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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.

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.

The study was published online in Plant Biotechnology Journal last week (25 January).

Link to full paper in Plant Biolotechnology Journal

Reference: Plant Biotechnology Journal doi: 10.1111/j.1467-7652.2006.00234.x (2007)