PDCD1 and cancer: Currently, the U.S. Food and Drug Administration (FDA) has approved ICIs such as CTLA-4, PD-1/PD-L1, and lymphocyte-activation gene 3 (LAG-3) for clinical cancer treatment, with many other therapeutic targets under development, such as Cluster of Differentiation 47(CD47), T-cell immunoglobulin and mucin domain-3 (TIM-3), and ITIM domain (TIGIT) (1–3).