Saturday, July 25, 2009

The Stem Cell Debate is Over?

These were the words of Dr. Oz to Michael J Fox on Oprah earlier this year. Sadly, though the science is settled, the debate rages on. Hopefully that can be changed.

I recently came across this article, which claims that Chinese scientists have created stem cells that are identical to embryonic stem cells. Here's the equivalent article form the Washington Post. So, what did they do, and what does it mean? This isn't supposed to be a comprehensive explanation of the topic, but I hope it will help you to understand the issues. For a more in depth discussion of the science involved you can visit the National Institute of Health. Of course, their information ignores some issues and is a bit out of date on some points, but you get the idea.

What is a Stem Cell?

You are composed of cells, trillions of them. Those cells are all 100% genetically identical, and uniquely you. However, most of your cells have special duties. Cells specialize to perform those duties by differentiating. That means that although they have the same DNA they express it differently. It like everybody having the same song book but reading different musical parts to sing in harmony. So instead of having all identical cells, you have a brain made of brain cells, a heart made of heart cells, skin made of skin cells and so on. If your liver fails, you can't take a kidney and move it to the right place and have it turn into a new liver. Stem cells are cells that aren't differentiated, so they can become other cells.

The hope of stem cell research is that we can learn to grow these cells and teach them to become other cells at will. So, when you have tissue damaged by disease or accident, you can regrow that tissue and replace the damaged part. By regrowing pancreatic cells we could potentially cure diabetes. By regrowing nerve cells we could potentially cure paraplegics, or parkinson's disease patients.

Why are there different kinds of Stem Cells?

Most Americans think (and have been encouraged to think) that stem cells are stem cells. It is unfortunate that the media often doesn't even report what type of stem cells they are talking about, because there are three different kinds, and there are very important differences between them. Let's talk about the different kinds.

At one time you were composed of just one cell, and all of the cells you have now came from that one cell that was you. So, at some point you had cells that could grow into any part of you. These cells are called "stem" cells, because all of the different kinds of cells stem from them. These cells are called embyronic stems cells because they are present in embryos.

Even today, if you get a cut in your skin you can grow new skin over the cut (as long as it's not too big). If you have a heart attack your heart can regenerate new muscle. The cells that can regenerate are also stem cells, but for some reason they can only grow into certain types of tissue. For instance, stem cells from your heart can grow heart tissue but can't grow brain tissue. These cells are called adult stem cells, because they are present in adults.

As I've mentioned, all of the cells in your body have the same DNA. That is to say, they all have the complete song book. So why can't we get the cell to look at the whole "book"; to "undifferentiate", or go back to the state it was in before it became a heart cell or a skin cell? It turns out we can. Scientists have learned to take skin cells and make them revert into stem cells. Cells produced this way are called induced pluripotent stem cells or iPS cells.

There are other types of stem cells, such as fetal and amniotic stem cells, but these are the "big three" that make the news all the time.

What's the difference?

There are drawbacks to each of these types of stem cells. The biggest drawback to embryonic stem cells is not a scientific one, but an ethical one. To extract these cells, an embryo, which is a whole living human being, must be killed. This makes them sort of like, well, Dracula, where the living are sacrificed and their "life essence" extracted to provide the vampire with life. Some scientist, politicians, actors, etc. would have you believe that an embryo is not a living human being, yet it is clearly human, or we could not use the cells, and clearly living, as we are extracting living tissue from it. In fact, just read an embryology textbook and you'll see that they are wrong.

Other scientists et. al. would argue that we'd only kill embryos that nobody wants anyway. That argument doesn't hold water ethically, as it's the same one used to justify the genocide of Jews in Nazi Germany. There is no ethical way known to obtain embryonic stem cells, and scientist, politicians - well, you know how - who say they will use them "ethically" are flat out liars, or completely ignorant of the facts.

OK, that's one drawback, but there are also scientific problems with them. The major scientific problem is related to the ethical problem; they are not your cells. If you attempt to cure diabetes by growing pancreatic cells, you are not growing your own body's pancreas, you are growing someone else's, and so you have all the problems of tissue rejection that people who receive transplants have. Then there is the fact that they don't behave like your own cells, and often go haywire in the environment of your body, turning cancerous.

The state of the art in embryonic stem cells is exemplified by the articles I quoted in an earlier post on stem cells. We see doctors struggling to find a way to keep the stem cells from forming dangerous tumors.

OK, what about adult stem cells? We can take adult stem cells from your body, grow them until we have as many as we need, and insert them back into the body, where they will happily grow into healthy tissue. There is no issue with rejection or cancer, because it is your own tissue. In fact this has been done successfully for many disease over the past years. The drawback is that adult stem cells can only become certain types of tissue, not any type. Therefore you need to take stem cells from the organ that needs to be repaired. Thus, to repair heart tissue, part of your heart needs to be surgically extracted. Also, it is not known how to extract stem cells for some types of tissue. So, while there have been many success stories (in fact, all of the successful "stem cell cures" discovered so far use adult stem cells), there's still a lot of work to be done.

Finally we come to iPS stem cells. These cells are the best of both worlds. Like adult stem cells, they are your own tissue. Like adult stem cells they are ethically "good". Like embryonic stem cells they seem to be able to become more than one type of tissue. So, what's the down side? The key word is seem. Nobody was sure if they coudl actually become any cell, or if embryonic stem cells still had an "edge" in that department.

What does the article really say?

The article I mentioned at the beginning of this post describes experiments done by researchers in China. They took iPS cells from a mouse and grew another complete mouse from those cells! If you can grow a complete organism from a stem cell, then clearly those stem cells are the exact equivalent of embryonic stem cells, and they can become any kind of tissue. This is definite proof, since if the cells couldn't become heart tissue, for example, the resulting mouse wold have no heart and would not live.

Now this does not mean there are no problems with iPS stem cells. We are still learning how to make them and how to use them, but it does mean that there is now no possible reason to use embryonic stem cells for research, as they can be replaced cell for cell by an iPS stem cell that doesn't have the ethical or rejection issues.


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