IMMUNIZATION WITH A SOLUBLE CD4-GP120 COMPLEX PREFERENTIALLY INDUCES NEUTRALIZING ANTI-HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ANTIBODIES DIRECTED TO CONFORMATION-DEPENDENT EPITOPES OF GP120

Preservation of the conformation of recombinant gp120 in an adjuvant, enabling it to elicit conformation-dependent, epitope-specific, broadl y neutralizing antibodies, may be critical for the development of any gpl20-based human immunodeficiency virus type 1 (HIV-1) vaccine. It wa s hypothesized that recombinant gp120 complexed with recombinant CD3 c ould stabilize the conformation-dependent neutralizing epitopes and ef fectively deliver them to the immune system. Therefore, a soluble CD4- gp120 complex in Syntex adjuvant formulation was tested with mice for its ability to induce neutralizing anti-gpl20 antibody responses. Seve nteen monoclonal antibodies (MAbs) were generated and characterized. I mmunochemical studies, neutralization assays, and mapping studies with gp120 mutants indicated that the 17 MAbs fell into three groups. Four of them were directed to what is probably a conformational epitope in volving the C1 domain and did not possess virus-neutralizing activitie s. Another four MAbs bound to V3 peptide 302-321 and exhibited cross-r eactive gp120 binding and relatively weak virus-neutralizing activitie s. These MAbs were very sensitive to amino acid substitutions, not onl y in the V3 regions but also in the base of the V1/V2 loop, implying a conformational constraint on the epitope. The last group of nine MAbs recognized conformation-dependent epitopes near the CD3 binding site of gp120 and inhibited the gp120-soluble CD4 interaction. Pour of thes e nine MAbs showed broadly neutralizing activities against multiple la boratory-adapted strains of HIV-1, three of them neutralized only HIVI IIB, and the two lower-affinity MAbs did not neutralize any strain tes ted. Collectively, the results from this study indicate that immunizat ion with the CD4-gp120 complex can elicit antibodies to conformational ly sensitive gp120 epitopes, with some of the antibodies having broadl y neutralizing activities. We suggest that immunization with CD4-gp120 complexes may be worth evaluating further for the development of an A IDS vaccine.