IMMU-53. ANTIGEN PRESENTATION BY TUMOR-ASSOCIATED MACROPHAGES MEDIATES PROGENITOR TO TERMINAL EXHAUSTION TRANSITION IN GBM AND OTHER SOLID TUMORS

Abstract While terminally exhausted T cells (Tex_term) retain important anti-tumor cytotoxic function, it is the relative preservation of renewable, stem-like progenitor exhaustion (Tex_prog) that better indicates immunotherapeutic responsivity. Although restraining the progression from Tex_prog to Tex_term thus takes on clinical significance, the cellular interactions in a tumor microenvironment (TME) governing such progression remain less established. Employing glioblastoma (GBM) and other solid tumors as models of severe exhaustion, we provide a detailed characterization of the progression from Tex_prog to Tex_term within the TME, where we observe a striking and disproportionate loss of Tex_prog over time, leading to a low progenitor exhaustion to terminal exhaustion ratio (PETER). We find exhaustion concentrated within tumor-specific T cell subsets, with cognate antigenic exposure requisite for acquisition of the Tex_term phenotype. However, we implicate tumor-associated macrophages (TAM), and not tumor cells, as the source of antigenic exposure governing the Tex_prog to Tex_term transition. Using cell – cell interaction analysis, we additionally highlight candidate receptor–ligand communications that may be specifically mediating the progression to Tex_term and resultant decline in PETER within the TME.