Mitt Romney was clearly primed for the inevitable question about human embryonic stem-cell research. So when it was his turn in Thursday's debate among Republican presidential hopefuls, he pounced like a grad student taking his orals. MSNBC's Chris Matthews said that "Mrs. Reagan wants to expand federal funding of embryonic stem-cell research. Will that progress under your administration?" To which Romney replied, "It certainly will. Altered nuclear transfer, I think, is perhaps the best course." Matthews apparently had no idea what he was talking about--he seemed to think it was a form of adult stem-cell research, since he fired back, "embryonic; embryonic"--but Romney was ready: "Altered nuclear transfer creates embryolike cells that can be used for stem-cell research. In my view, that's the most promising source."

Leaving aside the "most promising" part, Romney got the science right. Altered nuclear transfer is the latest darling of those in the pro-life camp who have decided that "pro-life" might strike a discordant note if it means that people suffering from Parkinson's disease, spinal-cord injury and other diseases and conditions that might be treated with embryonic stem cells or with drugs derived from stem-cell research are left to suffer and die. By "latest," however, we mean at least two years old. It was in the spring of 2005 that bioethicist William Hurlbut of Stanford University made the case for "Altered Nuclear Transfer as a Morally Acceptable Means for the Procurement of Human Embryonic Stem Cells" in a paper in the academic journal Perspectives in Biology and Medicine; he laid out the same case before the President's Council on Bioethics in December 2004. What makes this technique "morally acceptable" to Hurlbut and others who believe that human life begins at conception and that the 16-cell blastocyst is a human being is that the ball of cells you create in the lab can never develop into a fetus.

Let's back up one step. In all research on human embryonic stem cells, the goal is to obtain, well, stem cells, which have the potential to develop into any of the hundreds of kinds of cells in the human body--dopamine-making neurons to treat Parkinson's patients, say, or insulin-making beta cells to treat juvenile-diabetes patients. In the traditional approach, scientists take a human egg and remove its nucleus. They then fuse that egg with a nucleus taken from any cell in the body--a skin cell, let's say. The egg then begins dividing, just as it would if it had been fertilized by a sperm. Once it reaches the size of a period at the end of this sentence, typically in four or five days, it is a ball of cells whose inner mass consists of stem cells, ready to be studied or propagated for use as therapy. That, anyway, is the hope. But in harvesting the stem cells, you destroy the blastocyst, as biologists call the ball of cells, or "kill the embryo," as pro-lifers say.

Enter altered nuclear transfer. As Hurlbut laid it out to the President's Council, the key difference from the standard protocol is to produce embryonic stem cells "without the creation and destruction of a human embryo." Specifically, you do something to the goop inside the egg (called the cytoplasm), or to the nucleus you fuse with the egg, so that even as the egg starts merrily dividing and producing stem cells, it has no possibility of developing into a fetus even if you implanted it into a uterus and waited nine months. Again, Hurlbut: "[You] construct a biological entity that, by design and from its very beginning, lacks the attributes and capacities of a human embryo."

Is it biologically possible? Mouse studies suggest it may be. If you remove from the cytoplasm proteins or small molecules necessary for embryonic development, then yes, development stops. If you knock out, or silence, genes in the DNA you fused with the egg which are also crucial for embryonic progression, then again, mission accomplished--you'd still have the inner mass of embryonic stem cells, without the moral complication of taking them from an entity that has the potential to develop into a baby. In 2005, Alexander Meissner and Rudolf Jaenisch of the Massachusetts Institute of Technology developed a method to turn off certain genes so that the blastocyst cannot organize itself into a coherent mass. In a 2005 presentation at Johns Hopkins University, Hurlbut compared the result to a model airplane kit without the glue: "you can produce the parts, but no possibility of interaction among the parts." That means the blastocyst is not an embryo, but "a biological artifact."

Some obvious questions arise, however. Biologically, how do you know that what you did to the cytoplasm or the DNA to keep the blastocyst from developing into a fetus did not also alter the stem cells in some way that will keep them from being useful, or normal? At the moment, that remains unanswered.

Ethically, the questions seem even more devastating. Back to that "biological artifact" description. Some Catholic groups have endorsed altered nuclear transfer along the lines Hurlbut has laid out, concluding that a manipulation that removes the blastocyst's potential to become a fetus removes the ethical objections to embryonic stem-cell research. But if it's immoral to create life in the lab, how come it's OK to create defective life--a "biological artifact"? And if it's a sin to destroy human life at the blastocyst stage, why is it acceptable to destroy the possibility of life at the stage just before? You're still "killing" this biological entity in the sense of doing something to it that will keep it from becoming a baby--just as harvesting its stem cells keep it from becoming a baby.

Maybe Romney and others in the pro-life camp find the distinction between blastocyst and pre-blastocyst meaningful; the former has a moral status and the latter does not. But Romney does not find the distinction between fertilized egg and fetus meaningful--that is, they have the same moral status. We'll see how that that flies on the campaign trail.