Vaccines made in plants could offer vital disease protection.© Punchstock

Genetically modified potatoes can deliver the disease protection that normally comes from a vaccine shot, say scientists, which could be good news for developing nations.

The hepatitis B virus attacks the liver and claims the lives of more than half a million people each year. But conventional vaccines require cold storage, which can be hard to guarantee in the remote areas of developing countries with warm climates. And medical workers often have a tough time determining whether a delivery of the relatively costly hepatitis B vaccine has received accidental exposure to heat, rendering it ineffective, says biologist Charles Arntzen of Arizona State University in Tempe, who worked on the research.

So Arntzen and his colleagues have designed an edible vaccine that can be stored without refrigeration inside a humble potato. They took a gene out of the hepatitis B virus and incorporated it in the potato plant, which responded by producing the virus antigen. Once ingested, this antigen protein creates an immune response in the human body that acts as a booster shot against the hepatitis B virus.

The team says that although this approach is unlikely to supersede initial vaccinations, it could replace the repeated booster injections needed to maintain immunity. "This has the potential for a big impact on global health," says immunologist Julian Ma of St George's Hospital Medical School in London.

An edible vaccine would reduce the need for needles and make it simpler to administer on multiple occasions. This gives it an advantage over the full vaccination programme, which involves a series of three injections given over many months.

Super spuds

Participants in the study had already received the primary injections against hepatitis B between 1 and 15 years ago. Arntzen and his colleagues found that 19 of the 33 people in their study produced more antibodies against hepatitis B after eating the potatoes. One subject's protective antibodies increased 56-fold, the team reports in the Proceedings of the National Academy of Sciences¹.

The fact that the vaccine worked in nearly 60% of the participants came as good news. The researchers explain that even the commercial vaccine, which contains an extra ingredient that attracts immune cells to boost the body's response, does not work in 10% of subjects.

Process for progress

Arntzen's team have already incorporated two other vaccines into potatoes: one against a disease commonly known as travellers' diarrhoea, caused by toxin-producing Escherichia coli bacteria, and another against the Norwalk virus, which causes an intestinal illness.

"We've been delighted," says Arntzen. "We keep encountering cynics who say this won't work and so far we've solved all the problems," he says. Unlike travellers' diarrhoea and the Norwalk virus, the hepatitis B virus did not evolve to survive in the gut, which makes the success of this edible vaccine all the more surprising. For the hepatitis B vaccine to work, it must survive digestion before acting on the immune system.

But raw potatoes do not make an appetising dish and they contain relatively inconsistent vaccine doses. For this reason Arntzen and his colleagues are focusing on making genetically modified tomatoes and converting them into pills. "I expect we will never do another human clinical trial with unprocessed materials," he says. 

St. George's Hospital Medical School, London, UK

• References

  1. Thanavala Y., et al. Proc. Natl. Acad. Sci. USA published online. doi: 10.1073/pnas.0409899102 (2005).