BKV and JCV large T antigen-specific CD8+ T cell response in HLA A*0201+ kidney transplant recipients with polyomavirus nephropathy and patients with progressive multifocal leukoencephalopathy.

BACKGROUND: BK virus (BKV), which causes polyomavirus-associated nephropathy (PVN) in kidney transplant recipients (KTx), has 75% homology with JC virus (JCV), the etiologic agent of progressive multifocal leukoencephalopathy (PML). The large T-antigen (T-ag) is the main regulatory protein of polyomaviruses that is expressed early in the viral cycle. OBJECTIVES: To characterize epitopes of BKV and JCV T-ag recognized by CD8+ T-cells and explore the role of these cells in containing polyomavirus infection. STUDY DESIGN: We tested peripheral blood mononuclear cells of HLA A*0201+ BKV- and JCV-seropositive individuals, including patients with active BKV or JCV infection and healthy control subjects in a cross-sectional study. RESULTS: CD8+ T-cells that recognized the nonamer BKV Tp579, which is identical to JCV Tp578, were detected by tetramer staining in 10/13 (77%) healthy individuals, 3/10 (30%) KTx/PVN, and 4/9 (44%) patients with PML and/or HIV-infection. Conversely, BKV Tp398- and Tp410-specific CD8+ T cells were detected in 3/13 (23%) and 1/13 (8%) healthy individuals only. CONCLUSION: These data suggest that, as it is the case for the VP1 protein, the same population of CD8+ T-cells may recognize epitopes located on the BKV and JCV T protein. The overall cellular immune response against polyomavirus T-ag, however, is lower than against the VP1 protein and is more frequently detected in healthy individuals than in patients with active BKV or JCV infection.

Pharmacokinetics of mycophenolic acid, tacrolimus and sirolimus after gastric bypass surgery in end-stage renal disease and transplant patients: a pilot study.

BACKGROUND: Promising data regarding the safety and efficacy of gastric bypass surgery (GBS) as an option to address obesity in the transplant population are emerging. The data lack on how GBS may alter the pharmacokinetics (PK) of modern immunosuppression. The objective of this study was to describe the alterations in the PK of modern immunosuppressants and the GBS population. METHODS: Data are presented on six subjects who participated in this trial--four were on dialysis and two were renal transplant recipients. Dialysis-dependent bypass subjects received a single dose of 6 mg of sirolimus, two 4-mg doses of tacrolimus and two 1000-mg doses of mycophenolate mofetil (MMF) over the 24-h study period. Transplant recipients continued their current regimen. Maximum plasma concentration (C(max)), time to reach the maximum plasma concentration (T(max)) and the area under the plasma concentration vs. time curve (AUC(0-12) and AUC(0-infinity) where appropriate) were calculated for tacrolimus, sirolimus, mycophenolic acid (MPA) and mycophenolic acid glucuronide (MPAG). RESULTS: Significant inter-patient variability in the C(max), T(max) and AUC of tacrolimus, sirolimus MPA and MPAG was observed. A notable difference in the AUC:dose ratio for tacrolimus was seen when comparing data with published data in the non-bypass population. Similar differences in PK were seen with sirolimus, MPA and MPAG. CONCLUSIONS: When comparing the PK of sirolimus, tacrolimus, MPA and MPAG to published PK data in the non-bypass population, significant differences are observed. It is likely that transplant recipients with GBS would need higher doses of tacrolimus, sirolimus and MMF to provide similar exposure to a non-bypass patient.

Maribavir: a novel antiviral agent with activity against cytomegalovirus.

