Kidney transplant function and histological clearance of virus following diagnosis of polyomavirus-associated nephropathy (PVAN)

Treatment of BK virus-associated nephropathy with Cidofovir in renal transplantation

BK virus-associated nephropathy (BKVN) has become recognized as an important cause of allograft dysfunction among transplant recipients. Despite reduction in immunosuppression, 30%-40% of recipients progress to allograft loss. Cidofovir is an antiviral agent that has been proposed for treatment of BKVN. We describe the clinical course, renal function, and blood viral measurement in 6 renal transplant recipients with BKVN who were treated with low doses of cidofovir. Administration of cidofovir was associated with clearance of BK virus DNA from blood and stabilization of renal function in 5 cases. These data suggest that cidofovir may be useful as adjuvant therapy for BKVN.

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.

Polyomavirus nephropathy: a current perspective and clinical considerations

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

High frequency and diversity of rearrangements in polyomavirus bk noncoding regulatory regions cloned from urine and plasma of Israeli renal transplant patients and evidence for a new genetic subtype

Polyomavirus BK (BKV) establishes latent infection in various human tissues, including the kidney. Reactivation following renal transplantation (RT) may cause BKV-associated nephropathy, leading to graft loss. BKV reactivation is often associated with extensive rearrangements in the BKV noncoding regulatory region (NCRR). We explored the formation and predominance of the rearrangements versus the diversity of the rearrangements by cloning and characterizing PCR-amplified NCRR sequences from six Israeli RT patients. We found a high frequency and a high degree of diversity of rearrangements: NCRRs that contained major rearrangements (mrNCRRs), including large insertions and deletions, were detected in 0 to 100% of the clones from individual samples (mean, 50% and 67% in plasma and urine, respectively). In addition, we found a high frequency of mrNCRRs that contained single-nucleotide variations (snvNCRRs) among identical mrNCRRs and archetype clones. mrNCRRs were present in plasma and in concomitantly collected urine samples, but for each patient, only a subset of the mrNCRRs and snvNCRRs were present in both compartments at the same time and/or in subsequent samples from the same compartment. Some mrNCRRs were observed over several months, indicating the continuous replication of the viral genomes carrying them. Phylogenetic analysis based on the snvNCRR in the archetype clones grouped isolates from four of the patients into a new subgroup of genotype IV. Genotypes Ib-1 and Ib-2 were also found. Isolates from two patients had NCRRs from two genotypes, one concurrently with a RT and one after a second RT. Our study prompts further investigation of the functional consequences of NCRR rearrangements to assess their biological significance and their putative role in disease progression and prognosis.

Presence of urinary Haufen accurately predicts polyomavirus nephropathy

There are no accurate, noninvasive tests to diagnose BK polyomavirus nephropathy, a common infectious complication after renal transplantation. This study evaluated whether the qualitative detection of cast-like, three-dimensional polyomavirus aggregates ("Haufen") in the urine accurately predicts BK polyomavirus nephropathy. Using negative-staining electron microscopy, we sought Haufen in 194 urine samples from 139 control patients and in 143 samples from 21 patients with BK polyomavirus nephropathy. Haufen detection was correlated with pathology in concomitant renal biopsies and BK viruria (decoy cell shedding and viral load assessments by PCR) and BK viremia (viral load assessments by PCR). Haufen originated from renal tubules containing virally lysed cells, and the detection of Haufen in the urine correlated tightly with biopsy confirmed BK polyomavirus nephropathy (concordance rate 99%). A total of 77 of 143 urine samples from 21 of 21 patients with BK polyomavirus nephropathy (disease stages A-C) contained Haufen, and during follow-up (3 to 120 wk), their presence or absence closely mirrored the course of renal disease. All controls were Haufen-negative, however, high viremia or viruria were detected in 8% and 41% of control samples, respectively. kappa statistics showed fair to good agreement of viruria and viremia with BK polyomavirus nephropathy or with Haufen shedding and demonstrated an excellent agreement between Haufen and polyomavirus nephropathy (kappa 0.98). Positive and negative predictive values of Haufen for BK polyomavirus nephropathy were 97% and 100%, respectively. This study shows that shedding of urinary Haufen and not BK viremia and viruria accurately mark BK polyomavirus nephropathy. It suggests that the detection of Haufen may serve as a noninvasive means to diagnose BK polyomavirus nephropathy in the urine.

The effect of low-dose cidofovir on the long-term outcome of polyomavirus-associated nephropathy in renal transplant recipients

BACKGROUND

Polyomavirus-associated nephropathy (PVAN) has an unfavourable impact on graft survival. The cornerstone of therapy is early reduction of immunosuppressive medications; however, the rate of graft failure is still high. Antiviral drugs, such as cidofovir, are thought to have therapeutic effects, but the benefits of cidofovir in retarding the deterioration of PVAN are still a controversial issue.

