TGF-β and IL-10 secreted from myeloma cells mediate the defective DC function, which could be restored by IL-12 and interferon-gamma (IFN-γ) (14).Indoleamine 2,3-dioxygenase(IDO) is produced by immature DCs and can deactivate T cells (15). Here, IDO1 is linked to plasma cell myeloma.