Less than two years ago, it looked like the ethical debate over human embryonic stem cells might be coming to an end. In November 2007, two research groups, one at the University of Wisconsin-Madison and another at Kyoto University in Japan, announced that they had succeeded in directly reprogramming human skin cells into stem cells. Earlier this year, Canadian and British researchers reported even better news. They have developed a new way to create such cells without using viruses, which pose a risk of producing tumors by damaging the transformed cells' genes.
Yesterday, as many as 700 new stem cell lines were approved for use in federally funded research by the National Institutes of Health, reversing the policy of the George W. Bush administration to restrict funding to just a handful of approved cell lines on ethical grounds.
With the new stem cell lines comes a new round in the debate over cells and souls. "These guidelines encourage researchers to go out and destroy embryos for taxpayer-funded research," Richard Doerflinger of the U.S. Conference of Catholic Bishops told The Washington Post. "You and I were once human embryos, and each embryo has the inherent potential to grow into you and me."
Stem cells derived from skin cells sidestep the ethical concerns that some people have about destroying embryos to produce stem cells because they supposedly cannot develop into human fetuses, much less full-term babies. But is that so? In 2007, a team of researchers led by Massachusetts Institute of Technology biologist Rudolf Jaenisch showed that stem cells from mouse skin cells—induced pluripotent stem cells (iPSCs)—could be grown into mouse embryos. The team achieved this feat by injecting stem cells produced from mouse skin into special tetraploid blastocysts which can produce only placental tissue. Tetraploid blastocysts are produced by jamming mouse zygotes together so that they join to create cells that have twice the DNA of normal cells. The pre-implantation embryos composed of tetraploid cells and iPSCs can develop to term after being transferred into the womb of a surrogate mother. In other words, mouse skin cells can be transformed into mouse embryos. There is no reason to believe that this would not also work for human skin cells.
This development has prompted a biologist and a bioethicist to take on the argument that the "natural potentiality" of human embryos to develop themselves means that they must be accorded the full moral respect we give to adult human beings. As Duquesne University bioethicist Gerard Magill and Stowers Institute for Medical Research president and biologist William Neaves assert in the March 2009 issue of The Kennedy Institute of Ethics Journal (subscription required), "a reprogrammed human cell is not fundamentally different from a nuclear-transfer or natural fertilization zygote in its ability to become a fetus."
They acknowledge that a conventionally produced or cloned zygote makes its own placenta while the reprogrammed skin cells must be provided one. Is that enough to make a difference in the cells' moral status? Magill and Neaves don't think so. They point out that placental cells need signals from embryonic cells in order for a placenta to develop as well. Magill and Neaves go on to speculate about the possibility of using direct reprogramming to create induced totipotent stem cells from skin cells. In this case, the reprogrammed skin cells would have the capacity, if installed in a womb, to produce all embryonic stem cell lineages including placental cells.
Magill and Neaves conclude that the fact that ordinary body cells can be transformed into embryos argues against according a special moral status to early stage embryos, describing them as "matter that is inadequate for the so-called form of human personhood."
Naturally their argument has opponents. In the same journal issue, University of Utah neurobiologist Maureen Condic, Franciscan University of Steubenville bioethicist Patrick Lee, and Princeton University professor of jurisprudence Robert George claim that the details of biology of embryos and iPSCs make all the moral difference. Specifically, they assert that stem cells and iPSCs "will participate in embryonic development if they are injected into an embryo that is incapable of forming [an inner cell mass]." What can they mean by "injected into an embryo"? Are Condic, Lee, and George calling a tetraploid blastocyst—a group of cells that can only become placental tissue—an embryo? It is a very odd kind of "embryo" that can only form placental tissue, which is not tissue that can grow into a body.
The ethical analysis offered by Condic, Lee, and George turns chiefly on the question of whether or not a placenta is "a component of a supportive environment or a component of the embryo." They argue that Magill and Neaves are wrong to say that a "zygote makes its own placenta, while the reprogrammed skin cell must be provided with one, but the placenta never becomes part of the embryo itself." On their view, the fact that a regular zygote (conventionally produced or cloned) can produce the cells that make a placenta is ethically decisive.
If this is so, then it would seem that Condic, Lee, and George must be committed, at least, to the idea that an entity comprised of a tetraploid blastocyst and reprogrammed human skin cells must be the moral equivalent of a conventionally produced embryo—that is, the human equivalent of the mouse embryo produced by the MIT biologists.
Condic, Lee, and George apparently take their final stand when they argue that totipotency, the ability to produce both body cells and placental cells, requires the regulatory molecules in egg cytoplasm. "The oocyte is not simply a source of generic, chemical 'reprogramming factors,' it is a highly structured cell with unique material composition and a unique organization of these components—all of which are required for totipotency."
Perhaps Condic, Lee, and George are right. Maybe true induced totipotent* stem cells are impossible and it will always take the regulatory factors in human eggs to produce viable conventional, cloned, or iPSC human embryos. But do they really want to bet against researchers figuring out what those regulatory factors are and then using them to reprogram skin cells? Back in 1997, it was settled scientific doctrine that mammals could never be cloned; then along came a sheep named Dolly. In fact, Condic, Lee, and George may be wrong when they assert that human stem cells and iPSCs cannot make placental cells. Current data do not rule out the possibility that stem cells and iPSCs may be totipotent.
If it turns out that it is possible to reprogram skin cells directly into complete embryos, one can hope that the increasingly desperate and convoluted arguments against human embryonic stem cell research made by Condic, Lee, George, and other opponents will finally collapse.
As our biological knowledge and prowess increase, it is likely that opponents of stem cell research will one day be relegated to claiming that the moral status of a human cell depends on how a single molecule is positioned on a strand of DNA. More moral insight might be garnered from arguments about how many angels can dance on the head of a pin.
CORRECTION: Condic, Lee, and George are skeptical of the possibility of true induced totipotent stem cells, not true induced pluripotent stem cells.
Ronald Bailey is Reason magazine's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is now available from Prometheus Books.