Structural and functional characterization of a maize‐derived hepatitis B surface antigen (HBsAg) for the development of an oral vaccine

Abstract

Hepatitis B is a life‐threatening infection of the human liver. A vaccine against hepatitis B has been available since 1982 but still more than 780,000 people die every year due to hepatitis B. The overall costs associated with vaccines make it difficult for its worldwide administration. In addition, there are certain groups of people who are poor responders to the available vaccines. Both these problems may be overcome by the use of oral vaccine. To this end, HBsAg was produced in maize and orally fed to mice as a boosting dose. The oral vaccine produced a robust immune response both systemically and mucosally, as evidenced by high antibody titers. In order to characterize the active ingredient of the oral vaccine, the maize‐derived HBsAg was purified using a two‐step process. Gel filtration experiments show that maize derived HBsAg exists mostly as a higher order oligomer. TEM analysis shows that the HBsAg oligomer forms virus‐like particles (VLPs). The far UV‐CD spectrum shows minima at 208 nm and 222nm, typical of alpha helical structure. Further, we demonstrate that removal of fat from the maize material by supercritical fluid extraction (SFE) shows higher immunological response compared to full fat (FF) and hexane extracted material. The VLPs obtained from SFE were more regular in shape and size and form particles of ~ 20 nm in size. In contrast, VLPs obtained from FF seed material are of varying size ranging from 20 nm to 100 nm. Further immunological studies are underway but the work presented here advances the path toward the development of a more efficacious oral vaccine.