Mapping the protein surface of human immunodeficiency virus type 1 gp120 using human monoclonal antibodies from phage display libraries.

Panels of hybridoma-derived monoclonal antibodies against diverse epitopes are widely used in defining protein surface topography, particularly in the absence of crystal or NMR structural information. Here we show that recombinant monoclonal antibodies from phage display libraries provide a rapid alternative for surface epitope mapping. Diverse epitopes are accessed by presenting antigen to the library in different forms, such as sequential masking of epitopes with existing antibodies or ligands prior to selection and selection on peptides. The approach is illustrated for a recombinant form of the human immunodeficiency virus type 1 (HIV-1) surface glycoprotein gp120 which has been extensively mapped by rodent and human monoclonal antibodies derived by cellular methods. Human recombinant Fab fragments to most of the principal epitopes on gp120 are selected including Fabs to the C1 region, a C1/C5 epitope, a C1/C2 epitope, the V2 loop, the V3 loop and the CD4 binding domain. In addition an epitope linked to residues in the V2 loop and CD4 binding domain is identified. Most of these specificities are associated with epitopes presented poorly on native multimeric envelope, consistent with the notion that these antibodies are associated with immunization by forms of gp120 differing in conformation from that found on whole virus or infected cells.