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Hepatitis B infects millions of people annually and nearly 1 million die each year worldwide, despite the existence of safe and effective injectable vaccines. Vaccines that can be administered orally, such as the one for polio, stand a better chance of being successful in poorer countries that have high death rates from treatable maladies. To that end, results from human trials of edible vaccines delivered in potatoes offer new encouragement.
Yasmin Thanavala of the Roswell Park Cancer Institute in Buffalo, NY, and her colleagues grew potato plants engineered to carry a gene that encodes the hepatitis B surface antigen. Once they had a plant that expressed high levels of the protein, the researchers cloned it and grew a number of the plants in a greenhouse. Forty-two volunteers then participated in a placebo-controlled, double-blind study in which they ate bite-sized pieces of the transgenic spuds or regular ones on three different occasions. After feasting on the tubers, the subjects underwent blood tests to assess their levels of hepatitis B virus (HBV) antibodies. According to the report, 60 percent of the subjects that ate the transgenic potatoes showed marked increases in their immune responses to HBV.
The authors note that the study did not use any buffers for stomach pH or additional stimulants, which have been required in past studies of edible vaccines. Incorporating a type of one of these adjuvants could thus confer a substantial advantage to both the magnitude and rate of response, they posit. Reporting the findings in a paper published online this week in the Proceedings of the National Academy of Sciences, the team writes that "a plant-derived orally delivered vaccine for prevention of hepatitis B virus should be considered as a viable component of a global immunization program." According to study co-author Charles Arntzen of Arizona State University, future tests will focus on freeze-dried potatoes, which are less bulky than raw vegetables because they lack water, and can be encapsulated in gelatin pills.
