-This application focuses on completion of preclinical work supporting initiation of a clinical trial to identify the optimum dose and schedule of a next generation anthrax vaccine, AV7909. AV7909 is composed of Emergent BioSolutions'FDA-approved BioThrax (25) anthrax vaccine and the immunostimulatory oligonucleotide compound CPG7909 (VaxImmuneTM) developed by Coley Pharmaceutical Group. In a previous Phase 1/2 clinical trial evaluating safety and immunogenicity of a first generation AV7909 vaccine, AV7909 increased peak anti-protective antigen (PA) liters 6-fold and reduced the time to peak titer by 21 days compared to BioThrax alone. Also, only 2 doses of AV7909 were required to elicit the same serum anti-PA IgG levels achieved by three doses of BioThrax alone. No anthrax vaccine developed to date, delivered by any means, has demonstrated such dramatic immunogenicity so rapidly.
The specific aims for this proposal include: 1) cGMP manufacture of AV7909;2) nonclinical GLP safety and toxicity evaluation;and 3) development of a guinea pig post-exposure prophylaxis (PEP) aerosol challenge model appropriate for AV7909. A key component required of the next generation anthrax vaccine is its ability to be used in conjunction with antibiotics in a post-exposure situation. To be effective when administered therapeutically, the vaccine must induce high anti-protective antigen (PA) titers quickly and with a minimum number of doses. Additionally, the vaccine must be easy to administer in a massive post-exposure vaccination scenario. Even though the first generation AV7909 showed excellent immune responses in a previous Phase 1/2 trial, the vaccine was manufactured in two separate vials and mixed just before administration. To make the vaccine more user- friendly, Emergent is developing a co-formulation method in a single vial.
All specific aims for this proposal will be conducted with the new cGMP AV7909 vaccine lots manufactured by the new method. Also, even though rabbits and non-human primates (NHP) are generally considered the two preferred animal models for anthrax infection and have been widely used in anthrax vaccine efficacy studies, the rabbit model may not be suitable for evaluation of AV7909. Since studies indicate rabbits respond poorly to CpG molecules, we need to develop an alternative small animal model (e.g., guinea pig model) to satisfy the FDA's "Animal Rule" which requires two relevant animal models for evaluation of biodefense vaccines.