University of Virginia Health System

University of Virginia Researchers Receive $3 Million Grant to Develop Edible Vaccine

The project, which is supported by a $3.3 million, five-year grant from the National Institutes of Health (NIH), is a collaboration between U.Va., Virginia Tech and Blacksburg, Va.-based TechLab, Inc. and CropTech. The goal of the project is to produce an edible vaccine to prevent infection by Entamoeba histolytica, a parasitic ameba that causes amebiasis, a leading cause of death in children in tropical countries. Amebiasis causes dysentery and/or liver abscess and kills an estimated 100,000 people each year, according to the World Health Organization.

While amebiasis is primarily a disease affecting poor children in poor countries, if we can prove that an edible vaccine works for this disease, it opens the door to many diseases that we have in this country, said Dr. William Petri, an infectious disease specialist at U.Va. and the principal investigator of the project. An edible flu vaccine certainly would be preferable to a flu shot every year.

In previous studies, the U.Va. research team discovered that immunization with lectin, a sugar binding protein, prevents amebic infection in animals. By genetically engineering vegetables to express the amebic lectin, the researchers hope to produce, in essence, an edible vaccine. Children in developing countries would simply have to eat a specially developed tomato or carrot to be protected from the disease, Petri said.

An edible vaccine will have several advantages over the more traditional intramuscular vaccine for infections in the bowel, Petri said. Intramuscular vaccines are not very effective at stimulating the mucosal immune system, which protects humans from all kinds of bugs that are eaten. The best way to stimulate the mucosal immune system is to eat something, he said.

In addition, an edible vaccine should cost less since it won't require refrigeration or sterile syringes, an important factor for poor countries.

The vaccine would work by interrupting the process by which the parasitic ameba kills cells in the large intestine. In a process that takes only seconds, the ameba contacts a host cell and destroys it. The human cells are not killed directly, but are tricked into committing suicide by the ameba in a process call apoptosis, or programmed cell death, Petri said.

The molecule that sticks the ameba to the human cell to initiate suicide of that cell is lectin. This lectin binds to a sugar, called galactose, on the human cell.

In addition to the development of the vaccine, U.Va. investigators are working with children in a refugee camp in Bangladesh to better understand how the human immune system fights off this infection.

The U.Va. Tropical Disease Research Unit is one of only four centers funded by NIH. The other centers are at Notre Dame University, the University of Georgia and the University of California at San Francisco.

June 16, 1999