(1153) Characterization of CD3-Guided Anti-Thymocyte Globulin Dose Minimization for Renal Sparing Induction after Heart Transplant

PurposeRabbit antithymocyte globulin (rATG) is a polyclonal antibody that acts on T-cell surface antigens to deplete CD4 lymphocytes in patients undergoing orthotopic heart transplantation (OHT) for immunologic induction or renal sparing indication to allow delayed initiation of calcineurin inhibitors. Collection of post-rATG CD3 levels can be performed for determination of appropriateness of subsequent doses. The purpose of this study was to evaluate dosing and monitoring strategies utilized for OHT recipients who received rATG for immunologic induction and renal sparing indications.MethodsThis single-center, retrospective chart review included adult patients that underwent heart or heart and kidney transplantation and received peri-operative rATG for immunologic induction (target cumulative dose 3-4.5 mg/kg) or CD3-guided renal sparing indications (target CD3<25 without fixed dosing). The primary outcome was the cumulative rATG dose per patient. Secondary outcomes included CD3 count, time to initiation and therapeutic level of tacrolimus, adverse effects, and incidence of biopsy-proven acute rejection (BPAR) within 6 months.Results40 patients who received rATG between 2017 and 2022 were included. The median cumulative dose (mg/kg) was significantly higher in patients receiving rATG for immunologic induction (3.84 vs. 2.37; p=0.01), with similar pre-dose CD3 levels and post-dose depletion between groups. Median time to initiation of tacrolimus was significantly longer in the renal sparing group. Neither group had leukopenia-driven dose reductions, and no difference was noted in infection and rejection at 6 months and cancer diagnosis overall.ConclusionWith CD3 monitoring, we were able to use lower doses of rATG in non-immunologic indications, with comparable outcomes to protocolized immunologic induction. Prospective investigation of CD3-guided dose minimization is warranted to find the lowest tolerated dose for renal sparing induction. Rabbit antithymocyte globulin (rATG) is a polyclonal antibody that acts on T-cell surface antigens to deplete CD4 lymphocytes in patients undergoing orthotopic heart transplantation (OHT) for immunologic induction or renal sparing indication to allow delayed initiation of calcineurin inhibitors. Collection of post-rATG CD3 levels can be performed for determination of appropriateness of subsequent doses. The purpose of this study was to evaluate dosing and monitoring strategies utilized for OHT recipients who received rATG for immunologic induction and renal sparing indications. This single-center, retrospective chart review included adult patients that underwent heart or heart and kidney transplantation and received peri-operative rATG for immunologic induction (target cumulative dose 3-4.5 mg/kg) or CD3-guided renal sparing indications (target CD3<25 without fixed dosing). The primary outcome was the cumulative rATG dose per patient. Secondary outcomes included CD3 count, time to initiation and therapeutic level of tacrolimus, adverse effects, and incidence of biopsy-proven acute rejection (BPAR) within 6 months. 40 patients who received rATG between 2017 and 2022 were included. The median cumulative dose (mg/kg) was significantly higher in patients receiving rATG for immunologic induction (3.84 vs. 2.37; p=0.01), with similar pre-dose CD3 levels and post-dose depletion between groups. Median time to initiation of tacrolimus was significantly longer in the renal sparing group. Neither group had leukopenia-driven dose reductions, and no difference was noted in infection and rejection at 6 months and cancer diagnosis overall. With CD3 monitoring, we were able to use lower doses of rATG in non-immunologic indications, with comparable outcomes to protocolized immunologic induction. Prospective investigation of CD3-guided dose minimization is warranted to find the lowest tolerated dose for renal sparing induction.