IDO1 and melanoma: Pharmacological inhibition of IDO1 can improve the response to checkpoint antibodies targeting PD-1 or CTLA-4 in B16-F10 melanoma, but it has not yet been tried in combination with CD40-stimulating immunotherapy.34 Combining agonistic CD40 mAb therapy with epacadostat significantly reduced B16-F10 tumor growth as compared to control (Figure 5a).