METHODS

Fourteen renal kidney recipients were diagnosed to have biopsy-proven PVAN between 2001 and 2006 in Chung-Shan Medical University Center with nearly 600 renal transplant recipients. After the diagnosis of PVAN, all patients were treated with a reduction of their original immunosuppressive medications with/without converting tacrolimus to cyclosporine. Eight of the 14 patients agreed to receive low-dose cidofovir (0.5 mg/kg) every 2 weeks for a total of six doses.

RESULTS

During 30 +/- 18 months of follow-up, three (37%) patients in the cidofovir-treated and three (50%) patients in the non-cidofovir-treated group experienced graft loss (P = 0.64). The rejection rate before PVAN diagnosis or other baseline characteristics of the patients between two groups were not significantly different. The long-term survival rate to graft loss and major graft functional decline with Kaplan-Meier analysis between the two groups were not significantly different (P = 0.898 and P = 0.243). In all demographic and clinical characteristics, we found that there was a tendency towards long-term major graft functional decline in the patients with acute rejection prior to PVAN diagnosis (P = 0.04).

CONCLUSIONS

We concluded that (1) there was no obvious effect of low-dose cidofovir on long-term graft survival in patients with PVAN, and (2) acute rejection prior to PVAN diagnosis was a potential risk factor for poorer long-term graft outcome.

Antirejection treatment in kidney transplant patients with BK viruria

BACKGROUND

Kidney transplant recipients with BK virus nephropathy or viremia are generally treated with reduction of immunosuppression to facilitate virus eradication.

METHODS

Prompted by biopsy findings interpreted as acute rejection, we administered intravenous bolus steroids to five patients with BK virus in the plasma (BKP) (group 1) and also tried other antirejection therapies in 13 patients with BK virus in the urine (BKU) but no BKP (group 2).

RESULTS

All group 1 patients had continued viremia, whereas two viruric patients in group 2 developed viremia after therapy. Ultimately, after reduced immunosuppression both groups cleared BKP over 53+/-29 days and 50+/-6 days. BKU clearance was not consistently observed. One year postbiopsy, there were no graft failures (0%) in group 1 and 2 (15%) in group 2; however, suboptimal renal function was observed in 40% and 62%, respectively (P=0.6).

CONCLUSION

Cautious antirejection treatment to patients with active BKP or BKU can lead to two possible outcomes: (a) reduction in serum creatinine that is seemingly consistent with a diagnosis of acute rejection and (b) lack of clinical response, which in the absence of overt BK nephropathy, makes it difficult to distinguish between refractory rejection and virus-induced tissue inflammation.

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

BACKGROUND AND OBJECTIVES

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

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

Antirejection treatment in kidney transplant patients with BK viruria

BACKGROUND

Kidney transplant recipients with BK virus nephropathy or viremia are generally treated with reduction of immunosuppression to facilitate virus eradication.

METHODS

Prompted by biopsy findings interpreted as acute rejection, we administered intravenous bolus steroids to five patients with BK virus in the plasma (BKP) (group 1) and also tried other antirejection therapies in 13 patients with BK virus in the urine (BKU) but no BKP (group 2).

RESULTS

All group 1 patients had continued viremia, whereas two viruric patients in group 2 developed viremia after therapy. Ultimately, after reduced immunosuppression both groups cleared BKP over 53+/-29 days and 50+/-6 days. BKU clearance was not consistently observed. One year postbiopsy, there were no graft failures (0%) in group 1 and 2 (15%) in group 2; however, suboptimal renal function was observed in 40% and 62%, respectively (P=0.6).

CONCLUSION

Cautious antirejection treatment to patients with active BKP or BKU can lead to two possible outcomes: (a) reduction in serum creatinine that is seemingly consistent with a diagnosis of acute rejection and (b) lack of clinical response, which in the absence of overt BK nephropathy, makes it difficult to distinguish between refractory rejection and virus-induced tissue inflammation.

BK virus nephropathy in renal transplant patients in London

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Anti-BK virus activity of nucleoside analogs

Polyomavirus BK is an important pathogen in transplant recipients with no effective therapy. This study demonstrates that alkoxyalkyl esters of (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine and fatty acid derivatives of 9-[2-(phosphonomethyoxy)ethyl]adenine (P393 and P405) are potent and selective inhibitors of BK virus replication in vitro, with a 50% effective concentration in the micromolar-to-nanomolar range.

Recovery of BK virus large T-antigen-specific cellular immune response correlates with resolution of bk virus nephritis

BACKGROUND

BK virus (BKV) infection of kidney transplant patients is an increasing problem and is thought to be secondary to potent immunosuppressive therapy. BKV infection progresses to BKV nephritis (BKVN) in approximately 8% of transplants and in half of these cases the graft is lost.

