Adult mouse kidneys become permissive to acute polyomavirus infection and reactivate persistent infections in response to cellular damage and regeneration

The CXCR6-CXCL16 axis mediates T cell control of polyomavirus infection in the kidney

BK polyomavirus (PyV) establishes lifelong asymptomatic infections in the reno-urinary system of most humans. BKPyV-associated nephropathy is the leading infectious cause of kidney allograft loss. Using mouse PyV, a natural murine pathogen that also persists in the kidney, we define a dominant chemokine receptor-chemokine axis that directs T cell infiltration of the kidney. We found that CXCR6 was required for CD4+ and CD8+ T cells to be recruited to and retained in the kidney, respectively. Absence of CXCR6 impaired virus control in the kidney. The soluble form of CXCL16 was increased in kidneys of infected mice and in vivo CXCL16 neutralization reduced numbers of virus-specific CD8+ T cells infiltrating the kidney. In vivo administration of IL-12 upregulated CXCR6 expression on virus-specific CD8+ T cells, improved T cell recruitment to the infected kidney, and reduced virus levels. Notably, T cells in kidney biopsies from PyV-associated nephropathy patients express CXCR6 and transcriptional analysis shows significant upregulation of CXCR6 and CXCL16. These findings demonstrate the importance of the CXCR6-CXCL16 axis in regulating T cell responses in the kidney to PyV infection.

BK polyomavirus infection: more than 50 years and still a threat to kidney transplant recipients

BK polyomavirus (BKPyV) is a ubiquitous human polyomavirus and a major infection after kidney transplantation, primarily due to immunosuppression. BKPyV reactivation can manifest as viruria in 30%-40%, viremia in 10%-20%, and BK polyomavirus-associated nephropathy (BKPyVAN) in 1%-10% of recipients. BKPyVAN is an important cause of kidney graft failure. Although the first case of BKPyV was identified in 1971, progress in its management has been limited. Specifically, there is no safe and effective antiviral agent or vaccine to treat or prevent the infection. Even in the current era, the mainstay approach to BKPyV is a reduction in immunosuppression, which is also limited by safety (risk of de novo donor specific antibody and rejection) and efficacy (graft failure). However, recently BKPyV has been getting more attention in the field, and some new treatment strategies including the utilization of viral-specific T-cell therapy are emerging. Given all these challenges, the primary focus of this article is complications associated with BKPyV, as well as strategies to mitigate negative outcomes.

Biopsy-proven BK virus nephropathy in kidney transplant patients: risk factors, prevalence and treatment approach

Purpose: BK virus nephropathy (BKVN) is a latent infection and it is closely associated with immunsuppressive therapy. We aimed in this study to evaluate biopsy-proven BKVN and investigate frequency, risk factors and treatment management. Materials and Methods: In this study, 422 kidney transplant recipients were analysed retrospectively between April 2014 and April 2020 for biopsy-proven BK virus nephropathy. Group I included 16 kidney transplant patients with biopsy-proven BK nephropathy and group II included 36 kidney transplant patients with negative BK virus nephropathy. We aimed demographic, clinical features of kidney transplant recipients with BKVN (group I, n: 16 ) and non-BKVN (group II, n:36) were compared and the factors affecting of BKVN. Results: The mean age of grup I and group II were were 41±14.8 years and 39±15.2 respectively. The patients mean follow-up period of 43±11.2 months. Serum creatinine and proteinuria degree were significantly higher in the group with BKVN. In order to reduce the dose of immunosuppression in patients with BKVN, tacrolimus treatment was discontinued in 8 patients, and they were switched to everolimus + MMF + prednisone treatment, leflunamide + MMF + prednisone treatment in 4 patients, and sirolimus + MMF + prednisone treatment in 4 patients. The mean serum creatinine level of the patients who were followed up were observed as 1.78±0.98 mg/dl in group I. Conclusion: In our center, the prevalance of BKVN was found 3.92% during the study period. Reduction of dose immunosuppressive therapy is the most effective treatment. It is thought that there was no differences between Leflunamide and other approaches for treatment. Early diagnosis and screening (frequently intervals) seems to be most effective way for BKVN.

Comparison of BK virus nephropathy risk between double-J-stent with anti-reflux mechanism and standart double-J-stent: single-center experience

Aim: Ureteral stend use is a risk factor for BK nephropathy (BKVN). In 2015, we compared the patients with anti-reflux mechanism DJS (ARD-DJS) and those used standard DJS (st-DJS) in terms of BKV and BKVN frequency in 90 kidney transplant patients in two centers. With the increase in the number of our patients over time and lengthening of the follow-up duration, we needed to re-evaluate the data in one center. Material and Method: We retrospectively evaluated 211 patients who underwent kidney transplantation at Gazi Yaşargil Training and Research Hospital between September 2012 and September 2019. The following parameters were recorded, demographic data, immunosuppression protocols, presence of rejection, graft loss, plasma BKV levels, and presence of BKVN. Median and IQR follow-up time for ARD-DJS and St-DJS patients was 72 months (62,5-80,3 months) and 27,8 months (17,4-39,6 months) respectively. Results: Thirteen patients (6,1%) had BKV viremia. BKVN was revealed by kidney biopsy in 3 of 13 patients. However, graft loss due to BKVN was observed in only one patient. ARD-DJS was used in 4 of these cases and standard DJS was used in 9 of these cases. Patients in whom BKV revealed in the first 3 months were compared in the aspect of DJS technique, BKV was significantly less observed in the ARD-DJS group (ARD-DJS: 2 patients; St-DJS:9 patients), (p=0,046). Conclusion: In our study, BKV was observed less in patients with ARD-DJS that were clinically significant but not statistically significant. Therefore, prospective randomized studies with high patient numbers are needed to determine the effectiveness of ARD-DJS.

Duration of delayed graft function and its impact on graft outcomes in deceased donor kidney transplantation

BACKGROUND

There is controversy regarding the impact of delayed graft function (DGF) on kidney transplant outcomes. We hypothesize that the duration of DGF, rather than DGF itself, is associated with long-term kidney graft function.

