Evidence of allogeneic directed anti-tumor effects by CAR T cells in xenogeneic modeling 3389

Abstract Description Chimeric antigen receptor (CAR) T cells are FDA-approved for certain hematologic cancers. While CAR therapies use autologous T cells, preclinical modeling involves assessment of established tumor cell lines allogeneic to donor T cells. Classically, allogeneic T cell responses are strongly associated with naïve not memory T cell responses. However, the generation of CAR T cells converts T cells to a memory phenotype. Surprisingly, while potent anti-tumor effects were associated with CAR responses to antigen-positive tumors, we observed significant anti-tumor effects towards antigen-negative tumor lines. This non-antigen-specific response was observed both in vitro and in vivo and was associated with upregulation of both PD1 and CD25, markers indicative of T cell receptor (TCR) engagement. The addition of MHC I blocking antibody in vitro reduced these effects, suggesting non-antigen-specific effector function was due to TCR alloreactivity. Analysis using RNA-seq and TCR-seq revealed distinct gene expression profiles and clustering patterns between antigen-triggered and non-antigen-triggered CAR T cells. Our findings demonstrate that CAR T cells display both CAR-mediated and allogeneic T cell activity, which may contribute to graft-versus-host disease (GVHD) if third party CAR T cells are used. Additionally, these allogeneic responses could augment the anti-tumor effects of CAR therapy, highlighting the importance of using HLA-matched models to mirror autologous CAR therapies. Funding Sources CIRM TRAN1-13996 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)