Fms-like tyrosine kinase 3 （Flt-3）, also known as fetal liver kinase 2 （Flk-2）, is a receptor tyrosine kinase that plays a critical role in hematopoiesis and immune cell development. Flt-3 is primarily expressed on hematopoietic stem cells and early progenitor cells, where it regulates cell proliferation, differentiation, and survival. Activation of Flt-3 by its ligand, Flt-3 ligand （Flt-3L）, leads to the activation of downstream signaling pathways involved in hematopoietic cell growth and differentiation. Flt-3 is essential for the development of various immune cell lineages, including dendritic cells, natural killer cells, and B cells.