Risk factors for BK polyomavirus nephritis in renal allograft recipients1

Polyoma BK Virus in Kidney Transplant Recipients: Screening, Monitoring, and Management

Polyomavirus BK virus (BKPyV) infection is an important complication of kidney transplantation and allograft failure. The prevalence of viremia is 10%-15%, compared with BK-associated nephropathy (BKPyVAN) at 3%-5%. Given that there are no effective antiviral prophylaxis or treatment strategies for BKPyVAN, active screening to detect BKPyV viremia is recommended, particularly during the early posttransplant period. Immunosuppression reduction to allow viral clearance may avoid progression to severe and irreversible allograft damage. The frequency and duration of screening are highly variable between transplant centers because the evidence is reliant largely on observational data. While the primary treatment goals center on achieving viral clearance through immunosuppression reduction, prevention of subsequent acute rejection, premature graft loss, and return to dialysis remain as major challenges. Treatment strategies for BKPyV infection should be individualized to the recipient's underlying immunological risk and severity of the allograft infection. Efficacy data for adjuvant therapies including intravenous immunoglobulin and cidofovir are sparse. Future well-powered and high-quality randomized controlled trials are needed to inform evidence-based clinical practice for the management of BKPy infection.

Clinical manifestations of BK virus infection in pediatric kidney transplant patients

Background

Polyomavirus BK (BKV) infection is an important cause of graft loss in kidney transplant patients.

Purpose

The purpose of this study was to evaluate clinical findings and risk factors for BKV in pediatric patients after kidney transplantation.

Methods

This retrospective single-center study included 31 pediatric kidney transplant recipients from January 2002 to December 2017. Two patients received 2 transplantations during the study period, and each transplant was analyzed independently. Total number of cases is 33 cases with 31 patients. BKV infection was confirmed from blood samples via periodic quantitative polymerase chain reaction.

Results

The mean age at kidney transplantation was 11.0±4.7 years, and the male-to-female ratio was 2.7:1. Three patients had a past medical history of high-dose chemotherapy and autologous stem-cell transplantation for solid tumors. Nine patients (27.3%) developed BKV infection. The median period from kidney transplantation to BKV detection in blood was 5.6 months. There was no statistically significant difference in estimated glomerular filtration rate between patients with and those without BKV infection. Among 9 patients with BKV viremia, 7 were treated by reducing their immunosuppressant dose, and BKV was cleared in 6 of these 7 patients. In the other 2 BKV-positive patients, viremia improved without immunosuppressant reduction.

Conclusion

BKV infection is common in children with kidney transplantation and might not have affected short-term renal function in our patient sample due to early immunosuppressant reduction at the time of BKV detection.

Impact of human leukocyte antigen and calculated panel reactive antibody on BK viremia in kidney transplant recipients: A single-center experience and literature review

BACKGROUND

The aim of this retrospective analysis was to investigate the effect of human leukocyte antigen (HLA) and calculated panel reactive antibody (cPRA) on BK virus activation as evidenced by BK viremia (BKV).

PATIENTS AND METHODS

At our institution, 649 kidney transplant patients were screened for BKV from 2009 to 2017. Patients were considered to have BKV if they had >10 000 copies/mL of BK DNA in their blood. Donor and recipient HLA and cPRA, demographic, clinical and laboratory data, as well as immunosuppressive medications were collected.

RESULTS

We identified 122 BK positive and 527 BK negative patients. Only 25% of the patients had cPRA of 20% or more, and 64% had more than three HLA-A, -B, and -DR mismatches. In both univariate and multivariate analyses, male gender, age, and maintenance of steroid therapy significantly increased the risk of BKV (P = 0.005, 0.005 and <0.001, respectively). The degree of cPRA and the individual HLA allele and HLA allele matching did not significantly affect BKV.

CONCLUSION

Neither the degree of HLA mismatching nor cPRA appears to affect BKV. Moreover, no specific HLA allele, HLA allele matching, or cPRA were associated with BKV.

