Polyomavirus-associated nephropathy risk in kidney transplants: the influence of recipient age and donor gender

Protocol biopsy of kidney allograft enables early detection of BK virus nephropathy to preserve kidney allograft function

BACKGROUND

The Banff Working Group has updated the histological classification of BK virus nephropathy (BKVN), highlighting the importance of early detection. However, an early detection strategy for BKVN using biopsy has not yet been established. Our investigation aimed to assess the efficacy of protocol biopsy for the diagnosis of BKVN.

METHODS

We performed a retrospective cohort study of 314 patients who had undergone kidney transplantation between 2006 and 2021. Kidney allograft biopsies were performed as part of a protocol biopsy at 3 months and 1 year post-transplantation. Following the diagnosis of BKVN, the immunosuppressant dose was reduced.

RESULTS

Twelve patients (3.8%) were diagnosed with BKVN by biopsy. Most diagnoses are established during the early stages of BKVN (polyomavirus nephropathy class 1 in six, class 2 in five, and class 3 in one). Following the reduction in immunosuppressant dose, kidney allograft function did not deteriorate in any patients. Additionally, test for BK virus DNA in the blood was negative. All but one patient demonstrated histological resolution of BKVN, and the other had a very slight positivity for the simian virus 40 large T antigen. The median follow-up time after BKVN diagnosis was 6 years. One patient developed de novo donor-specific antibody and subclinical acute antibody-mediated rejection that was successfully cured.

CONCLUSIONS

Our analysis indicates that protocol biopsy may enable the early detection of BKVN, resulting in the preservation of kidney function.

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.

Clinical Outcomes of Older Kidney Transplant Recipients

BACKGROUND

Older kidney transplant recipients (OKTR) are vulnerable to infections and AKI, often prompting hospitalization. This study elucidates etiology of hospitalizations, AKI, and outcomes in OKTR.

METHODS

Retrospective study of 500 patients age ≥ 60, who underwent kidney transplantation from 2005-2015. Demographic, transplant, and outcomes data were collected.

RESULTS

OKTR had mean age 66 years; 59% males and 50% African Americans. 62% had at least one hospitalization post-transplant. Predictors of hospitalization were DGF, DM, panel reactive antibodies (PRA), dialysis duration. Hospitalization was mostly due to infection and surgical complications. Average length of stay was 6.4 days. OKTR with at least one hospitalization had 84% higher risk for graft loss (p=0.001). 56% of older kidney transplant recipients had at least one AKI episode post-transplant. Predictors of AKI included DGF, older, African American donor, and tacrolimus variability. The most common etiologies for AKI were infection, dehydration, and GI complications. OKTR with at least one AKI episode had 2.6-fold higher risk for graft loss (p<0.001).

CONCLUSIONS

Post-transplant hospitalization and AKI in OKTR significantly impact graft survival. Addressing comorbidities and risks in the pre-transplant and outpatient setting may help alleviate burden of hospitalization and risk of AKI in OKTR and improve graft outcomes.

The effect of human leukocyte antigen A1 and B35-Cw4 on sustained BK polyomavirus DNAemia after renal transplantation

Human leukocyte antigen (HLA) class I presentation pathway plays a central role in natural killer (NK) cell and cytotoxic T-cell activities against BK polyomavirus (BKPyV) DNAemia. We determined the risk of sustained BKPyV DNAemia in 175 consecutive renal transplant recipients considering the simultaneous effect of donor/recipient HLA class I antigens and pre- or post-transplant variables. Median (IQR) age was 53 (44-64) years, and 37% of patients were female. 40 patients (22.9%) developed sustained BKPyV DNAemia [median (IQR) viral load: 9740 (4350-17 125) copies/ml]. In the Cox proportional hazard analysis, HLA-A1 (HR: 3.06, 95% CI: 1.51-6.17) and HLA-B35-Cw4 (HR: 4.63, 95% CI: 2.12-10.14) significantly increased the risk of sustained BKPyV DNAemia, while 2 HLA-C mismatches provided a marginally protective effect (HR: 0.32, 95% CI: 0.10-0.98). HLA-Cw4 is a ligand for NK cell inhibitory receptor, and HLA-B35 is in strong linkage disequilibrium with the HLA-Cw4 allele. The association between HLA-B35-Cw4 expression and sustained BKPyV DNAemia supports the important role of cytotoxic T cells and NK cells that would normally control BKPyV activation through engagement with immunoglobulin-like killer receptors (KIRs). Further studies are required to investigate the effect of HLA-C alleles along with NK cell activity against BKPyV DNAemia.

