CD40, a tumor necrosis factor receptor superfamily member, is a promising immune-boosting target in cancer immunotherapy due to its role in promoting antitumor responses of immune cells. CD40 is also expressed on endothelial cells but the response of the tumor-associated vasculature to CD40-stimulating immunotherapy has not been studied. Herein, we have performed RNA-sequencing analysis of murine tumor endothelial cells (TECs) isolated from B16.F10 melanoma and MB49 bladder cancer treated with agonistic CD40 monoclonal antibody (mAb) or isotype control. Gene set and gene ontology enrichment analyses of the differentially expressed genes revealed that CD40 mAb treatment induces interferon-γ (IFNγ) signaling in the tumor microenvironment associated with up-regulation of immunosuppressive genes in TECs, including the enzyme indoleamine 2, 3-dioxygenase 1 (IDO1). Importantly, IDO1 was preferentially expressed in endothelial cells in the tumor and was positively correlated to infiltration of T-cells in the tumor microenvironment. In vitro, endothelial cells up-regulated IDO1 in response to T-cell-derived IFNγ, but not in response to CD40-stimulation. Collectively, our data suggest that IDO1 up-regulation in TECs occurs as a response to T-cell activation. Combining CD40 mAb therapy with the IDO1 inhibitor epacadostat delayed tumor growth and increased survival of B16.F10 tumor-bearing mice, which was associated with increased activation of cytotoxic T-cells. Hereby, we have uncovered a novel immunosuppressive feedback mechanism, in which the tumor vasculature limits the response to cancer immunotherapy by up-regulating IDO1.

Citation Format: Anna Dimberg, Alexandros Karampatzakis, Sander Tuit, Mohanraj Ramachandran, Grammatiki Fotaki, Luuk van Hooren, Hua Huang, Roberta Lugano, Kaunisto Aura, Peter Ellmark, Sara M Mangsbo, Joachim L. Schultze, Magnus Essand, Maria Georganaki. Tumor endothelial cells say IDO to CD40-stimulating immunotherapy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A128.