PDCD1 and neoplasm: Since CTLA-4 inhibits T cell activity in secondary lymphatic organs and PD-1/PD-L1 regulates T cell function in malignant tissues and the tumor microenvironment, PD-1/PD-L1 inhibitors due to the specificity of the PD-1/PD-L1 signaling pathway lead to minimal damage to healthy tissue.