We also do not observe significant levels of phosphorylated STAT3 (p-STAT3), a major signaling pathway downstream of the IL-6R, in leukemia cells in vivo before treatment (Fig. 2f) or significant differences in gene expression downstream of STAT3 in leukemic cells grown in WT and IL-6 KO mice (see below). This evidence concerns the gene IL6 and leukemia.