Severe Native BK Virus Nephropathy in a Patient with Primary Myelofibrosis Following Stem-Cell Transplantation (SCT)

Introduction: BK Virus is an opportunistic infection seen commonly in the kidney transplant population leading to decreased allograft function when the infection leads to nephropathy. However, it is unusual to see native kidney BK virus nephropathy (BKVN). Case Description: A 66 year old male with Primary Myelofibrosis s/p allogenic stem cell transplant complicated by chronic graft-versus host disease (GVHD) presented to the hospital for progressive renal decline. He had normal renal function two months prior to presentation (Cr 1.0 mg/dl); at presentation, serum creatinine was 3.25 mg/dL. Workup included a serum BK virus PCR level of 8,240,000 IU/ml and a urine quantification at >100,000,000 IU/ml. Renal biopsy was deferred initially due to significant thrombocytopenia. He was empirically treated with IVIG, reduction of immunosuppressive regimen (tacrolimus, mycophenolate, ruxolitinib discontinued) and eventually starting a BK viral specific T-cell therapy. Despite these interventions, the patient had worsening serum creatinine to 7.54 mg/dl with sC5ba9 grossly positive (>2000ng/ml) concerning for transplant-associated TMA for which he was treated with Eculizumab. Cidofovir was considered but deferred due to its renal toxicity. With improvement of thrombocytopenia, he ultimately underwent kidney biopsy which revealed severe polyomavirus nephropathy with extensive interstitial lymphocytic infiltrate, tubulitis, and SV40 positive staining enlarged nuclei. With continuation of T-cell therapy, there was interval improvements in BK PCR levels to 32,900 IU/ml over the span of eight months. Despite these improvements, he had progressive renal function decline and initiated peritoneal dialysis. Discussion: There is a paucity of literature related to native kidney BKVN in immunosuppressed patients after other non-renal solid organ transplants. This case adds to the growing literature of cases and queries the therapy following diagnosis beyond just reduction of immunosuppression. This case also highlights the importance for BKVN to be on the differential diagnosis for patients with dysregulated immune systems.