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.
Professor Robert Winston said the organs would then need to be rigorously tested to prove they are safe and effective.
The first transplant could take place in 10 years, he predicted.
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 "humanized" organs are unlikely to be rejected once they are transplanted into patients.
The human immune system would normally reject a pig organ because it recognizes proteins on the surface of the cells as "foreign."
But, by replacing the proteins with human versions, the transplants are likely to be successful.
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.
Winston's team is expected to start experiments in the United States shortly.