Anti-V3 Monoclonal Antibodies Display Broad Neutralizing Activities against Multiple HIV-1 Subtypes

Abstract

BackgroundThe V3 loop of the HIV-1 envelope (Env) glycoprotein gp120 was identified as the “principal neutralizing domain” of HIV-1, but has been considered too variable to serve as a neutralizing antibody (Ab) target. Structural and immunochemical data suggest, however, that V3 contains conserved elements which explain its role in binding to virus co-receptors despite its sequence variability. Despite this evidence of V3 conservation, the ability of anti-V3 Abs to neutralize a significant proportion of HIV-1 isolates from different subtypes (clades) has remained controversial.MethodsHIV-1 neutralization experiments were conducted in two independent laboratories to test human anti-V3 monoclonal Abs (mAbs) against pseudoviruses (psVs) expressing Envs of diverse HIV-1 subtypes from subjects with acute and chronic infections. Neutralization was defined by 50% inhibitory concentrations (IC50), and was statistically assessed based on the area under the neutralization titration curves (AUC).ResultsUsing AUC analyses, statistically significant neutralization was observed by ≥1 anti-V3 mAbs against 56/98 (57%) psVs expressing Envs of diverse subtypes, including subtypes A, AG, B, C and D. Even when the 10 Tier 1 psVs tested were excluded from the analysis, significant neutralization was detected by ≥1 anti-V3 mAbs against 46/88 (52%) psVs from diverse HIV-1 subtypes. Furthermore, 9/24 (37.5%) Tier 2 viruses from the clade B and C standard reference panels were neutralized by ≥1 anti-V3 mAbs. Each anti-V3 mAb tested was able to neutralize 28–42% of the psVs tested. By IC50 criteria, 40/98 (41%) psVs were neutralized by ≥1 anti-V3 mAbs.ConclusionsUsing standard and new statistical methods of data analysis, 6/7 anti-V3 human mAbs displayed cross-clade neutralizing activity and revealed that a significant proportion of viruses can be neutralized by anti-V3 Abs. The new statistical method for analysis of neutralization data provides many advantages to previously used analyses.

Antibodies Targeting the Envelope of HIV-1

“…Conventional neutralizing Abs (nAbs) also have a limited neutralizing potency in vitro, and while most tier 1 pseudoviruses are neutralized with low levels of nAbs (<<1 to 10 μg/ml), often >10 μg/ml are required to neutralize tier 2 pseudoviruses (21,22).…”

“…Both types of glycan-independent Abs specific for the V3 crown can neutralize most laboratory-adapted HIV-1 strains and tier 1 viruses but neutralize relatively few tier 2 viruses using standard neutralization assays (21,98,99). This is largely due to masking of the V3 loop by glycans (100) and by the V1V2 domain that is situated atop the trimer.…”

Polyclonal B Cell Responses to Conserved Neutralization Epitopes in a Subset of HIV-1-Infected Individuals

“…MAb 4E10 neutralizes more broadly, albeit usually at a lower magnitude. Other MAbs, including those directed to the V3 loop, usually exhibit a more limited profile of neutralization (51,80), while MAbs directed to CD4-induced epitopes usually fail to neutralize tier 2 viruses altogether (8,53,115).…”

Immunotypes of a Quaternary Site of HIV-1 Vulnerability and Their Recognition by Antibodies

“…Several sites of HIV-1 vulnerability have been identified on the assembled envelope (Env) spike, which is composed of three gp120 exterior units and three gp41 transmembrane molecules. These sites include the initial site of viral attachment to the cellular receptor CD4 (4,(29)(30)(31), a glycan site recognized by the 2G12 antibody (22,23), the V3 loop (6,9,10,32), and the external region of gp41 proximal to the membrane (25,33). Recently, an epitope composed of quaternary structure-dependent interactions of the V2 and V3 loops of gp120 was also identified (7,8,11,21,27,28).…”