Screening for BK Viremia/Viruria and the Impact of Management of BK Virus Nephropathy in Renal Transplant Recipients

OBJECTIVES

The prevalence of BK-induced nephritis in renal transplant recipients is estimated to be 1% to 10%; the rate of graft loss within 1 year is 30% to 65%. We conducted this study to evaluate screening of BK virus in blood and/or urine among renal transplant recipients and to assess the effects of different therapeutic modalities in renal transplant recipients with BK nephropathy.

MATERIALS AND METHODS

Kidney transplant recipients were screened at the time of transplant and then at 1, 2, 3, 6, 9, 12, 18, and 24 months posttransplant. Fiftynine patients were diagnosed with BK virus viremia. Patients were divided into 2 groups according to treatment: group 1 (n = 29) received an active treatment and group 2 (n = 30) received minimized immunosuppression.

RESULTS

Most patients required graft biopsies to confirm diagnosis (86.2% in group 1 vs 50% in group 2; P = .03). Both groups were comparable regarding demographic data. Initial posttransplant graft function was significantly better in group 1 (P = .017); ultimately, there was no significant difference between both groups regarding graft survival (P= .51). Fifty percent of patients had biopsy-proven acute T-cell-mediated rejection before BK virus-associated nephropathy diagnosis (significantly higher in group 1). Serum creatinine levels were significantly better in group 2 at 3, 4, and 5 years after BK nephropathy (P = .001, .017, and .003, respectively).

CONCLUSIONS

The prevalence of BK nephropathy in our renal transplant recipients was 5.9% with a rate of graft loss ranging from 43% to 51%. Regular screening, less intensive immunosuppressive therapy, and early intervention by reduction of immunosuppressive medications are advisable to obtain early diagnosis and to have better outcomes of BK virus-associated nephropathy with antiviral agents.

BK Virus: A Cause for Concern in Thoracic Transplantation?

Human BK polyomavirus (BKV) infection is poorly documented in heart and lung transplant patients. BK viruria and viremia have been estimated to affect 19% and 5% of heart transplant recipients, respectively. Data are limited, especially for lung transplantation, but the proportion of patients progressing from BK viruria to viremia or BKV-related nephropathy (BKVN) appears lower than in kidney transplantation. Nevertheless, a number of cases of BKVN have been reported in heart and lung transplant patients, typically with late diagnosis and generally poor outcomes. Risk factors for BKV infection or BKVN in this setting are unclear but may include cytomegalovirus infection and anti-rejection treatment. The relative infrequency of BKVN or other BK-related complications means that routine BKV surveillance in thoracic transplantation is not warranted, but a diagnostic workup for BKV infection may be justified for progressive renal dysfunction with no readily-identifiable cause; after anti-rejection therapy; and for renal dysfunction in patients with cytomegalovirus infection or hypogammaglobulinemia. Treatment strategies in heart or lung transplant recipients rely on protocols developed in kidney transplantation, with reductions in immunosuppression tailored to match the higher risk status of thoracic transplant patients.

