Human polyoma virus-associated interstitial nephritis in the allograft kidney

A correlation between polyomavirus JC virus quantification and genotypes in renal transplantation

OBJECTIVE

To determine whether the John Cunningham virus (JCV) viral load and the multigenotypes in viruria are correlated with transplant patients.

METHODS

The urine of 60 renal transplant patients and 60 healthy controls were screened. We used quantitative real-time polymerase chain reaction and capillary electrophoresis to assess viral load and genotype respectively.

RESULTS

The incidence of viruria and viral load were higher in transplant patients with P = .0092 and P = .0094, respectively. The incidence of different genotype in transplant patients versus controls was 8.3% versus 13.3% for single genotype, 26.7% versus 5% for 2 genotypes, and 5% versus 0% for multigenotypes (P = .0004). The incidence of more than 2 genotypes was high in people with a high viral load and closely related with the transplant patients (P = .007).

CONCLUSIONS

Not only viral load but also genotypes are important as a screening parameter to understand the immune milieu of the patients to prevent subsequent complications like polyomavirus nephropathy, infection, and malignancy.

Validation of noninvasive diagnosis of BK virus nephropathy and identification of prognostic biomarkers

BACKGROUND

BK virus nephropathy (BKVN) may cause renal allograft dysfunction and failure. The gold standard test is kidney biopsy, which is invasive and costly. A noninvasive, accurate biomarker for diagnosis of BKVN and prognostication of allograft function after BKVN infection may improve allograft survival.

METHODS

We tested the diagnostic accuracy of our previously reported cutoff value of 6.5x10(5) BKV viral capsid protein 1 (VP-1) mRNA/ng RNA in urinary cells (Ding et al., Transplantation 2002; 74: 987) using an independent cohort (n=89). We also examined whether urinary cell mRNA profiles obtained at the time of BKVN diagnosis identified patients at risk of subsequent decline in graft function.

RESULTS

BKVN was accurately diagnosed (sensitivity of 100% and specificity of 97%) using our previously reported cutoff value. Levels of granzyme B (GB) mRNA (P=0.002) and proteinase inhibitor (PI)-9 mRNA (P=0.01) in urinary cells were higher in BKVN patients with a subsequent decline in renal function (n=8) compared with patients with stable function (n=10), and were positively associated (GB, P=0.01; PI-9, P=0.04) with rise in serum creatinine from the time of BKVN diagnosis to 12 months after diagnosis. GB levels in the BKVN patients with a decline in renal function were similar to those in the acute rejection group (n=11, P>0.05), but higher than the normal biopsy group (n=36, P<0.001); levels in BKVN patients with stable function were lower than those in the acute rejection group (P<0.01) and not significantly different from the normal biopsy group (P>0.05).

CONCLUSIONS

Noninvasive diagnosis of BKVN and prognostication of renal allograft function after BKVN diagnosis are feasible by measurement of transcripts for BKV viral capsid protein 1 (VP-1), GB, and PI-9 in urine.

Treatment of polyomavirus infection in kidney transplant recipients: a systematic review

BACKGROUND.: Polyomavirus-associated nephropathy (PVAN) is an important cause of kidney graft loss but there is no consensus on its management. This study aimed to systematically document all published treatments for PVAN to determine the most effective therapy. METHODS.: A computerized search in MEDLINE, EMBASE, and Cochrane databases (1950-2008) was performed. References from review articles and published abstracts from the American Transplant Congress (2005-2008) were also included. Study selection criteria included (a) population: adult (>18 years) kidney-only, primary or repeat renal transplant recipients; (b) setting: polyoma viruria, viremia or biopsy-proven PVAN or both; and (c) treatment: immunosuppression reduction alone or with adjuvant agents. The primary outcome was graft failure rate, and secondary outcomes included acute rejection rate, elimination of viruria and viremia, graft function, patient survival, and adverse events. RESULTS.: Of 555 identified citations, 40 studies examining the effect of immunosuppression reduction alone or in combination with cidofovir, leflunomide, intravenous immunoglobulin, or ciprofloxacin were included for appraisal. Pooled results found a death-censored graft loss rate of 8/100 patient-years for immunosuppression reduction alone and 8 and 13/100 patient-years for the addition of cidofovir or leflunomide, respectively. CONCLUSIONS.: There does not seem to be a graft survival benefit of adding cidofovir or leflunomide to immunosuppression reduction for the management of PVAN. However, the evidence base is poor and highlights the urgent need for adequately powered randomized trials to define the optimal treatment of this important condition.

Quantitative real-time polymerase chain reaction detection of BK virus using labeled primers

CONTEXT

BK virus infections among immunocompromised patients are associated with disease of the kidney or urinary bladder. High viral loads, determined by quantitative polymerase chain reaction (PCR), have been correlated with clinical disease.

OBJECTIVE

To develop and evaluate a novel method for real-time PCR detection and quantification of BK virus using labeled primers.

DESIGN

Patient specimens (n = 54) included 17 plasma, 12 whole blood, and 25 urine samples. DNA was extracted using the MagNA Pure LC Total Nucleic Acid Isolation Kit (Roche Applied Science, Indianapolis, Indiana); sample eluate was PCR-amplified using the labeled primer PCR method. Results were compared with those of a user-developed quantitative real-time PCR method (fluorescence resonance energy transfer probe hybridization).

RESULTS

Labeled primer PCR detected less than 10 copies per reaction and showed quantitative linearity from 10(1) to 10(7) copies per reaction. Analytical specificity of labeled primer PCR was 100%. With clinical samples, labeled primer PCR demonstrated a trend toward improved sensitivity compared with the reference method. Quantitative assay comparison showed an R(2) value of 0.96 between the 2 assays.

CONCLUSIONS

Real-time PCR using labeled primers is highly sensitive and specific for the quantitative detection of BK virus from a variety of clinical specimens. These data demonstrate the applicability of labeled primer PCR for quantitative viral detection and offer a simplified method that removes the need for separate oligonucleotide probes.

