Protective efficacy of a recombinant protective antigen against Bacillus anthracis challenge and assessment of...

The efficacy of recombinant Bacillus anthracis Protective Antigen (rPA) produced in Bacillus subtilis and formulated in Alhydrogel or MPL-TDM-CWS (Ribi adjuvant) has been tested and compared to the licensed UK human vaccine in guinea pigs challenged by the aerosol route with the Ames strain of B. anthracis. rPA combined with the Ribi adjuvant was found to be the only formulation to provide 100% protection from challenge. Analysis of immunological parameters in the individual animals revealed significant differences between the rPA/Ribi vaccine group and rPA/Alhydrogel and human vaccine groups for antigen specific lymphocyte proliferation, PA neutralisation and antigen specific IgG2 levels, but indicated no significant differences in PA-specific IgG1 levels. rPA formulated in Alhydrogel induced a mainly IgG1 response whilst the rPA/Ribi vaccine produced a predominantly IgG2 response.