CHARACTERIZATION OF NEUTRALIZING MONOCLONAL-ANTIBODIES TO LINEAR AND CONFORMATION-DEPENDENT EPITOPES WITHIN THE 1ST AND 2ND VARIABLE DOMAINS OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 GP120

A number of linear and conformation-dependent neutralizing monoclonal antibodies (MAbs) have been mapped to the first and second variable (V 1 and V2) domains of human immunodeficiency virus type 1 (HIV-1) gp120 . The majority of these MAbs are as effective at neutralizing HIV-1 in fectivity as MAbs to the V3 domain and the CD4 binding site. The linea r MAbs bind to amino acid residues 162 to 171, and changes at residues 183/184 (PI/SG) and 191/192/193 (YSL/GSS) within the V2 domain abroga te the binding of the two conformation-dependent MAbs, 11/68b and CRA- 4, respectively. Surprisingly, a change at residue 435 (Y/H or Y/S), i n a region of gp120 near the CD4 binding site (M. Kowalski, J. Potz, L . Basiripour, T. Dorfman, W. C. Goh, E. Terwilliger, A. Dayton, C. Ros en, W. Haseltine, and J. Sodroski, Science 237:1351-1355, 1987; L. A. Lasky, G. M. Nakamura, D. H. Smith, C. Fennie, C. Shimasaki, E. Patzer , P. Berman, T. Gregory, and D. Capon, Cell 50:975-985, 1987; and U. O lshevsky, E. Helseth, C. Furman, J. Li, W. Haseltine, and J. Sodroski, J. Virol. 64:5701-5707, 1990), abrogated gp120 recognition by both of the conformation-dependent MAbs. However, both MAbs 11/68b and CRA-4 were able to bind to HIV-1 V1V2 chimeric fusion proteins expressing th e V1V2 domains in the absence of C4, suggesting that residues in C4 ar e not components of the epitopes but that amino acid changes in C4 may affect the structure of the V1V2 domains. This is consistent with the ability of soluble CD4 to block 11/68b and CRA-4 binding to both nati ve cell surface-expressed gp120 and recombinant gp120 and suggests tha t the binding of the neutralizing MAbs to the virus occurs prior to re ceptor interaction. Since the reciprocal inhibition, i.e., antibody in hibition of CD4-gp120 binding, was not observed, the mechanism of neut ralization is probably not a blockade of virus-receptor interaction. F inally, we demonstrate that linear sequences from the V2 region are im munogenic in HIV-1-infected individuals, suggesting that the primary n eutralizing response may be directed to both V2 and V3 epitopes.