CTLA4 and cancer: Immune checkpoint blockade therapies, such as with anti-CTLA-4 or anti-PD1 monoclonal antibodies (mAbs), have been shown to be effective against various types of cancer by enhancing endogenous anti-cancer immunity, and ultimately, cytotoxic T lymphocytes (CTLs) are thought to function as effector cells to kill cancer cells (Pardoll, 2012, Gong et al., 2018).