CD34 is a 115-kDa transmembrane glycoprotein. This highly glycosylated single pass membrane protein is expressed on the surface of most hematopoietic stem cells (HPSCs) and a few non-hematopoietic cell types including muscle satellite cells, interstitial cells, mesenchymal cells (MSCs), vascular endothelial progenitors, epithelial progenitors, and corneal keratocytes. CD34 is an important marker of hematopoietic stem cells (HSC) and hematopoietic progenitor cells. It is widely used in clinical applications as a marker for identifying and isolating hematopoietic stem cells and their progenitors ahead of bone marrow transplantation.