BK Polyomavirus Replication in Renal Tubular Epithelial Cells Is Inhibited by Sirolimus, but Activated by Tacrolimus Through a Pathway Involving FKBP-12

BK polyomavirus (BKPyV) replication causes nephropathy and premature kidney transplant failure. Insufficient BKPyV-specific T cell control is regarded as a key mechanism, but direct effects of immunosuppressive drugs on BKPyV replication might play an additional role. We compared the effects of mammalian target of rapamycin (mTOR)- and calcineurin-inhibitors on BKPyV replication in primary human renal tubular epithelial cells. Sirolimus impaired BKPyV replication with a 90% inhibitory concentration of 4 ng/mL by interfering with mTOR-SP6-kinase activation. Sirolimus inhibition was rapid and effective up to 24 h postinfection during viral early gene expression, but not thereafter, during viral late gene expression. The mTORC-1 kinase inhibitor torin-1 showed a similar inhibition profile, supporting the notion that early steps of BKPyV replication depend on mTOR activity. Cyclosporine A also inhibited BKPyV replication, while tacrolimus activated BKPyV replication and reversed sirolimus inhibition. FK binding protein 12kda (FKBP-12) siRNA knockdown abrogated sirolimus inhibition and increased BKPyV replication similar to adding tacrolimus. Thus, sirolimus and tacrolimus exert opposite effects on BKPyV replication in renal tubular epithelial cells by a mechanism involving FKBP-12 as common target. Immunosuppressive drugs may therefore contribute directly to the risk of BKPyV replication and nephropathy besides suppressing T cell functions. The data provide rationales for clinical trials aiming at reducing the risk of BKPyV replication and disease in kidney transplantation.

Changing Kidney Allograft Histology Early Posttransplant: Prognostic Implications of 1-Year Protocol Biopsies

Allograft histology 1 year posttransplant is an independent correlate to long-term death-censored graft survival. We assessed prognostic implications of changes in histology first 2 years posttransplant in 938 first kidney recipients, transplanted 1999-2010, followed for 93.4 ± 37.7 months. Compared to implantation biopsies, histology changed posttransplant showing at 1 year that 72.6% of grafts had minor abnormalities (favorable histology), 20.2% unfavorable histology, and 7.2% glomerulonephritis. Compared to favorable, graft survival was reduced in recipients with unfavorable histology (hazards ratio [HR] = 4.79 [3.27-7.00], p < 0.0001) or glomerulonephritis (HR = 5.91 [3.17-11.0], p < 0.0001). Compared to unfavorable, in grafts with favorable histology, failure was most commonly due to death (42% vs. 70%, p < 0.0001) and less commonly due to alloimmune causes (27% vs. 10%, p < 0.0001). In 80% of cases, favorable histology persisted at 2 years. However, de novo 2-year unfavorable histology (15.3%) or glomerulonephritis (4.7%) related to reduced survival. The proportion of favorable grafts increased during this period (odds ratio = 0.920 [0.871-0.972], p = 0.003, per year) related to fewer DGF, rejections, polyoma-associated nephropathy (PVAN), and better function. Graft survival also improved (HR = 0.718 [0.550-0.937], p = 0.015) related to better histology and function. Evolution of graft histologic early posttransplant relate to long-term survival. Avoiding risk factors associated with unfavorable histology relates to improved histology and graft survival.

What immunosuppression should be used for old-to-old recipients?

Elderly patients receiving a kidney from old donors (old-to-old) are a growing population of transplant recipients. This population cumulates risks of complications due to the co-morbidities and the immunodeficiency state and the frailty of the recipients together with the kidney senescence of the donors. In this context, the choice of immunosuppression is complicated and must take into account some contradictory principles explaining why no consensus exists today.

Observations on the use of cidofovir for BK virus infection in renal transplantation

BACKGROUND

In renal transplantation, BK virus infection can result in significant graft nephropathy and loss. While reduction in immunosuppression (IS) is considered standard therapy, adjunct agents may be warranted. Data are suggestive of a possible role of cidofovir for the management of BK. This study aims to describe the course of BK viremia (BKV) in a large cohort of renal transplant patients receiving adjunct cidofovir.

METHODS

We evaluated kidney and kidney-pancreas recipients who received cidofovir combined with reduced IS for management of high-level BKV or BK virus nephropathy (BKVN). We examined the rate and timing of BKV clearance, and performed a multivariate analysis to identify risk factors associated with long-term (>6 months) viremia.

