Identification of CD93 expression on hematopoietic stem cells in human neonatal umbilical cord blood cells

Human CD93 is a heavily O-glycosylated type I transmembrane protein consisting of unique C-type lectin domains (CTLDs) containing glycoprotein. CD93 is mainly expressed on myeloid cells (monocytes and granulocytes) and endothelial cells. However, the expression patterns of CD93 on various other kinds of cells are not well understood. In this study, we found that CD93 was recognized by a CD93 monoclonal antibody (mAb) (mNI-11) that was established in our laboratories and was expressed on a broad hematopoietic stem cell population (CD34 cells) from human neonatal umbilical cord blood cells (UCBCs), as shown using a two-color flow cytometric analysis. In addition, the CD93 recognized by mNI-11 was also expressed on a narrow hematopoietic stem cell population (CD34CD45 cells) in which the non-specific reactivity of CD34 mAb from human neonatal UCBCs was excluded using a three-color flow cytometric analysis. Taken together, these results provide the first evidence concerning the identification of CD93 expression on hematopoietic stem cells. These cell populations (CD34CD93 and CD34CD45CD93 cells) in human neonatal UCBCs are thought to have an important role in cell biology, transplantation, and immature/mature immune responses.