The first experimental operations to implant cells and organs from genetically modified pigs into people could be only four years away after the birth of a litter of cloned piglets marked a breakthrough in the field of animal to human transplants.
The piglets were born in Virginia on Christmas Day at a centre run by a US subsidiary of the Edinburgh-based biotech company, PPL Therapeutics, but PPL announced the birth only yesterday.
David Ayares, head of research at PPL's US lab, said the new litter - christened Noel, Angel, Star, Joy and Mary - represented "a critical milestone" in the effort to realise animal to human transplants, known as xenotransplantation. "This advance provides a near term solution for overcoming the shortage of human organs for transplants as well as insulin-producing cells to cure diabetes," he said.
The cloned animals are the world's first "knockout" pigs, meaning that scientists have zoomed in on a single one of the tens of thousands of genes in the pigs' DNA and knocked it out.
The gene codes for a protein called alpha 1,3 galactosyl, or alpha gal. Humans have the same gene, but it is inactive. If a normal pig organ is transplanted into a human, the human immune system reacts rapidly and aggressively to the alpha gal, sometimes causing the organ to fail within minutes.
PPL's cloned piglets, all female, have one of their two alpha gal genes knocked out. In February, PPL expects the birth of a male knockout litter.
When the knockout boars and sows are bred in the old-fashioned way, every fourth offspring will secrete no alpha gal at all. These animals will be founders of a new breed of pig, designed by the human race to provide spare parts for itself.
There are currently more than 5,500 people in Britain waiting for a transplant of a kidney, pancreas, heart, lungs, liver, or a combination of these organs. On average, adults have to wait over 500 days for a new kidney.
Alan Colman, PPL's head of research, said yesterday: "The promise of xenotransplantation is now a reality."
He said it might be necessary to add certain genes to the for-transplant breed before they were ready for trials, but this would not be a problem. "I think we are four or five years away from meaningful human clinical trials."
Just how risky the future for xenotransplantation is was starkly illustrated yesterday when PPL, despite its scientific success, announced it could not afford to run the research programme and was effectively putting the transplant side up for sale to concentrate on another GM animal project, the production of a protein in the milk of GM sheep to combat human emphysema.
PPL's shares soared on the Stock Exchange yesterday: as has become traditional, it initially announced its science milestone to the City.
