neutralization of divergent hiv1 isolates by conformationdependent human antibodies to gp120 the spectrum of human immunodeficiency virus type 1 hiv1 isolates neutralized by antibodies from hiv1infected humans is broader than the spectrum of isolates neutralized by sera from animals immunized with purified gp120 subunits this broader neutralization was due in part to the presence of antibodies to conserved gp120 conformational epitopes purified conformationdependent gp120specific human antibodies neutralized a wider range of virus isolates than human antibodies directed to linear determinants in gp120 and were also responsible for the majority of the gp120specific cd4blocking activity of hiv1infected human sera a gp120 subunit vaccine that effectively presents these conformationdependent neutralization epitopes should protect against a broader range of hiv1 variants than a vaccine that presents exclusively linear determinants