Effect of VB22B sc(Fv)2 on cell proliferation, in vitro megakaryocyte differentiation, and tyrosine phosphorylation. (A) TPO-dependent human cell line. M-07e cell proliferation activity of VB22B sc(Fv)2 or rhTPO was measured by in vitro assay. (B) Megakaryocyte lineage differentiation activity of VB22B sc(Fv)2 or rhTPO against CD34-positive cells was measured by in vitro differentiation assay. (C) Phosphorylations of JAK2 (left panel), STAT3 (middle panel), and STAT5b (right panel) by VB22B sc(Fv)2 or rhTPO stimulation were detected by immunoprecipitation and Western blotting.