Known to bind to cells that express the tyrosine kinase receptor, FLT3LG promotes long-term expansion and differentiation of human pro-B cells. Human FLT3LG also stimulates the proliferation of cells expressing murine FLT-3 receptors. In combination with SCF and IL3, FLT3LG can cause expansion of cells with the marker spectrum CD34(+)/CD38(-). Alone, FLT3LG 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. FLT3LG has only marginal effects on progenitors for erythroid cells and megakaryocytes. Recombinant Human FLT3LG expressed from human 293 cells is a monomeric glycoprotein with a molecular mass of 24 to 30 kDa.