UK agency tentatively approves proposals for research using hybrid human-animal embryos

British authorities on Thursday approved scientists' use of animal eggs to create human stem cells, a ruling that will boost the supply of stem cells for research.

"This is good news for research, but most importantly, it is good news for patients," said Sophie Petit-Zeman of the Association of Medical Research Charities.

British scientists want to use animal eggs because there is a shortage of human eggs. The decision means that researchers will be able to refine their techniques for producing human stem cells by practicing first on animal eggs, of which there is a steady supply.

Scientists have been exploring the use of stem cells to cure many degenerative diseases such as Parkinson's, since the cells have the ability to develop into any cell in the human body.

The Human Fertilization and Embryology Authority said it had granted conditional one-year licenses to two institutions to conduct research using mixed human-animal embryos. In Britain, all research involving human eggs and embryos must be approved by the authority.

Scientists from King's College and Newcastle University submitted applications last year to create human stem cells using animal eggs.

The process involves injecting an empty cow or rabbit egg with human DNA. A burst of electricity is then used to trick the egg into dividing regularly, so that it becomes a very early embryo, from which stem cells can be extracted.

"Cow eggs seem to be every bit as good at doing this job as human eggs," said Lyle Armstrong of Newcastle University.

Similar work involving human-animal stem cells is also under way in China and the United States.

Because the animal cell's nucleus would be removed before human DNA was added, scientists said the resulting egg would not be a chimera. The embryos would not be allowed to develop for more than two weeks.

"We will only use them as a scientific tool and we need not worry about cells being derived from them ever being used to treat human diseases," Armstrong said.

Many scientists were concerned that the applications would be rejected, after a government report last year proposed outlawing hybrid embryos.

The proposed human-animal embryos stirred debate across the country, with then-Prime Minister Tony Blair declaring that if the research could help people, it should go forward.

While critics warned that the decision sets a dangerous precedent for human genetic engineering, most scientists applauded the licenses.

"The HFEA's decision is excellent," said Robin Lovell-Badge, a stem cell expert at Britain's National Institute for Medical Research. "It adds to the arsenal of techniques United Kingdom scientists can use to provide understanding and eventually develop therapies for a wide range of devastating genetic diseases."