Mesenchymal Stem Cells and Endothelial Cells: A Common Ancestor?

Bone marrow mesenchymal stem cells (BM-MSCs) are commonly known as nonhematopoietic-nonendothelial cells based on in vitro expressed markers and properties. Despite the massive research on ex vivo expanded MSCs, their in vivo identity remains elusive. In this study, we report the existence of large multinuclear CD31 positive cells in the beginning of human BM-MSCs culture. Interestingly, the adjacent multinuclear cells occasionally formed tube-like structures. The large multinuclear cells then gave rise to mononuclear cells that fulfilled the criteria for BM-MSCs and were negative for CD31 but positive for other endothelial markers, CD54, CD106, and CD144. These observations, although primitive, imply that MSC ancestors may directly participate in the formation of new vessels. Further studies on BM-MSCs in the first few days of culture are definitely required to investigate the exact role of these cells in the vascular system.