We demonstrate that interactions between multimeric receptors and multivalent ligands are dramatically enhanced by recruiting a complementary templating receptor such as an endogenous multimeric protein but only when individual ligands are attached to a polymer as preorganized, covalent, heterobifunctional pairs. This effect cannot be replicated by a multivalent ligand if the same recognition elements are independently arrayed on the scaffold. Application of this principle offers an approach to create high-avidity inhibitors for multimeric receptors. Judicious selection of the ligand that engages the templating protein allows appropriate effector function to be incorporated in the polymeric construct, thereby providing an opportunity for therapeutic applications. The power of this approach is exemplified by the design of exceptionally potent Escherichia coli Shiga toxin antagonists that protect transgenic mice that constitutively express a human pentraxin, serum amyloid P component.

Bacterial capsular polysaccharides have been used as effective vaccines for adults but infants and seniors respond poorly to these immunogens because pure polysaccharides are unable to activate T-cells resulting in antibodies of low affinity and poor immunological memory. These deficiencies are addressed by conjugate vaccines composed of bacterial polysaccharide covalently attached to protein carriers such as tetanus or diphtheria toxoids. These vaccines activate T-cells and have been hugely effective in reducing the incidence of dangerous infectious diseases such as bacterial meningitis in infants and adults. The methods of conjugation often produce conjugate vaccines that contain polysaccharides with several cross links to one or more protein carrier molecules. Synthesis of large oligosaccharides derivatized to achieve single site attachment to protein has established the minimal size of an oligosaccharide that is required to produce protective antibody. Several examples are described where such oligosaccharides range in size from 8 to 16 monosaccharides. A more limited set of examples show that protective antibodies may be elicited by conjugate vaccines composed of tri and tetrasaccharide epitopes. One example is the β-mannan present in the phosphomannan glycoprotein of Candida albicans. Reverse engineering a protective antibody that recognizes this oligosaccharide revealed that a disaccharide was the minimal epitope. Further epitope mapping by functional group modification established that the internal mannose residue of a disaccharide was involved in the most important antibody–disaccharide interactions. NMR binding studies in combination with homology modeling of the bound β-mannan antigen suggested an optimum oligosaccharide for inclusion in a conjugate vaccine. Several conjugate vaccines were developed to test these conclusions. Immunization of mice or rabbits with conjugates containing disaccharide or trisaccharide conjugated to immunogenic proteins followed by live challenge experiments showed that the vaccines reduced fungal burden. The results of these and other studies suggest new approaches to novel synthetic conjugate vaccines.