Characterization of a novel human immunodeficiency virus type 1 neutralizable epitope within the immunodominant region of gp41

Previously, we generated human monoclonal antibodies using peripheral blood mononuclear cells from an asymptomatic human immunodeficiency virus type 1 (HIV-1)-seropositive donor. One of these monoclonal antibodies (designated clone 3, CL3) recognized 10 amino acids (GCSGKLICTT) within the immunodomi nant region (cluster I) of the transmembrane envelope glycoprotein gp41 and neutralized infection of target cells with different laboratory isolates. Because the epitope recognized by CL3 has two cysteine residues that could potentially produce a disulfide loop in gp41, we analyzed binding of our mo noclonal antibody to the cyclic and linear motif of the peptide sequence IW GCSGKLICTTAVP (residues 600-614). The CL3 antibody did not bind to the synt hetic cyclic peptide but did recognize the linear form. Two polyclonal rabb it sera against both the linear and cyclic peptides were then generated. Bo th antisera bound to viral glycoproteins gp41 and gp160, but neither sera n eutralized HIV-1 laboratory isolates. Using a set of alanine-substituted IW GCSGKLICTTAV peptides, we analyzed binding of polyclonal antisera and CL3. The profile of binding of polyclonal antisera to these peptides was differe nt from that of CL3 to the same peptides. This suggests that CL3 recognized a unique neutralizable core epitope, which was not immunogenic in either t he cyclic or the linear IWGCSGKLICTTAVP peptides used as immunogens in the rabbits. (C) 2000 Academic Press.