Human polyoma virus in renal allograft biopsies: morphological findings and correlation with urine cytology

Simian virus 40 induces lamin A/C fluctuations and nuclear envelope deformation during cell entry

The canonical gate of viruses and viral genomes into the nucleus in non-dividing cells is the nuclear pore, embedded within the nuclear envelope. However, we found that for SV40, the nuclear envelope poses a major hurdle to infection: FISH analysis revealed that the majority of viral DNA remains trapped in the ER; silencing of Lamin A/C rendered the cells more susceptible to infection; and proliferating cells are more susceptible to infection than quiescent cells. Surprisingly, we observed that following SV40 infection the nuclear envelope, including lamins A/C, B1, B2 and the nuclear pore complex, was dramatically deformed, as seen by immunohistochemistry. The infection induced fluctuations in the level of lamin A/C, dephosphorylation of an unknown epitope and leakage to the cytoplasm just prior to and during nuclear entry. Deformations were transient, and the spherical structure of the nuclear envelope was restored subsequent to nuclear entry. Nuclear envelope deformations and lamin A/C dephosphorylation depended on caspase-6 cleavage of lamin A/C. Notably, we have previously reported that inhibition of caspase-6 abolishes SV40 infection. Taken together the results suggest that alterations of the nuclear lamina, induced by the infecting virus, are involved in the nuclear entry of the SV40 genome. We propose that SV40 utilize this unique, previously unknown mechanism for direct trafficking of its genome from the ER to the nucleus. As SV40 serves as a paradigm for the pathogenic human BK, JC and Merkel cell polyomavirus, this study suggests nuclear entry as a novel drug target for these infections.

BK polyomavirus infection and nephropathy: the virus-immune system interplay

Reactivation of latent BK polyomavirus (BKV) infection continues to be a major challenge in renal graft recipients. Progression of BKV infection to BKV-associated nephropathy (BKVAN) leads to graft loss in up to 60% of affected patients. Interestingly, although >80% of healthy adults are seropositive for BKV, BKVAN occurs almost exclusively in transplanted kidneys, which raises questions about its underlying pathogenetic mechanisms. Intragraft inflammation and an insufficient antiviral immune response seem to be the most important risk factors. Early studies revealed an association between the rate of recovery of BKV-specific cellular immunity (which shows high interindividual variation) and BK viral clearance, which determines the clinical course of BKV infection. In patients with prompt recovery of BKV-specific T cells, BKV infection can be controlled at the early reactivation stage and does not progress to BKVAN. By contrast, in patients with persistent BKV reactivation caused by insufficient BKV-specific immunity, continued viral replication and inflammation ultimately lead to graft injury and/or BKVAN. As the chronic course of BKV infection can be prevented in most patients by prompt restoration of BKV-specific immunity, frequent monitoring of BK viral load and targeted, timely modification or reduction of immunosuppression is strongly recommended for affected patients.

Decoy cells and malignant cells coexisting in the urine from a transplant recipient with BK virus nephropathy and bladder adenocarcinoma

The search for decoy cells (DC) in urine is widely used as screening for BK virus (BKV) reactivation in transplant recipients. BKV cytopathic effect of DC must not be confused with high-grade urothelial carcinoma. This report presents a case of coexistence of DC and malignant cells in the urine from a transplant recipient with BKV-associated nephropathy (BKVN) and bladder adenocarcinoma. A 38-year-old female with type 1 diabetes mellitus and end-stage renal disease underwent a simultaneous pancreas and kidney transplant. Four years post-transplantation, BK virus studies were performed for renal dysfunction. Isolated DC and DC in casts were identified in urine. Also, the tests for BKV DNA were positive in serum and renal allograft biopsy. BKVN was treatment-resistant and the patient returned to hemodialysis. A kidney transplant nephrectomy was performed 2 years later. The next urine cytology showed, in addition to DC, other distinct cells with nuclear atypia highly suggestive of malignancy. Some cells showed both, malignant and DC features. A bladder adenocarcinoma was diagnosed on biopsy and BKV proteins were demonstrated on tumor cells, supporting a possible role for BKV in the oncogenic pathway in this clinical setting. The presence of DC in the urine from a transplant recipient is the hallmark of BKV activation, but it does not exclude the existence of carcinoma. Furthermore, the presence of highly atypical cells should raise, not eliminate, the possibility of neoplastic transformation of the bladder.

