Taters for tots provide an edible vaccineby J. Raloff
Consider the versatile potato. Even most children consume it in at least some form -- baked, mashed, French fried, the list goes on. Now, molecular biologists predict that through genetic engineering they can turn spuds into the darling of the medical world: low-cost, nutritious vaccines.
William H.R. Langridge and his coworkers at Loma Linda (Calif.) University School of Medicine say they have inserted into potatoes a gene that enables the tuber to make a nontoxic component of the cholera toxin. The research could lead to protection against a scourge that afflicts 5 million people annually, they assert.
Moreover, because the toxins produced by the bacterium that causes cholera and by the more common Escherichia coli are nearly identical, Langridge says, vaccines against one germ may head off or ameliorate disease caused by the other.
Cholera locks open crucial pores in cells lining the gut. "So water pours from the blood into the intestines and then out of the system," Langridge notes. People with this diarrhea can quickly become dehydrated and die.
Langridge's team added the cholera toxin's B-protein to potatoes. This portion of the toxin not only binds to cells in the gut, it also triggers the production of antibodies against cholera.
Mice ate the altered potato raw once a week for 4 weeks and downed a booster meal some 40 days later. The scientists then removed pieces of intestine from the animals and added cholera toxin to the tissues. In the March Nature Biotechnology, Langridge's team reports that tissue from the treated mice leaked about half as much as tissue from mice that ate only regular potato.
Because people seldom eat potatoes raw, the scientists cooked the medicinal spuds and found that at least half of the vaccine survived in biologically active form -- a donut-shaped ring of five linked B-protein molecules. Taking into account the fact that to develop immunity, people need far less of the vaccine than mice do, Langridge calculates that one cooked potato a week for a month should provide enough active B-protein to immunize against the cholera toxin. However, because immunity falls over time, periodic booster spuds would be required.
Langridge plans to refine the potato further, adding genes to make its vaccine target not just the toxin but also the bacterium that produces it. Such potatoes would constitute a medicine, he emphasizes, and should not be eaten too often. Overexposure to their vaccine could suppress a person's production of disease-fighting antibodies.
Charles J. Arntzen of Cornell University's Boyce Thompson Institute for Plant Research was one of the first scientists to engineer a potential vaccine into potatoes, but the E. coli protein he uses breaks down at high temperatures. He says he is especially interested in the results from cooked potatoes in the Loma Linda project.
Concern that heating would inactivate vaccines had led to an expectation that any useful ones would eventually need to go into foods eaten raw, such as bananas, observes Carol Tacket at the University of Maryland's Center for Vaccine Development in Baltimore. "But now that we know you can cook them, maybe potatoes will become the ultimate vehicle."
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Arntzen, C.J. 1997. Edible vaccines. Public Health Reports 112(MayJune):190.
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Raloff, J. 1995. Cholera toxin fights autoimmune disease. Science News 147(April 22):247.
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Charles J. Arntzen
Boyce Thompson Institute for Plant Research
Ithaca, NY 14853-1801
University of Maryland
Center for Vaccine Development
685 West Baltimore Street
Baltimore, MD 21201
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