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

Immune cell infiltration is a common feature of solid cancers, where T cells typically function as cytotoxic effectors to limit tumor growth, prompting therapies that activate 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 showed that these PD1+/TIGIT+ CD8+ terminally exhausted T cells are restricted to the tumor tissue, where they express paracrine factors necessary for OPG growth. Importantly, ICI treatments with anti-PD1 and anti-TIGIT antibodies attenuate Nf1-OPG tumor proliferation through suppression of cytokine-mediated immune axis support, rather than by T cell-mediated cytotoxicity. Collectively, these findings establish a previously unrecognized function for CD8+ exhausted T cells as specialized regulators of LGG maintenance. All experiments were performed under active Animal Studies Committee protocols at Washington University School of Medicine (Washington University in St Louis Institutional Animal Care and Use Committee). Mice harboring a neomycin cassette insertion in exon 31 (Nf1+/-) with GFAP-Cre-mediated Nf1 loss in neuroglial progenitors (Nf1flox/neo; GFAP-Cre, Nf1-OPG mice) (Bajenaru et al., 2003). Nf1+/−, WT or Nf1flox/flox mice were employed as controls. De-identified human PA samples (4 female sporadic PAs and 1 female NF1-PA; clinical information in Supplemental Table 3) were obtained under an approved Human Studies Protocol as dissociated frozen tumor single cells from the St. Louis Children’s Hospital Pediatric Tumor Bank.