Stem Cells Explained, Part 2: Why Do We Care?

To continue on in our discussion of stem cells, I thought it would be worthwhile to look at why stem cell biology is considered so exciting, both by scientists and in the media. I want to stress that this post is highlighting what we hope is possible; later on, I plan to look in more detail about how many of these hopes are realistic, and on what timeline. However, there are a lot of exciting potential uses for stem cells, many of which that are, in my opinion, under-reported in the popular press.

Direct Therapeutic Potential

There are many reasons why stem cell biology is of interest to the medical field, and to scientists in general. The number one reason, and the one which generates the most popular excitement, is the implication for medical treatments and transplant biology.

The future visioning looks something like this: embryonic stem cells in the body can become any human cell type. If we can figure out how to do the same to embryonic stem cells in the lab, we may be able to grow new adult tissues in a dish. Grand hopes include increasing the supply of organs available for transplants (by growing replacement tissues in the lab), and curing injuries that we currently can't treat by tissue donation (such as repairing spinal nerve damage). Contrary to what the media likes to suggest, I don't anticipate we'll be growing organs in a petri dish any time in the next handful of years. However, this is the hope of pluripotent stem cell research, and a major reason that it attracts so much funding.

Meanwhile, adult stem cell research has been around for a lot longer, and has had the benefit of avoiding the controversy surrounding embryonic stem cells (i.e. embryo destruction). The medical applications of adult stem cells are two-fold. The first is similar to embryonic stem cells: transplant biology. Bone marrow transplants were the first stem cell therapy, starting in the 1960s. Bone marrow contains hematopoietic (he-MA-toe-poh-EH-tic) stem cells, which give rise to the whole blood/immune system. For patients with otherwise-incurable blood cancers (e.g. leukemia), or with a significantly impaired immune system (the classic example being boy-in-the-bubble syndrome, otherwise known as Severe Combined Immunodeficiency (SCID)), bone marrow transplants replace the recipient's blood/immune system with cells from a donor, which over time will give rise to a full complement of blood cell types. 

The other advantage to adult stem cells, however, is that they are already in the body. Transplants carry a lot of risk, such as the possibility of rejection, and it would be much better if we could provide therapies using a patient's own cells. Again, this has been done in the blood field: for some types of cancer, patients' own bone marrow can be removed, treated in the lab to remove the cancer cells, and then put back in their own body. (This is called an autologous transplant, which basically means "self".) But there is also hope that if we learn enough about the body's existing adult stem cells, then we might be able to provide drugs which would coax the stem cells into doing what they are there to do anyway, without ever having to do surgery. (A good example here would be the hope that we could trigger neural stem cells to regenerate neurons following an injury.) Again, this field is very much in progress and I'm not claiming that we can do those things now; however, it's one major motivation for studying stem cells.

Cosmetics ad featuring "stem cell
technology" at a Vancouver bus stop

Incidentally, this strategy is also what is being claimed by ads for skin creams with "stem cell technology". Their technology is aimed to help trigger the skin (dermal) stem cells into higher levels of activity, which they hope will then lead to the production of chemicals which improve the skin's appearance. (More on this later too, I promise.)

Indirect Medical Benefits

In addition to the possible therapeutic applications, there are other reasons for studying stem cells. For starters, it's a way to study development. To try and take stem cells and make them into different kinds of mature, specialized cells, we are learning how this process actually happens in the body. (As someone who has worked with embryonic stem cells in the lab, trust me, it's not easy as it sounds.) I know many scientists, and I'd argue that I'm one as well, who would say that understanding how the body works and develops is an end in and of itself. Also, understanding these processes will hopefully make it easier for us to fix diseases that occur when these developmental processes break down in the body, even if an ultimate cure doesn't involve stem cells. Additionally, there are lots of cases where the developmental processes end up going a little haywire, or straight up get hacked: we call it cancer. Cancer develops when cells stop doing their specialized job, and start dividing like crazy. A lot of the tools that cancer cells exploit to do this are similar to the tools that stem cells use to do their job. The hope is that if we understand how these processes work normally, we can maybe figure out how to stop them working abnormally.

Yet another way that the medical field, and specifically pharma, is hoping to make use of stem cell technology is in toxicity testing for new drugs. Before drugs can be approved for use, they need to go through a rigorous process of screening to make sure that they don't have accidental toxic effects on people which outweigh their benefits. Initial toxicity tests are done in animal models and on cells in the lab. However, the better we can make our human laboratory models, the lower the risk of ever putting a harmful drug into humans. The liver is an especially important organ for testing the effects of drugs, because it's the organ that will ultimately process and clear the drug out of the body. Pharma companies are hoping to use embryonic stem cells, differentiated into liver cells (hepatocytes), in order to test the effect of the drugs in vitro ("in glass", i.e. in the lab).