Efficacy, heat stability and safety of intranasally administered Bacillus subtilis spore or vegetative cell vaccines expressing tetanus toxin fragment C.

Abstract Bacillus subtilis strains expressing tetanus toxin fragment C (TTFC) were tested as vaccine candidates against tetanus in adult mice. Mice received three intranasal (IN) exposures to 10 9 spores or 10 8 vegetative cells of B. subtilis expressing recombinant TTFC. Immunized mice generated protective systemic and mucosal antibodies and survived challenge with 2× LD 100 of tetanus toxin. Isotype analysis of serum antibody indicated a balanced Th1/Th2 response. Lyophilized vaccines stored at 45 °C for ≥12 months, remained effective. Immunized conventional and SCID mice remained well, and no histological changes in brain or respiratory tract were detected. Lyophilized/reconstituted B. subtilis tetanus vaccines administered IN to mice appear safe, heat-stable, and protective against lethal tetanus challenge.