You’re at a social gathering and someone asks, “So, what do you do?” It’s meant to be a casual conversation starter, but do you ever find yourself taking a mental breath before answering? As an immunologist studying stem cells, I take that mental breath to prepare for a dialogue that usually follows about stem cell research, a field that has captured my fascination… and seemingly many of yours.

Anyone who knows me well can attest to the fact that I like questions; in fact, as a scientist, my livelihood relies on it. I enjoy asking questions, and I admire those who ask questions in return. Someone recently continued our “So, what do you do?” chat by asking, “What even is a stem cell: just a tiny normal cell?” What a great question! What exactly is a stem cell?

When the phrase stem cell is used, there can be a plethora of meanings. There are two broad categories of stem cells: embryonic and adult stem cells. Embryonic stem cells, or ESCs, are from a very early stage of a forming embryo. ESCs are not yet specific for a certain tissue (referred to as undifferentiated), though have the ability to turn into various tissue-specific cell types upon appropriate stimuli, which is scientifically termed pluripotency. Therefore, ESCs are different from your “normal” differentiated cells (heart, lung, skin, etc.) because they are highly undifferentiated. These ESCs are also self-renewing, meaning they can duplicate themselves over and over.

Adult stem cells are also self-renewing and undifferentiated, though to a lesser extent than ESCs. Adult stem cells are more limited as to what cell types they can become, which is scientifically termed multipotency. Unlike ESCs, adult stem cells are located within various parts of our bodies and nestled next to our normal cells. You have stem cells within your

Used with permission from Microsoft.
Think of stem cells within your body as a spare tire that is lugged around in your car, ready to step in when damage is done to get you back on the road (to recovery).

heart (cardiac stem cells), brain (neural stem cells), skin (epidermal stem cells), gut (intestinal stem cells), bone marrow (mesenchymal and hematopoietic stem cells) and more! The main goal of an adult stem cell is to maintain and repair your tissues. Think of these cells within your organs as that spare tire that is lugged around in your car day after day- ready to step in when damage is done to get you back on the road. By understanding more about the various sources and functions of these adult stem cells, we may better understand their therapeutic potential. Interestingly, there have also been advancements in genetically reprogramming adult cells to mimic ESCs; these cells are termed induced pluripotent stem cells.

“So, what do you do?” I am an immunologist studying adult bone marrow stem cells and trying to understand how those spare tires become functional wheels or, more scientifically, how your bone marrow stem cells function to establish your immune system’s blood cells. So why does this all matter? Well, your immune system is your defense system against our pathogen-filled world, and your blood cells enable you to fight off intruders every single day.

So, are stem cells just tiny normal cells? No, they are extraordinary cells from various sources that have the ability to duplicate themselves and mature into your normal cells. Just like that spare tire has the potential to get us farther down the road, perhaps so will our stem cells.

Now I get to ask, “So, what do you do?”

Edited by Maria Torruella Suarez

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