It is well known that the active mesenchymal stromal cells in the tumour milieu inhibit the adaptive immune response by secreting mediators contained in exosomes (MSCs-EV) and soluble factors, such as IDO, TGFβ1, TNF-α, IFN-γ, PGE2, NO, HLA-G, HGF, IL-1β, IL-1α, IL-4 and IL-6; they can also do so by interacting with various immune cell types, including T cells, B cells, DC cells, NK cells, monocytes and TAMs. The gene discussed is IDO1; the disease is neoplasm.