Immunization with a plasmid encoding a modified hepatitis B surface antigen carrying the receptor binding site for hepatocytes.

Intramuscular injection of a plasmid encoding a modified hepatitis B surface antigen (HBsAg) induced humoral and cytotoxic responses in C57BL/6 mice. This modified HBsAg contains a preS1-derived peptide (amino acids 21 to 47), that carries the HBV receptor binding site for hepatocytes fused to the C-terminus of the small protein (at the position of amino acid 223). After a single DNA injection, the immunized mice elicited high titers of anti-HBs and anti-preS1 antibodies, and produced strong HBV specific cytotoxic T-lymphocyte (CTL) responses. The immune response induced after a single injection of this modified HBsAg gene in HBsAg-transgenic mice resulted in the clearance of circulating HBsAg and the appearance of anti-HBs and anti-preS1 antibodies. The high titers of preS1 antibody in transgenic mice were comparable to those found in non-transgenic controls and may be efficient to clear Dane particles existing in sera from chronic carriers. These data indicated that a genetic vaccine consisting of this modified HBsAg gene may have a potential use for both prophylactic and therapeutic purposes.