RESULTS

In total, 75 patients received a median of 13 doses of cidofovir in conjunction with reduced IS; 32 patients (43%) had short-term BKV (≤6 months), and 43 (57%) had long-term BKV. Overall, 53 of 75 patients (71%) eventually cleared BKV at a median of 4.2 months (interquartile range 2.1-9.3 months). Independent factors associated with long-term BKV included older age (odds ratio [OR] 1.1, P = 0.02), delayed graft function (OR 31.4, P = 0.01), and higher peak BKV (OR 12.8, P = 0.02), while BKV reduction by at least 1 log(10) copies/mL at 1 month of treatment was associated with clearance within 6 months (OR 49.3, P < 0.01). Patients with earlier clearance maintained stable graft function and no graft losses, while long-term BKV was associated with a 15% decline in estimated glomerular filtration rate.

CONCLUSIONS

Adjunct cidofovir resulted in preservation of renal function when viral clearance occurred within 6 months of initiation. This retrospective review defines factors predicting response to cidofovir in conjunction with reduced IS for BKVN or high-level BKV. Still, considering cost, frequency of administration, and treatment duration, a randomized trial is necessary to define the exact utility of cidofovir in the setting of BK virus infection.

Polyomavirus BK replication in de novo kidney transplant patients receiving tacrolimus or cyclosporine: a prospective, randomized, multicenter study

Polyomavirus BK (BKV)-associated nephropathy causes premature kidney transplant (KT) failure. BKV viruria and viremia are biomarkers of disease progression, but associated risk factors are controversial. A total of 682 KT patients receiving basiliximab, mycophenolic acid (MPA), corticosteroids were randomized 1:1 to cyclosporine (CsA) or tacrolimus (Tac). Risk factors were analyzed in 629 (92.2%) patients having at least 2 BKV measurements until month 12 posttransplant. Univariate analysis associated CsA-MPA with lower rates of viremia than Tac-MPA at month 6 (10.6% vs. 16.3%, p = 0.048) and 12 (4.8% vs. 12.1%, p = 0.004) and lower plasma BKV loads at month 12 (3.9 vs. 5.1 log(10) copies/mL; p = 0.028). In multivariate models, CsA-MPA remained associated with less viremia than Tac-MPA at month 6 (OR 0.60; 95% CI 0.36-0.99) and month 12 (OR 0.33; 95% CI 0.16-0.68). Viremia at month 6 was also independently associated with higher steroid exposure until month 3 (OR 1.19 per 1 g), and with male gender (OR 2.49) and recipient age (OR 1.14 per 10 years) at month 12. The data suggest a dynamic risk factor evolution of BKV viremia consisting of higher corticosteroids until month 3, Tac-MPA compared to CsA-MPA at month 6 and Tac-MPA, older age, male gender at month 12 posttransplant.

Polyomavirus BK replication in de novo kidney transplant patients receiving tacrolimus or cyclosporine: a prospective, randomized, multicenter study

Polyomavirus BK (BKV)-associated nephropathy causes premature kidney transplant (KT) failure. BKV viruria and viremia are biomarkers of disease progression, but associated risk factors are controversial. A total of 682 KT patients receiving basiliximab, mycophenolic acid (MPA), corticosteroids were randomized 1:1 to cyclosporine (CsA) or tacrolimus (Tac). Risk factors were analyzed in 629 (92.2%) patients having at least 2 BKV measurements until month 12 posttransplant. Univariate analysis associated CsA-MPA with lower rates of viremia than Tac-MPA at month 6 (10.6% vs. 16.3%, p = 0.048) and 12 (4.8% vs. 12.1%, p = 0.004) and lower plasma BKV loads at month 12 (3.9 vs. 5.1 log(10) copies/mL; p = 0.028). In multivariate models, CsA-MPA remained associated with less viremia than Tac-MPA at month 6 (OR 0.60; 95% CI 0.36-0.99) and month 12 (OR 0.33; 95% CI 0.16-0.68). Viremia at month 6 was also independently associated with higher steroid exposure until month 3 (OR 1.19 per 1 g), and with male gender (OR 2.49) and recipient age (OR 1.14 per 10 years) at month 12. The data suggest a dynamic risk factor evolution of BKV viremia consisting of higher corticosteroids until month 3, Tac-MPA compared to CsA-MPA at month 6 and Tac-MPA, older age, male gender at month 12 posttransplant.

