New anthrax vaccines involve immunization with rPA, an immunologic target of antibodies that neutralize anthrax toxin. We have evaluated a non-toxic nanoemulsion as an adjuvant for intramuscular (IM) and intranasal (IN) immunization with rPA.

Balb/c mice were immunized with three monthly administrations of 2.5 and 25 ug rPA. The protein was given alone, in a solution of 1% nanoemulsion or with the nanoemulsion and CpG-rich oligonucleotides.

IM injections of rPA with nanoemulsion resulted in higher titers of anti-PA IgG than IM administration of antigen alone, particularly with low doses of rPA. In contrast, nanoemulsion was absolutely required for the development of immunity after IN administration since anti-PA specific IgA (in bronchial lavage) and IgG (in serum) were observed only in animals receiving in rPA with nanoemulsion, whether or not CpG was present. No animal immunized IM with rPA developed a mucosal antibody response. rPA specific splenocyte activation was demonstrated by proliferative responses in vitro and was accompanied by markedly increased production of INFγ and TNF⍺, indicating that TH1 responses were induced by the nanoemulsion. Nanoemulsion increased in vitro binding of rPA to dendritic cells but not lymphocytes, suggesting dendritic cells participate in the induction of rPA mucosal immunity after IN immunization.

Nanoemulsions may serve as useful adjuvants for recombinant anthrax vaccines.