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

Abstract

Staphylococcal enterotoxin B (SEB), a shock-inducing exotoxin synthesized by Staphylococcus aureus, is an important cause of food poisoning and is a class B bioterrorism agent. SEB mediates antigen-independent activation of a major subset of the T-cell population by cross-linking T-cell receptors (TCRs) with class II major histocompatibility complex (MHC-II) molecules of antigen-presenting cells, resulting in the induction of antigen independent proliferation and cytokine secretion by a significant fraction of the T-cell population. Neutralizing antibodies inhibit SEB-mediated T-cell activation by blocking the toxin's interaction with the TCR or MHC-II and provide protection against the debilitating effects of this superantigen. We derived and searched a set of monoclonal mouse anti-SEB antibodies to identify neutralizing anti-SEB antibodies that bind to different sites on the toxin. A pair of non-cross-reactive, neutralizing anti-SEB monoclonal antibodies (MAbs) was found, and a combination of these antibodies inhibited SEB-induced T-cell proliferation in a synergistic rather than merely additive manner. In order to engineer antibodies more suitable than mouse MAbs for use in humans, the genes encoding the VL and VH gene segments of a synergistically acting pair of mouse MAbs were grafted, respectively, onto genes encoding the constant regions of human Ig and human IgG1, transfected into mammalian cells, and used to generate chimeric versions of these antibodies that had affinity and neutralization profiles essentially identical to their mouse counterparts. When tested in cultures of human peripheral blood mononuclear cells or splenocytes derived from HLA-DR3 transgenic mice, the chimeric human-mouse antibodies synergistically neutralized SEB-induced T-cell activation and cytokine production.

Detection and Measurement of Staphylococcal Enterotoxin-Like K (SEl-K) Secretion by Staphylococcus aureus Clinical Isolates

“…Despite sensitivity to antibiotics, complicated S. aureus infections still have high mortality and treatment failure rates (37,38). Several studies demonstrate that neutralization of SAgs with drugs or Abs improves outcomes in both intoxication and infection models (39)(40)(41)(42)(43). Specifically, a recent study from our laboratory performed with MAbs specific to SEB provides encouraging data with respect to the development of such Abs as adjunctive therapy for complicated S. aureus infections (44).…”

Interference of the T Cell and Antigen-Presenting Cell Costimulatory Pathway Using CTLA4-Ig (Abatacept) Prevents Staphylococcal Enterotoxin B Pathology

“…Abatacept reduces SEB-induced proliferation and proinflammatory cytokine and chemokine production of murine splenocytes in vitro SEB is known to induce T cell proliferation and proinflammatory cytokine production (8). In the MTT assay, treatment of cells exposed to SEB with abatacept resulted in a significant dose-dependent reduction in proliferation by 40% at 0.3 mg abatacept/ml and by 60% at 10 mg abatacept/ml (p = 0.0002; Fig.…”

“…Recent research has looked into the development of effective treatments for SEB exposure and intoxication, including agent-specific medical countermeasures (e.g., antitoxins) and wider-spectrum therapies (e.g., anti-inflammatory agents) to target the resulting immunopathology (8). The development of broad-spectrum therapeutic agents, that is, those that are effective against superantigens in general, is of particular interest.…”

A Single, Engineered Protein Therapeutic Agent Neutralizes Exotoxins from BothStaphylococcus aureusandStreptococcus pyogenes

“…As SpeA is considered one of the major virulence factors in streptococcal TSS (12,14,46), various approaches have been explored to neutralize its toxic activity. These include efforts to develop SpeA toxoid vaccines that induce neutralizing antibodies (5,33,38,51,52) or the generation of monoclonal antibodies, potentially for passive therapy (49). Our approach has involved the use of soluble, high-affinity receptors that could neutralize the toxins in much the same way as the TNF-␣-neutralizing agent Enbrel, a soluble form of the TNF-␣ receptor, neutralizes its target (6).…”