Nasal immunization with a dual antigen anthrax vaccine induced strong mucosal and systemic immune responses against toxins and bacilli

Anthrax-vaccine-adsorbed (AVA), the only anthrax vaccine licensed in the U.S., suffers from many major drawbacks. Therefore, there is a need to develop new generation anthrax vaccines that can be easily administered and induce strong immune responses not only against the anthrax toxins, but also against the toxin-producing vegetative anthrax bacilli. In the present study, we evaluated the feasibility of inducing strong mucosal and systemic immune responses against both anthrax toxins and bacilli after nasal immunization using a synthetic double-stranded RNA (dsRNA), polyriboinosinic–polyribocytidylic acid (poly(I:C) or pI:C), as the adjuvant. We have shown that the capsular poly-γ-d-glutamic acid (PGA) from bacillus was immunogenic when conjugated to a carrier protein and dosed intranasally to mice. We further demonstrated that nasal immunization with the PGA–carrier protein conjugate in combination with the anthrax protective antigen (PA) protein induced both anti-PGA and anti-PA immune responses in mouse sera and lung mucosal secretions. The anti-PA antibody (Ab) response was shown to have anthrax lethal toxin neutralization activity; and the anti-PGA Abs induced were able to activate complement and kill PGA-producing bacteria. These findings demonstrated that it is feasible to develop a novel dual-action nasal anthrax vaccine.