METHODS

We analyzed all deceased donor kidney transplants (DDKT) done at our center between 2008 to 2020. We determined factors associated with DGF duration. DGF duration was assessed at three 14-day intervals: < 14 DGF days, 14-27 DGF days, > 28 DGF days. We studied the impact of DGF duration on survival and graft function and resource utilization, including hospital length of stay and readmissions.

RESULTS

1714 DDKT recipients were included, 59.4% (n = 1018) had DGF. The median DGF duration was 10 days IQR (6,15). The majority of recipients (95%) had resolution of DGF within 28 days. Donor factors associated with DGF days were longer cold ischemia time, donor on inotropes, older age, donation after circulatory death, higher terminal creatinine, and hypertension. Recipient factors associated with increased DGF duration included male sex, length on dialysis before transplant, and higher body mass index. There were no differences in acute rejection events or interstitial fibrosis progression by 4 months when comparing DGF days. The median length of stay was 3 days. However, readmissions increased with increasing DGF duration. Death-censored graft survival was not associated with the length of DGF except when DGF lasted > 28 days.

CONCLUSIONS

Inferior graft survival was observed only in recipients of DDKT with DGF lasting beyond 28 days. DGF lasting < 28 days had no impact on graft survival. Duration of DGF, rather than DGF itself, is associated with graft survival.

TRIAL REGISTRATION

Retrospective study approved by Mayo Clinic IRB number ID: 20-011561.

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

BACKGROUND AND OBJECTIVES

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

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

PODCAST

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

The impact of prophylactic ureteral stenting during kidney transplantation on postoperative surgical outcomes

Background

The aim of this study was to evaluate the safety and feasibility of prophylactic ureteric stenting during kidney transplantation (KT).

Methods

The authors retrospectively reviewed patients who underwent KT between June 2016 and June 2019. The prophylactic ureteral stenting group (double-J [DJ]) and no-stent group (no-DJ) were compared with respect to the clinical data and surgical outcomes.

Results

A total of 42 patients underwent KT; 17 patients were classified into the DJ group and 25 patients into the no-DJ group. Antithymocyte globulin induction and donor-specific antibody positivity were significantly higher in the DJ group. There were no significant differences between the groups in terms of symptomatic urinary tract infection (UTI). The time to postoperative UTI was significantly shorter in the DJ group than in the no-DJ group (33.5±7.8 vs. 105.3±71.6 days, P=0.013). The development of postoperative BK viremia was significantly higher in the no-DJ group (0.0% vs. 16.0%, P=0.035). Urologic complications were significantly higher in the no-DJ group (0.0% vs. 16.0%, P=0.035). In the no-DJ group, urologic complications occurred in four patients ureteroneocystostomy stenosis in three patients and ureteroneocystostomy leakage in one patient. Percutaneous ureteral interventions were performed for all patients using percutaneous nephrostomy and reno-uretero-vesical stenting. However, there were no postoperative urologic complications in the DJ group.

Conclusions

Prophylactic ureteric stenting during KT may be safe and feasible without significantly increasing the incidence of UTI and BK viremia. Additionally, prophylactic ureteric stenting may reduce urologic complications after KT.

BK virus nephropathy in non-renal solid organ transplant recipients: Are we looking hard enough?

We retrospectively examined the clinical characteristics, pathological features, and outcomes of BK viremia and nephropathy in a population of non-renal solid organ transplant patients (NRSOT) referred for outpatient nephrology consultation over a period of 5 years. In the entire cohort of liver, heart, and lung transplant recipients referred to this clinic, 14% percent were found to have BK viremia with a median peak serum BK viral load of 35 500 copies/ml (range 250 to 21 100 000 copies/ml). BK viremia resolved in six of the seventeen patients (35%). Four out of five patients biopsied showed BK virus (BKV) nephropathy. Eleven out of seventeen patients with BK viremia developed advanced (stage 4 or 5) chronic kidney disease. Four patients developed rejection of their solid organ transplant within the first year post detection of BK viremia after immunosuppression reduction. We conclude that a multi-center study is required to evaluate whether implementation of a systematic BK screening program would be effective in early detection and management of this problem in the NRSOT population.

BK Polyomavirus Evades Innate Immune Sensing by Disrupting the Mitochondrial Network and Promotes Mitophagy

Immune escape contributes to viral persistence, yet little is known about human polyomaviruses. BK-polyomavirus (BKPyV) asymptomatically infects 90% of humans but causes premature allograft failure in kidney transplant patients. Despite virus-specific T cells and neutralizing antibodies, BKPyV persists in kidneys and evades immune control as evidenced by urinary shedding in immunocompetent individuals. Here, we report that BKPyV disrupts the mitochondrial network and membrane potential when expressing the 66aa-long agnoprotein during late replication. Agnoprotein is necessary and sufficient, using its amino-terminal and central domain for mitochondrial targeting and network disruption, respectively. Agnoprotein impairs nuclear IRF3-translocation, interferon-beta expression, and promotes p62/SQSTM1-mitophagy. Agnoprotein-mutant viruses unable to disrupt mitochondria show reduced replication and increased interferon-beta expression but can be rescued by type-I interferon blockade, TBK1-inhibition, or CoCl₂-treatment. Mitochondrial fragmentation and p62/SQSTM1-autophagy occur in allograft biopsies of kidney transplant patients with BKPyV nephropathy. JCPyV and SV40 infection similarly disrupt mitochondrial networks, indicating a conserved mechanism facilitating polyomavirus persistence and post-transplant disease.

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BK polyomavirus agnoprotein disrupts mitochondrial membrane potential and network

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Agnoprotein impairs nucleus IRF3 translocation and interferon-β expression

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Agnoprotein facilitates innate immune evasion during the late viral replication phase

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Damaged mitochondria are targeted for p62/SQSTM1 autophagy

Epidemiology of and Risk Factors for BK Polyomavirus Replication and Nephropathy in Pediatric Renal Transplant Recipients: An International CERTAIN Registry Study

BACKGROUND

BK polyomavirus-associated nephropathy (BKPyVAN) constitutes a serious cause of kidney allograft failure, but large-scale data in pediatric renal transplant recipients and a comprehensive analysis of specific risk factors are lacking.

