Question

You have isolated your MSC population and need to characterize the cells. Describe an example of why more than one antigen expression is required to characterize a MSC, and include a discussion of how you will detect the antigens and the challenges of antigen detection.

Answer 1

Mesenchymal stem cells (MSCs) are multipotent cells that adhere to plastic, have a fibroblast-like morphology, express a specific set of surface antigens, and differentiate into adipoc ytes, chondrocytes, and osteocytes.1 Clinically, MSCs are of interest for their ability to modulate the immune system as well as their potential to regenerate tissues. However, the translation of MSC-based therapies has been hindered by the heterogeneity of the isolated cells as well as the lack of standardized methods for their definition and characterization. At the forefront of these issues is the lack of a MSC-specific marker that can be used to definitively isolate and characterize MSCs. The absence of a MSC-specific marker limits the purity of MSCs isolated by methods such as positive and negative selection. As a result, MSCs are typically isolated by plastic adherence, which generates a heterogeneous population of cells that differ in their growth kinetics and differentiation potential. This heterogeneity can increase experimental variability, decrease the efficiency of differentiation, and contribute to conflicting data in the literature. In an attempt to increase consistency in the definition and verification of MSCs, the International Society for Cellular Therapy (ISCT) proposed minimal criteria for the definition of human MSCs based on plastic adherence, multipotency, and the expression of a panel of surface antigens (Box 1).1   Since proposing the minimal criteria in 2006, several advances in MSC characterization and marker identification have been made. These advances have led to improved methods for isolating, verifying, and assessing the quality of MSCs. This review summarizes the most recent MSC markers, definitions, and the latest methods used to characterize MSCs.