Background: The development of powerful immunosuppression has resulted in a decline of rejection rates of kidney allografts; however, the incidence and prevalence of opportunistic infections has risen accordingly. Polyoma virus-associated nephropathy (PVAN) has become a common complication; cytomegalovirus (CMV)and adenovirus also cause graft nephritis.

Patients and Methods: Sixteen cases of biopsy-proven graft nephritis from a single center were retrospectively reviewed (diagnosed 2003-2008). Standard immunosuppression consisted of anti-thymocyte globulin induction followed by tacrolimus, mycophenolate-mofetil and a steroid taper. Renal biopsies were obtained after graft dysfunction and were evaluated for rejection according to BANFF criteria. Viral immunohistochemical stains were performed.

Results: A single case of adenovirus nephritis was diagnosed after living-donor re-transplantation (Tx). Two cadaveric graft recipients (one re-Tx) developed CMV-associated nephritis. PVAN was diagnosed in 13 cases (all were first Tx, seven living and six cadaveric grafts; two with simoultaneous pancreatic grafts). Graft nephritis developed at a median 16.4 mn (range 2.5 - 47.1) post-Tx; 71% of patients had undergone prior treatment for rejection. Immunosuppression was tapered; the CMV nephritides were treated with ganciclovir, but both grafts were lost. The adenovirus nephritis resolved after reduction of immunosuppression; however, long-term graft function is poor. PVAN was treated with low-dose cidofovir in 11 cases and leflunemide in two cases, and nine patients received immunoglobulins. In nine cases therapy resulted in improvement of graft function, five patients lost their graft (one after PVAN relapse).

Conclusion: Renal allograft nephritis is most commonly caused by polyoma virus. Although previous studies have suggested that 75% of polyoma virus infections occur during the first year post-transplantation, 77% of PVAN occurred after the first year at our institution. Long-term monitoring for viral nephritides should therefore continue after the first year post-tranplantation