CD274 and neoplasm: In the immune microenvironment of EC, tumor elicited immunosuppression is mainly generated from the conjugation of over-expressed PD-L1 and PD-L2 on EC cells to PD-1 receptors on tumor infiltrating CD4+/ CD8+ T cells and CTLA-4 expressed on Treg to B7-1/B7-2 (the ligand of stimulatory receptor CD28) expressed on APC.