Hematopoietic stem cells (HSCs) are rare cells found in the bone marrow and peripheral blood of adults, fetal liver tissue, and umbilical cord blood. They represent 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, which results in identical daughter cells. Self-renewal maintains constant stem cell populations throughout a person’s life.
HSCs are not recognizable based on their morphology. They are small, mononuclear cells that appear to be small lymphocytes. Cell separation techniques that target specific antigens can differentiate HSCs. One of the most important is CD34, a glycoprotein found on HSCs, early progenitor cells, and vascular endothelial cells. Table 1 shows other markers and their role in hematopoiesis.
Table 1. 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 |
