Scientists have genetically engineered potatoes for the first time to deliver an edible vaccine against a common virus.
The researchers added to spuds the capsid protein that forms the shell around diarrhea-causing Norwalk virus. When eaten, the product stimulated volunteers’ immune systems to create a flood of antibodies. The response prevented Norwalk virus from latching onto cells lining the intestines, which causes disease.
Twenty volunteers ate two or three portions of raw, diced, genetically modified potatoes over 3 weeks. Four other volunteers consumed unaltered potatoes. Blood samples taken over the next 2 months revealed that 19 of 20 people getting the edible vaccine had elevated concentrations of antibodies against Norwalk virus, although the rise varied between individuals.
The researchers also detected antibodies in the feces of six of the people who had received the edible vaccine. That indicates that the immune agents were so plentiful in the gut that some were being excreted, and that’s a good sign, says study coauthor Charles J. Arntzen of the Boyce Thompson Institute for Plant Research at Cornell University.
Antibody concentrations remained unchanged in the volunteers receiving the untreated potatoes, Arntzen and his colleagues report in the July Journal of Infectious Diseases.
“It’s a great study, very forward thinking,” says Dennis R. Lang of the National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Md.
The intestinal virus is named for Norwalk, Ohio, where researchers first identified it in 1968. Norwalk or a related virus infects more than 23 million people in the United States every year, causing diarrhea, nausea, and stomach cramps, according to the Centers for Disease Control and Prevention in Atlanta.
Scientists consider Norwalk virus no more than a nuisance in the United States. It’s distressing but survivable. Natural antibodies form during a bout with the virus, and some of these linger indefinitely. “We’ve never seen a volunteer without any,” Arntzen says. Unfortunately, the antibodies decline to useless concentrations over a few years, leaving a person susceptible again.
In developing countries around the world, Norwalk’s occurrence can be more deadly, especially if children getting it become dehydrated, Arntzen says.
In those countries, injectable vaccines are costly to deliver and needles can transmit diseases, says Arthur O. Anderson of the U.S. Army Medical Research Institute of Infectious Diseases in Frederick, Md. An edible vaccine, therefore, might present a better approach to battling Norwalk virus outbreaks in developing countries, he says.
The scientists designed this initial experiment to gauge the safety of the edible vaccine. They won’t be able to measure its effectiveness until they give it to people who are then exposed to the actual virus. NIAID, which funded Arntzen’s study, is currently working out guidelines for such a test, Lang says.
Meanwhile, Arntzen and his colleagues plan to trade in potatoes for tomatoes as their vaccine carrier–possibly dried for better storage. They may eventually try to develop banana-based vaccines. They’re also targeting papilloma virus, which can lead to cervical cancer, as well as hepatitis B virus. A reliable injectable vaccine already exists for hepatitis B, but a less expensive, edible vaccine would be better, particularly for use in the developing world, Arntzen says.