Development of a real-time quantitative PCR assay for detection of a stable genomic region of BK virus

BACKGROUND

BK virus infections can have clinically significant consequences in immunocompromised individuals. Detection and monitoring of active BK virus infections in certain situations is recommended and therefore PCR assays for detection of BK virus have been developed. The performance of current BK PCR detection assays is limited by the existence of viral polymorphisms, unknown at the time of assay development, resulting in inconsistent detection of BK virus. The objective of this study was to identify a stable region of the BK viral genome for detection by PCR that would be minimally affected by polymorphisms as more sequence data for BK virus becomes available.

RESULTS

Employing a combination of techniques, including amino acid and DNA sequence alignment and interspecies analysis, a conserved, stable PCR target region of the BK viral genomic region was identified within the VP2 gene. A real-time quantitative PCR assay was then developed that is specific for BK virus, has an analytical sensitivity of 15 copies/reaction (450 copies/ml) and is highly reproducible (CV ≤ 5.0%).

CONCLUSION

Identifying stable PCR target regions when limited DNA sequence data is available may be possible by combining multiple analysis techniques to elucidate potential functional constraints on genomic regions. Applying this approach to the development of a real-time quantitative PCR assay for BK virus resulted in an accurate method with potential clinical applications and advantages over existing BK assays.

Viral Haufen are urinary biomarkers of polyomavirus nephropathy: New diagnostic strategies utilizing negative staining electron microscopy

Haufen, i.e. discrete three-dimensional cast-like polyomavirus aggregates in the urine, mark polyoma BK-virus nephropathy (BKN) with positive and negative predictive values of greater than 95%. They are novel diagnostic biomarkers of BKN, an important infectious complication post kidney transplantation. Here, we describe technical details of Haufen detection by negative staining electron microscopy. We studied more than 400 urine samples from over 180 patients and developed easy-to-follow protocols for optimal specimen preservation and preparation, including sample clarification and concentration. We detail diagnostic clues to detect Haufen and illustrate pitfalls, including "Haufen-look-alikes," which can hamper the interpretation. Urinary Haufen detection by negative staining electron microscopy is a new application of an old, well-established diagnostic technique. The protocols described here are useful for pathologists and electron microscopists to search for Haufen in voided urine samples, to predict BKN noninvasively, and to help clinicians managing renal allograft recipients.

Update on human polyomavirus BK nephropathy

Polyomavirus BK (BKV) has ebeen identified as the main cause of polyomavirus-associated nephropathy, a major cause of renal allograft failure. Although BKV-associated nephropathy develops in only 2% to 5% of renal transplant recipients, its prognosis when present is very poor, with irreversible graft failure developing in 45% of affected patients. While the use of urine cytology for the detection of decoy cells has been in use for decades, other diagnostic modalities to detect BKV have emerged, including tissue biopsy, polymerase chain reaction, viral culture, and serology. Currently, there is no consensus regarding the laboratory technique best suited for clinical monitoring. This review article will discuss essential and clinical features of polyomavirus, followed by a discussion pertaining to the various diagnostic modalities that contribute to detecting polyomavirus-associated nephropathy.

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.

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.

Diagnostic accuracy of blood qualitative nucleic acid testing for polyomavirus-associated nephropathy in kidney recipients

AIM

Polyomavirus-associated nephropathy (PVAN) is an important cause of graft loss following kidney transplantation and may only be diagnosed with kidney transplant biopsy. Early detection may improve outcomes by enabling early intervention. Serum polyomavirus polymerase chain reaction (PVPCR) has been used to identify patients at risk of PVAN, but prior studies have not assessed all patients with negative PVPCR with transplant biopsy, potentially overestimating test performance.

METHODS

We assessed the diagnostic accuracy of qualitative PVPCR for detection of PVAN in a population undergoing protocol biopsies. We included all patients receiving kidney or kidney-pancreas transplants and followed at Westmead Hospital, Sydney, Australia, between May 2002 and March 2007, excluding those with graft loss prior to 1 month post transplant or without PVPCR testing in the first 12 months. We compared PVPCR to contemporaneous transplant biopsies assessed with light microscopy and immunohistochemistry.

RESULTS

Of the 257 included patients, 246 (96%) underwent biopsy within 30 days of PVPCR. Eight of 36 patients with positive PVPCR had PVAN and one of 210 patients with negative PVPCR had PVAN. The point prevalence of PVAN was therefore 3.7%, with PVPCR sensitivity 89% (95% CI 57% to 99%) and specificity 88%(95% CI 83% to 92%). The negative predictive value is 99.5% (95% CI 97.3% to 100.0%).

CONCLUSION

Qualitative PVPCR on serum is a reliable triage test for excluding the presence of PVAN. Screening for PVAN need not include biopsy in patients with negative PVPCR.

