Mucosal targeting of a BoNT/A subunit vaccine adjuvanted with a mast cell activator enhances induction of BoNT/A neutralizing antibodies in rabbits.

George Deepe,Herman F Staats,Jeffrey R Fielhauer,Alice A Tripp,Soman N Abraham,Massimo Maddaloni,Ashley E Sobel,Afton L Thompson,David W Pascual

doi:10.1371/journal.pone.0016532

George Deepe, Herman F Staats + Show 7 more

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https://doi.org/10.1371/journal.pone.0016532

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Abstract

BackgroundWe previously reported that the immunogenicity of Hcβtre, a botulinum neurotoxin A (BoNT/A) immunogen, was enhanced by fusion to an epithelial cell binding domain, Ad2F, when nasally delivered to mice with cholera toxin (CT). This study was performed to determine if Ad2F would enhance the nasal immunogenicity of Hcβtre in rabbits, an animal model with a nasal cavity anatomy similar to humans. Since CT is not safe for human use, we also tested the adjuvant activity of compound 48/80 (C48/80), a mast cell activating compound previously determined to safely exhibit nasal adjuvant activity in mice.MethodsNew Zealand White or Dutch Belted rabbits were nasally immunized with Hcβtre or Hcβtre-Ad2F alone or combined with CT or C48/80, and serum samples were tested for the presence of Hcβtre-specific binding (ELISA) or BoNT/A neutralizing antibodies.ResultsHcβtre-Ad2F nasally administered with CT induced serum anti-Hcβtre IgG ELISA and BoNT/A neutralizing antibody titers greater than those induced by Hcβtre + CT. C48/80 provided significant nasal adjuvant activity and induced BoNT/A-neutralizing antibodies similar to those induced by CT.ConclusionsAd2F enhanced the nasal immunogenicity of Hcβtre, and the mast cell activator C48/80 was an effective adjuvant for nasal immunization in rabbits, an animal model with a nasal cavity anatomy similar to that in humans.

Highlights

Clostridium botulinum is a spore-forming anaerobe which produces seven distinct neurotoxin serotypes (A–G)
We previously reported that a recombinant immunogen containing botulinum neurotoxin type A (BoNT/A) heavy chain (Hc) b-trefoil domain (Hcbtre) induced complete protection against a 20,000 LD50 botulinum neurotoxin A (BoNT/A) challenge in mice when used as a nasal vaccine immunogen coadministered with cholera toxin as a mucosal adjuvant [7]
Our results demonstrate that Hcbtre-Ad2F is superior to Hcbtre for the induction of botulinum neurotoxins (BoNT)/A neutralizing antibodies after nasal delivery with adjuvant and that the mast cell activator compound 48/80 (C48/80) provides effective adjuvant activity for nasally-administered vaccines in rabbits

Summary

Introduction

Clostridium botulinum is a spore-forming anaerobe which produces seven distinct neurotoxin serotypes (A–G). The declining immunogenicity of the toxoid vaccine and the availability of molecular biology techniques to produce non-toxic subunit immunogens has lead to the development of generation botulinum vaccines that are based on recombinant fragments of the heavy chain [5]. A recombinant botulinum vaccine based on the cell binding domain (Hc) is currently being tested in human clinical trials (http://clinicaltrials.gov and [5]). We previously reported that the immunogenicity of Hcbtre, a botulinum neurotoxin A (BoNT/A) immunogen, was enhanced by fusion to an epithelial cell binding domain, Ad2F, when nasally delivered to mice with cholera toxin (CT). Since CT is not safe for human use, we tested the adjuvant activity of compound 48/80 (C48/80), a mast cell activating compound previously determined to safely exhibit nasal adjuvant activity in mice

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