This antibody reacts with extracellular class III epitope on CD34, a 110-115 kDa monomeric transmembrane phosphoglycoprotein expressed on hematopoietic progenitors cells and on the most pluripotential stem cells. It is gradually lost on progenitor cells. This antibody completely blocks binding of class II antibody QBEnd10 and class III antibodies BIRMA K3 and 8G12 on KG1a cell line.