A candidate DNA vaccine elicits HCV specific humoral and cellular immune responses

Abstract

Aim: To investigate the immunogenicity of candidate DNA vaccine against hepatitis C virus (HCV) delivered by two plasmids expressing HCV envelope protein 1 (E1) and envelope protein 2 (E2) antigens respectively and to study the effect of CpG adjuvant on this candidate vaccine.

Methods: Recombinant plasmids expressing HCV E1 and E2 antigens respectively were used to simultaneously inoculate mice with or without CpG adjuvant. Antisera were then collected and titers of anti-HCV antibodies were analyzed by ELISA. One month after the last injection, animals were sacrificed to prepare single-cell suspension of splenocytes. These cells were subjected to HCV antigen specific proliferation assays and cytokine secretion assays to evaluate the cellular immune responses of the vaccinated animals.

Results: Antibody responses to HCV E1 and E2 antigens were detected in vaccinated animals. Animals receiving CpG adjuvant had slightly lower titers of anti-HCV antibodies in the sera, while the splenocytes from these animals showed higher HCV-antigen specific proliferation. Analysis of cytokine secretion from the splenocytes was consistent with the above results. While no antigen-specific IL-4 secretion was detected for all vaccinated animals, HCV antigen-specific INF-gamma secretion was detected for the splenocytes of vaccinated animals. CpG adjuvant enhanced the secretion of INF-gamma but did not change the profile of IL-4 secretion.

Conclusion: Vaccination of mice with plasmids encoding HCV E1 and E2 antigens induces humoral and cellular immune responses. CpG adjuvant significantly enhances the cellular immune response.

Figure 1

Transient expression with plasmids used in vaccination. Plasmids used for transfection are indicated at the top of each lanes. E1 and E2 products are indicated by arrowheads.

Figure 2

E2-specific splenocyte proliferation. Error bars represent the standard errors. Asterisk indicates the significant difference of the average SI between animals injected with (pSecTagB/sE1 + pSecTagB/sE2 + CpG) and animals injected with (pSecTagB + CpG) (P = 0.005).

Figure 3

E2-specific cytokine secretion. Error bars represent the standard errors. Asterisk indicates the very significant difference of the average SI between animals injected with (pSecTagB/sE1 + pSecTagB/sE2 + CpG) and animals injected with (pSecTagB + CpG) in terms of INF-γ secretion (P = 0.0003).