IDO1 and inflammatory bowel disease: We demonstrated that IFN-γ- and KYNA-pretreated hADSCs increased IDO-1 and IL-10 expression, promoted M2 macrophage polarization, alleviated inflammation, stimulated epithelial regeneration, decreased ECM accumulation, inhibited epithelial–mesenchymal transition (EMT) progression, and had better therapeutic efficacy in a rat IBD colonic fibrosis model than non-pretreated hADSCs.