The third variable region (V3) of the HIV-1 gpl20 envelope glycoprotein is thought to induce potent

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.

Immunogenic regions of the gp4l transmembrane protein of human immunodeficiency virus type 1 (HIV-1) were previously mapped by examining polyclonal sera from HIV-infected patients and rodent polyclonal and monoclonal antibodies (MAbs) to peptides of gp4l. To define the epitopes within these regions to which infected humans respond during the course of infection, the specificity of human MAbs to these regions had to be studied. Using 10 human MAbs identffied initially by their reactivity to whole gp4l in HIV-1 lysates, the epitopes within the immunodominant region of gp4l and within a second immunogenic region of gp4l have been mapped. Thus, five MAbs (from five different patients) to the immunodominant domain of gp4l in the vicinity of the cysteines at positions 598 and 604 (hereinafter designated cluster I) reacted with a stretch of 11 amino acids from positions 590 to 600. Four of these five MAbs were reactive with linear epitopes, while one MAb required the conformation conferred by the disulfide bridge between the aforementioned cysteines. Three MAbs to cluster I revealed dissociation constants ranging from 10-6 to 10-8 M, depending on the MAb tested and the size of the synthetic or recombinant peptide used in the assay. Five additional MAbs reacted with a second immunogenic region between positions 644 and 663 (designated cluster II). Four of these five MAbs were specific for conformational determinants. Titration of sera from HIV-infected patients showed that there was about 100-fold more antibody to cluster I than to cluster II in patients' sera, confirming the immunodominance of cluster I.

Three of 16 human monoclonal antibodies (hu-mAbs) enhanced human immunodeficiency virus type 1 (HIV-1) infection of MT-2 target cells by means ofa mechanism that is dependent on complement. Enhanced infections are characterized by an increase in cytopathic effects and antigen synthesis as well as an increase in the production of progeny virus as detected by release of reverse transcriptase activity and infectious virus into the culture medium. Analyses by radioimmunoprecipitation, Western blot, and ELISA using the pENV9 envelope fragment localize the antigenic specificities of these three hu-mAbs to the N-terminal two-thirds of the transmembrane protein gp4l. Competitive binding experiments indicate that the hu-mAbs are reactive with immuno-