Encouraging results from attempting to breed genetically engineered pigs with organs that appear human to the immune system - which is responsible for tissue rejection - indicate that transplant surgery could be revolutionised sooner than was thought.
The aim is to be able to use hearts, lungs and other organs from pigs that produce key identifying proteins of the human immune system - which make tissue rejection by patients less likely.
Scientists believe that the proteins will prevent the 'highly complex cascade of events' that would cause the human immune system to punch holes in the cells of the transplanted heart or lungs. Using pigs as organ donors could also overcome the shortfall in human organs that has meant many ill patients going without transplants.
In size and anatomy, the organs of a pig are similar to those of humans. A 12-stone pig has a heart that is similar in size to that of a 12- stone man. Kidneys, lungs and insulin-producing cells of the pancreas are other candidates for transplants.
David White, lecturer in immunology at Cambridge University, said yesterday that the first 'transgenic' pigs, which have functional human genes, are now being reared with the prospect of being cross-bred with other transgenic swine. 'If all goes well we could start clinical trials with these pigs in three years' time.'
Dr White and John Wallwork, director of the heart-lung transplant team at Papworth Hospital in Cambridge, are collaborating on the research with Imutran, a privately financed biotechnology company.
Dr Wallwork said that the first transgenic pig, a sow called Astrid, was born at the end of last year. Since then, 37 pigs in total have been born that are known to have the necessary human genes that make cross-species transplants feasible. 'These are the first pigs that have been specifically genetically engineered for transplantation purposes,' Dr Wallwork said. Pigs that can meet the increasing demand for organ transplants would solve the medical profession's dilemma: 'We are relying on well people to die for sick people to live.'
Dr White said that the public have had a distorted idea about the ethics of such work. 'Most people have not really understood the science of what we are doing. They thought we are somehow turning pigs into human beings. All we are doing is playing a rather subtle trick on the human immune system.'
The scientists point out that heart valves and skin from pigs are already used in transplants and so there should be no new ethical issues raised. However, Dr Wallwork said: 'If our society decides not to have anything to do with this then that is society's decision.'