Polyomavirus BK replication in renal transplant recipients: combined monitoring of viremia and VP1 mRNA in urine

Introduction. Human polyomavirus BK (BKV) is worldwide distributed, with a seroprevalence rate of 70–90% in the adults. Following primary infection, BK remains latent in the renourinary tract as the epidemiologically most relevant latency site, and in B cell, brain, spleen and probably other tissues. Reactivation may occur in both immunocompetent subjects and immunocompromised patients. In renal transplantation, in the context of intense immunosuppression, viral replication may determine BKV-associated nephropathy (BKVAN) with interstitial nephritis and/or ureteral stenosis in 1–10% of the patients and leading to graft failure and return to haemodialysis in 30 to 80% of the cases (5). Screening of BKV replication represents the basic strategy to predict early the onset of BKVAN and may allow for earlier intervention with reduced allograft loss (3, 4). Nowadays, replication of BKV is monitored by quantification of BKV-DNA in serum and urine (2). The aim of this study was to evaluated the role of BKV VP1 mRNA in urine as a marker of viral replication in renal transplant recipients.