Polyomavirus BK replication in de novo kidney transplant patients receiving tacrolimus or cyclosporine: a prospective, randomized, multicenter study

Polyomavirus BK (BKV)-associated nephropathy causes premature kidney transplant (KT) failure. BKV viruria and viremia are biomarkers of disease progression, but associated risk factors are controversial. A total of 682 KT patients receiving basiliximab, mycophenolic acid (MPA), corticosteroids were randomized 1:1 to cyclosporine (CsA) or tacrolimus (Tac). Risk factors were analyzed in 629 (92.2%) patients having at least 2 BKV measurements until month 12 posttransplant. Univariate analysis associated CsA-MPA with lower rates of viremia than Tac-MPA at month 6 (10.6% vs. 16.3%, p = 0.048) and 12 (4.8% vs. 12.1%, p = 0.004) and lower plasma BKV loads at month 12 (3.9 vs. 5.1 log(10) copies/mL; p = 0.028). In multivariate models, CsA-MPA remained associated with less viremia than Tac-MPA at month 6 (OR 0.60; 95% CI 0.36-0.99) and month 12 (OR 0.33; 95% CI 0.16-0.68). Viremia at month 6 was also independently associated with higher steroid exposure until month 3 (OR 1.19 per 1 g), and with male gender (OR 2.49) and recipient age (OR 1.14 per 10 years) at month 12. The data suggest a dynamic risk factor evolution of BKV viremia consisting of higher corticosteroids until month 3, Tac-MPA compared to CsA-MPA at month 6 and Tac-MPA, older age, male gender at month 12 posttransplant.

Clinical role of the renal transplant biopsy

Percutaneous needle core biopsy is the definitive procedure by which essential diagnostic and prognostic information on acute and chronic renal allograft dysfunction is obtained. The diagnostic value of the information so obtained has endured for over three decades and has proven crucially important in shaping strategies for therapeutic intervention. This Review provides a broad outline of the utility of performing kidney graft biopsies after transplantation, highlighting the relevance of biopsy findings in the immediate and early post-transplant period (from days to weeks after implantation), the first post-transplant year, and the late period (beyond the first year). We focus on how biopsy findings change over time, and the wide variety of pathological features that characterize the major clinical diagnoses facing the clinician. This article also includes a discussion of acute cellular and humoral rejection, the toxic effects of calcineurin inhibitors, and the widely varying etiologies and characteristics of chronic lesions. Emerging technologies based on gene expression analyses and proteomics, the in situ detection of functionally relevant molecules, and new bioinformatic approaches that hold the promise of improving diagnostic precision and developing new, refined molecular pathways for therapeutic intervention are also presented.

Inhibition of polyomavirus BK-specific T-Cell responses by immunosuppressive drugs

BACKGROUND

Reducing immunosuppression is the treatment of choice for polyomavirus-associated nephropathy in kidney transplant (KT) patients, but strategies and targets are uncertain.

METHODS

Using interferon-gamma ELISpot assays, we investigated immunosuppressive drug levels and polyomavirus BK (BKV) large T-antigen-specific T-cell responses in KT patients in vivo and in healthy donors after titrating immunosuppression in vitro.

RESULTS

In KT patients, BKV-specific T-cell responses were inversely correlated with tacrolimus trough levels (R=0.28, P<0.002), but not with mycophenolate levels, prednisone, or overall immunosuppressive dosing. In vitro tacrolimus concentrations above 6 ng/mL inhibited BKV- and cytomegalovirus-specific T-cells more than 50%, whereas less than 30% inhibition was observed below 3 ng/mL. Inhibition by cyclosporine A was more than 50% at concentrations of 1920 ng/mL and less than 30% below 960 ng/mL, corresponding to clinical C0 trough levels of 200 and 100 ng/mL, respectively. However, mycophenolate up to 8 microg/mL, leflunomide 50 microg/mL, or sirolimus concentrations 64 ng/mL did not inhibit BKV-specific interferon-gamma production, but antigen-dependent T-cell expansion.

