New Engineered-Chimeric Botulinum Neurotoxin Mutant Acts as an Effective Bivalent Vaccine Against Botulinum Neurotoxin Serotype A and E.

Botulinum neurotoxins (BoNTs), including serotypes A and E, are potent biotoxins known to cause human poisoning. In addition to the critical protective antigen found in the full BoNT molecule, the receptor binding domain (Hc domain), BoNTs also harbour another essential protective antigen-the light chain-translocation domain (L-HN domain). Leveraging these pivotal protective antigens, we genetically engineered a series of inactivated chimeric molecules incorporating L-HN and Hc domains of BoNT/A and E. The structure of these chimeric molecules, mirror BoNT/A and E, but are devoid of enzyme activity. Experimental findings demonstrated that a lead candidate mEL-HN-mAHc harnessing the inactivated protease LCHN/E with the mutated gangliosides binding site Hc/A (mE-mA) elicited robust immune protection against BoNT/A and E simultaneously in a mouse model, requiring low immune dosages and minimal immunisations. Moreover, mE-mA exhibited high protective efficacy against BoNT/A and E in guinea pigs and New Zealand white rabbits, resulting in elevated neutralising antibody titres. Furthermore, mE-mA proved to be a more stable and safer vaccine compared to formaldehyde-inactivated toxoid. Our data underscore the genetically engineered mE-mA as a highly effective bivalent vaccine against BoNT/A and E, paving the way for the development of polyvalent vaccines against biotoxins.