Immune checkpoint inhibitors (ICIs), such as programmed cell death 1 (PD-1) [3,4], programmed death-ligand 1 (PD-L1) [5,6], and cytotoxic T-lymphocyte antigen 4 (CTLA-4) [2,7,8], have been developed as effective agents in cancer immunotherapy. Here, CTLA4 is linked to cancer.