Neutralization of staphylococcal enterotoxin B by soluble, high-affinity receptor antagonists

Abstract

Exotoxins of Staphylococcus aureus belong to a family of bacterial proteins that act as superantigens by activating a large subset of the T-cell population, causing massive release of inflammatory cytokines. This cascade can ultimately result in toxic shock syndrome and death. Therapeutics targeting the early stage of the pathogenic process, when the superantigen binds to its receptor, could limit the severity of disease. We engineered picomolar binding affinity agents to neutralize the potent toxin staphylococcal enterotoxin B (SEB). A single immunoglobulin-like domain of the T-cell receptor (variable region, Vbeta) was subjected to multiple rounds of directed evolution using yeast display. Soluble forms of the engineered Vbeta proteins produced in Escherichia coli were effective inhibitors of SEB-mediated T-cell activation and completely neutralized the lethal activity of SEB in animal models. These Vbeta proteins represent an easily produced potential treatment for diseases mediated by bacterial superantigens.

Potent Neutralization of Staphylococcal Enterotoxin B by Synergistic Action of Chimeric Antibodies

“…Many of these have sought to prevent or disrupt the formation of MHC-II/SAg/TCR complexes. These have ranged from explorations of active immunization with inactivated recombinant SEB vaccines (5, 26, 52), synthetic peptides (53), and proteasome-SEB toxoid combinations (29,30) to investigations of antibody-based passive immunoprophylaxis/immunotherapy (9,10,21,23,38,49), as well as synthetic peptides antagonists (1-3) and receptor mimics such as chimeric mimics of MHC-II-TCR (19,27,36) and of the TCR V␤ (7). Although all of these approaches have shown some promise, based on the long history of clinical experience with the use of antibodies, our approach has focused on demonstration of an approach to the derivation of forms of monoclonal anti-SEB antibodies that might be suitable for clinical use.…”

“…These include immunization with proteasome-SEB toxoid vaccines (29,30), inactivated recombinant SEB vaccine (5,26,52), and synthetic peptides (53) to induce anti-SEB antibodies, passive immunoprophylaxis and immunotherapy with intravenous immunoglobulin (IVIG) (9,10,21,23), the use of peptide antagonists (1)(2)(3), synthetic chimeric mimics of MHC-II/TCR complex (19,27,36) or mimics of TCR V␤ (7) engineered to interfere with the binding of SEB to the native forms of these receptors on APCs or T cells. Perhaps the most successful of these approaches have involved TCR V␤ chain mimics that blocked SEB activation in vitro and showed promising results when tested in vivo in a rabbit model (7). However, these TCR mimics reported by Buon-pane et al (7) have a short half-life (325 min) in rabbits and are likely to display short half-lives if deployed in clinical settings.…”

“…Perhaps the most successful of these approaches have involved TCR V␤ chain mimics that blocked SEB activation in vitro and showed promising results when tested in vivo in a rabbit model (7). However, these TCR mimics reported by Buon-pane et al (7) have a short half-life (325 min) in rabbits and are likely to display short half-lives if deployed in clinical settings. However, rapid in vivo turnover of SEB blocking agents can be avoided by use of antibodies well matched to the host's FcRn, a receptor responsible for protecting IgG from proteolysis and hence endowing it with a long half-life (24).…”

TCR recognition of peptide/MHC class II complexes and superantigens

“…Vβ domain-derived SAG antagonists that bind to their SAG targets, including SEC3, SEB and TSST, have been engineered with affinities up to a million-fold higher than the wild type SAG/Vβ interactions [54,66,67]. One of these Vβ variants completely neutralizes the lethal activity of SEB in animal models [66]. Beyond engineering anti-SAG therapeutics, the affinity maturation of a drug target's natural ligand to create a competitive inhibitor may constitute a generally applicable approach to therapeutic development.…”

Human Leukocyte Antigen Class II Transgenic Mouse Model Unmasks the Significant Extrahepatic Pathology in Toxic Shock Syndrome

“…Rabbits have been used in staphylococcal toxin research including staphylococcal enterotoxins even before their superantigenicity was established. 27 However, even the rabbit model of TSS seems to require sensitization with lipopolysaccharide to induce death, 28,29 or require continuous infusion of SAg for 7 days. 30 Moreover, even in the rabbit model of TSS, extensive investigation of the temporal changes in systemic cytokine and chemokine concentrations, an indepth immunopathologic characterization of multiple-organ disease, and ultimately the correlation between systemic inflammatory response, multiple-organ disease, and the outcome of TSS have not been performed.…”