IDO1 and cancer: Interferon signaling promotes anti-tumor immune response, but can also induce immunosuppressive mechanisms in cancer.31 To identify mechanisms leading to enhanced IDO1 and TRAIL expression in endothelial cells after CD40-stimulating immunotherapy, we analyzed gene regulation in human umbilical vein endothelial cells (HUVEC) and human dermal blood endothelial cells (HDBEC) in vitro.