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

Figure 2 The complexity of hepatocellular carcinoma and its microenvironment. A: Hepatocellular carcinoma and its tumor microenvironment are composed of various cell populations, including differentiated cancer cells, cancer stem cells, cancer associated fibroblasts, immune and endothelial cells; B: Programmed death-1 and programmed death ligand 1 interaction and inhibition by neutralizing antibodies in tumor growth. PD-1: Programmed death-1; PD-L1: Programmed death ligand 1; CSC: Cancer stem cells; CAF: Cancer associated fibroblast; ECM: Extracellular matrix; NK: Natural killer.