How Do Mesenchymal Stem Cells Actually Work?

If you have been reading about stem cell therapy for a sore knee or an autoimmune condition, you have probably come across the phrase "mesenchymal stem cells," or MSCs. Most clinics talk about them. Fewer explain what they actually do once they are inside your body.

The answer is more interesting than "they turn into new cartilage," and it affects how you should judge what a clinic tells you. If you want the basics first, start with our guide on what mesenchymal stem cells are, then come back here.

The old idea: stem cells become new tissue

For years, the popular explanation was simple. You inject MSCs into a damaged knee, they turn into cartilage cells, and the cartilage grows back. It is an easy story to tell, which is probably why it stuck.

MSCs can become bone, cartilage and fat cells in a lab dish, so the idea was not unreasonable. The problem is that a dish is not a joint. Once researchers started tracking what happens after cells are injected, the picture got messier. Many of the cells do not stay put, and very few appear to become new tissue.

What researchers think now: they send signals

The current view is that MSCs work more like a team of site managers than a crew of bricklayers. They release growth factors, small messenger particles and other molecules that change how nearby cells behave. This is often called paracrine signaling.

Here is what those signals are thought to do:

• Calm inflammation. MSCs can influence immune cells and shift the local environment from "irritated" toward "settled." This is a big reason they get studied for rheumatoid arthritis and multiple sclerosis, where the immune system is part of the problem.

• Protect cells that are struggling. Some signals may help stressed cells survive instead of dying off.

• Support blood supply. Growth factors from MSCs may encourage new small blood vessels, which healing tissue needs.

• Limit scarring. In some tissues, MSC signals appear to reduce the buildup of stiff scar tissue.

Most of this evidence comes from lab and animal studies, plus smaller human trials. It is promising, but it is still developing.

Why some scientists want a new name

One of the best known researchers in this field, Dr. Arnold Caplan, has argued that the name "mesenchymal stem cells" misleads people. In a 2017 paper in Stem Cells Translational Medicine, he suggested "medicinal signaling cells" would describe their job better. You can read it here.

His point is that the word "stem" makes patients picture cells rebuilding a damaged part of the body. That is not what the science mostly shows, and it sets expectations too high.

What this means if you are comparing clinics

Understanding the signaling idea gives you a better filter for the marketing you will see.

Be careful with "regrows your cartilage" claims. If a clinic promises that your knee osteoarthritis will be reversed, that is a stronger claim than the research supports. A more honest pitch is that the treatment may reduce pain and inflammation for some people. Results vary, and no outcome is guaranteed.

Ask where the cells come from. MSCs can be taken from fat (adipose-derived), from bone marrow, or from umbilical cord tissue. The source affects how many cells you get and how they behave. It also matters whether the clinic uses your own cells (autologous) or screened donor cells (allogeneic), because the rules differ from country to country.

Ask about cell counts and the protocol. How many cells, how many sessions, and where they are delivered all change what you are paying for. Vague answers are a red flag. We cover more of these in ten warning signs a stem cell clinic may not be trustworthy.

Know that cells are not the only option. Because so much of the benefit seems to come from signals, some clinics now offer exosome therapy, which uses the tiny messenger particles instead of whole cells. The research there is even earlier, so ask what evidence a clinic can actually show you.

A quick checklist before you book

1. Ask what the clinic expects the treatment to do, in plain language, and notice whether the answer is realistic.

2. Ask where the cells come from and how many will be used.

3. Check accreditation and the physician's background.

4. Read patient reviews that describe the whole experience, not only the results.

5. Take everything to your own doctor before you commit.

You can browse MSC therapy clinics side by side, or use Find a clinic to shortlist by condition, location and budget. If you are curious how we vet listings, our methodology page explains it.

The bottom line

MSCs probably help less by becoming new tissue and more by changing the conditions around damaged tissue. That is encouraging, but it is a different promise from "your joint will grow back," and the research is still catching up for most conditions. The clinics worth your time are the ones that tell you this themselves.

This article is for information only and is not medical advice. Always speak with a licensed physician before starting any treatment. Individual results vary and no outcome is guaranteed.