CD274 and hepatocellular carcinoma: The first anti-PD-1 drug to be used for HCC was nivolumab, a fully human IgG4 monoclonal antibody that blocks PD-1 interactions with PD-L1 and PD-L2; now, several other PD-1 inhibitors are available for the treatment of HCC and are currently undergoing clinical trials, including pembrolizumab, tislelizumab, toripalimab and camrelizumab, which are all humanized IgG4 antibodies, and sintiliamab, a fully human IgG4 monoclonal antibody [73,74].