The challenges of eliciting neutralizing antibodies to HIV-1 and to influenza virus

Antibody 14G7 is protective against lethal Ebola virus challenge and recognizes a distinct linear epitope in the prominent mucinlike domain of the Ebola virus glycoprotein GP. The structure of 14G7 in complex with its linear peptide epitope has now been determined to 2.8 Å. The structure shows that this GP sequence forms a tandem ␤-hairpin structure that binds deeply into a cleft in the antibody-combining site. A key threonine at the apex of one turn is critical for antibody interaction and is conserved among all Ebola viruses. This work provides further insight into the mechanism of protection by antibodies that target the protruding, highly accessible mucin-like domain of Ebola virus and the structural framework for understanding and characterizing candidate immunotherapeutics.

Section: Discussionmentioning

confidence: 99%

Structure of an Antibody in Complex with Its Mucin Domain Linear Epitope That Is Protective against Ebola Virus

Olal

Kuehne

Bale

et al. 2012

“…Plasma samples were studied for reactivity to HIV-1 Env protein antigens and V1V2 constructs by enzyme-linked immunosorbent assay (ELISA) as described previously (8,9,21). Blocking assays were performed as described previously (10,13) modified to use rhesus detection reagents (10,21). Plasma titers were determined using an initial 1:25 dilution (for Env reagents) or 1:30 (for V1V2 reagents), followed by a 3-fold dilution series; the background for each analyte was determined based on nonimmune plasma.…”

Section: Methodsmentioning

confidence: 99%

“…Studies have shown that adjuvants could permit antigen sparing (e.g., novel influenza vaccines that would require rapid deployment to combat new pandemics [7]) and could increase the potency and breadth of antibody responses (8,9). Adjuvants have also been suggested as a means to overcome the problems of inducing broadly neutralizing antibodies against both HIV-1 and influenza virus (10).…”

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confidence: 99%

“…Moreover, adjuvants can activate distinct innate immune pathways that profoundly alter both humoral and cellular immunity. Accordingly, the addition of TLR agonists have been used to boost vaccine responses and has been suggested as one means of enhancing the response to HIV-1 immunogens (10). Based on the similarity of TLR expression in rhesus macaques and humans (11), we undertook a systematic comparison of oil-in-water emulsions containing different combinations of TLR agonists formulated with a highly antigenic HIV-1 transmitted/founder envelope B.63521 gp140.…”

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confidence: 99%

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Toll-Like Receptor 7/8 (TLR7/8) and TLR9 Agonists Cooperate To Enhance HIV-1 Envelope Antibody Responses in Rhesus Macaques

Moody

Santra

Vandergrift

et al. 2014

The development of a vaccine that can induce high titers of functional antibodies against HIV-1 remains a high priority. We have developed an adjuvant based on an oil-in-water emulsion that incorporates Toll-like receptor (TLR) ligands to test whether triggering multiple pathogen-associated molecular pattern receptors could enhance immunogenicity. Compared to single TLR agonists or other pairwise combinations, TLR7/8 and TLR9 agonists combined were able to elicit the highest titers of binding, neutralizing, and antibody-dependent cellular cytotoxicity-mediating antibodies against the protein immunogen, transmitted/ founder HIV-1 envelope gp140 (B.63521). We further found that the combination of TLR7/8 and TLR9 agonists was associated with the release of CXCL10 (IP-10), suggesting that this adjuvant formulation may have optimally stimulated innate and adaptive immunity to elicit high titers of antibodies. IMPORTANCECombining TLR agonists in an adjuvant formulation resulted in higher antibody levels compared to an adjuvant without TLR agonists. Adjuvants that combine TLR agonists may be useful for enhancing antibody responses to HIV-1 vaccines.

“…Mechanisms that these viruses evolve to prevent antibody recognition include high sequence variability and heavily glycosylated Env (12)(13)(14)(15). The variable regions of Env, in particular the V1V2 region, can shield other conserved epitopes on Env, including the CD4 and CCR5 binding sites (16)(17)(18)(19).…”

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confidence: 99%

Loss of a Conserved N-Linked Glycosylation Site in the Simian Immunodeficiency Virus Envelope Glycoprotein V2 Region Enhances Macrophage Tropism by Increasing CD4-Independent Cell-to-Cell Transmission

Yen

Herschhorn

Haim

et al. 2014

Self Cite

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) strains differ in their capacity to replicate in macrophages, but mechanisms underlying these differences are not fully understood. Here, we identify a highly conserved Nlinked glycosylation site (N173 in SIV, corresponding to N160 in HIV) in the V2 region of the SIV envelope glycoprotein (Env) as a novel determinant of macrophage tropism and characterize mechanisms underlying this phenotype. Loss of the N173 glycosylation site in the non-macrophage-tropic SIVmac239 by introducing an N173Q mutation enhanced viral replication and multinucleated giant cell formation upon infection of rhesus macrophages, while the addition of N173 to SIVmac251 had the opposite effect. The removal of N173 in SIVmac239 enhanced CD4-independent cell-to-cell transmission to CCR5-expressing cells. SIVmac239 with N173Q mediated CD4-independent cell-cell fusion but could not infect CD4-negative cells in single-round infections. Thus, CD4-independent phenotypes were detected only in the context of cell-to-cell contact. Similar results were obtained in SIVmac251 with and without N173. N173 decreased the neutralization sensitivity of SIVmac251 but had no effect on the neutralization sensitivity of SIVmac239. The N173Q mutation had no effect on SIVmac239 binding to CD4 in Biacore assays, coimmunoprecipitation assays, and enzyme-linked immunosorbent assays (ELISAs). These findings suggest that the loss of the N173 N-linked glycosylation site increases SIVmac239 replication in macrophages by enhancing CD4-independent cell-to-cell virus transmission through CCR5-mediated fusion. This mechanism may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses in vivo. IMPORTANCEIn this study, we identify a genetic determinant in the viral envelope (N173) that increases replication and spreading infection of SIV strains in macrophages by enhancing cell-to-cell virus transmission. This effect is explained by a novel mechanism involving increased cell-to-cell fusion in the absence of CD4, the primary receptor that normally mediates virus entry. The same genetic determinant also affects the sensitivity of these viruses to inhibition by neutralizing antibodies. Most macrophage-tropic HIV/ SIV strains are known to be neutralization sensitive. Together, these findings suggest that this efficient mode of virus transmission may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses to cells expressing little or no CD4 in vivo. Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) strains differ in their ability to infect and replicate in macrophages. Macrophage tropism is determined primarily by the envelope glycoprotein (Env), which forms trimers composed of three noncovalently bound heterodimers of gp120 and gp41 subunits. The gp120 exterior subunit interacts with CD4 and a coreceptor, mainly CCR5 (1, 2),...