PDCD1 and leukemia: In fact, many immunotherapeutic methods have been applied in clinical practice, such as the typical immune checkpoint inhibitor that targets programmed cell death protein 1 (PD-1) for lung cancer (Gainor et al., 2020) and breast cancer (Barroso-Sousa et al., 2020), as well as CD19-specific CART (Shen et al., 2019) immune cell therapy for leukemia (June et al., 2018).