AAV-mediated delivery of actoxumab and bezlotoxumab results in serum and mucosal antibody concentrations that provide protection from C. difficile toxin challenge.

Clostridium difficile is the leading cause of antibiotic-associated nosocomial diarrhea in the developed world. When the host-associated colon microbiome is disrupted by the ingestion of antibiotics, C. difficile spores can germinate, resulting in infection. C. difficile secretes enterotoxin A (TcdA) and cytotoxin B (TcdB) that are responsible for disease pathology. Treatment options are limited as the bacterium demonstrates resistance to many antibiotics, and even with antibacterial therapies, recurrences of C. difficile are common. Actotoxumab and bezlotoxumab are human monoclonal antibodies that bind and neutralize TcdA and TcdB, respectively. In 2016, the US food and drug administration (FDA) approved bezlotoxumab for use in the prevention of C. difficile infection recurrence. To ensure the long-term expression of antibodies, gene therapy can be used. Here, adeno-associated virus (AAV)6.2FF, a novel triple mutant of AAV6, was engineered to express either actotoxumab or bezlotoxumab in mice and hamsters. Both antibodies expressed at greater than 90 μg/mL in the serum and were detected at mucosal surfaces in both models. Hundred percent of mice given AAV6.2FF-actoxumab survived a lethal dose of TcdA. This proof of concept study demonstrates that AAV-mediated expression of C. difficile toxin antibodies is a viable approach for the prevention of recurrent C. difficile infections.