Broadly neutralizing antibodies targeted to the membrane-proximal externalregion of human immunodeficiency virus type 1 glycoprotein gp41

The identification and epitope mapping of broadly neutralizing anti-human i mmunodeficiency virus type 1 (HIV-1) antibodies (Abs) is important for vacc ine design, but, despite much effort, very few such Abs have been forthcomi ng. Only one broadly neutralizing anti-gp41 monoclonal Ab (MAb), 2F5, has b een described. Here we report on two MAbs that recognize a region immediate ly C-terminal of the 2F5 epitope. Both MAbs were generated from HIV-1-serop ositive donors, one (Z13) from an antibody phage display library, and one ( 4E10) as a hybridoma. Both MAbs recognize a predominantly linear and relati vely conserved epitope, compete with each other for binding to synthetic pe ptide derived from gp41, and bind to HIV-1(MN) virions. By flow cytometry, these MAbs appear to bind relatively weakly to infected cells and this bind ing is not perturbed by pretreatment of the infected cells with soluble CD4 . Despite the apparent linear nature of the epitopes of Z13 and 4E10, denat uration of recombinant envelope protein reduces the binding of these MAbs, suggesting some conformational requirements for full epitope expression. Mo st significantly, Z13 and 4E10 are able to neutralize selected primary isol ates from diverse subtypes of HIV-1 (e.g., subtypes B, C, and E). The resul ts suggest that a rather extensive region of gp41 close to the transmembran e domain is accessible to neutralizing Abs and could form a useful target f or vaccine design.