NO can also up-regulate matrix metalloproteinases by reacting with ROS to produce ONOO−, and promote the degradation of tumor extracellular matrix26, so as to effectively improve the infiltration of T cells and drugs in tumor tissue (step 5); NO can also regulate the polarization of macrophage towards M1 phenotype, inhibit the expression of anti-programmed cell death ligand 1 (PDL1) in cancer cells, and suppress Treg cell level (step 6). The gene discussed is CD274; the disease is cancer.