Electron Microscopy in the Diagnosis of BK-Polyoma Virus Infection in the Transplanted Kidney

BK polyomavirus has become an important etiologic agent responsible for significant morbidity in renal transplant recipients. This virus can be detected in transitional cells in the urine (decoy cells) using cytology, but correlation with allograft function status and histologic evidence of renal involvement is poor. Accurate diagnosis of BK polyomavirus infection requires a high index of suspicion and utilization of ancillary diagnostic techniques in many cases. Electron microscopy is very sensitive in depicting the presence of BK virions, but the finding of viral particles is not by itself diagnostic of BK interstitial nephritis. Management of patients with polyoma virus nephropathy is difficult since there is no specific antiviral therapy available at this time.

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.

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).

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.

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.

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.

The prevalence of BK polyomavirus infection in outpatient kidney transplant recipients followed in a single center

BACKGROUND

BK polyomavirus (BKV) infection has emerged as an important cause of renal allograft loss. There is no proven therapy, and much basic clinical information is still lacking.

METHODS

We serially enrolled 95 outpatient renal transplant recipients (43% of whom were African American) in a single center cross-sectional screening study to determine the prevalence of BKV infection by whole blood polymerase chain reaction, and the prevalence of decoy cells by urinalysis and cytology. We also investigated the demographic and clinical factors associated with BKV infection, and the performance of urinalysis for decoy cells as a screening test for BKV infection.

RESULTS

The point prevalence of active BKV viremia was 7.4%. When subjects without active viremia but with a history of viremia and/or nephropathy were included, the overall prevalence was 15.8%. Urinary decoy cells were common, present in 50% of subjects at study entry. Urinalysis for decoy cells as a screen for BKV viremia had a sensitivity of 86%, specificity of 52%, positive predictive value of 13% and negative predictive value of 98%.

CONCLUSIONS

Decoy cells on urinalysis were the only factor independently associated with an increased risk of BKV infection on multivariate analysis. Although associated with BKV infection on univariate analysis, thymoglobulin, mycophenolate mofetil, and tacrolimus use were not independently associated with BKV infection on multivariate analysis, neither were history of acute rejection, gender, race, nor cause of end-stage renal disease.

Prospective study of urine cytology screening for BK polyoma virus replication in renal transplant recipients

OBJECTIVE

BK virus (BKV) may be associated with interstitial nephritis in renal transplant recipients and this can lead to irreversible chronic allograft dysfunction. Early diagnosis of BKV nephropathy determines its progress because no specific antiviral therapy exists. Urine cytology, detection of viral DNA in urine or blood and renal biopsy are the main diagnostic tools. The purpose of this study was to evaluate the use of urine cytology for diagnosis of BKV replication in renal graft recipients.

PATIENTS AND METHODS

We studied 32 de novo renal transplant recipients prospectively with sequential urine samples for a period of 1 year. Thin-Prep methodology was used to prepare the slides. Cytology results were correlated with polymerase chain reaction (PCR) in urine and blood.

RESULTS

Decoy cells indicative of BKV infection were detected in 14 (7.3%) of the 190 urine samples derived from 11 recipients. In three cases with positive decoy cells, BK viraemia and viruria were simultaneously identified. In a further three cases, BKV active replication was confirmed in urine by both cytology and PCR.

CONCLUSIONS

Urine cytology is an easy and rapid method of detecting decoy cells in cases where renal biopsy is not possible. However, the low incidence of detection of decoy cells in the present study, together with poor correlation with PCR results, questions its sensitivity and specificity in diagnosing BKV reactivation.

Does reduction in immunosuppression in viremic patients prevent BK virus nephropathy in de novo renal transplant recipients? A prospective study

BACKGROUND

BK virus nephropathy (BKVN) is a severe complication of renal transplantation, resulting in graft loss in >50% of cases. Because patients with BKV viremia are at high risk for developing BKVN, the aim of our study was to analyze whether early reduction of immunosuppression (IS) could prevent BKVN in viremic patients.

METHODS

BKV viruria was prospectively screened every 3 months by real-time polymerase chain reaction during the first year after transplantation in 123 consecutive renal transplant recipients. Plasma viral load was measured by polymerase chain reaction whenever viruria was positive; in viremic patients a graft biopsy was systematically performed and IS was reduced.

RESULTS

Viruria, viremia, and BKVN occurred in 48.8%, 10.5%, and 2.4% of patients, respectively. In the 13 patients with positive viremia, initial graft biopsy showed BKVN in two. After reduction of IS in patients without BKVN, viremia disappeared in 8 of 11, decreased in 2 of 11, and increased in one patient who eventually developed BKVN. In contrast, viremia remained positive in one patient with BKVN and disappeared in the second but renal function deteriorated in both of them. Initial viral load was higher in patients who developed BKVN.

