PDCD1 and leukemia: In recent years, ICBs have been widely used in tumor immunotherapy; this includes PD-1 and PD-L1, which are used as immunotherapeutic agents in many tumor types, including lung cancer, bladder cancer, renal cell carcinoma, melanoma, lymphoma, and leukemia (Mayor et al., 2016; Krishnamurthy and Jimeno, 2017; Kaplon and Reichert, 2018).