Abstract
Hepatitis B persists as a common human disease despite effective vaccines having been employed for almost 30 years. Plants were considered as alternative sources of vaccines, to be mainly orally administered. Despite 20-year attempts, no real anti-HBV plant-based vaccine has been developed. Immunization trials, based on ingestion of raw plant tissue and conjugated with injection or exclusively oral administration of lyophilized tissue, were either impractical or insufficient due to oral tolerance acquisition. Plant-produced purified HBV antigens were highly immunogenic when injected, but their yields were initially insufficient for practical purposes. However, knowledge and technology have progressed, hence new plant-derived anti-HBV vaccines can be proposed today. All HBV antigens can be efficiently produced in stable or transient expression systems. Processing of injection vaccines has been developed and needs only to be successfully completed. Purified antigens can be used for injection in an equivalent manner to the present commercial vaccines. Although oral vaccines require improvement, plant tissue, lyophilized or extracted and converted into tablets, etc., may serve as a boosting vaccine. Preliminary data indicate also that both vaccines can be combined in an effective parenteral-oral immunization procedure. A partial substitution of injection vaccines with oral formulations still offers good prospects for economically viable and efficacious anti-HBV plant-based vaccines.
Highlights
Hepatitis B persists as a common human disease despite effective vaccines having been employed for almost 30 years
Promoter, promoter of 35S RNA of Cauliflower Mosaic Virus; CHO, cell line derived from Chinese hamster ovary; CLPs, Capsid-Like Particles; CPMV, Cowpea Mosaic Virus; CT, Cholera toxin; CTB, Cholera toxin subunit B; DW, dry weight; EMA, European Medicines Agency; ER, endoplasmic reticulum; FDA, U.S Food and Drug Administration; FW, fresh weight; gut-associated lymphoid tissue (GALT), Gut-Associated
Efficient stable and transient plant expression systems have been developed for the production of each Hepatitis B virus (HBV) antigen, in addition to improved methods of plant tissue processing and antigen purification, as well as new effective immunization procedures
Summary
Hepatitis B virus (HBV), as an etiology of acute and chronic hepatitis (HepB), cirrhosis and hepatocellular carcinoma (HCC), was identified in the 1960s [1]. Expression of completely native M- and L-HBsAg in microorganisms, albeit possible [13,14], is still not regularly employed These antigens are usually produced in special yeast systems [15] or in. M- and L-HBsAg have been considered, together with the core antigen of HBV (HBcAg), as components of postulated therapeutic vaccines for chronic carriers [17,18]. Administered plant-associated antigens were reckoned as alternatives, or at least supplements for, injection vaccines derived from yeast or mammalian cells [20,21]. Outlays of vaccine production in plant-based expression systems were assumed to be comparable with microbial bioreactors and much lower than in mammalian cells. Plant-based vaccines, especially oral ones, were assumed to be cheap and easy, both in production, distribution and application, for developing countries. A leading project of that idea soon became a vaccine against HepB
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