Sex differences in transplantation

Sex plays a role in the incidence and progression of a wide variety of diseases and conditions related to transplantation. Additionally, a growing body of clinical and experimental evidence suggests that sex can impact the pharmacokinetics and pharmacodynamics of several commonly used immunosuppressive and anti-infective drugs in transplant recipients. A better understanding of these sex differences will facilitate advances in individualizing treatment for patients and improve outcomes of solid organ transplantation. Here, we provide a review of sex-related differences in transplantation and highlight opportunities for future research directions.

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.

Renal dysfunction by BK virus infection is correlated with activated T cell level in renal transplantation

BACKGROUND

BK virus (BKV) is known to be associated with nephropathy. Here, we investigated the relationships between BKV levels, T-cell activation, and kidney function in kidney transplant recipients.

MATERIALS AND METHODS

In renal transplant patients and controls, urine BKV levels were detected by quantitative real-time PCR, and the percentage of activated T lymphocytes in blood was determined by flow cytometry. The correlations between viral load, activated T cell percentage, and renal function were determined.

RESULTS

Urine BKV viral loads and the activated T cell percentage were significantly elevated in transplant recipients. Correlational analysis indicated that transplant recipients that had BKV levels of more than 10(6) copies/mL and an activated T lymphocyte percentage of less than 20% were likely to have poor renal function.

CONCLUSIONS

Urine BKV levels and the percentage of activated T lymphocytes can be used as clinical indices to optimize the dosage of immunosuppressive drugs.

The influence of immunosuppressive agents on BK virus risk following kidney transplantation, and implications for choice of regimen

The increasing incidence of BK-associated nephropathy following kidney transplantation has prompted an examination of strategies for risk reduction and management through immunosuppression manipulation. Evidence from retrospective and prospective studies suggests that BK viruria and viremia, and the need for BK virus treatment, are higher with tacrolimus than cyclosporine. Combined therapy with tacrolimus and mycophenolic acid may be associated with a particularly higher risk of BK infection, but data are conflicting as to whether mycophenolic acid per se is an independent risk factor. The incidence of BK-related events may be reduced in patients receiving mTOR inhibitors (everolimus or sirolimus) with cyclosporine vs a calcineurin inhibitor with mycophenolic acid. De novo immunosuppression regimens that avoid rabbit antithymocyte globulin and tacrolimus, particularly tacrolimus with mycophenolic acid, may be advantageous, whereas low-exposure cyclosporine with an mTOR inhibitor appears a favorable option. Routine screening for BK infection during the first 2 years posttransplant is recommended to allow preemptive modification of the immunosuppressive regimen. In patients at high risk of BK virus infection, appropriate de novo immunosuppression or very early conversion to an mTOR inhibitor to facilitate reduction or discontinuation of calcineurin inhibitors or antimetabolites should be considered. Extensive further research into optimal avoidance, screening, and treatment strategies is required.

AZA/tacrolimus is associated with similar outcomes as MMF/tacrolimus among renal transplant recipients

There have been several retrospective studies indicating benefits associated with mycophenalate mofetil (MMF) compared to azathioprine (AZA) for renal transplant recipients. However, these analyses evaluated outcomes prior to changes in utilization patterns of concomitant immunosuppression. Recent prospective trials have indicated similar outcomes among patients treated with MMF and AZA. The aim of this study was to evaluate outcomes in a broad group of patients in the more recent era. We evaluated adult solitary renal transplant recipients from 1998 to 2006 with the national SRTR database. Primary outcomes were time to patient death and graft loss, complications and renal function. Models were adjusted for potential confounding factors, propensity scores and stratified between higher/lower risk transplants and concomitant immunosuppression. Adjusted models indicated a modest risk among AZA patients for graft loss (AHR = 1.14, 95% CI 1.07-1.20); however, this was not apparent among AZA patients also treated with tacrolimus (AHR = 0.97, 95% CI 0.85-1.11]. One-year acute rejection rates were reduced for patients on MMF versus AZA (10 vs. 13%, p < 0.01); there were no statistically significant differences of malignancies, renal function or BK virus at 1 year. The primary findings suggest the association of MMF with improved outcomes may not be apparent in patients also receiving tacrolimus.

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

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

Risk factors for polyoma virus nephropathy

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

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.