CONCLUSIONS

Calcineurin-inhibitor concentrations are critical for BKV-specific T-cell activation. Reducing calcineurin inhibitors should be considered as first step, whereas conversion to mTOR inhibitors may be an attractive alternative or second step that should be validated in clinical BKV intervention trials.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

An OPTN analysis of national registry data on treatment of BK virus allograft nephropathy in the United States

INTRODUCTION

Published data for BK virus allograft nephropathy, a recently emerged graft-threatening complication of kidney transplantation, are from limited-center series. Since June 30, 2004, the Organ Procurement Transplant Network national registry in the United States started collecting data on treatment of BK virus (TBKV) on the kidney follow-up forms. This study determined the rates of TBKV within 24 months posttransplant time and elucidated the risk factors for TBKV from this multicenter database.

METHODS

We queried the database for all primary and solitary kidney transplant recipients transplanted between January 1, 2003 and December 31, 2006, followed through July 18, 2008, and who were reported to have TBKV. Cumulative incidence of TBKV over time was estimated using Kaplan-Meier (K-M) method to reduce potential under reporting. A Cox proportional hazards regression model was fitted to determine risk factors for TBKV development, and time dependent Cox model was fitted to determine if TBKV was associated with higher risk of graft loss.

RESULTS

We included 48,292 primary and solitary kidney transplants from the US Organ Procurement Transplant Network database. The cumulative K-M incidence of BKVAN kept rising over time (0.70% at 6 months posttransplant to 2.18% at 1 year, 3.45% at 2 years and 6.6% at 5 years). Risk for BKVAN was higher with certain immunosuppressive regimens that included rabbit antithymocyte globulin or tacrolimus/mycophenolate combinations. Higher center volume and living kidney donation exerted a protective effect. Of concern, TBKV rates were significantly higher in more recent transplant years. TBKV report was associated with higher risk of subsequent graft loss (adjusted hazard ratio=1.69, P<0.001).

Identifying specific causes of kidney allograft loss

The causes of kidney allograft loss remain unclear. Herein we investigated these causes in 1317 conventional kidney recipients. The cause of graft loss was determined by reviewing clinical and histologic information the latter available in 98% of cases. During 50.3 +/- 32.6 months of follow-up, 330 grafts were lost (25.0%), 138 (10.4%) due to death with function, 39 (2.9%) due to primary nonfunction and 153 (11.6%) due to graft failure censored for death. The latter group was subdivided by cause into: glomerular diseases (n = 56, 36.6%); fibrosis/atrophy (n = 47, 30.7%); medical/surgical conditions (n = 25, 16.3%); acute rejection (n = 18, 11.8%); and unclassifiable (n = 7, 4.6%). Glomerular pathologies leading to failure included recurrent disease (n = 23), transplant glomerulopathy (n = 23) and presumed nonrecurrent disease (n = 10). In cases with fibrosis/atrophy a specific cause(s) was identified in 81% and it was rarely attributable to calcineurin inhibitor (CNI) toxicity alone (n = 1, 0.7%). Contrary to current concepts, most cases of kidney graft loss have an identifiable cause that is not idiopathic fibrosis/atrophy or CNI toxicity. Glomerular pathologies cause the largest proportion of graft loss and alloinmunity remains the most common mechanism leading to failure. This study identifies targets for investigation and intervention that may result in improved kidney transplantation outcomes.

Treatment for BK virus: incidence, risk factors and outcomes for kidney transplant recipients in the United States

There has been a notable rise of BK virus among kidney transplant recipients. Single-center reports have identified risk factors for development of BK virus. However, there has not been an assessment of risk factors and incidence of this complication at a national level. This study utilized newly collected follow-up information from the national SRTR database to investigate incidence, risk factors and outcomes for solitary kidney transplant recipients associated with treatment for BK virus (TBKV) from 2004 to 2006. Logistic and Cox models were utilized to assess risk factors and evaluate graft survival associated with TBKV. Incidence of TBKV was 1.6% at 6 months and 2.6% at 1 year following transplantation. Patients with and without TBKV at 6 months had 79% and 90% 3-year overall graft survival respectively. Risk factors included advanced donor age, pediatric, African American and male recipients, human leukocyte antigen-mismatching and tacrolimus and thymoglobulin induction as baseline immunosuppression. Acute rejection episodes were more frequent prior to and following TBKV. TBKV is a common and rising incidence, varies based on transplant characteristics and should be included as a safety endpoint in studies investigating immunosuppressive protocols. Careful monitoring and further understanding of disease etiology and treatment strategies are needed.

