The monoclonal antibody AZD5148 confers broad protection against TcdB-diverse Clostridioides difficile strains in mice

Clostridioides difficile is the leading cause of antibiotic-associated intestinal infections. The pathogenesis of C. difficile infection (CDI) is driven by two protein exotoxins, TcdA and TcdB. The TcdB-targeting monoclonal antibody (mAb) bezlotoxumab (Zinplava) was indicated to reduce CDI recurrence in patients 18 years of age or older who are receiving antibacterial drug treatment for CDI and are at high risk for CDI recurrence. However, Zinplava has recently been discontinued, underscoring the need for additional therapeutics. AZD5148 is a humanized anti-TcdB mAb that neutralizes toxin activity by blocking the delivery of the enzymatic glucosyltransferase domain (GTD) into host cells. TcdB sequence variation influences receptor tropism and substrate specificity, with three major subtypes-TcdB1, TcdB2, and TcdB3-representing the dominant diversity among clinical isolates. In this study, we evaluated the protective efficacy of AZD5148 in vitro and in vivo against clinically relevant C. difficile strains expressing these three dominant TcdB subtypes. AZD5148 potently neutralized TcdB1 and TcdB2 in vitro, with EC50 values 1,000- to 14,000-fold lower than those of bezlotoxumab. In a mouse CDI model induced by TcdB1- or TcdB2-expressing strains, AZD5148 provided robust protection against weight loss and mortality at significantly lower doses than bezlotoxumab. Furthermore, the addition of the anti-TcdA mAb, PA50, provided no additional protective benefit. Although AZD5148 did not neutralize TcdB3 in vitro, it significantly reduced intestinal edema and inflammatory cell infiltration in mice infected with a TcdB3-producing strain. These findings demonstrate that AZD5148 offers broad-spectrum protection against C. difficile strains and retains in vivo efficacy even in the absence of in vitro neutralization. Its distinct mechanism of action and superior potency compared to bezlotoxumab support its continued development as a promising therapeutic candidate for the prevention of a first CDI episode and prevention of recurrence.