Mouse Flt3 Ligand (Flt3L) Recombinant Protein. FMS-related Tyrosine Kinase 3 Ligand (FLT-3 Ligand) is a growth factor important for the proliferation of hematopoietic cells. FLT-3 Ligand binds to, and transmits signals through, the receptor tyrosine kinase known as FMS-like Tyrosine Kinase-3 (FLT-3). 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. Human FLT-3 Ligand can stimulate the proliferation of cells expressing murine FLT-3 receptors.