CONCLUSION

Reduction of IS is probably an effective therapeutic option to clear viremia and prevent BKVN in viremic renal transplant patients.

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.

Structural basis of GM1 ganglioside recognition by simian virus 40

Simian virus 40 (SV40) has been a paradigm for understanding attachment and entry of nonenveloped viruses, viral DNA replication, and virus assembly, as well as for endocytosis pathways associated with caveolin and cholesterol. We find by glycan array screening that SV40 recognizes its ganglioside receptor GM1 with a quite narrow specificity, but isothermal titration calorimetry shows that individual binding sites have a relatively low affinity, with a millimolar dissociation constant. The high-resolution crystal structure of recombinantly produced SV40 capsid protein, VP1, in complex with the carbohydrate portion of GM1, reveals that the receptor is bound in a shallow solvent-exposed groove at the outer surface of the capsid. Through a complex network of interactions, VP1 recognizes a conformation of GM1 that is the dominant one in solution. Analysis of contacts provides a structural basis for the observed specificity and suggests binding mechanisms for additional physiologically relevant GM1 variants. Comparison with murine Polyomavirus (Polyoma) receptor complexes reveals that SV40 uses a different mechanism of sialic acid binding, which has implications for receptor binding of human polyomaviruses. The SV40-GM1 complex reveals a parallel to cholera toxin, which uses a similar cell entry pathway and binds GM1 in the same conformation.

Complications post renal transplantation: literature focus on BK virus nephropathy and diagnostic tools actually available

Clinical diagnosis of kidney transplants related illnesses is not a simple task. Several studies were conducted to define diseases and complications after renal transplantation, but there are no comprehensive guidelines about diagnostic tools for their prevention and detection.

The Authors of this review looked for the medical literature and pertinent publications in particular to understand the role of Human Polyomavirus BK (BKV) in renal failure and to recognize analytical techniques for BK virus associated nephropathy (BKVAN) detection.

Clinical course of kidney transplant patients with acute rejection and BK virus replication following Campath therapy

BACKGROUND

Kidney transplant recipients with active BK virus (BKV) replication are generally treated with reduction in immunosuppression to allow a successful immune response against the virus.

METHODS

We inadvertently administered Campath to two patients with BKV viruria, and one patient with BKV nephropathy, since allograft biopsies showed severe tubulitis or intimal arteritis, and results of PCR and in situ hybridization were not available at the time of therapeutic intervention.

RESULTS

Increased viral replication was observed, but not uniformly in all cases, and follow-up biopsies showed nephropathy in one additional case. Extra-renal dissemination did not occur. With subsequent reduction of immunosuppression or antiviral therapy, it was still possible to obtain clearance of viremia in all cases. Serum creatinine fell transiently after Campath in one patient; however, at one yr post-treatment all had increased levels over baseline. One graft was lost to persistent acute rejection that led to interstitial fibrosis and tubular atrophy.

CONCLUSION

These cases suggest that Campath treatment does not (i) irreversibly deplete cells believed to be important in mounting an immune response against BKV, or (ii) preclude subsequent eradication of viral DNA from the blood.

Monitoring of polyomavirus BK virus viruria and viremia in renal allograft recipients by use of a quantitative real-time PCR assay: one-year prospective study

We have developed a real-time quantitative PCR (rt-QPCR) assay to detect and kinetically monitor BK virus viruria and viremia in renal transplant recipients (RTRs). A total of 607 urine and 223 plasma samples were collected from 203 individuals including those with BK virus-associated nephropathy (BKVAN) (n = 8), those undergoing routine posttransplant surveillance (SV) (n = 155), those with nontransplant chronic kidney disease (NT-CKD) (n = 20), and healthy living kidney donors (LD) (n = 20). The rt-QPCR assay was found to be highly sensitive and specific, with a wide dynamic range (2.4 to 11 log(10) copies/ml) and very good precision (coefficient of variation, approximately 5.9%). There was a significant difference in the prevalences of viruria and viremia between the BKVAN (100% and 100%) and SV (23% and 3.9%) groups (P < 0.001). No viruria or viremia was detected in LD or in NT-CKD patients. The median (range) peak levels of BK virus viruria and viremia, in log(10) copies/ml, were 10.26 (9.04 to 10.83) and 4.83 (3.65 to 5.86) for the BKVAN group versus 0 (0 to 10.83) and 0 (0 to 5.65) for the SV group, respectively (P < 0.001). When the BK virus load in the urine was <7.0 log(10) copies/ml, no BK virus viremia was detected. When the BK virus load in the urine reached 7.0, 8.0, 9.0, and > or =10.0 log(10) copies/ml, the corresponding detection of BK virus viremia increased to 20, 33, 50, and 100%, respectively. We propose monitoring of BK virus viruria in RTRs, with plasma BK virus load testing reserved for those with viruria levels of > or =7.0 log(10) copies/ml.

