Human single cell RNA-sequencing reveals a targetable CD8+ exhausted T cell population that maintains mouse low-grade glioma growth

In solid cancers, T cells typically function as cytotoxic effectors to limit tumor growth, prompting therapies that capitalize upon this antineoplastic property (immune checkpoint inhibition; ICI). Unfortunately, ICI treatments have been largely ineffective for high-grade brain tumors (gliomas; HGGs). Leveraging several single-cell RNA sequencing datasets, we report greater CD8+ exhausted T cells in human pediatric low-grade gliomas (LGGs) relative to adult and pediatric HGGs. Using several preclinical mouse LGG models (Nf1-OPG mice), we show that these PD1+/TIGIT+ CD8+ exhausted T cells are restricted to the tumor tissue, where they express paracrine factors necessary for OPG growth. Importantly, ICI treatments with α-PD1 and α-TIGIT antibodies attenuate Nf1-OPG tumor proliferation through suppression of two cytokine (Ccl4 and TGFβ)-mediated mechanisms, rather than by T cell-mediated cytotoxicity, as well as suppress monocyte-controlled T cell chemotaxis. Collectively, these findings establish a previously unrecognized function for CD8+ exhausted T cells as specialized regulators of LGG maintenance. With the emergence of immune checkpoint inhibitor therapies for cancer, the authors use single-cell sequencing to assess exhausted T cell content in human glioma samples and leverage these findings in mouse models to define the mechanisms by which exhausted T cells regulate low-grade glioma growth.