Posted on: Monday, November 26, 2001

Experts say embryo-cloning far from making baby

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By Malcolm Ritter
Associated Press Science Writer

When most people hear "human cloning," they think of producing a genetically identical copy of a person.

Whether a six-cell embryo has the moral status of a person is a matter of debate. But experts say it's a long way from being a live-born baby. One researcher said it was much closer to a fertilized egg.

Scientists at Advanced Cell Technology, which reported yesterday it had cloned the first human embryo, emphasize they're not interested in producing babies by cloning. They say they want to create only embryos as a source of stem cells for treating disease.

But they made a six-cell embryo clone — a tiny ball of cells invisible to the naked eye — and natural embryos of that stage can be placed in a woman's womb and possibly grow into a baby.

Still, studies of other mammals show that many cloned embryos that reach the six-cell stage don't survive pregnancy.

In cattle and sheep, for example, about half of eggs fertilized develop to at least six cells, and of those, maybe one in 25 or 50 will produce a birth, cloning expert Steven Stice of the University of Georgia said yesterday.

"We know a lot more how to clone those animals than we do humans, so the odds are even less for humans, probably dramatically less," said Stice, who was a founder of Advanced Cell Technology but left the company in 1998.

Even in routine test-tube fertilization, the story is similar.

"A lot can go wrong," Dr. Sandra Ann Carson, director of the test-tube fertilization clinic at the Baylor College of Medicine in Houston, said Sunday.

At her clinic, she said, when six-cell embryos are transferred into women, only about one out of five will become a baby. That's typical for clinics, said Carson, who is president-elect of the American Society for Reproductive Medicine.

Those figures are for carefully chosen embryos, without any wild cards introduced by the cloning process. With the newly announced cloned embryo, which stopped growing in the lab after reaching at least six cells, it's not clear whether cloning would have prevented further development anyway, she said.

At that stage, none of the embryo's cells have taken on specialized jobs, starting down a developmental pathway that will produce a liver, for example, Carson said.

"This is much closer to a fertilized egg than it is to a baby," she said.