A single immunization with a dry powder anthrax vaccine protects rabbits against lethal aerosol challenge S.D. Klas 1,* , C.R. Petrie 1 , S.J. Warwood 1 , M.S. Williams 1 , C.L. Olds 1 , J.P. Stenz 1 , A.M. Cheff 1 , M. Hinchcliffe 2 , C. Richardson 1 , and S. Wimer 1 1 LigoCyte Pharmaceuticals, Inc. 2155 Analysis Drive, Bozeman, MT 59718 2 Archimedes Development Limited, Albert Einstein Centre, Nottingham Science & Technology Park, University Boulevard, Nottingham, NG7 2TN, UK Abstract Here we confirm that intranasal (IN) dry powder anthrax vaccine formulations are able to protect rabbits against aerosol challenge 9 weeks after a single immunization. The optimum dose of rPA in our dry powder anthrax vaccine formulation in rabbits was experimentally determined to be 150 μg and therefore was chosen as the target dose for all subsequent experiments. Rabbits received a single dose of either 150 μg rPA, 150 μg rPA + 150 μg of a conjugated 10-mer peptide representing the B. anthracis capsule (conj), or 150 μg of conj alone. All dry powder formulations contained MPL and chitosan (ChiSys®). Significant anti-rPA titers and anthrax lethal toxin neutralizing antibody (TNA) levels were seen with both rPA containing vaccines, although rPA-specific IgG and TNA levels were reduced in rabbits immunized with rPA plus conj. Nine weeks after immunization, rabbits were exposed to a mean aerosol challenge dose of 278 LD 50 of Ames spores. Groups immunized with rPA or with rPA + conj had significant increases in survivor proportions compared to the negative control group by Logrank test (p = 0.0001 and 0.003, respectively), and survival was not statistically different for the rPA and rPA + conj immunized groups (p = 0.63). These data demonstrate that a single immunization with our dry powder anthrax vaccine can protect against a lethal aerosol spore challenge 9 weeks later. 1. Introduction Bacillus anthracis is a gram-positive, spore forming, facultative anaerobic bacterium and the causative agent of anthrax. An anthrax infection can manifest in three ways depending on the route of transmission; cutaneous, inhalation and gastrointestinal anthrax [1]. Inhalation anthrax, the most likely form that will result from a bioterrorist attack, is relatively rare and usually fatal even with aggressive treatment [2]. Since the earliest symptoms of disease are non-specific [3–6] recognition of exposure and initiation of appropriate treatment may not occur soon enough to be effective. The only licensed vaccine, Anthrax Vaccine Adsorbed (BioThrax ® ), is probably effective and safe according to the Institute of Medicine. However, the Institute also recommended development of an improved vaccine that has a less daunting immunization schedule and reduced reactogenicity [7]. “Second-generation” anthrax vaccines *Corresponding Author: sheri.klas@ligocyte.com, Telephone: 406-585-2733, Fax: 406-585-2766. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ChiSys ® is a trade mark of Archimedes Development Ltd and is registered as a CTM, and as a US Registered Trademark and in certain other jurisdictions. NIH Public Access Author Manuscript Vaccine. Author manuscript; available in PMC 2009 October 9. Published in final edited form as: Vaccine. 2008 October 9; 26(43): 5494–5502. doi:10.1016/j.vaccine.2008.07.062. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript