Immunization against anthrax with Bacillus anthracis protective antigen combined with adjuvants

The protective efficacy of immunization against anthrax with Bacillus anthracis protective antigen (PA) combined with different adjuvants was tested in Hartley guinea pigs and CBA/J and A/J mice. Adjuvant components derived from microbial products that were tested included threonyl-muramyl dipeptide (threonyl-MDP); monophosphoryl lipid A (MPL); trehalose dimycolate (TDM); and the delipidated, deproteinized, cell wall skeleton (CWS) from either Mycobacterium phlei or the BCG strain of Mycobacterium bovis. Non-microbially derived adjuvants tested included aluminum hydroxide and the lipid amine CP-20,961. In guinea pigs, all adjuvants and adjuvant mixtures enhanced antibody titers to PA as well as survival after a parenteral challenge of virulent B. anthracis Ames spores. In contrast, PA alone or combined with either aluminum hydroxide or CP-20,961 failed to protect mice. Vaccines containing PA combined with threonyl-MDP or MPL-TDM-CWS protected a majority of female CBA/J mice. Statistical analysis of survival data in the guinea pigs indicated that PA-MPL-CWS and PA-MPL-TDM-CWS were more efficacious than the currently licensed human anthrax vaccine.