CD274 and neoplasm: M2 TAMs contribute to immunosuppression and tumor progression mainly through the secretion of cytokines (e.g., TGF-β, PGE2), expression of immune checkpoint ligands (e.g., PD-L1, VISTA), and the release of exosomal microRNAs (e.g., miR-21, miR-155-5p), all of which inhibit the activity of CD8+; T cells and limit the anti-tumor immune response (115, 116).