METHODS

We analyzed the data of 313 patients in the Cooperative European Pediatric Renal Transplant Initiative Registry, with an observation period of 3.3 years (range, 1-5). The net state of immunosuppressive therapy was assessed by the modified Vasudev score.

RESULTS

Presumptive BKPyVAN (defined as sustained [>3 wk] high-level BK viremia >10 copies/mL) within 5 years posttransplant occurred in 49 (15.8%) of 311 patients, and biopsy-proven BKPyVAN in 14 (4.5%) of 313. BKPyV viremia was observed in 115 (36.7%) of 311 patients, of whom 11 (9.6%) of 115 developed viremia late, that is, after the second year posttransplant. In 6 (12.5%) of 48 patients with high-level viremia and in 3 (21.4%) of 14 with BKPyVAN, this respective event occurred late. According to multivariable analysis, BKPyV viremia and/or BKPyVAN were associated not only with a higher net state of immunosuppression (odds ratio [OR], 1.3; P < 0.01) and with tacrolimus-based versus ciclosporin-based immunosuppression (OR, 3.6; P < 0.01) but also with younger recipient age (OR, 1.1 per y younger; P < 0.001) and obstructive uropathy (OR, 12.4; P < 0.01) as primary renal disease.

CONCLUSIONS

Uncontrolled BKPyV replication affects a significant proportion of pediatric renal transplant recipients and is associated with unique features of epidemiology and risk factors, such as young recipient age, obstructive uropathy, and overall intensity of immunosuppressive therapy. BKPyV surveillance should be considered beyond 2 years posttransplant in pediatric patients at higher risk.

Native kidney BK virus nephropathy, a systematic review

BACKGROUND

There is a growing base of literature describing BK nephropathy (BKVN) in patients outside of the setting of kidney transplant. Previous systematic reviews of the literature have been limited by methodology or by the scope of patients included.

STUDY DESIGN AND METHODS

Systematic Review (Prospero # CRD42018088524).

SETTING & POPULATION

Patients without kidney transplant who had biopsy-proven BKVN.

SELECTION CRITERIA FOR STUDIES

Full-text articles that describe native BKVN patient cases.

ANALYTICAL APPROACH

Descriptive synthesis.

RESULTS

The search identified 630 unique articles of which 51 were included in the final review. Sixty-five cases (including two new cases presented in this review) were identified, all but one occurred in the setting of known immunosuppression.

LIMITATIONS

The primary limitation was the exclusion of studies that did not fulfill the stringent review criteria. We excluded reports with only a clinical diagnosis of BKVN, such as those with viruria and/or viremia without biopsy.

CONCLUSIONS

As of May 2018, there are 65 reported cases of BKVN in native kidneys. This represents the most comprehensive description of biopsy-proven BKVN in native kidneys to date. Evaluation for BK nephropathy should be considered in immunocompromised patients who exhibit unexplained renal failure.

Externalized Percutaneous Stent Versus Internal Double J Stent: Short- and Long-term Complications After Kidney Transplantation

BACKGROUND

In patients undergoing kidney transplantation, ureteral stents are an established technique to reduce major urologic complications such as leakage and stenosis of the ureter. However, the best technique for ureteral stenting remains unclear. The aim of this study was to compare the outcome of percutaneous ureteral stents (PS) with internal double J stents (JJS) after kidney transplantation.

METHODS

All patients undergoing kidney transplantation between 2005 and 2014 were retrospectively analyzed. After excluding patients <18 years old, patients without stenting, and patients who underwent multiorgan transplantation, a total of 308 patients were included in the study. Two consecutive cohorts of patients were compared. In the cohort transplanted between 2005 and 2010, stenting was routinely performed using PS (216 patients), and in the second cohort, those transplanted after 2011, stenting was routinely performed using JJS (92 patients). For ureteric anastomosis, the Lich-Grégoir technique was used in all patients.

RESULTS

There was no statistical difference in postoperative urinary tract infections (P = .239) between the 2 cohorts. In patients with PS, the incidence of major urologic complications (11.6% vs 3.3%; P = .018), vesicoureteral reflux (14.3% vs 2.2%; P < .001), and urologic reinterventions (14.4% vs 5.4%; P = .031) was significantly higher when compared with JJS patients. Multivariable logistic regression revealed increased incidence of major urologic complications (odds ratio [OR] 3.66, 95% confidence interval [CI] 1.07-12.55, P = .039) and vesicoureteral reflux (OR 5.29, 95% CI 1.21-23.10, P = .027) in patients with PS compared with JJS.

CONCLUSION

Stenting of ureterovesical anastomosis using JJS is associated with reduced complications compared with PS after kidney transplantation.

The Murine Polyomavirus MicroRNA Locus Is Required To Promote Viruria during the Acute Phase of Infection

Polyomaviruses (PyVs) can cause serious disease in immunosuppressed hosts. Several pathogenic PyVs encode microRNAs (miRNAs), small RNAs that regulate gene expression via RNA silencing. Despite recent advances in understanding the activities of PyV miRNAs, the biological functions of PyV miRNAs during in vivo infections are mostly unknown. The studies presented here used murine polyomavirus (MuPyV) as a model to assess the roles of the PyV miRNAs in a natural host. This analysis revealed that a MuPyV mutant that is unable to express miRNAs has enhanced viral DNA loads in select tissues at late times after infection. This is consistent with the PyV miRNAs functioning to reduce viral replication during the persistent phase of infection in a natural host. Additionally, the MuPyV miRNA locus promotes viruria during the acute phase of infection as evidenced by a defect in shedding during infection with the miRNA mutant virus. The viruria defect of the miRNA mutant virus could be rescued by infecting Rag2^-/- mice. These findings implicate the miRNA locus as functioning in both the persistent and acute phases of infection and suggest a role for MuPyV miRNA in evading the adaptive immune response.IMPORTANCE MicroRNAs are expressed by diverse viruses, but for only a few is there any understanding of their in vivo function. PyVs can cause serious disease in immunocompromised hosts. Therefore, increased knowledge of how these viruses interact with the immune response is of clinical relevance. Here we show a novel activity for a viral miRNA locus in promoting virus shedding. This work indicates that in addition to any role for the PyV miRNA locus in long-term persistence, it also has biological activity during the acute phase. As this mutant phenotype is alleviated by infection of mice lacking an adaptive immune response, our work also connects the in vivo activity of the PyV miRNA locus to the immune response. Given that PyV-associated disease is associated with alterations in the immune response, our findings help to better understand how the balance between PyVs and the immune response becomes altered in pathogenic states.

