Vaccination of rabbits with an alkylated toxoid rapidly elicits potent neutralizing antibodies against botulinum neurotoxin serotype B.

New Zealand White (NZW) rabbits were immunized with several different nontoxic botulinum neurotoxin serotype B (BoNT/B) preparations in an effort to optimize the production of a rapid and highly potent, effective neutralizing antibody response. The immunogens included a recombinant heavy chain (rHc) protein produced in Escherichia coli, a commercially available formaldehyde-inactivated toxoid, and an alkylated toxoid produced by urea-iodoacetamide inactivation of the purified active toxin. All three immunogens elicited an antibody response to BoNT/B, detected by enzyme-linked immunosorbent assay (ELISA) and by toxin neutralization assay, by the use of two distinct mouse toxin challenge models. The induction period and the ultimate potency of the observed immune response varied for each immunogen, and the ELISA titer was not reliably predictive of the potency of toxin neutralization. The kinetics of the BoNT/B-specific binding immune response were nearly identical for the formaldehyde toxoid and alkylated toxoid immunogens, but immunization with the alkylated toxoid generated an approximately 10-fold higher neutralization potency that endured throughout the study, and after just 49 days, each milliliter of serum was capable of neutralizing 10(7) 50% lethal doses of the toxin. Overall, the immunization of rabbits with alkylated BoNT/B toxoid appears to have induced a neutralizing immune response more rapid and more potent than the responses generated by vaccination with formaldehyde toxoid or rHc preparations.