Murine monoclonal antibodies biologically active against the amino region of HIV-1 gp120: Isolation and characterization

The human immunodeficiency virus (HIV)-1 envelope glycoprotein is synthesiz ed as a precursor (gp160) and subsequently cleaved to generate the external gp120 and transmembrane gp41 glycoproteins, Both gp120 and gp41 have been demonstrated to mediate critical functions of HIV, including viral attachme nt and fusion with the cell membrane. The antigenic variability of the HIV- 1 envelope glycoprotein has presented a significant problem in the design o f appropriate and successful vaccines and offers one explanation for the ab ility of HIV to evade immune surveillance. Therefore, the development and c haracterization of functional antibodies against conserved regions of the e nvelope glycoprotein is needed. Because of this need, we generated a panel of murine monoclonal antibodies (MuMabs) against the HIV-1 envelope glycopr otein, To accomplish this, we immunized Balb/C mice with a recombinant glyc oprotein 160 (gp160) that was synthesized in a baculovirus expression syste m. From the growth-positive hybridomas, three MuMabs were generated that de monstrated significant reactivity with recombinant gp120 but failed to show reactivity against HIV-1 gp41, as determined by enzyme-linked immunosorben t assay (ELISA). Using vaccinia constructs that synthesize variant truncate d subunits of gp160, we were able to map reactivity of all three of the Mab s (ID6, AC4, and AD3) to the first 204 residues of gp120 (i.e., the N termi nus of gp120) via Western blot analysis. Elucidation of the epitopes for th ese Mabs may have important implications for inhibition of infection by HIV -1. Our initial attempts to map these Mabs with linear epitopes have not el ucidated a specific antigenic determinant; however, several physical charac teristics have been determined that suggest a continuous surface epitope, A lthough these antibodies failed to neutralize cell-free or cell-associated infection by HIV-1, they did mediate significant antibody-dependent cellula r cytotoxity (ADCC) activity, indicating potential therapeutic utility. In summary, these data suggest the identification of a potentially novel site in the first 200 aa of gp120 that mediates ADCC.