Mesenchymal Stem Cells vs. Mesenchymal Stromal Cells: Why the Name Is Still Debated

What This Article Covers

"MSC" is one of the most common abbreviations in regenerative medicine, but the field itself has never fully agreed on what the letters stand for. The scientific society that sets standards for these cells has formally recommended, more than once, that researchers use "mesenchymal stromal cells" rather than "mesenchymal stem cells" — not as a marketing preference, but because most cells in a typical MSC culture don't actually meet the strict biological definition of a stem cell. This article walks through why that distinction exists, what the actual guidance says, and why it's worth knowing if you're trying to evaluate any claim built on the word "MSC."

Where the Term Came From

The name "mesenchymal stem cell" was popularized in the 1990s to describe a population of cells isolated from bone marrow (and later fat tissue, umbilical cord, and other sources) that could stick to plastic in a culture dish, expand in number, and differentiate into bone, cartilage, and fat cells. That last property — multilineage differentiation — made "stem cell" feel like a natural label. The term spread quickly through both academic papers and commercial contexts.

The problem is that "stem cell," in the strict biological sense, implies something specific: a single cell that can both self-renew indefinitely and give rise to multiple specialized cell types, demonstrated at the level of that one cell (clonal evidence). Most isolated MSC populations are a mixed bag. Some cells in the dish may behave this way; many others are more limited, already partly committed, or simply supportive "stromal" cells that help organize tissue and signal to neighboring cells without being stem cells themselves. Calling the whole population "stem cells" overstates what's actually been shown for most of the cells in it.

The 2005-2006 ISCT Position Statements

The International Society for Cellular Therapy (ISCT) — later renamed the International Society for Cell & Gene Therapy, keeping the same ISCT abbreviation — took this on directly. In 2005, a position statement led by Edwin Horwitz and colleagues, published in the journal Cytotherapy, argued that the field needed clearer terminology and proposed "multipotent mesenchymal stromal cells" as the more defensible term, preserving "MSC" as an abbreviation while changing what it stood for.

The following year, a widely cited 2006 ISCT position statement led by Massimo Dominici laid out minimal criteria that a cell population should meet to even be called an MSC in a lab setting: plastic adherence under standard culture conditions, expression of a specific panel of surface markers (and absence of others, like blood and immune cell markers), and the ability to differentiate into bone, cartilage, and fat cells in vitro. Notably, these criteria describe what a population of cultured cells can do collectively — they do not require proof that individual cells within that population are each clonal, self-renewing stem cells. That gap is the heart of the naming debate.

The 2019 Reaffirmation

The terminology question didn't go away, and in 2019, ISCT's MSC Committee, in a paper led by Sowmya Viswanathan, revisited the issue directly in a statement titled "Mesenchymal stem versus stromal cells." The committee:

• Reaffirmed that "mesenchymal stromal cell" remains the more scientifically accurate default term for the heterogeneous, culture-expanded populations most labs actually produce
• Acknowledged that a genuine stem cell subpopulation likely does exist within some MSC preparations, but said this has not been reliably demonstrated across the field as a defining feature of the bulk population
• Recommended that researchers specify the tissue source and characterization method (for example, "bone-marrow-derived MSCs") rather than relying on "MSC" alone to convey precise meaning
• Noted that the abbreviation "MSC" could reasonably stay in use as a practical shorthand, even while the words behind it shifted from "stem" to "stromal"

This is a case where a scientific body revisited its own earlier guidance, which is a healthy and normal part of how standards get refined — not a sign that the underlying science is shaky.

Why the Loose Usage Persists

Despite this guidance, "mesenchymal stem cell" never disappeared from scientific papers, clinical trial names, regulatory filings, or marketing materials. Reasons for that include established usage in older literature, patient and public familiarity with "stem cell" as a term, and in some cases, a term that sounds more impressive to a prospective patient than "stromal cell" does. Neither term, on its own, tells you much about a specific product's potency, purity, or clinical effect — those depend on how the cells were sourced, processed, and tested, not on which two words precede "cell."

Why This Matters to You

If you're researching a potential therapy and see "mesenchymal stem cells" advertised, that phrase alone isn't a red flag, but it also isn't proof of anything. The more useful questions are: What tissue did these cells come from? How were they characterized? What specific markers or functional tests were used to define them? A provider or paper that can answer those questions with specificity is engaging with the actual science; one that only repeats "stem cells" as a selling point is leaning on the word's emotional weight rather than its biological precision.

Bottom Line

The "stem cell" versus "stromal cell" debate is a real, ongoing terminology question inside the scientific community, grounded in a legitimate gap between what a typical MSC culture is shown to do and what the strict definition of "stem cell" requires. ISCT's own position statements, from 2005 through 2019, have consistently leaned toward "stromal" as the more accurate term while acknowledging "MSC" is unlikely to disappear as shorthand. Knowing this distinction won't tell you whether a specific therapy works, but it will make you a sharper reader of the claims built around it.