Survey for the presence of BK, JC, KI, WU and Merkel cell polyomaviruses in human brain tissues

BACKGROUND

Recently three previously unknown polyomaviruses (KI, WU and Merkel cell polyomaviruses) have been identified from human specimens. The spectrum of clinical manifestations and their tissue tropism are currently unknown. Since a member of this virus family, JC virus, is well-known for its capacity to establish latency in human brain tissue where reactivation in immunocompromised individuals can result in fatal progressive multifocal leukoencephalopathy, we sought to examine for the presence of all the five known human polyomaviruses in a series of human brain tissues.

OBJECTIVES

To investigate the possibility of neuropersistence of the newly identified human polyomaviruses.

STUDY DESIGN

Autopsy brain tissues were collected from 10 different brain regions of 30 individuals who died from diseases unrelated to viral infections. Nested PCR was used to assess the presence or absence of viral DNA.

RESULTS

Ten samples collected from five individuals were found to harbour JCV DNA. In contrast, none of the 300 brain tissues examined showed positive results for BK, KI, WU or Merkel cell polyomavirus.

CONCLUSION

The newly identified KI, WU and Merkel cell polyomaviruses either do not, or have a much lower neuropersistent potential compared to JCV.

Hemorrhagic cystitis and possible neurologic disease from BK virus infection in a patient with AIDS

BK virus (BKV)-associated hemorrhagic cystitis occurs in bone marrow transplant recipients but is rare among other immunosuppressed patients. We present a rare case of BKV-associated hemorrhagic cystitis in a 48-year-old man with AIDS and previously diagnosed progressive multifocal leukoencephalopathy.

BK-virus and the impact of pre-emptive immunosuppression reduction: 5-year results

A 1-year, single-center, randomized trial demonstrated that the calcineurin inhibitor or adjuvant immunosuppression, independently, does not affect BK-viruria or viremia and that monitoring and pre-emptive withdrawal of immunosuppression was associated with resolution of BK-viremia and absence of clinical BK-nephropathy without acute rejection or graft loss. A retrospective 5-year review of this trial was conducted. In cases of BK viremia, the antimetabolite was withdrawn and for sustained viremia, the calcineurin inhibitor was minimized. Five-year follow-up was available on 97% of patients. Overall 5-year patient survival was 91% and graft survival was 84%. There were no differences in patient-survival by immunosuppressive regimen or presence of BK-viremia. Immunosuppression and viremia did not influence graft survival. Acute rejection occurred in 12% by 5-years after transplant, was less common with tacrolimus versus cyclosporine (9% vs. 18%; p = 0.082), and was lowest with the tacrolimus-azathioprine regimen (5%, p = 0.127). Tacrolimus was associated with better renal function at 5-years (eGFR 63 FK vs. 52 CsA mL/min, p = 0.001). Minimization of immunosuppression upon detection of BK-viremia was associated with excellent graft survival at 5-years, low rejection rates and excellent renal function. It is a safe, short and long-term strategy that resulted in freedom from clinically evident BK-virus nephropathy.

Human polyoma viruses and disease with emphasis on clinical BK and JC

Polyoma viruses are ubiquitous infecting many different mammalian species including humans. There are five known human polyoma viruses. JC virus and BK virus are two polyoma viruses identified nearly three decades ago. Recently WU, KI and Merkel cell polyoma viruses have been isolated from humans. The exact role of these three newly discovered viruses in human disease is not known. Most human polyoma disease is caused by BK and JC viruses which are usually acquired in childhood. Approximately 50-80% of humans have seropositivity to these viruses. Clinically apparent diseases in immunocompetent hosts are extremely rare. These viruses remain latent possibly in the lymphoid organs, neuronal tissue, and kidney and under the circumstances of severe immunosuppression both these viruses reactivate. Neurotropic JC virus reaches the brain and causes progressive multifocal leukoencephalopathy, a demyelinating disease of the central nervous system with a high mortality rate. BK virus is urotheliotropic and its reactivation causes a form of interstitial nephritis, known as BK or polyoma virus associated nephropathy which is associated with high graft loss if not recognized early. There are no known effective antiviral agents for any of the polyoma viruses.

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.

Functional analysis of polyomavirus BK non-coding control region quasispecies from kidney transplant recipients

Replication of the human polyomavirus BK (BKV) in renal tubular epithelial cells causes viruria and BKV-nephropathy in kidney transplant recipients. Following prolonged high-level BKV replication, rearrangement of the archetype non-coding control region (NCCR) leads to a mixture of BKV variants. The aim of this study was to compare potential functional differences of 12 rearranged (rr)-NCCR variants with the archetype (ww)-NCCR (WWT) found in allograft biopsies or urine from three kidney transplant recipients including two with BKV-nephropathy. Twelve different rr-NCCRs and one archetype ww-NCCR were inserted between the early and late protein coding region of BKV(Dunlop) to make recombinant BKV genomes for transfection into Vero cells. Immunoblotting, immunofluorescence staining, and quantitative PCR demonstrated that viral protein expression and extracellular BKV loads of 10 rr-NCCR variants were similar or higher than observed for the ww-NCCR BKV. Two rr-NCCR variants (RH-2 and RH-19) were non-functional. The functional rr-NCCRs produced infectious progeny successfully infecting primary renal proximal tubular epithelial cells. The number of infected cells and extracellular BKV loads corresponded to the activity seen in Vero cells. Three rr-NCCR variants (RH-1, RH-10, RH-13) only gave rise to a few infected cells similar to ww-NCCR, whereas seven variants had intermediate activity (RH-5, RH-6, RH-8, RH-9, RH-11) or high replication activity (RH-7 and RH-18) with several hundred infected cells per well. The results indicate that both functional and non-functional BKV rr-NCCR variants arise during BKV replication in kidney transplant recipients and that most functional rr-NCCR variants confer a higher replication capacity than archetype ww-NCCR.

