Purpose: To characterize BK virus infection and assess the efficacy of treatment strategies in pediatric renal transplant recipients.

Methods: Retrospective chart review of renal transplant patients from Dec. 2009 to Sep. 2012. Data collected include demographics, immunosuppression, laboratory results, and BK treatment.

Results: We obtained data on 30 renal transplant patients. All received induction with basiliximab and tacrolimus, mycophenolate mofetil (MMF), and prednisone maintenance immunosuppression. Of these, 15 patients developed BK viruria (50%), 14 patients developed BK viremia (47%), and 2 patients had biopsy proven BK nephritis (7%). No significant risk factors identified, including age at transplant or MMF dose, between patients with and without any BK infection. Among those with BK viremia (n=14), 12 patients had MMF reduced or discontinued. Comparing the patients who did (n=5) and did not (n=9) receive leflunomide, there was no significant difference between age (mean 5.7±3.1 vs 10.7±5.6 years, P=0.05) or time to first positive serum BK (237±209 vs 189±224 days, P=0.7). There was a significant association between peak BK viral load and days to clear from the serum in the non-leflunomide group (P=0.02). Median days to BK virus clearance from the serum was not significantly different between the two groups [64 (6, 255.5) vs 34 (18.5, 198.5) days, P=1], yet patients treated with leflunomide had a significantly higher mean peak serum BK viral load compared to those without (5.62±1.26 vs 3.87±0.9 log copies/ml, P=0.03). Mean teriflunomide level in the leflunomide group was 18.5±6.7 mcg/ml. No patients receiving leflunomide developed toxicity (leukopenia, anemia, thrombocytopenia, hepatotoxicity).

Conclusion: In our study group, the incidence of BK viruria seemed higher than in other pediatric studies. No significant risk factors for development of BK infection were identified. In patients with BK viremia, leflunomide did not shorten time to clearance compared to the non-leflunomide group. However, the treated patients had significantly higher peak BK viral loads, and 2 of the patients had BK nephritis. Leflunomide was well tolerated. It is possible that leflunomide accelerated viral clearance, however more data is needed.

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