PDCD1 and melanoma: Based on these promising results and distinct mechanisms of action, an additional phase 1 trial combining IDO1 vaccines with CTLA-4 inhibitor ipilimumab (Yervoy) for stage III or IV melanoma patients and a phase 1/2 clinical trial that tests a combination treatment with a PD-1 monoclonal antibody (nivolumab) and a PD-L1–IDO1 peptide vaccine, have been initiated.