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Tuesday, December 07, 2004

Eyes Without a Face, Part II: Fangs Without a Mouth 

William Saletan of Slate reports that the President's Council on Bioethics has put forth a couple of new proposals that could break the stem-cell impasse. One is quite conventional: take stem cells only from embryos that have just "died" (assuming that the moment of "death" can be successfully defined for an entity that is only potentially "alive"). The second is less conventional -- a little on the hairy side, in fact. If the presumed sanctity of unborn human life precludes the harvesting of stem cells, why not take them from a custom-tailored organism that's, uh . . . not . . . quite . . . human?
The distinction [council member William] Hurlbut wants to draw and exploit is between a whole embryo and its parts. He quotes Thomas Aquinas to the effect that an animal's life resides in its wholeness. "A living being is more than the sum of its parts," he argues. But while humanity may lie in the whole, utility may lie in the parts. As Hurlbut puts it in his presentation paper, "Incompletely constituted or severed from the whole, subsystems with partial trajectories of development may temporarily proceed forward with a certain biological momentum." In other words, the parts of an embryo—or the parts that normally would become an embryo—might produce stem cells, even if, to avoid the moral problem, we kept these parts incomplete or severed.

How could we create functioning parts of an embryo without the whole? By turning off one of the genes that guide embryo formation. Hurlbut's first choice is the human equivalent of cdx2, the gene in mice that directs the formation of the placenta. Without cdx2, the embryonic mouse cells divide but fail to take the shape of a mouse. The plan would be to follow the recipe for cloning—put the nucleus of a body cell into a gutted egg cell—but turn off cdx2. Then, once the cell begins to divide, reactivate the gene, too late to organize the embryo but early enough to make stem cells.

It sounds perfect, until you look up at the projection screen. Hurlbut has modeled his recipe on "aberrant products of fertilization" and teratomas, which, he explains, are "germ cell tumors that generate all three primary embryonic germ layers as well as more advanced cells and tissues, including partial limb and organ primordia." Limb and organ primordia? Yep, that's what's on the screen: a ball of tissue, grown inside some poor creature, full of bits and pieces of what would have been a body. Another slide shows an X-ray image of somebody's back. To the left of the spine, you can see a cluster of white spots that look like teeth. And that's exactly what they are, all dressed up and no place to chomp. You wanted disorganized development? You got it . . . .

Paul McHugh, one of the council's moderates, finds the idea gruesome. He calls the proposed creation a "weird genetic hybrid" that is "very embryolike" and has been engineered to die. Hurlbut replies, coldly but correctly, that according to the technical definition favored by opponents of stem-cell research, the thing can't die because it was never alive. Leon Kass, the council's chairman, agrees, describing the thing as a "re-engineered entity" that is "embryolike" but not "embryonic." Michael Gazzaniga, the council's most liberal member, calls Hurlbut's strategy a perversion of science. Instead of tinkering with language to fit biology, he observes, Hurlbut is tinkering with biology to fit language.
Now here's a research project we can get behind. Admittedly, we are no experts, and we cannot predict whether Dr. Hurlbut's sad, deformed creations might ultimately show us the way to a cure for spinal injuries or neurological disorders. But we remain cautiously optimistic that one of them might kill him, escape from the lab, and give Spider-Man all he can handle in installment #4 of the popular superhero franchise.

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