Epitope conservation of AZD5148, a broadly neutralizing anti-Toxin B monoclonal antibody, among diverse and global contemporary Clostridioides difficile isolates.

BACKGROUND C. difficile Toxin B is a virulence factor for C. difficile infections (CDI), and a clinically validated target for prevention of CDI recurrence. AZD5148 is a Toxin B neutralizing human monoclonal antibody that binds to an epitope on the Toxin B glucosyltransferase domain. Herein, we aim to evaluate the conservation of this binding epitope using a collection of 9,134 global C. difficile genomes obtained from a public repository to confirm that residues that are crucial for neutralization are conserved. METHODS Using isolates collected between 2015-2023 from two independent sources, we performed variant calling, sequence typing and phylogenetic analysis. We tested in vitro neutralization of cytotoxicity by AZD5148 using two different cell-lines. RESULTS Herein, we showed that the AZD5148 epitope is highly conserved across all geographic regions and sequence types (STs) and has a higher average conservation frequency in its binding site (99.58%) when compared to bezlotoxumab (82.47%). AZD5148 also exhibited broad neutralization in vitro against 8 recently circulating ribotypes. CONCLUSIONS Our comprehensive analysis of global sequences found the AZD5148 epitope to be highly conserved, and thus unlikely to be impacted by most of the genotypic variations in recently circulating C. difficile ribotypes and STs.