CD274 and oral cavity squamous cell carcinoma: EV-miR-21 from hypoxic oral squamous cell carcinoma cells inhibits the cytotoxicity and proliferation of γδ T-cells by promoting MDSC expansion and regulating PTEN/PD-L1 axis; combination of anti-PD-L1 treatment and miR-21 knockdown attenuates the protumoral effects of tumor-derived EVs in vivo [241].