The use of an aerosolizable form of
anthrax as a
biological weapon is considered to be among the most serious bioterror threats. Intranasal (IN) delivery of a dry
powder anthrax vaccine could provide an effective and non-invasive administration alternative to traditional intramuscular (IM) or subcutaneous (SC) injection. We evaluated a dry
powder vaccine based on the recombinant Protective
Antigen (rPA) of Bacillus anthracis for vaccination against
anthrax via IN immunization in a rabbit model. rPA powders were formulated and administered IN using a prototype
powder delivery device. We compared serum
IgG and toxin
neutralizing antibody (TNA) titers of rabbits immunized IN with 10 microg rPA of a
powder formulation with those immunized with the same dose of liquid rPA
vaccine, delivered either IN or by IM injection. In addition, each group was tested for survival after
aerosol spore challenge. Our results showed that IN vaccination with rPA powders elicited serum PA-specific
IgG and TNA titers that were equivalent to those raised by liquid rPA administered IN. Serum PA-specific
IgG and TNA titers after IN delivery were lower than for IM injection, however, after
aerosol spore challenge, rabbits immunized IN with powders displayed 100% protection versus 63% for the group immunized IN with the liquid
vaccine and 86% for the group immunized by IM injection. The results suggest that an IN
powder vaccine based on rPA is at least as protective as a liquid delivered by IM injection.