Map of life expectancy at birth from Global Education Project.

Wednesday, April 02, 2008

Some technical background

Returning now to Stem Cell Century, Prof. Korobkin argues along very much the same lines we have argued here about the moral status of the zygote and the embryo. It seems apparent that the qualities that give a creature moral status have to do, first of all, with sentience. We respect the rights of others because they can perceive, and feel, they are self-aware. Hence we generally agree, for example, that someone who is brain dead but whose body continues to live thanks to a respirator and a pacemaker is not really a living human being and that it's morally permissible to harvest the person's organs and turn off the machines.

Now, let us consider the process for obtaining human embryonic stem cells (HESCs). At the time Stem Cell Century went to the printer, there was one way it was already being done, and another way that seemed just over the horizon which offered potential advantages for medical applications. Since the book was published, there are indications that a third method may be possible, one that Prof. Korobkin did not consider at length because it did not yet seem plausible.

Both the methods he did consider require the creation of human embryos. They do not actually necessarily require the destruction of human embryos in principle, but the embryos in question are likely to be destroyed because nobody has any other use for them.

The first method is to use embryos created by in vitro fertilization. There are tens of thousands such embryos available that were created for infertile couples. Fertility clinics always create lots of extras because they want to select the best looking specimens, and because implantation can fail and they may need to try again. The surplus embryos are generally destroyed eventually, when the couple no longer has any potential use for them. So, just take one out of the freezer, thaw it out, remove one or more cells, and culture them.

This works fine for research purposes up to a point, but it will not be ideal should we come to actual therapeutic applications. The promise of HESCs is that they are "pluripotent" -- they can potentially yield every kind of human cell, and hence be coaxed to grow into replacement organs or tissues of any kind, thereby repairing the damage from a wide range of injuries or diseases. The problem with cells harvested from fertility clinic leftovers is that they will not be a genetic match to the recipient, and hence you have the same problems you do with organ transplants -- rejection by the host's immune system and the need to take immunosuppresive drugs.

The solution is a procedure called Somatic Cell Nuclear Transplant, or therapeutic cloning. This means taking the nucleus out of one of your cells -- a so-called somatic cell, any of the specialized cells of the adult body, probably a skin cell -- and inserting it into an ovum from which the nucleus has been removed. This is how Dolly the sheep was created. A full complement of paired chromosomes inside the cellular environment of an ovum equals a zygote, in other words you now have the equivalent of a fertilized egg, and with luck, it will begin to develop into an embryo, an embryo whose nuclear DNA is identical to that of the person who donated the nucleus.

The downside to this is that you need a supply of ova, and harvesting them from humans is painful and not 100% risk free. Some ethicists -- among them notably the feminists at Our Bodies, Ourselves, but others as well -- aren't comfortable with creating an extensive market in human ova. I won't get into that, but to answer Roger's question, that's why the researchers in the UK did SCNT with a human nucleus and bovine ovum -- to eliminate the need for human ova in doing this procedure.

So, now you end up with HESCs which it is hoped can be grown into organs or tissues that can be implanted in the person who donated the nucleus, which the person's immune system will perceive as self, eliminating the rejection problem. Yup, a brand new liver or new dopamine producing cells in the brain or whatever you might need, and it's really yours. Not quite -- the mitochondria, specialized organelles in the cells which are the engines of cellular metabolism, have their own DNA, which comes from the egg donor, human or, just maybe, cow. No matter, the immune system doesn't know the difference.

Okay now. Embryos are not sentient, they can't perceive, think or feel, they have no self-awareness. In fact, we are talking about balls of just sixteen cells that are nearly invisible to the eye. The people who did the trick with the cow ovum have no intention of allowing the embryo to develop beyond that stage, and even if they did, you would have a human embryo, that assuming it was otherwise normal would grow into a normal human being in every respect, except that a genetic test of its mitochondria would reveal something strange. (Conceivably bovine mitochondria are more or less efficient than human mitochondria and you would have some difference in metabolic rate or athletic ability as a result, but as far as I know that is not the case.)

So, two questions:

What, if anything, is morally wrong with harvesting HESCs from fertility clinic leftovers?

Is there something morally different about the SCNT embryos?

And finally (one which Korobkin did not consider), what about the SCNT embryos using non-human ova? Any ethical difference, for better or for worse?

These are matters of intense public controversy, which we will take up tomorrow.

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