ABSTRACT
Here, monophosphoryl lipid A (MPLA) and aluminum salt (Alum) were introduced into a hyaluronic acid (HA)-based combination vaccine adjuvant for hepatitis B vaccine (HBV). Although Alum is a well-known hepatitis B vaccine adjuvant that induces an enhanced humoral immune response, it cannot induce the cellular immune responses. On the other hand, MPLA has been generally reported to promote IFN-γ production via antigen-specific CD4(+) T cells, but it is not water soluble as a result of its long hydrophobic alkyl chains. To this end, water insoluble MPLA could be solubilized in an aqueous solution with the help of HA, which contains many carboxyl and hydroxyl groups that can be used to attach to the hydroxyl head groups of MPLA via hydrogen bonds. Three groups of mice were treated with either hepatitis B surface antigen (HBsAg) alone, HBsAg_Alum complex, or HBsAg_Alum_MPLA/HA complex. The group immunized with the HBsAg_Alum_MPLA/HA complex exhibited a high increase in cellular immune response as well as in humoral immune response relative to the other two groups. The antibody, cytokine and T cell levels were most elevated in the group of mice immunized with HBsAg_Alum_MPLA/HA complex, even at a 1µg/mice dose, and the magnitude was still maintained even after 8 weeks. Specifically, the antibody value was 120 times larger in mice vaccinated with HBsAg_Alum_MPLA/HA complex than in mice vaccinated with HBsAg_Alum complex designed similar to commercially available hepatitis B vaccine, Engerix B. The cytokine and T cell proliferation levels were 2 times and 6 times larger in mice adjuvanted with HBsAg_Alum_MPLA/HA complex than in those vaccinated with HBsAg_Alum. The results therefore indicate that incorporating MPLA and Alum with HA can be a potent strategy to increase both the magnitude and the persistence of HBsAg-specific immune responses to protect hosts against hepatitis B virus infection.
