Adult Stem Cells: What Are They Anyway?

Adult stem cells pop up everywhere in the news, and yet, much like most of politics, it’s hard to tell what’s really going on with them. So today I’ll explain the most important adult stem cell concepts for you, the everyday, non-scientist, healthcare consumer. And hopefully won’t bore you to tears in the process.

“Adult Stem Cells” Is A General Term

In my last post I shared the earth shattering fact that “stem cell” is a very broad term, and unfortunately “adult stem cell” has that same designation. Recall that a stem cell, by definition, is any cell capable of copying itself and turning into a different kind of cell.

A regular old stem cell that happens to be found in an “adult” tissue qualifies as an adult stem cell. And the whole adult designation misleads a bit, because it gives the impression of a stem cell found only in adults. But adult stem cells can be found in infants, the oldest person in the world, and everyone in between. Even Keith Richards.

Now, I know you’ve memorized every word of my last blog post. So I don’t need to mention the fact that adult stem cells are found in almost every tissue in your body. And we can just move onto the most important kind of adult stem cell, the mesenchymal stem cell.

Mesenchymal stem cells are the adult stem cell you hear about most frequently right now. But why?

Mesenchymal Stem Cells Are The Most Useful Adult Stem Cells*


I briefly touched on this topic in my last post, but I need to expand. Because these special adult stem cells are awesome.

Mesenchymal stem cells (MSCs) show up for the first time during embryonic development. In this cute animation, early stage embryonic stem cells separate into three layers: ectoderm, mesoderm, and endoderm. We care about the mesoderm layer, which creates muscle, blood and blood vessels, bone, and connective tissue.

During this super complicated process that somehow builds a complete human being almost every single time it happens, the stem cells from the mesoderm don’t disappear. Instead, some remain inside bones and hanging onto the outsides of blood vessels throughout the body, for literally the rest of a person’s life.

These stem cells that came from the mesoderm and made the daunting commitment to stay with us our whole lives are mesenchymal stem cells.

I know, a lifelong commitment seems pretty extraordinary. That must set them apart from all the other stem cells, right?

Didn’t Benjamin Franklin say that 80% of success is just showing up? This must be what he was talking about, eh?

Not exactly. First of all, Benjamin Franklin definitely didn’t say that. And second, MSCs have a variety of properties that make them A) wildly different versus other types of stem cells, and B) very powerful.

Surprisingly, most of those properties aren’t the thing most of you are thinking. You know, the thing where MSCs can make muscle, blood, blood vessels, connective tissue, and bone? Right, not that thing.

I’ve already mentioned the most useful characteristic of MSCs (in this other post): they live and function in the human body during every stage of development. So when we use them medically right now, they have all the signals they need to function correctly*.

*When they come from your body and then go to work in your body. If they come from someone else’s body, that’s a different story.

But, MSCs do so many other helpful things that they almost seem magical. Almost.

Let’s dig into those other properties so you can love MSCs as much as I do. And know when they might come in handy.

MSCs: Adult Stem Cells That Can Make Several Types Of Tissue

In humans ranging in age from embryo to centenarian, MSCs live in bone marrow and on blood vessels. That means you can find them scattered throughout almost every part of your body.

Despite living in so many places, MSCs still qualify as a rare cell type. They make up between 10 and 83 cells for every million cells in bone marrow and anywhere from 200 – 50,000 of every million cells in fat tissue.

So how do they do such a great job making tissue if they’re so rare?

Easy. They respond to homing signals.

Remember how MSCs live in bone marrow and on blood vessels? That makes them sort of like the homeland security surveillance team of the human body. Except they’re more into tissue repair than stopping terrorism. See, MSCs are perfectly positioned to receive signals sent out by damaged tissue. And once they notice them, the MSCs follow those signals to their starting point where they then do the work of tissue repair.

How do we know they actually make new tissue? Well this doctor used MSCs to repair broken bones, and this group used them to fix cartilage defects. This other group used them to repair cardiac tissue, and this one used them to grow blood vessels.

And that’s just a tiny sampling of MSCs creating new tissue in real live humans.

But MSCs do way cooler things that make them the best of the adult stem cells. So let’s talk about those!

MSCs: Adult Stem Cells That Decrease Scarring

We’ve all got scars, right? And I’m not just talking about the emotional ones from learning that no real live person EVER has Disney character hair. Ever. I’m talking about the physical scars (that hurt so much less, Disney).

My most annoying scar lives on my forearm where a piece of rogue chicken wire got me. It bled like a fire hose and scared the crap out of my mom. She thought amputation was inevitable. She wrung her hands and audibly worried about the number of stitches I’d need, but luckily her fears were unfounded.

That tiny cut became a scar that hasn’t changed in the last twenty years.

So what happened?

This awesome TedEd animation explains the process and is much easier on the eyes than all my words, so take a gander.

In short, my chicken wire gash didn’t finish healing. My skin went through all the steps of healing right up until the last phase, remodeling, and just stopped short. This is probably why my mom was always complaining about  me finishing projects.

