PDCD1 and hepatocellular carcinoma: In HCC, circulating PMN-MDSC had a substantial PD-L1 expression, and the expression was even higher in the PMN-MDSCTME [118] suggesting that PMN-MDSC are powerful players in T-cell exhaustion and important targets for anti-programmed cell death 1 (PD1) and/or anti-PD-L1 antibodies.