PDCD1 and neoplasm: If tumor‐specific antigen expression is too low and immunogenicity is weak, it is not enough to activate the original T cells; if the specific antigen structure is similar to immune‐tolerant antigens or autoantigens, APCs (antigen presenting cells) cannot recognize it and cannot initiate T‐cell activation, which leads to drug resistance of PD‐1/PD‐L1 blockers, such as low‐immunogenic tumors, pancreatic cancer and prostate cancer, and poor response to PD‐1/PD‐L1 antibody treatment to a large extent.5, 6