CAF-derived LRRC15 orchestrates macrophage polarization and limits PD-1 immunotherapy efficacy in glioblastoma

BACKGROUND: The effectiveness of PD-1/PD-L1 immune checkpoint blockade therapy in glioblastoma (GBM) is limited due to the tumor immunosuppressive microenvironment (TIME). Therefore, strategies of reprogramming TIME to a pro-inflammatory state offer a promising therapeutic approach. METHODS: We applied bioinformatics analysis of single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (stRNA-seq) to identify a significant accumulation of cancer-associated fibroblasts (CAFs) subclusters with elevated LRRC15 expression in the nonresponders to anti-PD-1 therapy. The molecular mechanism of LRRC15 was functionally validated in vitro and in vivo. RESULTS: These CAFs subclusters drive the infiltration of macrophages (Mφ) into the tumor microenvironment and promote their polarization toward the M2 phenotype. Deletion of Lrrc15 in CAFs significantly restrained tumor growth and prolonged survival in mouse models. Mechanistically, LRRC15 in CAFs promotes IL8 expression by activating the downstream FAK/SRC/NF-κB pathways, leading to Mφ migration and M2-like polarization. In turn, M2-like Mφs secrete TGF-β, which induces LRRC15 expression in CAFs via SMAD2-dependent transcriptional activation. Targeting CAFs subcluster with elevated LRRC15 expression in combination with anti-PD-1 treatment enhanced antitumor efficacy. CONCLUSIONS: Our findings suggest that targeting LRRC15 may provide a novel strategy to augment anti-PD-1 therapy and overcome immunotherapy resistance in GBM.