of 175 patients with an initial viral load (iVL) ≥ 3 on the log10 scale were evaluated within two iVL intervals (3-4 and 4-5). In the iVL 4-5 interval, the Reduction group showed potential effectiveness in terms of viral clearance without statistically significant differences. However, within the iVL 3-4 interval, the Reduction group demonstrated superior viral clearance and a lower incidence of biopsy-proven acute rejection (BPAR) than the Conversion group. The renal function over 12 months after BKV diagnosis showed no statistically significant difference. Reducing tacrolimus compared to converting to mTORi would be a more appropriate treatment approach for BK viral clearance in kidney transplantation. Further research is warranted in a large cohort of patients.

Epidemiology and Dynamics of BK Polyomavirus Replication after Kidney Transplantation

BACKGROUND/OBJECTIVES

In the absence of an effective antiviral treatment for BK polyomavirus (BKPyV), a better understanding of the epidemiology and time course of BKPyV replication after kidney transplantation is needed to limit the virus's impact on the graft outcome.

METHODS

In a 7-year study, we screened more than 430 kidney transplant recipients and analyzed the time course and virological characteristics of BKPyV replication.

RESULTS

Urinary viral replication was observed in 116 (27%) of the 430 patients, and 90 of the 116 (78%) had viral DNAemia. Thirty-eight patients (8.8%) were presumed to have nephropathy (DNAemia > 4 log10 copies/mL). Of the patients with BKPyV replication, 48%, 60%, 71%, and 80% were first found to be positive one, two, three, and four months post-transplantation. The initial viral load in the urine was below 7 log10 copies/mL in 100% of the patients with viral replication first detected before the first month, and this proportion was 57% when viral replication was first detected after the first month. When the BKPyV replication was first detected in a urine sample at month 3 or later, 81.5% of patients had concomitant BKPyV DNAemia. The predominant viral subtype was Ib2 (60%), and there was no apparent relationship between the subtype and the time course of BKPyV replication.

CONCLUSIONS

Urinary BKPyV replication occurs early after renal transplantation and in most patients will increase to a level requiring therapeutic intervention. Close monitoring for BKPyV in the early post-transplantation period would enable the pre-emptive adjustment of the immunosuppression regimen.

Trends in epidemiology and risk factors of opportunistic infections in kidney transplant recipients between 2004 and 2017

BACKGROUND

While opportunistic infections are a frequent and challenging problem in kidney transplant recipients, their long-term epidemiology remains hardly known.

METHODS

Opportunistic infections were recorded in 1144 recipients transplanted in our center between 2004 and 2015. Incidence rates and baseline risk factors were determined using joint frailty models.

RESULTS

After a median follow-up of 5.6 years, 544 opportunistic infections occurred in 373/1144 (33%) patients, dominated by viral infections (396/544, 72%), especially cytomegalovirus (CMV) syndromes and diseases (213/544, 39%). One-third of the infected patients experienced at least two opportunistic infections. The incidence of opportunistic infections was 10 times higher during the first year post-transplantation than after that (34.7 infections for 100 patient-years vs 3.64). Opportunistic infections associated with the age of the donor (P = .032), the age of the recipient (P = .049), the CMV serostatus (P < 10-6), a higher class II HLA mismatch (P = .032) and an induction treatment including rabbit anti-thymocyte globulins (P = .026). Repeated opportunistic infections associated with each other (P < 10-6) and with renal death (P < 10-6).

CONCLUSION

Opportunistic infections occur with a two-period incidence pattern and many susceptible patients suffer from repeated episodes. This knowledge may help tailor new prevention and follow-up strategies to reduce the burden of opportunistic infections and their impact on transplantation outcome.

The kinetics of Torque Teno virus plasma load following calcineurin inhibitor dose change in kidney transplant recipients

Torque Teno virus (TTV) is nonpathogenic, highly prevalent, and reflects the immune status of its host. Thus, TTV plasma load was suggested for the guidance of immunosuppression post solid organ transplantation. The present study was designed to determine the kinetics of TTV following changes in calcineurin inhibitor (CNI) dose. A total of 48 adult recipients of a kidney graft transplanted at the Medical University of Vienna between 2018 and 2019 with isolated changes in CNI dose were selected from the prospective TTV-POET trial. TTV plasma load was quantified by in-house PCR. At Day 30 following CNI dose adaptation (median 33% of daily dose) no changes in TTV load were noted. However, at Day 60, following CNI dose reduction a lower TTV load of 6.4 log10 c/mL (median; interquartile range [IQR] 4.9-8.1) compared with the baseline of 7.1 log10 c/mL (IQR 5.3-8.9) was noted (p = 0.001); there was also a trend toward a higher TTV load following CNI increase (6.6 log10 c/mL, IQR 4.1-9.7 vs. 5.2 log10 c/mL, IQR 4.5-6.8; p = 0.09). The data suggested that TTV load changes become noticeable only 2 months after CNI dose adaptation, which might be the ideal time point for TTV load monitoring.

Efficacy of mTOR Inhibitors and Intravenous Immunoglobulin for Treatment of Polyoma BK Nephropathy in Kidney Transplant Recipients: A Biopsy-Proven Study

OBJECTIVES

We investigated the efficacy of a predetermined protocol that consisted of immunosuppressive drug reduction/withdrawal and intravenous immunoglobulin administration for the treatment of polyoma BK virus nephropathy.

MATERIALS AND METHODS

Patients with biopsy-proven polyoma BK virus nephropathy received a treatment regimen based on discontinuation of both calcineurin inhibitors and antiproliferative agents and switching to mTOR inhibitors accompanied by intravenous immunoglobulin administration.

RESULTS

Our study included 508 patients, with polyoma BK viremia detected in 80 patients. The mean age was 45.3 ± 9.5 years (range, 18-71 y), 64% were male, and mean follow-up was 37 ± 21 months (6-94 mo). All 16 patients who developed polyoma BK virus nephropathy and 9 patients who had highgrade polyoma BK viremia without nephropathy received intravenous immunoglobulin treatment. Compared with patients with viremia, patients with polyoma BK virus nephropathy had significantly higher rates of graft loss due to rejection (18.8% vs 1.6%; P = .024) and all-cause graft loss (31.2% vs 6.3%; P = .014). Histopathologically, viral inclusion bodies disappeared and SV40 became negative after treatment in all 13 patients who underwent protocol biopsies. Unfortunately, histopathologically complete recovery without chronic tubular and interstitial tissue damage was achieved in only 4 patients after treatment. In addition, 3 patients lost their grafts due to acute antibody-mediated or mixed-type rejection (18.8%).

CONCLUSIONS

In patients with polyoma BK virus nephropathy, clearance of viremia and SV40 should not be the sole outcomes to obtain. Aggressive reductions in maintenance immunosuppression and switching to double-drug therapy combined with high-dose intravenous immunoglobulin leads to high rates of graft loss/rejection and sequalae of chronic histological changes.

