Adjuvant effect of B domain of staphyloccocal protein A displayed on the surface of hepatitis B virus capsid

The hepatitis B virus (HBV) capsid‐based recombinant particles, which display both major hydrophilic region of HBV surface antigen (HBV–MHR) and B domain of Staphylococcal protein A (SPA B ), were produced using Escherichia coli as expression host. SPA B was used as an adjuvant to elicit the immune response to HBV–MHR, and its adjuvant effect in the immunized mice was estimated with varying the position and amount of SPA B on the HBV capsid particles. Compared to the emulsified aluminum gel (alum gel) that is a currently commercialized vaccine adjuvant, SPA B caused the significantly higher level of anti‐HBV immunoglobulin G (IgG) titer and seroconversion rate, and notably SPA B at the most surface‐exposed position on the recombinant particle led to the highest immune response. Moreover, SPA B caused much lower ratio of IgG1 to IgG2a compared to alum gel, indicating that helper T‐cell 1‐mediated immune response (responsible for cytotoxic T‐cell stimulation) is relatively more stimulated by SPA B , unlike alum gel that mainly stimulates helper T‐cell 2‐mediated immune response (responsible for B‐cell stimulation). Although HBV–MHR and HBV capsid particle were used as proof‐of‐concept in this study, SPA B can be used as a highly effective adjuvant with other disease‐specific antigens on the surface of other virus‐like particles to produce various recombinant vaccines with high potency. Biotechnol. Bioeng. 2016;113: 268–274. © 2015 Wiley Periodicals, Inc.