Polyomaviruses and human diseases

Polyomaviruses are small, nonenveloped DNA viruses, which are widespread in nature. In immunocompetent hosts, the viruses remain latent after primary infection. With few exceptions, illnesses associated with these viruses occur in times of immune compromise, especially in conditions that bring about T cell deficiency. The human polyomaviruses BKV and JCV are known to cause, respectively, hemorrhagic cystitis in recipients of bone marrow transplantation and progressive multifocal leukoencephalopathy in immunocompromised patients, for example, by HIV infection. Recently, transplant nephropathy due to BKV infection has been increasingly recognized as the cause for renal allograft failure. Quantitation of polyomavirus DNA in the blood, cerebrospinal fluid, and urine, identification of virus laden "decoy cells" in urine, and histopathologic demonstration of viral inclusions in the brain parenchyma and renal tubules are the applicable diagnostic methods. Genomic sequences of polyomaviruses have been reported to be associated with various neoplastic disorders and autoimmune conditions. While various antiviral agents have been tried to treat polyomavirus-related illnesses, current management aims at the modification and/or improvement in the hosts' immune status. In this chapter, we provide an overview of polyomaviruses and briefly introduce its association with human diseases, which will be covered extensively in other chapters by experts in the field.

Polyomavirus-Associated Nephropathy in Renal Transplantation

Polyomavirus-associated nephropathy (PVAN) is an emerging disease in renal transplant patients with variable prevalence of 1-10% and graft loss up to 80%. BK virus (BKV) is the primary etiologic agent, but JC virus (JCV) and possibly simian virus SV40 may account for some cases. Intense immunosuppression is viewed as the most important risk factor. However, the preferential manifestation in renal transplants as compared to other allografts or to autologous kidneys of other organ transplants suggests that organ determinants and immunologic factors synergize: Renal tubular epithelial cells and their compensatory proliferation to restore tubular integrity after immunologic, ischemic or toxic injury may provide the critical cellular milieu supporting polyomavirus replication while immune control is impaired due to maintenance immunosuppression, anti-rejection treatment and HLA-mismatches. Patient determinants (older age, male gender, seronegative recipient), and viral factors (genotype, serotype) may have a contributory role. The definitive diagnosis of PVAN requires allograft biopsy which is, however, challenged by (i) limited sensitivity due to (multi-)focal involvement (sampling errors); (ii) varying presentations with cytopathic-inflammatory and/or fibrotic/scarring patterns; (iii) coexisting acute rejection which is difficult to differentiate, but impacts on intervention strategies. Screening for polyomavirus replication in the urine and in the plasma complements allograft biopsy by high sensitivity and allows for noninvasive monitoring. Thus, we suggest a terminology similar to invasive fungal diseases where viruria ("decoy cells") defines patients at risk ("possible PVAN") who should be evaluated for plasma viral load. Increasing BK viremia (>10,000 copies/mL) or urine VP-1 mRNA (>6.5x10(5) copies/ng total RNA) load defines "presumptive PVAN" for which an intervention of reducing immunosuppression should be considered even if the diagnosis could not be confirmed by allograft biopsy ("definitive PVAN"). The response to intervention should be monitored using plasma DNA or urine mRNA load.

Latent and Productive Polyomavirus Infections of Renal Allografts

Polyomavirus allograft nephropathy, also termed BK virus nephropathy (BKN) after the main causative agent, the polyoma-BK-virus strain, is a major complication following kidney transplantation. BKN is the most common viral infection affecting the renal allograft with a reported prevalence of 1% up to 10%. It often leads to chronic allograft dysfunction and graft loss. BKN is most likely caused by the reactivation of latent BK viruses which, under sustained and intensive immunosuppression, enter a replicative/productive cycle. Viral disease, i.e., BKN, is typically limited to the kidney transplant. It is histologically defined by the presence of intranuclear viral inclusion bodies in epithelial cells and severe tubular injury. Virally induced tubular damage is the morphological correlate for allograft dysfunction. In this chapter, different variants of polyomavirus intranuclear inclusion bodies [types 1 through 4] and adjunct techniques [immunohistochemistry, in-situ hybridization, electron microscopy and polymerase chain reaction (PCR)] that are used for proper characterization of disease are described. Special emphasis is placed on the clinical and pathophysiological significance of different histological stages of BKN.

