Characterization of a human immunodeficiency virus neutralizing monoclonal antibody and mapping of the neutralizing epitope

A monoclonal antibody was produced to the exterior envelope glycoprotein (gp120) of the human T-cell lymphotropic virus (HTLV)-III(B) isolate of the human immunodeficiency virus (HIV). This antibody binds to gp120 of HTLV-III(B) and lymphadenopathy-associated virus type 1 (LAV-1) and to the surface of HTLV-III(B)- and LAV-1-infected cells, neutralizes infection by cell-free virus, and prevents fusion of virus-infected cells. In contrast, it does not bind, or weakly binds, the envelope of four heterologous HIV isolates and does not neutralize the heterologous isolates HTLV-III(RF) and HTLV-III(MN). The antibody-binding site was mapped to a 24-amino-acid segment, using recombinant and synthetic segments of HTLV-III(B) gp120. This site is within a segment of amino acid variability known to contain the major neutralizing epitopes (S.D. Putney, T.J. Matthews, W.G. Robey, D.L. Lynn, M. Robert-Guroff, W.T. Mueller, A.J. Langlois, J. Ghrayeb, S.R. Petteway, K.J. Weinhold, P.J. Fischinger, F. Wong-Staal, R.C. Gallo, and D.P. Bolognesi, Science 234:1392-1395, 1986). These results localize an epitope of HIV type-specific neutralization and suggest that neutralizing antibodies may be effective in controlling cell-associated, as well as cell-free, virus infection.