BK Virus–Associated Nephropathy in Sirolimus-Treated Renal Transplant Patients: Incidence, Course, and Clinical Outcomes

BACKGROUND

Because the course of polyoma virus-associated nephropathy (PVAN) has not been evaluated in a large cohort of patients receiving sirolimus (SRL)-based regimens, we have herein presented the incidence, clinical characteristics, and outcomes of 378 renal transplant recipients treated with SRL-based immunosuppression.

METHODS

This retrospective single center study evaluated 344 kidney alone (KTX) and 34 simultaneous pancreas-kidney (SPK) transplantations performed between June 2000 and December 2004.

RESULTS

At a mean follow-up of 43.3 months, six kidney (1.7%) and three kidney-pancreas (9.0%) transplanted patients displayed biopsy-proven PVAN. The mean time to diagnosis after transplantation was 18.2 months (range: 3.5-31.1 months), with a higher incidence among patients exposed (4.23%) versus not exposed to rabbit antithymocyte globulin (rATG; 0.53%; P=0.019) or SPK (9.0%) versus KTX (1.7%) recipients (odds ratio: 5.43; confidence interval: 1.29-22.8; P=0.038). Despite treatment with cidofovir, reduced immunosuppression and maintenance therapy with no agents other than SRL (C0=10.2+/-2.7 ng/dL) plus modest doses of prednisone (< or =5 mg), five patients (55.5%) experienced renal allograft failure. No rejection episodes were documented during the PVAN treatment and pancreatic function continued to be excellent among the SPK patients.

CONCLUSIONS

Patients treated with SRL-based immunosuppression showed an incidence at the lower end of the range described with various other contemporaneous immunosuppressive regimens and with other cohorts not undergoing BK virus polymerase chain reaction surveillance. Exposure to rATG and SPK transplantation represented risk factors for the occurrence of PVAN, which showed a pernicious course despite withdrawal of calcineurin antagonists and/or mycophenolate mofetil.

Prevalence and clinical course of BK virus nephropathy in pancreas after kidney transplant patients

The influence of BK virus nephropathy (BKVN) in pancreas after kidney (PAK) transplantation is unclear. A retrospective analysis of PAK transplants performed at our center was conducted to determine the impact of BKVN. Among 40 PAK transplants performed using sequential immunosuppression, four patients developed BKVN, as defined by a >20% rise in serum creatinine and BK viremia (BK plasma load >4 log copies/mL), at a median of 19 months following PAK. In all four patients, treatment of BKVN consisted of reduction in tacrolimus, cessation of mycophenolate mofetil, and introduction of leflunomide. With this approach, two patients experienced improvement or stabilization of renal function. The remaining two patients progressed to dialysis dependence despite treatment. Plasma BK load < or =5 log copies/mL was associated with graft preservation. Gender, age, delay between transplants, cumulative Thymoglobulin dose, and type of kidney donor were not associated with BK virus infection. Pancreas graft rejection or dysfunction was not observed with the above immunosuppression modification. Mean amylase and lipase > or =6 months following BKVN treatment remained normal. BKVN is an important cause of kidney allograft loss in PAK patients. Screening and early treatment of BKVN may enable preservation of kidney and pancreas grafts.

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.

Comparison of Low Versus High Tacrolimus Levels in Kidney Transplantation: Assessment of Efficacy by Protocol Biopsies

BACKGROUND

The use of calcineurin inhibitors is generally guided by drug blood levels. However, those levels are chosen based on clinical experience, lacking adequate titration studies.

METHODS

In these analyses, we compared clinical and histologic endpoints in two groups of kidney transplant recipients: in the first (HiTAC, January 2000 to June 2002, n=245) tacrolimus levels were significantly higher than in the second (LoTAC, July 2002 to September 2004, n=330). This change in drug levels (15% reduction) was made in an attempt to reduce the incidence of polyoma virus nephropathy (PVAN). Other immunosuppressive medications were unchanged during these two time periods.

RESULTS

The recipient and donor demographics were not statistically different between the two groups. Compared to HiTAC, at one year posttransplant LoTAC had: 1) lower incidence of PVAN (10.5% vs. 2.5%, P<0.0001); 2) lower fasting glucose levels; 3) higher iothalamate glomerular filtration rate (52+/-19 vs. 59+/-17 ml/min/m, P<0.0001); and 4) on protocol one-year biopsies, lower incidence and severity of interstitial fibrosis (67% vs. 45%, P=0.003) and tubular atrophy (82% vs., 66%, P=0.01). The incidence and severity of acute rejection episodes was similar between both groups (7.8% versus 7.6%).

