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'Parthenotes' Expand the Debate on Stem Cells
By Rick Weiss
Washington Post Staff Writer
Monday, December 10, 2001; Page A11
When is an embryo not an embryo? It's a question fit for a Zen master, but it's one that will have to be answered by federal bureaucrats, researchers and ethicists as biologists explore the weird world of parthenogenesis.
Parthenogenesis, from the Greek word for "virgin birth," is an unusual mode of procreation in which, to put it plainly, the male might as well find something else to do. Female aphids and turkeys, and certain female reptiles, are among the critters that can reproduce this way. Their eggs can divide on their own as though they had been fertilized by a sperm, then go on to develop into embryos and offspring.
Using chemicals that mimic a sperm's arrival, scientists in recent years have triggered parthenogenesis in the eggs of a few mammals, including rabbits and mice, but the resulting "embryo" has never developed beyond the early fetus stage. Now, with the announcement two weeks ago of the first successful induction of parthenogenesis in human eggs, the Zen riddle arises: Is the resulting doomed entity an embryo, with the same moral standing that some people confer upon conventional and cloned human embryos? Or is it something else -- perhaps something that scientists can create and destroy with legal and moral impunity?
This question calls out for an answer -- at least on the level of public policy -- because the products of human parthenogenesis, which scientists call not embryos but "parthenotes," may prove to be a valuable source of human embryonic stem cells. Stem cells have the capacity to morph into all kinds of cells and tissues, and may someday prove useful in the treatment of degenerative diseases such as diabetes and Parkinson's. There is a roaring political and ethical debate about the use of human embryos as sources of stem cells. Should a similar debate surround work on parthenotes, although there is overwhelming evidence that they lack any potential to become people?
"It forces everybody to get far more nuanced in their thinking about what it is about early life forms that, in their minds, renders them morally significant," said R. Alta Charo, a professor of law and bioethics at the University of Wisconsin in Madison.
The new work was conducted by Michael West and colleagues at Advanced Cell Technology Inc. in Worcester, Mass. In one report, published in an online journal Nov. 25, the team said it had used chemicals to stimulate human eggs to grow into embryo-like balls of about 100 cells -- the first creation of human parthenotes. (The stimulus was applied before the egg underwent the normal ejection of half its chromosomes, which typically occurs at the time of fertilization to accommodate the sperm's DNA.)
Inexplicably, those parthenotes did not contain any stem cells. But related research, described by West at a scientific meeting Dec. 2, suggests the goal of obtaining stem cells from human parthenotes is achievable. The team made parthenotes from monkey eggs -- the first such success in our near-human relatives -- and retrieved from one of those parthenotes what appeared to be stem cells.
Those cells turned into intestine, skeletal muscle, retina, hair follicles, cartilage, bone and other cell types -- even heart cells beating in unison. Some turned into nerve cells that secreted the brain chemical dopamine, the kind of cell that is gradually lost by Parkinson's patients. The idea, West said, is to grow replacement cells and tissues from a patient's own eggs so they are genetically so similar to the woman that they won't be rejected by her immune system.
Men might also someday benefit from parthenote-based therapies, scientists said. Research in animals suggests that male parthenotes can be made by inserting two sperm into an egg whose own DNA has been removed, then stimulating that reconstructed egg to start dividing. Stem cells from the resulting parthenote would be near genetic matches to the male patient who had contributed the sperm.
Technical problems still loom large. No one knows, for example, whether parthenote cells are dangerously inbred because all their genes come from only one parent. "Are they completely normal? Are they prone to metastasize like tumor cells? There's really not enough information," said George Seidel, an embryologist at Colorado State University in Fort Collins. In mammals, both male and female chromosomes are required for normal development.
A practical complication, said Johns Hopkins stem cell researcher John Gearhart, is that viable eggs are difficult to retrieve from postmenopausal women -- who are more likely than younger women to be suffering from degenerative diseases.
But Jerry Hall, laboratory director at the Institute for Reproductive Medicine and Genetic Testing in Westwood, Calif., said his research on mouse parthenotes suggests the cells have promise. "We need to prove they are safe and effective," Hall said. "But I can tell you, they look very normal."
Even if the science goes well, the field will have to navigate ethical and political obstacles. Since 1996, Congress has attached a rider to the Health and Human Services appropriations bill that precludes federal funding of research in which human embryos are destroyed. The rider, attached again to the 2002 bill, which has yet to be signed into law, defines embryos to include parthenotes.
Privately funded research is not affected by that legislation, and some believe that federal funds should be allowed for research on parthenotes that have no potential to grow into people. After all, said Hall, even a skin cell has the potential to become a viable embryo through cloning technology. "If you look at it that way, then a body cell may have more rights or moral basis than a parthenote."
For society to decide what kinds of human entities deserve rights, said Charo, it must consider why rights exist and why society recognizes them. One view, she said, is that rights accrue only if they have some value to the rights-holder, leaving embryonic entities with no rights if they lack any potential for life.
Many critics of embryo research don't see it that way, said John Eppig, a researcher at Jackson Laboratory in Bar Harbor, Maine, who sat on a 1995 federal commission that gathered public comments on human embryo research. "The same people who were up in arms about doing research on embryos were up in arms about research on parthenotes," he said. "They correlated this with virgin birth. They correlated it with Christ."
Douglas Johnson of the National Right to Life Committee said he was unconvinced that parthenotes deserve no protection. "With respect to any of these things created with human genetic material," he said, "the burden of proof must rest with those who argue they are not human and that it's okay to kill them."
© 2001 The Washington Post Company
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