An observational cohort study of histological screening for BK polyomavirus nephropathy following viral replication in plasma

Systematic screening for BKPyV-DNAemia has been advocated to aid prevention and treatment of polyomavirus associated nephropathy (PyVAN), an important cause of kidney graft failure. The added value of performing a biopsy at time of BKPyV-DNAemia, to distinguish presumptive PyVAN (negative SV40 immunohistochemistry) and proven PyVAN (positive SV40) has not been established. Therefore, we studied an unselected cohort of 950 transplantations, performed between 2008-2017. BKPyV-DNAemia was detected in 250 (26.3%) transplant recipients, and positive SV40 in 91 cases (9.6%). Among 209 patients with a concurrent biopsy at time of first BKPyV-DNAemia, 60 (28.7%) biopsies were SV40 positive. Plasma viral load showed high diagnostic value for concurrent SV40 positivity (ROC-AUC 0.950, 95% confidence interval 0.916-0.978) and the semiquantitatively scored percentage of tubules with evidence of polyomavirus replication (pvl score) (0.979, 0.968-0.988). SV40 positivity was highly unlikely when plasma viral load is below 4 log10 copies/ml (negative predictive value 0.989, 0.979-0.994). In SV40 positive patients, higher plasma BKPyV-DNA load and higher pvl scores were associated with slower viral clearance from the blood (hazard ratio 0.712, 95% confidence interval 0.604-0.839, and 0.327, 0.161-0.668, respectively), whereas the dichotomy positivity/negativity of SV40 immunohistochemistry did not predict viral clearance. Although the pvl score offers some prognostic value for viral clearance on top of plasma viral load, the latter provided good guidance for when a biopsy was unnecessary to exclude PyVAN. Thus, the distinction between presumptive and proven PyVAN, based on SV40 immunohistochemistry, has limited clinical value. Hence, management of BKPyV-DNAemia and immunosuppression reduction should be weighed against the risk of occurrence of rejection, or exacerbation of rejection observed concomitantly.

Randomized Trial to Assess the Clinical Utility of Renal Allograft Monitoring by Urine CXCL10 Chemokine

SIGNIFICANCE STATEMENT

This study is the first randomized controlled trial to investigate the clinical utility of a noninvasive monitoring biomarker in renal transplantation. Although urine CXCL10 monitoring could not demonstrate a beneficial effect on 1-year outcomes, the study is a rich source for future design of trials aiming to explore the clinical utility of noninvasive biomarkers. In addition, the study supports the use of urine CXCL10 to assess the inflammatory status of the renal allograft.

BACKGROUND

Urine CXCL10 is a promising noninvasive biomarker for detection of renal allograft rejection. The aim of this study was to investigate the clinical utility of renal allograft monitoring by urine CXCL10 in a randomized trial.

METHODS

We stratified 241 patients, 120 into an intervention and 121 into a control arm. In both arms, urine CXCL10 levels were monitored at three specific time points (1, 3, and 6 months post-transplant). In the intervention arm, elevated values triggered performance of an allograft biopsy with therapeutic adaptations according to the result. In the control arm, urine CXCL10 was measured, but the results concealed. The primary outcome was a combined end point at 1-year post-transplant (death-censored graft loss, clinical rejection between month 1 and 1-year, acute rejection in 1-year surveillance biopsy, chronic active T-cell-mediated rejection in 1-year surveillance biopsy, development of de novo donor-specific HLA antibodies, or eGFR <25 ml/min).

RESULTS

The incidence of the primary outcome was not different between the intervention and the control arm (51% versus 49%; relative risk (RR), 1.04 [95% confidence interval, 0.81 to 1.34]; P = 0.80). When including 175 of 241 (73%) patients in a per-protocol analysis, the incidence of the primary outcome was also not different (55% versus 49%; RR, 1.11 [95% confidence interval, 0.84 to 1.47]; P = 0.54). The incidence of the individual end points was not different as well.

CONCLUSIONS

This study could not demonstrate a beneficial effect of urine CXCL10 monitoring on 1-year outcomes (ClinicalTrials.gov_ NCT03140514 ).

Single-Cell, High-Content Microscopy Analysis of BK Polyomavirus Infection

By adulthood, the majority of the population is persistently infected with BK polyomavirus (BKPyV). Only a subset of the population, generally transplant recipients on immunosuppressive drugs, will experience disease from BKPyV, but those who do have few treatment options and, frequently, poor outcomes, because to date there are no effective antivirals to treat or approved vaccines to prevent BKPyV. Most studies of BKPyV have been performed on bulk populations of cells, and the dynamics of infection at single-cell resolution have not been explored. As a result, much of our knowledge is based upon the assumption that all cells within a greater population are behaving the same way with respect to infection. The present study examines BKPyV infection on a single-cell level using high-content microscopy to measure and analyze the viral protein large T antigen (TAg), promyelocytic leukemia protein (PML), DNA, and nuclear morphological features. We observed significant heterogeneity among infected cells, within and across time points. We found that the levels of TAg within individual cells did not necessarily increase with time and that cells with the same TAg levels varied in other ways. Overall, high-content, single-cell microscopy is a novel approach to studying BKPyV that enables experimental insight into the heterogenous nature of the infection. IMPORTANCE BK polyomavirus (BKPyV) is a human pathogen that infects nearly everyone by adulthood and persists throughout a person's life. Only people with significant immune suppression develop disease from the virus, however. Until recently the only practical means of studying many viral infections was to infect a group of cells in the laboratory and measure the outcomes in that group. However, interpreting these bulk population experiments requires the assumption that infection influences all cells within a group similarly. This assumption has not held for multiple viruses tested so far. Our study establishes a novel single-cell microscopy assay for BKPyV infection. Using this assay, we discovered differences among individual infected cells that have not been apparent in bulk population studies. The knowledge gained in this study and the potential for future use demonstrate the power of this assay as a tool for understanding the biology of BKPyV.

A cluster of broadly neutralizing IgG against BK polyomavirus in a repertoire dominated by IgM

The BK polyomavirus (BKPyV) is an opportunistic pathogen, which is only pathogenic in immunosuppressed individuals, such as kidney transplant recipients, in whom BKPyV can cause significant morbidity. To identify broadly neutralizing antibodies against this virus, we used fluorescence-labeled BKPyV virus-like particles to sort BKPyV-specific B cells from the PBMC of KTx recipients, then single-cell RNAseq to obtain paired heavy- and light-chain antibody sequences from 2,106 sorted B cells. The BKPyV-specific repertoire was highly diverse in terms of both V-gene usage and clonotype diversity and included most of the IgM B cells, including many with extensive somatic hypermutation. In two patients where sufficient data were available, IgM B cells in the BKPyV-specific dataset had significant differences in V-gene usage compared with IgG B cells from the same patient. CDR3 sequence-based clustering allowed us to identify and characterize three broadly neutralizing "41F17-like" clonotypes that were predominantly IgG, suggesting that some specific BKPyV capsid epitopes are preferentially targeted by IgG.

Incidence, Risk Factors, and Outcomes of Kidney Transplant Recipients With BK Polyomavirus-Associated Nephropathy

Introduction

BK polyomavirus-associated nephropathy (BKPyVAN) is associated with graft dysfunction and loss; however, knowledge of immunosuppression reduction strategies and long-term graft, and patient outcomes across the disease spectrum is lacking.

Methods

This cohort study included 14,697 kidney transplant recipients in Australia and New Zealand (2005-2019), followed for 91,306 person years.

Results

BKPyVAN occurred in 460 recipients (3%) at a median posttransplant time of 4.8 months (interquartile range, 3.1-10.8). Graft loss (35% vs. 21%, P < 0.001), rejection (42% vs. 25%, P < 0.001), and death (18% vs. 13%, P = 0.002) were more common in the BKPyVAN group. The most frequent changes in immunosuppression after BKPyVAN were reduction (≤50%) in tacrolimus (172, 51%) and mycophenolate doses (134, 40%), followed by the conversion of mycophenolate to leflunomide (62, 19%) and tacrolimus to ciclosporin (20, 6%). Factors associated with the development of BKPyVAN included (adjusted hazard ratio [HR]; 95% confidence interval) male sex (1.66; 1.34-2.05), recipient age (≥70 vs. <20 [2.46; 1.30-4.65]), recipient blood group (A vs. B [2.00; 1.19-3.34]), donor age (≥70 vs. <20 [2.99; 1.71-5.22]), earlier era (1.74; 1.35-2.25), donor/recipient ethnic mismatch (1.52; 1.23-1.87), tacrolimus use (1.46; 1.11-1.91), and transplantation at a lower-volume transplant center (1.61; 1.24-2.09). The development of BKPyVAN was associated with an increased risk of all-cause (1.75; 1.46-2.09) and death-censored graft loss (2.49; 1.99-3.11), but not mortality (1.15; 0.91-1.45).

