Broad neutralization of human immunodeficiency virus type 1 mediated by plasma antibodies against the gp41 membrane proximal external region

Abstract

We identified three cross-neutralizing plasma samples with high-titer anti-membrane proximal external region (MPER) peptide binding antibodies from among 156 chronically human immunodeficiency virus type 1-infected individuals. In order to establish if these antibodies were directly responsible for the observed neutralization breadth, we used MPER-coated magnetic beads to deplete plasmas of these specific antibodies. Depletion of anti-MPER antibodies from BB34, CAP206, and SAC21 resulted in 77%, 68%, and 46% decreases, respectively, in the number of viruses neutralized. Antibodies eluted from the beads showed neutralization profiles similar to those of the original plasmas, with potencies comparable to those of the known anti-MPER monoclonal antibodies (MAbs), 4E10, 2F5, and Z13e1. The anti-MPER neutralizing antibodies in BB34 were present in the immunoglobulin G3 subclass-enriched fraction. Alanine scanning of the MPER showed that the antibodies from these three plasmas had specificities distinct from those of the known MAbs, requiring one to three crucial residues at positions 670, 673, and 674. These data demonstrate the existence of MPER-specific cross-neutralizing antibodies in plasma, although the ability to elicit such potent antiviral antibodies during natural infection appears to be rare. Nevertheless, the identification of three novel antibody specificities within the MPER supports its further study as a promising target for vaccine design.

FIG. 1.

Adsorption of anti-MPER antibodies from plasmas BB34, BB81, and BB105. MAb 4E10 and plasma samples were adsorbed with MPER-peptide-coated beads or blank beads or left untreated. (A) All samples were assayed by ELISA for binding to the MPER or V3 peptide and tested for neutralization of the HIV-2-HIV-1 MPER chimera C1C. OD, optical density; conc, concentration. (B) Adsorbed plasmas were tested for neutralization of the HIV-1 envelope-pseudotyped viruses COT6.15, CAP206.8, and Du156.12.

FIG. 2.

Antibodies eluted from MPER-coated beads contain cross-neutralizing activity. (A) Neutralization of C1C by eluates from MPER-coated beads of plasmas BB34, CAP206, and SAC21 and MAbs 4E10, Z13e1, and 2F5. conc, concentration. (B) Neutralization of HIV-1 subtype C envelope-pseudotyped viruses COT6.15, ZM197M.PB7, Du156.12, and CAP206.8 and subtype B TRO.11 and JR-FL.

FIG. 3.

Comparison of the IgG subclass profiles between original plasmas and eluates from MPER-coated beads. The pie charts represent the IgG subclasses found in the BB34, CAP206, and SAC21 plasmas and eluates. The table shows the IgG subclass concentrations in plasmas and in eluates. b.d, below detection level.

FIG. 4.

Neutralizing anti-MPER antibodies are IgG3 in BB34 but not in CAP206. (A and B) IgG subclass profiles of total IgG, FTpA, and EpA of BB34 (A) and CAP206 (B). (C) BB34 fractions were tested for neutralization of C1C and HIV-1 envelope-pseudotyped viruses, as well as binding to the MPER peptide in ELISA. OD, optical density; conc, concentration. (D) CAP206 fractions were tested for neutralization of C1C and HIV-1 envelope-pseudotyped viruses.