Anyway, scars are a real thing that happen to most of us, and can sometimes interfere with our day to day lives. You may just not like how a scar looks, or a scar may actually keep you from moving the way you want. Either way,

MSCs are the adult stem cells that can save the day.

When MSCs arrive at the source of the homing signals (broken or healing tissue), they dump proteins onto the cells around them. Some of those proteins help the cells in the area to create tissue more like the surrounding tissue. Less like my shiny smooth forearm scar.

Other MSC proteins also decrease the activity of malfunctioning scar cells. That allows the correctly functioning cells to make more of the new tissue, resulting in a less scar-like scar.

Researchers the world over are currently looking for ways to use this MSC skill to improve severe scar cases. And if you’re reading this right now, you’ll probably see the results of those efforts in your lifetime. #WhatATimeToBeAlive

MSCs: Adult Stem Cells That Kill Germs

I’ve mentioned the basic function of the immune system before, but let’s review. Your immune system has two basic jobs: (1) distinguish between things that are you and things that are not you, and (2) kill things that are not you.

Sounds pretty simple, right? Well then why do we get infections?

Well y’all, sometimes things don’t work the way they’re supposed to. You might accidentally encounter a terrifying and rare bacteria in your neighbor’s hot tub. (That’ll teach you to go hot tubbing after Kenneth Parcell told you hot is the devil’s temperature!) Or you learn the hard way that grandma was wrong, and that milk really was too far gone.

The point is: sometimes your immune system needs an assist. And in some of those cases, MSCs provide the assist. MSCs can supercharge the activity of regular immune cells, and they can fight invading microbes directly. They’ve also been used together with another kind of immune system adult stem cell to cure infected bones, and it worked!

I must have you convinced that MSCs are THE adult stem cell, but I’ve got two more cool properties to share.

MSCs: Adult Stem Cells That Control Inflammation

Inflammation is a natural part of healing. In fact healing can’t happen without inflammation. So why would we need to control it?
:: coughs loudly ::

Sometimes things don’t work the way they’re supposed to. Instead of channeling the body’s healing cells and proteins to repair and replace damaged tissue, sometimes inflammation just hangs out doing nothing. Except causing trouble.

Don’t worry though, MSCs can wrangle their fair share of troublemakers.

MSCs actually make more inflammation controlling proteins than I would ever list here. But just for scale purposes, let’s say it’s on par with the number of ice cream flavors you can find at a Baskin Robbins.

MSCs are so good at controlling inflammation that they’ve been used (in very small studies) to treat inflammation related diseases like Crohn’s disease and Lupus.*

*Please note, these are early stage studies and not currently available treatments. If you have Crohn’s disease or Lupus, remain incredibly skeptical of anyone offering you a stem cell based treatment. Unless you hear “this is experimental” and “it probably won’t work, but it might,” the treatment likely leans in the direction of shady. And if you’re not sure, just shoot me a message! (Using the contact form, definitely not a gun, please.) <– I’m in Texas, so I have to say it.

MSCs: Adult Stem Cells That Rescue Other Cells

I love weird things, y’all. People, places, books, phrases. If it’s weird, I’m probably into it. And that’s been true since long before I moved to Austin. So don’t go blaming that personality quirk on the city of weird, because it’s all me.

This fact is relevant on account of this last property being my favorite. Because it’s pretty weird and unexpected.

MSCs save dying cells. As a kid fascinated with biology and chemistry, I never dreamed there were cells bumping around inside our bodies just waiting to counsel other cells when they despair of life. And yet, that’s exactly what MSCs do.

See, sometimes things change in your body temporarily. In a heart attack, part of the heart muscle doesn’t get enough oxygen, which makes those heart cells hit the self-destruct button. And just like every over-dramatic villain movie, once self-destruct mode activates, it can’t be undone. Even if the temporary change has been addressed, and the heart muscle has oxygen again.


Yes, you guessed it, your new favorite adult stem cell can save the day again.

MSCs do a couple of different things that de-activate a cell’s self-destruct mode. They directly touch dying cells (like a hug, but for cells!), and they make proteins that prevent self-destructing cells from finishing the job.

Isn’t that cool?

Sometimes the results after MSC treatment seem like they’ve lasted way longer than they should have. And I think this property accounts for that. By saving some of the dying cells, the MSCs have a much longer lasting effect on the tissue. Because those saved cells can live for months or even years in some cases, all the while contributing to better tissue function and a happier human owner.

Alright y’all, that was a whirlwind. If you stayed with me this whole time, thanks for coming along!

If you’re still with me, let’s walk back through all that info real quick. And probably leave you wondering why the next three sentences weren’t this entire post.

Just a quick recap:

Adult stem cells are regular stem cells found in an “adult” tissue, which means all humans have them.

Mesenchymal stem cells are the most useful adult stem cells, because they live and work in our bodies at every stage of developmentthey make new tissue, decrease scarring, control inflammation, kill germs, and save dying cells.



Do you have questions about adult stem cells that I didn’t answer? Or did I make things super confusing? Let me know in the comments, or use the contact form to complain directly in my inbox!

Thanks for reading, y’all!

Photo by Louis Reed on Unsplash