Toward the identification of mesenchymal stem cells in bone marrow and peripheral blood for bone regeneration

Background: The advent of monoclonal antibody stem cell marker technology has made it possible to identify a variety of human stem cells and their progeny. Specific markers exist for cells related to bone healing and bone regeneration. These include but are not limited to hematopoietic, mesenchymal, endothelial, angiogenic, and vasculargenic precursor cells. Purpose: The purpose of this investigation was to (1) to identify, by means of cell markers, the presence of stem cells needed for bone formation within peripheral blood and bone-marrow aspirate, and (2) to ascertain whether more of those stem cells were present in the bone-marrow aspirate than the peripheral blood. Materials: Samples of autogenous bone-marrow aspirate and peripheral blood from 6 patients ranging in age,from 23 to 73 were analyzed with 6-column flow cytometry using cell markers for stem cells relating to bone growth and bone healing. Six monoclonal antibody cell markers were utilized: CD14, CD34, CD36, CD105, CD106, and CD309 (also known as vascular endothelial growth factor receptor or KDR). Subgroups reacting to these markers or combinations of markers were then further tested with. other marker combinations. Results: The expression of specific monoclonal antibody cell markers revealed that bone marrow contained more osteogenic stem cells than peripheral blood. Bone marrow contained a higher percentage of cells that reacted with the CD34 and CD14 markers. This suggests that bone marrow contains more hematopoietic stem cells that proliferate to become myeloid progenitor cells, megakaryocytes, monocyte/macrophages, and osteoclast progenitors. When the fractions of bone marrow and peripheral blood samples that reacted with both CD34 and CD14 were further tested for CD105, more of the fraction from bone marrow reacted to CD105 than that from peripheral blood, suggesting more osteogenic potential in the bone marrow than the peripheral blood. When the fraction of bone marrow and peripheral blood samples that reacted with CD34 and CD14 were tested for the combination of CD105, CD106, and CD36, a smaller percentage of cells from the bone marrow reacted with CD36 than those from peripheral blood, suggesting that CD36 does not express for mesenchymal stem cells (MSCs). Conclusion: Bone-marrow aspirate seems to contain a significantly greater percentage of hematopoietic, endothelial, and MSCs than peripheral blood. Of particular significance is the higher percentage of bone-marrow cells reacting to CD105, an indication of the presence of MSCs. The ability of multipotent MSCs to form osteoblasts for bone regeneration makes transplanted bone-marrow aspirate a promising tool for enhancing bone regeneration.