Antigen presentation by tumor-associated macrophages (TAM) mediates progenitor to terminal exhaustion transition in glioblastoma and other solid tumors

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. CD3+CD4+ or CD3+CD8+ were sorted from D13 (n = 16) and D19 (n = 4) intracranial tumors. Four mice were pooled for each D13 replicate to achieve desired number of cells. 10X 5' Chromium chemistry was utilized. 10,000 total cells from each timepoint were targeted with an average read depth of 36,000 reads per cell for the gene expression library. Reads were sequenced on a NovaSeq S1 flow cell. For the TCR library, 9,000 reads per cell were targeted and sequenced on a NovaSeq SP.