PDCD1 and neoplasm: However, in tumor cells, PD-1/PD-L1 and CTLA-4, the most broadly studied immune checkpoints, lead to T cells with tumor-killing inactivation and promote tumor cells growth and invasion (Figure 1A) (Jiang et al., 2021; Liu et al., 2021; Song et al., 2021; Sun S et al., 2021; Yang et al., 2024).