A MODIFIED HEPATITIS-B VIRUS SURFACE-ANTIGEN WITH THE RECEPTOR-BINDING SITE FOR HEPATOCYTES AT ITS C-TERMINUS - EXPRESSION, ANTIGENICITY AND IMMUNOGENICITY

A modified hepatitis B virus (HBV) surface antigen, the SA-28 protein, was constructed and expressed by recombinant vaccinia virus in mammalian cells. This protein was composed of a PreS 1 region-derived peptide (amino acids 21 to 47) that contained the hepatocyte receptor-binding site, joined to the C terminus of the major S protein at amino acid position 223. This modified surface antigen could be efficiently assembled into particles with a density of 1.23 g/ml and could be secreted from several mammalian cell lines. The results of immunoprecipitation revealed that the SA-28 protein was recognized by both the anti-S protein antibody and the anti-PreS1 antibody. A strong antibody response, against both the S protein and PreS1 epitopes, was induced in BALB/c mice immunized by the SA-28 particles, indicating good immunogenicity. These results suggested that the HBV surface antigen consisting of the SA-28 protein could be a promising candidate as a new HBV vaccine with higher efficacy.