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

Inhibition of polyomavirus BK-specific T-Cell responses by immunosuppressive drugs

BACKGROUND

Reducing immunosuppression is the treatment of choice for polyomavirus-associated nephropathy in kidney transplant (KT) patients, but strategies and targets are uncertain.

METHODS

Using interferon-gamma ELISpot assays, we investigated immunosuppressive drug levels and polyomavirus BK (BKV) large T-antigen-specific T-cell responses in KT patients in vivo and in healthy donors after titrating immunosuppression in vitro.

RESULTS

In KT patients, BKV-specific T-cell responses were inversely correlated with tacrolimus trough levels (R=0.28, P<0.002), but not with mycophenolate levels, prednisone, or overall immunosuppressive dosing. In vitro tacrolimus concentrations above 6 ng/mL inhibited BKV- and cytomegalovirus-specific T-cells more than 50%, whereas less than 30% inhibition was observed below 3 ng/mL. Inhibition by cyclosporine A was more than 50% at concentrations of 1920 ng/mL and less than 30% below 960 ng/mL, corresponding to clinical C0 trough levels of 200 and 100 ng/mL, respectively. However, mycophenolate up to 8 microg/mL, leflunomide 50 microg/mL, or sirolimus concentrations 64 ng/mL did not inhibit BKV-specific interferon-gamma production, but antigen-dependent T-cell expansion.

CONCLUSIONS

Calcineurin-inhibitor concentrations are critical for BKV-specific T-cell activation. Reducing calcineurin inhibitors should be considered as first step, whereas conversion to mTOR inhibitors may be an attractive alternative or second step that should be validated in clinical BKV intervention trials.

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.

Repeat renal allografts treated with sirolimus, cyclosporine, anti-thymocyte globulin induction and continuous steroids achieve similar immunosuppressive efficacy as primary transplants

OBJECTIVE

We sought to examine repeat versus primary renal transplantations using sirolimus-based regimens.

METHODS

We compared 98 repeat versus 200 matched primary recipients treated de novo with sirolimus plus cyclosporine. Every repeat case received polyclonal antibody induction and continuous steroids. Outcomes were evaluated over a mean five-year follow-up by univariate and multivariate techniques. Kaplan-Meier plots were analyzed with using log-rank statistics with significance at P < or = 0.05.

RESULTS

Significant differences in demographic features included greater panel reactive antibody (PRA), younger age, fewer HLA-mismatches and more pre-emptive repeat versus primary grafts. Neither graft and patient survivals, nor incidences of biopsy-proven acute rejection (BPAR), chronic vasculopathy or tubular atrophy/interstitial fibrosis among biopsies performed for cause were significantly different at 1 and 5 years. Younger recipients, better HLA matches and absence of diabetes promoted repeat graft survival; whereas older age, longer cold ischemia time and BPAR reduced primary transplant outcomes. Renal function was similar at 1, 3, 12, 24, 48 and 60 months.

CONCLUSION

At 5 years this sirolimus regimen achieved similar efficacy for repeat versus primary transplantations.

Fifteen years of clinical studies and clinical practice in renal transplantation: reviewing outcomes with de novo use of sirolimus in combination with cyclosporine

Over the course of 15 years the use of sirolimus, a macrocyclic lactone, has evolved from an adjunct to calcineurin inhibitors (CNI) to the foundation of therapy due to the drug's unique properties: First, it displays synergistic pharmacodynamic interactions with CNI. Even among high immunologic risk patients, this regimen attenuates the risk of acute allograft rejection episodes when used in combination with cyclosporine or tacrolimus. Indeed >80% reduction in CNI exposure de novo yields better long-term renal function than full cyclosporine (CsA) doses, a useful tradeoff, despite the augmented occurrence of lymphoceles and impaired wound healing. Second, by inhibiting mammalian target of rapamycin (mTOR), it exerts profound anti-neoplastic effects reducing the incidence and mediating the regression of tumors displaying PTEN-deletions and/or Akt-activations in transplant and non-transplant patients. Third, it is relatively non-nephrotoxic although it may exacerbate that property of CNI agents. Fourth, it allows prompt withdrawal of steroid therapy. Fifth, it displays reduced rates of cytomegalovirus, and BK virus infections. The major adverse reactions can generally be controlled with countermeasure therapy. Myelosuppressive effects, which tend to be transient (unless sirolimus is combined with mycophenolic acid), are readily amenable to treatment with granulocyte colony stimulating factor for leukopenia, interleukin 11 for thrombocytopenia and erythropoietin for anemia. Combinations of statins and fibrates represent effective countermeasure therapy for hypercholesterolemia and hypertriglyceridemia, respectively. Idiosyncratic reactions include hypoxemic pulmonary toxicity, refractory edema and diarrhea. Thus, sirolimus represents the vanguard of a new class of maintenance agents for immunosuppression.

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.

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.

Genetic prediction of renal transplant outcome

PURPOSE OF REVIEW

In the present study, we reviewed recent publications regarding potential genetic predictors of transplant outcome, including acute rejection, metabolism of immunosuppressive medications, long-term transplant outcome, and posttransplant complications.

