However, we were unable to detect IDO protein and/or kynurenine production and tryptophan consumption by any ALL sample tested, either at baseline or after in vitro stimulation with IFN-γ (Figure 1B and 1C), in spite of the ability of IFN-γ to up-regulate phosphorylated STAT3 (data not shown). This evidence concerns the gene STAT3 and acute lymphoblastic leukemia.