Tmic-72. all-trans retinoic acid induces durable tumor immunity in idh mutant gliomas and circumvents repression of crbp1-retinoic acid axis

Abstract Diffuse gliomas are fatal, immunologically cold tumors characterized by mutations in isocitrate dehydrogenase 1 or 2 (IDH1/2) genes. IDH mutations have been shown to result in global genomic hypermethylation and drastically altered transcriptomic landscape. We and others have shown that IDH mutation is direct responsible for the immunological cold landscape observed in IDH mutated glioma. Using a combination of animal models and patient-derived glioma stem cells (GSCs), we identify retinoic acid signaling as a primary regulator of innate and adaptive immune activation in IDHm gliomas. Using the Sleeping Beauty (SB) orthotopic murine model of IDH glioma, which faithfully recapitulates the TME seen in patients, we show that intracellular accumulation of oncometabolite 2-HG leads to hypermethylation and transcriptional repression of Retinol Binding Protein-1 (RBP1), which encode CRBP1, a key chaperone protein required for intracellular all-trans-retinoic-acid biosynthesis in glial cells. Restoration retinoic acid signaling through the addition of all-trans retinoic acid (ATRA) resulted in spontaneous tumor regression and prolonged survival. ATRA administration is further correlated with increased CD8, NK, M1 macrophages and decreased Treg and MDSC populations within the TME. Single-cell sequencing of the TME shows increased type I interferon signaling, myeloid cell polarization, T cell activation, and TCR diversity. Using knockdown and overexpression techniques in patient-derived GSCs, we show that CRBP1 activity is critical for NK mediated immune surveillance and cytotoxicity through regulation of NKG2D ligand expression and immune cell migration through differential regulation of CXCL12 and CCL2. In summary, epigenetic silencing of RBP1 by 2-HG induced hypermethylation leads to a global immune dysregulation resulting in an immunologically cold landscape. Restoration of retinoic acid signaling is a promising immunotherapeutic approach for the treatment of IDHm gliomas.