Plasma cell infiltrates in polyomavirus nephropathy

Polyomavirus (PV) associated nephropathy (PVAN) has become an important cause of allograft dysfunction. We studied plasma cells (PCs) - which have not yet been characterized - present in the cellular infiltrate of 20 PVAN cases using immunohistochemistry and morphometry. The results were correlated with morphological, clinical and anti-BK virus serological findings. PC-rich cellular infiltrates occurred in 50% of cases (>15% PCs in the cellular infiltrate) and in these IgM producing PCs were commonly seen (70%): IgM PC predominance in 50% of cases and a comparable number of IgM and IgG PCs in 20% of cases. We found a significant correlation not just between the absolute numbers (P < 0.034) and the percentage values of IgM PCs (P < 0.004 in relation to all cells) and the serum IgM-Ab anti-BKV activity, but also between the ratio of IgG/IgM PCs and the ratio of serum IgG/IgM-Ab activities (P < 0.0001). We showed that IgM PC counts in biopsies correlate with titers of circulating anti-BK virus IgM antibodies. Every case except one was C4d negative in peritubular capillaries (PTC). As IgG PCs characterize PC-rich rejection cases, we suggest that in the presence of IgM PCs in PC-rich infiltrate with PTC C4d negativity, a search for possible PVAN infection should be initiated.

The significance of renal C4d staining in patients with BK viruria, viremia, and nephropathy

Peritubular capillary C4d staining in allograft kidney is an important criterion for antibody-mediated rejection. Whether BK virus infection can result in complement activation is not known. We studied 113 renal allograft biopsies from 52 recipients with a history of BK virus activation. The samples were classified into four groups according to the concurrent detection of BK virus DNA in urine, plasma, and/or biopsy: BK-negative (n=37), viruria (n=53), viremia (n=7), and nephropathy (n=16) groups. The histological semiquantitative peritubular capillary C4d scores in the viremia (0.3+/-0.8) and BK nephropathy (0.6+/-0.9) groups were lower than those in the BK-negative group (1.2+/-1.1, P=0.05 and P=0.06, respectively) and the viruria group (1.2+/-1.1, P=0.04 and P=0.06, respectively). Diffuse or focal peritubular capillary C4d staining was present in 9/76 (12%) and 14/76 (19%) of all samples with concurrent BK virus reactivation (viruria, viremia, and nephropathy). The diagnosis of antibody-mediated rejection could be established in 7/9 (78%) and 5/14 (36%) of these samples, respectively. Diffuse tubular basement membrane C4d staining was restricted to BK nephropathy cases (4/16, 25%). Semiquantitative tubular basement membrane C4d scores were higher in BK nephropathy (1.2+/-1.3) compared with BK-negative (0.05+/-0.3, P=0.017) and viruria (0.0+/-0.0, P=0.008) groups. Bowman's capsule C4d staining was more frequent in BK nephropathy (5/16) compared with the aforementioned groups (2/36 (P=0.023) and 4/51 (P=0.03), respectively). Within the BK nephropathy group, samples with tubular basement membrane stain had more infected tubular epithelial cells (12.1+/-7.6% vs 4.4+/-5.0%, P=0.03) and a trend toward higher interstitial inflammation scores. In conclusion, peritubular capillary C4d staining remains a valid marker for the diagnosis of antibody-mediated rejection in the presence of concurrent BK virus infection. A subset of biopsies with BK nephropathy shows tubular basement membrane C4d staining, which correlates with marked viral cytopathic effect.

Evolution of the BK polyomavirus: epidemiological, anthropological and clinical implications

BK polyomavirus (BKV) is essentially ubiquitous in all human populations worldwide. Asymptomatic infection with this virus occurs during early childhood, leading to life-long persistence in the kidney. BKV has four subtypes that can be identified using serological and genotyping methods. The evolutionary aspects of BKV have remained poorly understood due to the limited availability of BKV genomes, since urinary excretion of BKV DNA is detected primarily in immunocompromised individuals. However, we have found that BKV DNA sequences can often be amplified from non-immunocompromised elderly individuals, using a highly sensitive polymerase chain reaction (PCR) with highly concentrated urinary DNA as the source of viral DNA. Using this approach, we have PCR-amplified and sequenced a large number of partial and complete BKV genomes from various human populations worldwide and conducted a series of evolutionary studies using these sequences. We have shown that subtypes I and IV evolved into four and six subgroups, respectively, with each having a close relationship with a particular human population. In addition, we have provided evidence supporting the hypothesis that BKV strains with the archetypal transcriptional control region (TCR) circulate in the human population. In this review, we describe these findings and discuss their epidemiological, anthropological and clinical implications.

Maintenance immunosuppressive agents as risk factors for BK virus nephropathy: a case-control study

BACKGROUND

The specific role of different immunosuppressive agents as risk factors for BK virus nephropathy (BKN) has not been well studied.

METHODS

In this case-control study, we examined the association of tacrolimus (TAC), mycophenolate mofetil (MMF), and prednisone with BKN in renal allograft recipients transplanted between 1997 and 2004 at our center who underwent biopsies for allograft dysfunction. Drug levels or doses were recorded during the 3 months before the index biopsy. Random effects logistic modeling was used for data analysis.

RESULTS

There were 33 cases with BKN, biopsied at 16.4+/-2.8 months and 66 matched controls with biopsies at 21.5+/-2.1 months posttransplant (P=0.16). After adjusting for sex, race, retransplant status, diabetes, donor source, and induction agent, TAC blood level was associated with increased risk of BKN (odds ratio [OR] 1.3, 95% confidence interval [CI] 1.02-1.7, P=0.03), whereas MMF dose was not (OR 1.0, 95% CI 0.99-1.0, P=0.2). Moreover, prednisone dose was also found to be a significant risk factor for BKN (OR 1.22, 95% CI 1.04-1.4, P=0.02).

