In Vitro Cell Surface Marker Expression on Mesenchymal Stem Cell Cultures does not Reflect Their Ex Vivo Phenotype

Area of Science:

• Cell Biology
• Stem Cell Research
• Tissue Engineering

Background:

• Mesenchymal stem or stromal cells (MSC) are defined in vitro by cell surface marker expression.
• The in vivo origin and self-renewal capacity of cultured MSCs based on marker expression remain unclear.
• Investigating markers like CD73 and CD90 is crucial for understanding MSC identity.

Purpose of the Study:

• To evaluate the expression of 15 putative MSC markers in primary cultured cells from periosteum and cartilage.
• To determine if marker expression reflects the differentiation state or in vivo self-renewal of cell populations.
• To assess the reliability of commonly used markers for defining MSCs.

Main Methods:

• Primary cells from human periosteum and cartilage were cultured.
• Expression of 15 cell surface markers was analyzed.
• Cells were sorted based on marker expression (CD90, CD34, CD73, CD26) and cultured under different conditions (e.g., extracellular matrix coatings, osteogenic differentiation).

Main Results:

• Cultured cells consistently expressed high levels of CD73, CD90, and PDPN, regardless of the culture surface.
• Osteogenic differentiation led to loss of CD106 and CD146 but retention of CD73 and CD90.
• Primary periosteal cells capable of CFU-F formation universally expressed CD73 and CD90 and lacked CD34 in vitro, irrespective of ex vivo expression.

Conclusions:

• In vitro expression of CD73 and CD90 is acquired during cell culture and does not necessarily reflect their in vivo status.
• Phenotypic convergence occurs in vitro, where cultured cells adopt a consistent marker profile.
• The study demonstrates that in vitro expression of many cell surface markers is unrelated to their pre-culture state.