Great ideas come in the strangest packages. For Charles Arntzen, inspiration struck in the form of a banana. This “eureka moment,” as he calls it, happened while he was traveling through Thailand in 1991.

“I had a weekend off and went to the floating market north of Bangkok,” recalls the ASU plant biologist. “There was an old lady with a boat full of bananas. A mother came along and bought a bunch. She had a child in her arms that started to cry. The mother took out a sweet, ripe banana, rubbed it on her finger, and stuck it in the kid’s mouth.”

A year earlier, the Children’s Vaccine Initiative asked scientists to develop new ways of making and delivering vaccines. Arntzen had been thinking about that challenge during his trip. The woman in the market gave him an idea. “I thought, ‘Gee, if we put genes for vaccines in bananas, every mother in Thailand knows how to get it in their kid’s mouth!’” he says.

Arntzen and his research team have been working to grow vaccines in food crops ever since. He is working on vaccines for cholera and hepatitis B, among other diseases.

Making vaccines you can eat isn’t really as easy as feeding a child a banana, however. First, the researchers need to make sure the vaccines will not be destroyed by stomach acid before having a chance to work. And they have to be sure that the vaccine will attract the attention of the immune system.

“How do we put the gene in? How do we improve the gene? How do we get the gene in the fruit as opposed to the root or the leaves?” Arntzen asks. These are all questions he must answer.

Although his inspiration came in the form of a banana, Arntzen has been working with tomato plants to make his vaccines. But tomatoes— or any other fruits—come in different sizes.

“I started out with a rather naïve view that we would simply harvest, say, a banana,” says Arntzen. “But you can't just grow a crop and put it out into the public. You have to standardize doses and meet regulations.”

To do this, the researchers purify the fruit, removing seeds and skins. Then they freeze-dry it, powder it, and put it into capsules.

Plant-based vaccines are much cheaper to make than traditional vaccines. They also do not need to be refrigerated. As a result, developing countries can produce and distribute the products on their own without relying on drug companies in Europe or the United States.

“You don’t have to build a big, expensive factory to do what we do,” explains Richard Mahoney, a chemist who works with Arntzen. “A modern vaccine factory costs from $80 million to $250 million to build. For plant vaccines, you’re talking about a greenhouse. Even if the vaccine tomatoes cost ten times the price of regular tomatoes, it’s still just pennies a dose.”