Abstract 5580: Incorporation of pro-memory transcription factors in fourth generation CARs enhances CAR T cell immunotherapy against solid tumors in an immunocompetent murine model

Abstract

Abstract A major obstacle in current T cell-based immunotherapy against solid tumors is the widely observed T cell exhaustion and loss of functionality within the tumor microenvironment (TME). We, and others, have demonstrated that chronic antigenic signaling is the predominant factor that drives TCR tumor-reactive, and CAR T cell exhaustion in the TME. To combat this exhaustion, we have engineered CD19-targeted third generation CAR constructs to express pro-memory transcription factors associated with longevity, polyfunctionality and/or enhanced responsiveness to immune checkpoint blockade in cancer immunotherapy. Using an immunocompetent murine model of syngeneic solid tumors expressing truncated human-CD19 (hCD19t), we demonstrate that ectopic expression of pro-memory transcription factors in the 4th generation transcription factor-CARs (TF-CARs) augments CAR T cell therapeutic efficacy against solid tumors. Amongst CAR T cells recovered from established solid tumors, the 4th generation TF-CAR T cells retained a memory-precursor effector (MPEC) T cell like phenotype, while the 3rd generation CAR T cells largely displayed a terminally exhausted phenotype (TEx). Importantly, the inclusion of select pro-memory transcription factors did not compromise CAR T cell proliferation or expression of the effector cytokines IFN-γ and TNFα following restimulation. In addition to superior control of primary tumors, the TF-CAR T cells instilled greater long-term protection from tumor relapse in mice, which cleared primary tumors (6/7) compared to 3rd generation CAR T cells (3/7). Collectively, these data present incorporation of pro-memory transcription factors as an attractive engineering strategy to intrinsically combat CAR T cell exhaustion in the TME and promote long-term CAR T cell memory and protection from tumor relapse. Citation Format: Steven J. Reed, Samantha J. Tower, Ryma Toumi, Vandana Kalia, Surojit Sarkar. Incorporation of pro-memory transcription factors in fourth generation CARs enhances CAR T cell immunotherapy against solid tumors in an immunocompetent murine model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5580.