CMTM6 drives glioblastoma progression by promoting M2 polarization and suppressing antigen presentation in microglia/macrophages.

backgroundImmune checkpoint blockade therapies, particularly targeting PD-1/PD-L1 axis, have shown limited efficacy in glioblastoma (GBM), primarily due to the profoundly immunosuppressive tumor microenvironment dominated by glioma-associated microglia and macrophages (GAMs). While CMTM6 is known to stabilize PD-L1 in tumor cells by preventing its ubiquitin-mediated degradation, its role in microglia remains undefined.

methodsWe employed a multi-omics approach to evaluate CMTM6 expression and function. By analyzing the bulk RNA-seq data sets from TCGA and CGGA, as well as single-cell data sets (TISCH2 and UCSC), the expression of CMTM6 across different glioma grades and immune cell populations was examined. Immunohistochemistry and immunofluorescence were used to validate CMTM6 expression and co-localization with microglial/macrophage markers in GBM tissues. In vitro, CMTM6 knockdown was performed in HMC3 microglial cells to assess changes in cytokine and immune checkpoint expression. In vivo, a tamoxifen-induced, microglia/macrophage-specific Cmtm6 conditional knockout mouse model was used to investigate tumor growth and survival outcomes.

resultsCMTM6 was significantly upregulated in high-grade gliomas and enriched in M2-like microglia/macrophages. Immunostaining confirmed elevated CMTM6 and CD68 expression in GBM samples, with CMTM6 co-localizing with microglial markers (CD68, IBA1, and TMEM119). By knocking down CMTM6 in HMC3 cells, the levels of CD274 (PD-L1) and TGFβ isoforms decreased, while the expression of pro-inflammatory cytokines IL6 and CCL3 increased, suggesting a shift toward an M1-like phenotype. In vivo, microglia/macrophage-specific deletion of Cmtm6 suppressed tumor growth, delayed body weight loss, and extended survival duration.

conclusionsThis study identifies CMTM6 as a critical regulator of the immunosuppressive phenotype of microglia/macrophages in GBM. Targeting CMTM6 in microglia/macrophages may represent a novel strategy to reprogram the tumor immune microenvironment and improve the efficacy of immunotherapy in GBM.