IDO1 and acute lymphoblastic leukemia: The relevance of BMP4 is further supported by the results showing that BMP4 overexpression in ALL cells enhances the generation of immunosuppressive DCs which in addition exhibit a higher pro-tumoural activity, revealed by an upregulated expression of the immunosuppressive and tumour growth promoting factors TGF-β, IL-6, IL-1β, IL-8, IDO1 and MMP9, and a concomitant reduced allostimulatory capacity.