CONCLUSIONS

The results of this study show that BKN is associated with TAC level and prednisone dose and not with MMF dose. This suggests that reducing TAC and prednisone dose and maintaining MMF may be a more appropriate initial approach for the treatment of BKN. Further studies are needed to compare the efficacy and safety of this approach with the currently recommended one.

The decade of polyomavirus BK-associated nephropathy: state of affairs

In the last 10 years, better immunosuppression drugs have decreased the rates of acute rejection in kidney transplantation but have also led to the emergence of polyomavirus-associated nephropathy (PVAN). This occurs in 1% to 10% of patients with kidney transplantion and is caused by BK virus in more than 95% of cases. Less than 5% of cases are attributed to the JC virus. Initially, lack of recognition or late diagnosis of PVAN resulted in rapid loss of graft function in more than 50% of patients. In recent years, it has become clear that early diagnosis and timely reduction in immunosuppression is the only proven measure, which significantly affects the outcome of PVAN. Diverse interventions have been explored including the adjunctive use of cidofovir, leflunomide, fluoroquinolones, and intravenous immunoglobulins. Allograft histology is needed to definitively establish the diagnosis of PVAN, but is of limited sensitivity in the early stage of disease. Well-established techniques and protocols for systematic screening by urine cytology and quantitative molecular-genetic techniques allow now for timely intervention before irreversible parenchymal changes occur. Moreover, preemptive reduction in immunosuppression is most effective in presumptive PVAN as defined by surrogate markers (i.e., high BK virus viremia). In this setting, preservation of graft function can be considered the rule. Nevertheless, the recovery of BK virus-specific T-cell immunity may require prolonged periods during which cytopathic damage may continue to accumulate. Despite remarkable progress in the field, important challenges remain, such as the rare patient with PVAN refractory to any intervention and the newly recognized association of PVAN with urogenital tumors.

HLA-A01-, -A03-, and -A024-binding nanomeric epitopes in polyomavirus BK large T antigen

Polyomavirus BK (BKV) infections are increasingly recognized. The development of immune-monitoring strategies against BKV requires definition of antigenic epitopes. Bioinformatic algorithms were used to identify 60 BKV large T-antigen (LT-Ag) peptides predicted to bind HLA class I alleles. In vitro peptide binding was used to select a subset of 19 peptides for interferon (IFN)-gamma ELISPOT assays in 13 healthy subjects and 12 kidney transplant recipients. Four A01-, nine A03-, and five A24-binding immunogenic peptides were identified in 1 to 3 (14-67%) tested subjects in each group. BKV epitope sequences were identical to homologous JC virus sequences for 3 of 19 peptides and homologous SV40 sequences for 5 of 19 peptides. Homology modeling localized these epitopes to the helicase, origin of DNA binding, or J domains, respectively. In conclusion, we have identified multiple 9-mer BKV LT-Ag-derived immunogenic epitopes that bind HLA-A01, -A03, or -A24 molecules. Sequence alignments indicate that two epitopes, FLICKGVNK and RYWLFKGPI, are common to BKV, JC virus, and SV40 virus.

Polyomavirus nephropathy: a current perspective and clinical considerations

During the last decade, the human polyomaviruses (BK virus and, much less commonly, JC virus) have entered the realm of routine clinical decision making for providers caring for kidney transplant recipients. The emergence of polyomavirus-associated nephropathy (PVAN) as an important clinical entity coincided with the development and use of more potent immunosuppression agents, currently the only clear risk factor for reactivation of the virus. Ongoing efforts to define the pathogenesis, clinical presentation, and appropriate management of PVAN have led to a greater ability to prevent and control viral-induced interstitial nephritis despite continued deficiencies in our understanding of risk factors for disease and lack of published prospective polyomavirus-specific antiviral trials. The purpose of this review is to summarize advances made during the last decade and highlight emerging data that address common clinical considerations the clinician currently faces in the understanding and management of PVAN.

Identification of species-specific and cross-reactive epitopes in human polyomavirus capsids using monoclonal antibodies

The human antibody response to polyomavirus capsid proteins is not well characterized. Recombinant BK virus (BKV), JC virus (JCV) and simian virus 40 (SV40) virus-like particles (VLP) were produced in a baculovirus system, and mouse monoclonal antibodies (mAbs) to these proteins were generated using standard methods. Nine of 12 BKV mAbs showed neutralizing activity. The non-neutralizing antibodies also bound BKV pseudocapsids in an ELISA binding assay. Most antibodies recognized conformational species-specific epitopes, but several exceptions were found: (i) BKV mAb BK-F11 cross-reacted with a linear buried epitope common to both JCV and SV40 pseudocapsids, (ii) two of six JCV antibodies (JC-6.7 and JC-7.9) and two of 13 SV40 antibodies (VP1-H2 and VP1-I2) recognized linear buried epitopes common to all three viruses and (iii) SV40 antibody VP1-E5 recognized a linear surface epitope on JCV pseudocapsids.

Reactivation and mutation of newly discovered WU, KI, and Merkel cell carcinoma polyomaviruses in immunosuppressed individuals

BACKGROUND

Infection with the human polyomaviruses BK (BKV) and JC (JCV) is almost ubiquitous, asymptomatic, and lifelong. However, reactivation during immunosuppression, associated with mutations in the transcriptional control region (TCR) that up-regulates viral replication, can cause life-threatening disease. In this study, we investigated whether the recently discovered WU and KI polyomaviruses (WUPyV and KIPyV) and Merkel cell polyomavirus (MCPyV) could, like BKV and JCV, persist, mutate, and reactivate in immunodeficient subjects.

METHODS

Autopsy samples of lymphoid tissue from 42 AIDS-immunosuppressed subjects and 55 control samples were screened by polymerase chain reaction for all 5 polyomaviruses. TCR sequences from KIPyV and WUPyV recovered from both immunosuppressed and nonimmunosuppressed subjects were compared.

