Vaccine-Induced HIV-1 Envelope gp120 Constant Region 1-Specific Antibodies Expose a CD4-Inducible Epitope and Block the Interaction of HIV-1 gp140 with Galactosylceramide

Abstract

Mucosal epithelial cell surface galactosylceramide (Galcer) has been postulated to be a receptor for HIV-1 envelope (Env) interactions with mucosal epithelial cells. Disruption of the HIV-1 Env interaction with such alternate receptors could be one strategy to prevent HIV-1 entry through the mucosal barrier. To study antibody modulation of HIV-1 Env-Galcer interactions, we used Galcer-containing liposomes to assess whether natural-and vaccine-induced monoclonal antibodies can block HIV-1 Env binding to Galcer. HIV-1 Env gp140 proteins bound to Galcer liposomes with K d s (dissociation constants) in the nanomolar range. Several HIV-1 ALVAC/AIDSVAX vaccinee-derived monoclonal antibodies (MAbs) specific for the gp120 first constant (C1) region blocked Galcer binding of a transmitted/founder HIV-1 Env gp140. Among the C1-specific MAbs that showed Galcer blocking, the antibody-dependent cellular cytotoxicity-mediating CH38 IgG and its natural IgA isotype were the most potent blocking antibodies. C1-specific IgG monoclonal antibodies that blocked Env binding to Galcer induced upregulation of the gp120 CD4-inducible (CD4i) epitope bound by MAb 17B, demonstrating that a conformational change in gp120 may be required for Galcer blocking. However, the MAb 17B itself did not block Env-Galcer binding, suggesting that the C1 antibody-induced gp120 conformational changes resulted in alteration in a Galcer binding site distant from the CD4i 17B MAb binding site. IMPORTANCEGalactosyl ceramide, a glycosphingolipid, has been postulated to be a receptor for the HIV-1 envelope glycoprotein (Env) interaction with mucosal epithelial cells. Here, we have mimicked this interaction by using an artificial membrane containing synthetic Galcer and recombinant HIV-1 Env proteins to identify antibodies that would block the HIV-1 Env-Galcer interaction. Our study revealed that a class of vaccine-induced human antibodies potently blocks HIV-1 Env-Galcer binding by perturbing the HIV-1 Env conformation.

Antibody Fc effector functions and IgG3 associate with decreased HIV-1 risk

“…Although we examined vaccine-matched Env among other diverse 505 (6), this finding is consistent with the hypothesis that emerged from the RV144 HIV-1 vaccine trial that Env IgA circulating in the blood was either a surrogate for another response associated with increased HIV-1 risk or that Env IgA could compete with Env IgG for Fc effector functions (17,18). It is important to note that antiviral functions of circulating IgA are likely different from antiviral functions of mucosal IgA, and that other antiviral IgA mechanisms (19,(42)(43)(44)(45) not tested here could be involved in protective efficacy. Given our systems immunology analysis, a possible synergistic effect between FcγRIIa binding, ADCP, IgG3, serum IgA, and CD8 + T cells may also explain potential protection; absence of serum IgA may enable FcγRIIa-mediated phagocytosis to eliminate infectious virions and/or cells in parallel with CD8 + T cellmediated antiviral functions such as virus inhibition elicited by this vaccine regimen (46) and/or through mechanisms associated with the polyfunctional responses by these vaccine-elicited CD8 + T cells (5).…”

Neutralization Takes Precedence Over IgG or IgA Isotype-related Functions in Mucosal HIV-1 Antibody-mediated Protection

“…Thus, even at peak mAb levels (1.5–9.7 μg/mL CH38 mIgA2 or 5–22 μg/mL CH54 IgG) in rectal secretions (Fig. S3), neither CH38 mIgA2, which blocks gp120 binding to the alternative receptor GalCer on epithelial cells (Dennison et al, 2014), nor CH54 IgG, which mediates ADCC in vitro (Bonsignori et al, 2012, Pollara et al, 2014) could protect against SHIV Bal acquisition or dampen viral replication after high-dose intrarectal challenge. These results may reflect insufficient accessibility of the CD4i epitopes (Veillette et al, 2014, Von Bredow et al, 2016).…”

“…These included IgG and IgA isotype variants of a VRC01-like bnAb (CH31) and several nnAbs exhibiting known alternative effector functions such as ADCC (gp120 C1-specific mAbs), phagocytosis (V2-specific CH58 and gp41-specific 7b2), virus capture (7b2), and GalCer blocking (CH38 IgA2). Many of these mAbs displayed multiple in vitro functions and the isotype variants of the same mAb have altered functional profiles (Bonsignori et al, 2012, Dennison et al, 2014, Liu et al, 2013, Pollara et al, 2014, Santra et al, 2015, Tomaras et al, 2013, Tay et al, 2016, Zhang et al, 2016). In vitro ADCC assay parameters influence the potency ascribed to gp120 C1-specific mAbs (Bonsignori et al, 2012, Veillette et al, 2014, Von Bredow et al, 2016) and the accessibility of these CD4i epitopes are not well-understood in vivo , warranting investigation of these mAbs in more physiologically relevant models.…”

“…Using these mAbs, the impact of various IgA forms on the functional capacity of neutralizing and non-neutralizing mAbs was investigated in various assays and models of HIV-1 transmission. This panel has been extensively characterized in a variety of in vitro assays supporting their potential to exert various antiviral functions in vivo , such as phagocytosis (Tay et al, 2016), virus capture (Liu et al, 2013, Liu et al, 2014), virus aggregation (Stieh et al, 2014, R. Shattock, personal communication), blocking of virus binding to galactosyl ceramide (GalCer) (Dennison et al, 2014), ADCC (Tomaras et al, 2013, Pollara et al, 2014, Bonsignori et al, 2012) and neutralization (Santra et al, 2015). Here, we have evaluated the protective capacity of these mAbs ex vivo in a human vaginal tissue explant model and in vivo in an NHP intrarectal model of HIV-1 infection to identify key Ab properties associated with early mucosal protection that may guide the development of effective prevention strategies.…”

Tailored placement of a turn-forming PA tag into the structured domain of a protein to probe its conformational state

“…In addition to the utility as an immunological detection agent, monoclonal antibodies can sometimes be used as probe or reporter for certain functional states of a protein, particularly when the protein undergoes a large conformational change during its biological action (Dennison et al, 2014;Humphries et al, 2003;Irannejad et al, 2013;Walker et al, 2004). If the 3D structure of the protein is known, it is theoretically possible to place a short peptide tag at a desired position and to use a monoclonal antibody against the tag to determine the function of the protein, as well as to modulate the function of the protein.…”