Plant-Based Vaccines Against Hepatitis B

Abstract

Hepatitis B is one of the most common, complex, and dangerous human diseases. One third of the global population still lives in regions of a high prevalence of hepatitis B virus (HBV). Among infected people, up to 40 % develop major liver dysfunction or chronic hepatitis, cirrhosis, and hepatocellular carcinoma, which in total cause up to 1 million deaths/year. Mass immunization programs using highly effective subunit vaccines resulted in partial control of the virus. Nowadays, several tens of prophylactic vaccines are available based mainly on the small-surface antigen of HBV, and also on other surface antigens, as well as some therapeutics are exploited. However, the epidemiologic situation has improved only in industrialized countries, while the others remain under the threat of HBV. Hence, plant-based oral vaccines have been supposed as an alternative to classic injections. Yet, years of research have brought not only successes but stoppages, too. Production technology of the viral antigens in plants progressed significantly, and obtained yields reached several tens or even hundreds of micrograms per gram of tissue. However, the elaboration of a vaccine form, both effective and practical in use, appeared to be a real challenge. Plant-based vaccines evolved from edible vaccines to processed formulations, e.g., tablets or pellets, administered as a part of combined parenteral–oral immunization. In parallel, immunization trials via injection using purified plant-produced HBV antigens were performed. Both vaccine types revealed comparable effectiveness to commercial products. In conclusion, while the original idea of plant-based vaccines needs revision, they still can be considered as one of the possible tools for economical, simple, and mass vaccination against HBV.