This is consistent with depletion of CD8+ T-cells or IFNγ-deficiency diminishing IDO1 expression in tumor stroma in murine melanoma.36 IFNγ-induced expression of IDO1 in endothelial cells has previously been observed in a model of allotransplantation, where CD40Ig-induced graft acceptance of a complete MHC-mismatched heart was due to Treg induction of IFNγ-induced expression of IDO1 in graft endothelial cells.37 The present report is the first to show a specific role of endothelial IDO1 in participating in negative regulation of T-cell activation in response to cancer immunotherapy. Here, IDO1 is linked to melanoma.