RESULTS

Combined polyomavirus detection frequencies were much higher for the immunosuppressed group, compared with the nonimmunosuppressed group (35.7% vs. 3.6%), with viral loads in lymphoid tissues ranging from < or = 8.4 x 10(5) to > 1.5 x 10(5) viral genome copies per 10(6) cells. MCPyV was recovered from only 1 HIV-negative study subject. TCR sequences from reactivated WUPyV and KIPyV variants showed a number of point mutations and insertions that were absent in viruses recovered from respiratory tract specimens obtained from nonimmunosuppressed subjects.

CONCLUSIONS

KIPyV and WUPyV show reactivation frequencies comparable to those of BKV and JCV during immunosuppression. TCR changes that potentially lead to transcriptional dysregulation may have pathogenic consequences equivalent in severity to those observed for JCV and BKV.

Cellular immune responses to BK virus

PURPOSE OF REVIEW

Defects in cellular immunity to persistent viral infections are associated with an increased frequency and severity of viral diseases after transplantation. Polyomavirus BK (BKV) infection has emerged as an important cause of virus-related nephropathy after kidney allograft. Cell-mediated immunity seems to have a central role in preserving BKV latency. However, characterization of BKV-specific immunity has only recently begun.

RECENT FINDINGS

Immune responses to BKV are not fully understood, but pioneer work points to cell-mediated immunity as a critical factor for the control of viral replication and recovery from BKV disease.

SUMMARY

Advances in immunological techniques will provide further insight into the specificity and patterns of cellular response to BKV, which should assist translation into improved patient management and development of immunotherapeutic approaches.

Immunophenotyping of interstitial infiltrate does not distinguish between BK virus nephropathy and acute cellular rejection

INTRODUCTION

BK virus nephropathy (BKVN) is a significant cause of late renal allograft loss. It is characterized histologically by an interstitial nephritis that can be difficult to distinguish from acute cellular rejection (ACR). We investigated whether immunophenotyping of the infiltrate would aid this distinction.

METHODS

Ten cases of biopsy-proven BKVN, following renal transplantation, were identified from a single transplant centre. The infection was confirmed by renal biopsy and staining for SV-40 T-antigen. Biopsies from 20 consecutive patients with ACR were identified and used as controls. There was no evidence of BK infection serologically or histologically in these patients. Immunohistochemical staining with anti-CD20, perforin and granzyme B was performed on remaining tissue samples.

RESULTS

Clustered B cells were demonstrated in both BKVN and ACR. Hence, the CD20-stained component within the interstitial infiltrate was not useful in distinguishing these biopsies. Perforin-stained slides demonstrated fewer cytotoxic T cells in the biopsies with BK virus (average 2.4 +/- 1.4 cells per 100 lymphocytes per field) compared with those samples with acute rejection (8.6 +/- 5.7 cells per 100 lymphocytes, P < 0.0001). No significant difference in granzyme B staining was detected between ACR and BKVN.

CONCLUSION

Clustered B cells and granzyme B staining did not differentiate between ACR and BKVN. However, ACR cellular infiltrate was rich in perforin positive cells suggesting that perforin staining may be a useful marker to discriminate between these conditions.

Mutations in the BC-loop of the BKV VP1 region do not influence viral load in renal transplant patients

The reactivation and replication of the BK polyomavirus (BKV) leading to BKV-associated nephropathy (BKVAN) is one of the major complications in renal transplantation patients. BKV isolates were classified into four subtypes (I-IV) based on genotype variations within the VP1-coding region. The type-specific amino acid differences cluster within the BC-loop of the major capsid protein VP1. As demonstrated in vitro, mutations in this region also play a role in the infectivity, attachment and stability of viral particles. Therefore, we analyzed the prevalence of BC-loop mutations in isolates of kidney transplant patients and compared their viral load in the urine. The VP1 subtyping regions of BKV isolates obtained from urine samples of 45 renal transplant patients were sequenced. The phylogenetic analysis of these sequences revealed that subtype I (66.67%) is the most prevalent genotype. The remaining isolates belong to subtype IV (33.33%). A high frequency of changes to specific amino acids within the BC-loop was identified among the BKV isolates from renal transplant patients. Patients with BKVAN exhibited a higher viral replication than patients without nephropathy. Although titers of isolates of subtype I were higher than titers of subtype IV isolates, the difference did not reach statistical significance. In addition, amino acid changes in the BC-loop did not influence the viral load and the incidence of BKVAN. These in vivo results demonstrate that high replication rates which serve as a predictive marker for BKVAN are not caused by altered receptor binding or affinity via mutated BC-loops.

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.

Decline in native kidney function in liver transplant recipients is not associated with BK virus infection

BK virus (BKV) infection is an established cause of allograft dysfunction in renal transplant recipients. The relationship between BKV infection and chronic kidney disease (CKD) post-orthotopic liver transplantation (OLT) is not well understood. This study aimed to determine the prevalence of BKV infection, its relationship to CKD and renal function loss over time in patients receiving OLT. Prevalence of BK viruria and viremia were studied in 41 post-OLT patients after a mean 6.5 +/- 4.7 years posttransplantation. Renal function was assessed using estimated glomerular filtration rate (eGFR) calculated from the yearly serum creatinine levels using the Modification of Diet in Renal Disease (MDRD) formula. Polymerase chain reaction (PCR) was performed for detection of BKV DNA in urine and plasma. BK viruria was present in 24.2% of patients, but none of these OLT recipients had detectable BK viremia. Decoy cells in the urine were found in 9.7% patients, although none of these patients had BK viruria. CKD, defined as eGFR <60 mL/minute/1.73 m(2), was found in 83% of OLT recipients. The yearly decline in eGFR was -6.9 +/- 17 and -9.2 +/- 18 mL/minute/year in BK viruria-positive and BK viruria-negative patients, respectively (P = 0.39). There was no relationship between the presence or absence of BK viruria and either current eGFR, yearly decline in eGFR, number and type of immunosuppressive agents, or etiology of liver failure. In OLT recipients, BK viruria is not associated with BK viremia or native kidney dysfunction. It appears that the most probable pathway for the development of BKV nephropathy requires a second hit, such as kidney inflammation, kidney ischemia, or donor-recipient human leukocyte antigen mismatch.

