IDO1 and melanoma: Beyond several immunosuppressive molecules (e.g., IDO, IL-10, ARG1, VEGF and PD-L1), which are induced by PGE2 in MDSCs [149,150], we recently reported that tumor-derived PGE2 drives p50 NF-κB-dependent epigenetic reprogramming of M-MDSCs, diverting their response to IFNγ toward NO-mediated immunosuppression in preclinical models of fibrosarcoma and melanoma [7].