Monoclonal Antibodies Raised against Covalently Crosslinked Complexes of Human Immunodeficiency Virus Type 1 gp120 and CD4 Receptor Identify a Novel Complex-Dependent Epitope on gp120

Abstract

The binding of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, gp120, to its cell surface receptor, CD4, represents a molecular interaction involving distinct alterations in protein structure. Consequently, the pattern of epitopes presented on the gp120-CD4 complex should differ from those on free gp120. To investigate this concept, mice were immunized with covalently crosslinked complexes of viral HIV-1IIIBgp120 and soluble CD4. Two monoclonal antibodies (MoAbs) obtained from the immunized mice exhibited a novel epitope specificity. The MoAbs were marginally reactive with HIV-1IIIBgp120, highly reactive with gp120-CD4 complexes, and unreactive with soluble CD4. The same pattern of reactivity was seen in solid-phase assays using HIV-1(451)gp120. A similar specificity for complexes was evident in flow cytometry experiments, in which MoAb reactivity was dependent upon the attachment of gp120 to CD4-positive cells. In addition, MoAb reactivity was detected upon the interaction of CD4 receptors with purified HIV-1IIIB virions. Notably, seroantibodies from HIV-positive individuals competed for MoAb binding, indicating that the epitope is immunogenic in humans. The results demonstrated that crosslinked gp120-CD4 complexes elicit antibodies to cryptic gp120 epitopes that are exposed during infection in response to receptor binding. These findings may have important implications for the consideration of HIV envelope-receptor complexes as targets for virus neutralization.

Immunogenicity of Constrained Monoclonal Antibody A32-Human Immunodeficiency Virus (HIV) Env gp120 Complexes Compared to That of Recombinant HIV Type 1 gp120 Envelope Glycoproteins

“…Human CD4 induces anti-CD4 antibodies that themselves neutralize HIV-1. Indeed, absorption of anti-CD4 antibodies removed some but not all of the crosssubtype neutralizing activity induced by CD4-rgp120 complexes (5,9). Second, CD4, when complexed to rgp120, can be part of a new neutralizing determinant in the complex and/or induce new neutralizing determinants on rgp120 following induction of conformational changes in rgp120 by CD4 (5,6,9).…”

“…DeVico et al have shown that expression of CD4-induced neutralizing determinants defined by MAbs raised against CD4-rgp120 complexes vary in their expression on native gp120s, being constitutively expressed on some gp120s and less so on others (5). In this regard, rgp120 89.6 had constitutive low-level expression of MAb 17b (7) binding that increased after MAb A32 binding while rgp120 BaL had no constitutive MAb 17b binding.…”

Antibodies to CD4-induced sites in HIV gp120 correlate with the control of SHIV challenge in macaques vaccinated with subunit immunogens

“…Purified soluble human and macaque CD4 (sCD4) was obtained from Biogen (Cambridge, MA). Cross-linked complexes were prepared with HIV BaL gp120 and sCD4 by using bis-sulfosuccinimidyl suberate (Pierce, Rockford, IL) as previously described (35). The rhFLSC was generated from a single-chain HIV BaL gp120-human CD4D1D2 complex (24) by replacing the human D1D2 component with a D1D2 gene fragment from rhesus macaque CD4.…”

Role of Neutralizing Antibodies in Protective Immunity Against HIV

“…51,76,77,175,176 Attempts have been made by various groups to evaluate such triggered Env (gp120-CD4 complexes) as potential vaccine candidates. 75,177 It was demonstrated that gp120-CD4 complexes can induce broadly neutralizing antibody responses, but they need to be stabilized using cross-linking reagents. 177 In a proof of concept study, we have demonstrated that triggered Env (gp120-CD4 complexes) induced strong immune responses against both gp120 and CD4 101 and these antibodies neutralized both a primary isolate (SF162) as well as a T-cell adapted isolate (SF2).…”

“…75,177 It was demonstrated that gp120-CD4 complexes can induce broadly neutralizing antibody responses, but they need to be stabilized using cross-linking reagents. 177 In a proof of concept study, we have demonstrated that triggered Env (gp120-CD4 complexes) induced strong immune responses against both gp120 and CD4 101 and these antibodies neutralized both a primary isolate (SF162) as well as a T-cell adapted isolate (SF2). 178 To elucidate the contribution of anti-Env antibodies to neutralization, we affinity purified the anti-Env antibodies from anti-CD4 antibodies and showed that these antibodies neutralized two subtype B and one subtype C primary HIV-1 isolates that were tested.…”