OBJECTIVETo study the HBsAg transient expression in HepG2 or COS-7 cells with eukaryotic expression plasmids inserting HBsAg gene (pCI-S and pcDNA3.1-S) and the efficacy of naked DNA immunization in mice.

METHODSFirstly, the recombinant plasmids of pCI-S and pcDNA3.1-S were constructed by the cloning technique and the accuracy of these constructs was confirmed by restriction enzyme digestion and DNA sequencing. Secondly, plasmids of pCI-S and pcDNA3.1-S were transferred into HepG2 and COS-7 cells, respectively by means of cationic liposome. HBsAg transient expression was assayed by ELISA in cell culture supernatants and cell lysates. Thirdly, plasmids were injected into quadriceps muscles of BALB/C mice and serum samples were obtained from individual immunized or control mice 4 weeks after injection and boost injection, respectively. Anti-HBs were assayed in mice sera by ELISA. HBsAg-specific CTL responses of spleen cells from immunized mice were tested by the LDH method.

RESULTSPlasmids of pCI-S and pcDNA3.1-S allowed HBsAg transient expression in cell culture supernatants and cell lysates of HepG2 or COS-7 cells. Intramuscular immunization of BALB/C mice with plasmids of pCI-S or pcDNA3.1-S elicited the antibody and cytotoxic T lymphocyte responses to HBsAg.

CONCLUSIONSThe vectors used in this study are effective to induce prime antibody and HBsAg-specific-cytotoxic T lymphocyte responses to HBsAg in mice after intramuscular immunization.