Proinflammatory cytokines produced in tumor microenvironment resulted in eradication of anti-tumor immunity and enhanced tumor cell survival. Kynurenine (Kyn) was required for IDO-mediated T cells function via aryl hydrocarbon receptor (AhR)/Foxp3. Additionally, T cell-mediated adaptive immunity indeed played a critical role in CRC progression. Inhibition of IDO could be an effective strategy for the prevention and treatment of inflammation-related CRC.BACKGROUND & AIMS: Chronic inflammation in colon section is associated with an increased risk of colorectal cancer (CRC). Proinflammatory cytokines were produced in a tumor microenvironment and correlated with poor clinical outcome. Tumor-infiltrating T cells were reported to be greatly involved in the development of colon cancer. In this study, we demonstrated that kynurenine (Kyn), a metabolite catalyzed by indoleamine 2,3-dioxygenase (IDO), was required for IDOmediated T cell function, and adaptive immunity indeed played a critical role in CRC.METHODS: Supernatant of colon cancer cells was used to culture activated T cells and mice spleen lymphocytes, and the IDO1-Kyn-aryl hydrocarbon (AhR) receptor axis was determined in vitro. In vivo, an azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced CRC model was established in IDO -/-, Rag1 -/-, and wild-type mice, and tumor-associated T lymphocyte infiltration and Kyn/AhR signaling pathway changes were measured in each group. RESULTS: Kyn promoted AhR nuclear translocation increased the transcription of Foxp3, a marker of regulatory T cells (Tregs), through improving the interaction between AhR and Foxp3 promoter. Additionally, compared WT mice, IDO -/mice treated with AOM/DSS exhibited fewer and smaller tumor burdens in the colon, with less Treg and more CD8 þ T cells infiltration, while Kyn administration abolished this regulation. Rag1 -/mice were more sensitive to AOM/DSS-induced colitisassociated colon cancer (CRC) compared with the wild-type mice, suggesting that T cell-mediated adaptive immunity indeed played a critical role in CRC.
CONCLUSIONS:We demonstrated that inhibition of IDO diminished Kyn/AhR-mediated Treg differentiation and could be an effective strategy for the prevention and