The team re-engineered plant viruses to produce high levels of specially designed "virus-like" nanoparticles in tobacco plants. At about 25 nanometers in diameter, the particles are about the same size as the norovirus, but they consist only of the outer surface protein - the portion of the virus recognized by the human immune system. The particles contain none of the infectious material of the original virus, but they stimulate a robust immune response to fight off an actual infection.

To battle each new strain of the norovirus and to keep full resistance to older strains, Arntzen says the vaccine could be administered as a booster every 12 to 18 months. After successful experiments in mice, his team is developing a nasal delivery system for the virus-like particles. Arntzen expects to start clinical trials in late 2009 or early 2010.

Several companies, most notably pharmaceutical heavyweight Bayer, are investing in new facilities to create plant-based vaccines for cancer, as well as other pharmaceutical proteins. He suggests the first plant-based vaccines should be publically available within four to five years.

"Mammalian and insect-based vaccines are tried and true - some have barely changed in nearly 60 years," says Arntzen. But that doesn't necessarily mean they are the best in terms of manufacturing costs or flexibility. It simply means that the industry is not accustomed to using plant biotechnology.

"Among other factors, the uncertainty on how such products would be viewed in the FDA approval process has created uncertainty in big pharma companies, and uncertainty is often a 'kiss of death' in product development that can involve hundreds of millions of development cost." But, he adds, "the current pipeline of new products now working their way to FDA approval is sure to change these opinions in coming years."

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