Immune checkpoint inhibitors (ICIs) are anti-cancer medications which reinvigorate the host immune system to attack tumor cells by targeting immune co-inhibitory receptors, such as programmed cell death 1 (PD-1) and cytotoxic T lymphocyte antigen 4 (CTLA-4), expressed on the surface of T-cells (Sadeghi Rad et al., 2021). Here, PDCD1 is linked to cancer.