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Human-cow hybrid embryos made in lab

UK researchers say they have created embryos and stem cells using human cells and the egg cells of cows. But they say such experiments will not lead to hybrid human-animal babies, or even to direct medical therapies.

Dr Lyle Armstrong of Newcastle University presented preliminary data on his work to Israel's parliament last week.

It has not been reviewed by other experts in the field, the university says, but the researchers intend to have their work peer-reviewed.

The researchers say they have hollowed out the egg cells of cattle, inserted human DNA to create a growing embryo, and then taken it apart to get embryonic stem cells.

There is no possibility of creating a human that is part-animal, according to the researchers. They say the animal egg only acts as a shell for the human DNA.

They add the hybrid embryos will not be implanted and by law that any that are created have to be destroyed at 14 days.

Stepping stone to other research

Other experts say such work would only be an interim step aimed at understanding the biology of embryonic stem cells, the body's ultimate master cells that can give rise to all of the other cells and tissues.

"If the team can produce cells which will survive in culture it will open the door to a better understanding of disease processes without having to use precious human eggs," says Professor John Burn, head of the university's Institute of Human Genetics.

"Cells grown using animal eggs cannot be used to treat patients on safety grounds but they will help bring nearer the day when new stem cell therapies are available."

Scientists hope to use stem cells to create a new field of so-called regenerative medicine. Doctors hope for eventual treatments for spinal cord injuries, diseases such as diabetes and even cancer.

Opponents of human embryonic stem cell research object to the destruction of human embryos and say even the tiniest embryo must be treated with dignity.

Ethics of creating hybrids

"This is one of the most controversial ethical issues in all of cloning and stem cell research," says US researcher Dr Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania.

Caplan notes many people may be disgusted or frightened by such work.

"In my view there is no risk of making monsters this way. The biology will not work. Nor is that the intent of any of these experiments anyway, so I don't think that fear is justified," he says.

"I come down on the side that says if you can make great gains by making embryo hybrids in preventing premature death and understanding disease then a limited amount of such research is morally justifiable."

Dr David King, of the UK watchdog Human Genetics Alert, disagrees.

"Even if stem cells were ever to be produced, like cloned animals, they would have so many errors of their metabolism that they would produce completely misleading data," he told the BBC.

Newcastle University says Armstrong was granted a licence by the UK's Human Fertilisation and Embryology Authority to use animal eggs in such research.

Caplan notes the US government does not regulate such work. President George Bush has vetoed several bills that would regulate the field because they would also all permit work on human embryos.

Dr Robert Lanza of Massachusetts-based Advanced Cell Technology says his company tried, but failed, to create stem cells in a similar way in the late 1990s.

Chimeras

When two species are mixed together the result is called a chimera. While some are fanciful - a centaur, for example - others exist, such as sheep spliced with human genes that produce human proteins in their milk.

Many researchers are trying to do this to understand the secrets of stem cells and revolutionise medicine.

In 2004, Chinese researchers said they had created embryos by putting human DNA into a rabbit cell.

Experts are pursuing various ways to create stem cells.

Several teams say they have re-programmed ordinary skin cells to act like human embryonic stem cells, but stress that many different approaches need to continue before anyone fully understands how to regenerate human tissue and organs.