PDCD1 and hepatocellular carcinoma: To comprehensively inspect the immune microenvironment of HCC TME, we firstly compared gene expression of immune inhibitory checkpoint molecules between tumor tissues and normal (peri-tumor) tissues, including CD274, CTLA4, HAVCR2, LAG3, PDCD1, PDCD1LG2, TIGIT, and SIGLEC15.