STAT3 and leukemia: While all cells remained CD11b+ (Fig. 2A), solely leukemia cells expressing both STAT3 isoforms responded to G-CSF by notable upregulation of the granulocytic surface marker Gr-1 (Fig. 2B), while on the mRNA level expression of the G-CSF receptor (Csf3r) was comparable in suspension culture (Fig. 2C).