Currently, several ICIs including blockers of PD-1 (nivolumab, pembrolizumab, and cemiplimab), PD-L1 (atezolizumab, avelumab, and durvalumab), and CTLA-4 (ipilimumab) have received approval by the US Food and Drugs Administration (FDA) for treating cancers, having been shown to improve overall survival (OS) of cancer patients [54,55]. Here, PDCD1 is linked to cancer.