PDCD1 and hepatocellular carcinoma: However, the tumor response rates remain relatively low due to some barriers [23, 24] such as an immunosuppressive microenvironment [25, 26] Present and previous studies [27, 28] showed the microenvironment of residual viable tumors after RFA of HCC is highly immunosuppressive, with the increased infiltration of immunosuppressive cells and the up-regulated expression of PD-1 and CTLA-4 in CD8+T cells.