Evolutionary Dynamics of the Glycan Shield of theHuman Immunodeficiency Virus Envelope during Natural Infection andImplications for Exposure of the 2G12Epitope

Abstract

Elucidation of the kinetics of exposure of neutralizing epitopes on the envelope of human immunodeficiency virus type 1 (HIV-1) during the course of infection may provide key information about how HIV escapes the immune system or why its envelope is such a poor immunogen to induce broadly efficient neutralizing antibodies. We analyzed the kinetics of exposure of the epitopes corresponding to the broadly neutralizing human monoclonal antibodies immunoglobulin G1b12 (IgG1b12), 2G12, and 2F5 at the quasispecies level during infection. We studied the antigenicity and sequences of 94 full-length envelope clones present during primary infection and at least 4 years later in four HIV-1 clade B-infected patients. No or only minor exposure differences were observed for the 2F5 and IgG1b12 epitopes between the early and late clones. Conversely, the envelope glycoproteins of the HIV-1 quasispecies present during primary infection did not expose the 2G12 neutralizing epitope, unlike those present after several years in three of the four patients. Sequence analysis revealed major differences at potential N-linked glycosylation sites between early and late clones, particularly at positions known to be important for 2G12 binding. Our study, in natural mutants, confirms that the glycosylation sites N295, N332, and N392 are essential for 2G12 binding. This study demonstrates the relationship between the evolving "glycan shield " of HIV and the kinetics of exposure of the 2G12 epitope during the course of natural infection.Until recently, it was thought that low levels of neutralizing antibodies to autologous viruses develop slowly throughout human immunodeficiency virus type 1 (HIV-1) infection (6,7,26,27,36). However, two recent studies based on elegant recombinant virus assays provided major new information about the kinetics of the neutralizing antibody response to HIV (39,49). It is now clear that the autologous neutralizing response is generally strong and develops rapidly. However, the neutralizing antibody response exerts a selective pressure that continuously drives the evolution of neutralizing escape mutants, allowing them to persist in the host. This strong, early autologous neutralizing response is generally inefficient against heterologous viruses (39, 49). Broadly neutralizing antibodies, which are able to neutralize a broad spectrum of primary isolates, are rarely found in HIV-1-infected individuals (3,7,26). When detected, they appear late, at least several years after primary infection, mainly in long-term asymptomatic patients (11, 52). A few human monoclonal antibodies (MAbs) with broadly neutralizing activities have been isolated from such individuals (8,12,13,14,25,28,29,45,47,48). Among them, three major MAbs have been characterized in depth: immunoglobulin G1b12 (IgG1b12), 2G12, and 2F5. The epitopes recognized by IgG1b12 and 2G12 are located on the surface envelope glycoprotein gp120. IgG1b12 binds to an epitope overlapping the CD4 receptor site (32,40,43,53), whereas 2G12 binds to a carbohydrate-dependen...

Influences on the Design and Purification of Soluble, Recombinant Native-Like HIV-1 Envelope Glycoprotein Trimers

“…Unlike 92UG037.8, CZA97.012 gp120 lacks a glycan at residue 295. This glycan site is generally considered to be one of the principal components of the 2G12 epitope (58)(59)(60)(61)(62)(63). Nonetheless, we observed that 2G12 could still bind efficiently to the CZA97.012 Env proteins in the SPR assay (Fig.…”

Role of Neutralizing Antibodies in Protective Immunity Against HIV

“…91 Furthermore, Dacheux and colleagues have studied the antigenicity and exposure of critical neutralizing epitopes recognized by 2F5, b12 and 2G12 mAbs in 94 full length Env clones present during the early infection and at least 4 years later in four HIV-1 clade B infected patients. 92 Minor exposure differences were observed for 2F5 and b12 epitopes in early isolates versus late isolates. However, Env glycoprotein of the HIV-1 quasi species present during the primary infection did not expose the 2G12 neutralizing epitope.…”

The V1V2 Domain and an N-Linked Glycosylation Site in the V3 Loop of the HIV-1 Envelope Glycoprotein Modulate Neutralization Sensitivity to the Human Broadly Neutralizing Antibody 2G12

“…HIV-1 has evolved multiple mechanisms to shield the conserved epitopes from binding of neutralizing antibodies. The exposed surface of gp120 is heavily glycosylated, with a continuous shift in vivo of the sugar moiety positions, generating a protective dynamic glycan shield preventing antibody binding by steric hindrance (5,9,29,37).…”

“…It binds to a cluster of high-mannose glycans, with ␣132 terminal mannose residues as essential components (31,32,33,35). Characterization of the 2G12 epitope through extensive sitedirected mutagenesis studies on prototype subtype B strains showed the implications of three major potential N-glycosylation sites (PNGS) at positions 295, 332, and 392 that are critical for 2G12 binding and two additional N-glycans at positions 339 and 386 that likely play indirect roles (9,31,32,35). The crystal structures of Fab 2G12 revealed an unusual structure with swapped variable domains that allow it to make multivalent interactions matching the geometrical constraints for recognition of the carbohydrate cluster (6,7).…”