BK Polyomavirus and the Transplanted Kidney: Immunopathology and Therapeutic Approaches

BK polyomavirus is ubiquitous, with a seropositivity rate of over 75% in the adult population. Primary infection is thought to occur in the respiratory tract, but asymptomatic BK virus latency is established in the urothelium. In immunocompromised host, the virus can reactivate but rarely compromises kidney function except in renal grafts, where it causes a tubulointerstitial inflammatory response similar to acute rejection. Restoring host immunity against the virus is the cornerstone of treatment. This review covers the virus-intrinsic features, the posttransplant microenvironment as well as the host immune factors that underlie the pathophysiology of polyomavirus-associated nephropathy. Current and promising therapeutic approaches to treat or prevent this complication are discussed in relation to the complex immunopathology of this condition.

Reducing persistent polyomavirus infection increases functionality of virus-specific memory CD8 T cells

Mouse polyomavirus (MuPyV) causes a smoldering persistent infection in immunocompetent mice. To lower MuPyV infection in acutely and persistently infected mice, and study the impact of a temporal reduction in viral loads on the memory CD8 T cell response, we created a recombinant MuPyV in which a loxP sequence was inserted into the A2 strain genome upstream of the early promoter and another loxP sequence was inserted in cis into the intron shared by all three T antigens. Using mice transgenic for tamoxifen-inducible Cre recombinase, we demonstrated that reduction in MuPyV load during persistent infection was associated with differentiation of virus-specific CD8 T cells having a superior recall response. Evidence presented here supports the concept that reduction in viral load during persistent infection can promote differentiation of protective virus-specific memory CD8 T cells in patients at risk for diseases caused by human polyomaviruses.

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

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

Ureteral stent placement and immediate graft function are associated with increased risk of BK viremia in the first year after kidney transplantation

Ureteral stent (UrSt) placement has been shown to be a significant independent risk factor for BK viruria, viremia, and BK virus nephropathy. We assessed whether this observation could be validated at our high volume kidney transplant center that has had a strong historical focus on BK virus nephropathy detection. We performed a retrospective case-control study of adults receiving a kidney-only transplant and followed for 1 year between 2004 and 2011 with uniform immunosuppression and use of blood BK virus PCR screening protocol. Among 1147 patients, 443 (38.6%) received a UrSt and 17.2% with a UrSt had BK viremia versus 13.5% without stent (odds ratio 1.33; 95% CI: 1.00-1.78). We confirmed a previously reported association between immediate graft function (IGF) and higher rate of BK viremia (15.7% vs. 5.9% in patients without IGF). On multivariable competing risks Cox regression in patients with IGF, UrSt (adjusted hazard ratio [aHR] 1.35; 95% CI: 1.04-1.75) and African American race (aHR 1.47; 95% CI: 1.04-2.09) significantly increased the risk for BK viremia. In the largest sample size to date, we confirmed that UrSt placement during kidney transplant surgery is a risk factor for BK viremia within the first year post-transplant and that IGF is associated with BK viremia.

Nephropathy Evolving Within the First Two Posttransplant Months With No Typical Cytopathic Lesions: Two Cases Presentation

BACKGROUND

We report 2 cases of polyomavirus-associated nephropathy (PyVAN) emerging within the initial 8 posttransplant weeks. These cases were characterized by intraepithelial BK virus replication without typical nuclear inclusions in epithelial cells.

METHODS AND RESULTS

A 70-year-old male recipient of a cadaveric kidney transplant had experienced unsatisfying graft function since the time of transplantation (Tx). One month after Tx, results of a graft biopsy revealed mild tubulointerstitial inflammation. No intraepithelial nuclear inclusions suggestive of viral infection were present at that time. The patient received intravenous methylprednisolone, and the dosage of tacrolimus was increased. Due to a further drop in the glomerular filtration rate, a subsequent kidney biopsy was performed during posttransplant week 10, which revealed lesions typical of PyVAN. Retrospectively performed SV40 staining revealed that intragraft polyomavirus replication was already present on posttransplant day 30. Basic immunosuppression reduction and ciprofloxacin administration were followed by BK viremia elimination, stabilization of graft function, and resolution of PyVAN. In another patient, a 62-year-old male recipient of a cadaveric renal graft, BK viremia was monitored from the time of Tx. Two months after Tx, the patient was found to have a BK viral load of 6 × 4 log(10)/mL. Results of the graft biopsy revealed fully preserved tubular epithelium, but SV40 staining was positive in some of these cells. After basic immunosuppression reduction and introduction of ciprofloxacin, the BK viral load dropped to 1 × log(10)/mL with graft function stabilization.

CONCLUSIONS

PyVAN may emerge as early as 4 weeks after Tx, with near-normal or acute rejection-like graft morphology. The early monitoring of plasma BK viral load, as well as SV40 staining, avoids misdiagnosis of this severe posttransplant complication.

