Mesenchymal stem cells (MSCs) are a type of adult stem cell found in various tissues, including bone marrow, adipose tissue, and umbilical cord. These cells possess unique regenerative potential, making them a subject of scientific interest. To accurately identify and distinguish MSCs from other cell types, scientists rely on specific molecular and functional characteristics, often referred to as markers.
These markers allow researchers to confirm the presence of MSCs within a mixed cell population. This systematic identification ensures consistency in studies and confirms that cells used in experiments or for potential therapies are indeed MSCs.
Why Identify Mesenchymal Stem Cells?
Accurate identification of mesenchymal stem cells is important for consistency in research and the safety of potential therapeutic applications. MSCs can be isolated from various tissues, and their characteristics may vary depending on their source and isolation method. This variability highlights the need for standardized identification criteria.
Confirming MSC identity ensures the purity of cell populations used in experiments, which is necessary for reliable scientific findings. Without precise identification, research outcomes could be inconsistent, hindering knowledge advancement. For clinical applications, identification protocols ensure patients receive the correct and pure cell population, minimizing risks and maximizing treatment potential.
Key Surface Markers for Mesenchymal Stem Cells
The International Society for Cell & Gene Therapy (ISCT) has established minimal criteria for identifying human MSCs, including specific surface markers. These markers are proteins on the cell’s outer membrane. Their expression is typically analyzed using techniques like flow cytometry or immunocytochemistry.
MSCs are characterized by the positive expression of three specific surface markers: CD73, CD90, and CD105. CD73, also known as ecto-5′-nucleotidase, is an enzyme involved in cell signaling pathways. CD90, or Thy-1, is a glycoprotein found on various cell types, including MSCs. CD105, or endoglin, is a component of the transforming growth factor-beta (TGF-β) receptor complex and is expressed on endothelial cells and MSCs. The presence of these three markers on at least 95% of the cell population is an indicator of MSC identity.
MSCs should also show minimal expression (typically less than 2%) of certain markers to distinguish them from other cell types, especially blood cells. These include:
- CD34: Found on primitive hematopoietic progenitors and endothelial cells.
- CD45: A pan-leukocyte marker present on most white blood cells.
- MHC class II markers (specifically HLA-DR): Differentiate MSCs from immune cells.
- CD11b, CD14, and CD19: Found on monocytes, macrophages, and B-cells, respectively.
Functional Characteristics for Mesenchymal Stem Cell Identification
Beyond surface markers, MSC identification also relies on their distinct functional properties. Two primary functional characteristics are adherence to plastic surfaces and their multipotent differentiation capacity.
MSCs adhere to plastic surfaces when cultured in laboratory conditions. This property is an initial step in isolating MSCs from various tissues. When cell preparations are plated, MSCs readily attach to the culture vessel, forming what were historically called colony-forming unit fibroblasts (CFU-F).
MSCs possess multipotent differentiation potential, meaning they can change into at least three distinct cell types under specific laboratory conditions. These include osteocytes (bone cells), adipocytes (fat cells), and chondrocytes (cartilage cells). To test this, MSCs are exposed to specific growth factors and culture conditions that encourage their development into these lineages. Osteogenic differentiation is confirmed by the formation of mineralized bone matrix, adipogenic by the accumulation of lipid droplets, and chondrogenic by the production of cartilage-specific extracellular matrix components.
Ensuring Mesenchymal Stem Cell Identity for Use
Combining surface marker analysis and functional assays ensures the identity and purity of mesenchymal stem cell populations. This comprehensive evaluation is important for quality control in both research settings and in the development of potential clinical therapies. Using these established criteria helps maintain consistency across scientific studies, allowing researchers to compare results and advance the field.
Identification protocols also prevent contamination with unwanted cell types, which could compromise research outcomes or patient safety. For example, ensuring the absence of hematopoietic markers confirms that the MSC population is not mixed with blood cells. This characterization is important for developing safe and effective cell therapies, as it confirms that the correct and pure cell population is being utilized.