Introduction.

Polyomavirus-associated nephropathy (PVAN) is now recognized as an important cause of graft dysfunction and early kidney transplant loss. Over-immunosuppression is the main risk factor for the development of PVAN. Donor and recipient characteristics do play a role but conclusive evidences are still lacking.

Methods.

In this single centre cohort study performed analysing data retrieved from a prospectively collected database we evaluated incidence, outcomes and risk factors of Polyomavirus infection in 639 consecutive kidney transplants performed between 2007 and 2013.

Results.

During a mean follow up of 4.5 years, viremia was detected in 54/639 patients (8%); 26/639 recipients (4%) had biopsy-proven PVAN. Death-censored graft loss rate was significantly higher in patient with PVAN compared to recipients with no viremia: 42% (10/24) vs. 14% (76/523), respectively (p<0.05). After immunosuppression reduction, 43/54 patients (80%) effectively managed to clear the virus with preserved renal function; 4 patients (7%) experienced biopsy-proven acute rejection. Two cases (4%) of ureteral stenosis were observed. The risk factors for Polyomavirus active infection were: higher recipient BMI, Afro-Caribbean recipient, older donor age, higher HLA DR and overall mismatch, lack of CMV prophylaxis, and biopsy-proven rejection (p<0.05). Induction (ATG vs. anti-IL-2 receptor antagonists) and baseline immunosuppression (Tacrolimus vs. Cyclosporine) did not affect Polyomavirus viremia or PVAN rates.

Conclusions.

Our results show that PVAN significantly reduces kidney allograft survival and identifies a need for post-transplant aggressive screening, prompt reduction of the net state of immunosuppression and possibly use of more reliable tools to assess virus-specific immune response. It also supports our hypothesis that high immunological risk characteristics are more relevant than immunosuppressive regimens.

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