RGS2 reverses the Flt3-ITD–induced block of differentiation. Stable 32D/Flt3-WT, 32D/Flt3-ITD, or 32D/Flt3-ITD cells cotransfected with RGS2 and parental 32D cells were used for these experiments. Cells were grown for 12 days in the presence of G-CSF without IL-3. Granulocytic differentiation was determined by flow cytometric CD11b surface expression.