Antibody polyspecificity and neutralization of HIV-1: A hypothesis

Self Cite

139

164

Next-generation sequencing of antibody transcripts from HIV-1-infected individuals with broadly neutralizing antibodies could provide an efficient means for identifying somatic variants and characterizing their lineages. Here, we used 454 pyrosequencing and identity/divergence grid sampling to analyze heavy-and lightchain sequences from donor N152, the source of the broadly neutralizing antibody 10E8. We identified variants with up to 28% difference in amino acid sequence. Heavy-and light-chain phylogenetic trees of identified 10E8 variants displayed similar architectures, and 10E8 variants reconstituted from matched and unmatched phylogenetic branches displayed significantly lower autoreactivity when matched. To test the generality of phylogenetic pairing, we analyzed donor International AIDS Vaccine Initiative 84, the source of antibodies PGT141-145. Heavy-and light-chain phylogenetic trees of PGT141-145 somatic variants also displayed remarkably similar architectures; in this case, branch pairings could be anchored by known PGT141-145 antibodies. Altogether, our findings suggest that phylogenetic matching of heavy and light chains can provide a means to approximate natural pairings.antibody-affinity maturation | antibodyomics | B-cell ontogeny | DNA sequencing | immunological tolerance

Section: Resultsmentioning

confidence: 99%

Mining the antibodyome for HIV-1–neutralizing antibodies with next-generation sequencing and phylogenetic pairing of heavy/light chains

Zhu

Ofek

Yang

et al. 2013

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139

164

“…It has been previously proposed that these difficulties related to the suggested reactivity of 2F5 and 4E10 with cardiolipin, an endogenous phospholipid (25,43). Explicitly, the hypothesis is that the MPER antigenically mimics cardiolipin, an autoantigen; therefore, MPER immunogens fail to induce neutralizing anti-MPER antibodies because B cells with autoreactive antibody specificities are negatively regulated by tolerance mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Aromatic residues at the edge of the antibody combining site facilitate viral glycoprotein recognition through membrane interactions

Scherer

Leaman

Zwick

et al. 2010

107

118

The broadly neutralizing anti-HIV antibody 4E10 recognizes an epitope very close to the virus membrane on the glycoprotein gp41. It was previously shown that epitope recognition improves in a membrane context and that 4E10 binds directly, albeit weakly, to lipids. Furthermore, a crystal structure of Fab 4E10 complexed to an epitope peptide revealed that the centrally placed, protruding H3 loop of the antibody heavy chain does not form peptide contacts. To investigate the hypothesis that the H3 loop apex might interact with the viral membrane, two Trp residues in this region were substituted separately or in combination with either Ala or Asp by site-directed mutagenesis. The resultant IgG variants exhibited similar affinities for an epitope peptide as WT 4E10 but lower apparent affinities for both viral membrane mimetic liposomes and Env(−) virus. Variants also exhibited lower apparent affinities for Env(+) virions and failed to significantly neutralize a number of 4E10-sensitive viruses. For the extremely sensitive HXB2 virus, variants did neutralize, but at 37-to >250-fold lower titers than WT 4E10, with Asp substitutions exerting a greater effect on neutralization potency than Ala substitutions. Because reductions in lipid binding reflect trends in neutralization potency, we conclude that Trp residues in the antibody H3 loop enable membrane proximal epitope recognition through favorable lipid interactions. The requirement for lipophilic residues such as Trp adjacent to the antigen binding site may explain difficulties in eliciting 4E10-like neutralizing antibody responses by immunization and helps define a unique motif for antibody recognition of membrane proximal antigens.4E10 | gp41 | HIV | neutralizing antibody | tryptophan

“…One hypothesis for the failure of such vaccines to elicit broadly neutralizing antibodies is that the Env epitopes presented to host B cells are not in the correct envelope conformation; for the MPER, this conformation may be the transient, prehairpin gp41 intermediate (11,12). Another hypothesis is that 2F5 and 4E10 mAbs, which are unusual in having long hydrophobic CDR3 loops, may be particularly effective in reaching epitopes near the virion lipid bilayer, but may be difficult to induce because of down-regulation of polyreactive B cell clones through B cell tolerance mechanisms (13)(14)(15)(16)(17)(18).…”

Section: Immunogen | Broadly Neutralizing Antibodiesmentioning

confidence: 99%

Prolonged exposure of the HIV-1 gp41 membrane proximal region with L669S substitution

Shen

Dennison

Liu

et al. 2010

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The conserved membrane-proximal external region (MPER) of HIV-1 envelope is a target for the rare broadly neutralizing 2F5, Z13, and 4E10 monoclonal antibodies (mAbs). One strategy to elicit such antibodies is to design an immunogen with increased exposure of the 2F5 and 4E10 mAb epitopes. In this study we characterize a single leucine to serine substitution at position 669 (L669S) in the gp41 Env MPER that confers >250-fold more neutralization sensitivity to 2F5 and 4E10 mAbs than does the wild-type gp41 sequence. On synthetic liposomes, increased solvent exposure of MPER tryptophan residues and stable docking of 2F5 and 4E10 mAbs to mutant MPER peptide liposomes indicate more favorable membrane orientation of MPER neutralizing epitopes with L669S substitution. The time during which virus is sensitive to 2F5 mAb-mediated neutralization is approximately 3-fold longer when the mutation is present. These data suggest that a major contribution to the L669S mutant virus phenotype of enhanced susceptibility to MPER mAbs is prolonged exposure of the MPER neutralizing epitope during viral entry. immunogen | broadly neutralizing antibodiesA major challenge for an effective HIV-1 vaccine is the inability of immunogens to induce broadly neutralizing antibodies (nAbs). One goal for antibody-based HIV-1 vaccine strategies is to elicit broadly neutralizing antibodies similar in breadth to the membrane-proximal external region (MPER) 2F5 and 4E10 monoclonal antibodies (mAbs) that neutralize a majority of transmitted viruses (1). MPER-specific broadly neutralizing antibodies are rarely made in HIV-1 infection (2-4), but recent studies from our group and others have shown that 2F5-like antibodies responsible for neutralization breadth can be found in ≈0.3% of HIV-1 infected subjects (5), whereas 4E10-like antibodies can be found in ∼3% of HIV-1 positive subjects (6). Vaccination with antigenic envelope constructs expressing 2F5 and 4E10 epitopes has not induced high-titered neutralizing antibodies (7-10). One hypothesis for the failure of such vaccines to elicit broadly neutralizing antibodies is that the Env epitopes presented to host B cells are not in the correct envelope conformation; for the MPER, this conformation may be the transient, prehairpin gp41 intermediate (11,12). Another hypothesis is that 2F5 and 4E10 mAbs, which are unusual in having long hydrophobic CDR3 loops, may be particularly effective in reaching epitopes near the virion lipid bilayer, but may be difficult to induce because of down-regulation of polyreactive B cell clones through B cell tolerance mechanisms (13-18).Previous work has identified two amino acid substitutions (T569A, I675V) (19) and L669S (5) in the MPER that increased neutralization sensitivity by MPER antibodies; however, the mechanism by which neutralization sensitivity was increased was not determined (5,19). We now report that the mechanism of enhanced neutralization sensitivity of a single amino acid substitution (leucine to serine substitution at position 669, L669S) in the heptad re...