The Big Question: Should we allow the creation of embryos which are animal-human hybrids?

Why does the question arise now?

The Human Fertilisation and Embryology Authority (HFEA) is meeting today to decide whether to allow scientists to use animal eggs for the creation of "hybrid" human embryos. By removing the cell nucleus of a cow or rabbit egg and inserting the nucleus of a human skin cell into the empty "shell", it is possible to create a cloned embryo that is 99.5 per cent human and 0.5 per cent animal in terms of its total genetic complement. The current Human Fertilisation and Embryology Act, drawn up more than 16 years ago, does not cover this new technique, so the authority has to decide whether it falls within the current law.

Would the embryos be 'chimeras'?

Technically, a chimera is an organism comprised of a mixture of cells from two different species. In this case, however, all the DNA of the animal's cell nucleus has been removed prior to the insertion of the human cell nucleus. The only genetic material of the animal left is the DNA of structures outside the nucleus called mitochondria, which are the power-generating part of the cell. So the resulting animal-human embryo is neither a chimera nor a hybrid - the result of cross-breeding. Such embryos do not have a scientific name, although someone has suggested "cybrid" because it merges the cytoplasm of the animal egg with the nucleus of the human cell.

Why create animal-human embryos?

Scientists want to use animal eggs to create cloned human embryos because of the shortage of human eggs for research purposes. A scientist can go to a slaughterhouse and acquire 200 good quality cow eggs in one day, whereas it would take a month to get just two human eggs for use in such research. The aim is to produce embryos at the six-day stage of development which can then be used in the production of embryonic stem cells. These cells have the ability to develop into any one of the many dozens of specialised tissues of the body - such as heart muscle, nerve cells or hormone-producing tissue. Scientists seeking permission to carry out this work emphasise that there is no intention of allowing these embryos to develop beyond the 14-day stage - which would in any case be illegal. Neither do they intend to use any of the resulting stem cells in the subsequent treatment of patients.

So why do scientists want them?

Stem cells acquired from animal-human embryos would be used for the fundamental understanding of diseases. The nucleus of a skin cell taken from someone suffering from Parkinson's disease, for example, could be placed into the empty "shell" of a cow egg, and then cloned into a six-day-old embryo. If stem cells are then extracted from the embryo, they could be grown into mature brain cells affected by Parkinson's. These cells could be used in experiments to shed light on the genetic nature of Parkinson's brain cells by directly comparing them with normal brain cells. It could be possible to develop new treatments for many incurable and serious diseases, especially those with a strong genetic component.

Who wants to do this research?

Three groups:Stephen Minger heads a group at King's College London that is particularly interested in creating embryonic stem cells from patients suffering from diseases with a genetic basis, such as Alzheimer's, spinal muscular atrophy and Parkinson's.

A second licence application has been made by Lyle Armstrong and colleagues at Newcastle University, who want to use the technique to study how stem cells develop into the different specialised tissues of the body. They hope to be able to grow these tissues for transplant operations.

Finally, a group led by Chris Shaw of King's College London and Professor Ian Wilmut of Edinburgh University are considering to apply for a licence to use embryonic stem cells to help patients suffering from motor neurone disease.

Who opposes this work?

There are many pressure groups and religious organisations who have voiced their opposition on the grounds that it is unethical or immoral to mix germ cells from humans and animals to create potentially viable embryos. They believe that it undermines respect for human life, and some believe it is also demeaning to animals. But there is a body of expert opinion in academia and government that also appears to be opposed. For instance, a White Paper published at the end of last year on the review of the Human Fertilisation and Embryology Act said that it is the Government's intention not to allow the creation of hybrid and chimera embryos in the laboratory. However, the Government said that it also proposes that the new law should contain a power that allows the creation of hybrid embryos under licence for certain research purposes.

A public consultation into the issue of creating embryos by combining animal and human material produced a massive response against such research. This is said to have spooked the Department of Health in particular into calling for an outright ban. Critics have argued, however, that the consultation had been hijacked by pressure groups opposed to all research on human embryos.

Nevertheless, a major report on stem-cell research in 2000 by a group of high-level experts led by Liam Donaldson, the Chief Medical Officer, concluded: "The use of eggs from a non-human species to carry a human cell nucleus was not a realistic or desirable solution to the possible lack of human eggs for research or subsequent treatment."

Is this research allowed elsewhere?

China seems to be leading the field, having created human embryonic stem cells using rabbit eggs. American scientists have also claimed to have produced similar stem cells - although federal funding of such research is banned by the US Government. Many other countries do not have explicit bans on such research, although there are some notable exceptions such as Australia.

What is likely to happen today?

The HFEA will meet and discuss the ethical and legal implications of the work. The authority members will not look at individual licence applications yet, but instead will concentrate on whether or not to allow the research in general to go ahead. One possibility is that the authority will decide to issue temporary licences for six or nine months. Whatever the HFEA decide, it is bound to be opposed either by those supporting the work, or by those wanting it banned.

Are 'hybrid' human-animal embryos a good idea?

Yes...

* They allow scientists to produce embryonic stem cells for research purposes

* Animal eggs are in plentiful supply and hybrid embryos overcome the shortage of human eggs

* No one will allow them to develop beyond 14 days and the stem cells will not be used in medicine

No...

* It is immoral to mix animal and human stem cells, and is demeaning to life

* Stem cells can be extracted from adult humans, so there is no need to create embryos that are then destroyed

* Allowing such research is the slippery slope to the day when someone clones a hybrid embryo and implants it into a womb