OBJECTIVE: To review the pharmacology, pharmacokinetics, efficacy, and safety of maribavir, a novel antiviral agent in the benzimidazole drug class. DATA SOURCES: Articles were identified through searches of MEDLINE (January 1998-July 2008). Abstracts from recent scientific meetings and the manufacturer were also included. STUDY SELECTION AND DATA EXTRACTION: All English-language in vitro and in vivo studies and abstracts evaluating maribavir were reviewed and considered for inclusion. All human studies were included. DATA SYNTHESIS: Maribavir has significant activity against both human cytomegalovirus (CMV) and Epstein-Barr virus, but not other herpesviruses. Unlike ganciclovir, which needs to be phosphorylated by UL 97 kinase to become an active inhibitor of DNA polymerase, maribavir directly inhibits UL 97 kinase. UL 97 kinase is an early viral gene product involved in viral DNA elongation, DNA packaging, and egress or shedding of capsids from viral nuclei. Maribavir has also been found to be effective against ganciclovir-resistant CMV strains. Maribavir differs from current CMV antiviral agents in its adverse event profile. Maribavir is not associated with nephrotoxicity or hematologic toxicities, but has been associated with taste disturbances. In February 2007, maribavir was granted Food and Drug Administration orphan drug status for prevention of CMV viremia and diseases in at-risk populations. Maribavir Phase 2 trials in stem-cell transplant recipients have been completed, and there are ongoing Phase 3 trials in stem-cell and organ transplant recipients. CONCLUSIONS: Maribavir may be an option for treatment of ganciclovir-resistant CMV infections. Its bioavailability is greater than that of oral ganciclovir, but less than that of valganciclovir. No differences in pharmacokinetics were seen in renally impaired patients, although dialysis-dependent patients were not evaluated. Maribavir is not associated with hematologic toxicities; however, the high prevalence of taste disturbances may limit its tolerability.

Posttransplant lymphoproliferative disorder.

OBJECTIVE: To define and discuss the pathogenesis, clinical presentation, diagnosis, risk factors, and current preventive and treatment strategies of posttransplant lymphoproliferative disorder (PTLD). DATA SOURCES: MEDLINE was searched for articles published from January 1966 to July 2007. Search terms used include posttransplant lymphoproliferative disease, posttransplant malignancy, antiviral agents, interferon-alfa, rituximab, immunosuppression, chemotherapy, radiation, and surgery. Additional articles were identified by a hand search of references. STUDY SELECTION AND DATA EXTRACTION: Studies in English of pediatric and adult solid organ transplantation populations published were selected and analyzed. Data from these studies and information from review articles were included in this review. DATA SYNTHESIS: PTLD occurs in 1-20% of organ recipients following solid organ transplantation. PTLD risk factors include recipient pretransplant Epstein-Barr virus (EBV) negative serostatus, type of transplant, intensity of immunosuppression, and age. The PTLD presentation is variable. Some patients present asymptomatically; in others, early symptoms can be nonspecific. To prevent PTLD, minimizing immunosuppression burden and using antiviral agents active against EBV are useful strategies. PTLD treatment may require reduction of immunosuppression, radiation, surgical excision, monoclonal antibodies, interferon-alfa, and chemotherapy. CONCLUSIONS: Screening for patients at risk and balancing the intensity of immunosuppressive regimens against the risk of rejection can substantially reduce the risk of developing PTLD. If PTLD occurs, an individualized treatment plan including decreased immunosuppression and other agents should be chosen based on the severity and extent of disease.

Pharmacotherapeutic options for the management of human polyomaviruses.

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

Polyomavirus-associated nephropathy in renal transplantation: interdisciplinary analyses and recommendations.

Polyomavirus-associated nephropathy (PVAN) is an emerging cause of kidney transplant failure affecting 1-10% of patients. As uncertainty exists regarding risk factors, diagnosis, and intervention, an independent panel of experts reviewed the currently available evidence and prepared this report. Most cases of PVAN are elicited by BK virus (BKV) in the context of intense immunosuppression. No specific immunosuppressive drug is exclusively associated with PVAN, but most cases reported to date arise while the patient is on triple immunosuppressive combinations, often comprising tacrolimus and/or mycophenolate mofetil plus corticosteroids. Immunologic control of polyomavirus replication can be achieved by reducing, switching, and/or discontinuing components of the immunosuppressive regimen, but the individual's risk of rejection should be considered. The success rate of this intervention is increased with earlier diagnosis. Therefore, it is recommended that all renal transplant recipients should be screened for BKV replication in the urine: 1) every three months during the first two years posttransplant; 2) when allograft dysfunction is noted; and 3) when allograft biopsy is performed. A positive screening result should be confirmed in <4 weeks and assessed by quantitative assays (e.g. BKV DNA or RNA load in plasma or urine). Definitive diagnosis of PVAN requires allograft biopsy. If PVAN and concurrent acute rejection is diagnosed, antirejection treatment should be considered, coupled with subsequently reducing immunosuppression. The antiviral cidofovir is not approved for PVAN, but investigational use at low doses (0.25-0.33 mg/kg intravenously biweekly) without probenicid should be considered for refractory cases. Retransplantation after renal allograft loss to PVAN remains a treatment option for patients clearing polyomavirus replication.

