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J Mol Biol. 2019 Mar 27. pii: S0022-2836(19)30148-2. doi: 10.1016/j.jmb.2019.03.017. [Epub ahead of print]

Potent Neutralization of Staphylococcal Enterotoxin B In Vivo by Antibodies that Block Binding to the T-Cell Receptor.

Author information

1
Banting and Best Department of Medical Research, Department of Molecular Genetics, and the Terrence Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada.
2
Integrated Biotherapeutics, Inc., Rockville, MD 20850, USA.
3
Department of Chemistry, Washington University in St. Louis, St Louis, MO 63130, USA.
4
Department of Chemistry, Washington University in St. Louis, St Louis, MO 63130, USA; Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA.
5
Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA.
6
Integrated Biotherapeutics, Inc., Rockville, MD 20850, USA. Electronic address: javad@integratedbiotherapeutics.com.
7
Banting and Best Department of Medical Research, Department of Molecular Genetics, and the Terrence Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada. Electronic address: sachdev.sidhu@utoronto.ca.

Abstract

To develop an antibody (Ab) therapeutic against staphylococcal enterotoxin B (SEB), a potential incapacitating bioterrorism agent and a major cause of food poisoning, we developed a "class T" anti-SEB neutralizing Ab (GC132) targeting an epitope on SEB distinct from that of previously developed "class M" Abs. A systematic engineering approach was applied to affinity-mature Ab GC132 to yield an optimized therapeutic candidate (GC132a) with sub-nanomolar binding affinity. Mapping of the binding interface by hydrogen-deuterium exchange coupled to mass spectrometry revealed that the class T epitope on SEB overlapped with the T-cell receptor binding site, whereas other evidence suggested that the class M epitope overlapped with the binding site for the major histocompatibility complex. In the IgG format, GC132a showed ~50-fold more potent toxin-neutralizing efficacy than the best class M Ab in vitro, and fully protected mice from lethal challenge in a toxic shock post-exposure model. We also engineered bispecific Abs (bsAbs) that bound tetravalently by utilizing two class M binding sites and two class T binding sites. The bsAbs displayed enhanced toxin neutralization efficacy compared with the respective monospecific Ab subunits as well as a mixture of the two, indicating that enhanced efficacy was due to heterotypic tetravalent binding to two non-overlapping epitopes on SEB. Together, these results suggest that class T anti-SEB Ab GC132a is an excellent candidate for clinical development and for bsAb engineering.

KEYWORDS:

SEB toxin; hydrogen–deuterium exchange coupled to mass spectrometry; phage display; protein engineering; synthetic antibody

PMID:
30928493
DOI:
10.1016/j.jmb.2019.03.017

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