Investigators at the University of Central Florida (Orlando, USA) genetically engineered tobacco and lettuce plants by inserting genes into their chloroplasts that encoded for the production of the toxin-B subunit (CTB) of Vibrio cholerae (cholera antigen) fused to malaria vaccine antigens apical membrane antigen-1 (AMA1) and merozoite surface protein-1 (MSP1). Analysis of chloroplasts from the transgenic plants showed that CTB-AMA1 and CTB-MSP1 fusion proteins accumulated up to 13.17% and 10.11% (total soluble protein) in tobacco and up to 7.3% and 6.1% in lettuce, respectively.

To test the efficacy of the plant-produced antigens the investigators administered lyophilized chloroplast proteins either orally or by injection to nine groups of mice (10 animals in each group). Results published in the December 28, 2009, online edition of the journal Plant Biotechnology revealed that animals receiving the plant antigens produced significant levels of antigen-specific antibody titers. These antibodies completely inhibited proliferation of the malaria parasite and cross-reacted with the native parasite proteins in immunoblots and immunofluorescence studies. Protection against cholera toxin challenge correlated with CTB-specific titers of intestinal or serum IgA and IgG1. The vaccinated animals demonstrated long-term (>300 days or 50% of mouse life span) dual immunity against these two major infectious diseases.

"I am very encouraged because our technique worked well and provides an affordable way to get vaccines to people who need them most and can least afford them," said senior author Dr. Henry Daniell, professor of molecular biology and microbiology at the University of Central Florida.

"Producing vaccines in plants is less expensive than traditional methods because it requires less labor and technology," said Dr. Daniell. "We are talking about producing mass quantities for pennies on the dollar, and distribution to mass populations would be easy because it could be made into a simple pill, like a vitamin, which many people routinely take now. There is no need for expensive purification, cold storage, transportation, or sterile delivery via injections."

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