Mesenchymal stem cells are multipotent cells isolated from adult tissues and grown in the laboratory, where they can become bone, fat and cartilage cells. Research interest today centers on their effects on inflammation and the immune system.
For the wider picture of how cell-based approaches fit alongside other repair strategies, see what is regenerative medicine. This page covers how mesenchymal cells are defined, where they come from, what researchers study them for and where regulators draw the line between research and approved use.
What mesenchymal stem cells are and why the name varies
The abbreviation MSC is used for several names at once. A review of the field explains that the terms MSC and MSCs have become the preferred acronym for multipotential stem/progenitor cells commonly referred to as mesenchymal stem cells, multipotential stromal cells, mesenchymal stromal cells, and mesenchymal progenitor cells. Readers will therefore see “stem cell” and “stromal cell” used for the same population, and the choice of word often reflects how cautious an author wants to be about how much stem-cell behavior the cells show.
The same review says MSCs can differentiate to important lineages under defined conditions in vitro and in limited situations after implantation in vivo. That wording matters. Turning into other cell types in a dish is a laboratory property, and it does not by itself show that the cells will rebuild tissue inside a person.
The International Society for Stem Cell Research places this group among tissue-specific stem cells. In its overview of stem cell types, multipotent stem cells are described as more limited than pluripotent cells, able to develop into more than one specialized cell type in a given tissue but not into every cell type of the adult body. Mesenchymal cells follow that same pattern. The differences between embryonic and tissue-derived cells are laid out in the comparison of embryonic vs adult stem cells.
How researchers define MSCs in the laboratory
Because groups isolated and grew these cells by different methods, early studies were hard to compare. To address that, the Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy proposed a shared definition in a position statement on minimal criteria for human MSC. The statement set out three tests.
- The cells must be plastic-adherent when maintained in standard culture conditions.
- They must express the surface markers CD105, CD73 and CD90, and lack expression of CD45, CD34, CD14 or CD11b, CD79alpha or CD19 and HLA-DR surface molecules.
- They must differentiate to osteoblasts, adipocytes and chondroblasts in vitro, meaning bone, fat and cartilage cell types.
The authors added that the criteria would probably require modification as new knowledge unfolds, and that the aim was to foster a more uniform characterization of MSC and facilitate the exchange of data among investigators. In short, the definition is a lab standard for comparing studies, not a promise about clinical performance.
Where mesenchymal cells come from
MSCs are not tied to a single organ. One review describes them as a rare heterogeneous subset of cells that can be isolated from many different adult tissues. The FDA describes the first approved MSC therapy as made from cells isolated from the bone marrow of healthy adult human donors. Fat tissue is another source named in FDA materials. Research on adipose stem cells looks at that route in more detail.
The word “heterogeneous” in that review is worth noticing. Results from one preparation should not be assumed to apply to another, which is why shared criteria and careful reporting matter in this field.
What researchers study MSCs for
The research focus is on signaling and immune effects more than on replacing tissue cell for cell. The review of MSC cell biology states that MSCs have broad anti-inflammatory and immune-modulatory properties, and that these currently provide the greatest focus of human MSCs in clinical testing. A second review notes that MSCs possess remarkable immunosuppressive properties, suppressing T-cell and NK cell functions and modulating dendritic cell activities.
The scale of testing is large. The same cell-biology review says the medical utility of MSCs continues to be investigated in over 950 clinical trials, and it also says that while much promise is evident, careful new work is still needed. Trials vary widely in design, cell source, dose and condition, so the number of trials is not a measure of how much has been proven.
Regulatory status of MSC products
An approval for one product does not extend to other cell products. On December 18, 2024, the FDA announced that it approved an allogeneic (donor) bone marrow-derived mesenchymal stromal cell therapy indicated for the treatment of steroid-refractory acute graft-versus-host disease in pediatric patients, and called it the first FDA-approved MSC therapy. Graft-versus-host disease is a complication that can follow a donor blood stem cell transplant. The approval covers that specific use and that specific product only.
Approval also does not mean the absence of risk. The FDA release lists the most common adverse reactions in study participants who received the therapy as infections, fever, hemorrhage, edema, abdominal pain and hypertension. It adds that complications such as hypersensitivity and acute infusion reactions, transmission of infectious disease or agents and ectopic tissue formation may occur following treatment. Each of these points comes from the product’s review for one narrow indication, and none of them can be assumed to describe other MSC preparations, which is a further reason the evidence has to be read product by product and condition by condition.
Elsewhere the position is different. The FDA’s consumer alert on regenerative medicine products states that none of the widely promoted products it lists, including those derived from adipose tissue, umbilical cord blood, Wharton’s jelly or amniotic fluid, have been approved for the treatment of any orthopedic condition, such as osteoarthritis. The alert also says none have been approved to treat neurological disorders such as multiple sclerosis or Parkinson’s disease.
So the research literature and the approved-product list answer different questions. A cell type can be intensively studied for inflammation-related uses while a given marketed product has no approval for the condition it is advertised for. Choices about any treatment belong with a licensed physician who knows the reader’s own situation.
The scientific questions that remain are also stated openly in the literature. The cell-biology review says important questions remain to be answered, and it points to developing methods to unlock MSC potential through intracellular and intercellular signaling, biomedical engineering, delivery methods and patient selection. That description is a list of open research problems: how the cells signal, how they are delivered and which patients might respond. Until those are resolved, claims that treat MSCs as a settled solution for a condition go beyond what the published evidence supports.
Frequently asked questions
Are mesenchymal stem cells the same as mesenchymal stromal cells?
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The two names are used for the same population, and the abbreviation MSC covers both. Which word an author prefers often reflects how strongly they claim stem-cell behavior.
What tests define a mesenchymal stem cell in the lab?
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The International Society for Cellular Therapy criteria require plastic adherence in standard culture, a defined pattern of surface markers, and the ability to differentiate into bone, fat and cartilage cell types in vitro.
Is there an FDA-approved mesenchymal cell therapy?
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Yes, one. The FDA approved a donor bone marrow-derived mesenchymal stromal cell therapy for steroid-refractory acute graft-versus-host disease in pediatric patients, and that approval does not cover other uses.
Do MSCs work by becoming new tissue?
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Reviews describe differentiation as occurring under defined conditions in vitro and in limited situations in vivo. Much of the clinical research focuses on anti-inflammatory and immune-modulatory properties instead.
