Oral immunization with a lettuce-derived Escherichia coli heat-labile toxin B subunit induces neutralizing antibodies in mice

Transgenic plants serve as attractive systems for the production and delivery of subunit vaccines, thus expression of an enterotoxigenic Escherichia coli (ETEC) antigen in an edible plant may lead to the development of a viable oral vaccine against cholera and ETEC diarrhea. In this study, expression of the heat labile toxin B subunit (LTB) from ETEC was performed in lettuce, and its immunological characterization was investigated. A total of 27 independent transgenic lines were established following Agrobacterium-mediated transformation. Selected lettuce lines were subjected to GM1-ELISA to confirm the proper quaternary structure of the LTB protein. Levels of accumulation of the pentameric LTB reached up to 0.05% of the total soluble protein (TSP) in T1 and T2 progenies of these lines. Oral immunization of Balb/c mice was conducted using three weekly doses of lettuce-derived LTB. This elicited specific and significant antibody responses in both serum and intestinal tissues. Moreover, mice immunized with lettuce-derived LTB showed diminished intestinal fluid accumulation following challenge with the cholera toxin. This study demonstrated that this plant-based vaccine may contribute to immunization practices against diarrheal diseases.