The incomplete definition of immunologic parameters that correlates with the protection against HCV infection has limited the development of a vaccine against this pathogen. Several studies advocate for the induction of strong cellular immune response against viral antigens, as well as neutralizing antibodies against HCV E2 envelope protein, as a success criteria. However, the influence of several antigens against each others in a protein preparation and the impact on the immunogenicity, have not been explored yet. In the present study a factorial design was used to generate several HCV vaccine preparations with the structural core, E1 and E2 proteins as antigens. An optimal antigen composition was chosen based on the lymphoproliferative response against HCV as well as protection against challenge with a surrogate virus in BALBC/c mice. The protein ratio (1:160:160), with 0.1 µg of Co.120-16.7 µg of E1.340-16.7 µg E2.680 (Co-E1-E2) was selected as the optimal composition to induce a functional immune response in mice. Additionally, strong humoral immune response against the 412-438 amino acid region from HCV E2 protein was detected when African green monkeys were immunized with Co-E1-E2. This region includes a conserved epitope, involved in T cell lymphoproliferative response against Co.120 and E2.680 proteins as well as in HCV neutralization. The results evidenced the relevance of proportion between HCV structural antigens in vaccine preparations for eliciting successful immune response.

Humoral and cellular immune responses are currently induced against hepatitis C virus (HCV) core following vaccination with core-encoding plasmids. However, the anti-core antibody response is frequently weak or transient. In this paper, we evaluated the effect of different additives and DNA-protein combinations on the anti-core antibody response. BALB/c mice were intramuscularly injected with an expression plasmid (pIDKCo), encoding a C-terminal truncated variant of the HCV core protein, alone or combined with CaCl2, PEG 6000, Freund's adjuvant, sonicated calf thymus DNA and a recombinant core protein (Co.120). Mixture of pIDKCo with PEG 6000 and Freund's adjuvant accelerated the development of the anti-core Ab response. Combination with PEG 6000 also induced a bias to IgG2a subclass predominance among anti-core antibodies. The kinetics, IgG2a/IgG1 ratio and epitope specificity of the anti-core antibody response elicited by Co.120 alone or combined with pIDKCo was different regarding that induced by the pIDKCo alone. Our data indicate that the antibody response induced following DNA immunization can be modified by formulation strategies.