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

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)).

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 immunoadsorbent assay (ELISA) and HBsAg specific cytotoxic T lymphocytes (CTLs) activity was measured by (51)Cr 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.

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.

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.