Consistently, when we triggered STAT3 phosphorylation (Figure 6A) with IL-6 (20 ng/ml) or IL-15 (20 ng/ml), key cytokines in LGL leukemia development [9, 24], after one hour culture we observed an increase of Fas ligand transcription levels (1.59- and 2.01-fold after IL-6 and IL-15, respectively, Figure 6B). Here, IL15 is linked to T-cell large granular lymphocyte leukemia.