*Purpose: The mainstay of treatment for BK infection is immunosuppression (IS) reduction, however limited literature provides guidance for treatment of patients with a belatacept-based IS regimen. Our center primarily utilizes a belatacept-based regimen coupled with an 11-month tacrolimus overlap period, mycophenolate (MMF), and prednisone. We assessed BK viremia clearance using different IS reduction strategies in patients on a belatacept-based regimen.

*Methods: This single-center, retrospective review included kidney transplant recipients on a belatacept-based regimen who developed BK viremia (BK DNA PCR of > 4 log 10 copies/mL) within one-year post-transplant between March 1, 2015 and January 1, 2019. Patients were placed into two cohorts based upon whether MMF or tacrolimus was reduced first after BK viremia diagnosis. BK viremia clearance was defined as BK DNA PCR of < 3 log 10 copies/mL at one year follow up. Secondary outcomes included biopsy confirmed BK virus associated nephropathy (BKVN) or rejection, graft loss with positive BK viremia, and time until viremia clearance. The primary outcome was compared using the Chi-square test and secondary outcomes with either Fischer’s Exact test or Student’s t-test.

*Results: 88 patients were included for analysis: 70 patients with tacrolimus reduction first and 18 patients with MMF. Both groups were similar in demographics. Overall patient age was 51.3 ± 13.1 years at time of transplant and 71.4% (n=50) were African American. Patients developed BK viremia (4.58 ± 0.51 log 10 copies/mL) 121 days (IQR 71.5, 175) post-transplant (p=0.131, p=0.102). There was no statistically significant difference in BK viremia clearance between groups, although the time to viremia clearance was shorter in the MMF group [6 months Vs. 4.5 months (p=0.172)]. The percentage of patients with biopsy proven rejection trended higher in the tacrolimus reduction group [37% Vs. 17%, p=0.159].

*Conclusions: Choice of initial IS reduction did not affect BK viremia clearance however more acute rejection with early tacrolimus reduction suggests this may be a suboptimal approach. Additional studies with larger sample sizes may help further elucidate the optimal IS reduction strategy in this population.

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