Immunotherapy against programmed death-1/programmed death ligand 1 in hepatocellular carcinoma: Importance of molecular variations, cellular heterogeneity, and cancer stem cells

Figure 1 Regulatory mechanism of programmed death-1/programmed death ligand 1 signaling in cancer. The interaction between programmed death-1 and programmed death ligand 1 (PD-L1) leads to the inhibition of T cell functional activation. PD-L1 expression in cancer cells is regulated by aberrant oncogenic pathways. PD-1: Programmed death-1; PD-L1: Programmed death ligand 1; TCR: T cell receptor; ITSM: Immunoreceptor tyrosine-based switch motif; ITIM: Immunoreceptor tyrosine-based inhibitory motif; IRF: Interferon regulatory factor.