Wellington - An American gene researcher said he has cloned a miniature pig in a development he called a major step towards transplanting pig organs into humans.
Randall Prather, a professor at the University of Missouri-Columbia, announced on Monday that he has cloned a miniature pig - without the gene that has kept doctors from successfully transplating pig organs into humans.
Pigs are potential human lifesavers because they are physiologically similar to people and more plentiful than nonhuman primates, such as baboons.
However, pigs are born with a gene that coats their organs with a sugar molecule, called a-1,3-galactosyltransferase or GGTA1, which triggers organ rejection when transplated into humans.
Prather told the International Embryo Transfer Society in Auckland that the cloning process for his female pig, Goldie, born November 18 in Columbia, Missouri, blocked both copies of the gene.
"We have only one (pig) living which has both gene copies modified so they're nonfunctional," said Prather, a professor of reproductive biotechnology.
He said checks of the pig's cells confirmed that both copies of the gene producing GGTA1 "have been knocked out".
Prather said the work still must be reviewed by independent scientists. He is writing up the results for publication in a science journal.
But he called Goldie's birth "the first step through the brick wall" separating scientists and doctors from transplanting pig organs into humans, known as xenotransplantation.
Dr David Cooper, professor of surgery at Harvard Medical School and a former president of the International Xenotransplantation Association, called the development "a very important step forward."
Goldie's birth means "we're well on the way to considering a clinical trial of xenotransplantation of pig organs into humans" within three years or so, he said on Tuesday from Massachusetts.
Overcoming the body's massive immune response after it perceives a foreign organ is one of the greatest hurdles to animal-to-human organ transplants.
Without the sugar, the antibodies can't attach, and therefore the rejection process can't begin, Prather said.
He anticipated other rejection problems to emerge as the work develops.
Cooper noted that miniature pigs have been studied intensively for 25 years.
"We know a lot about their tissue typing and because of that, I think it puts us in a much stronger position to deal with any problems that will come in the future," he said by telephone.
Julia Greenstein, chief executive of Immerge BioTherapeutics, a Massachusetts firm that sponsored Prather's project, called Goldie a "biological breakthrough". Cooper also has worked with Immerge as a consultant.
Prather and Immerge announced a year ago in the journal Science that they had successfully cloned the world's first single knock-out miniature swine.
The genetic material from these swine was then re-engineered to knock out the second copy of the GGTA1 gene.
Prather said he had used Yucatan miniature swine as they have better potential as organ sources for human transplants because of their size. A typical mature miniature pig weighs between 70-114kg.
Another United States research group, PPL Therapeutics, has created a pig that lacks one of the two usual copies of the sugar-making gene.
Prather and Immerge plan to test organs from their pigs in baboons with a goal of long-term survival and a herd of miniature pigs for use in transplant surgery.
Human trials could start in three to five years, Greenstein said. - Sapa-AP