IDO inhibition by epacadostat does not affect the ability of DCs to cross‐present soluble antigen to T cells. Blood DCs were stimulated overnight with R848 (pDCs) or R848 and poly(I:C) (cDCs) in medium containing 1 μM tryptophan, with or without epacadostat, and loaded with gp100(154‐162) (irrelevant), gp100(280‐288) (short), or gp100(272‐300) (long) peptide. After overnight culture, T cells expressing the T cell receptor recognizing gp100(280‐288) were added at a 1:5 DC:T cell ratio for 24 h. CD69 expression by T cells was used as a readout for DC‐induced T cell stimulation and was measured by flow cytometry. Mean frequency of CD69high cells among live CD3+ T cells is shown, with at least seven different donors per condition from 11 independent experiments, with technical duplicates for cDC2 and pDC conditions. Significance was determined by two‐tailed paired t‐test, comparing absence versus presence of IDO inhibitor (ns, non‐significant).