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Study of pig virus eases worry about animal organ transplants WASHINGTON (August 19, 1999 7:29 p.m. EDT http://www.nandotimes.com) - The most rigorous study ever on the safety of transplanting animal parts into humans found no evidence that people caught a worrisome pig virus. The reassuring finding could lead to additional experiments using pigs and other animals as organ donors. At issue is "xenotransplantation," transplanting organs or cells from one species into another. Doctors hope this still highly experimental field could one day save thousands of lives by easing a worldwide shortage of donated organs. But some scientists fear animal-to-human transplants also could cause new epidemics. The AIDS virus is thought to have jumped from monkeys to people long ago, and just last year pigs in Malaysia were sickened by a deadly new virus that they spread to people. So scientists are breeding pigs - the most likely species for xenotransplants - specially tested against infections. But concern rose when researchers recently discovered the genes of all pigs harbor a previously unknown virus that test-tube experiments showed could infect human cells. The virus did not harm the pigs, but nobody knew if it would hurt humans. The new study, published in Friday's edition of the journal Science, suggests this so-called "porcine endogenous retrovirus," also known as PERV, is not a big threat. Scientists at the British biotechnology company Imutran Ltd., a unit of Novartis AG, tracked down 160 patients from eight countries who were treated experimentally with living pig tissue. Using the most rigorous viral testing available - and supported by testing at the U.S. Centers for Disease Control and Prevention - Imutran scientists found no evidence PERV had infected the 160 patients. Among the virus-free patients were 36 people deemed at high risk because they had very weak immune systems. "It's really good news for all those people waiting for this potentially lifesaving technology," said lead researcher Dr. Khazal Paradis of Imutran, which is developing ways to transplant entire animal organs. The study is not proof that xenotransplantation is safe, cautioned CDC's Dr. Louisa Chapman. "It's a substantial advance that ... gives us more confidence" about allowing certain experiments to proceed, she said. But all xenotransplants must continue to be closely watched for viruses, she added. The patients studied included diabetics who had received transplants of pig pancreas cells, burn victims who had temporary pigskin grafts, or liver- or kidney-failure patients who had their blood filtered through pig livers or kidneys outside the body while awaiting a human organ transplant. The study's biggest surprise: Pig cells remained alive, with no detectable ill effects, inside a small group of Russian patients eight years after they had an unusual treatment. "We did not expect the pig cells to survive for that long," Paradis said. The Russians had undergone therapy apparently used nowhere else. The blood of 100 child burn victims was filtered through a fresh pig spleen for one hour to help them fight severe infection. Blood normally runs through the spleen, part of the immune system, and Russian scientists have contended this therapy works. Regardless, Paradis found living pig cells in 23 of the 100 Russians. In most other experiments, the human immune system quickly has killed animal cells - another roadblock to attempting transplants of entire animal organs. The downside when animal cells survive is that "any virus may not be seen by the immune system either," said Dr. Jonathan Allan, a virus expert at the Southwest Foundation for Biomedical Research in San Antonio, who has been outspoken about the potential risk of xenotransplantation. "This study is not a green light" to rush ahead, warned Allan, who wants xenotransplant experiments limited to small numbers of closely monitored patients. For now, that is the U.S. Food and Drug Administration's approach. It is allowing a few small pig-to-people experiments, including implants of fetal pig cells into Parkinson's disease patients' brains, while scientists hunt potential infections. By LAURAN NEERGAARD Copyright 1999 Nando Media Copyright 1999 Associated Press <http://www.nandotimes.com/>