Cloned Pigs Seen As Organ Advance

Friday, August 18th 2000, 12:00 am

By: News On 6

WASHINGTON (AP) â€” The cloned barnyard has a new resident: the pig, a creature researchers say holds promise for growing organs to replace ailing hearts, livers and kidneys in humans.

A team led by Japanese and American researchers announced in the journal Science that a single piglet had been cloned. Separately, a Scottish company said it had cloned a litter of five pigs.

``Pigs have an enormous potential for'' transplanting organs to humans, said Tony Perry, a Rockefeller University researcher and co-author of the Science study. ``This is a breakthrough toward that goal.''

The pig, he said, is considered the best species to use for growing organs to replace ailing hearts, livers and kidneys in humans.

``The pig organs roughly match the size of human adult organs,'' Perry said. ``They also are amiable to transplant surgery.''

Work on the litter of pigs cloned by PPL Therapeutics Inc. of Scotland involved some of the same researchers who cloned a sheep called Dolly. That was the first use of cells from an adult mammal to clone another animal.

The PPL success was reported in a study released electronically Wednesday by the peer-reviewed British scientific journal Nature, five months after the researchers made public their work in the popular press.

In the Science report, researchers said they cloned a single piglet, named Xena, from the skin cells of a pig fetal.

They removed the nucleus, which contains DNA, and injected it into a pig egg from which the nucleus had been removed. An electrical pulse stimulated the egg to grow into an embryo, which was transplanted into a surrogate mother.

The researchers said four sows were transplanted with a total of 110 embryos. Xena was the only healthy animal produced.

Perry's co-authors were scientists at the National Institute of Animal Industry in Tusukuba, Japan, and the Prima Meatpackers in Tsuchiura, Japan.

The Scottish company researchers began with cells from an adult animal and cycled the transplanted nucleus through two different pig eggs.

Since Dolly's birth in 1997, research teams have used similar techniques to clone goats and cows. Dolly and some of the cloned cows have given birth to normal offspring.

Perry said swine have proved harder to clone.

``People have been trying since 1986,'' he said. ``It has been an elusive species, but one that people have really wanted to succeed with.''

Michael D. Bishop, president of Infigen Inc. of DeForest, Wis., a cloning research company that has cloned more than 100 cows, said the announcement by Perry and his co-authors is a ``real breakthrough'' because it showed that problems with pig cloning have been solved.

Before pigs can be used to grow organs for human transplant, Perry said scientists must overcome several problems, chief of which is the human body's rejection of the transplant. Cross-species transplants, he said, are usually ``rejected within minutes.''

``It will be necessary to modify the genes of the pig so that the transplanted organs will not be rejected,'' Perry said. ``This would make the organ invisible so that the host immune system will not recognize the organ as foreign.''

It may take several generations of clones and ``many years'' to weed out the genes that cause rejection, Perry said.

Some researchers are concerned that using pig organs for transplantation could cause humans to contract some unusual swine viruses. These viruses have been infecting pigs for thousands of generations and now are part of the swine genes, passed along from parents to offspring.

Another study in Nature showed that mice receiving pig tissue transplants did become infected with a swine virus.

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