• 29 June 2006
• NewScientist.com news service
• Andy Coghlan

GENETICALLY modified tomatoes containing edible vaccine are to be used to challenge two of the world's most lethal viruses.

The aim is to create affordable vaccines for HIV and the hepatitis B virus (HBV) that could be easily grown and processed in the countries where they are most needed. So far, none of the 90 or so potential vaccines against HIV have proved successful and, though a vaccine already exists for HBV, it is too expensive to be used by poorer countries.

Rurik Salyaev at the Siberian Institute of Plant Physiology and Biochemistry in Irkutsk, Russia, and his colleagues used the soil bacterium Agrobacterium tumefaciens to shuttle a synthetic combination of HIV and HBV DNA fragments into tomato plants. These include fragments of genes for various HIV proteins and the gene for an HBV protein called HBV surface antigen.

The tomato plants then manufacture the proteins and, like the oral polio vaccine, when the tomatoes are eaten, these proteins prompt the body to create antibodies against the viruses.

Mice fed a solution containing the tomatoes in powdered form developed high levels of antibodies in their blood to both viruses. Equally important, the researchers found antibodies on mucosal surfaces, where the viruses can gain entry to the body through sexual contact. "That's where you want it to be protective," says Rose Hammond of the US Department of Agriculture's Agricultural Research Service in Beltsville, Maryland, which is collaborating with the Russian researchers.

The results were presented at a meeting of the International Society for Infectious Diseases in Lisbon, Portugal, last month, by team leader Sergei Shchelkunov of Russia's Vector Institute in Koltsovo.

If the tomato-based vaccines work in humans they could be given in tablet form, since giving people the tomatoes directly would make it difficult to control how much protein they received.

"You wouldn't have to refrigerate the vaccine, and you wouldn't need to inject it with needles, which pose an infection risk," says Hammond. These would be big advantages in poorer countries. "If an oral vaccine worked out, it would probably be inexpensive and relatively easy to make and administer," says Pat Fast, at the International AIDS Vaccine Initiative in New York. However, an ideal vaccine would trigger production of protective T-cells as well as antibodies, she says.

Tomatoes are not the first vegetables people have used to make vaccines. Charles Arntzen of Arizona State University in Tempe has produced potatoes that stimulate protective antibodies against HBV when eaten raw, although the recipients had previously been vaccinated against the virus, potentially masking the effects. Arntzen is awaiting permission to continue his research.