Stem cells, Part 1, Introduction and Ethics

We've heard it all by now. "Stem cells will cure everything." "Stem cells kill embryos." "Stem cells are overrated." We hear a lot less about the science of it all. (Oh, no! Not science!) And that's too bad, because it can tell us a lot about the rest of what we hear. Let's get right to it.

Think of stem cells like tiny organ transplants, and you'll be pretty close to grasping the essentials. If you could grow a new heart from your own tissues, there wouldn't be any need to worry about transplant rejection. That's how adult stem cells work when used in the adult they came from. Used in another person, they're like a transplant. Anti-rejection drugs need to be taken for the duration.

So, conceptually, stem cells are simple. Politically, it's another matter. I'm going to try to give the Cliff Notes version of both the science and my take on the ethics, as well as what we can realistically expect in the way of cures in the near term. I tried, I really tried, to make it as short as possible, but it's going to have to be in three installments. (Part 2: embryonic stem cells; part 3: adult stem cells; with related ethical issues in each section.) Come along for the ride, stay for the links.

Intro ... at warp speed

Adult stem cells are a very rare cell type, are hard to grow, and are hard to turn into useful tissues. Embryonic stem cells are easier to find because they're present in much higher proportions relative to the total number of cells in the embryo. The earlier the embryonic stage, the more stem cells, until at the very earliest stages (zygote, blastula) it's pretty much all stem cells. Embryonic stem cells are easier to grow and mature. They can generally be coaxed to mature into a wider variety of tissues.

Also, the earlier the stage, the less developed the immune system is, so the less chance there is of rejection even when the tiny cell transplant is given to an unrelated person. However, due to research restrictions in the US, there hasn't been enough work done here to know whether rejection will be an issue or not. Research is being carried forward elsewhere (Britain, South Korea, Australia, Singapore, China, Brazil, and other countries), but I haven't heard about definitive results on this question yet.

The downside of stem cells is that they can have a nasty tendency to turn cancerous. There's some evidence (eg here, and here) that at least some cancers get their start as stem cells that lose the fine-grained regulation necessary to grow and differentiate into something useful. Instead, they just grow. However, it's still not clear whether so-called cancer stem cells start as normal stem cells or just look like them in some ways.

There are also other down sides. One is that more research really does need to be done. We're just taking the first baby steps in this field.

Some results are being obtained now, and those are therapies for conditions due to malfunction of a single cell type. Things like macular degeneration blindness (retinal cells), replacing insulin-producing cells, and regrowing damaged nerve cells, such as in Parkinson's (simpler, here, and brain or spine damage. But we're years away from growing new organs.

[update, Sept. 4. The hardest thing about writing this post is that the field overtakes me before I have the paragraphs finished. The scuttlebutt is that Israeli researchers have grown a whole heart from embryonic stem cells. So we're obviously not years away from growing new organs. We're not even days away, if that report is right.]

Getting a stem cell to mature into one cell type is just a matter of figuring out how to trigger it and then keep the cells alive while they grow. An organ is dozens (hundreds?) of cell types, all of which have to be perfectly placed together in order to function. At this point, we're miles (but not light years) away from understanding cell growth regulation well enough to know how to do that. Figuring out how far away we are from growing new hearts or limbs is an unknown itself. It's like trying to figure out how far away a mountain peak is when you're hiking. If you're seeing the whole mountain, it's on the horizon and maybe fifty miles away. If you're only seeing the tip, then the base is around the curve of the Earth somewhere and it could be 500 miles away. We don't know enough about growth regulation to know how far we have to go, but we can see the peaks in the distance.

And then there's the huge downside that people get hung up on stem cells, especially when they're from an embryo. So let's just dive right into that issue, since it has to be addressed before anything else can be done.

Ethics of stem cells

The scientific facts are one layer, the ethics a very different layer. Starting with the science, what does the embryo actually feel when dissolved into separate cells in petri dishes?

