FLT-3 ligand promotes long- term expansion and differentiation of human pro-B-cells in the presence of IL-7 or in combination of IL-7 and IL-3.The human FLT-3 ligand also stimulates the proliferation of cells expressing murine FLT-3 receptors. In combination with SCF and IL-3, FLT-3 ligand can cause expansion of cells with the marker spectrum CD34（+） CD38（-）. Alone, FLT-3 ligand supports the survival of precursors in the lineage of blood-forming cells such as CFU-GM, CFU- GEMM, and the very primitive high proliferative potential colony-forming cells, HPP- CFC. flt-3 ligand only has marginal effects on progenitors for erythroid cells and megakaryocytes.