IDO is widely expressed in various types of cells, including most tumor cells, dendritic cells, macrophages, microglia, eosinophils, fibroblasts, and endothelial cells (142, 191–197), the most significant and effective inducers of IDO expression mainly are cytokines (such as IFN-γ, IFN-α, IFN-β and IL-10), as well as signaling through TLRs (198–200). This evidence concerns the gene IDO1 and neoplasm.