What Are Mesenchymal Stem Cells? A Plain-English Guide

In 2006, a committee at the International Society for Cellular Therapy sat down to solve an actual problem. Labs around the world were all calling different cells "mesenchymal stem cells," using different collection methods, and publishing results that could not be fairly compared to each other. Their fix, published in the journal Cytotherapy, was a short checklist: to count as one of these cells in a lab, a sample has to stick to the plastic of a culture dish under standard conditions, carry a specific set of surface markers, and lack a different set. That checklist, not a marketing description, is still the working definition of a mesenchymal stem cell today.

This guide explains what that means for a patient looking at treatment options, where these cells actually come from, and what current evidence does and does not support.

What a stem cell actually is

Before "mesenchymal" means anything, it helps to know what stem cell means on its own. According to the ISSCR's patient guide, a stem cell is defined by two properties: it can divide to make more of itself, and it can generate specialized cell types, such as skin, muscle, or blood cells.

There are two broad types. Pluripotent stem cells can become any cell type in the body. This category includes embryonic stem cells, which exist only at the earliest stage of development, and induced pluripotent stem cells, which scientists create in a lab by converting an adult cell, such as a skin cell, back into a state with the same properties as an embryonic one.

Tissue-specific stem cells, also called adult or somatic stem cells, are more limited. They generate some or all of the cell types in the particular tissue where they are found, but not every cell type in the body. Blood stem cells replacing cells in the blood and immune system are one well-known example.

So where does "mesenchymal" fit in?

A mesenchymal stem cell is a tissue-specific stem cell, not a pluripotent one. A 2018 review in Stem Cells International describes them as multipotent stromal cells able to differentiate into tissue types such as bone, fat, cartilage, and muscle tissue. Multipotent is the operative word: these cells can become several related tissue types, not any cell type in the body, which is a meaningfully smaller claim than what pluripotent stem cells can do.

Where mesenchymal stem cells actually come from

For a patient comparing treatment options, the source of the cells matters more than the name on the marketing page. Three sources come up most often.

Bone marrow. One of the original, most studied sources. Cells are extracted directly from a patient's own bone marrow, usually from the hip bone, through a needle aspiration procedure.

Adipose tissue, meaning a patient's own fat. Collected through a liposuction-style extraction procedure, then processed to isolate the stem cell fraction.

Umbilical cord tissue. Specifically, a gel-like matrix inside the cord called Wharton's jelly. A 2021 systematic review in the journal Pharmaceuticals describes Wharton's jelly as a routinely discarded birth tissue that contains a higher concentration of these cells per milliliter than other tissue types, and notes that cells from this source can be expanded into many clinically usable doses from a single donation. Collection happens after informed consent from the mother and approval from a local ethics committee, with donor screening covering obstetric factors such as the baby's birth weight, the mother's age, the stage of the pregnancy, and the mode of delivery.

Autologous versus allogeneic: your own cells or a donor's

This distinction shows up on almost every consent form, and it is worth understanding plainly.

Autologous means the cells come from your own body and are given back to you. Bone marrow and fat both fall into this category. There is no donor-matching issue, since the cells are genetically yours, but you do need an extraction procedure first, and the number and condition of the cells you can collect depends on your own body.

Allogeneic means the cells come from someone else, most often donated umbilical cord tissue. There is no extraction procedure for the patient receiving treatment, and because cord tissue can be expanded into multiple doses, cells from one donation can potentially be processed for more than one patient. As with any donor tissue, the screening and processing standards behind it matter, which is part of why regulators pay close attention to how these products are manufactured.

What "cultured" or "expanded" actually means

A small sample of cells collected from bone marrow, fat, or cord tissue is not, by itself, a treatment dose. To reach a usable number, labs often grow that sample in a nutrient-rich culture over a period of weeks, multiplying it into millions of cells. This step is what "cultured" or "expanded" refers to on a treatment description or consent form.

It is not a minor technical detail. It is the exact line Thailand's regulators now use to decide how a cell product is regulated. Under a 2026 ministerial decree, simple processing, cutting, spinning, or separating cells, stays outside the drug framework, while culture-expanded products are classified as medicines requiring formal registration. We cover what that means for a patient in Is stem cell therapy legal in Thailand?

What is actually established, and what is not

It helps to see what real regulatory evidence looks like, because it sets a useful baseline against marketing claims. As of this writing, the US FDA has approved exactly one mesenchymal stromal cell product: Ryoncil, cleared on December 18, 2024, for steroid-refractory acute graft-versus-host disease in pediatric patients 2 months of age and older. The approval rested on a single-arm trial of 54 children, not a placebo-controlled study, in which 30 percent had a complete response and 41 percent a partial response 28 days after treatment.

That is one product, for one narrow pediatric condition, based on one named trial with its own limits. It is the clearest illustration available of how far current evidence for this cell type actually extends.

For nearly everything else these cells are used for today, joint conditions, general wellness infusions, anti-aging protocols, the ISSCR's own patient guide is direct about the gap: beyond certain blood cancers and immune conditions, "there are very few conditions for which stem cell-based therapies are established" with convincing evidence of safety and efficacy. Most other current uses are either being tested inside a registered clinical trial, which the ISSCR calls investigational, or offered outside any trial process at all, which it calls unproven and warns "can cause physical, psychological, and/or financial harm."

Why this matters if you are weighing treatment

A consent form full of words like "multipotent" and "allogeneic" can feel intimidating, and it is fine to ask a clinic to explain any word on it in plain language before you sign anything. None of the biology above tells you whether a specific treatment is right for your condition. It gives you the vocabulary to ask better questions: what is the source of these cells, are they autologous or allogeneic, have they been cultured or expanded, and what specific evidence exists for the condition you actually have. For the price side of those questions, see How much does stem cell therapy cost? Thailand price guide 2026. For the legal side, including what "investigational" requires in Thailand specifically, see Is stem cell therapy legal in Thailand?

Frequently asked questions

What is the difference between a stem cell and a mesenchymal stem cell?

Stem cell is the broad category: any cell that can copy itself and turn into specialized cell types. Mesenchymal stem cell is one specific kind within that category, limited to becoming tissues like bone, fat, cartilage, and muscle, not any cell type in the body.

Are umbilical cord stem cells taken from a baby?

No. They come from the umbilical cord itself, specifically the gel-like tissue inside it called Wharton's jelly, which is routinely discarded after birth. Collection requires the mother's informed consent and screening of factors like gestational stage and delivery mode.

Is my own fat a good source of stem cells?

Fat tissue is one of the two most commonly used sources for a patient's own mesenchymal stem cells, alongside bone marrow. "Good" depends on the specific use and your own health, which is a question for a physician reviewing your case, not something this guide can answer generally.

What does "expanded" or "cultured" mean on a treatment consent form?

It means the cells collected from you or a donor were grown in a lab over a period of time to multiply their numbers before being used. This step involves more processing than simply separating or spinning cells, which is why regulators increasingly treat expanded cell products differently from minimally processed ones.

Has any mesenchymal stem cell treatment actually been approved by a major regulator?

Yes, one. The US FDA approved Ryoncil (remestemcel-L) on December 18, 2024, for steroid-refractory acute graft-versus-host disease in children 2 months and older, based on a single-arm trial of 54 patients. It is the only FDA-approved mesenchymal stromal cell therapy to date.

What is the difference between autologous and allogeneic stem cells?

Autologous means the cells come from your own body and are given back to you, which requires a collection procedure first. Allogeneic means the cells come from a donor, most often umbilical cord tissue, so there is no collection procedure for the patient, but donor screening and processing standards matter instead.