Therapy with mTOR Inhibitors in Polyomavirus Allograft Nephropathy (PVAN): A Five Year Follow Up

Polyomavirus allograft nephropathy (PVAN) is an important post-transplant complication. Despiteits low incidence, around 5%, graft loss occurs in about 50% of cases [1]. In established PVAN (stage B), reduction in immunosuppressive therapy is considered as a safe strategy, in order to retard graft loss. However, the best approach remains controversial. While some groups suggest reduction of mycophenolate doses, others consider calcineurin inhibitors withdrawal or converting therapy to mTOR inhibitors or azathioprine [2].


Introduction
Polyomavirus allograft nephropathy (PVAN) is an important post-transplant complication. Despiteits low incidence, around 5%, graft loss occurs in about 50% of cases [1]. In established PVAN (stage B), reduction in immunosuppressive therapy is considered as a safe strategy, in order to retard graft loss.
However, the best approach remains controversial. While some groups suggest reduction of mycophenolate doses, others consider calcineurin inhibitors withdrawal or converting therapy to mTOR inhibitors or azathioprine [2].
Experimental data showed that Polyomavirus activates mTOR pathway in epithelial tubular cells. In Polyomavirus infected tubular cells culture, sirolimus and/or lefl unomide reduced the expression of BKvirus large T antigen, suppressing the infection [3].

Abstract
Polyomavirus nephropathy (PVAN) has a negative impact on renal allograft survival. Therapy options include reduction of immunosuppression and antiviral drugs.
Aim: Evaluate the effect ofmTORi based immunosuppression on PVAN.
Methods: Cross-sectional cohort of 21 renaltransplant recipients with PVAN. Initial immunosuppression based on MPA/tacrolimus was changed to mTOR/steroids at diagnosis, if urine protein/creatinine ratio <0.5 g/l. Patients weremonitored by urine cytology, qualitative PCR in peripheral blood, serum creatinine andprotein/creatinine ratio.
Results: PVAN was suspected 14.3±19.3 months post-transplant, by thepresence of decoy cells in serial urine cytology. At this point, serum creatinine was 1.4 ± 0.5 mg /dL, through levels of tacrolimus (TAC) was 8.6 ± 3.5 ng/dL. TAC dose was reduced (through level 6.8 ± 2.8 ng/dL). However, in presence of persistent viruria and allograft dysfunction (creatinine 2.5 ± 0.7 mg/dL), a biopsy was performed 30.0±18.1 months post-transplant, with the fi nal diagnosis of PVAN stage 2. MPA and TAC were withdrawn and immunosuppressive therapy maintained with mTORi (sirolimus or everolimus) plus steroids. No rejection episodes were observed. In a 5-year follow up, 10/21 (47.6%) grafts were lost due progression of PVAN. Risk factors for graft loss were higher creatinine at fi rst viruria (1.7 ± 0.7 versus 1.4 ± 0.4 mg/dl, p<0.05) or at biopsy (3.1 ± 0.6 versus 2.3 ± 0.7 mg / dl), compared to group with a functioning graft after 5 years. In the latter group, after 70 months of follow-up, renal function remained stable (creatinine 2.0 ± 0.5 mg/dl); with negative viruria 16 weeks post mTORi.

Conclusion:
In this series, the change of immunosuppression to mTORi and prednisone was safe with cleared viruria onaverage 16 weeks after conversion. In patients with earlier renal biopsy and with better renal function, this strategy preserved the allograft function.
Based on these data, we hypothetized that early changes in immunosuppression to proliferation signal inhibitors (PSI-

Results
Twenty-one patients fulfi ll the inclusion criteria, and were converted to mTOR inhibitor (sirolimus) at diagnosis of PVAN.

Discussion
Polyomavirus has a negative impact on renal graft function, with a higher rate of graft loss [1]. Despite progress in diagnosis and classifi cation of severity of PVAN, there is no consensus about therapy. A metanalysis of PVAN therapy concluded that the only benefi t was in reducing immunosuppressive therapy [2]. However, the best protocol is not a consensus. While some groups suggest to avoid mycophenolate, others consider avoid tacrolimus or add mTOR inhibitors to therapy [2]. Analysis of clinical trials with mTORi showed a lower incidence of viral infections, for both cytomegalovirus and Polyomavirus [5,6].
Also, data from cell culture showed that mTORi (sirolimus) inhibits BKvirus large T antigen expression [3]. Based on these data, we designed aprotocol for PVAN therapy. When BK virus infection was suspected, by detecting decoy cells in  urine cytology, tacrolimus dose was reduced in 50%. If viruria persists and PVAN was observed at biopsy, tacrolimus and MPA were withdrawn and replaced by sirolimus and steroids. When the whole group was analyzed, data was promising. However, in a long term follow up graft loss was 47.6%, comparable to previous reports. In order to identify responders (negative viruria) and nonresponders (persistent or recurrent analysis) we decided for a sub group study. The fi rst interesting fi nding was that a group of patients (16/21) had a rapid decline in viruria after converting to mTORi. We were not able to identify in demographic or transplant related data, risk factors for this pattern. However, during follow up, part of the responder group (6/16) had recurrent viruria, with need for late allograft biopsy. Long-term analysis showed that graft loss was comparable between patients with persistent or recurrent viruria, in about 80%, suggesting that the changes in immunosuppression were not effi cient to control PVAN [7]. However, patients with negative viruria had a better prognosis, with graft loss of 10% and a stable graft function after 5 years of PVAN diagnosis. Unfortunately, at diagnosis, there is no clear data that suggests the rate of progression of PVAN or the response to mTORi therapy. In conclusion, therapy with mTOR inhibitors was safe in patients with PVAN. However, its effi cacy was of 50% in the whole group. Patients with rapid response to mTORi, with negative viruria, should be closely monitored, as recurrence of viruria can occur, with a high risk for graft loss. Persistence of negative viruria was associated with a better graft survival.