Protective Immunity Evoked Against Anthrax Lethal Toxin After a Single Intramuscular Administration of an Adenovirus-Based Vaccine Encoding Humanized Protective Antigen

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Abstract
Because of the need to develop a vaccine to rapidly protect the civilian population in response to a bioterrorism attack with Bacillus anthracis, we designed AdsechPA, a replication-deficient human serotype 5 adenovirus encoding B. anthracis protective antigen (PA) with codons optimized for expression in mammalian cells. With a single intramuscular administration to mice of 109 particle units of AdsechPA, a dose that can be scaled to human use, anti-PA antibodies were evoked more rapidly and at a higher level than with a single administration of the new U.S. military recombinant PA/Alhydrogel vaccine. Importantly, AdsechPA afforded approximately 2.7-fold more protection than the recombinant PA vaccine against B. anthracis lethal toxin challenge 4 weeks after a single vaccination. Even at 11 days postvaccination, AdsechPA provided some survival benefit, whereas the rPA/Alhydrogel vaccine provided none. In the context that equivalent human doses of Ad vectors have already been demonstrated to be safe in humans, a single administration of AdsechPA may provide the means to rapidly protect the civilian population against B. anthracis in response to a bioterrorism attack.