Conclusions

BKPyVAN is associated with an increased risk of all-cause and death-censored graft loss, but not death. Interventional trials are urgently needed to evaluate the efficacy of immunosuppression reduction and novel strategies to minimize the adverse outcomes associated with BKPyVAN.

Characteristics, risk factors and outcome of BKV nephropathy in kidney transplant recipients: a case-control study

BACKGROUND

Following kidney transplantation, BK virus associated nephropathy (BKVN) occurs in 1 to 10% of kidney transplant recipients (KTR) and represents a major cause of graft loss. We aim at identifying factors associated with biopsy proven BKVN among KTR.

METHODS

We conducted a retrospective case-control study including all KTR with a biopsy-proven diagnosis of BKVN between 2005 and 2019. Clinical characteristics and outcome were described. For each case, one control KTR without BKV infection was identified and matched by age, transplant date, and donor status. Factors associated with BKVN diagnosis were identified using exact conditional logistic regression. Comparative survival was described using Kaplan-Meier estimator.

RESULTS

Sixty-four cases of BKVN were identified among 1737 new kidney transplantation (3.7% prevalence). Clinical characteristics did not differ between groups, except for a higher c-PRA among cases. BKVN occurred in a median time of 11 (5-14.5) months after KT, and was associated with a significantly impaired graft function at diagnosis. Following BKVN, 61 (95%) of the patients had immunosuppression reduction, which led to BKV DNAemia resolution in 49% of cases. In multivariate analysis, factors associated with BKVN diagnosis were lymphopenia < 500/mm³ and a prednisone dose > 7.5 mg/day. Median duration of follow-up was 40 months for both groups. BKVN was associated with a significantly increased risk of graft rejection (P = 0.02) and return to dialysis (P = 0.01).

CONCLUSIONS

BKVN remains a severe complication in KTR and is associated with an increased risk for acute rejection and return to dialysis. Lymphopenia below 500/mm³ and corticosteroid maintenance therapy are significantly associated with biopsy-proven BKVN diagnosis.

BK DNAemia in pediatric kidney transplant recipients: Predictors and outcomes

BACKGROUND

Pediatric data on risk factors and the clinical course of BK DNAemia are limited. We aimed to determine the effects of BK DNAemia on transplant outcomes and delineate the safety and efficacy of various treatment approaches.

METHODS

This retrospective-cohort study included 161 transplants (age ≤ 21 years) performed at a single center between 1/1/2012 and 1/1/2020. We used Cox proportional models to evaluate the effects of BK DNAemia on patient survival (PS), graft survival (GS), and acute rejection (AR), using BK as a time-dependent covariate. We also assessed the effects of pharmacological intervention on BK DNAemia duration using intervention as a time-dependent covariate.

RESULTS

BK-free survival was 69.1% at 1-year and 54.6% at 3-year posttransplant. After multivariate adjustment, BK DNAemia was associated with young age at transplant (aHR, age 5-<12 vs. ≥12 (years): 2.5 (1.4-4.5); p = .001) and steroid-based immunosuppression (IS) (aHR: 2.2 [1.1-4.5]; p = .03). We found no effect of DNAemia on AR (aHR: 1.25; p = .5), PS (aHR: 2.85; p = .22), and GS (aHR: 0.56; p = .41). Of 70 patients with DNAemia, 22 (31.4%) received no treatment, 20 (28.6%) received IS reduction alone, and 28 patients (40%) received treatment with at least one pharmacological agent (leflunomide, IVIG, ciprofloxacin, cidofovir). Sixty-three patients (90%) cleared DNAemia with median time to resolution of 2.4 months (IQR:1.4-5.6). We found no significant effect of BK-directed pharmacological treatment on time to resolution (aHR: 0.64;p = .13). BK-directed agents were well tolerated.

CONCLUSIONS

BK DNAemia is associated with a young age at transplant and steroid-based maintenance IS. We found no effect of BK DNAemia on AR, GS, and PS.

Development of de novo donor-specific antibodies in renal transplant recipients with BK viremia managed with immunosuppression reduction

BACKGROUND

Reduction of immunosuppression (IS) upon detection of Polyomavirus (BK) viremia is widely used to prevent BK virus nephropathy. This retrospective case-control study assesses the frequency of de novo donor-specific antibodies (dnDSA) in renal transplant recipients with IS modulation due to BK viremia and the associated risk of antibody mediated rejection.

METHODS

Our cohort included recipients of kidney transplantation between 2007 and 2017 with clinical, HLA antibody, and biopsy data. BK positivity was defined as viremia >10 000 c/ml or biopsy proven BK nephropathy. A total of 190 BK cases matched our inclusion criteria, each case was matched with two controls based on gender, donor type, and transplant within 1 year (N = 396).

RESULTS

Despite lower number of HLA antigen mismatches (mean = 3.5 vs. 4.4, p < .001), dnDSA rates were higher in BK cases than in control group (22.1% vs. 13.9%, p = .02), with the majority detected following IS reduction for BK infection, and arising earlier posttransplant compared with no BK infection (294d vs. 434d, p < .001). Antibody mediated rejection rates were similar between cases and controls (8.9% and 8.3%, respectively), but rejection was more likely to occur earlier posttransplant in the BK cases (354d vs. 602d, p = .03).

CONCLUSION

Our data suggest a link between IS reduction and the generation of dnDSA and/or rejection, supporting close monitoring for DSA in patients with reduced IS due to BK infection given their increased risk to develop dnDSA.

Conversion to mTOR-Inhibitors Plus IV Immunoglobulins in Kidney-Transplant Recipients with BKV Infection: A Retrospective Comparative Study

BK virus-associated nephropathy (PvAN) increases the risk of graft failure justifying treatment. Conversion to mammalian target of rapamycin inhibitors (mTORi) and Human polyclonal immunoglobulins (IVIg) could prevent the risk of PvAN. Our retrospective study assessed the efficacy of mTORi associated with IVIg therapy (mTORi±IVIg group) versus standard immunosuppression reduction to clear BKV DNAemia. Among forty-three kidney-transplanted patients with positive BKV DNAemia, we included twenty-six patients in the mTORi±IVIg group and reduced immunosuppression therapy for seventeen patients. We focused on BKV DNAemia clearance on the first-year. Renal function, rejection rate, evolution to PvAN, and complications of immunosuppression were assessed. BKV DNAemia decreased faster and significantly in the control group as compared to the mTORi±IVIg group (p < 0.001). Viral clearance was significantly higher in the control group compared to the mTORi±IVIg group (88% vs. 58%; p = 0.033). Death-censored graft loss, rejection rates and kidney-graft function at 12 months did not significantly differ. Multivariate analyses significantly associated BKV DNAemia clearance with reducing immunosuppression (OR = 0.11 (0.06−0.9), p = 0.045), female kidney donor (OR = 0.10 (0.01−0.59/)], p = 0.018) and time to first DNAemia, (OR = 0.88 (0.76−0.96), p = 0.019). In our study, the standard treatment for BKV DNAemia had better outcomes than an mTORi±IVIg conversion.

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.

In Vitro Study Evaluating the Effect of Different Immunosuppressive Agents on Human Polyomavirus BK Replication

BACKGROUND

Human polyomavirus BK (BKPyV) is the etiologic agent of polyomavirus-associated nephropathy, a leading cause of kidney transplant dysfunction. Because of the lack of antiviral therapies, immunosuppression minimization is the recommended treatment. This strategy offers suboptimal outcomes and entails a significant risk of rejection. Our aim was to evaluate the effect of different immunosuppressive drugs (leflunomide, tacrolimus, mycophenolic acid, sirolimus, and everolimus) and their combinations in an in vitro model of BKPyV infection.

