What are mesenchymal stem cells?

Mesenchymal stem cells (MSCs) are multipotent cells that can develop into bone, cartilage, and fat cells. They also release molecules that help calm inflammation and regulate the immune response. MSCs can come from bone marrow, fat, or umbilical cord tissue.

These cells are used in most joint and pain injections sold today and are part of the broader field of regenerative medicine. However, these uses are not FDA approved.

This explainer looks at what MSCs are, where they come from, why clinics use them, and what the evidence does, and does not, show. It does not claim that MSCs repair, regrow, or cure anything. It reflects the science and regulatory status as they stand in 2026.

What MSCs are

Stem cells are the broad category of cells that can multiply and develop into other, more specialized cell types. Mesenchymal stem cells (MSCs) are one specific adult stem cell type within that category, marked by two defining traits. First, they are multipotent, meaning they can become a limited set of cell types: bone, cartilage, and fat. Second, they are strong signalers.

That second trait now drives most research interest. MSCs release anti-inflammatory and immune-regulating molecules, which is why early trials tested them in graft-versus-host disease and autoimmune conditions. As our how it works guide explains, this signaling role matters more than direct tissue-building.

MSCs are not embryonic stem cells. Embryonic stem cells are pluripotent, meaning they can become nearly any cell type in the body, while MSCs are multipotent and limited to a narrow set: bone, cartilage, and fat. That limit is important when a clinic implies MSCs can rebuild a whole joint.

Stem Cells or Stromal Cells?

The scientific literature calls them mesenchymal stromal cells. Clinic marketing calls them stem cells. Both names point at the same cells. In 2005 the International Society for Cellular Therapy, now the International Society for Cell & Gene Therapy, said these cells do not meet accepted criteria for stem cell activity and should be called multipotent mesenchymal stromal cells. The society followed in 2006 with minimal criteria a laboratory must meet to use the name. Arnold Caplan coined the name in 1991. In a 2017 paper he asked the field to stop calling them stem cells at all, because the label oversells what the cells do.

A laboratory has to show three things before it can call a cell an MSC:

• The cells stick to plastic in standard culture conditions.
• At least 95 percent carry the surface markers CD105, CD73 and CD90, and almost none carry CD45, CD34, CD14 or CD11b, CD79 alpha or CD19, or HLA-DR.
• The cells can be turned into bone, cartilage and fat cells in the dish.

A clinic injecting a same-day preparation has run none of those tests, so “MSC injection” on an invoice describes an intention rather than a verified cell type. Ask what testing was done on the batch going into you.

One more cell type gets confused with these. Induced pluripotent stem cells are ordinary adult cells reprogrammed in a lab back to an embryo-like state, and they can become nearly any tissue. They are also expensive, slow to make, and confined to research, so no clinic is selling you one. Our sources guide covers how they differ from the adult cells clinics use.

Where MSCs come from

MSCs come from several tissues, and the source changes their behavior, cost, and risk. Three sources dominate clinical use.

Our adipose guide and umbilical cord guide cover the second and third rows in full, including how each is harvested and what each costs. Smaller amounts of MSCs also exist in dental pulp, placenta, and amniotic tissue. Research summarized on PubMed finds umbilical cord MSCs proliferate fastest and show the fewest senescence markers, while bone marrow MSCs have the deepest track record.

Autologous vs donor MSCs

The source also decides whether the cells are yours or a donor’s. Bone marrow and fat MSCs are autologous, taken from your own body the same day. Umbilical cord MSCs are allogeneic, from a donor.

Autologous cells carry almost no rejection risk. Donor cells are marketed as “younger and stronger,” but potency claims do not remove the donor-related infection and immune questions. Neither source is proven better for joints.

Why clinics use MSCs

Clinics use MSCs mainly for their anti-inflammatory signaling, not because the cells become new tissue. The pitch has quietly shifted over the years, and knowing the current version helps you read a claim.

The older pitch was that MSCs “turn into” fresh cartilage. The newer, better-supported view is that MSCs briefly signal to nearby cells and calm inflammation, then clear from the body. That is a weaker, more temporary mechanism than regrowth.

A common failure mode is a clinic page that describes MSCs as “regenerative,” then lets the reader assume that means cartilage regrowth. Regenerative is a research label about signaling potential, not a promise your knee will rebuild.

How MSC Therapy Is Actually Given

MSC therapy reaches a patient by one of two routes, and clinics rarely explain which one they are proposing or why. An intra-articular injection places the concentrate directly into a joint. An intravenous infusion sends it into the bloodstream, where the lungs filter out most cells within hours.

That filtering is the practical difference. Cells trapped in lung capillaries are not reaching a knee, so an infusion offered for a localized joint problem has a weaker rationale than an injection into the joint itself. Clinics favor infusions for systemic claims like autoimmune disease or aging, where no controlled evidence supports the use at all.

Dose is the other question worth asking. Trials typically report cell counts in the tens to hundreds of millions, while a same-day bone marrow or fat preparation yields a far smaller and unmeasured MSC fraction, because the concentrate is mostly other blood and tissue cells. A clinic quoting millilitres rather than viable cells has not told you the dose. Ask for the cell count in writing, and ask whether the product was cultured to expand it, since culture-expanded cells fall under stricter FDA rules.

A course of three infusions spaced weeks apart is the common commercial package. No trial has established that interval or shown a second dose adds benefit over a first, so treat a multi-dose plan quoted before your first treatment as a pricing structure. Our injection procedure guide covers what the appointment itself involves, and the cost guide covers what each route is priced at.

