Raesdeaercnh Aortivcleirus F Protein As A Delivery Vehicle For Botulinum B

Clapp et al. BMC Immunology 2010, 11:36 http://www.biomedcentral.com/1471-2172/11/36

RESEARCH ARTICLE
Research article

Open Access

Adenovirus F protein as a delivery vehicle for botulinum B
Beata Clapp1, Sarah Golden1, Massimo Maddaloni1, Herman F Staats2 and David W Pascual*1

Abstract Background: Immunization with recombinant carboxyl-terminal domain of the heavy chain (Hc domain)of botulinum neurotoxin (BoNT) stimulates protective immunity against native BoNT challenge. Most studies developing a botulism vaccine have focused on the whole Hc; however, since the principal protective epitopes are located within β-trefoil domain (Hcβtre), we hypothesize that immunization with the Hcβtre domain is sufficient to confer protective immunity. In addition, enhancing its uptakesubsequent to nasal delivery prompted development of an alternative vaccine strategy, and we hypothesize that the addition of targeting moiety adenovirus 2 fiber protein (Ad2F) may enhance such uptake during vaccination. Results: The Hcβtre serotype B immunogen was genetically fused to Ad2F (Hcβtre/B-Ad2F), and its immunogenicity was tested in mice. In combination with the mucosal adjuvant, choleratoxin (CT), enhanced mucosal IgA and serum IgG Ab titers were induced by nasal Hcβtre-Ad2F relative to Hcβtre alone; however, similar Ab titers were obtained upon intramuscular immunization. These BoNT/B-specific Abs induced by nasal immunization were generally supported in large part by Th2 cells, as opposed to Hcβtre-immunized mice that showed more mixed Th1 and Th2 cells. Using a mouseneutralization assay, sera from animals immunized with Hcβtre and Hcβtre-Ad2F protected mice against 2.0 LD50.
Conclusion: These results demonstrate that Hcβtre-based immunogens are highly immunogenic, especially when genetically fused to Ad2F, and Ad2F can be exploited as a vaccine delivery platform to the mucosa.

Background Clostridium botulinum is a Gram-positive, spore-forming anaerobe commonlyfound in soil, and is responsible for production of botulinum neurotoxin (BoNT), a potent lethal toxin [1]. Seven BoNT serotypes (A-G) have been identified [2]: serotypes A, B, E, and F are primarily responsible for human botulism; serotypes C and D are mostly limited to intoxication of animals [3]; and host specificity for serotype G has not been fully determined [4]. Three clinical manifestationsare related to naturally acquired botulism: foodborne, infant, and wound botulism [5]. However, recently, three other forms have been described [6]: undefined or adult intestinal, inadvertent injection-related and inhalational botulism. All forms of BoNT intoxication present with the same clinical syndrome of symmetrical and descending flaccid paralysis of
* Correspondence: dpascual@montana.edu
1Veterinary Molecular Biology, Montana State University, Bozeman, MT 597173610, USA

motor and autonomic nerves, which can cause respiratory arrest and death [7,8]. Since natural exposure to C. botulinum spores is rare, the necessity to create a vaccine is primarily for high-risk individuals. Moreover, an intentional release to contaminate food and water supplies or for use as an aerosolizedweapon [3] warrants the development of vaccines to protect high-risk groups. Currently, there are no certified vaccines for preventing human botulism. In the United States, an investigational pentavalent botulinum toxoid that includes serotypes A through E is used to vaccinate high risk individuals [9]. Although toxoid-based vaccines can be conveniently produced, these have a number of limitations,including isolation of active toxins, loss of essential neutralizing epitopes by formalin treatment, and multiple immunizations required to sustain elevated Ab titers [10]. To overcome these limitations, recent efforts have shifted to adapting recombinant BoNT heavy (H) chain to develop subunit vaccines [11,12], as well as employing DNA vac-

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