IDH1 Mutant Glioma Favors Group 3 Innate Lymphoid Cells and Is Resistant to Immune Checkpoint Expression

BACKGROUND: Isocitrate dehydrogenase 1 (IDH1) mutations confer distinct biological properties to gliomas, including the reshaping of the tumor immune microenvironment. While T cell dysfunction in glioblastoma has been extensively characterized, the role of innate lymphoid cells (ILCs)-critical regulators of tissue homeostasis and early immune responses- remains poorly understood. METHODS: We investigated how IDH1 mutations and their oncometabolite D-2-hydroxyglutarate (D-2HG) influence ILC subset distribution, immune checkpoint expression, and cytokine production in glioma patients, glioma-conditioned medium (GCM) models, and in vivo mouse experiments. Tumor and peripheral blood samples from 32 glioma patients (WHO 2021 classification, grades II-IV) were analyzed by flow cytometry to assess ILC subsets and immunecheckpoint molecules (PD-1, CTLA-4, KLRG1). Tonsil-derived human ILCs were co-cultured with IDH1-mutant or wild-type glioma cells and their GCM. In vitro, ILCs were exposed to graded concentrations of D-2HG, whereas in vivo studies involved intraperitoneal administration of D-2HG or L-2HG in mice to evaluate ILC distribution across lymphoid and mucosal tissues. RESULTS: IDH1-mutant gliomas exhibited increased ILC3 and decreased ILC1 frequencies in both tumor tissue and peripheral blood. ILC3s in IDH1-mutant tumors expressed higher PD-1, whereas ILC2s showed reduced PD-1 levels. In co-culture assays, IDH1-mutant glioma cells and their GCM suppressed PD-1 and CTLA-4 expression on ILCs while promoting proliferation. Exposure to D-2HG recapitulated these effects in a dose-dependent manner, reducing checkpoint expression and enhancing IFN-γ and TNF-α secretion. In vivo, D-2HG and L-2HG differentially altered ILC subset distribution across mucosal and lymphoid compartments. CONCLUSIONS: IDH1 mutations and their associated oncometabolite D-2HG remodel the innate lymphoid cell landscape in gliomas, driving an ILC3-biased phenotype with reduced checkpoint receptor expression. These findings identify ILCs as key modulators of glioma immunity and suggest that targeting innate immune pathways could complement existing immunotherapeutic approaches.