Polyomavirus Persistence

Mammalian polyomaviruses are characterized by establishing persistent infections in healthy hosts and generally causing clinical disease only in hosts whose immune systems are compromised. Despite the fact that these viruses were discovered decades ago, our knowledge of the mechanisms that govern viral persistence and reactivation is limited. Whereas mouse polyomavirus has been studied in a fair amount of detail, our understanding of the human viruses in particular is mostly inferred from experiments aimed at addressing other questions. In this review, we summarize the state of our current knowledge, draw conclusions when possible, and suggest areas that are in need of further study.

Evaluation of the Gastrointestinal Tract as Potential Route of Primary Polyomavirus Infection in Mice

BACKGROUND

Detection of Polyomavirus (PyV) DNA in metropolitan rivers worldwide has led to the suggestion that primary viral infection can occur by the oral route. The aim of this study was to test this notion experimentally.

METHODS

Mouse PyV (MPyV) was used to infect C57BL/6J mice by the nasal or intragastric route. Viral load kinetics was studied 3, 7, 10, 14, 21 and 28 days post-infection (dpi) using quantitative PCR.

RESULTS

Following nasal infection, MPyV DNA was readily detected in many organs including lung, heart, aorta, colon, and stool with viral loads in the range of 10(3)-10(6) copies/mg wet weight that peaked 7-10 dpi. Complete viral clearance occurred in the serum and kidney by 28 dpi, while clearance in other organs was partial with a 10-100 fold decrease in viral load. In contrast, following intragastric infection peak detection of PyV was delayed to 21 dpi, and viral loads were up to 3 logs lower. There was no detectable virus in the heart, colon, or stool.

CONCLUSIONS

The intragastric route of MPyV infection is successful, not as efficacious as the respiratory route, and associated with delayed viral dissemination as well as a lower peak MPyV load in individual organs.

BK Polyomavirus Infection and Renourinary Tumorigenesis

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

A Preliminary Study Into the Significance of Intrarenal Reflux in BK Virus Nephropathy After Kidney Transplantation

Background

The BK virus typically colonizes the lower urinary tract and is the causative agent in BK virus nephropathy (BKVN), which can progress to allograft dysfunction and graft loss. Urinary reflux in kidney allografts is induced by vesicoureteral reflux or disturbances in intrarenal reflux (IRR), believed to be associated with BKVN. This study was designed to elucidate the relationship between BKVN and IRR.

Methods

We examined 30 renal transplant recipients histologically diagnosed with BKVN using anti-Simian virus 40 immunohistochemistry and 60 clinically matched control recipients. The BKVN patients were divided into stable (n = 12) and progressive (n = 18) groups according to allograft kidney function 1 year after diagnosis. Histological rejection scores according to the pathological classification of rejection in renal allografts (Banff classification), histological BKVN stages, and histological polyomavirus load levels (pvl) proposed by the Banff working group were evaluated. The IRR was quantified by histological reflux scores defined with retention and reflux of immunostained Tamm-Horsfall protein in renal tubules and glomeruli.

Results

Higher reflux scores were observed in the BKVN group compared with that in the control group. No differences in clinical parameters were observed between the BKVN and control groups. Reflux scores and pvl were significantly higher in the progressive group than in the stable BKVN group with no significant difference in BK stage observed between groups. Reflux scores were found to be significantly correlated with pvl.

Conclusions

Our preliminary study suggested that IRR might be a predisposing and prognostic factor in BKVN.

Simultaneous pancreas/kidney transplant recipients present with late-onset BK polyomavirus-associated nephropathy

BACKGROUND

Infections have increased in simultaneous pancreas/kidney transplant recipients (SPKTRs) with BK polyomavirus (BKV)-associated nephropathy (BKVN) being the most important infectious cause of allograft loss. Comparisons of BKVN with kidney transplant recipients (KTRs), however, are lacking.

METHODS

We studied all SPKTRs and KTRs at our transplant centre between 2003 and 2012. Eleven of 106 SPKTs (10.4%) and 21 of 1062 KTRs (2.0%) were diagnosed with BKVN with allograft loss in 1 SPKTR (9.1%) and 2 KTRs (9.5%). A control of 95 SPKTRs without BKVN was used for comparison.

RESULTS

SPKTRs showed an increased incidence of BKVN compared with KTRs (P < 0.001). Onset of BKVN in SPKTRs was significantly later compared with KTRs (P = 0.033). While 67% of KTRs showed early-onset BKVN, 64% of SPKTRs developed late-onset BKVN. Older recipient age and male gender increased the risk of BKVN in SPKTRs (P < 0.05). No differences were observed for patient and allograft survival (P > 0.05). However, SPKTRs with BKVN showed inferior estimated glomerular filtration rate and a higher incidence of de novo donor-specific antibodies compared with SPKTRs without BKVN in long-term follow-up (P < 0.05). SPKTRs showed higher peak BKV loads, a need for more intense therapeutic intervention and were more likely not to recover to baseline creatinine after BKVN (P < 0.05).

CONCLUSIONS

Our results suggest a higher incidence, more severe course and inferior outcome of BKVN in SPKTRs. An increased vulnerability of the allograft kidney due to inferior organ quality may predispose KTRs to early-onset BKVN. In contrast, SPKTRs present with late-onset BKVN in the presence of high-dose immunosuppression.

BK polyoma virus infection and renal disease in non-renal solid organ transplantation

BK virus (BKV) is a non-enveloped DNA virus of the polyomaviridae family that causes an interstitial nephritis in immunosuppressed patients. BKV nephropathy is now a leading cause of chronic kidney disease and early allograft failure following kidney transplantation. It is also known to cause renal disease with a progressive decline in kidney function in non-renal solid organ transplant (NRSOT) recipients, although the disease may not be recognized nor its impact appreciated in this patient population. In this report, we review the existing literature to highlight our current understanding of its incidence in NRSOT populations, the approaches to diagnosis and the potential treatment options.

