The bacteria that cause cholera infect the gut and bloody the stool of victims. Roughly 200,000 cases occur each year in Africa, India and Russia, among other places. The microbe that causes it—Vibrio cholerae—travels from host to host in water and on washed food, where it can persist for almost a week. Vaccines exist but provide short-lived protection; some require refrigeration from when they are brewed in an industrial vat to the moment they are injected into a patient. Now Japanese researchers have created a strain of rice that can act as a vaccine and last for more than a year and a half at room temperature.
Immunologist Hiroshi Kiyono of the University of Tokyo and his colleagues inserted the genetic material from the microbe responsible for producing cholera toxin into a rice plant, whose genome has recently been sequenced. The plants produced the toxin and when the rice grains were fed to mice they provoked immunity from the diarrhea-causing bacterium. "We are considering rice as a new vaccine production and storage system, and natural vaccine delivery vehicle," Kiyono says. "The vaccine expressed in rice, or rice-based vaccine, will become a new form of vaccine production and delivery to [the] digestive tract for the initiation of antigen-specific mucosal and systemic immune responses."
Rice offers several advantages over traditional vaccines: it does not require needles, purification or refrigeration. In fact, the rice proved just as potent after 18 months of storage at room temperature and the vaccine did not dissolve when exposed to stomach acids, the researchers report in Proceedings of the National Academy of Sciences USA. But the immune response itself will require periodic updating. "Oral boosting should be necessary for the induction of antigen-specific immune response," Kiyono notes.
Because rice grains contain varying amounts of the vaccine—roughly 30 micrograms per seed—a pill of some kind would need to be created to make sure people get the proper dose. The rice plants would also have to be grown under carefully controlled conditions to ensure appropriate vaccine production. "We do not have any plan to deliver the vaccine as a form of steamed rice," Kiyono says. "A powder form of rice-based vaccine will be given in a tablet or capsule form."
The researchers point out that because rice plants do not scatter their pollen as widely as some of the other crops genetically modified to produce vaccines—corn, wheat, tomatoes—and are widely grown (unlike vaccine-producing bananas and potatoes), they pose less risk of contaminating normal crops and have broader utility. Such rice-based vaccines need not stop at cholera, Kiyono adds. The same technique could be used to create rice grains bearing protection against the flu, botulism or anthrax, among other diseases. Someday, the adage may be: A bowl of rice a day, keeps the needle away.