Clone BV10A4H2 recognizes the human CD135 antigen, a single-pass type I membrane protein also known as Fms-like tyrosine kinase receptor 3 (FLT3) or fetal liver kinase-2 (FLK-2). CD135 belongs to the same family as FMS, KIT, and the two genes encoding PDGFRα and β. CD135 is normally expressed by hematopoietic stem and progenitor cells and expression is lost as hematopoietic cells differentiate. Although CD135 expression is usually lost upon HSC differentiation, dendritic cells are an exception, as mature DCs display persistent FLT3 expression. CD135 is also expressed on malignant hematopoietic cells including AML, ALL, and CML-BC. All hematopoietic cells develop from CD135 negative hematopoietic stem cells through CD135 positive progenitor cells. In synergy with other growth factors like G-CSF, GM-CSF, SCF, and IL-3, ligation of CD135 with FLT3 ligand promotes the differentiation, proliferation, and survival of hematopoietic progenitor cells and of dendritic cells. As a result early B cell lineage differentiation as well as expansion of monocytes and immature dendritic cells are stimulated.