An IDO1 enzyme inhibitor was also shown to improve the efficacy of anti-CTLA-4 and anti-PD-L1 antibody therapy in a mouse B16 melanoma model [69] and further induce the proliferation, survival, and functions of antitumor immune cells in vitro and enhance antitumor immunity in vivo against Pan02 cells [70]. Here, IDO1 is linked to melanoma.