Friday, May 21, 1999 Published at 10:10 GMT 11:10 UK
No safety in numbers for clones
This cloned calf died just seven weeks after birth
By Helen Briggs of BBC Science
Animal cloning is being hailed as one of the century's great scientific breakthroughs. Doctors hope that it will revolutionise medicine, providing an endless supply of organs for transplant and a cure for major killers like heart disease.
Many of the clones have developmental abnormalities and die late in pregnancy or soon after being born.
Dolly the Sheep, the world's first mammal cloned from an adult cell, appears perfectly normal. But Dr Harry Griffin, from the Roslin Institute, knows there is still much to learn about the technology that created her.
"In our experiments, we produced 20 live lambs of which six have died soon after birth and a high rate of neonatal death is common in all the experiments to clone both sheep and calves.
"The reason? In cloning from an adult animal you're trying to re-programme a specialised cell, trying to persuade it to start off its life all over again, become a whole animal - it's surprising it works at all."
Dr Wolf Reik from the Babraham Institute in eastern England says the secret of cloning is persuading an adult cell to return to its childhood.
"Imagine that you take a cell from a breast cell, in the case of Dolly that was the case," he says.
"Then all the genes that are active to make that a mammary cell, a breast cell, need to be switched off when this nucleus goes back into the egg recipient. Then all the genes that are required for normal development need to be switched on again as development proceeds. That is a very, very complex process."
James Robl from the University of Massachusetts has been looking at a problem that affects cloned calves. The off-spring can become large with an accumulation of fluid in the placenta.
"We know that as you manipulate embryos that the percentage of the calves that have the defect goes up," he says.
It is likely to be years before cloning can be made safer. And, although the cloning of humans is still in the realms of science fiction, most agree that the potential health risks of cloning must be taken into account in debates on human cloning.
In the publically-funded labs in the US, and throughout Australia, China, Israel, and most European countries, scientists are prevented by law from carrying out research into human cloning.
And many experts agree that although in theory human cloning might be possible, morally it is unacceptable.
"I think there is a general awareness now that this technology is risky, that it would be wholly unsafe to use in humans," says Dr Griffin. "It would be fundamentally wrong to use the technique in young women and I think that there is now more sanity coming into the debate about human cloning.
If scientists really can crack the problems associated with cloning, the potential benefits to humankind are immense. Already animals have been engineered to produce human proteins, such as clotting factors, in their milk. And cloned animals may one day provide organ banks for transplant, tailored to a patient's specific tissue type.
The fact that Dolly, like a host of other cloned animals, is alive and well shows the technology works. But understanding how cloning works and making it safer will be the challenge of the future.