While child vaccination campaigns have reduced the threat of hepatitis B in the United States, the virus remains a worldwide health problem. Experts estimate that over 350 million people now carry hepatitis B worldwide, and in many places vaccination has not been viable because some countries cannot afford to buy or refrigerate injectable vaccines.

Hepatitis B is a serious illness caused by a virus that attacks the liver. The virus can cause lifelong infection, cirrhosis of the liver, liver cancer, liver failure and death. In the U.S., children usually receive the vaccine in infancy, followed by booster shots as they grow.

Using genetically modified plants, lead researcher Charles J. Arntzen, co-director of the Center for Infectious Diseases and Vaccinology at Arizona State University's Biodesign Institute, said he and his colleagues hope to increase hepatitis B immunization rates around the world.

"We have been able to produce a form of the hepatitis B vaccine that can be delivered orally, that triggers a robust and lasting response in humans," Arntzen said.

In their experiment, Arntzen's team genetically modified ordinary potatoes to carry the gene for hepatitis B surface antigen. These potatoes were then cloned and cultivated. The researchers then tested the vaccine on 42 volunteers. Of these, about 60 percent had signs of immunity against hepatitis B after eating bite-sized pieces of the modified raw potato.

The report appears in this week's issue of the Proceedings of the National Academy of Sciences.

The problem with the current hepatitis B vaccine is that only 40 percent of the children around the world receive it, Arntzen said. "The other 60 percent don't get vaccinated due to a combination of factors," he added.

These barriers include cost, problems with delivery and a lack of professional health-care workers. "Our focus is to devise a system [so] that we can bio-manufacture the hepatitis B vaccine, but deliver it not by needles, but rather orally," Arntzen said.

Arntzen's next step is to convert the plant material, either potato or other vegetable, such as tomatoes, into something that looks like a traditional pill. "We use food processing to freeze dry the plant material and grind it into a powder. Then we pack the dry powder into gelatin capsules so we can measure accurate doses," he explained.

He believes that by using accurate doses, doctors in the field will achieve more than a 60 percent response.

The process is still being tested in animals, but Arntzen hopes to begin human trials in the foreseeable future. He hopes this method can be used for both primary and booster vaccinations.

According to the Arizona researcher, plant-based delivery might also work with other vaccines, such as those for measles and cholera.

In addition, when vaccines are eventually developed for diseases such as dengue fever, river blindness and malaria, this process will make oral vaccines more widely available. "In the next decade, we will make these vaccines," Arntzen said. "Our challenge is how to get them out to the people who need them."

"Producing oral vaccines that don't require refrigeration would vastly simplify the distribution of vaccines for global immunization," Arntzen said. "Our strategy is to work on vaccines that are not getting around the world as they should."

"The authors envision a day when most, perhaps nearly all, important vaccines will be mass-produced in some genetically modified plant, and delivered by ingestion," said Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine. "Such a system would overcome many of the factors that limit global immunization today, among them cost, availability, vaccine stability and the logistical demands of administration by injection."

But Katz is cautious. "There are miles to go before science can keep such promises," he said. "While the glass of plant-derived, ingestible vaccines may not be more than half full at present, it was, until recently, empty. The progress is clearly a cause for optimism, provided it is coupled with patience."

More information

The U.S. Centers for Disease Control and Prevention can tell you more about hepatitis B