<i>EGFR</i> Mutant Lung Adenocarcinoma Cells-Derived Exosomal miR-651-5p <i>Induces CD8⁺ T Cell Apoptosis via Downregulating BCL2 Expression</i>

Background: The efficacy of programmed cell death 1 (PD-1) or ligand 1 (PD-L1) inhibitors in epidermal growth factor receptor (EGFR) mutant non-small cell lung cancer (NSCLC) patients is not satisfactory. Studies have indicated that the ratio of CD8+ tumor infiltration lymphocytes (TILs) was associated with immunotherapy efficacy, however, it was significantly lower in EGFR mutant than wild-type patients. The underlying mechanisms need to be studied. Methods: Database analysis, clinical specimens, small RNA sequencing, and single-cell sequencing were used to analyze miRNA expression and immune cell infiltration. Cell co-culture and flow cytometry were conducted to detect immune cell apoptosis. The mouse model was performed to analyze the influence of miR-651-5p antagomir on the tumor microenvironment. Results: The miR-651-5p was found to be highly expressed in EGFR mutant lung adenocarcinoma cell-derived exosomes which could promote CD8+ T cell apoptosis, while miR-651-5p inhibitor decreased the ratio of PC9 secreted exosomes induced apoptosis. Mechanistically, the EGFR signaling pathway promoted the expression of miR-651-5p by activating the transcription factor FOS in EGFR-mutant lung adenocarcinoma cell lines. BCL2 was identified as the target of miR-651-5p, and miR-651-5p could promote T cell apoptosis by inhibiting BCL2 expression. Besides, miR-651-5p antagomir increased T cells infiltration and enhanced the efficacy of PD-1 inhibitor treating EGFR mutant lung adenocarcinoma in a humanized mouse model. Conclusions: EGFR mutant lung adenocarcinoma promotes T cell apoptosis through exosomal miR-651-5p. miR-651-5p antagonists increase immune cell infiltration and enhance the anti-tumor effect of PD-1 inhibitor, suggesting a potential mechanism to improve the efficacy of immunotherapy in this group.