PARIS - Opinion polarised sharply on Friday after South Korean and British scientists announced they had created nearly three dozen cloned embryos in the search for stem cell cures for disease and injury.
On one side were medical researchers, who hailed the work as massive progress in the endeavour to reverse degenerative disease or fix damaged spinal nerves, retinas and other tissues.
On the other side were anti-abortion groups who consider embryonic stem cell research to be murder, and some voices warned the latest work would tempt maverick scientists to try to create a cloned baby.
President George W. Bush threatened on Friday to veto any legislation that eases restrictions on federal funding for embryonic stem cell research in the United States.
Bush -- who did not mention the new research specifically -- said he remained a "strong supporter of adult stem cell research," in which the material is sourced from adults rather than embryos.
"But I`ve made it very clear to the Congress that the use of federal money, taxpayers` money, to promote science which destroys life in order to save life, I`m against that. And therefore, if the bill does that, I will veto it," he said.
"I`m very concerned about cloning," Bush added. "I worry about a world in which cloning becomes acceptable."
The bigger of the two breakthroughs came from a team led by Seoul National University professor Woo Suk Hwang.
They derived 11 stem cell lines from 31 cloned embryos, using eggs whose nucleus, which contains the DNA programme for life, had been reprogrammed with DNA from skin cells taken from volunteers with disease or spinal-cord injury. A British team also announced it had created three cloned embryos but no stemcell lines had resulted.
None of these embryos was allowed to become a baby. Within a few days, the tiny cluster of cells was harvested for their value in therapeutic research.
Embryonic stem cells are like blank slates. Discovered two decades ago, they are cells that develop in the first six days after an egg is fertilised. At this stage, they are "pluripotent" -- they can develop into any of the body`s cell types.
The big hope is to grow self-replicating lines of these cells, and find a way of coaxing them into specific cell types so that they can then be transplanted into the body as replacement for tissues that are damaged or destroyed.
But for this to work, the cells first have to overcome the problem of rejection by the body`s immune system. Cloned cells would in theory would not be rejected, as the immune guardians would consider them friends rather than intruders.
Scientists gave a highly enthusiastic response to the South Korean work, saying that its biggest achievement was technical -- to create, simply and efficiently, a large number of clones that are apparently free of chromosome damage.
That means it will become easier to explore hypotheses about stem cells and the way diseases develop, they said. And it should also make it easier to use these cells in therapy if, at some distant time, they are ever authorised for treatment.
Ian Wilmut, the British scientist who led the cloning team that created Dolly the Sheep in 1996, said the work was "a very significant and important step forward."
French genetics pioneer Axel Kahn described it as "a technical tour de force... news of prime importance." Another leading French geneticist, Marc Peschanski, said it was a "scientific revolution," a "spectacular" advance on previously cloning performance.
But Peschanski also acknowledged that some of the technical barriers to creating a cloned human "have now been lowered."
That scenario was evoked by the British organisation Life, which campaigns against abortion as well as embryo research.
"If, as they claim, these South Korean scientists can reliably produce cloned embryos healthy enough to survive to the blastocyst stage for cell harvesting, we can assume that they can reliably produce embryos healthy enough to try implanting them in women," it said.
"This Frankenstein science should be banned in every civilised country," it said.

05/20/2005 17:58 GMT