The original hepatitis B virus (HBV) large surface antigen gene was synthesized. In order to optimize the expression of this gene in tomato plants, the tobacco pathogenesis-related protein S signal peptide was fused to the 5 end of the modified gene and the sequence encoding amino acids S, E, K, D, E, and L was placed at the 3 end. The gene encoding the modified HBV large surface antigen under the control of a fruit-specific promoter was constructed and expressed in transgenic tomato plants. The expression of the antigen from transgenic plants was confirmed by PCR and reverse transcriptase PCR. Enzyme-linked immunoassays using a monoclonal antibody directed against human serum-derived HBsAg revealed that the maximal level of HBsAg was about 0.02% of the soluble protein in transgenic tomato fruit. The amount of HBsAg in mature fruits was found to be 65-to 171-fold larger than in small or medium fruits and leaf tissues. Examination of transgenic plant samples by transmission electron microscopy proved that HBsAg had been expressed and had accumulated. The HBsAg protein was capable of assembling into capsomers and virus-like particles. To our knowledge, this is the first time the HBV large surface antigen has been expressed in plants. This work suggests the possibility of producing a new alternative vaccine for human HBV.Hepatitis B virus (HBV) is a major cause of acute and chronic hepatitis. HBV DNA was found in most of the newborns from hepatitis B surface antigen (HBsAg)-positive mothers (27). The current HBV vaccine is a biotechnology product that falls in the category of "subunit vaccines" and is made from yeast cells grown by fermentation. The vaccines have prevented numerous infections. However, administration of the vaccine intramuscularly causes some pain, and it is not widely accepted, especially for children. In addition, current vaccines have the safety limitations of syringe-and-needle vaccination programs. In recent years, a novel production system of vaccines-"edible vaccines" or "oral vaccines"-has been developed. Compared to traditional vaccines, oral vaccines can serve multiple immunization priorities and offer advantages, including simplicity of use, lesser expense, greater convenience for storage, an increase in compliance (as a result of increased comfort of delivery), enhanced immune responses at mucosal sites, and stimulation of humoral immunity.So far, much has been achieved in production of oral vaccines and proteins by using transgenic plants (1, 4, 17). The results of tests involving humans who ingested transgenic potato and lettuce expressing recombinant HBsAG (rHBsAg) have been reported, and the special antibody was detected in the ser of volunteers who were given edible tissues of transgenic plants (14). As we know, potatoes and lettuce cannot be eaten raw in certain populations. However, the cooking process would destroy the target protein and affect its immunogenicity. Transgenic edible raw crops can be produced at low cost. The agricultural infrastructure of any given country can ac...

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