Comparison of anti-reflux mechanism between Double-J-Stent and standart Double-J-Stent use for risk of BK nephropathy and urinary tract Infection in kidney transplantation

OBJECTIVES

There are studies that show that double J stenting (DJS) increase BK nephropathy (BKN) 4 fold. DJS may cause vesicoureteral reflux (VUR) with normal bladder contraction. The aim of this study is to comparison risk of BKN, urinary tract infections (UTI) and postoperative urologic complications with the use DJS with anti-reflux device (ARD-DJS) and standart double J stent (St-DJS). Matherial and methods: Ninety patients (male/female: 50/40) that had undergone kidney transplantations in Diyarbakır Training and Research Hospital and Dicle University, Faculty of Medicine Hospital between January 2012 and April 2015 were enrolled in the study. Demographic data, immunosuppression protocols, presence of rejection, graft loss, postoperative urologic complications, UTI, plasma BK levels of the patients were evaluated retrospectively.

RESULTS

Median and IQR follow up time for ARD-DJS and St-DJS patients were 14 (12-18) months and 25 (16-30) months respectively. Five cases (5.5%) had BK viremia (P=0.025). All 5 cases with BK viremia were St-DJS users.

CONCLUSION

As a result for postoperative UTI and postoperative urinary complication risk there were no statistically significant difference between ARD-DJS use and St-DJS use during ureteral anastomosis. BKN univariate analysis were significantly less than those st-DJS used. Risc factors were evaluated. But results were not statistically significant in the logistic regression analysis. We think that to demonstrate this benefit, we need randomized controlled studies with more patients and longer follow up.

Risk factors for BK virus infection and BK virus-associated nephropathy under the impact of intensive monitoring and pre-emptive immunosuppression reduction

BACKGROUND

BK virus (BKV) nephropathy (BKVN) is an increasingly recognized cause of kidney allograft loss and is thought to be related to the newer, more potent immunosuppressive agents. However, the risk factors for different types of BKV infection under the impact of intensive monitoring and reduction of maintenance immunosuppression are not well understood.

METHODS

Quantitative BKV DNA surveillance in plasma/urine and cytological testing in urine were performed regularly within the first year post-transplantation in 229 kidney recipients. Patients with BK viremia and BKVAN treated with immunosuppression reduction were monitored for BKV every 3-6 months. All the patients were followed up for a minimum of 5 years to exclude later development of BKVAN. Potential variables were compared and analyzed using logistic regression model multivariate analysis to assess and rank the BKV infection-related factors.

RESULTS

Seventy-eight (34.1%) patients had decoy cells, 99 (43.2%) BK viruria, 38 (16.6%) BK viremia, and 7 (3.1%) BKVAN. Risk for decoy cells, BK viruria, and viremia, and BKVAN in univariate analyses were higher with tacrolimus (Tac) and deceased kidney donation. Multivariate analysis showed that Tac ([HR, 2.7; P = .008], [HR, 2.3; P = .016], [HR, 2.9; P = .032]) and deceased kidney donation ([HR, 2.5; P = .004], [HR, 2.6; P = .002], [HR, 2.1; P = .071]) were risk factors for BK decoy cells, BK viruria, and viremia, respectively. BKVAN was inclined to the patients with the combination of Tac and mycophenolate mofetil and longer BKV clearance time.

CONCLUSIONS

Tac and deceased kidney donation are independent risk factors for BKV infection under the impact of therapeutic drug monitoring.

Polyomavirus-Specific Cellular Immunity: From BK-Virus-Specific Cellular Immunity to BK-Virus-Associated Nephropathy?

In renal transplantation, BK-virus (BKV)-associated nephropathy has emerged as a major complication, with a prevalence of 1-10% and graft loss in >50% of cases. BKV is a member of the polyomavirus family and rarely induces apparent clinical disease in the general population. However, replication of polyomaviruses, associated with significant organ disease, is observed in patients with acquired immunosuppression. Monitoring of specific immunity combined with viral load could be used to individually assess the risk of viral reactivation and virus control. We review the current knowledge on BKV-specific cellular immunity and, more specifically, in immunocompromised patients. In the future, immune-based therapies could allow us to treat and prevent BKV-associated nephropathy.

Different risk factor profiles distinguish early-onset from late-onset BKV-replication

Two of three reactivations of latent BKV-infection occur within the first 6 months after renal transplantation. However, a clear differentiation between early-onset and late-onset BKV-replication is lacking. Here, we studied all kidney transplant recipients (KTRs) at our single transplant center between 2004 and 2012. A total of 103 of 862 KTRs were diagnosed with BK viremia (11.9%), among which 24 KTRs (2.8%) showed progression to BKV-associated nephropathy (BKVN). Sixty-seven KTRs with early-onset BKV-replication (65%) and 36 KTRs with late-onset BKV-replication (35%) were identified. A control group of 598 KTRs without BKV-replication was used for comparison. Lymphocyte-depleting induction, CMV-reactivation, and acute rejection increased the risk of early-onset BKV-replication (P < 0.05). Presensitized KTRs undergoing renal retransplantation were those at increased risk of late-onset BKV-replication (P < 0.05). Among KTRs with BK viremia, higher doses of mycophenolate increased the risk of progression to BKVN (P = 0.004). KTRs with progression to BKVN showed inferior allograft function (P < 0.05). KTRs with late-onset BK viremia were more likely not to recover to baseline creatinine after BKV-replication (P = 0.018). Our data suggest different risk factors in the pathogenesis of early-onset and late-onset BKV-reactivation. While a more intensified immunosuppression is associated with early-onset BKV-replication, a chronic inflammatory state in presensitized KTRs may contribute to late-onset BKV-replication.

Prevalence of BK polyomavirus infection and association with renal dysfunction in pediatric heart transplant recipients

BACKGROUND

BK polyomavirus (BKV) infection and nephropathy complicate renal allografts; however, their effect in the native kidneys of pediatric heart transplant (HTx) recipients is unknown. We assessed the prevalence of BKV infection and its association with kidney dysfunction in survivors of pediatric HTx.

