The abundance of myeloid-derived suppressor cells (MDSCs), Tregs, TAMs, and other immunosuppressive cells in the peripheral blood or in the tumor lesion has been associated with poor prognosis in cancer patients.185 Immunosuppressive cells, together with tumor cells and stromal cells, can produce inhibitory cytokines (e.g., IL-10 and TGF-b) and factors (e.g., arginase, IDO, and collagen) and express checkpoint ligands to dampen the immune response.185,186. This evidence concerns the gene IDO1 and neoplasm.