IDO1 and metastatic melanoma: A phase 1/2 study evaluating an immunomodulatory vaccine against IDO and PD-L1 combined with nivolumab (anti-PD-1 ICI) demonstrated high ORR (80%) in metastatic malignant melanoma, suggesting that targeting both IDO1 and PD-L1/PD-1 is a potential strategy to enhance the efficacy of immunotherapy.33