Mechanism of immune checkpoints in HCC in absence (A) and presence (B) of ICI. The figure is reused from the article below Mohr R, Jost-Brinkmann F, Özdirik B, et al. Lessons From Immune Checkpoint Inhibitor Trials in Hepatocellular Carcinoma. Front Immunol 2021;12:652172. APC, antigen presenting cell; CTLA-4, cytotoxic T-lymphocyte associated protein 4; HCC, hepatocellular carcinoma; ICI, immune checkpoint inhibitor; MHC, major histocompatibility complex; PD-1, programmed cell death 1 protein; PD-L1, programmed death-ligand 1; TCR, T cell receptor.