Josephson MA et al. (2006) Treatment of renal allograft polyoma BK virus infection with leflunomide. Transplantation 81: 704–710

Polyoma BK virus nephropathy, which occurs in 3–8% of renal transplant recipients, can be effectively treated with leflunomide—an immunosuppressant drug commonly used to treat rheumatoid arthritis. This is the exciting conclusion of a small, retrospective analysis of renal allograft recipients with BK nephropathy at the University of Chicago Hospitals and Texas Transplant Institute.

The 26 subjects received either leflunomide plus cidofovir (n = 7) or leflunomide alone (n = 19). After 6 months, mean BK virus load in the blood and urine was significantly less than at baseline in both groups (both P <0.001). The virus was undetectable in the blood of 11 patients (8 of whom also had no trace of the virus in their urine). During the first 9 months of treatment, mean renal function (determined by serum creatinine levels) did not significantly deteriorate in either group. After 6–40 months of follow-up, graft loss occurred in four patients, all of whom had advanced renal damage or inflammation at baseline. Because the required daily dose of leflunomide was higher than the recommended dose for treating arthritis, blood levels of leflunomide's active metabolite were closely monitored. The dose was reduced if the blood levels of the metabolite consistently exceeded target levels. No serious adverse events were reported.

The mechanisms for the dual immunosuppressant and antiviral activities of this single agent must be identified and might have important implications for the care of renal transplant recipients; currently, the only available strategy for controlling BK viral replication is reducing immunosuppression.