Late-onset BK polyomavirus nephropathy can occur years after kidney transplant without intensified immunosuppressionLate BK Virus Can Harm Kidney Transplants Years Later

BK polyomavirus–associated nephropathy (BKPyVAN) results from primary infection or reactivation of BK polyomavirus (BKPyV) and remains a significant complication in kidney transplant recipients, contributing to allograft dysfunction and premature allograft loss. Most cases occur within the first 2 years post-transplant, when cell-mediated immunity is most suppressed due to induction immunosuppression. Here, we describe two unusual cases of late-onset BKPyVAN occurring in the absence of intensified immunosuppression and provide a review of potential mechanisms underlying its development in kidney transplant recipients. In the first patient, BKPyVAN developed 9 years after transplantation during maintenance dual immunosuppression with tacrolimus and mycophenolic acid, without prior rejection episodes or exposure to intensified immunosuppression. In the second patient, BKPyVAN first occurred 3 years post-transplant in the setting of concomitant cytomegalovirus colitis, also during dual immunosuppression with tacrolimus and mycophenolic acid. Despite reduction of immunosuppression, BKPyVAN persisted at 1-year follow-up and was associated with a gradual decline in allograft function. These cases highlight that late-onset BKPyVAN may develop even without intensified immunosuppression and can lead to significant allograft injury. Improved strategies are needed to identify patients at risk for late-onset BKPyVAN and to optimize therapeutic management.