IDO1 and melanoma: To rule out that remaining amounts of solvent, epacadostat, IFNγ or HPI-1 in the conditioned media account for changes in T cell proliferation independent of their effects on IDO1 activity in melanoma cells, control supernatants containing the respective concentration of epacadostat, IFNγ and HPI-1 alone or in combination were tested on stimulated PBMCs (Fig. S8D).