METHODS

Human renal tubular epithelial cells were infected with BKPyV and treated with leflunomide, tacrolimus, mycophenolic acid, sirolimus, and everolimus, administered alone or in some combination thereof. Viral replication was assessed every 24 hours (up to 72 hours) by BKPyV-specific quantitative real-time polymerized chain reaction for the VIRAL PROTEIN 1 sequence in cell supernatants and by western blot analysis targeting the viral protein 1 and the glyceraldehyde 3-phosphate dehydrogenase on total protein lysates. Results were described as viral copies/mL and compared between treatments at any prespecified time point of the study.

RESULTS

The highest inhibitory effects were observed using leflunomide or everolimus plus mycophenolic acid (mean BKPyV replication log reduction 0.28). The antiviral effect of everolimus persisted when it was used in combination with tacrolimus (mean BKPyV replication log reduction 0.27).

CONCLUSIONS

Our experience confirms that everolimus has anti-BKPyV properties and prompts future research to investigate possible mechanisms of action. It also provides a rational basis for targeted clinical trials evaluating alternative immunosuppressive modification strategies.

Clinical Relevance of Absolute BK Polyoma Viral Load Kinetics in Patients With Biopsy Proven BK Polyomavirus Associated Nephropathy

Introduction: The absolute BK viral load is an important diagnostic surrogate for BK polyomavirus associated nephropathy (PyVAN) after renal transplant (KTX) and serial assessment of BK viremia is recommended. However, there is no data indicating which particular viral load change, i.e., absolute vs. relative viral load changes (copies/ml; percentage of the preceding viremia) is associated with worse renal graft outcomes.

Materials and Methods: In this retrospective study of 91 biopsy proven PyVAN, we analyzed the interplay of exposure time, absolute and relative viral load kinetics, baseline risk, and treatment strategies as risk factors for graft loss after 2 years using a multivariable Poisson-model.

Results: We compared two major treatment strategies: standardized immunosuppression (IS) reduction (n = 53) and leflunomide (n = 30). The median viral load at the index biopsy was 2.15E+04 copies/ml (interquartile range [IQR] 1.70E+03–1.77E+05) and median peak viremia was 3.6E+04 copies/ml (IQR 2.7E+03–3.3E+05). Treatment strategies and IS-levels were not related to graft loss. After correction for baseline viral load and estimated glomerular filtration rate (eGFR), absolute viral load decrease/unit remained an independent risk factor for graft loss [incidence rate ratios [IRR] = 0.77, (95% CI 0.61–0.96), p = 0.02].

Conclusion: This study provides evidence for the prognostic importance of absolute BK viremia kinetics as a dynamic parameter indicating short-term graft survival independently of other established risk factors.

Urinary Tract Infections: Virus

Although viruses are common in the urinary tract in healthy people, viral infections can become a major concern in immunocompromised individuals. Patients undergoing hematopoietic stem cell or solid organ transplantation may be particularly susceptible to BK and other viruses, and experience a high risk of mortality. The most common presentation in this setting is hemorrhagic cystitis. The treatment is mostly supportive, including the reduction of immunosuppression; a variety of experimental agents has also been proposed. A different context is offered by chronic (HBV, HCV, HIV) or acute/subacute (Dengue, Hantavirus, etc.) infections, where the kidneys can be secondarily involved and suffer from several glomerular syndromes. Many protocols based on different oral direct-acting antivirals and combined antiretrovirals are available, according to the systemic infection. Viral infections can be classified according to the organ involved, i.e. lower (bladder) or upper urinary tract (kidneys, ureters), and to the mechanism of injury. A section is dedicated to the current breakout of SARS-CoV-2, which does not spare the urinary tract, sometimes with serious implications. Even if this topic is mostly the discipline of ultra-dedicated physicians, this overview has a practical approach and could be useful to a wider medical audience, especially in times of viral pandemics.

Current Status, Prevention and Treatment of BK Virus Nephropathy

All renal transplant recipients should undergo a regular screening for BK viral (BKV) viremia. Gradual reduction of immunosuppression is recommended in patients with persistent plasma BKV viremia for 3 weeks after the first detection, reflecting the presence of probable or suspected BKV-associated nephropathy. Reduction of immunosuppression is also a primary intervention in biopsy proven nephropathy associated with BKV (BKVN). Thus, allograft biopsy is not required to treat patients with BKV viremia with stabilized graft function. There is a lack of proper randomised clinical trials recommending treatment in the form of switching from tacrolimus to cyclosporin-A, from mycophenolate to mTOR inhibitors or leflunomide, or the additive use of intravenous immunoglobulins, leflunomide or cidofovir. Fluoroquinolones are not recommended for prophylaxis or therapy. There are on-going studies to evaluate the possibility of using a multi-epitope anti-BKV vaccine, administration of BKV-specific T cell immunotherapy, BKV-specific human monoclonal antibody and RNA antisense oligonucleotides. Retransplantation after allograft loss due to BKVN can be successful if BKV viremia is definitively removed, regardless of allograft nephrectomy.

Polyoma BK Virus in Kidney Transplant Recipients: Screening, Monitoring, and Management

Polyomavirus BK virus (BKPyV) infection is an important complication of kidney transplantation and allograft failure. The prevalence of viremia is 10%-15%, compared with BK-associated nephropathy (BKPyVAN) at 3%-5%. Given that there are no effective antiviral prophylaxis or treatment strategies for BKPyVAN, active screening to detect BKPyV viremia is recommended, particularly during the early posttransplant period. Immunosuppression reduction to allow viral clearance may avoid progression to severe and irreversible allograft damage. The frequency and duration of screening are highly variable between transplant centers because the evidence is reliant largely on observational data. While the primary treatment goals center on achieving viral clearance through immunosuppression reduction, prevention of subsequent acute rejection, premature graft loss, and return to dialysis remain as major challenges. Treatment strategies for BKPyV infection should be individualized to the recipient's underlying immunological risk and severity of the allograft infection. Efficacy data for adjuvant therapies including intravenous immunoglobulin and cidofovir are sparse. Future well-powered and high-quality randomized controlled trials are needed to inform evidence-based clinical practice for the management of BKPy infection.

Belatacept Use after Kidney Transplantation and Its Effects on Risk of Infection and COVID-19 Vaccine Response

Introduction: Belatacept is a common immunosuppressive therapy used after kidney transplantation (KT) to avoid calcineurin-inhibitor (CNI) use and its related toxicities. It is unclear whether its use exposes KT recipients (KTx) to a greater risk of infection or a poorer response to vaccines. Areas covered: We reviewed PubMed and the Cochrane database. We then summarized the mechanisms and impacts of belatacept use on the risk of infection, particularly opportunistic, in two settings, i.e., de novo KTx and conversion from CNIs. We also focused on COVID-19 infection risk and response to SARS-CoV-2 vaccination in patients whose maintenance immunosuppression relies on belatacept. Expert opinion: When belatacept is used de novo, or after drug conversion the safety profile regarding the risk of infection remains good. However, there is an increased risk of opportunistic infections, mainly CMV disease and Pneumocystis pneumonia, particularly in those with a low eGFR, in older people, in those receiving steroid-based therapy, or those that have an early conversion from CNI to belatacept (i.e., <six months post-transplantation). Thus, we recommend, if possible, delaying conversion from CNI to belatacept until at least six months post-transplantation. Optimal timing seems to be eight months post-transplantation. In addition, KTx receiving belatacept respond poorly to SARS-CoV-2 vaccination.

