BRITISH patients will be the first in the world to be offered transplants using hearts and
kidneys from genetically altered pigs.
Cambridge scientists said yesterday that they had succeeded in transplanting transgenic
pigs' hearts into monkeys, regarded as the biggest advance in transplants since the
introduction of the drug that suppresses organ rejection 10 years ago.
Heart and kidney transplants using the pigs' organs will be offered for the first time to
chronically ill patients next spring if research continues as expected, the Cambridge team
said. The organs could be generally available in five years. "This will give hope to hundreds
of thousands of patients around the world who would otherwise die waiting for a heart, lung
or kidney," said Christopher Samler, chief executive of Imutran, the company responsible
for the research.
Dr David White, the Cambridge immunologist who founded the company in 1984, said that
the team had succeeded in creating a biomedical illusion.
"The data clearly shows that we have found a way to trick the immune system of the primate into accepting a pig organ."
In Britain 6,000 people are waiting for organs, 5,000 for kidneys and the remainder for
hearts, lungs and livers. The list grows at five per cent a year, but only 1,750 kidney,
500 heart or heart and lung and 650 liver transplants are done a year. In America 30,000
are waiting. Only half receive the organ they need.
John Wallwork, the director of the transplant service at Papworth Hospital, Cambridge,
and a co-founder of Imutran, said that if all went well the team would be able to solve the
"chronic" transplant shortage.
"It could remove the lottery for life that patients face on the transplant list." The use of pigs'
livers is not being considered at this stage.
The problem with xenotransplantation - transplanting organs between different species -
is "hyperacute" rejection. This can be so extreme that a normal pig's heart transfused with
human blood can be destroyed in 15 minutes.
When allografts are used - transplanting organs between humans who are related - rejection
is overcome by the closet possible tissue matching and the long-term use of the
immuno-suppressant drugs.
The Imutran procedure involves injecting a pig embryo with a human gene to persuade
the human immune system to accept the foreign animal organ.
Normally, enzymes known as complement are activated in response to an intrusion,
which attack the foreign body very effectively.
These are controlled by another mechanism called "regulators of complement activity".
To prevent its destruction the animal organ needs to contain these human regulator proteins.
The gene inserted into the pig embryo contains instructions that enable the pig to produce
human regulator proteins. After a transplant the human complement "sees" the transgenic
animal organ as if it were human.
In the trial the transgenic pigs' hearts showed no signs of hyperacute rejection by the monkeys and were still beating after 60 days. The median survival in the 10 monkeys used was more than 40 days.
The best result achieved in America, reported in May, was only 30 hours' survival.
The announcement of the British development is not likely to raise major ethical problems,
since pig insulin is already used for diabetes and pig heart valves in heart repair surgery.
However, the farming of large numbers of animals for human medical use raises another issue.
Stephen Dorrell, the Health Secretary, announced yesterday that Ian Kennedy, Professor of
medical law and ethics, King's College, London, had agreed to chair a new ethics committee
on xenotransplantation.
Michael Thick, a surgeon of Freeman Hospital Trust who was speaking yesterday on artificial organs at the British Association meeting in Newcastle, said that the demand for hearts was 200 per million people per year; only 10 per million a year were supplied in Britain.
Transgenic kidneys would be more important than hearts, Mr Thick added, reducing the cost
