Properties of modified hepatitis B virus surface antigen particles carrying preS epitopes.

The current hepatitis B virus (HBV) vaccines contain the small (S) and middle (M) viral envelope proteins in particulate form but lack the large (L) protein. Although these particles elicit protective immunity to HBV, inclusion of the immunogenic preS1 region of the L protein may enhance their efficacy. To present preS1-derived epitopes on secretable subviral particles we rearranged the HBV envelope ORF by fusing part or all of the preS1 region to either the N or C terminus of the S protein. Fusion of the first 42 residues of preS1 to either site allowed efficient secretion of the modified particles and rendered the linked sequence accessible at the surface of the particle. Conversely, fusion of preS1 sequences to the C terminus of the M protein completely blocked secretion. This block to secretion could be rescued by provision of a heterologous N-terminal signal sequence. All these particles displayed preS1, preS2 and S protein antigenicity. In mice, each construct elicited high titres of preS1-specific antibodies which recognized the authentic L protein. Particles composed of the modified M protein also induced a preS2-specific response. Unexpectedly, however, neither particle elicited S protein-specific antibodies. Nonetheless, the genetic approach employed here represents a strategy to incorporate preS1-derived epitopes both in high density and in highly immunogenic form into their authentic carrier matrix.