HSCs are rare cells that can be found in the bone marrow and peripheral blood of adults, fetal liver tissue, and umbilical cord blood. They represent from 0.05-0.5% of the cellularity of the normal bone marrow. HSCs are responsible for the production of all hematopoietic cells. They are also capable of self-renewal that results in identical daughter cells. Self-renewal maintains constant stem cell populations throughout a person’s life.
HSCs are not recognizable on the basis of their morphology. They are small, mononuclear cells that appear to be small lymphocytes. HSCs can be differentiated by cell separation techniques that target specific antigens. One of the most important of these is CD34, a glycoprotein found on HSCs, early progenitor cells, and vascular endothelial cells. Other markers and their role in hematopoiesis are shown in the table.
HSC Markers for Differentiation
Marker | Role in Hematopoiesis |
CD34 | Adhesion to stroma in the bone marrow |
Thy-1 | T-lymphocyte adhesion |
CD49f | Cell adhesion |
CD38 | Indicates absence of differentiation markers |
Lin- | T-lymphocyte adhesion |
HLA-DR | Determine histocompatibility |
TPO-R | Receptor for thrombopoietin |