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Animal Organ Transplants Explored

September 18, 1998

WASHINGTON (AP) _ Researchers are looking to make it possible to transplant animal organs into people without being rejected quickly by the human immune system.

In one possible solution, scientists at Massachusetts General Hospital are genetically re-engineering the transplant recipient’s bone marrow so the animal organ will not seem so foreign.

So far, it has worked in mice, immunologist John Iacomini reports in today’s edition of the journal Science.

Mammals except humans and apes have a carbohydrate called alpha-Gal on their cells. Humans and apes have strong immune system antibodies that attack alpha-Gal.

Pig organs are the most likely to be used if ``xenotransplantation,″ organ transplants between species, ever occurs because their major organs are similar in size and structure to people’s. But put a pig organ inside a person and the pig’s alpha-Gal acts as a red flag signaling human antibodies to immediately attack.

Drugs that suppress the immune system can’t solve this problem. So Iacomini theorized that putting the gene that produces alpha-Gal into a transplant recipient’s bone marrow, where immune cells are made, could help. If the alpha-Gal was already there, newly forming antibodies wouldn’t know to attack it elsewhere in the body.

First, he bred mice that didn’t naturally produce alpha-Gal. Then Iacomini genetically altered their bone marrow, and true to his theory, they didn’t produce detectable alpha-Gal antibodies.

Now he’s studying baboons, whose immune systems are similar to humans’, to see if the marrow altering works well enough for a transplanted pig organ to survive.

``It’s a very interesting study,″ said microbiologist Uri Galili of Allegheny University, who helped uncover alpha-Gal’s role in transplant rejection.

An alternative solution is genetically engineering pigs to produce more human-like organs, something biotech companies are attempting. ``Both directions are important to pursue,″ Galili said.

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