A novel vaccine strategy: induction of a specific antibody response by a conformâtionally biased agonist of human c5a

Interactions between the complement system and mediators of acquired im munity provide a basis for rational design of complement based vaccines. To determine if a C5a peptide agonist could enhance the immunogenicity of a denned peptide, mice were immunized with a human MUC1 peptide coupled to a C5a agonist. We have developed a conformationally biased decapeptide agonist of human C5a, that has potency and biological activity approaching that of native C5a. A peptide conjugate with the MUCl peptide toward the amino terminus and the C5a moiety on the carboxyl terminus (MUClC5a), has C5a activity: it inhibited the binding of ¹²⁵I - C5a to PMNs, and it stimulated smooth muscle contraction and β-glucuronidase release with a similar potency to the C5a agonist. In contrast, a peptide with the MUCl peptide on the C-terminus and C5a moiety on the N-terminus (C5a-MUCl) did not. C57 B16 mice immunized with the MUCl-C5a peptide produced a significant antibody response specific for the MUCl epitope (IgG2a, IgG2b, and IgM), whereas no antibody response was induced in animals immunized with the biologically inactive peptide C5a-MUCl, the MUCl peptide alone, the C5a agonist alone, or a coinjection of the MUCl peptide and C5a agonist. MUCl specific antibodies recognized MUCl protein by western blotting and cell surface associated MUCl as detected by immunofluorescence assays. These studies show that a C5a mediated adjuvant effect significantly enhances the immunogenicity of a defined peptide epitope.