Abstract
Staphylococcal enterotoxin B (SEB) is a potent toxin that can cause toxic shock syndrome and act as a lethal and incapacitating agent when used as a bioweapon. There are currently no vaccines or immunotherapeutics available against this toxin. Using phage display technology, human antigen-binding fragments (Fabs) were selected against SEB, and proteins were produced in Escherichia coli cells and characterized for their binding affinity and their toxin neutralizing activity in vitro and in vivo. Highly protective Fabs were converted into full-length IgGs and produced in mammalian cells. Additionally, the production of anti-SEB antibodies was explored in the Nicotiana benthamiana plant expression system. Affinity maturation was performed to produce optimized lead anti-SEB antibody candidates with subnanomolar affinities. IgGs produced in N. benthamiana showed characteristics comparable with those of counterparts produced in mammalian cells. IgGs were tested for their therapeutic efficacy in the mouse toxic shock model using different challenge doses of SEB and a treatment with 200 μg of IgGs 1 h after SEB challenge. The lead candidates displayed full protection from lethal challenge over a wide range of SEB challenge doses. Furthermore, mice that were treated with anti-SEB IgG had significantly lower IFNγ and IL-2 levels in serum compared with mock-treated mice. In summary, these anti-SEB monoclonal antibodies represent excellent therapeutic candidates for further preclinical and clinical development.
Highlights
Staphylococcal enterotoxin B (SEB) is a potent superantigen that can cause toxic shock in humans and can be incapacitating and lethal when used as a bioweapon
Seventy-five clones showed both positive signal in spot phage Enzyme-linked Immunosorbent Assay (ELISA) and over 50% inhibition in the presence of 10 nM solution phase SEB in single-point competitive phage ELISA
Neutralization of virulence factors of bacterial pathogens is a key component of therapeutic and prophylactic strategies to counter the detrimental effects of bacterial infections
Summary
SEB is a potent superantigen that can cause toxic shock in humans and can be incapacitating and lethal when used as a bioweapon. Staphylococcal enterotoxin B (SEB) is a potent toxin that can cause toxic shock syndrome and act as a lethal and incapacitating agent when used as a bioweapon. Staphylococcal enterotoxins and TSST-1 bind to human class II major histocompatibility complex (MHC) on antigen-presenting cells and certain subsets of T cell receptor on T lymphocytes [4] This peptide-independent cross-linking results in massive stimulation of up to 30% of lymphocytes triggering a cytokine storm that can lead to toxic shock syndrome (TSS) [5, 6]. Hyperimmune intravenous immunoglobulin could be produced upon donor stimulation with a recombinant attenuated SEB vaccine because this approach has been successful for several other infectious agents This approach is complicated by the need for maintaining a donor cohort, the high dose needed for protection, manufacturing and safety issues, and cost. We report the discovery and characterization of highly effective synthetic human antibody therapeutics for prophylactic and postexposure treatment of SEB-induced disease and lethality
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