A Fully Human Monoclonal Antibody Cocktail Provides Therapeutic Protection Against Botulinum Neurotoxin A1

Botulism is a fatal disease characterized by flaccid paralysis caused by botulinum neurotoxin (BoNT). In adults, human botulism is currently treated with equine-derived antitoxins, which have provided substantial clinical benefit and remain the mainstay of treatment. However, these equine antitoxin products carry a risk of adverse reactions due to heterologous proteins and have limitations in stable supply. Here, we developed three fully human monoclonal antibodies (HuMAbs)—BT-015, BT-175, and NT-320—against botulinum neurotoxin subtype A1 (BoNT/A1), a major cause of human botulism. BT-015 and BT-175 bound to recombinant LHN, which comprises the catalytic domain (light chain) and the N-terminal translocation domain of the heavy chain, whereas NT-320 bound to the C-terminal receptor-binding domain of the heavy chain (HC). Competition assays further showed that BT-015 and BT-175 recognize largely distinct binding sites within LHN. Each antibody showed neutralizing activity in mice, whereas the three-antibody cocktail provided the greatest protective effect and completely protected mice against the BoNT/A1 medium progenitor toxin complex (M-PTC) under the conditions tested. Moreover, treatment with the cocktail shortly after the onset of clinical signs following oral challenge with the BoNT/A1 large progenitor toxin complex (L-PTC) improved survival and promoted recovery from clinical signs. These findings highlight the therapeutic potential of the HuMAb cocktail for botulism.