Renal allograft loss as the result of polyomavirus interstitial nephritis after simultaneous kidney-pancreas transplantation: results with kidney retransplantation.

BACKGROUND: Polyomavirus (PV) infection in kidney transplant patients has been reported to cause interstitial nephritis and subsequent graft loss. The cornerstone of current therapy is a reduction in immunosuppression, which can subsequently lead to kidney allograft rejection. This dilemma becomes even more challenging in the setting of simultaneous kidney-pancreas transplantation, because a reduction in immunosuppression may result in rejection of the pancreas allograft. Antiviral therapy has not been shown to be clinically successful in decreasing the risk of graft loss secondary to PV infection. Furthermore, because of limited experience, the decision to perform retransplantation in patients who lost their primary kidney grafts to PV interstitial nephritis becomes a difficult one. METHODS: Retrospective review and case studies. RESULTS: We report two successful living donor kidney retransplants in simultaneous kidney-pancreas transplant patients who lost their first kidney grafts to PV infection. Both patients are receiving rimantadine therapy and performing well, with functioning kidney and pancreas grafts and no evidence of recurrent PV interstitial nephritis 22 and 37 months after retransplantation. CONCLUSIONS: Although follow-up is limited, our initial experience would indicate that graft loss secondary to PV interstitial nephritis is not an absolute contraindication for kidney retransplantation.

Recurrence risk after organ transplantation in patients with a history of Hodgkin disease or non-Hodgkin lymphoma.

This study defines the incidence and recurrence risk of Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL) after organ transplant. Patients from the United States with a history of HD or NHL before organ transplantation reported to the Israel Penn International Transplant Tumor Registry from 1968 to 2001 were analyzed. A total of 91 patients underwent organ transplantation with a lymphoma history: HD (38 patients) and NHL (53 patients). Median disease-free interval pretransplant was 99 (range 0-459.1) months, and median follow-up posttransplant was 25.7 (0.4-131.1) months. Ten patients were excluded from further analysis because of lack of follow-up information (n=9) or they never achieved remission (n=1). Recurrence incidence was 8 of 81 patients (10%) (HD=3/34 [9%] vs. NHL=5/47 [11%]). Gender, race, allograft type and source, age at lymphoma diagnosis, and immunosuppression did not influence recurrence. Patients with less than a 2-year period between diagnosis and transplant seem to be at increased risk of relapse. Median disease-free interval before transplant was longer for patients without recurrence (115 vs. 30.2 months, P=0.24), but was not statistically significant. Median time to recurrence posttransplant was 18.7 (range 1.9-82.2) months (HD=3.7 vs. NHL 23.6 months, P=0.10). Survival after recurrence was poor (HD [1/3] and NHL [1/5], median survival 6.8 [range 0-22.1] months). There is no difference in recurrence rates for HD and NHL. The outcome for recurrent lymphoma is poor. The low risk of recurrence (10%) indicates that preexisting HD and NHL need not be an absolute contraindication to transplantation.

Donors with central nervous system malignancies: are they truly safe?

BACKGROUND: In an era of organ shortage, the use of expanded or marginal donors has been attempted to increase transplantation rates and diminish waiting list mortality. One strategy is the use of organs from patients with a history of or active central nervous system (CNS) tumor. METHODS: Sixty-two recipients were identified as the recipients of organs from donors with a history of or active CNS malignancy. Patient demographics, donor tumor management, incidence of tumor transmission, and patient survival were examined. RESULTS: Of the organs recovered and transplanted from donors with astrocytoma, 14 were associated with at least one risk factor including high-grade tumor (n=4), prior surgery (n=5), radiation therapy (n=4), and systemic chemotherapy (n=4). One tumor transmission was identified at 20 months posttransplant with the patient expiring from metastatic disease. Twenty-six organs were transplanted from glioblastoma patients with 15 demonstrating risk factors including high-grade tumor (n=9) and prior surgery (n=10). Eight transmissions were identified with a range of 2 to 15 months posttransplant, with seven patients dying as the result of metastatic disease. Seven organs were used from donors with a medulloblastoma. Three transmissions were identified at a range of 5 to 7 months, all associated with ventriculoperitoneal shunts. Two medulloblastoma recipients died as the result of metastatic disease, whereas the third is alive with diffuse disease. The rate of donor tumor transmission, in the absence of risk factors, was 7%, whereas in the presence of one or more risk factor this rate dramatically rose to 53% (P<0.01). CONCLUSIONS: Organs from donors with CNS tumors can be used with a low risk of donor tumor transmission in the absence of the following risk factors: high-grade tumors, ventriculoperitoneal or ventriculoatrial shunts, prior craniotomy, and systemic chemotherapy.

