Inhibition of RAB7 promotes CD8 T cell activation via the STING/IRF1/CCL5/CXCL10 signaling axis to promote PD-1-mediated anti-lung cancer efficacy.

Programmed cell death protein 1 (PD-1) antibody is facing the challenge of drug resistance in cancer therapy. RAB7 plays a key role in autophagic lysosomal fusion, but its function in tumor immune regulation, especially whether it can enhance the efficacy of PD-1 inhibitors, is not clear. RAS-associated binding protein 7 (RAB7) and stimulator of interferon gene (STING) were knocked down by siRNA in lung squamous cell carcinoma (LUSC) cells. The effects of RAB7 and STING on the malignant phenotype of cells were evaluated. The autophagy flux and cytoplasmic double-stranded DNA (dsDNA) accumulation were observed by Western blot, RFP-GFP-LC3B tandem fluorescent probe, transmission electron microscopy and immunofluorescence. The expression of STING/interferon regulatory factor 1 (IRF1) pathway was analyzed by Western blot. CD8 T cells were co-cultured with lung cancer cells to investigate RAB7 knockdown effects on CD8 T cell activation. Finally, mouse subcutaneous xenograft models were established to explore RAB7 knockdown combined with anti-PD-1 treatment. RAB7 was highly expressed in lung cancer, and its knockdown blocked autophagy flux, leading to cytoplasmic dsDNA accumulation, which in turn activated the STING/IRF1 signaling axis and up-regulated C-C motif chemokine ligand 5 (CCL5) and C-X-C motif chemokine ligand (CXCL) 10. In the co-culture system, knockdown of RAB7 promoted CD8 T cell proliferation and cytotoxicity, up-regulated Perforin expressions, and decreased the levels of PD-1 and CD39. The combined application inhibited tumor growth, which was accompanied by activation of STING/IRF1 pathway, increased tumor infiltration and CD8 T cell function. STING knockdown reversed all anti-tumor and immune activation effects mediated by RAB7 knockdown. In summary, knockdown of RAB7 activated the STING/IRF1/CCL5/CXCL10 signaling pathway by blocking autophagy flux, enhanced the activation and infiltration of CD8 T cells, and significantly enhanced PD-1 antibody efficacy against lung cancer.