In vitro correlate of immunity in a rabbit model of inhalational anthrax

A serological correlate of vaccine-induced immunity was identified in the r abbit model of inhalational anthrax. Animals were inoculated intramuscularl y at 0 and 4 weeks with varying doses of Anthrax Vaccine Adsorbed (AVA) ran ging from a human dose to a 1:256 dilution in phosphate-buffered saline (PB S). At 6 and 10 weeks, both the quantitative anti-protective antigen (PA) I -G ELISA and the toxin-neutralizing antibody (TNA) assays were used to meas ure antibody levels to PA. Rabbits were aerosol-challenged at 10 weeks with a lethal dose (84-133 LD50) of Bacillus anthracis spores. All the rabbits that received the undiluted and 1:4 dilution of vaccine survived, whereas t hose receiving the higher dilutions of vaccine (1: 16, 1:64 and 1:256) had deaths in their groups. Results showed that antibody levels to PA at both 6 and 10 weeks were significant (P < 0.0001) predictors of survival. Publish ed by Elsevier Science Ltd.