590. Recombinant Adenovirus Vaccines Against Anthrax (2006)

Anthrax, the disease caused by Bacillus anthracis, is highly lethal and has emerged as a serious bioterrorism threat. A vaccine exists, however it requires six doses over eighteen months plus yearly boosts. Furthermore, the vaccine is made from the culture supernatant of an attenuated strain of B. anthracis which contains contaminants that can result in painful reactions at the injection site. In the present study we employ two strategies using adenovirus to stimulate a humoral response against B. anthracis protective antigen, the common binding subunit of anthrax toxins. In the first approach an E1, E3- deleted adenovirus vector expressing the immunoprotective domain 4 of protective antigen (Ad.D4) was constructed. Balb/c mice immunized with Ad.D4 mounted an antibody response against protective antigen two weeks after a single intramuscular injection which was further increased after boosting. Serum from immunized mice was able to neutralize lethal toxin in vitro and immunized micechallenged with lethal toxin showed significant survival after only two vaccine doses. We are now evaluating DNA/adenovirus prime- boost strategies for their ability to protect mice from anthrax spore challenge. Our second strategy aims to take advantage of the immune response generated against components of the adenovirus capsid. In particular, a robust, serotype specific antibody response is elicited against the hexon protein. Structural data and sequence analysis of hexons from different serotypes have shown that poorly conserved loops on the capsid surface, termed hypervariable regions (HVRs), are responsible for eliciting the serotype specific antibody response. We have genetically inserted a subdomain of B. anthracis protective antigen into one of these surface loops and assessed the ability of this vector to stimulate a protective humoral response against lethal toxin. The effects of peptide insertion on virus life cycle and capsid stability are also examined. Anthrax, the disease caused by Bacillus anthracis, is highly lethal and has emerged as a serious bioterrorism threat. A vaccine exists, however it requires six doses over eighteen months plus yearly boosts. Furthermore, the vaccine is made from the culture supernatant of an attenuated strain of B. anthracis which contains contaminants that can result in painful reactions at the injection site. In the present study we employ two strategies using adenovirus to stimulate a humoral response against B. anthracis protective antigen, the common binding subunit of anthrax toxins. In the first approach an E1, E3- deleted adenovirus vector expressing the immunoprotective domain 4 of protective antigen (Ad.D4) was constructed. Balb/c mice immunized with Ad.D4 mounted an antibody response against protective antigen two weeks after a single intramuscular injection which was further increased after boosting. Serum from immunized mice was able to neutralize lethal toxin in vitro and immunized micechallenged with lethal toxin showed significant survival after only two vaccine doses. We are now evaluating DNA/adenovirus prime- boost strategies for their ability to protect mice from anthrax spore challenge. Our second strategy aims to take advantage of the immune response generated against components of the adenovirus capsid. In particular, a robust, serotype specific antibody response is elicited against the hexon protein. Structural data and sequence analysis of hexons from different serotypes have shown that poorly conserved loops on the capsid surface, termed hypervariable regions (HVRs), are responsible for eliciting the serotype specific antibody response. We have genetically inserted a subdomain of B. anthracis protective antigen into one of these surface loops and assessed the ability of this vector to stimulate a protective humoral response against lethal toxin. The effects of peptide insertion on virus life cycle and capsid stability are also examined.