CONCLUSIONS

Modest reductions in tacrolimus exposure early posttransplant are associated with significant beneficial effects for the patient and the allograft without an increased immunologic risk.

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.

BK virus nephropathy in a heart transplant recipient: case report and review of the literature

The human polyomavirus BK virus (BKV) remains latent in the urinary tract and may be reactivated in immunocompromised states. BKV is noted to be the etiologic agent of polyomavirus-associated nephropathy (PVAN), which is a significant cause of allograft failure in renal transplant patients. Renal dysfunction following non-renal solid organ transplantation is common and is typically attributed to drug toxicity or patient comorbidities. In this article we describe a case of PVAN in the native kidneys of a heart transplant recipient and review the literature. Although this is only the fourth case reported, BKV nephropathy should be considered in the differential diagnosis of new renal failure following non-kidney solid organ transplantation, as early diagnosis of PVAN is necessary to prevent irreversible renal damage.

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

Polyomavirus-associated nephropathy (PVAN) is managed by reduced immunosuppression with or without antiviral therapy. Data from 55 patients with biopsy-proven PVAN were analyzed for adverse outcomes and influence of baseline variables and interventions. During 20+/-11 months follow-up, the frequencies of graft loss, major and any functional decline were 15%, 24% and 38%, respectively. Repeat biopsies were performed in 45 patients with persistent PVAN in 47%. Low-dose cidofovir, IVIG and cyclosporine conversion were used in 55%, 20% and 55% of patients. No single intervention was associated with improved outcome. Of the variables examined, only degree of interstitial fibrosis at diagnosis was associated with kidney function decline. In contrast, donor source, interstitial fibrosis, proportion of BKV positive tubules and plasma viral load at diagnosis were all associated with failure of histological viral clearance. This retrospective, nonrandomized analysis suggests that: (i) Graft loss within 2 years of PVAN diagnosis is now uncommon, but ongoing functional decline and persistent infection occur frequently. (ii) Low-dose cidofovir, IVIG and conversion to cyclosporine do not abrogate adverse outcomes following diagnosis. (iii) Fibrosis at the time of diagnosis predicts subsequent functional decline. Further elucidation of the natural history of PVAN and its response to individual interventions will require prospective clinical trials.

Prednisone withdrawal in pediatric kidney transplant recipients on tacrolimus-based immunosuppression: four-year data

Corticosteroids have been used in renal transplant immunosuppression for over 40 yr. Despite their adverse effects, steroid therapy continues to be part of early as well as maintenance immunosuppression in most pediatric renal transplant centers. The association of steroids with growth retardation, weight gain, and acne may be particularly distressing during the critical years of adolescence and young adulthood, increasing the risk of medication non-adherence. This study reviews the outcomes of pediatric renal transplant patients treated with low-dose tacrolimus, mycophenolate mofetil, or azathioprine, and planned prednisone withdrawal. Thirty-seven pediatric renal transplant recipients were withdrawn from steroids. The mean follow-up after steroid withdrawal was 42+/-19 months. Graft and patient survival were 100%. The mean serum creatinine levels and calculated creatinine clearances remained stable throughout the period of observation. The mean creatinine clearance was 96+/-24 mL/min/1.73 m2 at steroid withdrawal and 93+/-20 mL/min/1.73 m2 at the latest follow-up. Five patients restarted prednisone; in four (11%) it was for suspected or confirmed acute rejection. Improvements were observed in serum lipid profiles, blood pressure, and body mass index. Most patients experienced catchup or stable growth after prednisone withdrawal. Four patients developed viral infections; all were successfully treated. The potential benefits of steroid withdrawal in pediatric renal transplantation are supported by our results.

“Decoy Cells” in Urine

BK virus-associated nephropathy is an emerging cause of kidney transplant loss. Tapering immunosuppressive drugs and antiviral agents are the only therapy. The diagnosis is based on immunohistochemical findings or polymerase chain reaction on renal biopsy. Phase-contrast microscopy without staining is a simple test to screen the urine of transplant recipients for BK nephritis. Any kidney transplant unit should have the ability to detect decoy cells by phase-contrast microscopy on a spot urine.

