Cloned Pigs Open Door
For Transplant Organ Farms
By Maggie Fox - Health and Science Correspondent
WASHINGTON (Reuters) - Two separate teams of researchers reported on Wednesday that they had managed to clone pigs, a tricky accomplishment that opens the door to breeding herds of genetically engineered pigs to farm for organ transplants to people.
But other scientists said they had found tough barriers to such an attempt -- saying they had shown that human cells can be infected with potentially dangerous viruses from pigs.
So far sheep, cattle, goats, mice and monkeys have been cloned. One idea is to breed genetically identical farm animals that can produce human products such as proteins for use in medicines. Another is the production of prime meat.
But pigs offer another prospect. Because they are similar in size and other aspects of biology to humans, they have been seen as a potential source of organs and tissue for transplant into people.
Last March, a team at PPL Therapeutics Plc (quote from Yahoo! UK & Ireland: PTH.L) in Edinburgh, Scotland, said they had produced a litter of five piglets using cloning technology. On Wednesday, the science journal Nature made public their report, to be published later this month.
At the same time, rival journal Science is publishing a paper from an international team of researchers who say they have cloned a pig using slightly different technology.
Akira Onishi of Japan's National Institute of Animal Industry and colleagues said they had cloned a piglet from a pig foetus. Named Xena, their piglet had a dark coat while her surrogate mother was white.
They used the same method as used by a team at the University of Hawaii to clone mice.
The PPL scientists said they had used a new method that may make it easier to get their clones to survive.
``All five of the pigs, now three months old, are extremely healthy, in contrast to the usual 50 percent postnatal loss of nuclear transfer (cloned) animals,'' they wrote.
The researchers, best known for their work in cloning Dolly the sheep, the first adult mammal ever cloned, said they hope they can genetically engineer pigs in the future so that their organs and tissues are easier to transplant into human beings.
The main target will be a sugar called alpha-1,3,-galactose, which pigs and many other animals have on their cells but which humans do not have. The sugar causes an extreme rejection of animal tissues by the human immune system.
Getting rid of this sugar may go a long way ``towards the ultimate goal of providing an unlimited supply of compatible pig organs for human transplantation,'' the PPL team wrote.
But a second study in Nature poured cold water on the idea that this can be done any time soon.
Daniel Salomon of the Scripps Research Institute in La Jolla, California and colleagues found that human cells can be infected with viruses that exist in all pig cells, known as porcine endogenous retroviruses (PERVs).
``Here we show that pig pancreatic islets produce PERV and can infect human cells in culture,'' they wrote.
This is bad news for diabetes researchers, who had hoped that perhaps the cells, which produce insulin, could be used to treat people with diabetes. There is a shortage of human cells and pig cells were considered a possible alternative.
Research published a year ago had suggested that pig tissue did not infect humans. The studies involved mostly people whose blood had been filtered using pig cells or who had received pig tissue transplants.
But Salomon's team said that study had looked only at the blood of human patients. They said the viruses may not infect blood cells, but other cells.
``That is really significant,'' Dr, John Gearhart, an expert on cloning technology at Johns Hopkins University, said in a telephone interview.
He said it may slow down the race to develop pigs for animal-to-human transplants, known also as xenotransplants.
Earlier this week, the director of Scotland's Roslin Institute, which has been associated with PPL, said it would re-direct funding away from its pig-cloning programme.
U.S.-based Geron Corp. (NasdaqNM:GERN - news) bought Roslin Biomed with an eye to acquiring this programme, but said it would reduce such funding.
Cloning expert Dr. James Robl of the University of Massachusetts said it might be because cloning pigs is difficult and expensive.
``It is something that long-term and would require a substantial amount of funding,'' he said in a telephone interview. ``Not everybody is going to be able to take a position in the xenotransplantation area with pigs.''
Other companies researching xenotransplantation include Imutran, a British subsidiary of Switzerland's Novartis , Nextran Inc., a division of Baxter Healthcare Corporation (NYSE:BAX - news), DeForest, Wisconosin-based Infigen, Alexion Pharmaceuticals Inc., (NasdaqNM:ALXN - news) based in New Haven, Connecticut and Boston's Genzyme Corp. (NasdaqNM:GZSP - news).

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