CD274 and colon carcinoma: For instance, Gordon et al. found that the PD-1 expressed on the surface of TAMs could bind with the PD-L1, which exists on the membrane of colon carcinoma cells, subsequently attenuating the phagocytosis ability of TAMs [168], suggesting that the PD-1/PD-L1 axis not only suppresses the anti-tumor function of cytotoxic T cells, but also inhibits the phagocytosis of macrophages.