Neutralization of tetanus toxin by a novel chimeric monoclonal antibody

Purpose: Tetanus is a life-threatening disease characterized by muscle spasm caused by neurotoxin of Clostridium tetani. Given the current passive immunotherapy of tetanus with human anti-toxin polyclonal antibodies (PAbs) and the limitations of such preparations, neutralizing monoclonal antibodies (MAbs), especially chimeric or human antibodies with reduced immunogenicity might be considered as an alternative source. Methods: A mouse-human chimeric MAb, designated c-1F2C2, was generated and its binding specificities to various recombinant fragments of tetanus toxin, generated in E. coli, were determined. In vivo toxin neutralizing activity of c-1F2C2 was evaluated and compared with that of a commercially available human anti-toxin PAb in a mouse model. The possible mechanisms of toxin neutralizing activity of c-1F2C2 were investigated by assessing its inhibitory effects on toxin receptors binding, including GT1b ganglioside receptor and those expressed on PC12 cells. Results: In vivo neutralizing assay showed that c-1F2C2 was able to protect mice against tetanus toxin with an estimated potency of 7.7 IU/mg comparing with 1.9 IU/mg of the commercial human anti-toxin PAb for 10 MLD toxin and 10 IU/mg versus 1.9 IU/mg of the PAb for 2.5 MLD toxin. c-1F2C2 recognized fragment C of the toxin, which is responsible for binding of the toxin to its receptor on neuronal cells. Accordingly, the chimeric MAb partially prevented the toxin from binding to its receptors on PC12 cells (37% inhibition). Conclusion: The chimeric MAb c-1F2C2 displayed similar structural and functional characteristics compared to its murine counterpart and might be useful for passive immunotherapy of tetanus.