Production of hepatitis B surface antigen in transgenic plants for oral immunization

Abstract

Here we present data showing oral immunogenicity of recombinant hepatitis B surface antigen (HBsAg) in preclinical animal trials. Mice fed transgenic HBsAg potato tubers showed a primary immune response (increases in HBsAg-specific serum antibody) that could be greatly boosted by intraperitoneal delivery of a single subimmunogenic dose of commercial HBsAg vaccine, indicating that plants expressing HBsAg in edible tissues may be a new means for oral hepatitis B immunization. However, attainment of such a goal will require higher HBsAg expression than was observed for the potatoes used in this study. We conducted a systematic analysis of factors influencing the accumulation of HBsAg in transgenic potato, including 5' and 3' flanking elements and protein targeting within plant cells. The most striking improvements resulted from (1) alternative polyadenylation signals, and (2) fusion proteins containing targeting signals designed to enhance integration or retention of HBsAg in the endoplasmic reticulum (ER) of plant cells.

Immunogenicity in humans of an edible vaccine for hepatitis B

“…Frito-Lay 1607 (FL1607). The transformed FL-1607 was cured of the A. tumefaciens and clonally propagated, and the FL-1607 HB114-16 line was selected for its high level of HBsAg expression (14). This line then was clonally propagated to multiply the number of plants, potted in soil, and grown in a greenhouse to produce the potato tubers that were used in this clinical trial.…”

Medical molecular farming: production of antibodies, biopharmaceuticals and edible vaccines in plants

“…Plant-derived recombinant hepatitis-B surface antigen induced only a low level serum antibody response in a small human study, probably reflecting the low level of expression (1-5 ng g −1 fresh weight) in transgenic lettuce 27 . In spite of recent improvements in expression levels in potato with a view to clinical trials 31 , expression levels should be increased further for practical purposes. Also, even though Norwalk virus capsid protein expressed in potatoes caused oral immunization when consumed as food, expression levels are too low for large-scale oral administration (0.37% of total soluble protein) 16,26 .…”

“…Thus, achieving a high level of expression is crucial. The expression of vaccine components in plants has been increased by using a range of leader and polyadenylation signals 31 and by optimizing codon usage for plants 22,29,30 . Expression could also be raised through crosses of transformed lines to various genetic backgrounds, an approach that has been successfully applied to boost protein production in corn.…”

“…Favored locations for the expression of selected subunit vaccine components are the cell surface and the endoplasmic reticulum and Golgi body 14,18,29,31,32 . As with antibodies, transient expression systems (in which candidate vaccine sequences are incorporated into plant viral surface proteins) have also been investigated extensively and high levels of expression have been achieved.…”

Rice-based mucosal vaccine as a global strategy for cold-chain- and needle-free vaccination

“…Since then, many vaccine antigen candidates, including bacterial diarrhea antigens, hepatitis B antigen, Norwalk virus antigen, and respiratory syncitial virus antigen, have been expressed in tobaccos or potatoes to demonstrate the feasibility of edible plant-based vaccines (14)(15)(16)(17)(18)(19)(20)(21). However, these plant-based vaccines have remained a function of sophisticated bench-driven experiments and have not yet advanced to practical application.…”