Urine cytology findings of polyomavirus infections

Polyomaviruses of the BK- and JC-strains often remain latent within the transitional cell layer of the bladder, ureters and the renal pelvis as well as in tubular epithelial cells of the kidney. Slight changes in the immune status and/or an immunocompromised condition can lead to the (re)activation of latent polyomaviruses, especially along the transitional cell layer, resulting in the shedding of viral particles and infected cells into the urine. A morphologic sign of the (re)activation of polyomaviruses is the detection of typical intranuclear viral inclusion bearing epithelial cells, so-called "decoy cells", in the urine. Decoy cells often contain polyoma-BK-viruses. The inclusion bearing cells are easily identified and quantifiable in routine Papanicolaou stained urine cytology specimens. With some experience, decoy cells can also be detected in the unstained urinary sediment by phase contrast microscopy. Different morphologic variants of decoy cells (types 1 through 4) are described and ancillary techniques (immunohistochemistry, electron microscopy (EM), and fluorescence-in-situ-hybridization (FISH)) for proper identification and characterization are discussed. Special emphasis is placed on the clinical significance of the detection of decoy cells as a parameter to assess the risk for disease, i.e., polyoma-BK-virus nephropathy (BKN) in kidney transplant recipients. The sensitivity and specificity of decoy cells for diagnosing BKN is 99% and 95%, respectively, the positive predictive value varies between 27% and more than 90%, and the negative predictive value is 99%. The detection of decoy cells is compared to other techniques applicable to assess the activation of polyomaviruses in the urine (polymerase chain reaction (PCR) and EM).

Role of urinary cytology in detecting human polyoma bk virus in kidney transplant recipients. A preliminary report

OBJECTIVE

To report data on the evaluation of the efficacy of urine cytology in detecting BK virus (BKV).

MATERIAL AND METHODS

Papanicolaou-stained cytospin preparations of randomly collected urine samples from 8 renal transplant (RTR) patients (5 males, 3 females, age: 23-63 years) who previously tested positive for BKV by PCR in urine or blood or both were studied. Urine sediment from 3 of the patients was processed for ultrastructural examination (EM). Renal biopsies before and after BKV detection were also evaluated.

RESULTS

The interval between renal transplant and urine cytology ranged between 2 and 5 years. Urine from females was difficult to assess due to vaginal contamination. In 2 of the 5 urine specimens from male recipients BKV-infected decoy cells were identified. Viral particles suggestive of BKV were identified on EM in 2 of the 3 specimens studied. Kidney biopsies showed morphologic features suggestive of BKV infection in 2 cases, 1 each detected on cytology and EM, respectively.

CONCLUSION

Screening for the presence of decoy cells in urine provides a simple sensitive means for the diagnosis of BKV nephropathy in RTR.

Polyomavirus nephropathy in native kidneys and renal allografts: an update on an escalating threat

Polyomavirus nephropathy, also termed BK-virus nephropathy (BKN) after the main causative agent, the polyoma-BK-virus strain, is a significant complication after kidney transplantation. BKN is the most common viral infection that affects renal allografts with a prevalence of 1-9% on average 8-13 months post surgery. It can also occur sporadically in native kidneys. Viral nephropathy is caused by the (re)activation of latent BK viruses that enter into a replicative cycle under sustained and intensive immunosuppression. Pure productive kidney infections with JC- and SV-40 polyomaviruses are exceptionally rare. BKN is morphologically defined by the presence of intranuclear viral inclusion bodies in epithelial cells and tubular injury, which is the morphological correlate for renal dysfunction. Renal disease can progress through different histologic stages (from early BKN stage A to late fibrotic stage C) that carry prognostic significance; disease stages B and C often result in chronic kidney (allograft) dysfunction and end-stage renal disease. The clinical goal is to diagnose viral nephropathy in disease stage A and to limit chronic renal injury. Strategies to recognize, classify, and manage BKN are critically discussed including ancillary techniques for risk assessment and patient monitoring: (i) urine cytology and the search for so-called 'decoy cells'; (ii) PCR analyses for viral load measurements in the plasma and urine; and (iii) negative staining urine electron microscopy to identify viral particles.

Urine cytology screening for polyoma virus infection following renal transplantation: the Oxford experience

OBJECTIVE

To review the first year of a monthly urine cytology screening service, introduced to identify renal transplant patients at risk of polyoma virus nephropathy (PVN), at an early, potentially treatable, stage.

