HBV DNA vaccine with adjuvant cytokines induced specific immune responses against HBV infection

AIM: To seek for an effective method to improve the immune responses induced by DNA vaccine expressing HBV surface antigen (pCR3.1-S) in Balb/c mice (H-2(d)). METHODS: The pCR3.1-S plasmid and the eukaryotic expression vectors expressing murine IL-2 (pDOR-IL-2) or IL-12 (pWRG3169) were injected into mice subcutaneously. The immune responses to pCR3.1-S and the adjuvant effect of the cytokines plasmid were studied. Meanwhile the effect of pCR3.1-S on anti-translated subcutaneous tumor of P815 mastocytoma cells stably expressing HBsAg (P815-HBV-S) was also studied. Anti-HBs in serum was detected by enzyme-linked immunoadsordent assay (ELISA) and HBsAg specific cytotoxic T lymphocytes (CTLs) activity was measured by Cr-51 release assay. After three weeks of DNA immunization, the cells of P815-HBV-S were inoculated into mice subcutaneously and the tumor growth was measured every five days. The survival rate and living periods of mice were also calculated. RESULTS: After 8 wk DNA immunization, the A 450 nm values of sera in mice immunized with pCR3.1, pCR3.1-S and pCR3.1-S codeliveried with IL-2 or IL-12 plasmids were 0.03 +/- 0.01, 1.24 +/- 0.10, 1.98 +/- 0.17 and 1.67 +/- 0.12 respectively. Data in mice codeliveried pCR3.1-S with IL-2 or IL-12 plasmids were significantly higher than that of mice injected pCR3.1 or pCR3.1-S only. The HBsAg specific CTL activities in mice coinjected with pCR3.1-S and IL-2 or IL-12 eukaryotic expression vectors were (61.9 +/- 7.1) % and (73.3 +/- 8.8) %, which were significantly higher than that of mice injected with pCR3.1 (10.1 +/- 2.1) % or pCR3.1-S (50.5 +/- 6.4) %. The HBsAg specific CTL activities in mice injected with pCR3.1, pCR3.1-S, pCR3.1-S combined with IL-2 or IL-12 eukaryotic expression vectors decreased significantly to (3.2 +/- 0.8) %, (10.6 +/- 1.4) %, (13.6 +/- 1.3) % and (16.9 +/- 2.3) % respectively after the spleen cells were treated by anti-CD8(+) monoclonal antibody, but presented no significant change to anti-CD4(+) monoclonal antibody or unrelated to monoclonal antibody. The HBV-S DNA vaccine (pCR3.1-S) could evidently inhibit the tumor growth, prolong the survival period of mice and improve the survival rate of mice and these effects could be improved by IL-12 gene codeliveried. CONCLUSION: HBV DNA vaccine has a strong antigenicity in humoral and cellular immunities, which can be promoted by plasmid expressing IL-2 or IL-12. CD8(+) cells executed the CTL activities. DNA vaccine may be useful for both prophylaxis and treatment of HBV infection.