SYNTHETIC PEPTIDES REPRESENTING DISCONTINUOUS CD4 BINDING EPITOPES OFHIV-1 GP120 THAT INDUCE T-CELL APOPTOSIS AND BLOCK CELL-DEATH INDUCEDBY GP120

A vaccine against HIV-1 virus would block initial infection and must t arget conserved residues. Since initial infection depends on binding o f the viral envelope protein gp120 to CD4 on the cell surface, the CD4 binding site of gp120 is a target for vaccine design, To identify the optimal biologically active site, we synthesized a series of 32-mer p eptides, based on conserved residues in the C3 and C4 regions of gp120 . These included three of five sequence discontinuous residues known t o be involved in CD4 binding, one or two of which were substituted wit h alanine, We also synthesized a 44-mer peptide with an additional bra nch to incorporate an extra C4 region sequence including a fourth CD4 binding residue. All these peptides used an oxidized Cys-X-Cys bridge to link the discontinuous sequence elements in a manner suggested by t he known conserved disulfide bridges in gp120, Polyclonal sera raised to these peptides indicate that they all contain both B and T lymphocy te epitopes, Binding of the peptides to CD4-transfected HeLa cells rev eals a hierarchy dependent on the number of relevant CD4 binding resid ues present. Furthermore, antibody cross-linking of peptides bound to the surface of human T cells results in apoptosis that is similar to t he known properties of gp120, The peptide incorporating three CD4 bind ing residues competitively inhibited gp120-induced T lymphocyte apopto sis, Thus, we have synthesized novel, branched peptides incorporating conserved discontinuous sequences from two different conserved domains of HIV-1 gp120 that contain T and B lymphocyte epitopes and mimic bio logical functions of the native protein, These synthetic peptides are candidates for future vaccine development.