BKV reactivation in renal transplant recipients: diagnostic and therapeutic strategy--case reports

The Polyomaviridae family includes several viruses that are ubiquitous with specific host spectra. The human polyoma viruses BK and JC were discovered in 1971. Following primary infection, transmitted by the respiratory and probably the oral route, BK remains latent in uroepithelial cells, in B lymphocytes, or in other tissues (spleen, brain). Reactivation with asymptomatic viruria may occur in both immunocompetent subjects and immunocompromised patients. In renal transplant recipients, BKV replication may cause tubulointerstitial nephropathy (BKVAN) with increasing prevalence rates--1% in 1995, 8% in 2007--leading to the loss of the transplanted organ in 30% to 80% of cases. With the availability of diagnostic programs (decoy cells in urine, amplification of viral DNA by polymerase chain reaction (PCR) on serum and urine, real time (RT)-PCR test for mRNA VP1 urine (mRNA-VP1), and renal biopsy accompanied by reduction in immunosuppression, administration of leflunomide, cidofovir (after hydration), and N-acetylcysteine, as well as immunoglobulin by intravenous injection (IVIg), the incidence of renal loss caused by BKVAN infection has been reduced by 10% to 80%. In this study, we have described 12 patients: 6 treated with tacrolimus (FK), mycophenolate mofetil (MMF), and steroids, and 6 treated with cyclosporine or with mTOR inhibitors. Two patients from the first group showed BKVAN about 3 months posttransplantation. Early diagnosis and therapeutic intervention (cidofovir + IVIg) led to reduction in the viral load, with improvement and stabilization in renal function. Considering the high positive predictive value (98%) of mRNA VP1, it should be possible to avoid renal biopsy. The level of immunosuppression--rather than the immunosuppressive drug itself (FK and MMF)--seemed to be associated with BKV reactivation.