*Purpose: A primary reason for conversion from tacrolimus (TAC) to belatacept (BELA) is to avoid nephrotoxicity. Previous published experiences with BELA-conversion regimens have shown increased rejection risk suggesting a potential need for prolonged TAC taper. The purpose of this study is to compare outcomes of kidney transplant recipients converted from TAC to BELA-based regimens using Reduced-Dose (RDCP) and Labeled-Dose conversion protocols (LDCP) with immediate or early withdrawal of TAC under corticosteroid withdrawal.

*Methods: This retrospective analysis included kidney transplant recipients at a single center converted to BELA-based regimens using a RDCP with immediate TAC withdrawal or 2-4 week tac taper or using a LDCP with immediate TAC withdrawal between Sep 2013-Sep 2019. Both protocols were used with no planned maintenance corticosteroids. The LDCP and RDCP included total initial BELA doses of 65 mg/kg and 50 mg/kg respectively. The primary outcome is mean estimated glomerular filtration rates (eGFRs) at 1-year post-conversion. Secondary outcomes include mean eGFRs at 6 months post-conversion, change in eGFR at 6 and 12 months post-conversion, graft and patient survival, biopsy-proven acute rejection (BPAR), cytomegalovirus (CMV) and BK virus, and leukopenia (defined as white blood cells <2000 cells/mm³) and/or neutropenia (defined as <1500 cell/mm³) within 6 months of conversion.

*Results: 49 patients were converted to BELA-based regimens. There were no differences in induction (~25% of patients per group were considered high immunologic risk). Patients were converted using LDCP (N=22) or RDCP (N=27). Results are in table 1.

*Conclusions: Renal function is comparable at 6 and 12 months post-conversion with both LDCP and RDCP. Use of LDCP was associated with greater improvement in eGFR at 6 and 12 months compared to those converted with RDCP, which may be due to more DGF in the LDCP group; however, there was more CMV viremia in the LDCP group. Both protocols were associated with increased eGFRs compared to pre-conversion eGFRs. BELA conversion from TAC can be successful with LDCP or RDCP using immediate TAC withdrawal or a 2-4 weeks taper with low BPAR rates (10%) that do not have a negative impact on kidney function nor graft survival (LDCP 90.9% vs. RDCP 92.6%) and excellent patient survival (LDCP 90.9% vs. RDCP 92.6%). Due to a lower CMV rate and trend toward less rejection, the RDCP may be more favorable overall.

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