Polyomavirus interstitial nephritis and concurrent post-transplant lymphoma in a renal allograft: coincidence or more?

We describe a case of an Epstein-Barr virus (EBV)-negative post-transplant large B-cell non-Hodgkin lymphoma located in the renal allograft, spleen, liver and left inguinal lymph node of a renal recipient and accompanied by a simultaneous polyomavirus-associated nephropathy. To our knowledge, this is the first report of a simultaneous polyomavirus infection and post-transplant lymphoproliferative disorder.

Polyoma virus nephropathy in native kidneys after lung transplantation

Polyoma virus nephropathy is recognized as an emerging clinical problem in renal transplantation; however, polyoma in native kidneys is unusual. We report a patient who developed polyoma nephropathy in his native kidneys 15 months after successful lung transplantation. His immunosuppression consisted of tacrolimus, mycophenolate mofetil, and large doses of steroids because of three rejection episodes. When the condition was recognized, cidofovir was an effective treatment (3 doses of 2-3mg/kg); however, his renal function deteriorated nonetheless. Tubulitis and interstitial cell infiltration in his native kidneys were evidence that the changes were in response to viral injury. Polyoma nephropathy of native kidneys is unusual. An earlier course of cisplatin treatment because of metastatic seminoma prior to lung transplantation may have been contributory to pre-existing renal injury. After cidofovir was begun, the polyoma viral load in serum and urine decreased substantially; however, after high-dose steroid treatment of two rejection episodes, each time a significant increase in viral load was seen. We stained biopsies of native kidneys from 30 recipients of other organs. The biopsies were done for various reasons but not because polymoma virus was suspected. We found no additional cases.

Adjuvant low-dose cidofovir therapy for BK polyomavirus interstitial nephritis in renal transplant recipients

BK virus interstitial nephritis (BKVIN) is a serious complication after kidney grafting, necessitating drastic reduction of immunosuppressive therapy in order to enable viral clearance. Despite these measures, progressive graft dysfunction and graft loss occur in the majority of recipients. We diagnosed BKVIN in 21 recipients grafted between 1998 and 2004. Eight of 21 patients were treated with weekly, adjuvant low-dose cidofovir in addition to reduction of immunosuppressive therapy. BKVIN caused irreversible deterioration of graft function in all patients but renal function stabilized after antiviral treatment (creatinine clearance: 51.8-32 mL/min; p=0.001) and no graft loss occurred in cidofovir-treated recipients during 24.8 (8-41) months follow-up. Peak serum cidofovir concentrations were dose-dependent and attained approximately one-tenth of thein vitroEC50 for cidofovir against BK-virus, while pre-treatment with probenecid did not alter peak serum concentrations nor affected the incidence of nephrotoxicity. In fact, no cidofovir-related renal toxicity occurred; few patients had minor transient side effects (nausea, skin rash). In contrast, 9 of 13 patient who received no adjuvant cidofovir therapy lost their graft after median 8 (4-40) months. In this selected group of recipients with BKVIN, the use of adjuvant low-dose cidofovir therapy resulted in prolonged graft survival and stabilized graft function.

BK virus: opportunity makes a pathogen

More than 70% of the general population worldwide has serological evidence of exposure to Polyomavirus hominis type 1, better known as BK virus (BKV). BKV infection typically occurs during childhood, without specific symptoms, followed by a state of nonreplicative infection in various tissues, with the urogenital tract as the principal site. Asymptomatic reactivation and low-level replication with viruria is observed in 5% of healthy individuals. Persistent high-level BKV replication is the hallmark of polyomavirus-associated nephropathy in renal transplantation and of hemorrhagic cystitis in bone marrow transplantation. Since these manifestations are rare in other types of immunocompromised patients, the presence of specific cofactors is postulated. The role of BKV in autoimmune disease and cancer is a controversial topic and is difficult to determine, because the pathology no longer depends on BKV replication. This article discusses current views of pathogenesis, diagnosis, and treatment.