[BK virus infections in stem cell transplant recipients]

BK virus (BKV) belongs to the Polyomaviridae family. It is widespread in adults. Primary infection typically occurs during childhood, without specific symptoms, followed by a state of non-replicative infection in various tissues, with the urogenital tract as the principal site. Immunosuppression promotes reactivation and replication of BKV. After kidney allograft, active infections can cause interstitial nephritis up to graft loss. In hematopoietic stem cell transplant (HSCT) recipients,BKVinfections are associated with hemorrhagic cystitis (HC). The pathogenesis of HC after HSCT represents an interplay between urotoxicity of the conditioning regimen, BKV infection and alloimmune reactions from donor lymphocytes targeting the recipient uroepithelial cells. The diagnosis is based on the quantification of BKV DNA by PCR in urine and blood. The current standard of care for HC is symptomatic, since to date no antiviral drug with proven efficacy against BKV replication has been licensed.