A human bispecific antibody neutralizes botulinum neurotoxin serotype A

Abstract

Botulinum neurotoxin (BoNT) shows high lethality and toxicity, marking it as an important biological threat. The only effective post-exposure therapy is botulinum antitoxin; however, such products have great potential for improvement. To prevent or treat BoNT, monoclonal antibodies (mAbs) are promising agents. Herein, we aimed to construct a bispecific antibody (termed LUZ-A1-A3) based on the anti-BoNT/A human monoclonal antibodies (HMAb) A1 and A3. LUZ-A1-A3 binds to the Hc and L-HN domains of BoNT/A, displaying potent neutralization activity against BoNT/A (124 × higher than that of HMAb A1 or HMAb A3 alone and 15 × higher than that of the A1 + A3 combination). LUZ-A1-A3 provided effective protection against BoNT/A in an in vivo mouse model. Mice were protected from infection with 500 × LD50 of BoNT/A by LUZ-A1-A3 from up to 7 days before intraperitoneal administration of BoNT/A. We also demonstrated the effective therapeutic capacity of LUZ-A1-A3 against BoNT/A in a mouse model. LUZ-A1-A3 (5 μg/mouse) neutralized 20 × LD50 of BoNT/A at 3 h after intraperitoneal BoNT/A administration and complete neutralized 20 × LD50 of BoNT/A at 0.5 h after intraperitoneal BoNT/A administration. Thus, LUZ-A1-A3 is a promising agent for the pre-exposure prophylaxis and post-exposure treatment of BoNT/A.

Isolation and characterization of Hc-targeting chimeric heavy chain antibodies neutralizing botulinum neurotoxin type B

“…The neutralizing ability of anti-BoNT products are estimated in international units (IU), and 1 IU of antitoxin protects mice from 10000 × LD 50 BoNT/B ( 36 ). In our study, the antitoxin potency was calculated as IU/mg, 1 IU/mg means 1 mg antibody neutralize 10000 × LD 50 BoNT/B ( 37 ). The results showed that 0.66 µg of B20-hFc could provide 50% protection against 20 × LD 50 BoNT/B, the theoretically neutralization capacity was approximately 30300 × LD 50 /mg, which was the equivalent of 3 IU/mg; 0.5 µg of B14-hFc could provide 50% protection against 20 × LD 50 BoNT/B, the theoretically neutralization capacity was approximately 40000 × LD 50 /mg, which was the equivalent of 4 IU/mg; 0.28 µg of B12-hFc could provide 50% protection against 20 × LD 50 BoNT/B, the theoretically neutralization capacity was approximately 71000 × LD 50 /mg, which was the equivalent of 7 IU/mg; 0.2 µg of B5-hFc could provide 50% protection against 20 × LD 50 BoNT/B, therefore, the theoretical neutralization capacity was approximately 10 5 × LD 50 /mg, which was the equivalent of 10 IU/mg; and 0.1 μg of B9-hFc provided 50% protection in mice against 20 × LD 50 , indicating that B9-hFc had the strongest activity to neutralize the BoNT/B, and the theoretical neutralization capacity was about 2 × 10 5 × LD 50 /mg, which was the equivalent to 20 IU/mg.…”

“…Most of the neutralizing antibodies against botulinum neurotoxin have focused on serotype A ( 37 , 42 – 45 ). Numerous reports have described either murine or human BoNT/B-neutralizing antibodies ( 10 , 46 – 48 ).…”

“…A combination of antibodies against different domains of BoNT (such as the HN or L domains) could improve the neutralization effect, which is supported by previous studies ( 10 , 14 ). Another effective strategy is to construct multivalent or multispecific antibodies by enhancing the combination of monoclonal antibodies ( 37 ). In the future, we might screen for effective antibodies against other domains of BoNT/B to produce combination or multispecific antibodies.…”

“…Therefore, it is of great significance to screen neutralizing antibodies against BoNT/B. Most of the neutralizing antibodies against botulinum neurotoxin have focused on serotype A (37,(42)(43)(44)(45). Numerous reports have described either murine or human BoNT/B-neutralizing antibodies (10,(46)(47)(48).…”