Synthetic CD4 exocyclic peptides antagonize CD4 holoreceptor binding and T cell activation.

We have developed peptide analogs to analyze precise human CD4 substructures involved in MHC class II binding. Forms of the complementarity determining-like regions (CDRs) of the D1 domain of human CD4 were reproduced as synthetic aromatically modified exocyclic (AME) analogs and tested for their ability to block CD4-MHC II interactions and T cell activation. The exocyclic derived from CDR3 (residues 82-89) of human CD4, which specifically associated with CD4 on the T cell surface to create a heteromeric CD4 complex, blocked IL-2 production and antagonized the normal function of the CD4 receptor. The approach of creating novel synthetic antagonistic receptor complexes may represent a new receptor specific pharmaceutical approach to modulate biological function.