Retransplantation in patients with graft loss caused by polyoma virus nephropathy.

The characteristics and outcome in 10 patients who underwent retransplantation after losing their renal grafts to BK virus-associated nephropathy (BKAN) are described. The patients underwent retransplantation at a mean of 13.3 months after failure of the first graft. Nephroureterectomy of the first graft was performed in seven patients. Maintenance immunosuppression regimens after the first and second grafts were similar, consisting of a combination of a calcineurin inhibitor, mycophenolate mofetil, and prednisone. BKAN recurred in one patient 8 months after retransplantation, but stabilization of graft function was achieved with a decrease in immunosuppression and treatment with low-dose cidofovir. After a mean follow-up of 34.6 months, all patients were found to have good graft function with a mean creatinine of 1.5 mg/dL. From this collective experience from five transplant centers (although the follow-up after retransplantation was not extensive), it can be concluded that patients with graft loss caused by BKAN can safely undergo retransplantation. The risk of recurrence does not seem to be increased in comparison with the first graft.

MALToma: a Helicobacter pylori-associated malignancy in transplant patients: a report from the Israel Penn International Transplant Tumor Registry with a review of published literature.

BACKGROUND: Mucosa-associated lymphoid tissue lymphoma (MALToma) is a Helicobacter pylori-related tumor of B-cell origin, the malignant potential for which remains to be defined in immunosuppressed patients. METHODS: Review of the Israel Penn International Transplant Tumor Registry identified six cases of gastric MALToma. Patient demographics, management, and outcomes were compared and published literature was reviewed. RESULTS: MALToma developed in six transplant recipients (three kidney, two heart, one kidney-pancreas). All were treated with immunosuppression minimization and therapy for H. pylori, resulting in disease regression in five patients. One patient developed progression to high-grade MALToma despite documented H. pylori eradication, required surgery and chemotherapy, and died, with significant disease at autopsy. CONCLUSIONS: Treatment of MALToma with immunosuppression minimization and anti-H. pylori therapy results in a majority of patients becoming disease free. Observation of malignant degeneration into an aggressive, high-grade lymphoma in one patient indicates the malignant potential. Diligent follow-up of these patients with endoscopy and biopsy is therefore indicated.

Experience with 274 cardiac transplant recipients with posttransplant lymphoproliferative disorder: a report from the Israel Penn International Transplant Tumor Registry.

BACKGROUND: Posttransplant lymphoproliferative disorder (PTLD) is a life-threatening complication that occurs in a small but significant minority of solid organ transplant recipients. Published experiences with PTLD in cardiac transplant recipients are limited to relatively small single-center reports. METHODS: This report presents experience with 274 cases of PTLD in cardiac transplant recipients reported to the Israel Penn International Transplant Tumor Registry (IPITTR). RESULTS: PTLD carried an ominous prognosis: Kaplan Meier survival after PTLD diagnosis was 45%, 33%, 30%, and 13%, respectively, at 1, 3, 5, and 10 years. Common causes of death included: PTLD, cardiovascular collapse, and infection; all occurred at a median of less than 6 months. Risk of death from cardiovascular collapse secondary to immunosuppression withdrawal was substantial (28%), indicating that a fine balance exists between death from PTLD and from sudden cardiac death due to acute rejection. PTLD therapy in the majority of patients consisted of combination therapy (49%). Survival in patients receiving immunosuppression minimization (ISM) alone was 32%, with ISM plus other therapy was 27%, and with other therapies not containing ISM was 11% (P < 0.01). CONCLUSION: PTLD in cardiac transplant recipients is associated with low long-term survival rates. Analysis of PTLD therapies and outcomes suggest that immunosuppression minimization, when applied, improves survival. However, risk of sudden death may mitigate the positive effect of ISM. This observation has important implications for ISM in PTLD therapy in cardiac transplant recipients. Carefully designed prospective studies are needed to evaluate the positive and negative effects of ISM in cardiac transplant recipients with PTLD.

