AIM To develop a safe and effective DNAvaccine for inducing humoral and cellularimmunological responses against hepatitis Bvirus surface antigen(HBsAg).METHODS BALB/c mice were inoculated withNV-HB/s,a recombinant plasmid that had beeninserted S gene of hepatitis B virus genome andcould express HBsAg in eukaryotes.HBsAgexpression was measured by ABC immunohis-tochemical assay,generation of anti-HBs byELISA and cytotoxic T lymphocyte(CTL),byMTT method,existence of vaccine DNA bySouthern blot hybridization and activation ofoncogene C-myc by in situ hybridization,RESULTS With NV-HB/s vaccination byintramuscular injection,anti-HBs was initiallypositive 2 weeks after inoculation while all micetested were HBsAg positive in the muscles.Thetiters and seroconversion rate of anti-HBs weresteadily increasing as time went on and weredose-dependent.All the mice inoculated with100 μg NV-HB/s were anti-HBs positive onemonth after inoculation,the titer was 1:1024 ormore.The humoral immune response was similarinduced by either intramuscular or intradermalinjection.CTL activities were much stronger(45.26%)in NV-HB/s DNA immunized mice as compared with those(only 6%)in plasma-derived HBsAg vaccine immunized mice.Twomonths after inoculation,all muscle sampleswere positive by Southern-blot hybridization forNV.HB/s DNA detection,but decreased to 25%and all were undetectable by in situhybridization after 6 months.No oncogene C-myc activation was found in the muscle ofinoculation site.CONCLUSION NV-HB/s could generatehumoral and cellular immunological responsesagainst HBsAg that had been safely expressed insitu by NV-HB/s vaccination. AIM To develop a safe and effective DNAvaccine for inducing humoral and cellularimmological responses against hepatitis B virus surface antigen (HBsAg) .METHODS BALB / c mice were inoculated with NV-HB / s, a recombinant plasmid that had been inserted S gene of hepatitis B virus genome andcould express HBsAg in eukaryotes. HBsAgexpression was measured by ABC immunohis-tochemical assay, generation of anti-HBs by ELISA and cytotoxic T lymphocyte (CTL), by MTT method, existence of vaccine DNA by Southern blot hybridization and activation of oncogene C-myc by in situ hybridization, RESULTS With NV-HB / s vaccination byintramuscular injection, anti-HBs was initiallypositive for 2 weeks after inoculation were all micetested were HBsAg positive in the muscles.Thetiters and seroconversion rate of anti-HBs weresteadily increasing as time went on and weredose-dependent. All the mice inoculated with 100 μg NV-HB / s were anti-HBs positive one month after inoculation, the titer was 1: 1024 ormore. The humoral immune response wa s similarinduced by either intramuscular or intradermalinjection. CTL activities were much stronger (45.26%) in NV-HB / s DNA immunized mice as compared to those (only 6%) in plasma-derived HBsAg vaccine immunized mice.Twomonths after inoculation, all muscle sampleswere positive by Southern-blot hybridization for NV.HB / s DNA detection, but decreased to 25% and all were undetectable by in situ hybridization after 6 months. No oncogene C-myc activation was found in the muscle of inoculation site. CONCLUSION NV-HB / s could generate humoral and cellular immunological responses to damage HBsAg that had been safely expressed in insitu by NV-HB / s vaccination.