Cloned pigs may offer organ transplants - studies
WASHINGTON - Rival teams of scientists said last week that they had genetically engineered pigs and then cloned them in a first step toward making pigs suitable for animal-to-human transplants.
Companies hope to create animals that can fill the ever-growing need for organs and tissues for transplant.
The pigs are missing a copy of a gene that animals have but that humans and some monkeys do not. The gene produces an enzyme called alpha 1,3 galactosyltransferase, which causes animal organs to die quickly when transplanted into humans.
It is the biggest barrier to animal-to-human transplants, also called xenotransplants. But two separate groups announced they had \"knocked out\" this gene in pigs and then cloned the pigs, to create litters of both genetically engineered and identical piglets.
Liangxue Lai, Randall Prather and colleagues at the University of Missouri and at Immerge BioTherapeutics in Charlestown, Massachusetts, said they had created four cloned piglets that were missing one copy of the gene.
\"The four piggies we have are very healthy,\" Prather, who was one of the first scientists to clone pigs, in 2000, said in a telephone interview.
His team\'s announcement is published in the journal Science, in its online version at www.sciencexpress.org
FIVE PIGS PRODUCED IN VIRGINIA
On Wednesday, PPL Therapeutics in Scotland, the firm associated with the scientists who cloned the first adult mammal, Dolly the sheep, said its researchers had produced a litter of five cloned pigs, also missing one copy of the gene. They were born at the company\'s farm in Virginia.
Because only one copy of the gene is missing, the pigs still produce the enzyme and thus are not suitable themselves to use for transplants, Prather said.
\"What we will be able to do is do inbreeding, and get an animal where both (copies of the gene) are knocked out,\" Prather said.
\"The point is we have introduced the (genetic change) into the population and now we can use conventional breeding to make more. We won\'t have to clone again. Once you have it, it is there, and you can just use conventional breeding.\"
More than 70,000 Americans and hundreds of thousands of people around the world are on waiting lists for new organs, but there are not nearly enough to go around. An estimated 10 people die every day in the United States alone while waiting for a heart, liver, kidney or other organ.
Pigs are considered a possible good source for organs, as they are readily available, easily bred and are about the same size as people. Heart valves from pigs, which contain no cells but simply cartilage, are already very widely used in people.
SPECIFIC PIG STUDIED
Besides the enzyme, the other barrier to using pigs as sources of tissue and organs has been viruses that exist in all pig cells, known as porcine endogenous retroviruses (PERVs).
Experiments have shown that PERVs can be transmitted to human cells, although no one knows if they would cause disease in a human.
But Prather said his team had used miniature swine, a breed of pig specifically studied for human transplants. And in August 2000, Charlestown, Massachusetts-based BioTransplant Inc. said it had bred miniature swine that carried the viruses, but that did not transmit them to human cells the way normal pigs do.
Immerge, which worked with Prather\'s group, is a joint venture of BioTherapeutics and Swiss-based Novartis Pharma AG.
\"We believe this line of miniature swine offers the greatest potential for clinical use in humans, and we\'re working closely with the University of Missouri-Columbia and our commercial partner, Infigen Inc., to develop these swine with this goal in mind,\" Robert Hawley, associate director of animal genetic engineering for Immerge, said in a statement.
Infigen Inc., a private firm based in DeForest, Wisconsin, also has cloned cattle that carry a human gene. The company says its cloned animals are healthy and normal in every way they have measured.
Prather said his team\'s work had implications for more than xenotransplants. He said the work showed that scientists can insert or delete a gene in a precise manner.
The same methods, he said, could be used to produce pigs that have fewer pollutants in their manure, for example, or animals with other desirable genetic characteristics.
Story by Maggie Fox, Health and Science Correspondent
REUTERS NEWS SERVICE
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