Abstract
Clostridioides difficile is the causative bacterium in 15–20% of all antibiotic associated diarrheas. The symptoms associated with C. difficile infection (CDI) are primarily induced by the two large exotoxins TcdA and TcdB. Both toxins enter target cells by receptor-mediated endocytosis. Although different toxin receptors have been identified, it is no valid therapeutic option to prevent receptor endocytosis. Therapeutics, such as neutralizing antibodies, directly targeting both toxins are in development. Interestingly, only the anti-TcdB antibody bezlotoxumab but not the anti-TcdA antibody actoxumab prevented recurrence of CDI in clinical trials. In this work, 31 human antibody fragments against TcdB were selected by antibody phage display from the human naive antibody gene libraries HAL9/10. These antibody fragments were further characterized by in vitro neutralization assays. The epitopes of the neutralizing and non-neutralizing antibody fragments were analyzed by domain mapping, TcdB fragment phage display, and peptide arrays, to identify neutralizing and non-neutralizing epitopes. A new neutralizing epitope within the glucosyltransferase domain of TcdB was identified, providing new insights into the relevance of different toxin regions in respect of neutralization and toxicity.
Highlights
By the end of the 1970s, Clostridioides difficile (CDiff) was identified as the causative pathogen of antibiotic treatment associated diarrhea (CDAD) (Bartlett et al, 1978)
In standard therapy for mild to moderate C. difficile infection (CDI), CDiff is targeted with metronidazole, vancomycin or fidaxomicin (Tedesco et al, 1978; Bolton and Culshaw, 1986; Goldstein et al, 2012)
We describe the generation of a panel of human antibodies targeting different domains of TcdB by a phage display approach using the naïve human antibody libraries HAL9 and HAL10 (Kügler et al, 2015)
Summary
By the end of the 1970s, Clostridioides (former Clostridium) difficile (CDiff) was identified as the causative pathogen of antibiotic treatment associated diarrhea (CDAD) (Bartlett et al, 1978). In 2011, CDiff caused ∼453,000 incident infections in the USA with ∼29,000 deaths (Lessa et al, 2015). Due to its association with antibiotic treatment and the resulting high potential for development of antibiotic resistance, the Centers for Disease Control and Prevention (CDC) classify CDiff as an urgent threat (Centers of Disease Control Prevention, 2013). In standard therapy for mild to moderate CDI, CDiff is targeted with metronidazole, vancomycin or fidaxomicin (Tedesco et al, 1978; Bolton and Culshaw, 1986; Goldstein et al, 2012). Antibiotic therapy presumably further disrupts the gut microbiome that confers
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