METHODS AND RESULTS

Monthly urine samples (n = 392) were received from 97/108 transplant recipients in 2005. Of 56 patients with follow-up >6 months, 20% and 9% had significant (>10 decoy cells/cytospin) and non-significant positive cytology, respectively. The first positive urine samples occurred most commonly in the second and third month post-transplantation and patients with significantly positive samples had higher 3-month and 6-month serum creatinine levels than patients with negative urine cytology (p<0.01). Four patients with positive urine cytology had a subsequent positive plasma BK virus PCR; 3/97 patients had biopsy-proven PVN, all in the third month, 1-6 weeks after first positive urine samples.

CONCLUSIONS

Significant PV viruria is common following renal transplantation with onset usually within the first 3 months. Viruria is associated with worse graft function at 3 and 6 months. The time between urine positivity and clinical PVN is short. More frequent early urine screening would be required to achieve clinical benefit.

Negative-staining electron microscopy of the urine for the detection of polyomavirus infections

Negative-staining electron microscopy (EM) has played a pivotal role in diagnostic virology. It is a rapid technique for viral detection in the urine and can provide an easy means for monitoring viral activity and productive infections. EM of urine for the detection of polyomaviruses has hitherto not been systematically evaluated as a screening tool for renal transplant patients at risk for BK polyomavirus nephropathy (BKN). Here, the authors discuss technical aspects of negative-staining EM of urine (n = 76 samples) and present a simple and rapid protocol for the semiquantitative evaluation of patient samples. In two patient populations (either with (n = 15 samples) or without (n = 15 samples) an established diagnosis of BKN), EM results were compared with two previously established techniques for monitoring polyomavirus activation: (1) cytology for the quantitation of decoy cells, and (2) quantitative PCR assays for the detection of BK virus DNA load levels. In both patient groups, the dynamics of decoy cell shedding by urine cytology closely paralleled free viral particle shedding by EM, and viral load levels as measured by PCR. A trend toward higher readings was observed in patients with BKN (median values, control versus BKN groups: decoy cells 21 versus 50/slide; free virions by EM: 32 versus 66 viral particles/10 high-power fields; PCR: 3.5 x 10(8) versus 5.4 x 10(8) BK virus copies/ml; all differences not statistically significant). The authors conclude that negative-staining EM and the semiquantitative assessment of free viral particles in the urine can be a useful clinical method to identify patients at increased risk for BKN. EM can be used alone or in combination with urine cytology or PCR assays.

Immunoglobulin G, A, and M responses to BK virus in renal transplantation

Immunoglobulin G (IgG), IgA, and IgM antibodies were measured in serum samples from 71 organ donors, 81 kidney transplant recipients at transplantation, and 67 patients during the posttransplant period by using a virus-like particle-based enzyme-linked immunosorbent assay (ELISA). BK virus (BKV) and JC virus DNA were detected in urine and plasma by real-time PCR. IgG antibodies to BKV were demonstrated in the majority (80.3 to 100%) of patients irrespective of clinical category, but titers were highest in patients with active viral replication. IgA antibodies were present with greater frequency (72.7 to 81.3% versus 0 to 23.6%; P < 0.001) and higher titer (mean optical density, 0.11 to 0.15 versus 0.05 to 0.08; P < 0.001) in patients who were BKV DNA positive than those who were BKV DNA negative. IgM antibodies showed a similar pattern of reactivity but lower frequency in the setting of active viral replication (9.1 to 43.7% versus 0 to 1.4%; P < 0.001). A rise in IgG level of >0.577 optical density (OD) units or a rise in IgA or IgM level of >0.041 OD units was strongly associated with active viral replication. Urine viral load showed a positive correlation with IgM titer (r = 0.22) but a negative correlation with IgG titer (r = -0.28) and IgA titer (r = -0.1). Chronic dialysis patients typically did not have serologic or virologic evidence of active BKV infection. Anti-BKV titers did not rise in patients with JC viruria. In conclusion, measurement of anti-BKV antibody titer and class response can be used to detect the onset of viral replication. ELISAs can be quite specific despite considerable sequence homology between BK virus and JC virus.

Identification of polyoma BK virus in kidney transplant recipients by shell vial cell culture assay and urine cytology

Urine cytology often is used to identify BK virus in kidney transplant recipients in the cytology laboratory. To assess the usefulness of the shell vial cell culture assay to identify BK virus, urine samples from 42 kidney transplant recipients were tested by the urine cytology and shell vial cell culture assays. The shell vial cell culture assay is just as sensitive and specific as urine cytology for the identification of BK virus in kidney transplant recipients.