Polyomavirus BK replication dynamics in vivo and in silico to predict cytopathology and viral clearance in kidney transplants

Fast BK virus (BKV) replication in renal tubular epithelial cells drives polyomavirus-BK-associated nephropathy (PVAN) to premature kidney transplant (KT) failure. BKV also replicates in urothelial cells, but remains asymptomatic in two-thirds of affected KT patients. Comparing 518 day-matched plasma-urine samples from 223 KT patients, BKV loads were approximately 3000-fold higher in urine than in plasma (p < 0.000001). Molecular and quantitative parameters indicated that >95% of urine BKV loads resulted from urothelial replication and <5% from tubular epithelial replication. Fast BKV replication dynamics in plasma and urine with half-lives of <12 h accounted for daily urothelial and tubular epithelial cell loss of 4 x 10(7) and 6 x 10(7), respectively. BKV dynamics in both sites were only partly linked, with full and partial discordance in 36% and 32%, respectively. Viral expansion was best explained by models where BKV replication started in the kidney followed by urothelial amplification and tubular epithelial cell cross-feeding reaching a dynamic equilibrium after approximately 10 weeks. Curtailing intrarenal replication by 50% was ineffective and >80% was required for clearing viremia within 7 weeks, but viruria persisted for >14 weeks. Reductions >90% cleared viremia and viruria by 3 and 10 weeks, respectively. The model was clinically validated in prospectively monitored KT patients supporting >80% curtailing for optimal interventions.

Aggressive immunosuppression minimization reduces graft loss following diagnosis of BK virus-associated nephropathy: a comparison of two reduction strategies

BACKGROUND AND OBJECTIVES

BK virus-associated nephropathy (BKVAN) has emerged as a leading cause of kidney graft loss, with no known predictors for graft loss and no consensus regarding treatment other than reduction of immunosuppression.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

A single-center retrospective analysis was performed of all cases of BKVAN from 1999 to 2005 for clinical predictors of graft loss, with evaluation of the impact of immunosuppression withdrawal (3-drug to 2-drug immunosuppression) within the first month versus reduction of immunosuppression.

RESULTS

Of 910 kidney transplants, 35 (3.8%) cases of BKVAN were diagnosed at a median of 15 months after transplant (range, 5.5 to 90 months after transplant), 16 (46%) of which progressed to graft failure at a median of 11 months (range, 2 to 36 months) after diagnosis. Depleting antibody induction was a significant risk factor for graft loss on univariate analysis, whereas early drug withdrawal (<1 mo following diagnosis) protected against graft loss. On multivariate analysis, these findings were independent predictors of graft outcomes. Additionally, when patients were comanaged by referring nephrologists and the transplant center before the diagnosis of BKVAN, the risk of graft loss was 11-fold higher (P = 0.03) than if patients were managed solely by the transplant center.

CONCLUSIONS

Increased awareness and early diagnosis of BKVAN, with aggressive tapering of immunosuppression once established, is critical to preserve kidney graft function. Early drug withdrawal to low-dose two-drug therapy maintenance may be preferable to a general reduction of agents.

Quantitation of BK virus DNA for diagnosis of BK virus-associated nephropathy in renal transplant recipients

Quantitative measurement of BK virus DNA (Q-BKDNA) has been used for the early diagnosis and monitoring of BK virus-associated nephropathy (BKVAN). This study was designed to determine the BKDNA cutoff for the diagnosis of BKVAN. Between June 2005 and February 2007, 64 renal transplant recipients taken renal biopsies due to renal impairment submitted plasma and urine for Q-BKDNA. Eight BKVAN patients (12.5%) had median viral loads of 6.0 log10 copies/mL in plasma and 7.3 log10 copies/mL in urine. Among 56 non-BKVAN patients, 45 were negative for Q-BKDNA; 4 were positive in plasma with a median viral load of 4.8 log10 copies/ mL, and 10 were positive in urine with a median viral load of 4.8 log10 copies/mL. Receiver operating characteristic curve analysis showed that a cutoff of 4.5 log10 copies/mL in plasma and a cutoff of 5.9 log10 copies/mL in urine had a sensitivity of 100% and a specificity of 96.4%, respectively. A combined cutoffs of 4 log10 copies/ mL in plasma and 6 log10 copies/mL in urine had better performance with a sensitivity of 100% and a specificity of 98.2% than each cutoff of urine or plasma. QBKDNA with the combined cutoffs could reliably diagnose BKVAN in renal transplant recipients.

Epidemiology of BK virus in renal allograft recipients: independent risk factors for BK virus replication

BACKGROUND

Identification of risk factors for BK virus (BKV) replication may improve transplant outcome. We investigated the impact of immunosuppressive drugs on the prevalence of BKV replication in recipients of human renal allografts.

METHODS

One hundred twenty renal allograft recipients were studied prospectively at 1, 3, and 6 months posttransplantation to identify risk factors for BKV replication. BKV replication was quantified by measurement of urinary cell BKV VP1 mRNA levels using BKV specific primers and TaqMan probe in a real-time quantitative polymerase chain reaction assay. Levels of urinary cell mRNA for granzyme B, CD103, and transforming growth factor-beta1 were measured to ascertain whether BKV replication is associated with an inflammatory signature.

