PDCD1 and hepatocellular carcinoma: In terms of mechanism, immune checkpoint inhibitors (ICIs), such as atezolizumab, durvalumab, nivolumab, and pembrolizumab, inhibit programmed cell death protein-1 (PD-1) or programmed death-ligand 1 (PD-L1) in restoring the function of effector CD8+ T cells (Teffs) in patients with HCC [4].