ASU biologist pioneers edible vaccines

As Archimedes could attest, inspiration can strike anywhere. Legend has it that the ancient Greek thinker discovered the mathematical laws governing buoyancy in a bathhouse while idly watching soap float. The nature of scientific research has changed since the 3rd century B.C., but the spirit of observational inquiry that led to Archimedes' principle is still active.

When Dr. Charles Arntzen of Arizona State University visited Thailand in 1992, he was not expecting a moment of scientific "eureka" that would redirect his career. However, after observing a young Thai mother soothing her fussy infant with bits of banana, this plant molecular biologist was struck with an idea that is both startling and ingenious. What if, in addition to quieting her child, the mother could also administer a life-saving vaccine in the banana?

Arntzen's vision is well on its way to becoming reality thanks to a combination of dedication and applied biotechnology. As the president emeritus of the Boyce Thompson Institute for Plant Research, founding director of the Arizona Biomedical Institute, and member of the President's Council of Advisors on Science and Technology, Arntzen is well equipped to handle the challenge he has undertaken. His breakthrough lies in forging a link between green plants, foreign DNA, and vaccines.

Vaccination stands as one of modern medicine's greatest success stories. Early experiments by Edward Jenner and Louis Pasteur taught physicians that they could prevent disease merely by exposing a patient to a weakened or inactivated pathogen. While his protocols violate today's clinical trials regulations, Dr. Jenner was able to prevent children from getting smallpox--even when he deliberately exposed them to it--after first inoculating them with the pus from cowpox.

Today, most new vaccines contain a specific protein or proteins from a pathogen of interest and not the pathogen itself. A protective immune response can result from this more limited (and inherently less risky) exposure. Though materially different from those developed by Jenner and Pasteur, modern vaccines, including Arntzen's, still build upon the same fundamental principle: if the immune system is trained to recognize a pathogen prior to infection, the actual disease can be prevented when the pathogen is encountered.

Disease-prevention via an edible vaccine is great news for people around the globe. The problem with current vaccination protocols-- and the passion behind Arntzen's research--is that what works in the developed world is often much more difficult to deliver in the developing world, or simply too costly for them to buy. A vaccine that requires a sterile syringe, refrigeration prior to injection, and repeat booster shots is difficult to implement in many countries. Unfortunately, this often means that the people who most need a vaccine cannot get it. In a discussion of his work, Arntzen points out that "each year diarrhea kills about two and one-half million children under the age of five." Arntzen persuasively uses such horrendous statistics to champion his cause. In his own words, It's hard to be pro-infant mortality."

While Arntzen's edible vaccine is likely to win approval from children everywhere, there are actually significant medical advantages to this route of administration. An oral vaccine incorporated into a plant bypasses the need for sterile syringes, costly refrigeration, or multiple injections. Furthermore, since many of the developing world's most deadly diseases--cholera, rotavirus, or E. coli to name a few--enter the body through the gastrointestinal tract, a vaccine that is ingested may actually provide the best protection because it mimics the natural route of infection.

The trick with an edible vaccine is convincing a plant to express the genes of a foreign organism. Fortunately, Arntzen's prior work prepared him to face this challenge. As a biochemist, his career focused on unraveling the means by which photosynthetic membranes in plants capture solar energy. "What we've done for the last ten years is try to change the cellular machinery of a plant by adding a new gene, cause that gene to make a new protein, and coax the new protein into folding to the desired shape so that it accumulates. I took knowledge about plants proteins under normal circumstances and used that for something new." That something new was vaccine development.

When Arntzen started investigating the vaccine issue in the early 1990's, scientists were already using genetically engineered yeast to produce proteins for injection vaccines. Arntzen's experience with green plants led him to consider other options. He remembers thinking at the time, "Would it be possible to use a higher plant instead of a lower plant, something we already know is an agricultural crop? Can we take a potato or tomato and turn it into a green factory?"

Indeed, modern technology enables Arntzen to insert specific genes from a foreign organism into the genome of a green plant. Progeny plants will then produce the foreign protein. If the foreign protein happens to be an immunity-inducing pathogen protein, an edible vaccine is in the making.

Yet the challenges of science are not the only obstacles Arntzen faces. This type of project requires a multidisciplinary approach, incorporating the skills of many types of basic and clinical scientists as well as experts in product regulation and distribution. Says Arntzen, "No biochemist can make progress in moving something forward on his own. I need linkages with people who do immunology. I need people in vaccine development. I also have increasingly found that I have to understand the regulatory environment."

In fact, satisfying regulatory policies has been one of the most painstaking elements of Arntzen's work. He is determined to demonstrate that his vaccine passes the rigorous requirements of the Food and Drug Administration, thereby silencing any critics who would accuse him of "dumping" experimental technology on the world's poor.

His most recent clinical trials are particularly exciting. Human volunteers who enrolled in a study at the University of Maryland in Baltimore started producing antibodies against Norwalk virus (which causes acute bouts of diarrhea) after eating Arntzen's creations-- genetically engineered potato. Negotiations are currently in progress to start clinical trials abroad with the International Vaccine Institute in Korea, a new center funded in large part by the Bill and Melinda Gates Foundation. Clinical trials of cholera vaccines are also planned to take place there as well as in Vietnam and Cambodia, regions where cholera is still a serious medical concern.

In addition, during a recent scientific conference held at the Flinn Foundation's Phoenix office, tentative connections were made with company representatives from Egypt and India. This meeting, organized by Arizona Biodesign Institute on behalf of the ProVACS Ceneter (Production of Vaccines from Applied Crop Sciences), highlighted technical advances in plant-based vaccines. Arntzen, the keynote speaker at the meeting, says, "We intend to visit India. They're willing to fund clinical trials there - we could send vaccine materials to them and they're interested in developing the product."

For now, all such clinical trials will involve modified potatoes or tomatoes. Both products can be easily freeze-dried, transported, and reconstituted. Since many target countries have a long history of herbal medicine, Arntzen is interested in working within already-existing ideas. "Our goal is not to make the decision for how we want it (the freeze-dried dose) introduced," he says. "We want to work with them."

In the meantime, Arntzen is still working on the banana vaccine. Tomatoes and potatoes have shorter growing seasons and are easier to manipulate in an experimental setting, but Arntzen has not given up on the popular yellow fruit that sparked his initial idea. Currently, there are several transgenic banana trees growing in his greenhouses on the ASU-East campus.

Once the foreign proteins are expressed in the target plant, the same concerns for a traditional vaccine--efficacy, quality control, and dosage regulation--also become an issue. Arntzen's original, utopian vision was of a communal banana tree where villagers could dose themselves. This has been replaced by a more practical vision, perhaps a controlled dose of freeze-dried tomato or, later, a banana chip. Practicality hasn't inhibited Arntzen's idealism however. To this day he keeps a jar of Gerber's baby food--banana of course--on the corner of his desk for inspiration.

Arizona's sunny skies and warm weather are known to attract people from all over the world--who can resist playing golf in short sleeves in December? Arizonans are fortunate that warm weather is also good for growing plants. A combination of ASU's offer of the Florence Ely Nelson Presidential Endowed Chair and greenhouse opportunities brought Arntzen to Phoenix. He sounds remarkably like a winter tourist when he exclaims, "The weather is perfect!" Yet unlike the tourists, Arntzen is excited about greenhouse horticulture, not golf. In its own way, a functional edible vaccine would indeed be a hole-in-one.