PP2Ac Deficiency Enhances Tumor Immunogenicity by Activating STING–Type I Interferon Signaling in Glioblastoma

Glioblastoma (GBM) is an immunologically “cold” tumor that does not respond to current immunotherapy. Here, we demonstrate a fundamental role for the a-isoform of the catalytic subunit of protein phosphatase-2A (PP2Ac) in regulating glioma immunogenicity. Genetic ablation of PP2Ac in glioma cells enhanced double-stranded DNA (dsDNA) production and cGAS–type I IFN signaling, MHC-I expression, and tumor mutational burden. In coculture experiments, PP2Ac deficiency in glioma cells promoted dendritic cell (DC) cross-presentation and clonal expansion of CD8^þ T cells. In vivo, PP2Ac depletion sensitized tumors to immune-checkpoint blockade and radiotherapy treatment. Single-cell analysis demonstrated that PP2Ac deficiency increased CD8^þ T-cell, natural killer cell, and DC accumulation and reduced immunosuppressive tumor-associated macrophages. Furthermore, loss of PP2Ac increased IFN signaling in myeloid and tumor cells and reduced expression of a tumor gene signature associated with worse patient survival in The Cancer Genome Atlas. Collectively, this study establishes a novel role for PP2Ac in inhibiting dsDNA–cGAS–STING signaling to suppress antitumor immunity in glioma.