Regulators in Britain have agreed in principle to allow human-animal embryos to be created and used for research.
Scientists wanting to use hybrids will need to make individual applications, the Human Fertilisation and Embryology Authority (HFEA) said in its decision Wednesday.
Researchers want to conduct research using animal eggs to create human stem cells. The process would involve placing human DNA into cow or rabbit eggs that have had their genetic material removed.
The resulting embryo is called a "cybrid" or "cytoplastic hybrid" embryo, and differs from "human chimeras," which involve injecting human cells into animal embryos, or a true hybrid, which would be created by the fusion of a human sperm and an animal egg.
Two teams from Kings College London and Newcastle University have already applied to the HFEA to use hybrid embryos.
Scientists say they need to use animal eggs because the supply of human eggs is limited. At the moment, the only eggs available are those that are left over from fertility treatment.
But the use of animal eggs has raised ethical worries, with many against the idea of merging animal and human life.
An HFEA consultation showed the British public was "at ease" with the idea when told it could pave the way for therapies for conditions such as Alzheimer's disease. The survey of 2,000 Britons found that 61 per cent gave their backing to the technology if the hybrids would help understand some diseases. That support fell to 35 per cent if the hybrids were being created for non-specific research.
The researchers insist that they will allow the eggs to develop for only a few days, and destroy them within 14 days.
They also say that a human embryo made in the shell of an animal egg would contain only a minute amount of animal genes. The resulting egg would contain 13 animal genes compared with some 20,000-25,000 human genes.
It is now expected that individual hearings for the applications from Kings College and Newcastle will be held in November, with other scientists to follow.
Dr. David King, the director of the independent watchdog group Human Genetics Alert, says his group is very much against allowing the research.
"These experiments are scientifically useless and morally very problematic," he said.
Current legislation in Canada bans the creation of human-animal embryos.
