CD135, also known as Flk-2, Flt3, and Ly-72, is a type III tyrosine kinase receptor. It is expressed on early B lymphoid lineage cells in bone marrow, on primitive myeloid progenitors within the BM CD34+ cell population. Ligation of Flk-2 with Flt3 ligand regulates the growth of hematopoietic stem cells and promotes the survival of primitive hematopoietic progenitor cells with myeloid as well as B lymphoid potential. It was reported that the receptor tyrosine kinase Flt3 is required for dendritic cell development. Combined signaling through interleukin-7 receptors and Flt3 selectively promotes B-cell commitment and differentiation from uncommitted murine bone marrow progenitor cells.