Enhancement of the immune responses of mice to <Emphasis Type="Italic">Bacillus anthracis</Emphasis> protective antigen by CIA07 combined with alum

Anthrax is an acute zoonotic disease caused by infection with Bacillus anthracis. B. anthracis spores are highly resistant to environmental degradation and are used as a biological weapon. In this study, we investigated the adjuvant activity of CIA07 to anthrax protective antigen (PA). A/J mice were immunized intraperitoneally once, or twice with a 4-week interval, with recombinant PA alone or combined with alum, CpG1826, or CIA07 as adjuvant, and serum anti-PA IgG antibody responses were measured 4 weeks after each immunization. All three adjuvants significantly enhanced anti-PA IgG antibody titer 4 weeks after the priming and boosting immunizations, and alum gave the highest titer. In order to evaluate the adjuvant activity of CIA07 in the presence of alum, Balb/c mice were immunized 3 times at 1-week intervals with PA in combination with alum, CIA07 or alum plus CIA07, and the immune responses were assessed 2 weeks after the third immunization. The serum anti-PA IgG antibody titer of the CIA07-treated group was 14-fold higher than the group given PA alone, and the coadministration of CIA07 with alum further increased the titer 3.5-fold (P < 0.05). The toxin neutralizing activity of the sera from the mice given the combination of CIA07 and alum was 109-times higher than the animals given PA alone. The mice given CIA07 plus alum also showed a marked increase in the number of IFN-γ-, IL-2-, and IL-4-producing CD4⁺ T cells among their splenocytes. These data suggest the potential of CIA07 in combination with alum as an adjuvant for the development of a potent anthrax vaccine.