*Purpose: The BEST Trial (Belatacept-based Early Steroid Withdrawal) compared two belatacept (BELA)-based early corticosteroid withdrawal (ESW) regimens and alemtuzumab (ALEM) or rabbit antithymocyte globulin (rATG) induction with a tacrolimus (TAC)-based ESW regimen and rATG induction. The purpose of this study was to compare the impact of rejection on renal function in BELA-treated pts vs TAC-treated pts.

*Methods: Pts with biopsy-proven acute rejection (BPAR) were identified. Protocol treatment of BPACR Banff IA or IB was high dose CS with a taper; BPACR >IIA, was rATG for 7-14 days of CD3 suppression. TAC rescue (10-15 ng/mL goal trough) was used for AR refractory to CS or rATG. Rejection reversal was defined as return of serum creatinine to 115% of baseline or histologic reversal. Data analysis was performed using descriptive statistics.

*Results: Outcomes of pts with and without BPAR are in Table 1. 53 BPAR episodes were reported: ALEM/BELA (Grp A n=20/107, 18.7%), rATG/BELA (Grp B n=26/104, 25%) and rATG/TAC (Grp C n=7/105, 7%). There was significantly more early BPAR in Grp A vs B (p=0.006). BPACR was more frequent in Grp B vs C (p=0.009) with first BPACR >IIA in Grp B greater than Grp C (p=0.032) (Table 2). In African American pts, BPAR was significantly more frequent in Grp B vs A (p=0.002). Grps A and B had 20% and 23.1% steroid resistant BPAR respectively compared to 0% in Grp C. eGFR values were similar in BPAR pts, however renal function was better in pts without BPAR, particularly in BELA groups. For pts without BPAR, a higher % of pts with low eGFR (eGFR <45 ml/min/1.73m²⁾ at 24 mos was observed in Grp C vs B (p=0.001). For pts without BPAR, proteinuria was more common in Grp C vs B (p=0.003). BELA treated pts (Grps A and B) with BPAR who remained on BELA experienced higher eGFRs with a reduced % of pts with eGFR <45ml/min at 24 mo (Table 3). Pts with BPAR in Grp A or B who were converted to TAC-based regimens experienced lower eGFRs similar to those with BPAR in Grp C. Graft and patient survival were similar between groups. The majority of BPAR pts in Grp A and B continued on a BELA-based regimen.

*Conclusions: BPAR was associated with worse renal function irrespective of treatment regimen, but was more evident in TAC pts and in BELA pts who were converted to a TAC-based regimen. Longer-term observations are required to determine if the impact of BPAR on renal function is overcome when a BELA-based regimen is maintained.

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