The current approved ICIs consist of blocking antibodies against programmed cell death protein 1 (PD-1), programmed cell death ligand 1 (PD-L1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), and lymphocyte activation gene 3 (LAG3), and these checkpoint inhibitors are approved for over twenty different cancer types (3). Here, PDCD1 is linked to cancer.