RECENT FINDINGS

Recent studies are based on the candidate gene analysis; specifically, cytokine genes and innate immune response molecules present popular targets for studies of acute rejection and long-term outcome. Pharmacogenomic studies are mostly focused on the genes of drug targets or the corresponding enzymes metabolizing the drug. Posttransplant complications (i.e. infections, diabetes, and malignancies) are associated with a variety of genes of different pathways. Most of the studies are based on just recipient, but not donor, genotype analysis. Positive results are balanced by reports of no association when evaluating the same genetic polymorphisms. Some of the reports might be affected by insufficient study design, including small sample size, lack of adjustment for potential confounders, and multiple comparisons.

SUMMARY

The field remains controversial because of differences in populations, study design, and statistical methods. Studies are based on candidate gene analysis; however, genome-wide association studies are lacking. Future research should be directed at better designed studies, larger sample size, evaluating both recipients and donors, and implementation of genome-wide association studies.

Low-dose Cidofovir for the Treatment of Polyomavirus-Associated Nephropathy: Two Case Reports and Review of the Literature

Background

Polyomavirus-associated nephropathy (PVAN) is a serious complication and cause of graft loss in kidney transplant recipients. In the absence of specific antiviral drugs, early detection of the disease and reduction of immunosuppressive regimen is the cornerstone of therapy. Cidofovir, a nucleoside analogue, has been found to inhibit BK virus (BKV) replication in vitro and has been proposed as treatment of refractory PVAN at low doses; however, its efficacy has never been demonstrated in randomized controlled trials.

Methods

Cidofovir therapy (0.5 mg/kg at a 2-week interval for eight consecutive doses) was initiated in two patients with biopsy-proven PVAN and persistent BKV DNA viraemia (≥10,000 copies/ml despite sustained reduction of the immunosuppressive regimen). In addition to these two case reports, we performed a critical review of the literature on the use of cidofovir in PVAN.

Results

No significant decrease of BKV viral load in blood was observed during cidofovir therapy and in follow-up of the two patients treated with cidofovir. Our literature review identified 21 publications reporting the use of cidofovir for the treatment of PVAN. All were case reports or small series. The efficacy of cidofovir therapy could not be assessed in 17 of these publications because of lack of data or concomitant reduction of immunosuppressive regimen. The four remaining publications were case reports.

Conclusions

In vitro and clinical data to support the efficacy of cidofovir in the treatment of PVAN are currently lacking. More promising compounds should be identified for further clinical studies.

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.

Quantitation of BK virus DNA for diagnosis of BK virus-associated nephropathy in renal transplant recipients

Quantitative measurement of BK virus DNA (Q-BKDNA) has been used for the early diagnosis and monitoring of BK virus-associated nephropathy (BKVAN). This study was designed to determine the BKDNA cutoff for the diagnosis of BKVAN. Between June 2005 and February 2007, 64 renal transplant recipients taken renal biopsies due to renal impairment submitted plasma and urine for Q-BKDNA. Eight BKVAN patients (12.5%) had median viral loads of 6.0 log10 copies/mL in plasma and 7.3 log10 copies/mL in urine. Among 56 non-BKVAN patients, 45 were negative for Q-BKDNA; 4 were positive in plasma with a median viral load of 4.8 log10 copies/ mL, and 10 were positive in urine with a median viral load of 4.8 log10 copies/mL. Receiver operating characteristic curve analysis showed that a cutoff of 4.5 log10 copies/mL in plasma and a cutoff of 5.9 log10 copies/mL in urine had a sensitivity of 100% and a specificity of 96.4%, respectively. A combined cutoffs of 4 log10 copies/ mL in plasma and 6 log10 copies/mL in urine had better performance with a sensitivity of 100% and a specificity of 98.2% than each cutoff of urine or plasma. QBKDNA with the combined cutoffs could reliably diagnose BKVAN in renal transplant recipients.

Cidofovir inhibits polyomavirus BK replication in human renal tubular cells downstream of viral early gene expression

The human polyomavirus BK (BKV) causes nephropathy and hemorrhagic cystitis in kidney and bone marrow transplant patients, respectively. The anti-viral cidofovir (CDV) has been used in small case series but the effects on BKV replication are unclear, since polyomaviruses do not encode viral DNA polymerases. We investigated the effects of CDV on BKV(Dunlop) replication in primary human renal proximal tubule epithelial cells (RPTECs). CDV inhibited the generation of viral progeny in a dose-dependent manner yielding a 90% reduction at 40 microg/mL. Early steps such as receptor binding and entry seemed unaffected. Initial large T-antigen transcription and expression were also unaffected, but subsequent intra-cellular BKV DNA replication was reduced by >90%. Late viral mRNA and corresponding protein levels were also 90% reduced. In uninfected RPTECs, CDV 40 microg/mL reduced cellular DNA replication and metabolic activity by 7% and 11% in BrdU and WST-1 assays, respectively. BKV infection increased DNA replication to 142% and metabolic activity to 116%, respectively, which were reduced by CDV 40 microg/mL to levels of uninfected untreated RPTECs. Our results show that CDV inhibits BKV DNA replication downstream of large T-antigen expression and involves significant host cell toxicity. This should be considered in current treatment and drug development.