Where do stem cells come from? Expert answers – The Niche

We often talk about stem cells but there are some pretty basic, important questions that often go unanswered like where do stem cells come from?

Its a more complicated and interesting question than you might think, and some of the answers point to novel ways in which stem cells may be used to treat human diseases. Note that if you are looking for information in a language other than English, my stem cell outreach pages have key facts about stem cells in dozens of languages. The website A Closer Look at Stem Cells is also a good resource.

As a stem cell biologist myself and professor of a research lab working on stem cells for 14+ years, the origins and properties of stem cells are questions Ive been thinking about for a few decades. I enjoy discussing these issues. This post is likely to be of special interest to people or patients interested in stem cells, other stem cell biologist, scientists more generally, and students who want to learn more, perhaps for an upcoming test that will include questions on stem cells and their origins.

Lets start by discussing the adult sources of stem cells, which have great medical promise. In the old days people would widely classify stem cells as adult or embryonic, but this binary way of thinking was in part driven more by antiquated views of good and bad stem cells than by science. For instance, since induced pluripotent stem cells or IPS cells (more on them below) were not made from embryos they were sometimes classified as adult stem cells, which to me doesnt make sense.

Where can adult stem cells come from?

For todays article, well classify adult stem cells as stem cells that are from individuals who are already born but may still be children. In this sense, the term adult is a bit odd, but it seems like the best classification approach. So, for example, stem cells from the bone marrow of a six-year-old girl would be considered adult stem cells.

In addition to the examples above, one theory is that every adult tissue or organ has its own population of stem cells. In this sense, there may be stem cells right now in every part of your body including your brain, kidney, liver, lungs, etc. Scientists periodically debate whether certain organs have meaningful populations of stem cells and it seems like the topics of adult humanbrain stem cells and heart stem cells are particularly contentious. My own sense is that nearly every adult organ has stem cells, but in some cases like in the heart they may either be absent or present in such small numbers that they do not seem at this time to have much significance for health.

These adult stem cells are there for two main reasons. First, they help to maintain that particular tissue or organ. Every day some of the cells in our bodies randomly die even under normal conditions and the adult stem cells help replace those. Second, should a tissue or organ get damaged or become infected, the adult stem cells in it will help it heal.

As their name suggests, embryonic stem cells are largely generated using embryos. In the case of human embryonic stem cells, they are derived from human embryos left over from IVF procedures done to help infertile couples have babies.

These human embryos are at a very early stage of development only a few days after fertilization and have around 100 cells.

They have no specific tissues or organs yet, as those will come much later. Instead they are essentially a ball of mostly uniform cells.

While years ago humanembryonic stem cells were the source of quite a bit of debate, today they are much more widely accepted by the public including in the U.S.

Still, some folks are opposed to making or using human embryonic stem cells.

Embryonic stem cells can also be made through a process called somatic cell nuclear transfer or SCNT. In this process, the nucleus of an adult cell is transferred into an egg (or one-cell embryo) that has had its own nucleus removed. Sometimes if this all goes right the hybrid cell will go on with development normally even though it has the nucleus from another cell.

Such cloning is widely used to make more farm animals. To my knowledge it has never been used to make a human clone, but the topic often comes up. If the SCNT procedure is done with human cells, instead of trying to make a cloned person those early embryos can instead be used to make human embryonic stem cells, which could be very useful in medicine. For this reason, this process is sometimes called therapeutic cloning. It remains unclear whether SCNT-derived human embryonic stem cells are really needed given the innovation of IPS cells, which Ill now discuss.

Induced pluripotent stem cells or IPS cells were first reported using mouse and human cells in 2006 and 2007, respectively. Where do IPS cells come from? They are made through a process called reprogramming, which in a nutshell means that adult cells are transformed into IPS cells using specific molecules that have the power to convince cells they are like embryonic stem cells.

One analogy is that cellular reprogramming is sort of like installing a new operating system on your computer to make it function differently, but in the case of cells this new operating system does physically changes the resulting cells as they make new proteins, RNAs, etc.

The bottom line is that the resulting IPS cells act just like embryonic stem cells, but no embryo is needed to make them. The IPS cells can be differentiated into just about any cell type for use as therapies including making adult stem cells.

An increasing number of clinical trials are ongoing using IPS cells across the globe including both here in the US and in Japan, just to name two hubs of IPS cell work.

A related method called direct reprogramming is also in the mix. Direct reprogramming (also called dedifferentiation) in a way skips the IPS cell step.

In this way, typical adult stem cells like from blood can be directly changed into totally different kinds of cells like brain cells without having to go through the IPS cell step.

Yes, us humans are amazing in some ways with our big brains and such, but when it comes to stem cells some other animals are way cooler than us. Certain species have far more stem cells than we do and even what seem like non-stem cells in these animals can convert to a stem cell-like state under stress. While some researchers believe that in humans some non-stem cells can change into stem cells under stress like disease, this remains a more controversial idea.

One of the more amazing creatures from a stem cell perspective is the type of amphibians called axolotls. You can see a picture of an axolotl above. If they are attacked by a predator deep within their habit like a pool in a cave in Mexico and lose an arm or a leg, they have so many stem cells that they can regrow a new arm or leg. They could also regrow a new part of their head or of a damaged organ in some cases. By doing research on such creatures the hope is that it will unlock the stem cell-based regenerative potential of humans too.

In a way, whats more important than where particular stem cells come from is what those stem cells can do. A second important question goes hand-in-hand and that is what risks particular stem cells might pose. Overall, what biomedical scientists and patients should focus on is the ratio of potential benefit to potential risk. still, I understand that the source of stem cells is an important issue as well to many people.

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Where do stem cells come from? Expert answers - The Niche