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Scientists have genetically engineered tobacco plants to produce a protein
for a vaccine against amoebiasis ? a disease predominantly affecting Central
and South America, Africa and Asia, February 2007 by Wagdy Sawahel.

The World Health Organization estimates that amoebiasis, caused by the
parasite Entamoeba hisolytica, causes 50 million cases and 100,000 deaths a
year. There is currently no approved vaccine against the disease.

According to the researchers, the method used achieves high production
levels at a low cost, and also prevents modified genes from crossing to
other plants in the environment.

Henry Daniell and colleagues at the University of Central Florida in the
United States added the gene for a molecule that prompts an immune response
in humans ? the antigen ? to the chloroplasts of the tobacco plant.
Chloroplasts are the parts of the cells which contain the pigment that makes
leaves green.

With this method, the gene is not carried in the plant's pollen and so
cannot migrate to other plants.

The tobacco-derived antigen successfully prompted an immune response in
animal tests that was 4?20 times higher than that from other engineered
antigens.

The researchers calculate that an average yield of 24 milligrams of vaccine
antigen per plant could produce 29 million doses of vaccine per acre of the
transgenic crop.

The researchers say future development should be directed toward using
carrot or lettuce plants, paving the way for a cheap oral vaccine. Tobacco
was used initially, as it is easy to engineer in the lab.

Mohammed Ahmed Hamoud, professor of plant molecular biotechnology at Tanta
University, Egypt, welcomed the news. He said a plant-derived vaccine would
be environmentally safe, cheap and could be produced in larger amounts than
were usually possible with conventional vaccine production methods.

"However, it remains to be seen whether this technology will be available
for developing countries to produce their own drugs and vaccines locally,"
Hamoud told SciDev.Net. He hoped human clinical trials would begin soon.

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