FLT3 ligand is a receptor for the Flt3 cytokine and has a tyrosine-protein kinase activity & a growth factor that regulates proliferation of early hematopoietic cells. Flt3-Ligand synergizes with other CSFs and interleukins to induce growth and differentiation. Human flt3-Ligand (flk2-ligand) stimulates the proliferation and colony formation of certain bone marrow precursor cells including CD34+ cells.