IDO1 and melanoma: Given that the synergy of IDO1 inhibitor and ICPIs was confirmed in B16 melanoma models[80], several phase I/II clinical trials were then initiated to investigate epacadostat in combination with ipilimumab[95] (NCT01604889), pembrolizumab[76] (NCT02178722) and nivolumab[77] (NCT02327078) for the treatment of unresectable or metastatic malignant melanoma.