The criteria used to identify mesenchymal stem cells can vary, as identification s can be accomplished through assessing either physical or functional attributes.

Physical Assessment of Mesenchymal Stem Cells (MSCs)

The first approach is physical assessment. Morphologically, MSCs have a small cell body with long, thin cell processes that can give the cells a “stretched” appearance.  The cell body contains a large, round nucleus with a prominent nucleolus.  The cells present with symmetrical morphology.

MSCs tend to be broadly dispersed within an extracellular matrix (ECM) that contains a few reticular fibrils but lacks other types of collagen fibrils.

Functional Attributes of Mesenchymal Stem Cells (MSCs)

A second approach for identifying mesenchymal stem cells is through functional assessment.  Criteria for identifying MSCs are presented below:

• Able to be isolated by plastic adherence
• Have multi-potential and multi-lineage capability (plasticity)
• Distinctive Surface Markers, specifically: CD73, CD90, CD105[1]
• Lack of Lineage-Specific Markers, including: CD34, CD14, CD45[2]
• Immuno-favorable characteristics that include little to no expression of MHC class I antigens and very limited expression of MHC class II antigens[3]
• Lack of co-stimulatory molecules of the B7 family that are required to initiate an immune response

In addition, functional assessment can include analyzing cells for characteristic cytokine production or gene expression profiles.  However, the difficulty with this approach is that the “characteristic” cytokines produced or genes expressed by MSCs can vary by source of origin. For instance, bone marrow-derived MSCs and adipose-derived MSCs exhibit different, source-specific, cytokine production.[4]

FOOTNOTES:

[1] Klingemann H, et al. Mesenchymal Stem Cells, Sources and Applications. Transfusion Medicine and Hemotherapy 2008; 35: 272-277
[2] Friedman R, Betancur M, Tuncer H, Boissel L, Klingemann H. Umbilical cord mesenchymal stem cells: Adjuvants for human cell transplantation. Biol Blood Marrow Transplant 2007; 13: 1477–1486.
[3] Friedman R, Betancur M, Tuncer H, Boissel L, Klingemann H. Umbilical cord mesenchymal stem cells: Adjuvants for human cell transplantation. Biol Blood Marrow Transplant 2007; 13: 1477–1486.
[4] Gonzalez-Rey E, et al. Human adipose-derived mesenchymal stem cells reduce inflammatory and T cell responses and induce regulatory T cells in vitro in rheumatoid arthritis. Ann Rheum Dis 2010; 69: 241-248.