Hepatitis B core antigens (HBcAg) and hepatitis B surface antigens (HBsAg) are the main structural
antigens of hepatitis B virus (HBV). Both antigens are potent immunogens for experimental animals
as well as in acutely infected patients. A novel formulation based on the combination of HBsAg
and HBcAg has been developed as a therapeutic vaccine candidate, aimed at inducing an immune
response capable of controlling the infection. An immunization schedule was conducted to evaluate the
immunogenicity of this formulation after simultaneous immunization by the intranasal and parenteral
routes using different schedules and doses. Humoral and cellular immune responses generated in
blood and spleen were evaluated by engyme-linked immunosorbent assay (ELISA) and enzymeliked
immunospot (ELISPOT) assays respectively. A first experiment evaluated two groups of mice
simultaneously immunized by intranasal (IN) and subcutaneous (SC) routes, one including alum by
SC route and, in the other, the formulation was injected without adjuvant.
As a result, alum adjuvant did not increase the immunogenicity under the studied conditions.
In fact, the group without alum induced the most potent immune response. The immune response
was enhanced by combining IN and SC immunization compared to the SC route alone. In a second
experiment, mice were immunized by different mucosal routes at the same time, and compared to
the simultaneously (IN/SC) immunized groups. It was demonstrated that there is no improvement on
the resulting immune response by using multiple routes of immunizations simultaneously; however,
the increase of the antigen dose induced a superior immune response. Interestingly, the increase
of antigen dose only by SC route did not favor the resulting immunogenicity. In conclusion, the use
of HBsAg transgenic mice has proven useful to optimize the formulation, avoiding the unnecessary
use of alum as adjuvant as well as provided information of the role of different mucosal immunization
routes and antigen dose on the resulting immune response.