*Purpose: BK virus-associated nephropathy (BKVAN) is a common cause of renal dysfunction early after renal transplant. BKVAN is much rarer in non-renal solid organ transplant, where data regarding diagnosis and management is limited. We present 2 cases of renal failure secondary to biopsy-proven BKVAN in lung transplant recipients.

*Methods: We reviewed the infectious courses of BK viremia in two bilateral lung transplant recipients from our center: a 59-year-old female transplanted in July 2019 (patient A), and a 76-year-old female transplanted in September 2016 (patient B), both secondary to IPF.

*Results: Patient A had an uneventful early postoperative course with preserved renal function (baseline serum creatinine: 0.98 mg/dL) up to 5 months post-transplant while receiving tacrolimus for maintenance immunosuppression and trimethoprim-sulfamethoxazole for Pneumocystis pneumonia prophylaxis. At 5 months, an acute rise in serum creatinine (1.42 mg/dL) was observed and attributed to her medication regimen. Despite altering her medications, serum creatinine continued to rise (2.52-3.21 mg/dL). Investigation for infectious causes revealed elevated BK viral loads in plasma (260,000 copies/mL), prompting a renal biopsy which demonstrated tubules staining positive for BK virus with tubulointerstitial fibrosis – consistent with BKVAN. Leflunomide was initiated with gradual viral clearance. Her serum creatinine has since trended down (2.26 mg/dL), but remains elevated from baseline. Patient B also had an uneventful postoperative course, with stable allograft function through 3 years post-transplant. At 38 months, she was admitted for decline in lung function secondary to Nocardia infection requiring prolonged hospital stay. Gradual rise in serum creatinine was observed over the course of the next two months (baseline: 1.6 mg/dL), attributed to medications. Despite altering her regimen, serum creatinine continued to rise (2.34-3.10 mg/dL), prompting investigation that revealed BK viremia (39,000 copies/mL). Renal biopsy findings were consistent with BKVAN, and leflunomide was initiated with gradual viral clearance; serum creatinine remains elevated (2.7 mg/dL) from baseline.

*Conclusions: BKVAN can lead to irreversible kidney injury in lung transplant recipients despite reduction in immunosuppression, leflunomide therapy, and reduction in viral load.

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