Submitted to: Vaccine
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/2/2006
Publication Date: 11/2/2006
Citation: Moravec, T., Schmidt, M.A., Herman, E.M., Woodford-Thomas, T. 2006. Production of Escherichia coli heat labile toxin (LT) B subunit in soybean seed and analysis of its immunogenicity. Vaccine. 25:1647-1657. Interpretive Summary: The synthesis of foreign proteins in plants offers the prospect to produce proteins that are expensive to produce in cell cultures in any inexpensive crop platform that can reduce the cost to produce a unit of protein by orders of magnitude. One of the limitations in exploiting this technology is to develop procedures and protocols to induce plants to produce large quantities of correctly formed proteins. In the present manuscript a model vaccine protein was produced in transgenic soybean seeds. Soybeans contain about 40% protein by weight and if only a small fraction of this capacity was used to produce a foreign protein this would create the capacity to make large quantities of protein inexpensively. The data in this paper shows that 2-3% of the protein synthesis capacity of soybean can be diverted to make a model vaccine protein with the result that over 1% of the weight of the soybean consists of the foreign protein. Biochemical and immunological analysis shows that the vaccine protein is correctly formed as its five-unit structure and that the protein binds to a reagent showing it is active. Tests of the vaccine protein in the soybean shows that direct consumption of the soybean without purifying the protein yields an immunological response in mice that protects them from the action of the disease-produced toxin. This study is significant in that transgenic soybeans were produced containing sufficient levels of vaccine protein that whole soybean can be used to induce a protective response. This indicates that similar soybeans producing a variety of vaccine-type proteins could be fabricated into soy products that would be easy to deliver for oral immunization. The data included in this paper offers the prospect of new-value added products for soybean using the protocols developed. This information will be of interest to industry and academics developing value-added products in plants. The potential to produce high value products in crops like soybean can offer midwest, and US, farmers/producers to add value-added products as a new crop opportunity.
Technical Abstract: Expression of the heat-labile toxin B subunit of enterotoxigenic Escherichia coli (LT) B was directed to the endoplasmic reticulum (ER) of soybean seed storage parenchyma cells for immunogen sequestration in de novo synthesized, ER-derived protein accretions in transgenic seed. Pentameric LTB accumulated to 2.4% of the total seed protein and was stable in dessicated seed. LTB-soybean extracts administered orally to mice induced significant systemic IgG and IgA, and sIgA antibody responses. Sera from immunized mice blocked ligand binding in vitro. Immunized mice exhibited partial protection against LT challenge. These results demonstrate the utility of soybean as an efficient production platform for the potential use as an oral vaccine delivery system.