Influence of a low-dose tacrolimus protocol on the appearance of de novo donor-specific antibodies during 7 years of follow-up after renal transplantation

BACKGROUND

Tacrolimus (TAC) is a key immunosuppressant drug for kidney transplantation (KTx). However, the optimal serum trough level of TAC for good long-term outcomes remains unclear. This study aimed to investigate the relationship between the maintenance TAC trough level and the appearance of de novo donor-specific anti-human leukocyte antigen (HLA) antibodies (dnDSAs).

METHODS

A total of 584 KTx recipients were enrolled in this study, of whom 164 developed dnDSAs during the follow-up period and 420 did not.

RESULTS

We found no significant relationship between TAC trough level during the follow-up period and dnDSA incidence. Patients who developed dnDSAs had a significantly greater number of HLA-A/B/DR mismatches (3.4 ± 1.3 versus 2.8 ± 1.5; P < 0.001), were more likely to have preformed DSAs (48.2% versus 27.1%; P < 0.001) and showed poor allograft outcome.

CONCLUSIONS

There was no clear relationship between TAC trough level and dnDSA incidence for KTx recipients whose TAC trough levels were kept within the narrow range of 4-6 ng/mL during the immunosuppression maintenance period.

Chronic Kidney Allograft Disease: New Concepts and Opportunities

Chronic kidney disease (CKD) is increasing in most countries and kidney transplantation is the best option for those patients requiring renal replacement therapy. Therefore, there is a significant number of patients living with a functioning kidney allograft. However, progressive kidney allograft functional deterioration remains unchanged despite of major advances in the field. After the first post-transplant year, it has been estimated that this chronic allograft damage may cause a 5% graft loss per year. Most studies focused on mechanisms of kidney graft damage, especially on ischemia-reperfusion injury, alloimmunity, nephrotoxicity, infection and disease recurrence. Thus, therapeutic interventions focus on those modifiable factors associated with chronic kidney allograft disease (CKaD). There are strategies to reduce ischemia-reperfusion injury, to improve the immunologic risk stratification and monitoring, to reduce calcineurin-inhibitor exposure and to identify recurrence of primary renal disease early. On the other hand, control of risk factors for chronic disease progression are particularly relevant as kidney transplantation is inherently associated with renal mass reduction. However, despite progress in pathophysiology and interventions, clinical advances in terms of long-term kidney allograft survival have been subtle. New approaches are needed and probably a holistic view can help. Chronic kidney allograft deterioration is probably the consequence of damage from various etiologies but can be attenuated by kidney repair mechanisms. Thus, besides immunological and other mechanisms of damage, the intrinsic repair kidney graft capacity should be considered to generate new hypothesis and potential therapeutic targets. In this review, the critical risk factors that define CKaD will be discussed but also how the renal mechanisms of regeneration could contribute to a change chronic kidney allograft disease paradigm.

Chk1 and the Host Cell DNA Damage Response as a Potential Antiviral Target in BK Polyomavirus Infection

The human BK polyomavirus (BKPyV) is latent in the kidneys of most adults, but can be reactivated in immunosuppressed states, such as following renal transplantation. If left unchecked, BK polyomavirus nephropathy (PyVAN) and possible graft loss may result from viral destruction of tubular epithelial cells and interstitial fibrosis. When coupled with regular post-transplant screening, immunosuppression reduction has been effective in limiting BKPyV viremia and the development of PyVAN. Antiviral drugs that are safe and effective in combating BKPyV have not been identified but would be a benefit in complementing or replacing immunosuppression reduction. The present study explores inhibition of the host DNA damage response (DDR) as an antiviral strategy. Immunohistochemical and immunofluorescent analyses of PyVAN biopsies provide evidence for stimulation of a DDR in vivo. DDR pathways were also stimulated in vitro following BKPyV infection of low-passage human renal proximal tubule epithelial cells. The role of Chk1, a protein kinase known to be involved in the replication stress-induced DDR, was examined by inhibition with the small molecule LY2603618 and by siRNA-mediated knockdown. Inhibition of Chk1 resulted in decreased replication of BKPyV DNA and viral spread. Activation of mitotic pathways was associated with the reduction in BKPyV replication. Chk1 inhibitors that are found to be safe and effective in clinical trials for cancer should also be evaluated for antiviral activity against BKPyV.

Intravenous immunoglobulins do not prove beneficial to reduce alloimmunity among kidney transplant recipients with BKV-associated nephropathy

Reduced immunosuppression during BKV-DNAemia has been associated with T-cell mediated rejection (TCMR), de novo donor-specific antibodies (DSA) and antibody-mediated rejection (ABMR). Intravenous immunoglobulins (IVIG) may reduce alloimmunity. We studied 860 kidney transplant recipients (KTRs) for the development of BKV-DNAuria and BKV-DNAemia (low-level <10 000 IE/ml, high-level >10 000 IE/ml). 52/131 KTRs with high-level BKV-DNAemia received IVIG. The HLA-related immunological risk was stratified by the Predicted Indirectly Recognizable HLA Epitopes (PIRCHE) algorithm. BKV-DNAuria only was observed in 86 KTRs (10.0%), low-level BKV-DNAemia in 180 KTRs (20.9%) and high-level BKV-DNAemia in 131 KTRs (15.2%). KTRs with low-level BKV-DNAemia showed significantly less TCMR compared to KTRs with high-level BKV-DNAemia (5.2% vs. 25.5%; P < 0.001) and no BKV-replication (13.2%; P = 0.014), lowest rates of de novo DSA (21.3%), ABMR (9.2%) and flattest glomerular filtration rate (GFR) slope (-0.8 ml/min). KTRs with low-level BKV-DNAemia showed significantly higher median (interquartile range) total PIRCHE if they developed TCMR [100.22 (72.6) vs. 69.52 (49.97); P = 0.020] or ABMR [128.86 (52.99) vs. 69.52 (49.96); P = 0.005]. Administration of IVIG did not shorten duration of BKV-DNAemia (P = 0.798) or reduce TCMR, de novo DSA and ABMR (P > 0.05). KTRs with low-level BKV-DNAemia showed best protection against alloimmunity, with a high number of PIRCHE co-determining the remaining risk. The administration of IVIG, however, was not beneficial in reducing alloimmunity.

Nephrotoxicity of calcineurin inhibitors as a risk factor for BK polyomavirus replication after kidney transplantation

BK polyomavirus-associated nephropathy (PyVAN) is responsible for a significant percentage of transplanted kidneys prematurely terminating their function. Its occurrence is closely related to the intensity of immunosuppressive therapy. In a group of 161 newly transplanted patients, we prospectively evaluated 457 protocol renal biopsies performed within the first year after transplantation. Using the calcineurin inhibitors (CI) nephrotoxicity score, the incidence of nephrotoxicity was monitored as a manifestation of excessive immunosuppression. Findings were correlated with clinical evidence of active BK polyomavirus (BKPyV) replication and PyVAN. Compared to the normal histology, nephrotoxicity was associated with more frequent BKPyV viremia and viruria (p = .01 and p < .01, respectively) and more common occurrence of PyVAN. The persistence of toxicity in the subsequent biopsy proved to be a negative risk factor of viremia and viruria (p = .03 and p < .01, respectively), independently of the initial BKPyV status. Toxicity could also be used as a predictor of viremia and viruria (p = .04 and p < .01, respectively) even in the absence of viral replication at the time of initial biopsy. The early histological manifestation of CI nephrotoxicity was associated with significant BKPyV reactivation in the risky first posttransplant year.