An amoeba, a somewhat mobile single-celled creature, reacts to a touch at the cell surface by moving away, so it obviously has some way of registering that sensation. Embryonic cells don't react to touch and don't show any internal changes I've ever heard about. Embryonic stem cells are taken within a few days of fertilization, before the cells have differentiated, since that's the whole point. You're trying to get undifferentiated, i. e. stem, cells.

Once a nervous system has differentiated, which is very early on after the first month of pregnancy, the nerves carry signals. There is, at that point, no developed brain to process the signals, but signals can travel through the embryo. The type of signal, though, is very different to what we think of as feeling. The embryo's nerves are unmyelinated. Myelin acts as an insulator. Without it, the nerve carries the signal the same way an uninsulated wire would carry electricity if it were lying on the ground. The wire is still conductive, but the charge won't get very far. In relatively primitive organisms like clams, all nerves are unmyelinated. In humans, some nerves remain unmyelinated, and those holdovers from early evolutionary time can't be anesthetised. So, for instance, if you get novocaine at a dentist's, you can still feel pressure and vibration. Those sensations are coming via unmyelinated nerves, and give you some idea of the level of sensation in an embryo.

(Myelin sheaths start forming in the fourth month of pregnancy when the embryo becomes a fetus. Because of the magnitude of developmental changes between the third and fourth months, biologists use different terms: "embryo" during months one to three, and "fetus" during months four to nine.)

Biologically, the only objective fact about the feelings of embryos is that they have, at most, the nerves of a clam.

Which brings us out of the scientific weeds and into the ethical ones.

It should go without saying that lack of sensation has nothing to do with whether an embryo is considered a person or not. Just because someone has no feeling, such as a person in a coma, is no reason to deprive them of rights. The discussion from this point on tends to be about the relative rights of embryos versus those other beings who can greet you in the morning. (See, e.g., the reasonable summary on Wikipedia.)

I think there's a step missing. First figure out whether an embryo actually is a full human being with all the rights thereof, then start weighing whose rights are more important.

That first step is indeed a hugely difficult question. Books have been written about how to define what is human. Socrates struggled with it. In the Cliff Notes version here, it's enough to say that the more you think about the issue of what actually defines "personhood," the harder it becomes to figure out. (Bit more on that in an earlier post of mine.) The ultimate fallback definition used by some people is having human DNA, but they obviously don't really believe it or they'd want people who've had transplants to carry two ID cards. The more thoroughly you go into it, the clearer it becomes that there simply is no objective way to define what constitutes a human person. Neither science nor logic has an answer to this question.

That means objectively defining who is a human person with full rights is not a difficult question. It is an impossible one.

The only way to arrive at a definition is by examining one's assumptions or beliefs about what is essentially human. I have yet to see a philosophical or religious treatise on the subject that doesn't come down to; "This is what I think (or God thinks) it means to be human." On an individual level, that can take lots of thought and soul-searching, but on a social level, it simplifies the answer to something totally obvious. The operative word is belief. As in anything based on beliefs, it's an answer everyone has to find for themselves. And, as in all matters of belief, everyone has to be free to live according to their own.

So weighing the rights of embryos versus adults is an individual decision, and on that level it can be a difficult one.

But on a social level, the question goes away. The freedom to live according your own beliefs is a fundamental right in free societies. The government has no business telling people what to believe. If I have no problem with stem cell research, I must be able to live according to my lights. Someone who does have an issue with it, must be able to avoid therapies based on it. In a free country, stem cell research really does fall into the same category as abortion. If you're against abortion, then don't have one. If you're against stem cell research, don't use it.

That leaves the question of whether people opposed to stem cell research should have to worry about their tax dollars going to fund it. Ideally, no. But there are also people desperately opposed to war, who have no legal choice but to fund it. People are opposed to the death penalty, and have to fund it. Either all conscientious objectors should be respected, or none should. Exceptions for just one class of objectors look unprincipled to me.

Many people genuinely believe that something with less nervous system than a clam is not a human person. For us, there is nothing ethically dubious about stem cell research.

[Part 2 here. Part 3 here]

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