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DENVER, Feb. 16, 2003 (UPI) -- A vaccine for the Norwalk virus that is grown in tomatoes and delivered in pills containing freeze-dried tomato juice is now awaiting approval for clinical studies in humans, researchers reported late Saturday.
If the vaccine passes those tests, the hope is its distribution could begin throughout the developing world, said geneticist Charles Arntzen of Arizona State University in Tempe, who has been working for more than a decade on pharmaceuticals that could be delivered cheaply via food plants.
"Norwalk virus in the first world is primarily an inconvenience," Arntzen told United Press International, but in the developing world it is often deadly, in particular to young children, who die of dehydration caused by disease-induced diarrhea.
Speaking at the annual meeting of the American Association for the Advancement of Science, Arntzen said he used tomatoes because the processing technology is "off-the-shelf." To make the Norwalk vaccine, Arntzen and colleagues took the gene responsible for developing the protein coat of the virus and transferred it into tomato plants, which are grown in high-tech, sealed greenhouses at the University of Arizona in Tucson.
Although the protein coat cannot cause the disease, it can elicit an immune response, Arntzen explained. Most people already have antibodies to the virus, although usually not enough to prevent it, he said.
Arntzen's approach to vaccine production has been criticized, he said, because of the danger of genetically modified plants invading the food supply. On the other hand, he added, using non-food plants such as tobacco would require developing new ways of extracting the pharmaceuticals.
More important, he said, there currently is no vaccine available for Norwalk virus and the World Health Organization reports 2.5 million children younger than age 5 die of diarrhea every year in the developing world. Even in North America, however, Norwalk can have serious consequences, Arntzen said. For example, between 60 percent and 80 percent admissions to U.S. hospitals are people reporting Norwalk- like symptoms -- diarrhea, nausea and vomiting.
Norwalk is known as the "cruise ship virus," because of well- publicized outbreaks aboard vessels embarking from U.S. ports and elsewhere. But the virus also has caused closings at hospital emergency wards, schools and nursing homes.
"What we're looking at is product safety," said John Howard, a biotechnology consultant and adjunct professor at Texas A&M University in College Station. "The issue is keeping it out of the food chain," Howard told UPI. If it can be guaranteed that the genetically modified tomatoes do not wind up in pasta sauce or ketchup, he said, "I don't have any prejudice about putting (the vaccine) into food plants."
Freeze-drying the juice and putting it in pills is also one way of ensuring the vaccine stays out of the general food supply, a danger that Arntzen has said is worrisome.
Most so-called "transgenic" drugs use a similar technology, but use microbes or cultured animal cells to produce the protein, Howard explained. Howard, who works with transgenic plants, said it is possible to use plants to do the same thing -- the protein trypsin, usually made in cow cells, is now being grown in genetically-modified maize and sold for use in pharmaceutical production.
The animal-based trypsin carries the danger of transmitting disease, Howard said, and supplies are limited.