Incidental diagnosis of gastric cancer in transplant recipients improves patient survival.

BACKGROUND: Gastric cancer in the United States is often diagnosed at advanced stages, resulting in dismal outcomes. In the immunosuppressed transplant recipient population, little is known about the clinical staging and outcome of these compromised patients. METHODS: All US cases reported to the Israel Penn International Transplant Tumor Registry were retrospectively examined for patient demographics, immunosuppressive therapy, tumor characteristics, therapeutic modalities, and mortality. Statistical analysis was performed with Students t test, chi-square analysis, and log-rank analysis by the method of Kaplan-Meier. RESULTS: Gastric cancer was identified in 34 recipients: 28 (82%) were male; 24 (71%) were white. Mean age at diagnosis was 58 +/- 11 years. Twenty-four (71%) patients received kidney transplants, 7 (21%) received heart transplants, and 3 (9%) received liver transplants. Fifty percent received induction therapy, whereas 94% were maintained on calcineurin inhibitors and corticosteroids. Thirty-five percent of patients were diagnosed during evaluation for gastrointestinal symptoms, with the remaining cases discovered incidentally during endoscopy (53%) or during computed tomography (12%) performed for other reasons. Stage varied at presentation as follows: stage I (n = 6), stage II (n = 11), stage III (n = 13), and stage IV (n = 4). Incidental diagnoses resulted in a lower stage malignancy (P <.001) and greater 1-year and 5-year survivals (P <.05) compared with those patients whose were diagnosed after being evaluated of gastrointestinal symptoms. CONCLUSION: In the United States, because gastric cancer in the transplant recipient is frequently identified at an earlier stage (50% were stages I and II) than in the general population, survivals are equivalent despite continued administration of immunosuppression. This early identification may be attributed to more frequent presymptom diagnosis and staging, resulting from incidental detection of these malignancies during posttransplant upper endoscopy or computed tomography. Early detection has resulted in a 29% 5-year survival for the entire transplant recipient group compared with a 5% to 15% 5-year survival in the general population.

The role of immunosuppression in lymphoma.

Post-transplant lymphoproliferative disorder (PTLD) is a well-recognized yet serious complication in solid organ transplant recipients and currently represents the second most common de novo malignancy following solid organ transplantation. PTLD has been noted in all transplant immunosuppressive eras including the pre-cyclosporine, cyclosporine, and post-cyclosporine eras. The time from organ transplantation to PTLD presentation varies widely from less than 1 month to several years. PTLD presents with a broad spectrum of clinical manifestations depending on the transplanted organ, immunosuppressive therapy and patient age. Intense immunosuppressive therapy is a major risk factor for development of PTLD. Whenever a new agent is introduced, there is a learning curve that leads to dosing modifications, which in turn result in optimization of its immunosuppressive efficacy and reduction of toxicities, including PTLD. We review the major historical and recent immunosuppression trials to assess the impact of individual immunosuppressive agents and regimens on PTLD risk.

Donor transmitted malignancies.

Early experiences in transplantation, which pre-dated brain death laws, utilized organs from donors with active malignancies. The use of organs from such donors occasionally resulted in the transmission of malignancy from the donor to an unknowing recipient. Over a period of three decades, Israel Penn, M. D. catalogued some two hundred and fifty cases of organs transplanted from donors with a history of malignancy; carefully examining each reported case for tumor histology, donor risk factors, method of tumor presentation and recipient outcome. Some recipients never developed malignancies, while others were less fortunate, developing cancers that were suspicious for donor origin. The evolution of transplantation has resulted in improved patient survival, which in turn has led to an increased demand for organ transplantation. Unfortunately, the supply of organs available for transplantation has failed to keep pace with the demand, with the worldwide deficit growing annually. In an effort to bridge the widening gap, utilization of older and more marginal donors has been suggested. However, use of older donors is accompanied by the likelihood that a significant proportion may have undiagnosed malignancies. Multiple transplant programs have considered the use of donors with tumors of non-malignant or even low-grade malignant histology, most often involving the central nervous system (CNS). According to a survey from the United Network for Organ Sharing (UNOS), central nervous system malignancies are among the most commonly identified malignancies found in potential donors. This study examines the distribution of potential donor transmitted malignancies reported to the Israel Penn International Transplant Tumor Registry. The incidence of tumor transmission is examined in the overall group as well as among individual histologies. We also seek to identify specific factors associated with the risk of malignancy transmission from donor to recipient, in an effort to minimize future transmission of donor tumors to unwitting recipients. The study is based on voluntary registry data, which some argue can be criticized for a lack of true incidence data. In reality, however, this data may provide a more accurate insight since it is based on transmissions from high-risk donors rather than from the general population.