RESULTS

The prevalence of BKV replication increased over time and was highest at 6 months compared with 1 or 3 months posttransplantation (P<0.001). A logistic regression model analysis demonstrated that steroid maintenance therapy (odds ratio: 8.3, P=0.003) and induction with rabbit anti-human thymocyte globulin (odds ratio: 5.8, P=0.008) were independent risk factors for BKV replication. Neither mycophenolate mofetil dose nor tacrolimus dose or trough levels were different between those with or without BKV replication. The development of acute rejection or antirejection treatment with methylprednisolone did not increase the risk of BKV replication. BKV replication was associated with heightened levels of urinary cell mRNA for granzyme B (P<0.002), CD103 (P<0.005) but not for transforming growth factor-beta1 (P>0.05).

CONCLUSIONS

Steroid maintenance therapy and induction with antithymocyte globulin are independent risk factors for BKV replication in renal allograft recipients treated with tacrolimus and mycophenolate mofetil.

Prospective monitoring of BK virus replication in renal transplant recipients

BACKGROUND

BK virus-associated nephropathy (BKVAN) can be diagnosed only with renal graft biopsy. Definitive diagnosis of BKVAN requires demonstration of BK virus (BKV) replication in renal allograft tissues. Non-invasive analysis of urine and blood is considered essential in screening renal transplant recipients.

PATIENTS AND METHODS

This study evaluated prospectively the replication of BKV in plasma and urine with qualitative and quantitative real-time polymerase chain reaction in 32 de novo (group A) and 34 chronic (group B) renal transplant recipients and the long-term impact on graft function.

RESULTS

In group A, 456 samples (228 plasma, 228 urine) were examined and BKV was detected in 31 (31/228, 14%) samples of plasma and 57 (57/228, 25%) samples of urine in 20 (20/32, 62.5%) and 23 (23/32, 72%) recipients, respectively. Incidence of viremia and viruria increased during the first 6 months presenting a peak the third postoperative month (viremia: 28% and viruria: 31%). Immune suppressive treatment with tacrolimus showed significant relation with viremia. Renal graft function in de novo renal transplant recipients remained stable throughout the follow-up period without influence of BKV replication. In group B, incidence of viremia and viruria were 3% (1/34) and 9% (3/34) correspondingly, indicating that after the first post-transplant year the risk of BKV re-activation is diminished.

CONCLUSION

The highest incidence of BK viremia and viruria is observed the third post-transplantation month, confirming previously published studies in Europe and the United States, and long-term follow up shows that BKV replication decreases significantly after the third post-transplant month and even transient viremia or viruria does not have an impact on renal function.

Human alpha-defensins inhibit BK virus infection by aggregating virions and blocking binding to host cells

BK virus (BKV) is a polyomavirus that establishes a lifelong persistence in most humans and is a major impediment to success of kidney grafts. The function of the innate immune system in BKV infection and pathology has not been investigated. Here we examine the role of antimicrobial defensins in BKV infection of Vero cells. Our data show that alpha-defensin human neutrophil protein 1 (HNP1) and human alpha-defensin 5 (HD5) inhibit BKV infection by targeting an early event in the viral lifecycle. HD5 treatment of BKV reduced viral attachment to cells, whereas cellular treatment with HD5 did not. Colocalization studies indicated that HD5 interacts directly with BKV. Ultrastructural analysis revealed HD5-induced aggregation of virions. HD5 also inhibited infection of cells by other related polyomaviruses. This is the first study to demonstrate polyomavirus sensitivity to defensins. We also show a novel mechanism whereby HD5 binds to BKV leading to aggregation of virion particles preventing normal virus binding to the cell surface and uptake into cells.

BK virus large T and VP-1 expression in infected human renal allografts

OBJECTIVE

We investigated the expression of early and late phase BK virus (BKV) proteins and their interactions with host cell proteins in renal allografts, with ongoing polyomavirus associated nephropathy (PVAN), and correlated this with the nuclear and cell morphology.

METHODS

Frozen sections from three patients with renal allografts (two biopsies, one explant) with PVAN were analysed by indirect immunofluorescence using BKV specific anti-polyoma large T-antigen and anti-VP-1 antibodies, as well as anti-p53, anti-Ki67, anti-caspase-3, anti-bcl2 and anti-cytokeratin 22 antibodies. Nuclear morphology and size were estimated by DNA Hoechst staining.

RESULTS

In infected tubular cells the early and late phases of infection could be distinguished according to expression of large T-antigen or VP-1. The early phase revealed almost normal nuclear proportions, whereas in later phases nuclear size increased about 2 to 3 fold. Expression of large T-antigen was strongly associated with accumulation of p53 in the nucleus, accompanied by the activation of the cell cycle associated cell protein Ki67. In contrast, expression of BKV VP1 correlated only weakly with p53. Virus dependent cell lysis was due to necrosis, since neither caspase 3 nor nuclear nor cytoskeleton changes indicated apoptosis.

CONCLUSION

In our selected patients with PVAN a clear distinction between early and late phases was possible, according to the protein expression patterns of BKV markers. Striking nuclear enlargement is only present in the late phase of infection. In the inflammatory setting of PVAN, BKV dependent effects appear to be mediated by the inhibition of p53, resulting in the activation of the cell cycle. We assume that in PVAN similar BKV mechanisms are operative as in certain in vitro systems.

