Accumulating results were reported by recent clinical trials involving cancer immunotherapy with various immune checkpoint inhibitors (ICIs)—including antibodies against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and monoclonal antibodies (mAbs) against both programmed cell death-1 and the dysfunction/activation of cytotoxic T lymphocytes [1,2,3,4,5,6,7,8]. Here, PDCD1 is linked to cancer.