Source: Telegraph.co.uk

By Roger Highfield

Why do scientists want to create hybrid animal-human embryos?

Human eggs are in short supply — being also in demand for fertility treatment — and are expensive, costing about £3,000 per woman. Moreover, the procedure carries risks. Rabbit or cow eggs would enable scientists to do basic stem cell research more cheaply and safely.

How will it be done?
 
The animal egg will be emptied of its nuclear DNA and fused with DNA from a human cell, as was done with Dolly the sheep, or fused with an entire human cell. The latter method will mean that human DNA will also replace the second type of DNA — that in power plants of cells, called mitochondria — to some extent so that the resulting cloned embryos are even more human.

Has this been done before?

Yes. This method has been pioneered by Dr Hui Zhen Sheng's team at the Shanghai Second Medical University, China, where she fused human cells with rabbit eggs to produce early stage embryos, which in turn yielded human stem cells.

What is the result?

These embryos have only one type of nuclear DNA and are called hybrids or "cybrids."

Is the Chinese work convincing?

Yes. Dr Sheng's team used donor cells from the foreskins of a five-year-old boy and two men, and facial tissue from a woman. They fused the nuclei (containing DNA) of the human cells with rabbit eggs from which they had removed the nuclei. The resulting embryos were dismantled and used to derive six lines of stem cells, flexible cells that can develop into any type.

Is this regulated?

The use of cybrids is "a grey area" in terms of current regulations, which are under review. The work raises a basic question — if you take a human nucleus and put it in a rabbit egg, is it a human embryo? Whatever, it is still counted as a human embryo by the fertility watchdog, the HFEA.

So why not use hybrid cells to repair patients?

They would not be used for stem cell treatments of patients because of concerns about disease and because cybrid cells may still contain rabbit DNA in mitochondria, the "batteries" of the cell. The few rabbit genes present may generate proteins that would be attacked by the human immune system, for example.

Will the cells of the hybrids have other benefits?

Yes. Although cybrid stem cells could not be used for treatments and will not be allowed to develop beyond an early stage, they will prove invaluable for studies of how to clone embryonic stem cells more efficiently — so human eggs could eventually be used — and could be used to test drugs on cell lines created from people with Alzheimer's disease, and shed light on the basic disease process.