Abstract
The binding subunit of Escherichia coli heat labile enterotoxin (LT-B) is a highly active oral immunogen. Stable genetic transformation of tobacco and potato was achieved using the gene encoding LT-B or a chimeric gene encoding an LT-B fusion protein with a C-terminal microsomal retention sequence (SEKDEL). The transgenic plants expressed the foreign peptides, which retained the property of binding ganglioside, the natural ligand for LT-B on intestinal epithelia. Immunization of mice with partially purified leaf extracts delivered by oral intubation elicited serum and secretary anti-LT-B immunoglobulins which neutralized the enterotoxin in in-vitro cell protection assays. Direct feeding of fresh transgenic potato tubers expressing the LT-B fusion protein also elicited anti-LT-B serum and secretary antibodies. In order to obtain higher levels of expression of LT-B in plants, a synthetic gene was designed with optimal plant-codon usage. The putative polyadenylation signals and MRNA instability signals were removed. Studies of expression of the designed gene encoding LT-B suggests an elevated level of expression compared to the native LT-B gene. These experiments demonstrate that a candidate oral immunogen can be produced in plants and, more importantly, serum and mucosal immune responses can be elicited when it is presented simply as a component of a food source; this is "proof of concept" that plants can be used to produce and deliver recombinant oral (edible) vaccines.
Haq, Tariq Ansarul (1996). Production of orally immunogenic bacterial protein in transgenic plants. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -H366.