FLT3 and leukemia: Finally, we determined the functional relevance of Hmga2 and Flt3 co-expression in G12D/E2-KO HSPCs by measuring the colony-forming activity, which is commonly used to assess hematopoietic or leukemia stem cell activity, with or without FLT3 inhibition and/or HMGA2 depletion (Fig. 4h).