Risk factors for polyoma virus nephropathy

BACKGROUND

Polyoma virus-associated nephropathy (PVN) is a common cause of renal transplant failure. The risk factors for the development of PVN have not yet been studied in large cohorts of patients for periods of 20 years.

METHODS

We collected clinical, renal biopsy and urinary cytology data from all patients with renal transplantations performed at the University Hospital of Basel from 1985 to 2005. All patients with a renal biopsy and urine cytology were included (n = 880). Renal transplants were divided into three groups, according to evidence of polyoma virus (PV) infection (decoy cells in the urine) and biopsy-proven PVN: Renal transplants without evidence of a PV infection (n = 751). Renal transplants with PV reactivation, e.g. decoy cell (DC) found by urinary cytology, but without PVN (n = 90). Renal transplants with PVN (n = 39).

RESULTS

The prevalence of biopsy-proven PVN in this cohort of patients was 3.3%. Immunosuppression with mycophenolate and/or tacrolimus, ATGAM, male gender of the recipient and a higher number of transplant rejection episodes were factors significantly associated with PVN development.

CONCLUSIONS

The most important risk factors for the development of PVN are acute rejection and ATGAM used as induction therapy as well as tacrolimus and mycophenolate as maintenance therapy. Therefore, we conclude that patients with tacrolimus and mycophenolate maintenance therapy should be carefully monitored for the development of PVN.

BK virus nephropathy in renal transplant patients in London

BACKGROUND

BK nephropathy (BKN) is an important cause of renal transplant dysfunction, believed to be associated with higher levels of immunosuppression. We assessed the experience of BKN in renal transplant patients in the London region.

METHODS

All six London transplant centers participated and case notes of patients with BKN in 2004 to 2005 were reviewed.

RESULTS

There were 17 cases of BKN, giving an incidence of 2.1%. Median time to diagnosis was 9 months. Median baseline creatinine rose from 150 to 196 mumol/L. At diagnosis, 16 patients were on tacrolimus, 15 on mycophenolate mofetil, and 10 on triple therapy with tacrolimus, mycophenolate mofetil, and prednisolone. Management of BKN involved reducing immunosuppression; cidofovir was used in two patients and methylprednisolone in five for acute rejection. Median follow-up time was 29.2 months. Creatinine returned to baseline in four patients, remained elevated in 12 and one patient lost his graft. The new median baseline creatinine was 216 mumol/L. Eight patients underwent repeat biopsies of which four became negative for BKV and three subsequently cleared the virus on blood and urine polymerase chain reaction and urine decoy cells. Overall, eight patients cleared the virus. None of age, sex, viral load, or biopsy characteristics (Banff ct score, Drachenberg grade, and number of BKV positive cells) were associated with poorer outcome when patients with increase in creatinine of less than 30% (n=7) or more than 30% (n=10) from baseline were compared.

CONCLUSION

The incidence of BKN in this study is comparable with previous studies, with more favorable outcomes. It supports the association of BKN with potent immunosuppression.

BK virus nephritis after renal transplantation

BK virus nephritis is an increasing problem and is posing a threat to improving renal transplant graft survival. The pathogenesis of this condition remains to be investigated. Higher prevalence of BK virus infection in recent years has been correlated with declining acute rejection rates and the use of potent immunosuppressive agents. Patients with this infection usually have asymptomatic viremia and/or nephritis with or without worsening of renal function. The diagnosis of this disease is based on detecting the virus or its effects in urine, blood, and renal tissue. In the past, approximately 30 to 60% of patients with BK virus nephritis developed graft failure. In recent years, the combination of early detection, prompt diagnosis, and therapies including preventive measures have resulted in better outcomes.