Experts say animal-human heart transplants risky, for now

WASHINGTON (Reuters) -- It is too soon to start experimenting with animal-to-human transplants of hearts or lungs because the procedure is still far too risky, an international transplant group said on Friday.

Although taking organs from farm animals such as pigs offers the possibility of an almost limitless supply, the organs still do not work well in people and there is too big a chance that an unknown virus could pass into the human population, the International Society for Heart and Lung Transplantation said.

"There are two major concerns -- one is, can we get the immunology right, can we get the science right," said Dr. David Cooper, a former transplant surgeon and president of the International Xenotransplantation Association, said in a telephone interview.

"The other major concern is, are we going to do any harm by transferring infectious agents to the patient ... then infect the community."

Several studies have shown that pigs carry viruses known as porcine endogenous retroviruses (PERVs). People carry their own versions of such viruses, and it is not clear whether they can be passed on from tissue or organ transplants, although they have been shown to pass from one species to another.

"We wanted to add our weight to the fact that we felt this should not be considered safe and at the moment there is not enough information about it," Cooper, who worked on the statement and who is currently at Massachusetts General Hospital and Harvard Medical School in Boston, said.

Scientists fear that not only could the patient be infected but that the viruses could change in their bodies, become more dangerous and then spread to the population at large.

In August, 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. It hopes to further develop the pigs.

But even before that hurdle is crossed, Cooper pointed out there is the bigger problem of making such transplants work in the first place.

"No transplanted pig lung has functioned for even 24 hours," the group pointed out in its report, published in Friday's issue of the Journal of Heart and Lung Transplantation.

The reason is that pig cells are covered with a sugar that human bodies reject. Scientists are trying to genetically engineer pigs whose cells lack this sugar.

Cooper said his group felt there was a lot of discussion about the issue of animal to human transplants, known as xenotransplants, and too few guidelines.

"So we decided to come up with our own recommendations," he said. "There is quite a bit of research going on in this field. The society thought it would be better to plan ahead and not wait until somebody came up and said 'I am ready to do it'."

Among their recommendations -- that 60 percent of primates such as a baboon live for at least three months with an organ transplanted from another animal before tests on humans could even be considered.

There is a dire need for organs. 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.

Cooper said he feared that reports of using pig organs would make people less likely to donate their own or their relative's organs.

"It has got to be made clear to the public that we are not ready for xenotransplants at the present time," he said.

Companies researching xenotransplantation include Geron, Imutran, a British subsidiary of Switzerland's Novartis, Nextran Inc., a division of Baxter Healthcare Corporation, DeForest, Wisconsin-based Infigen, Alexion Pharmaceuticals Inc. of New Haven, Connecticut and Boston's Genzyme Transgenics Corp..

Copyright 2000 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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