Importance of Identifying MSCs Correctly
Accurate identification of mesenchymal stem cells (MSCs) is crucial for both scientific research and clinical applications. Proper MSC characterization ensures that the cells used truly possess the functional and phenotypic properties expected of multipotent stem cells. Misidentification can compromise the outcomes of regenerative therapies and lead to unreliable research findings.
In clinical settings, quality control is non-negotiable. For MSCs to be approved as clinical-grade stem cells, they must be validated under GMP (Good Manufacturing Practice) conditions. This includes confirming their identity through surface markers, differentiation ability, and absence of hematopoietic markers. Regulatory bodies and scientific institutions, such as the International Society for Cell and Gene Therapy (ISCT), have established strict criteria to maintain consistency and safety.
Why It Matters:
Core Surface Markers for MSC Identification (ISCT Criteria)
The International Society for Cell & Gene Therapy (ISCT) has set standardized criteria to define and authenticate mesenchymal stem cells (MSCs), ensuring reproducibility and clinical-grade consistency. According to these guidelines, MSCs must exhibit specific surface markers that confirm their identity as mesenchymal stromal cells.
Positive MSC Markers:
MSCs must express the following core surface markers:
Negative Markers to Exclude Other Cell Types
To ensure the purity and specificity of mesenchymal stem cells (MSCs), it is equally important to confirm the absence of certain markers that are typically expressed by hematopoietic, endothelial, or immune cells. This negative selection step is crucial in MSC immunophenotyping and is required by the ISCT guidelines for identifying clinical-grade stem cells.
MSCs must not express the following markers:
Why Negative Markers Matter:
Methods Used to Detect MSC Markers
To confirm the identity and purity of mesenchymal stem cells (MSCs), researchers rely on advanced lab techniques to detect both positive and negative surface markers. These methods form the backbone of phenotypic profiling and are essential in both research and clinical-grade stem cell production.
These tools are crucial for flow cytometry analysis, GMP-compliant stem cell validation, and ensuring accurate phenotypic profiling before any clinical or experimental use.
Variability in MSC Markers by Tissue Source
While mesenchymal stem cells (MSCs) share a core set of surface markers (like CD73, CD90, and CD105), their exact expression profiles can vary depending on the tissue source. These tissue-specific MSC characteristics influence their biological behavior, differentiation potential, and therapeutic application.
MSC Marker Differences by Tissue Type:Bone Marrow-Derived MSCs (BM-MSCs)
Express classical markers strongly and are well-characterized. They typically show moderate proliferation and higher osteogenic potential.
Adipose-Derived MSCs (AD-MSCs)
Often display higher expression of CD36 and CD34 (in early passage), associated with their fat tissue MSC markers. Known for strong adipogenic and angiogenic potential.
Umbilical Cord-Derived MSCs (UC-MSCs)
Exhibit lower immunogenicity and high proliferation. Unique neonatal stem cell markers such as CD146 and CD271 may be present depending on isolation techniques.
Dental Pulp & Synovial MSCs
Known for neuroregenerative and chondrogenic potential, respectively. These cells may express higher levels of neural or cartilage-related surface antigens.
Functional Role of MSC Markers
Mesenchymal stem cell (MSC) markers are not only used for identification—they often have functional roles that influence how MSCs behave in the body. These markers can actively participate in processes like immunomodulation, angiogenesis, and cell migration, all of which are crucial for the success of regenerative therapies. Key Functional Contributions of MSC Markers:
Immunomodulation
Markers like CD73 contribute to anti-inflammatory effects by generating adenosine, which plays a role in MSC immunomodulatory function and immune suppression.
Angiogenesis
CD105 (Endoglin) is involved in regenerative signaling by enhancing vascular endothelial growth factor (VEGF) responses, promoting blood vessel formation in damaged tissues.
Cell Adhesion & Migration
CD90 (Thy-1) supports stem cell trafficking and cellular adhesion, allowing MSCs to home to injury sites more effectively.
These functional roles make certain markers not just identifiers, but also contributors to the therapeutic potential of MSCs.
Challenges in MSC Marker Standardization
Standardizing mesenchymal stem cell markers remains a challenge due to variations in marker expression that can occur during cell culture. As MSCs are passaged repeatedly for expansion, they may undergo phenotypic drift, where surface marker expression gradually changes, affecting identity and potency.
Additionally, culture conditions, such as the choice of basal media, serum type (e.g., FBS vs. hPL), oxygen levels, and substrate materials, can influence the MSC surface marker profile. These culture-induced variabilities complicate consistent identification, especially in clinical-grade production.
Moreover, cell passage effects can lead to reduced functionality or unintended differentiation, making quality control crucial during large-scale MSC expansion.
Emerging and Functional MSC Markers
Beyond the classical ISCT-defined markers CD73, CD90, and CD105, research is now exploring novel MSC surface antigens that offer deeper insight into functional MSC subsets. These advanced markers may correlate with enhanced immunosuppressive capacity, tissue-homing ability, or proliferation rate, making them valuable for precision therapies.
Examples of emerging markers include:
This advanced MSC profiling paves the way for developing customized stem cell therapies based on tissue-specific functional markers, ensuring higher efficacy in regenerative medicine applications.
