Synthetic peptide mimotope of the CAMPATH-1 (CD52) antigen, a small glycosylphosphatidylinositol-anchored glycoprotein

Background: CAMPATH-1 (CD52) antibodies are among the most powerful and specific lympholytic agents in humans and have numerous potential applications for human therapy. The CD52 antigen is a GPI-anchored glycoprotein with an exceptionally short peptide sequence of only 12 amino acids and a single, complex, N-linked oligosaccharide. Antibodies bind to the deglycosylated antigen and to a proteolytic fragment, but not to the synthetic peptide alone. Objectives: To characterise the antigenic epitope more precisely and to construct a synthetic analogue. Such an analogue would be useful for assay and purification of the therapeutic CAMPATH-1 antibodies as well as for studies of the antibody-antigen binding site. Study Design: Collections of synthetic peptides based on the natural sequence were screened with a panel of CD52 antibodies. Results and Conclusion: A synthetic peptide composed of the natural C-terminal amino acids plus two additional residues was found to mimic the antigen with sufficient affinity to be useful for a variety of assays and for construction of an affinity matrix for antibody purification. Systematic mutation of this peptide enabled the definition of the critical residues for antibody binding, which will be of great help in building a model of the antibody-antigen interaction. Peptide mimotopes synthesised using a natural sequence as a starting point, rather than a completely random library, may be useful in many other similar circumstances.