Appleton, Elizabeth

Abstract Introduction We have shown that combining CAR T cells with oncolytic viruses (OVs) generates a subpopulation of highly cytotoxic CAR T cells that can mediate long-term solid tumor therapy. Methods To profile these CAR T cells, we used C57BL/6 mice bearing B16F10 tumors expressing EGFRviii, treated with anti-EGFRviii CAR T cells and the OV vesicular stomatitis virus (VSV). TCR signaling in CAR T cells was investigated using the novel Tocky transgenic mouse model, which reports T cell activation over time using an unstable fluorescent protein reporter of Nr4a3. We further investigated CAR T phenotypes using CyTOF and scRNA-Seq. Results Using an MHC I tetramer for the dominant VSV epitope VSV N52-59, we found that 20-50% of transfused CAR T adopted TCR specificity against VSV N (referred to as TCR-primed), indicating significant in vivo expansion. Ex vivo, these TCR-primed CAR T produced increased levels of granzyme B and IFNγ over tetramer-negative CAR T against either TCR or CAR targets. However, TCR-primed CAR T cells were notably less activated via Nr4a3 as compared to non-TCR-primed CAR T. CyTOF and scRNA-Seq analyses demonstrated a hypereffector phenotype among TCR-primed CAR, with increased expression of T-bet, CD44, granzyme B, IFNγ, and perforin. TCR sequencing revealed hyperexpansion of VSV N-specific CAR T cells and little overlap in clonotypes between CAR T co-treated with PBS versus VSV. These TCR-primed CAR T cells exhibited a CD4-helped phenotype with increased expression of chemotactic and migratory transcripts. When CAR T and OV were administered with antibody-mediated CD4 depletion, the TCR-primed CAR population was significantly diminished, emphasizing the importance of the immune triad for CAR T expansion. Conclusion Overall, CAR T cells that undergo endogenous anti-viral TCR priming and signaling adopt a unique phenotype that promotes their expansion and cytotoxic function. Interactions with CD4 T cells appear to be integral for the generation of this subpopulation of CD8 CAR T cells. Funding Source NIH Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

Chimeric antigen receptor (CAR) T cell therapy faces many challenges against solid tumors including T cell exhaustion and poor CAR durability. Here, we show that engaging the CAR T cell endogenous T cell receptor (TCR) using an oncolytic virus enhances CAR T cell functionality, durability, and therapy. Upon combination therapy of solid tumors with CAR T cells and vesicular stomatitis virus (VSV), a subpopulation of antiviral, TCR-primed CAR T cells was generated with enhanced effector functions, altered activation states, and differential gene and protein expression when compared to non–TCR-primed CAR T cells. Single-cell RNA sequencing showed clonal expansion of anti-VSV CAR T cells and enhancement of effector-associated genes with VSV-mediated CAR T cell expansion. CD4 T cells played a pivotal role in the development of these TCR-primed CAR T cells. These results provide a strong rationale both for a novel use of systemic oncolytic virotherapy and for directly exploiting the CAR T cell TCR to fine tune the CAR T cell phenotype and function.