Efficacy of mTOR Inhibitors and Intravenous Immunoglobulin for Treatment of Polyoma BK Nephropathy in Kidney Transplant Recipients: A Biopsy-Proven Study

Objectives: We investigated the efficacy of a predetermined protocol that consisted of immunosuppressive drug reduction/withdrawal and intravenous immunoglobulin administration for the treatment of polyoma BK virus nephropathy. Materials and Methods: Patients with biopsy-proven polyoma BK virus nephropathy received a treatment regimen based on discontinuation of both calcineurin inhibitors and antiproliferative agents and switching to mTOR inhibitors accompanied by intravenous immunoglobulin administration. Results: Our study included 508 patients, with polyoma BK viremia detected in 80 patients. The mean age was 45.3 +/- 9.5 years (range, 18-71 y), 64% were male, and mean follow-up was 37 +/- 21 months (6-94 mo). All 16 patients who developed polyoma BK virus nephropathy and 9 patients who had highgrade polyoma BK viremia without nephropathy received intravenous immunoglobulin treatment. Compared with patients with viremia, patients with polyoma BK virus nephropathy had significantly higher rates of graft loss due to rejection ( 18.8% vs 1.6%; P =.024) and all-cause graft loss (31.2% vs 6.3%; P =.014). Histopathologically, viral inclusion bodies disappeared and SV40 became negative after treatment in all 13 patients who underwent protocol biopsies. Unfortunately, histopathologically complete recovery without chronic tubular and interstitial tissue damage was achieved in only 4 patients after treatment. In addition, 3 patients lost their grafts due to acute antibody-mediated or mixed-type rejection (18.8%). Conclusions: In patients with polyoma BK virus nephropathy, clearance of viremia and SV40 should not be the sole outcomes to obtain. Aggressive reductions in maintenance immunosuppression and switching to double-drug therapy combined with high- dose intravenous immunoglobulin leads to high rates of graft loss/rejection and sequalae of chronic histological changes.