METHODS

A single-center retrospective study compared pediatric (aged <18 years ) HTx recipients, with and without BKV (controls), who received an allograft from May 1989 to July 2013. Screening of urine for BKV was performed in patients with chronic kidney disease (CKD) stage ≥2 since 2006, and since April 2012 in all HTx recipients at least at an annual evaluation. Serum for BKV DNA was assayed if BK viruria was present. Data collected included recipient and donor demographics, the immunosuppressive regimen, and history of Epstein-Bar virus (EBV) and cytomegalovirus infection. Statistics included Fisher's exact test, chi-square test, Student's t-test, and multivariate logistic regression.

RESULTS

Of 98 eligible recipients, 83 (85%) were screened: 28 (34%) had BK viruria, and 7 had BK viremia. One viremic patient had biopsy-proven BKV nephropathy that progressed to end-stage renal disease. Risk factors for BK viruria were (1) longer duration since HTx (6.02 vs 2.95 years; p = 0.01), (2) worsening estimated glomerular filtration rate (71.3 vs 86.3 ml/min/1.73 m(2), p = 0.03), (3) history of EBV infection (p = 0.0002), and (4) use of sirolimus (p = 0.0003). After multivariate logistic-regression, only history of EBV infection remained associated with BKV infection (p = 0.015).

CONCLUSIONS

BKV may lead to BK viremia and BK nephropathy in pediatric HTx patients. Routine screening for BK viruria should be considered.

Ureteral Stent Placement Increases the Risk for Developing BK Viremia after Kidney Transplantation

The placement of ureteral stent (UrSt) at kidney transplantation reduces major urological complications but increases the risk for developing nephropathy from the BK virus. It is unclear whether UrSt placement increases nephropathy risk by increasing risk of precursor viral replication or by other mechanisms. We retrospectively investigated whether UrSt placement increased the risk for developing BK Viremia (BKVM) in adult and pediatric kidney transplants performed at the University of Florida between July 1, 2007, and December 31, 2010. In this period all recipients underwent prospective BKV PCR monitoring and were maintained on similar immunosuppression. Stent placement or not was based on surgeon preference. In 621 transplants, UrSt were placed in 295 (47.5%). BKVM was seen in 22% versus 16% without UrSt (P = 0.05). In multivariate analyses, adjusting for multiple transplant covariates, only UrSt placement remained significantly associated with BKVM (P = 0.04). UrSt placement significantly increased the risk for BKVM. Routine UrSt placement needs to be revaluated, since benefits may be negated by the need for more BK PCR testing and potential for graft survival-affecting nephritis.

BK virus replication in patients with anti-neutrophil cytoplasmic antibody-associated vasculitis

BACKGROUND

BK virus (BKV) is an important cause of renal dysfunction in kidney transplant (KTX) recipients. Immunosuppression intensity is a major risk factor for BKV replication in these patients. The prevalence of BKV replication in immunosuppressed patients with granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) without transplant is not known.

METHODS

Consecutive patients (n = 37) with a diagnosis of GPA (n = 25) or MPA (n = 12) without history of KTX were evaluated for plasma BKV replication by quantitative PCR (group A). Descriptive data were collected. BKV replication in this nontransplant immunosuppressed vasculitis cohort was compared with a historical cohort of vasculitis KTX recipients (group B).

RESULTS

Group A patients had mean disease duration of 75 months. Mean age was 57 years and 54% were female. Mean time from vasculitis onset to BKV testing was 36 months, and 19/37 patients were tested within 24 months of induction therapy. At the time of BKV testing, 73% were on prednisone (P) with azathioprine, mycophenolate mofetil (MMF), methotrexate or leflunomide. None of the nontransplanted vasculitis patients had detectable plasma BKV. Among 35 patients in group B, 16 were tested for BKV; 5/16 (31%) had detectable virus in plasma at a mean of 6 months after TX (p = 0.002). Most (94%) were on maintenance therapy with MMF, P and tacrolimus.

CONCLUSION

Immunosuppressed patients with GPA/MPA without KTX had no evidence of plasma BKV. However, BKV was common in GPA/MPA patients after KTX, suggesting that replication may be related to differences in immunosuppression, alloimmune activation or differences in host defense mechanisms.

Precision diagnostics in transplantation: from bench to bedside

The Canadian and American Societies of Transplantation held a symposium on February 22, 2012 in Quebec City focused on discovery, validation and translation of new diagnostic tools into clinical transplantation. The symposium focused on antibody testing, transplantation pathology, molecular diagnostics and laboratory support for the incompatible patient. There is an unmet need for more precise diagnostic approaches in transplantation. Significant potential for increasing the diagnostic precision in transplantation was recognized through the integration of conventional histopathology, molecular technologies and sensitive antibody testing into one enhanced diagnostic system.

Ureteral stent placement and BK viremia in kidney transplant recipients

INTRODUCTION

BK virus (BKV) infection is an important cause of kidney transplant dysfunction. A possible association of double-J ureteral stent placement and BK viremia has been suggested in previous studies; however, risk factors for BK are incompletely understood. We aimed to determine if stent placement is an independent risk factor for BK viremia.

METHODS

Data were collected on consecutive kidney-only transplant recipients between December 1, 2006 and June 30, 2010. All patients had at least 12 months of follow-up.

RESULTS

Of 600 consecutive kidney transplants, BK viremia within the first post-transplant year was detected in 93 patients (15.5%); in 70 of these cases, the peak BKV polymerase chain reaction was ≥10,000 copies/mL. By multivariate analysis, significant risk factors for BK viremia were recipient age (P = 0.02) and stent placement (P = 0.03). Stents were placed in 49.2% and removed at a median of 46 days (range: 11-284) post transplantation; removals occurred within 0-30, 30-60, 60-90, 90-120, 120-150, and >150 days post transplantation in 18.4%, 67.2%, 10.5%, 2.4%, 1.0%, and 0.3% of cases, respectively. No association was found of BK viremia with stent duration >46 days (P = 0.70) or by the 6-level groupings (P = 0.92).

CONCLUSIONS

Although we observed a significant association of BK viremia with stent placement, no dose-dependent effect was seen.

