IDO1 and hepatocellular carcinoma: Although the present study utilized the racemic mixture of 1-MT (1-Methyl-DL-Tryptophan) as a pan inhibitor of IDO, future studies are warranted to identify the relative effects of D and L enantiomers and preclinical pipeline IDO inhibitors (Le Naour et al., 2020) in promoting HCC immunolysis.