Is CD34 truly a negative marker for mesenchymal stromal cells?

Area of Science:

• Stem cell biology
• Immunophenotyping
• Cell biology

Background:

• Mesenchymal stromal cells (MSC) are widely believed to be CD34-negative, distinguishing them from CD34-positive hematopoietic stem cells (HSC).
• The Stro-1 antibody, used for MSC identification, was developed using CD34-positive cells, suggesting a potential link.
• Evidence for MSC being CD34-negative primarily comes from cultured cells, not tissue-resident populations.

Purpose of the Study:

• To investigate the expression of CD34 in tissue-resident mesenchymal stromal cells (MSC).
• To clarify the discrepancy regarding CD34 expression in MSC versus hematopoietic stem cells (HSC).
• To determine the effect of cell culturing on CD34 expression in MSC.

Main Methods:

• Analysis of CD34 expression in uncultured human bone marrow nucleated cells.
• Flow cytometry analysis of freshly isolated adipose-derived MSC (ADSC).
• Comparison of CD34 expression in freshly isolated versus cultured MSC.

Main Results:

• Mesenchymal stromal cells (including bone marrow-derived MSC and adipose-derived MSC) express CD34 in their native tissue environment.
• CD34 expression is lost or significantly reduced when MSC are propagated in cell culture.
• The distinction between MSC and HSC based solely on CD34 expression is not absolute.

Conclusions:

• Tissue-resident MSC, including bone marrow-derived MSC (BMSC) and adipose-derived MSC (ADSC), are CD34-positive.
• Cell culturing leads to the downregulation of CD34 expression in MSC.
• The prevailing view of MSC as CD34-negative is likely an artifact of cell culture conditions.