Recombinant Human Monoclonal Antibody IgG1b12 Neutralizes Diverse Human Immunodeficiency Virus Type 1 Primary Isolates

Abstract

The CD4-binding domain of human immunodeficiency virus type 1 (HIV-1) gp120 elicits antibodies that are present in infected human sera. Monoclonal antibodies that recognize the HIV-1 gp120 CD4-binding domain have been isolated. Some of these antibodies can neutralize laboratory-adapted strains of HIV-1 and probably mediate neutralization by interfering with virus binding to its cellular CD4 receptor. However, most anti-CD4 binding domain antibodies do not neutralize primary HIV-1 isolates. We used primary HIV-1 isolates in an infectivity reduction assay to test the uniquely derived anti-CD4 binding domain recombinant human monoclonal antibody, IgG1b12. All of the tested HIV-1 isolates were neutralized by this antibody. Additional studies indicated that neutralization of a primary isolate with MAb IgG1b12 did not require continuous exposure of human peripheral blood mononuclear cell cultures to the antibody. Finally, a complete IgG1 molecule of an in vitro-selected b12 FAb mutant with a > 400-fold increase in affinity was assembled, expressed in mammalian cells, and evaluated in the infectivity reduction assay in comparative studies with the parent IgG1b12 antibody. The mutant did not retain the level of primary isolate neutralization potency that was a property of the parent molecule. Thus, we confirm that recombinant IgG1b12 has a unique specificity, and that it can neutralize all primary isolates tested in human PBMC cultures in vitro.

Rapid evolution of the neutralizing antibody response to HIV type 1 infection

“…To address whether a generalized or inherent neutralization susceptibility of the patients' viruses accounted for this variability, viruses derived from two subjects who did not generate neutralization responses (TN-2 and TN-4) and two subjects who did generate neutralization responses (TN-1 and TN-3) were tested against three well characterized, broadly neutralizing monoclonal antibodies (b12, 2F5, and 2G12) ( Table 5; refs. [22][23][24]. Monoclonal antibody neutralization patterns did not correlate with the presence or absence of an autologous neutralizing antibody response.…”

Role of Neutralizing Antibodies in Protective Immunity Against HIV

“…65 The most potent and well-characterized monoclonal antibody against the CD4BS, b12, 50 neutralizes a broad range of primary isolates and confirms the critical role of the CD4BS in HIV-1 infection. 66,67 Interestingly, other CD4BS monoclonal antibodies such as 559/64D, 15e, F105, b3 and b6 do not neutralize primary isolates. 68,69 The reasons for this discrepancy are not yet understood, but b12 differs from all the other CD4BS antibodies in its sensitivity to V1-V2 loop deletion.…”

Increased Affinity and Stability of an Anti-HIV-1 Envelope Immunotoxin by Structure-based Mutagenesis

“…3B3 was derived by mutagenesis of b12, a Fab isolated from a combinatorial phage display library constructed from bone marrow RNA of an HIV-1 infected long-term nonprogessor. b12 and 3B3 tightly bind to and neutralize a broad range of laboratory strains and primary isolates of HIV-1 (12)(13)(14)(15)(16).…”