Researchers at the Oregon Health & Science University have created for the first time cloned embryos of monkeys from which they extracted stem cells. Despite the apparent success, the technique has a very high rate of failure: of 304 eggs from 14 rhesus macaque monkeys, only two stem cell lines resulted.

The study was published in the Nov. 14 online edition of the journal Nature and its findings were independently verified. This type of verification is much needed, especially after South Korean scientist Hwang Woo-suk published fake research in Science on human cloning.

"There has been worry that primates may prove to be difficult in terms of cloning," Robin Lovell-Badge, a stem cell scientist with the U.K. National Institute for Medical Research, told BBC News. Indeed, there appears to be an exponentially increasing difficulty in cloning mammals as you go farther up the ladders of evolution towards the humans.

"The clear risk of an experiment [in human reproductive cloning] is of a deformed baby and maternal suffering," said Helen Wallace of Genewatch UK, a British group that monitors cloning and other activities in biotechnology, to AFP. "In Britain, we don't think that the technology is going to go that far because there are laws against reproductive cloning," she said. "However, in most countries around the world, there are no legal safeguards."

Stem cells are primal cells found in all multi-cellular organisms, which have the potential of differentiating themselves into a diverse range of specialized cell types. Embryonic stem cells, derived from blastocysts, are derived from the inner cell mass of an early stage embryo. They are capable of turning into any type of cell type, whereas multipotent progenitor cells found in the adult can only be coaxed into forming some tissue types.

The US team at the Oregon Health & Science University have taken skin cells from a male monkey and extracted the DNA which they put in 304 eggs from 14 rhesus macaque monkeys. Subsequently, they managed to extract two stem cell lines from these days-old monkey embryos.

"The ability to produce embryo stem cells from cloned human embryos would create entirely new opportunities to study inherited diseases," said Ian Wilmut, director of the Scottish Centre for Regenerative Medicine at the University of Edinburgh. He is a member of the team that cloned Dolly the sheep in 1997. "Cloned cells produced with the genetic material of a patient who has inherited a disease would have the abnormalities associated with the disease," Wilmut added.