Vaccine for enterotoxigenic Escherichia coli based on synthetic heat-stable toxin crossed-linked to the B subunit of heat-labile toxin.

Synthetically produced Escherichia coli heat-stable toxin (ST) was conjugated to the nontoxic B subunit of the heat-labile toxin (LT) by the carbodiimide reaction. Modifying the molar ratio of toxins mixed and the ratio of carbodiimide added to the toxins permitted synthesis of conjugates with any desired degree of proportional antigenicity for each toxin component. Immunization of rats by the parenteral/peroral routes with cross-linked vaccine containing 39% ST and 61% B subunit antigenicity, with 0.06% residual ST toxicity, evoked fourfold to sevenfold increases over control values of serum IgG and mucosal secretory IgA antitoxin titers to each of the component toxins, thus providing significant (P less than 0.001) protection against challenge with either LT or ST or with viable heterologous strains which produce these toxins. These observations show that cross-linking synthetic ST to the B subunit results in a nontoxic vaccine that provides protection against all types of enterotoxigenic E. coli.