BK viral reactivation in cardiac transplant patients: evidence for a double-hit hypothesis

BACKGROUND

BK nephropathy is a significant cause of renal dysfunction in renal allograft recipients. The question of whether BK viral infection plays a role in renal dysfunction in cardiac transplantation patients remains to be answered.

METHODS

We prospectively examined the prevalence of BK viral reactivation in the setting of cardiac transplantation and performed a cross-sectional analysis of 111 cardiac transplantation patients. We also assessed the prevalence of viremia in a cohort of 29 renal transplant recipients.

RESULTS

We found urinary decoy cells in 28 cardiac transplantation patients. Of these, 14 patients had evidence of BK viral DNA in the urine. None, however, had evidence of BK viremia. Mean age, gender, levels of pre- and post-transplant serum creatinine, cardiopulmonary bypass time, and ischemic time were not significantly different between the groups. We found that 7 of 29 renal transplant recipients studied had BK viral DNA in their urine.

CONCLUSION

These findings are evidence of BK virus reactivation in the setting of cardiac transplantation at a percentage similar to that seen in renal allograft recipients. In contrast to renal allograft recipients, none had evidence of viremia. Thus, even in the setting of established BK virus reactivation, immunosuppression in combination with renal allograft dysfunction and renal ischemic injury is usually insufficient to cause BK viremia and nephropathy, and it appears that a second, organ-specific hit is necessary, such as kidney inflammation, kidney ischemia, or donor-recipient human leukocyte antigen mismatch.

Polyomavirus-associated nephropathy: update in diagnosis

The histological diagnosis of BK or JC polyomavirus allograft nephritis (PVAN) requires evaluation of a renal biopsy with demonstration of the polyomavirus cytopathic changes and confirmation with an ancillary technique such as immunohistochemistry. Three histological patterns of PVAN (A, B, and C) are identified in renal biopsies. Pattern A corresponds to the early disease, whereas patterns B and C identify intermediate and very advanced histological changes, respectively. The histological pattern found in the first biopsy correlates with graft outcome. Because PVAN affects the kidney in a random, multifocal manner, a negative biopsy does not rule out the disease. Patients with BK PVAN characteristically have high levels of BK viruria and viremia. Although the cutoff values of viral loads have not been fully determined, there is general agreement that BK viruria of >10(7)/mL and BK viremia of >10(4) are typical of patients with a biopsy showing BK PVAN. Prospective evaluation of viruria with urine cytology (decoy cells) and/or quantitative polymerase chain reaction can aid in the identification of patients at risk for developing PVAN. In addition to histological evaluation, viremia has emerged as the most specific test for the diagnosis of BK PVAN. JC PVAN is very infrequent in comparison with BK PVAN, but is also characterized by large viruria (>10(4)). On the other hand, JC viremia appears to be lower, in the order of 10(3)/mL. The inflammatory changes in PVAN need further characterization. Currently, there are no tools to differentiate acute cellular rejection from viral specific T-cell response.

Pharmacotherapeutic options for the management of human polyomaviruses

Polyomaviruses [BK virus (BKV), JC virus (JCV) and simian virus 40 (SV40)] have been known to be associated with diseases in humans for over thirty years. BKV-associated nephropathy and JCV-induced progressive multifocal leukoencephalopathy (PML) were for many years rare diseases occurring only in patients with underlying severe impaired immunity. Over the past decade, the use of more potent immunosuppression (IS) in transplantation, and the Acquired Immune Deficiency Syndrome (AIDS) epidemic, have coincided with a significant increase in the prevalence of these viral complications. Prophylactic and therapeutic interventions for human polyomavirus diseases are limited by our current understanding of polyomaviral pathogenesis. Clinical trials are limited by small numbers of patients affected with clinically significant diseases, lack of defined risk factors and disease definitions, no proven effective treatment and the overall significant morbidity and mortality associated with these diseases. This chapter will focus on a review of the current and future research related to therapeutic targets and interventions for polyomavirus-associated diseases.

The pathobiology of polyomavirus infection in man

This article traces the discovery of polyomaviruses and outlines investigations, which shed light on potential modes of transmission of this increasingly important group of human pathogens. The pathobiology of the virus is summarized with particular reference to interactions with host cell receptors, cell entry, cytoplasmic trafficking, and targeting of the viral genome to the nucleus. This is followed by a discussion of sites of viral latency and factors leading to viral reactivation. Finally, we present biochemical mechanisms that could potentially explain several key elements of tissue pathology characteristic of BKV mediated damage to human kidney.