METHODS

We used an interferon-gamma enzyme-linked immunosorbent spot (ELISPOT) assay to measure the cellular immune response to peptides encoding BKV large T antigen. Eight kidney transplant patients with BKVN were tested at the time of diagnosis of BKVN and then after resolution of active BKV infection.

RESULTS

When total spot counts from all peptide pools were combined, the mean ELISPOT signal per 10,000 cells at the time of BKVN diagnosis was 23.1 (range 3.4-59.7), with a median of 21.8. This increased to 70.2 (range 5.4-189.4) with a median of 37.0 (P=0.1216) after resolution of active BKV infection. To further increase specificity of response, we counted the number of peptide pools with ELISPOT activity of greater than 10 spots per well after subtraction of background. The mean number of pools fitting this criteria at the time of BKVN diagnosis was 2.1 (range 0-8) with a median of 1.5; this increased to 8 (range 1-18) and a median of 6.5 after recovery (P=0.0338).

CONCLUSION

This demonstrates that recovery of cellular immune response to large T antigen corresponds with resolution of active BKV infection. This may prove useful in monitoring patients' cellular immunity and recovery from active BKV infection when treated with reduction in immunosuppressive therapy.

Prospective monitoring of polyomavirus BK replication and impact of pre-emptive intervention in pediatric kidney recipients

Polyoma BK virus (BKV)-associated nephropathy (PVAN) is a relevant cause of poor renal allograft survival. In a prospective analysis, we monitored BKV DNA in blood and urine samples from 62 consecutive pediatric kidney recipients. In patients with BKV replication, we analyzed the impact of reduction of maintenance immunosuppression on viral load kinetics and PVAN in patients with BKV replication. BKV-specific immunity was concomitantly evaluated on blood samples of viremic patients, by measuring the frequency of BKV-specific interferon-gamma-producing and cytotoxic T cells, and BKV IgG antibody levels. At a median follow-up of 24 months, BK viruria was observed in 39 of 62 patients, while BK viremia developed in 13 patients (21%). In all viremic patients, immunosuppression reduction resulted in the clearance of viremia, and prevented development of PVAN, without increasing the rate of acute rejection or causing graft dysfunction. As a consequence of immunosuppression adjustment, an expansion of BKV-specific cellular immunity was observed that coincided with viral clearance. We conclude that treating pediatric kidney transplant patients pre-emptively with immunosuppression reduction guided by BKV DNA in blood is safe and effective to prevent onset of PVAN. BKV-specific cellular immunity may be useful to guide this intervention.

BK virus nephropathy and kidney transplantation

Nephropathy from BK virus (BKV) infection is an evolving challenge in kidney transplant recipients. It is the consequence of modern potent immunosuppression aimed at reducing acute rejection and improving allograft survival. Untreated BKV infections lead to kidney allograft dysfunction or loss. Decreased immunosuppression is the principle treatment but predisposes to acute and chronic rejection. Screening protocols for early detection and prevention of symptomatic BKV nephropathy have improved outcomes. Although no approved antiviral drug is available, leflunomide, cidofovir, quinolones, and intravenous Ig have been used. Retransplantation after BKV nephropathy has been successful.

Polyomavirus polymerase chain reaction as a surrogate marker of polyomavirus-associated nephropathy

BACKGROUND

Polyomavirus-associated nephropathy (PVAN) is a significant cause of allograft loss after renal transplantation. A noninvasive assay that can guide the evaluation of PVAN would be of clinical value. We compared the utility of BK virus (BKV) polymerase chain reaction (PCR) and urine cytology in screening for concurrent PVAN.

METHODS

We used PCR to test urine and plasma samples from renal recipients simultaneously for BKV DNA. Additionally, we tested urine samples for decoy cells. Sample results were correlated with biopsy-proven PVAN. Receiver-operator characteristic curves were used to determine viral load thresholds associated with concurrent PVAN.

RESULTS

In this cross-sectional study, BKV viruria, viremia, and urinary decoy cells were detected in 24%, 9%, and 13% of renal recipients, respectively. Among 114 patients who had renal allograft biopsy, four (3.5%) were diagnosed with PVAN. Using pathology as gold standard for the diagnosis of PVAN, BKV viremia threshold of >1.6E+04 copies/mL had 100% sensitivity, 96% specificity, 50% positive predictive value, and 100% negative predictive value. A BKV viruria threshold of >2.5E+07 copies/mL had 100% sensitivity, 92% specificity, 31% positive predictive value, and 100% negative predictive value. In contrast, urine decoy cells had 25% sensitivity, 84% specificity, 5% positive predictive value, and 97% negative predictive value for the diagnosis of concurrent PVAN.

