Introduction: BK polyomavirus virus (BKV) infection is an important cause of graft kidney loss in renal transplant patients. In previous reports, in incidence of BK viremia (BKV) were around 30% of renal transplant recipients. Current guidelines from the American Society of Transplantation Infectious Diseases Community of Practice suggested reducing immunosuppressants as primary intervention for biopsy proved BKV associated nephropathy. Common treatment for such groups including switching from tacrolimus to cyclosporine-A, from mycophenolate to mTOR inhibitors or prescribing leflunomide for the patients. However, currently study lack definite evidence on how best to switch drugs or reduce the dose of immunosuppressants.
Method: In the study, the transplant recipients from a single center, Chang Gung Memorial Hospital Linkou branch from 2015~2024 were included. The data of the patients were collected retrospectively through medical records. The patient’s basic characteristics including age, sex, Body mass index, renal function, BKV viral load were recorded. Biopsy proven rejection rate for the patients were calculated as our primary outcome.
Results: In our study, we retrospectively analyzed two different approaches on reducing immunosuppressants in patients with BKV associated nephropathy. The patients were classified into 2 groups: One with rapid reduction of mycophenolate mofetil (MMF) and calcineurin inhibitor (CNI) and another without. Lower BKV viral load was noted in the group with rapid reduction of MMF and CNI (no statistically significance was noted). The patients renal function (Glomerular Filtration Rate) and biopsy proven rejection rate showed no statistically difference between the 2 groups.  
Conclusion: Currently, no consensus was reached on how best to reduce immunosuppressants for renal transplant patients with suspected BKV nephropathy. Our study showed that rapid reduction of MMF and CNI may be potentially beneficial for such patient due to lower BKV viral noted in the group. Although no statistically significance was conducted from our study, our study still offer another approach for such patients and may invite further studies with potentially larger patient numbers.