What the evidence shows

The evidence for MSCs is a split picture: safety looks reasonable, but proof of benefit is thin outside a few approved uses. This is the 2026 status.

• Safety in early-phase trials has generally looked acceptable, with mostly mild, short-term side effects.
• Efficacy is the open question. A Cochrane review of stem cell injections for knee osteoarthritis rated the evidence low-certainty and the benefit uncertain.
• Scale of research. More than 1,000 MSC clinical trials have been registered worldwide, yet only about a dozen MSC therapies are approved anywhere, which shows how often promising trials do not translate into approved products.

So MSCs are heavily studied and rarely approved. That gap is the key fact for any patient weighing a joint injection, and our success rate guide shows how it gets hidden behind a clinic’s advertised percentage.

FDA status of MSC treatments

Only one MSC drug is FDA approved, and it is not for joints. In December 2024, the FDA approved Ryoncil (remestemcel-L), the first MSC therapy, for steroid-refractory acute graft-versus-host disease in children.

Every other MSC use sold in US clinics, including all knee, hip, back, and anti-aging injections, is unapproved. The FDA has warned that many products marketed as MSC injections contain few or no living stem cells. Our FDA status page covers what approval means here.

MSCs vs exosomes and PRP

MSCs are often confused with two related products clinics also sell: exosomes and PRP. Knowing the difference helps you understand what you are actually buying.

Exosomes and PRP skip the cells and use their signals or growth factors instead. That is telling: if MSCs mainly work by signaling, some clinics reason, why not sell the signals directly? None of these are FDA approved for joints. Our PRP and exosomes hub and PRP vs stem cell guide compare them in detail.

What this means before you pay

Knowing what MSCs are should sharpen the questions you ask a clinic. Ask which source the cells come from, whether they are living, and what published trial supports that exact use for your condition.

Then set expectations to match the evidence: possible short-term, anti-inflammatory relief for some people, not proven regrowth. Weigh that against a cheaper, proven option, and check the real cost of the full recommended course.

The bottom line

Mesenchymal stem cells are multipotent, strongly signaling cells drawn from bone marrow, fat, or umbilical cord tissue, and they power most joint injections on the market. Their likely role is short-term anti-inflammatory signaling, not cartilage regrowth, and only one MSC drug is FDA approved, for a childhood condition. Treat MSC joint therapy as experimental, check the source and the evidence, and read “regenerative” as a research term, not a cure.

Frequently asked questions

What are mesenchymal stem cells?

Mesenchymal stem cells (MSCs) are multipotent cells that can develop into bone, cartilage, and fat cells, and that release anti-inflammatory and immune-signaling molecules. They come from bone marrow, fat, and umbilical cord tissue. Clinics use them for joints and pain, though most such uses are not FDA approved.

Where do mesenchymal stem cells come from?

MSCs come mainly from bone marrow, adipose (fat) tissue, and umbilical cord tissue, with smaller amounts in dental pulp and placenta. Bone marrow MSCs are the most studied. Umbilical cord MSCs are younger and multiply faster but come from a donor.

Are mesenchymal stem cell treatments FDA approved?

Only one MSC drug is FDA approved: Ryoncil (remestemcel-L), cleared in December 2024 for a graft-versus-host condition in children. No MSC product is approved for knees, arthritis, back pain, or anti-aging. Those uses are experimental.

Why do clinics use mesenchymal stem cells?

Clinics use MSCs mainly for their anti-inflammatory and immune-signaling effects, not because they rebuild tissue. Research suggests MSCs work by signaling to nearby cells rather than becoming new cartilage. The benefit for joints and pain is still unproven in strong trials.

What is the difference between MSCs from bone marrow and umbilical cord?

Bone marrow MSCs are your own cells, most studied, but decline with age. Umbilical cord MSCs come from donated tissue, multiply faster, and show fewer aging markers, but they carry a small donor-related infection and immune risk. Neither is proven superior for joints.

Do mesenchymal stem cells regrow cartilage?

No strong evidence shows MSC injections regrow cartilage in patients. Most injected cells clear within days and act by signaling, not by becoming new tissue. Claims of cartilage regrowth go beyond what current trials support.

Are mesenchymal stem cells the same as the stem cells used in bone marrow transplants?

No. A bone marrow transplant uses hematopoietic stem cells (HSCs), the blood-forming cells that rebuild the immune system. A joint injection instead uses mesenchymal stem cells (MSCs), which form bone, cartilage, and fat. Both types can be harvested from bone marrow, but the National Cancer Institute treats them as separate cell lines with different jobs. See our stem cell therapy vs transplant guide for the full comparison.

What is the difference between mesenchymal stem cells and mesenchymal stromal cells?

They are the same cells under two names. The International Society for Cellular Therapy, now the International Society for Cell & Gene Therapy, asked researchers in 2005 to call them mesenchymal stromal cells, because the cells do not meet accepted criteria for stem cell activity. Journals and cell suppliers now use stromal, while clinic marketing still says stem, which is why the same product can appear under both labels.

Why are mesenchymal stem cells controversial?

Mesenchymal stem cell therapy draws criticism mainly because marketing has moved faster than the clinical evidence. More than 1,000 MSC trials have been registered worldwide, yet only about a dozen MSC therapies are approved anywhere, so the gap between promise and approval is wide. A second objection targets donor sourcing: umbilical cord MSCs come from donated tissue, which raises consent and screening questions distinct from the older embryonic stem cell debate. A third is safety oversight, since unapproved products skip the testing FDA-approved drugs require.