<p>Glioma is a highly aggressive central nervous system malignancy characterized by profound immune evasion, the underlying mechanisms of which remain incompletely defined. This study investigated how the transcription factor RBP-J drives immune suppression through activation of NNMT in cancer-associated fibroblasts (CAFs). By integrating single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST), we identified a CAF-specific NNMT-high subpopulation enriched at the tumor margin and closely associated with M2 macrophages. Bioinformatic analyses using Seurat and Monocle3 delineated a stromal–immune regulatory network and highlighted RBP-J as a potential upstream regulator of NNMT. Mechanistic experiments demonstrated that RBP-J directly binds to the NNMT promoter and activates its transcription, leading to intracellular SAM depletion, reduced H3K27me3 levels, and epigenetic upregulation of SAA3. Elevated SAA3 promoted M2 macrophage recruitment and polarization, resulting in CD8⁺ T cell exhaustion and immune suppression. In vivo experiments using an orthotopic glioma model confirmed that NNMT-high CAFs accelerated tumor growth, increased M2 macrophage infiltration, and diminished CD8⁺ T cell activity. Importantly, combined treatment with an NNMT inhibitor and αPD-1 partially reversed the immunosuppressive microenvironment and significantly enhanced therapeutic efficacy. Collectively, this study identifies the RBP-J/NNMT/SAA3 axis as a critical stromal-driven mechanism of immune evasion in glioma and provides a rationale for targeting metabolic–epigenetic pathways to improve immunotherapy outcomes.</p><p></p>