PDCD1 and cancer: ICIs are monoclonal humanized antibodies that bind to and inhibit the receptors mediating immune tolerance found on the surface of T cells (Immune Checkpoints), such as Cytotoxic T-Lymphocyte Associated Protein 4 (CTLA-4) and Programmed cell death protein 1 (PD-1) or on cancer cells, such as Programmed cell death protein ligand 1 (PD-L1) (Table 4).