IDO1 and melanoma: These improved physicochemical properties equipped Epacasome-2 with significantly enhanced anti-melanoma activities and enabled more tumour-infiltrating CTLs, DCs, reduced immunosuppressive effects from Tregs, G-MDSCs and repolarized the macrophages through more effective targeting of the IDO1 enzyme, as well as allowed Epacasome-2 to possess better ability to potentiate the efficacy of the PD-1 inhibitor compared with free EPA (Fig. 4).