CD274 and cancer: Within the TME, different immunosuppressor cells can be found, including myeloid-derived suppressor cells (MDSCs) [176,177], cancer-associated fibroblasts (CAFs) [178,179], tumor-associated macrophages (TAMs) [180,181] and Treg lymphocytes [182,183], producing immunosuppressive mediators such as IL-10, TGF-β, VEGF, PGE2, and PD-L1 [184].