CD274 and cancer: Examples of inhibitory mechanisms of the cancer immunity cycle are the CTLA4 pathway, which prevents antigen-presenting cells from priming and activating T cells; the PD-L1/PD-1 pathway, which prevents the killing of cancer cells; vascular endothelial factors and the endothelin B receptor, which prevent T cells from infiltrating tumors and reduce the expression of the proteins of the major histocompatibility complex by the cancer cells (Figure 1) [27].