M2-TAMs promote immunoresistance in lung adenocarcinoma by enhancing METTL3-mediated m6A methylation

BACKGROUND: Immunotherapy has become the first-line treatment for advanced non-small-cell lung cancer (NSCLC), but most patients still fail to benefit or have disease progression following treatment. M2 phenotype tumor-associated macrophages (M2-TAMs) are important cellular components in the immunosuppressive microenvironment of NSCLC, but how they contribute to immunoresistance remains unclear. This study was conducted to investigate the role and mechanism of M2-TAMs in NSCLC immunoresistance. METHODS: We collected postoperative tumor samples for detection of M2-TAMs and other immune cells infiltration by immunofluorescence detection and flow cytometry. We then constructed a non-contact cell co-culture system using Transwell chambers. CCK-8, colony formation, wound healing and invasion assays were performed to evaluated the effect of M2-TAMs on the proliferation, migration and invasion abilities of lung adenocarcinoma (LUAD) cells in vitro. Xenograft model were performed to analysis the effect of M2-TAMs on the tumorigenesis and metastasis of LUAD cells in vivo. RESULTS: M2-TAMs were greatly increased in the tumor tissue of patients with immunoresistant LUAD. They could significantly promote the proliferation, invasion, and migration of LUAD cells, and improve their resistance to cytotoxic T lymphocytes (CTL) cytotoxicity. Further research showed M2-TAMs could considerably enhance the expression of METTL3 and total m6A RNA level in LUAD cells and interfering with METTL3 could significantly reverse the impairment of M2-TAMs on the efficacy of CTL in killing tumor cells. CONCLUSIONS: In conclusion, M2-TAMs could promote LUAD immunoresistance by enhancing METTL3-mediated m6A methylation. Our results suggest METTL3 could be a potential therapeutic target for reversing immunoresistance and shed new light on the mechanism of M2-TAMs promoting LUAD immunoresistance.