As the name suggests, ICB utilizes specific mAbs developed against immunosuppressive proteins, such as cytotoxic T-lymphocyte associated protein 4 (CTLA4) or programmed cell death-1 (PD-1) expressed on T cells or programmed cell death ligand-1 (PD-L1) expressed on cancer cells which help them escape the immune surveillance by cytotoxic T cells (152). Here, PDCD1 is linked to cancer.