Fully Human Monoclonal Antibodies Effectively Neutralizing Botulinum Neurotoxin Serotype B

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/Bl) using a murine-human chimera fusion partner cell line named SPYMEG. Of these HuMAbs, M2, which specifically binds to the light chain of BoNT/Bl, showed neutralization activity in a mouse bioassay (approximately 10 i.p. [LD.sub.50]/100 [micro]g of antibody), and M4, which binds to the C-terminal of heavy chain, showed partial protection. The combination of two HuMAbs, M2 (1.25 [micro]g) and M4 (1.25 [micro]g), was able to completely neutralize BoNT/Bl (80 i.p. [LD.sub.50]) with a potency greater than 80 i.p. LDso/2.5 [micro]g 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/Bl, BoNT/B2, and B0NT/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.