Conserved archetypal configuration of the transcriptional control region during the course of BK polyomavirus evolution

BK polyomavirus (BKV) is widespread among humans, asymptomatically infecting children and then persisting in renal tissue. The transcriptional control region (TCR) of the BKV genome is variable among clinical isolates. Thus, archetypal TCRs with a common basic configuration generally occur in BKV isolates from the urine of immunocompromised patients, but rearranged TCRs that possibly arise from the archetypal configuration have also been detected in clinical specimens. To examine the hypothesis that archetypal strains represent wild-type strains circulating in the human population (the archetype hypothesis), we analysed 145 complete viral genomes amplified directly from the urine of non-immunocompromised individuals worldwide. These genomes included 82, three, two and 58 sequences classified as belonging to subtypes I, II, III and IV, respectively. Rearranged TCRs with long duplications or deletions were detected from two subtype I and two subtype IV genomes, but not from the other 141 genomes (thus, the TCRs of these genomes were judged to be archetypal). The variations in the archetypal TCRs were nucleotide substitutions and single-nucleotide deletions, most of which were unique to particular subtypes or subgroups. We confirmed that the four complete BKV genomes with rearranged TCRs did not form a unique lineage on a phylogenetic tree. Collectively, the findings demonstrate that the archetypal TCR configuration has been conserved during the evolution of BKV, providing support for the archetype hypothesis. Additionally, we suggest that 'archetype' should be used as a conceptual term that denotes a prototypical structure that can generate various rearranged TCRs during viral growth in vivo and in vitro.

longitudinal analysis of levels of immunoglobulins against BK virus capsid proteins in kidney transplant recipients

This study sought to evaluate serology and PCR as tools for measuring BK virus (BKV) replication. Levels of immunoglobulin G (IgG), IgM, and IgA against BKV capsids were measured at five time points for 535 serial samples from 107 patients by using a virus-like particle-based enzyme-linked immunosorbent assay. Viral DNA in urine and plasma samples was quantitated. The seroconversion rate was 87.5% (14/16); 78.6% (11/14) and 14.3% (2/14) of patients who seroconverted developed viruria and viremia, respectively. Transient seroreversion was observed in 18.7% of patients at 17.4 +/- 11.9 weeks posttransplant and was not attributable to loss of antigenic stimulation, changes in immunosuppression, or antiviral treatment. Titers for anti-BK IgG, IgA, and IgM were higher in patients with BKV replication than in those without BKV replication. A rise in the optical density (OD) of anti-BK IgA (0.19), IgM (0.04), or IgG (0.38) had a sensitivity of 76.6 to 88.0% and a specificity of 71.7 to 76.1% for detection of viruria. An anti-BK IgG- and IgA-positive phenotype at week 1 was less frequent in patients who subsequently developed viremia (14.3%) than in those who subsequently developed viruria (42.2%) (P = 0.04). Anti-BK IgG OD at week 1 showed a weak negative correlation with peak urine viral load (r = -0.25; P = 0.05). In summary, serial measurements of anti-BKV immunoglobulin class (i) detect onset of viral replication, (ii) document episodes of seroreversion, and (iii) can potentially provide prognostic information.

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.

Cidofovir inhibits polyomavirus BK replication in human renal tubular cells downstream of viral early gene expression

The human polyomavirus BK (BKV) causes nephropathy and hemorrhagic cystitis in kidney and bone marrow transplant patients, respectively. The anti-viral cidofovir (CDV) has been used in small case series but the effects on BKV replication are unclear, since polyomaviruses do not encode viral DNA polymerases. We investigated the effects of CDV on BKV(Dunlop) replication in primary human renal proximal tubule epithelial cells (RPTECs). CDV inhibited the generation of viral progeny in a dose-dependent manner yielding a 90% reduction at 40 microg/mL. Early steps such as receptor binding and entry seemed unaffected. Initial large T-antigen transcription and expression were also unaffected, but subsequent intra-cellular BKV DNA replication was reduced by >90%. Late viral mRNA and corresponding protein levels were also 90% reduced. In uninfected RPTECs, CDV 40 microg/mL reduced cellular DNA replication and metabolic activity by 7% and 11% in BrdU and WST-1 assays, respectively. BKV infection increased DNA replication to 142% and metabolic activity to 116%, respectively, which were reduced by CDV 40 microg/mL to levels of uninfected untreated RPTECs. Our results show that CDV inhibits BKV DNA replication downstream of large T-antigen expression and involves significant host cell toxicity. This should be considered in current treatment and drug development.

BK polyoma virus nephropathy among Iranian renal transplant recipients

BACKGROUND

BK virus nephropathy (BKVN) is recognized as a cause of graft loss in renal transplant patients. The disorder may be related to the introduction of new, potent immunosuppressive regimens. We sought to assess the prevalence, outcome, and clinical characteristics of BKVN.

MATERIALS AND METHODS

We retrospectively analyzed 160 specimens from episode biopsies. BKVN was diagnosed by light microscopic examination and positive immunohistochemical staining.

RESULTS

Among 160 patients, 21 (13.1%) were diagnosed as BKVN. The mean interval between biopsy and transplantation was 13.6 +/- 10.67 months. There were no significant differences between BKVN patients and non-BKVN patients with respect to age, sex, interval between diagnosis and transplantation, cyclosporine blood level, and azathioprine versus mycophenolate mofetil immunosuppression. Graft loss occurred in 57.1% of BKVN versus 12.2% of non-BKVN subjects (P = .005). There was a significant difference between antilymphocyte globulin (ALG)- and non-ALG-treated groups with respect to the incidence of BKVN (6.6% in non-ALG versus 19% in ALG groups; P < .01). BKVN was diagnosed by immunohistochemistry in 61% of specimens with acute rejection according to light microscopic evaluation.

CONCLUSIONS

This is the first report of BKVN in Iranian renal allograft recipients. In our hospital, the prevalence of BKVN was higher than that previously reported for non-Iranian recipients. BKVN had a negative impact on graft survival.

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.

Viral infection after renal transplantation: surveillance and management

Viral infections remain a significant cause of morbidity and mortality following renal transplantation. Although cytomegalovirus is the most common opportunistic pathogen seen in transplant recipients, numerous other viruses have also affected outcomes. In some cases, preventive measures such as pretransplant screening, prophylactic antiviral therapy, or post transplant viral monitoring may limit the impact of these infections. Recent advances in laboratory monitoring and antiviral therapy have improved outcomes. This review will summarize the major viral infections seen following transplant and discuss strategies for prevention and management of these potential pathogens.