Enhancement of human immunodeficiency virus type 1 envelope-mediated fusion by a CD4-gp120 complex-specific monoclonal antibody

Abstract

The entry of human immunodeficiency virus type 1 (HIV-1) into cells is initiated by binding of the viral glycoprotein gp120-gp41 to its cellular receptor CD4. The gp120-CD4 complex formed at the cell surface undergoes conformational changes that may allow its association with an additional membrane component(s) and the eventual formation of the fusion complex. These conformational rearrangements are accompanied by immunological changes manifested by altered reactivity with monoclonal antibodies specific for the individual components and presentation of new epitopes unique to the postbinding complex. In order to analyze the structure and function of the gp120-CD4 complex, monoclonal antibodies were generated from splenocytes of BALB/c mice immunized with soluble CD4-gp120 (IIIB) molecules (J. M. Gershoni, G. Denisova, D. Raviv, N. I. Smorodinsky, and D. Buyaner, FASEB J. 7:1185-1187 1993). One of those monoclonal antibodies, CG10, was found to be strictly complex specific. Here we demonstrate that this monoclonal antibody can significantly enhance the fusion of CD4 ؉ cells with effector cells expressing multiple HIV-1 envelopes. Both T-cell-line-tropic and macrophage-tropic envelope-mediated cell fusion were enhanced, albeit at different optimal doses. Furthermore, infection of HeLa CD4 ؉ (MAGI) cells by HIV-1 LAI, ELI1, and ELI2 strains was increased two-to fourfold in the presence of CG10 monoclonal antibodies, suggesting an effect on viral entry. These findings indicate the existence of a novel, conserved CD4-gp120 intermediate structure that plays an important role in HIV-1 cell fusion.

CD4-Induced Conformational Changes in the Human Immunodeficiency Virus Type 1 gp120 Glycoprotein: Consequences for Virus Entry and Neutralization

“…The CG10 monoclonal antibody was raised by im-munization with the HIV-1 gp120 glycoprotein from the T-cell line-tropic IIIB strain complexed with sCD4. The CG10 antibody recognizes neither gp120 nor sCD4 alone, but only the gp120-sCD4 complex (27,35). This finding suggests that the CG10 antibody recognizes either a neoepitope created by the binding of gp120 and CD4 or an epitope on gp120 or CD4 that is exposed or induced only in the presence of the other ligand.…”

In silico Analysis of HIV-1 Env-gp120 Reveals Structural Bases for Viral Adaptation in Growth-Restrictive Cells

“…Virological ( Moore et al, 1992 ; Lee et al, 1997 ) and structural ( Huang et al, 2005 ; Julien et al, 2013 ; Lyumkis et al, 2013 ; Pancera et al, 2014 ; Do Kwon et al, 2015 ) studies consistently suggest that following CD4 binding, the gp120 surface undergoes conformational changes from co-receptor-binding-incompetent to -competent form. To address this issue, we constructed a full-length gp120 model in a CD4-bound state ( Figure 3A ).…”

Allosteric induction of the CD4-bound conformation of HIV-1 Gp120

“…For this, a random phage display peptide library (complexity = 5 × 10 9 ) was screened using monomeric T-cell lab-adapted HIV-1 CDC451 gp120 as bait. Multiple rounds of biopanning of the phage display peptide library led to the isolation of a phage, designated m1 (amino acid sequence displayed: C-DRRDLPQWAKRE-C ), which not only bound to gp120 but also enabled the binding of the stringent CD4i mAb CG10 [ 14 , 16 , 17 , 38 , 39 ] (Figure 1 A and B).…”

“…The murine anti-gp120 mAb CG10, which stringently recognizes the CD4i conformation of gp120 [ 14 , 17 , 38 , 39 ], the murine anti-gp120 mAbs LG4 (targets a conserved epitope at the carboxy-terminus of gp120), 9G3 and 1B6 [ 85 ], the murine anti-CD4 mAb CG9 [ 14 ], the murine anti-M13 Y2D mAb [ 86 ] and the rabbit polyclonal anti-M13 serum were produced at Tel Aviv University. The human anti-gp120 mAb N12-i15, which stringently recognizes the CD4i conformation of gp120, was produced at the Institute of Human Virology, University of Maryland School of Medicine, Baltimore, MA, USA [ 15 , 25 , 40 ].…”