Neutralizing antibodies and immunoprotection against pertussis and tetanus obtained by use of a recombinant pertussis toxin-tetanus toxin fusion protein.

The currently available diphtheria-tetanus-whole-cell pertussis (DTP) vaccines are associated with a variety of problems, including undesirable side effects and inconsistent efficacy. These problems are probably related to the poor definition of such vaccines, especially with respect to the whole-cell component against pertussis. Ideal vaccines should include only immunoprotective antigens with no toxin activity. As an initial step towards obtaining a well-defined and simplified DTP vaccine, a pertussis toxin-tetanus toxin chimeric protein was constructed. A soluble form of the pertussis toxin S1 subunit was fused to the protective fragment C of tetanus toxin, and the recombinant hybrid protein was produced in Escherichia coli. The 75-kDa fusion protein (p75) was overexpressed as a soluble molecule and purified to near homogeneity by two consecutive chromatographic steps. Purified p75 retained its ability to bind to ganglioside GT1b, the receptor for tetanus toxin, and to be recognized by protective and neutralizing anti-pertussis toxin antibodies specific for conformational epitopes. When administered to mice, the hybrid protein was found to be nontoxic but immunogenic. In addition, it was capable of inducing strong protection against tetanus and some protection against pertussis, as well as eliciting a pertussis toxin-neutralizing antibody response. Although the levels of anti-pertussis toxin antibodies were rather low, neutralizing titers of the immunized mice correlated well with anti-pertussis toxin titers, indicating that protective epitopes are conserved in the recombinant protein.