Longitudinal scRNA-Seq of immune cells from GL261 murine brain Tumors and MHC class II deficient tumor-mircoenvironments. Longitudinal scRNA-Seq of immune cells from GL261 murine brain Tumors and MHC class II deficient tumor-mircoenvironments

Longitudinal phenotyping of T cells and myeloid cells in early (day 14) and late (day26) GL261 tumors. Single cell RNA sequencing of CD45+ immune cell from intracranial murine GL261-SIINFEKL tumors 20 days after inoculation. SIINFEKL-reactive T cells were sorted based on dextramer staining. Using time-resolved scRNA-seq of murine tumor-infiltrating immune cells from early (d14) and late stage (d26) syngeneic GL261 gliomas we observed constant MHCII expression by murine microglia over time and overall high but decreasing MHCII expression in late stage bbm indicating a dynamic process of MHCII expression. We show that loss of major histocompatibility complex (MHC) class II (MHCII)-restricted antigen presentation on bbm drives dysfunctional intratumoral tumor-reactive CD8+ T cell states through increased expression of Tox, a critical regulator of T cell exhaustion. By calculating the normalized abundance of T cell states along the pseudotime trajectory of SIINFEKL-reactive CD8+ T cells retrieved from myeloidMHCII-proficient and -deficient microenvironments, we found an enrichment of a distinct T cell state in myeloidMHCIIKO CD8+ T cells that was defined by peak expression of exhaustion markers. Mechanistically, MHCII-dependent activation of CD4+ T cells restricts myeloid-derived osteopontin that triggers a chronic activation of nuclear factor of activated T cells (Nfat)2 in tumor-reactive CD8+ T cells. In summary, we provide evidence that MHCII-restricted antigen presentation on bbm is a key mechanism to directly maintain functional cytotoxic T cell states in brain tumors.