Protection against Clostridium difficile infection with broadly neutralizing antitoxin monoclonal antibodies

Abstract

The spore-forming bacterium Clostridium difficile represents the principal cause of hospital-acquired diarrhea and pseudomembranous colitis worldwide. C. difficile infection (CDI) is mediated by 2 bacterial toxins, A and B; neutralizing these toxins with monoclonal antibodies (mAbs) provides a potential nonantibiotic strategy for combating the rising prevalence, severity, and recurrence of CDI. Novel antitoxin mAbs were generated in mice and were humanized. The humanized antitoxin A mAb PA-50 and antitoxin B mAb PA-41 have picomolar potencies in vitro and bind to novel regions of the respective toxins. In a hamster model for CDI, 95% of animals treated with a combination of humanized PA-50 and PA-41 showed long-term survival relative to 0% survival of animals treated with standard antibiotics or comparator mAbs. These humanized mAbs provide insight into C. difficile intoxication and hold promise as potential nonantibiotic agents for improving clinical management of CDI.

Figure 1.

Neutralization of purified toxins by murine and humanized monoclonal antibodies (mAbs). A, Humanized PA-50 and murine PA-50 (mPA-50) were compared for neutralization of purified toxin A on T-84 cells. B, Humanized PA-41 and mPA-41 were compared for neutralization of toxin B on CHO-K1 cells.

Figure 2.

Neutralization of toxins produced by diverse strains of Clostridium difficile. A, Humanized PA-50 and comparator CDA1 antitoxin A monoclonal antibodies (mAbs) were tested for neutralization of the cytotoxicity of C. difficile culture supernatants against T-84 cells. B, Humanized PA-41 and comparator CDB1 antitoxin B mAbs were tested for neutralization of the cytotoxicity of C. difficile culture supernatants against CHO-K1 cells.

Figure 3.

Survival outcomes and weight changes in the hamster efficacy study. A, Kaplan-Meier survival curves of Clostridium difficile-infected animals that received treatment with a 1:1 combination of humanized PA-50/PA-41; vancomycin; a 1:1 combination of comparator monoclonal antibodies (mAbs); or no treatment. B, Mean (±SD) body weights of animals over time in the different treatment groups compared with those of uninfected control animals. Dosing regimens are described in Table 2. Survival outcomes were similar for both the 20 mg/kg and the 50 mg/kg doses of PA-50/PA-41 and of CDA1/CDB1 (Table 2); therefore, combined data are shown for the purpose of illustration.