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

Abstract

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.