Tumor cells also secrete exosomes carrying inhibitory ligand, PD-L1, to peripheral blood to exert inhibitory effects on T cells outside of TME, which include inducing apoptosis of CD8+ T cells, inhibiting proliferation of CD4+ T cells, upregulating the suppressive function of Tregs, and downregulating the expression level of NKG2D on the surface of NK cells (44). This evidence concerns the gene CD8A and neoplasm.