Abstract
SUMMARY: Research on expanded human stem cells has become an increasing field of interest during the last decade. The increasing interest in adult stem cells, especially mesenchymal stem and mesenchymal stromal cells, in hematology and regenerative medicine is also based on the simplicity of isolation and ex vivo expansion of these cells. These processes require an adequate quality control of source and product. In this review, we summarize various different attempts to characterize mesenchymal stem cells based on surface protein expression by flow cytometry and to define multipotent subpopulations of mesenchymal stem cells for prospective isolation. The importance of defining functional assays and a unique marker panel to characterize mesenchymal stem cells for clinical trials as well as the factors that can modulate the marker expression is discussed.