Given the choice between a needle in your arm and a few lunches of (raw) potato chips containing a vaccine, which would you prefer? Though still far from reality, edible vaccines have come a small step closer: in todays issue of Nature Biotechnology, Hugh Mason, Charles Arntzen and their colleagues from New York State report that a hepatitis B protein produced in potatoes leads to an immune response in mice. They also improved the technique for making the protein in potatoes.
The scientists fed mice three doses of raw potatoes containing the hepatitis B surface antigen (HBsAg) and also gave them cholera toxin, an adjuvant that stimulates the immune response. After three weeks, the mice developed antibodies against hepatitis B; this response declined within weeks. But when the mice were injected with a low dose of a commercial vaccine at this point ("low" meaning not enough to make them immune), the antibodies came back to very high levels. Thus, the potato vaccine had probably created memory cells that the injection activated.
In the second part of their study, the researchers tested various methods to increase the yield of HBsAg production in potatoes. Sufficient yield is a crucial factor for successful edible vaccines because the stomach and intestines digest most of the useful protein before it can reach the immune system. The greatest improvements resulted when the scientists used a different signal sequence--called polyadenylation signal--at the end of the HBsAg gene. This signal might stabilize the messenger RNA from which the protein gets translated.
The next step will be to test the effects of the potato hepatitis vaccine in humans. This testing has already been done with edible vaccines against the Norwalk virus and against pathogenic forms of E.coli, which both cause diarrhea. Ultimately, a cheap plant vaccine for hepatitis B could help the two billion people who are infected, many of them in developing countries.