Deceased-Donor Acute Kidney Injury and BK Polyomavirus in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

BK polyomavirus (BKV) infection commonly complicates kidney transplantation, contributing to morbidity and allograft failure. The virus is often donor-derived and influenced by ischemia-reperfusion processes and disruption of structural allograft integrity. We hypothesized that deceased-donor AKI associates with BKV infection in recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We studied 1025 kidney recipients from 801 deceased donors transplanted between 2010 and 2013, at 13 academic centers. We fitted Cox proportional-hazards models for BKV DNAemia (detectable in recipient blood by clinical PCR testing) within 1 year post-transplantation, adjusting for donor AKI and other donor- and recipient-related factors. We validated findings from this prospective cohort with analyses for graft failure attributed to BKV within the Organ Procurement and Transplantation Network (OPTN) database.

RESULTS

The multicenter cohort mean kidney donor profile index was 49±27%, and 26% of donors had AKI. Mean recipient age was 54±13 years, and 25% developed BKV DNAemia. Donor AKI was associated with lower risk for BKV DNAemia (adjusted hazard ratio, 0.53; 95% confidence interval, 0.36 to 0.79). In the OPTN database, 22,537 (25%) patients received donor AKI kidneys, and 272 (0.3%) developed graft failure from BKV. The adjusted hazard ratio for the outcome with donor AKI was 0.7 (95% confidence interval, 0.52 to 0.95).

CONCLUSIONS

In a well-characterized, multicenter cohort, contrary to our hypothesis, deceased-donor AKI independently associated with lower risk for BKV DNAemia. Within the OPTN database, donor AKI was also associated with lower risk for graft failure attributed to BKV.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_03_10_CJN18101120_final.mp3.

Antivirals against human polyomaviruses: Leaving no stone unturned

Human polyomaviruses (HPyVs) encompass more than 10 species infecting 30%-90% of the human population without significant illness. Proven HPyV diseases with documented histopathology affect primarily immunocompromised hosts with manifestations in brain, skin and renourinary tract such as polyomavirus-associated nephropathy (PyVAN), polyomavirus-associated haemorrhagic cystitis (PyVHC), polyomavirus-associated urothelial cancer (PyVUC), progressive multifocal leukoencephalopathy (PML), Merkel cell carcinoma (MCC), Trichodysplasia spinulosa (TS) and pruritic hyperproliferative keratinopathy. Although virus-specific immune control is the eventual goal of therapy and lasting cure, antiviral treatments are urgently needed in order to reduce or prevent HPyV diseases and thereby bridging the time needed to establish virus-specific immunity. However, the small dsDNA genome of only 5 kb of the non-enveloped HPyVs only encodes 5-7 viral proteins. Thus, HPyV replication relies heavily on host cell factors, thereby limiting both, number and type of specific virus-encoded antiviral targets. Lack of cost-effective high-throughput screening systems and relevant small animal models complicates the preclinical development. Current clinical studies are limited by small case numbers, poorly efficacious compounds and absence of proper randomized trial design. Here, we review preclinical and clinical studies that evaluated small molecules with presumed antiviral activity against HPyVs and provide an outlook regarding potential new antiviral strategies.

BK Polyomavirus Nephropathy in Kidney Transplantation: Balancing Rejection and Infection

BK polyomavirus nephropathy (BKVN) and allograft rejection are two closely-associated diseases on opposite ends of the immune scale in kidney transplant recipients. The principle of balancing the immune system remains the mainstay of therapeutic strategy. While patient outcomes can be improved through screening, risk factors identification, and rapid reduction of immunosuppressants, a lack of standard curative therapy is the primary concern during clinical practice. Additionally, difficulty in pathological differential diagnosis and clinicopathology’s dissociation pose problems for a definite diagnosis. This article discusses the delicate evaluation needed to optimize immunosuppression and reviews recent advances in molecular diagnosis and immunological therapy for BKVN patients. New biomarkers for BKVN diagnosis are under development. For example, measurement of virus-specific T cell level may play a role in steering immunosuppressants. The development of cellular therapy may provide prevention, even a cure, for BKVN, a complex post-transplant complication.

BK Polyomavirus-specific T Cells as a Diagnostic and Prognostic Marker for BK Polyomavirus Infections After Pediatric Kidney Transplantation

BACKGROUND

After kidney transplantation, uncontrolled BK polyomavirus (BKPyV) replication causes kidney graft failure through BKPyV-associated nephropathy (BKPyVAN), but markers predicting outcome are missing. BKPyV-specific T cells may serve as a predictive marker to identify patients at risk of persistent DNAemia and BKPyVAN.

METHODS

Out of a total of 114 pediatric kidney recipients transplanted between 2008 and 2018, 36 children with posttransplant BKPyV-DNAemia were identified. In a prospective noninterventional study, BKPyV-specific CD4 and CD8 T cells were measured in 32 of 36 viremic pediatric kidney recipients using intracellular cytokine staining and flow cytometry. The course of the BKPyV replication was monitored with regard to duration of BKPyV-DNAemia and need of therapeutic intervention and diagnosis of proven BKPyVAN.

RESULTS

Levels of BKPyV-specific T cells negatively correlated with subsequent duration of BKPyV-DNAemia. Patients with BKPyV-specific CD4 T cells ≥0.5 cells/µL and/or BKPyV-specific CD8 T cells ≥0.1 cells/µL had transient, self-limiting DNAemia (PPV 1.0, NPV 0.86). BKPyV-specific CD4 and CD8 T cells below these thresholds were found in children with persistent BKPyV-DNAemia and biopsy-proven BKPyVAN with need for therapeutic intervention. After reducing immunosuppressive therapy, levels of BKPyV-specific CD4 T cells increased while plasma BKPyV-DNAemia declined.

CONCLUSIONS

This study found that BKPyV-specific T cell levels may help to distinguish patients with transient, self-limiting BKPyV-DNAemia from those with persisting BKPyV-DNAemia and biopsy-proven BKPyVAN, who would benefit from individualized therapeutic interventions such as reduced immunosuppression. Thereby the risk for rejection because of unnecessary reduction of immunosuppression in case of self-limiting BKPyV-DNAemia can be minimized.

BK Virus-Associated Nephropathy after Renal Transplantation

Recent advances in immunosuppressive therapy have reduced the incidence of acute rejection and improved renal transplantation outcomes. Meanwhile, nephropathy caused by BK virus has become an important cause of acute or chronic graft dysfunction. The usual progression of infection begins with BK viruria and progresses to BK viremia, leading to BK virus associated nephropathy. To detect early signs of BK virus proliferation before the development of nephropathy, several screening tests are used including urinary cytology and urinary and plasma PCR. A definitive diagnosis of BK virus associated nephropathy can be achieved only histologically, typically by detecting tubulointerstitial inflammation associated with basophilic intranuclear inclusions in tubular and/or Bowman’s epithelial cells, in addition to immunostaining with anti-Simian virus 40 large T-antigen. Several pathological classifications have been proposed to categorize the severity of the disease to allow treatment strategies to be determined and treatment success to be predicted. Since no specific drugs that directly suppress the proliferation of BKV are available, the main therapeutic approach is the reduction of immunosuppressive drugs. The diagnosis of subsequent acute rejection, the definition of remission, the protocol of resuming immunosuppression, and long-term follow-up remain controversial.

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.

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.

Total nephroureterocystectomy and urethrectomy due to urothelial carcinoma associated with the BK polyomavirus infection after kidney transplantation: a case report with literature review

Background

BK polyomavirus (BKPyV) infection after kidney transplantation is an important cause of graft failure among kidney transplant recipient and may cause malignant tumor, although the association between BKPyV infection and malignant tumor has been controversial yet.