CONCLUSION

BKV PCR may be a clinically useful noninvasive test to identify renal recipients with concurrent PVAN. BKV DNA >1.6E+04 copies/mL of plasma and >2.5E+07 copies/mL of urine were highly associated with concurrent PVAN whereas a negative PCR test makes the diagnosis of PVAN highly unlikely.

Leflunomide treatment for polyomavirus BK-associated nephropathy after kidney transplantation

Polyomavirus-associated nephropathy (PVAN) affects 1-10% of kidney-transplant (KT) patients, with graft failure/loss in approximately 90% of cases. Reducing immunosuppression is the key treatment option, but addition of leflunomide may improve BK Virus (BKV) clearance and graft survival. In a prospective open-labeled study, 12 KT patients with biopsy-proven PVAN were treated with reduced immunosuppression and leflunomide. BKV viremia and graft function were followed. PVAN was diagnosed at 6 months (3-192) post-transplant; median serum creatinine concentration (sCC) was 189 micromol/l (92-265). After 16 months (8-30) of follow-up, the sCC was 150 micromol/l (90-378, NS). Renal function improved in six cases (50%), remained stable in two (16.6%) and deteriorated in four (33.4%), with graft loss in two (17%). Clearance of BKV viremia was observed in five (42%) cases. Side effects included anemia in six cases leading to leflunomide withdrawal in two patients, and mild thrombocytopenia. In KT patients diagnosed with PVAN, leflunomide plus reduced immunosuppression improved graft function in 66.6%, cleared BKV viremia in 42%, and resulted in side effects in 17%. This limited efficacy contrasts with other reports and falls short of expectation. We conclude that active screening, earlier diagnosis and intervention remain the cornerstones of treatment.

Diurnal blood pressure changes one year after kidney transplantation: relationship to allograft function, histology, and resistive index

Loss of circadian BP change has been linked to target organ damage and accelerated kidney function loss in hypertensive patients with and without chronic kidney disease. Ambulatory BP-derived data from 119 consecutive kidney transplant recipients who presented for the first annual evaluation were examined in relation to allograft function, histology, and ultrasound findings. A total of 101 (85%) patients were receiving antihypertensive medications (median 2), and 85 (71%) achieved target awake average systolic BP (SBP) of <135 mmHg. A day-night change in SBP by 10% or more (dippers) was detected in 29 (24%). Dipping status was associated with younger recipient age, lack of diabetes, low chronic vascular score, and low resistive index. Nondippers and reverse dippers had lower GFR compared with dippers (P = 0.04). For every 10% nocturnal drop in SBP, GFR increased by 4.6 ml/min per 1.73 m(2) (R = 0.3, P = 0.003). Nondippers and reverse dippers were equally common in recipients with normal histology and in those with pathologic findings on surveillance biopsy. On multivariate analysis, percentage of nocturnal fall in SBP and elevated resistive index independently correlated with GFR. This study indicates that lack of nocturnal fall in SBP is related to poor allograft function, high chronic vascular score, and high resistive index irrespective of allograft fibrosis. Further studies are needed to determine whether restoration of normal BP pattern will confer better allograft outcome.

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

Polyomavirus-associated nephropathy (PVAN) is a frequent cause of kidney transplant failure. We determined the risk factors for biopsy-proven PVAN among 1027 recent kidney transplant recipients by univariate and multivariate analyses. The rate of PVAN was determined over an univariate and multivariate analysis over an average of 30 months of follow-up of patients receiving predominantly living donor grafts with antibody induction and sequential surveillance biopsies to detect subclinical graft disease. Seventy-four transplant recipients were diagnosed with PVAN with the finding made on surveillance biopsy in 40 patients. These 40 cases did not differ from the 34 non-surveillance cases with respect to baseline clinical characteristics or initial histological features. Older recipient age and female donor gender were independent risks associated with PVAN. Factors not linked to PVAN risk included the use and type of induction agent, use of tacrolimus vs sirolimus, the number of human lympocyte antigen (HLA) mismatches, or the frequency of acute rejection. We conclude that PVAN preferentially affects older age patients and allografts from female donors but is unrelated to immunological risk, choice of immunosuppression, or rejection history.

BK virus subtype IV nephropathy occurring 5 years after kidney transplantation

We report on a BK virus-associated nephropathy in a 28-year-old man. His symptoms occurred 5 years after he had received a kidney transplantation. He was treated with tacrolimus, azathioprine, and prednisolone. The progress of the disease was monitored by quantitative real-time polymerase chain reactions for BK virus DNA. An analysis of viral DNA showed that the BK virus in the patient's plasma belonged to genotype IV.

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.