ABSTRACT
Objective:In order to obtain safer HBV DNA vaccine,recombinant kanamycin resistance eukaryotic expression plasmid containing the gene of HBV surface antigen was constructed and used to study humoral immune response in BALB/c mice.Methods:HBV antigen middle protein(preS2+S) encoding gene fragment was isolated from the recombinant eukaryotic expression plasmid pcDNA-S 2S;subcloned into eukaryotic expression vector pVAX1.After confirmed the presence of the gene by restriction endonuclease analysis,it was used to immunize the healthy BALB/c mice at different doses,and the levels of anti-HBs in serum was determined by ELISA.Results:Restriction endonuclease analysis confirmed recombinant plasmid pVAX-S 2S was what was expected.Serum anti-HBs was detected at the 2nd week after DNA vaccination at all three doses(100 ?g,50 ?g,10 ?g per mice)and their titers were increased with time.Quantitative comparison of the serum anti-HBs levels revealed significant(P