Case presentation

We report a case of a 39-year-old-male kidney transplantation (KTx) recipient with urine BKPyV replication who developed a graft pelvic tumor with the positive Simian virus 40 large T antigen (SV40 TAg). The patients received a living-related KTx from his 65-year-old mother. A protocol biopsy at 14 months after KTx showed BKPyV-associated nephropathy. Therefore, the dose of immunosuppressants was reduced, resulting in improved BKPyV viremia, but viruria persisted. About 117 months after KTx, urine cytology showed atypical cells suspicious for malignancy. Cystoscopy revealed a tumor on the neck of the bladder. Transurethral resection of the bladder tumor (TUR-BT) was performed; however, the diagnosis of malignancy was not confirmed at that time. Six months after the TUR-BT, urine cytology showed atypical cells definite for malignancy. Computed tomography and retrograde pyelography showed no evidence of urinary tract tumor and metastasis. Subsequently, total nephroureterocystectomy and urethrectomy were performed. Histological examination of the graft ureter revealed a high-grade urothelial carcinoma, with glandular differentiation, pT1. Immunohistochemically, the tumor showed positivities for SV40 TAg and p53, along with increased Ki67 labeling cells were increased. By contrast, nonneoplastic cells were negative for SV40 TAg. At the time of writing the present manuscript, the patient is free from recurrence or residual tumor and being closely monitored without additional therapy, 32 months after the surgery.

Conclusion

The relationship between BKPyV infection after KTx and bladder carcinogenesis remains to be elucidated. However, when the KTx recipients who continue to have BKPyV infection for a long time are treated, the possibility of risk factors for renourinary carcinoma should always be carefully considered.

Advances in BK Virus Complications in Organ Transplantation and Beyond

Reactivation of BK virus (BKV) remains a dreaded complication in immunosuppressed states. Conventionally, BKV is known as a cause for BKV-associated nephropathy and allograft dysfunction in kidney transplant recipients. However, emerging studies have shown its negative impact on native kidney function and patient survival in other transplants and its potential role in diseases such as cancer. Because BKV-associated nephropathy is driven by immunosuppression, reduction in the latter is a convenient standard of care. However, this strategy is risk prone due to the development of donor-specific antibodies affecting long-term allograft survival. Despite its pathogenic role, there is a distinct lack of effective anti-BKV therapeutics. This limitation combined with increased morbidity and health care cost of BKV-associated diseases add to the complexity of BKV management. While summarizing recent advances in the pathogenesis of BKV-associated nephropathy and its reactivation in other organ transplants, this review illustrates the limitations of current and emerging therapeutic options and provides a compelling argument for an effective targeted anti-BKV drug.

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.

Increasing net immunosuppression after BK polyoma virus infection

BACKGROUND

Reducing immunosuppression can effectively treat BK viremia (BKV) and BK nephropathy, but has been associated with increased risks for acute rejection and development of donor-specific antibodies (DSA). To date there have been no systematic evaluations of re-escalating immunosuppression in transplant patients with resolving BKV. Importantly, the safety of this approach and impact on graft survival is unclear.

METHODS

We performed a single-center retrospective review of kidney transplant recipients between July 2011 and June 2013 who had immunosuppression reduction after developing BKV (plasma PCR ≥ 1000 copies/ml). Changes in immunosuppression and patient outcomes were tracked until occurrence of a complication event: biopsy-proven acute rejection (BPAR), detection of de novo DSA, or recurrent BKV. Patients were grouped according to whether or not net immunosuppression was eventually increased.

RESULTS

Out of 88 patients with BKV, 44 (50%) had net immunosuppression increased while the other 44 did not. Duration of viremia, peak viremia, induction, and sensitization status were similar between the two groups. In a Kaplan-Meier analysis, increasing immunosuppression was associated with less BPAR (P = .001) and a trend toward less de novo DSA development (P = .06). Death-censored graft survival (P = .27) was not different between the two groups. In the net immunosuppression increase group, recurrent BKV occurred in 22.7% without any BKV-related graft losses.

CONCLUSION

These findings support potential benefits of increasing immunosuppression in patients with low-level or resolved BKV, but prospective trials are needed to better understand such an approach.

BK Polyomavirus-Specific CD8 T-Cell Expansion In Vitro Using 27mer Peptide Antigens for Developing Adoptive T-Cell Transfer and Vaccination

BACKGROUND

BK polyomavirus (BKPyV) remains a significant cause of premature kidney transplant failure. In the absence of effective antivirals, current treatments rely on reducing immunosuppression to regain immune control over BKPyV replication. Increasing BKPyV-specific CD8 T cells correlate with clearance of BKPyV DNAemia in kidney transplant patients. We characterized a novel approach for expanding BKPyV-specific CD8 T cells in vitro using 27mer-long synthetic BKPyV peptides, different types of antigen-presenting cells, and CD4 T cells.

METHODS

Langerhans cells and immature or mature monocyte-derived dendritic cells (Mo-DCs) were generated from peripheral blood mononuclear cells of healthy blood donors, pulsed with synthetic peptide pools consisting of 36 overlapping 27mers (27mP) or 180 15mers (15mP). BKPyV-specific CD8 T-cell responses were assessed by cytokine release assays using 15mP or immunodominant 9mers.

RESULTS

BKPyV-specific CD8 T cells expanded using 27mP and required mature Mo-DCs (P = .0312) and CD4 T cells (P = .0156) for highest responses. The resulting BKPyV-specific CD8 T cells proliferated, secreted multiple cytokines including interferon γ and tumor necrosis factor α, and were functional (CD107a+/PD1-) and cytotoxic.

CONCLUSIONS

Synthetic 27mP permit expanding BKPyV-specific CD8 T-cell responses when pulsing mature Mo-DCs in presence of CD4 T cells, suggesting novel and safe approaches to vaccination and adoptive T-cell therapies for patients before and after kidney transplantation.

BK polyomavirus-specific antibody and T-cell responses in kidney transplantation: update

PURPOSE OF REVIEW

BK polyomavirus (BKPyV) has emerged as a significant cause of premature graft failure after kidney transplantation. Without effective antiviral drugs, treatment is based on reducing immunosuppression to regain immune control over BKPyV replication. The paradigm of high-level viruria/decoy cells, BKPyV-DNAemia, and proven nephropathy permits early interventions. Here, we review recent findings about BKPyV-specific antibody and T-cell responses and their potential role in risk stratification, immune monitoring, and therapy.

RECENT FINDING

Kidney transplant recipients having low or undetectable BKPyV-specific IgG immunoglobulin G (IgG) are higher risk for developing BKPyV-DNAemia if the donor has high BKPyV-specific IgG. This observation has been extended to neutralizing antibodies. Immunosuppression, impaired activation, proliferation, and exhaustion of BKPyV-specific T cells may increase the risk of developing BKPyV-DNAemia and nephropathy. Clearance of BKPyV-DNAemia was correlated with high CD8 T cell responses to human leukocyte antigen (HLA)-types presenting BKPyV-encoded immunodominant 9mers. For clinical translation, these data need to be assessed in appropriately designed clinical studies, as outlined in recent guidelines on BKPyV in kidney transplantation.

SUMMARY

Evaluation of BKPyV-specific immune responses in recipient and donor may help to stratify the risk of BKPyV-DNAemia, nephropathy, and graft loss. Future efforts need to evaluate clinical translation, vaccines, and immunotherapy to control BKPyV replication.

Persistent BK Polyomavirus Viruria is Associated with Accumulation of VP1 Mutations and Neutralization Escape

To investigate the relationship between neutralization escape and persistent high-level BK polyomavirus replication after kidney transplant (KTx), VP1 sequences were determined by Sanger and next-generation sequencing in longitudinal samples from KTx recipients with persistent high-level viruria (non-controllers) compared to patients who suppressed viruria (controllers). The infectivity and neutralization resistance of representative VP1 mutants were investigated using pseudotype viruses. In all patients, the virus population was initially dominated by wild-type VP1 sequences, then non-synonymous VP1 mutations accumulated over time in non-controllers. BC-loop mutations resulted in reduced infectivity in 293TT cells and conferred neutralization escape from cognate serum in five out of six non-controller patients studied. When taken as a group, non-controller sera were not more susceptible to neutralization escape than controller sera, so serological profiling cannot predict subsequent control of virus replication. However, at an individual level, in three non-controller patients the VP1 variants that emerged exploited specific “holes” in the patient’s humoral response. Persistent high-level BK polyomavirus replication in KTx recipients is therefore associated with the accumulation of VP1 mutations that can confer resistance to neutralization, implying that future BKPyV therapies involving IVIG or monoclonal antibodies may be more effective when used as preventive or pre-emptive, rather than curative, strategies.

