Upon occurrence of PD-L1 binding to PD-1, PD-1/PD-L1 phosphorylated ITSM and ITIM in the intracellular region of T lymphocytes, activating RAS and phosphatidylinositol-3-kinase (PI3K)/protein kinase B protein kinase B (PKB) signaling pathways, inhibiting the activation of downstream T lymphocytes and immune microenvironment of the tumor, and promoting the proliferation and tumor cell escape. The gene discussed is PDCD1; the disease is neoplasm.