Tu142 - CAR-Tregs Synergize with Anti-thymocyte Globulin and Rapamycin to Delay Skin Allograft Rejection

Robert Wright – BC Children’s Hospital Research Institute; Isaac Rosado-Sanchez – BC Children’s Hospital Research Institute; Madeleine Speck – BC Children’s Hospital Research Institute; Majid Mojibian – BC Children’s Hospital Research Institute; Giorgio Raimondi – Department of Plastic and Reconstructive Surgery – Johns Hopkins University School of Medicine; Megan Levings – BC Children’s Hospital Research Institute

Abstract Text: Regulatory T cell (Treg) therapy is as an alternative to traditional post-transplant immunosuppression. Modified Tregs expressing a donor-specific chimeric antigen receptor (A2-CAR) show promise in delaying HLA-A2+ skin and heart graft rejection. However, in the absence of adjunct immunosuppression their persistence and suppressive effect is transient. To enhance A2-CAR-Treg efficacy, we investigated the impact of anti-thymocyte globulin (ATG, rabbit anti-mouse), rapamycin, and A2-CAR-Tregs as a combination therapy in a haplo-mismatched 2W-Ova-BALB/c x B6.HLA-A2 F1 skin to B6 recipient transplant mouse model. ATG recipients received two intraperitoneal injections (500ug/dose, day -1 and 3) and rapamycin (1mg/kg) was given for 10 consecutive days from day 15. The median graft survival for untreated or A2-CAR-Treg alone was 14 days. Treatment with ATG alone, ATG and A2-CAR-Tregs, or ATG and rapamycin moderately extended median graft survival to 20-26 days. However, the combination of ATG, rapamycin and A2-CAR-Tregs resulted in significant prolongation, extending median graft survival to 41 days. Mechanistically, ATG and rapamycin increased A2-CAR-Treg engraftment and proliferation, as measured by increased ki67 expression. Ongoing studies are determining effects on donor-specific antibodies as well as donor T cells specific for the 2W or Ova transgenes. In summary, these data show that A2-CAR-Tregs can be successfully used in combination with ATG and rapamycin and have important implications for the application of A2-CAR Tregs in humans.