Posttransplant malignancy.

In the past few decades, great advances have been made in the field of solid-organ transplantation. A greater understanding of immune system function, the development of modern immunosuppression, and advancements in surgical technique have led to marked improvements in both recipient and graft survivals, as well as recipients' quality of life. However, improved survival rates have also led to prolonged exposure to chronic immunosuppression, which increases the risk for the development of posttransplant malignancies. In addition, older transplant candidates are being considered, carrying with them the increased likelihood of preexisting malignancy. Consequently, the potential risk of posttransplant malignancy must be considered. Moreover, as long-term transplant survivors continue to age, posttransplant malignancies will be seen more frequently. This review presents the more commonly encountered posttransplant malignancies and the measures that are currently being utilized to prevent and treat them.

Polyomavirus nephropathy in kidney transplantation.

Polyomavirus nephropathy has become an important complication in kidney transplantation, with a prevalence of 1% to 8%. Unfortunately, the risk factors for polyomavirus nephropathy and renal allograft loss are not well defined. The definitive diagnosis is made through assessment of a kidney transplant biopsy. Recently, noninvasive urine and serum markers have been used to assist in polyomavirus nephropathy diagnosis and monitoring. Primary treatment is immunosuppression reduction, but must be balanced with the risks of rejection. No antiviral treatments for polyomavirus nephropathy have been approved by the Food and Drug Administration. Although cidofovir has shown in vitro activity against murine polyomaviruses, and has been effective in some patients, it is associated with significant nephrotoxicity. Graft loss due to polyomavirus nephropathy should not be a contraindication to retransplantation; however, experience is limited. This review presents potential risk factors, screening, diagnostic and monitoring methods, therapeutic management, and retransplantation experience for polyomavirus nephropathy.

Basic and clinical research in polyomavirus nephropathy.

Over the last decade, polyomavirus nephropathy (PVN) has emerged as an important cause of renal allograft dysfunction and graft loss. PVN occurs with a prevalence of 1%-8% in renal transplant recipients and is most commonly reported within the first 12 months posttransplant. The human polyomavirus, BK virus, is thought to be the primary etiologic agent of PVN. Risk factors for PVN are not well defined and are most likely a result of a complex interaction between multiple donor and recipient factors. Definitive diagnosis of PVN is made through histological assessment of a renal allograft biopsy. Recent studies have also evaluated noninvasive urine and serum markers for screening of BK virus replication and as adjunct tools in PVN diagnosis and monitoring. The principal treatment for PVN is immunosuppression reduction, but this must be balanced against the risks of rejection. If rejection occurs concurrently with PVN, a brief increase in immunosuppression to treat the rejection episode followed by a subsequent reduction in immunosuppression is recommended. No antiviral treatments for PVN have been approved by the Food and Drug Administration. Although the antiviral drug cidofovir has shown in vitro activity against murine polyomaviruses, and has been effective in some patients, it is associated with significant nephrotoxicity. Small series of patients treated with leflunomide and intravenous immune globulin therapy for PVN have also recently been reported. Retransplantation after graft loss due to PVN is feasible, but experience is limited. Current research is focusing on identifying PVN risk factors, refining screening, diagnostic and monitoring methods, and developing therapy for prophylaxis and treatment of PVN with the goals of decreasing the prevalence of PVN and improving allograft outcomes in renal transplant recipients diagnosed with PVN. This review will present recent advances in basic and clinical research related to PVN and renal transplantation.