CD274 and oral cavity squamous cell carcinoma: Li et al. observed that miR-21 contained in sEVs derived from hypoxic oral squamous cell carcinoma (OSCC) increases the PD-L1 expression of MDSCs, thus decreasing the antitumor ability of γδ T cells (through a miR-21/PTEN/PD-L1 regulation axis) [133].