CTLA4 and cancer: Currently, cancer immunotherapy manipulates the immune system from three main aspects: (1) immune checkpoint blockade (ICB) therapy, which blocks checkpoint proteins such as programmed death protein 1 (PD-1), programmed death-ligand 1(PD-L1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to allow T cells to kill cancer cells; (2) cancer vaccines and (3) adoptive-cell-transfer (ACT) therapy [6–8].