Fully Human Monoclonal Antibodies Effectively Neutralizing Botulinum Neurotoxin Serotype B

Abstract

Botulinum neurotoxin (BoNT) is the most potent natural toxin known. Of the seven BoNT serotypes (A to G), types A, B, E, and F cause human botulism. Treatment of human botulism requires the development of effective toxin-neutralizing antibodies without side effects such as serum sickness and anaphylaxis. In this study, we generated fully human monoclonal antibodies (HuMAbs) against serotype B BoNT (BoNT/B1) using a murine-human chimera fusion partner cell line named SPYMEG. Of these HuMAbs, M2, which specifically binds to the light chain of BoNT/B1, showed neutralization activity in a mouse bioassay (approximately [≥] 100 i.p. LD50/mg of antibody), and M4, which binds to the C-terminal of heavy chain, showed partial protection. The combination of M2 and M4 was able to completely neutralize BoNT/B1 with a potency greater than 10,000 i.p. LD50/mg of antibodies, and was effective both prophylactically and therapeutically in the mouse model of botulism. Moreover, this combination showed broad neutralization activity against three type B subtypes, namely BoNT/B1, BoNT/B2, and BoNT/B6. These data demonstrate that the combination of M2 and M4 is promising in terms of a foundation for new human therapeutics for BoNT/B intoxication. IMPORTANCEBotulinum neurotoxins (BoNTs) produced by Clostridium botulinum and related species cause human botulism. Immunotherapy is the most effective treatment for botulism and equine immune serum formulations are used in cases of human botulism. However, these antisera may cause serum sickness or anaphylaxis. Additionally, the production of immune sera involves complicated and time-consuming manufacturing processes and quality management. Therefore, the development of safe, effective, and higher productive antibodies is required. Here we generated fully human monoclonal antibodies against serotype B BoNT (BoNT/B). We found that the combination of these antibodies (M2+M4) had potent and broad neutralization activity against BoNT/B, and showed therapeutic and preventive effects against botulism in mouse models. These data indicate that M2+M4 are promising candidates for the development of human therapeutics and prophylactics for BoNT/B intoxication.