The activation of the PD-1/PD-L1 signaling pathway inhibits the proliferation and activation of CD4+ T cells and CD8+ T cells, suppresses the expression of cytokines, alters the tumor microenvironment, weakens the body’s surveillance and clearance ability against tumor cells, and promotes tumor cells to evade immune surveillance and killing by the body (16). This evidence concerns the gene CD4 and neoplasm.