Humanized staphylococcal enterotoxin B (SEB)-specific monoclonal antibodies protect from SEB intoxication and Staphylococcus aureus infections alone or as adjunctive therapy with vancomycin

Staphylococcal enterotoxin B (SEB), a potential biological warfare agent, is a potent superantigen that contributes to the virulence of methicillin-resistant Staphylococcus aureus (MRSA), which is a major health threat in the United States. Efforts to develop toxin-neutralizing antibodies as adjunctive therapies are justified, given the high mortality and frequent failure of therapy despite available antibiotics. Methods. Murine SEB-specific mAb 20B1 was humanized, and treatment benefits of Hu-1.6/1.1 and Hu-1.4/1.1 variants were investigated in mice in an SEB intoxication model, as well as in sepsis and deep-tissue infection models. Results. Hu-1.6/1.1 and Hu-1.4/1.1 protected mice against SEB-induced lethal shock. Hu-1.6/1.1 also enhanced survival of mice that developed fatal sepsis after challenge with a SEB-producing MRSA strain. Combined treatment of Hu-1.6/1.1 with vancomycin further increased survival and altered cytokine responses, compared with monotherapy with either monoclonal antibody or vancomycin alone. Efficacy was also demonstrated in the deep-tissue infection model, where Hu-1.4/1.1 bound to SEB in vivo and decreased abscess formation, as well as proinflammatory cytokine levels. Conclusions. SEB-neutralizing mAb 20B1 was successfully humanized. The mAb affects outcome by modulating the proinflammatory host response in both the sepsis and the intoxication models, which justifies further development.