Clostridioides difficile Toxin B subverts germinal center formation and antibody recall responses by stimulating a drug-treatable CXCR4-dependent mechanism

Recurrent Clostridioides difficile infection (CDI) results in significant morbidity and mortality. We previously established that CDI in mice did not protect against reinfection and was associated with poor pathogen-specific B cell memory (Bmem), recapitulating our observations with human Bmem. Herein, we demonstrate that the secreted toxin TcdB2 is responsible for subversion of Bmem responses. TcdB2 from an endemic C. difficile strain delayed IgG class switch following vaccination, attenuated IgG recall to a vaccine booster, and prevented germinal center formation. The mechanism of TcdB2 action included increased B cell CXCR4 expression and responsiveness to its ligand CXCL12, accounting for altered cell migration and a failure of germinal center-dependent Bmem. These results were reproduced in a C. difficile infection model and an FDA-approved CXCR4-blocking drug rescued germinal center formation. We therefore provide mechanistic insights into C. difficile-associated pathogenesis and illuminate a target for clinical intervention to limit recurrent disease. Female mice (n=4 per group) were given 200 µl PBS vehicle control, 10 ng D270N, or 10 ng TcdB2 in PBS by the s.c. route. Seven days post treatment, RNA was purified from aLNs and iLNs. Gene expression was quantified using the Nanostring™ nCounter SPRINT profiler platform.