Obstructive uropathy is associated with polyomavirus viremia in pediatric kidney transplantation

BKVN leads to allograft dysfunction following kidney transplantation and is preceded by BK viremia. Studies in pediatric kidney transplant recipients reveal an incidence of viruria ranging from 18% to 33%, viremia 6-16%, and BKVN 2-8%. Specific risk factors have not been clearly elucidated. Retrospective chart review of pediatric kidney transplants performed from January 2005 through December 2009; to identify risk factors associated with BK viremia in pediatric kidney transplant recipients from a single center. Of the 93 patients who received kidney transplants in the study period, 22 (24%) developed BK viruria, including 12 (13%) who developed viremia. One patient with viremia (1.6%) had BKVN. Obstructive uropathy was identified as the cause of ESKD in 22 (24%) of all recipients. 27% (n = 6) of these 22 patients developed viremia, while only 8.5% (6/71) with ESKD from another cause had viremia (p = 0.001). No other examined variable differed between the two groups. Although the overall incidence was no higher than other reported series, we identified that BK disease was more frequent in children with OU. A higher index of suspicion for invasive BK disease is necessary in patients with OU who receive kidney allografts. Transplant protocols may need to consider underlying cause of ESKD when designing screening protocols for BK disease in children after kidney transplantation.

Adaptive immunity rather than viral cytopathology mediates polyomavirus-associated nephropathy in mice

Nephropathy associated with BK polyomavirus causes kidney allograft dysfunction and failure. Understanding the pathogenesis of polyomavirus-associated allograft nephropathy (PVAN) is hampered by the species specificity of Polyomaviridae family members. Using a mouse polyomavirus (MPyV) kidney transplant model, we investigated clinically relevant variables that may contribute to PVAN. We found that the timing and source (i.e. donor vs. recipient) of MPyV infection and the titer of the viral inoculum have significant effects on the extent of allograft injury, with acute infection of the recipient by high-titer MPyV inoculums producing the most profound PVAN. In contrast, altering the degree of MHC matching or increasing ischemia/reperfusion injury by prolonging the cold ischemic time of the allograft did not affect the severity of PVAN. Survival correlated positively with serum creatinine levels, but not with viral loads in the kidney allograft. Using splenectomized alymphoplasia mice, which are unable to mount primary adaptive immune responses, we further demonstrate that persistent high viral loads in the kidney are not sufficient to cause advanced PVAN. These findings suggest that the mechanism of PVAN in mice is not a direct consequence of viral cytopathology, but rather involves interplay between viral infection and the recipient antidonor immune response.

Human bocavirus: still more questions than answers

The human bocavirus was first detected in 2005 and since then has been found in both respiratory secretions from patients with airway infections and in stool samples from patients with gastroenteritis. Meanwhile, four different genotypes have been identified that most likely derive from recombination events. Although the modified Koch’s postulates have not yet been fulfilled completely, owing to the lack of an animal model or a simple cell culture system, there is increasing evidence that the human bocaviruses are serious participants in infectious diseases of the respiratory and the GI tracts. This article reviews the current status of the clinical features of human bocaviruses and provides an overview of the latest findings concerning the biology, phylogeny, epidemiology and diagnostic tools related to human bocaviruses. Furthermore, it discusses the potential pathogenicity of human bocavirus, as well as its persistence and reactivation in hosts.

Antigen-specific T cell responses to BK polyomavirus antigens identify functional anti-viral immunity and may help to guide immunosuppression following renal transplantation

Infection with the polyoma virus BK (BKV) is a major cause of morbidity following renal transplantation. Limited understanding of the anti-viral immune response has prevented the design of a strategy that balances treatment with the preservation of graft function. The proven utility of interferon-gamma enzyme-linked immunospot (ELISPOT) assays to measure T cell responses in immunocompetent hosts was the basis for trying to develop a rational approach to the management of BKV following renal transplantation. In a sample of transplant recipients and healthy controls, comparisons were made between T cell responses to the complete panel of BKV antigens, the Epstein-Barr virus (EBV) antigens, BZLF1 and EBNA1, and the mitogen phytohaemagglutinin (PHA). Correlations between responses to individual antigens and immunosuppressive regimens were also analysed. Antigen-specific T cell responses were a specific indicator of recent or ongoing recovery from BKV infection (P < 0·05), with responses to different BKV antigens being highly heterogeneous. Significant BKV immunity was undetectable in transplant patients with persistent viral replication or no history of BKV reactivation. Responses to EBV antigens and mitogen were reduced in patients with BKV reactivation, but these differences were not statistically significant. The T cell response to BKV antigens is a useful and specific guide to recovery from BKV reactivation in renal transplant recipients, provided that the full range of antigenic responses is measured.

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.

Reversible ureteral obstruction due to polyomavirus infection after percutaneous nephrostomy catheter placement

BK virus (BKV) is a human polyomavirus that remains latent in the urinary tract epithelium in most individuals. However, in immunocompromised states, including after hematopoietic stem cell transplantation (HSCT), BKV may reactivate and cause infection predominantly affecting the bladder, commonly manifested as hemorrhagic cystitis. Renal insufficiency, occasionally requiring hemodialysis, is not uncommon and was previously attributed to medications or the development of tubulointestitial nephritis. We report a series of 6 HSCT recipients who developed obstructive uropathy of the upper urinary tract system secondary to inflammation and hemorrhage involving the upper uroepithelium, causing ureteral stenosis. Temporary placement of a percutaneous nephrostomy catheter relieved the obstruction and significantly improved kidney function, successfully preventing progression to more advanced renal disease in these patients.

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.

Lessons in signaling and tumorigenesis from polyomavirus middle T antigen

The small DNA tumor viruses have provided a very long-lived source of insights into many aspects of the life cycle of eukaryotic cells. In recent years, the emphasis has been on cancer-related signaling. Here we review murine polyomavirus middle T antigen, its mechanisms, and its downstream pathways of transformation. We concentrate on the MMTV-PyMT transgenic mouse, one of the most studied models of breast cancer, which permits the examination of in situ tumor progression from hyperplasia to metastasis.