Viral load and duration of BK polyomavirus viraemia determine renal graft fibrosis progression: histologic evaluation of late protocol biopsies

BACKGROUND

Polyomavirus BK (BKV) infection of the renal allograft causes destructive tissue injury with inflammation and subsequent fibrosis.

METHODS

Using a prospective cohort of patients after kidney transplantation performed between 2003 and 2012, we investigated the role of BKV viraemia in the development and progression of interstitial fibrosis and tubular atrophy (IFTA). The primary outcome was moderate-to-severe IFTA assessed by protocol biopsy at 36 months.

RESULTS

A total of 207 consecutive recipients were enrolled. Of these, 57 (28%) developed BKV viraemia with 10 (5%) cases of polyomavirus-associated nephropathy (PVAN). Transient (<3 months) BKV viraemia occurred in 70% of patients, and persistent (≥3 months) BKV viraemia in 30%. A high viral load (≥10 000 copies/mL) was detected in 18% and a low viral load (<10 000 copies/mL) in 61%, while the viral load could not be determined in 21%. Moderate-to-severe IFTA was significantly increased in high [71%; odds ratio (OR) = 12.1; 95% confidence interval (CI) 1.62-90.0; P = 0.015] or persistent BKV viraemia (67%; OR = 6.33; 95% CI 1.19-33.7; P = 0.031) with corresponding rise in 'interstitial fibrosis + tubular atrophy' scores. Only patients with transient low BKV viraemia showed similar incidence and progression of IFTA to the no-BKV group. Persistent low BKV viraemia was uncommon yet the progression of fibrosis was significant. Only recipients with PVAN experienced inferior graft survival at 5 years.

CONCLUSIONS

These data suggest that only transient low BKV viraemia does not negatively affect the progression of allograft fibrosis in contrast to excessive risk of severe fibrosis after high or persistent BKV viraemia.

Immunosuppression, BK polyomavirus infections, and BK polyomavirus-specific T cells after pediatric kidney transplantation

BACKGROUND

After kidney transplantation, immunosuppressive therapy increases risk of BK polyomavirus-associated nephropathy (BKPyVAN). Outcomes of BKPyV viremia are various and prognostic markers are missing. The impact of different immunosuppressive regimens on BKPyV infections is currently under discussion.

METHODS

We analyzed immunosuppressive therapy and BKPyV-specific cellular immunity to distinguish patients at risk of BKPyVAN from those with self-limiting viremia for purposes of risk-stratified BKPyV management. In a retrospective analysis, 46 pediatric kidney recipients with BKPyV viremia were analyzed with regard to duration of BKPyV viremia and immunosuppressive therapy; in addition, in 37/46 patients, BKPyV-specific CD4 and CD8 T cells were measured.

RESULTS

Nine patients showed persistent BKPyV viremia and BKPyVAN, and required therapeutic intervention, while 37 patients had asymptomatic, self-limiting viremia. At onset of viremia, 78% of patients with persistent viremia and BKPyVAN were treated with tacrolimus, whereas tacrolimus therapy was significantly less frequent in patients with self-limiting viremia (14%). The majority of patients with transient, self-limiting viremia received cyclosporine A (81%) and/or mTOR inhibitors (81%). Patients with persistent BKPyV viremia and BKPyVAN showed lack of BKPyV-specific CD4 and CD8 T cells (6/6), whereas the majority of patients with self-limiting viremia (27/31) had detectable BKPyV-specific CD4 and/or CD8 T cells ≥ 0.5 cells/μl (p < 0.001).

CONCLUSIONS

These results indicate that tacrolimus enhances risk of BKPyVAN with need of therapeutic intervention, whereas under cyclosporine A and mTOR inhibitors, the majority of pediatric kidney recipients showed self-limiting viremia. In patients at risk of BKPyV infections, combination of cyclosporine A and mTOR inhibitor may be advantageous.

Low-dose cidofovir and conversion to mTOR-based immunosuppression in polyomavirus-associated nephropathy

BACKGROUND

Polyomavirus-associated nephropathy (PVAN) remains a relevant complication following kidney transplantation with allograft loss rates of up to 50%. Reduction in overall immunosuppression is a cornerstone of therapy, whereas no specific antiviral regimen has shown conclusive benefit to date. The present case series demonstrates the efficacy of a dual therapeutic approach with low-dose cidofovir and conversion to mTOR-based immunosuppression in PVAN.

METHODS

Patients with biopsy-proven PVAN having received low-dose cidofovir (0.25 mg/kg) according to the Tübingen Cidofovir Protocol and been converted to mTOR-based immunosuppression were analyzed retrospectively.

RESULTS

Twenty-three patients with a median follow-up of 2.24 [IQR 1.55-5.01] years were included in the analysis. Median time to PVAN diagnosis was 268 [IQR 153-869] days after transplantation. Polyomavirus clearance from plasma was achieved in 78% of patients after a median of 118 [IQR 76-293] days. Of the 23 patients, nine patients (39%) lost their allograft function during follow-up, but only three of these (13%) due to PVAN. Fourteen patients (61%) stabilized or improved allograft function. The cidofovir protocol allowed for specific antiviral therapy without adverse nephrotoxicity, even in patients with low allograft function.

CONCLUSIONS

Low-dose cidofovir and conversion to mTOR-based immunosuppression allow for effective virus clearance and preservation of allograft function in a high proportion of patients with PVAN and progressive allograft dysfunction and may prolong allograft survival in these patients.

JC polyomavirus-specific antibody responses in pediatric kidney transplant recipients

BKPyV is widely recognized in KTRs, but little is known about rates of primary and secondary JCPyV exposure in pediatric KTRs. We evaluated JCPyV exposure in pediatric KTRs using antibody responses in the first 12 months post-transplant. Of 46 children transplanted between 2009 and 2014, 6 lacked any samples for serologic testing, leaving 40 KTRs for study. JCPyV-specific IgG and IgM antibodies were measured using a normalized VLP ELISA. Significant JCPyV exposure was defined as IgG seroconversion, increasing IgG levels of >0.5 nOD units, or IgM detection. Of 40 recipients (median age 3.2 years), 11 (27.5%) were seropositive, 20 (50%) seronegative for JCPyV-IgG, while 9 (22.5%) had no specimen at the time of transplantation, but were confirmed as seronegative in post-transplant samples. Of 29 (72.5%) at risk, JCPyV-IgG seroconversion occurred in 15/29 (51.7%) including JCPyV-IgM in 6 patients (20.7%). Two patients (6.9%) developed only JCPyV-IgM. Among JCPyV-IgG-positive KTRs, six (12.5%) had significant IgG increases. Altogether 23 of 40 patients (57.5%) had serological evidence of primary or secondary JCPyV exposure. In these patients, kidney function tended to be lower during the 2 years of follow-up, but only one patient lost the graft due to JCPyV nephropathy. Thus, JCPyV exposure is common in pediatric KTR and may present serologically as primary or secondary infection. Although only one case of JC-PyVAN occurred, a trend toward lower renal function was seen. Dedicated studies of larger cohorts are warranted to define impact of JCPyV in pediatric KTR.