The first genetically modified pig organs designed for human transplants could be ready in just two years, according to one of Britain's best known scientists

According to Professor Robert Winston, after the organs are completely modified, they will need to be rigorously tested to prove they are safe and effective. If so, the first transplant could take place in 10 years.

Lord Winston is already conducting experiments that could lead to pig cells being modified with human genes.

Speaking at a London press conference, he said these "humanised" organs are unlikely to be rejected once they are transplanted into patients.

A new source of organs is desperately needed.  One patient is added to the transplant list world-wide every 15 minutes. But many die before an organ is available.

The human immune system would normally reject a pig organ because it recognises proteins on the surface of the cells as "foreign".  But, by replacing these proteins with a human version, transplants are likely to be successful.

Lord Winston said the hunt is now on for the combination of genes that makes the outside of a cell appear human.

Those genes would be cut and pasted into the DNA of a virus, which in turn would be injected into the testes of pigs.

The virus is known to infect the stem cells that produce sperm, so in theory, offspring of the boars would carry the new genes and produce human proteins on the surface of their cells.

"You could hit the button and find the right gene combination straight away; or it could take a bit longer.  But we could have organs within two to three years," he said.

Scientists would then need to prove that the organs are safe and effective before they are cleared for human transplants.

Pigs can carry viruses that cause human diseases; but Lord Winston insists the pigs he uses are virus-free.

Lord Winston's team has been banned from mating pigs that have been genetically modified.  He is expected to start experiments in the United Statessoon.

The work is being led by a spin-off company from Imperial College in London called Atazoa.  Lord Winston is a director of the company.