CD105 (Endoglin) Expression on Hematopoietic Stem/Progenitor Cells

Abstract

Endoglin (CD105) is a component of the transforming growth factor-β (TGF-β) receptor (TGF-βR) complex. Together with betaglycan, CD105 is considered as a TGF-βR accessory molecule (also called TGF-βRIII), but its functions in the receptor-ligand interactions are still poorly understood. A small subset of human CD34+ hematopoietic stem/progenitor cells that has phenotypic and functional features suggestive of very primitive hematopoietic cells expresses the CD105 antigen. CD34+/CD105+ cells recirculate in the peripheral blood of mobilized subjects and can be purified by immunomagnetic isolation strategies. The hematopoietic potential of these CD34+/CD105+ cells appears to be sustained by a combination of hematopoietic and non-hematopoietic cytokines, which comprises Flt3 ligand, erythropoietin, interleukin-15 and vascular endothelial growth factor. Endogenous TGF-β1 is a crucial factor for the maintenance of CD34+/CD105+ immaturity acting through positive modulation of both CD105 and CD34 molecules in the absence of relevant effects on the cell cycle profile. CD105 is absent on very primitive CD34-/lineage-/CD45+ (CD34-Lin-) human hematopoietic cells isolated from cord blood. However, in vitro exposure of CD34-Lin-cells to exogenous TGF-β1 causes the appearance of a discrete population of CD34+/CD105+ cells. Collectively, available data on CD105 expression and function in primitive hematopoiesis indicate that this molecule could cooperate with the dissociation of TGF-β1 cell cycle effects from its other effects on cell survival and differentiation.

Key Words:

• hematopoiesis
• stem cells
• CD105
• TGF-β1