Targeting the cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death protein (PD-1) axis, which are typical negative regulators of T cells or NK cells that induce cell exhaustion, garnered great success (and is now FDA-approved) by eliciting cytotoxic T cell activation in various cancers such as melanoma, non-small lung cancer, renal cancer, and bladder cancer [35]. Here, CTLA4 is linked to cancer.