Cell lines secreting IgG1 human monoclonal antibodies (mAbs) to the envelope glycoprotein, gpl2O, of human immunodeficiency virus (IRV) have been produced by transformation of peripheral blood cells front IIV-infected individuals and by fusion of transformed cells to a humanmouse heteromyeloma cell line (SHM-D33). Two human mAbs were site-selected by means of a 23-mer synthetic peptide spanning a portion of the third variable domain of gpI20 from the MN strain of HIV. The two heterohybridomas produce three times more IgG than do their parent lymphoblastoid cell lines. The specificities of these mAbs have been mapped to sequences near the tip of the disulfide loop of the gpl20 third variable domain, Lys-Arg-lle-His-Ile and His-Ie-Gly-Pro-GlyArg, respectively. The mAbs have dissociation constants of 3.7 x 10-6 M and 8.3 x 10-7 M, neutralize HIVMN in vitro at nanogram levels, and bear the characteristics of antibodies associated with protective immunity in vivo.

Based on the finding that cells producing antibodies to human immunodeficiency virus (HIV) circulate in the peripheral blood of HIV-infected individuals, attempts were made to immortalize such B cells with Epstein-Barr virus.

Three IgG1 human monoclonal antibodies (MAbs) directed against conformational epitopes of the gp120 envelope protein of HIV-1 were produced, as was a single human MAb to a linear epitope spanning amino acids 487-509 in the C-terminal portion of gp120. All three conformation-dependent MAbs reacted optimally with recombinant gp120 (rgp120) captured on plastic via its carbohydrate moieties with Concanavalin A. These MAbs were able to block the interaction between recombinant CD4 (rCD4) and rgp120; they were also able to achieve 50% neutralization of HTLV-IIIB and MN strains of HIV-1 in a concentration range of 0.5-12.8 micrograms/mL. The MAb to the linear determinant is the first reported human MAb specific for the immunodominant portion of gp120; this MAb was most reactive with rgp120 when it was coated directly on plastic. It could neither inhibit rCD4-rgp120 binding nor neutralize either HTLV-IIIB or MN. The binding affinities of the four human MAbs for rgp120 in solution, reflected by their dissociation constants (Kd), ranged from 0.5 x 10(-8) to 7.5 x 10(-8) M.