Sequence variation within botulinum neurotoxin serotypes impacts antibody binding and neutralization

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Botulinum neurotoxins (BoNTs) are Category A biothreat agents requiring effective countermeasures.
• Existing vaccines and antibody therapies must address extensive BoNT sequence variability across and within serotypes.

Purpose of the Study:

• To analyze BoNT sequence variability within serotypes.
• To determine the impact of BoNT subtype sequence differences on monoclonal antibody (MAb) binding and neutralization capacity.

Main Methods:

• Analysis of 49 complete published BoNT sequences to assess intra-serotype variability.
• Evaluation of binding affinity and in vivo neutralization of six BoNT/A MAbs against BoNT/A1 and BoNT/A2 subtypes.

Main Results:

• BoNTs exhibit significant sequence variability within serotypes (2.6–31.6%).
• Three of six BoNT/A MAbs showed 500- to >1,000-fold reduced binding affinity to BoNT/A2 compared to BoNT/A1.
• MAb neutralization capacity correlated with binding; MAbs ineffective against A2 showed minimal neutralization, while broadly binding MAbs neutralized both subtypes.

Conclusions:

• Intra-serotype sequence variability in BoNTs significantly impacts MAb recognition and neutralization.
• Diagnostic and therapeutic antibody development must consider BoNT subtype sequence variability for efficacy.