ADJUVANT ACTIVITY OF QS-21 FOR EXPERIMENTAL ESCHERICHIA-COLI-018 POLYSACCHARIDE VACCINES

Three types of experimental vaccines containing O-side-chain polysacch aride from the enterotoxigenic str ain Escherichia coli 018 were evalu ated. The immunogenicity of free O-polysaccharide (PS), a polysacchari de-diphtheria toroid conjugate (PS-conj), and detoxified lipopolysacch aride (dLPS) was tested in female ICR mice, either alone or in combina tion with QS-21, a purified saponin adjuvant derived from the bark of the tree Quillaja saponaria Molina. Both the number of individual mice responding and the titres of O-polysaccharide specific antibodies in pools of sera were increased by the addition of QS-21. The immune resp onse to both O-specific polysaccharide and carrier was primarily IgM a nd IgG1. The addition of QS-21 not only increased the level of IgG1, b ut also had a significant adjuvant effect on antigen-specific IgG2a, I gG2b and IgG3.