Anti-phospholipid human monoclonal antibodies inhibit CCR5-tropic HIV-1 and induce beta-chemokines

Increased expression of TIGIT and KLRG1 correlates with impaired CD56bright NK cell immunity in HPV16-related cervical intraepithelial neoplasia

BACKGROUND

The onset and progression of cervical intraepithelial neoplasia (CIN) are closely associated with the persistent infection of high-risk HPV (especially type16), which is mainly caused by immune escape. Natural killer (NK) cells play an important role against virally infected cells and tumor cells through a fine balance of signals from multiple surface receptors. Overexpression of non-MHC-I specific inhibitory receptors TIGIT, KLRG1, Siglec-7, LAIR-1, and CD300a on NK cells correlates with cellular exhaustion and immune evasion, but these receptors have not been investigated in CIN. The aim of the present study was to examine the potential role of NK cell non-MHC-I specific inhibitory receptors expression in immune escape from HPV16(+)CIN patients.

METHODS

The subset distribution, IFN-γ and TNF-α expression levels and immunophenotype of TIGIT, KLRG1, Siglec-7, LAIR-1, and CD300a of NK cells were investigated in peripheral blood mononuclear cell samples by flow cytometry from 82 women who were HPV16(+) with CIN grades 0, I, II-III or HPV(-) CIN 0. Immunohistochemistry was applied to detect the expression of ligands for NK receptors in the cervical tissues. HPV types were identified by PCR assays.

RESULTS

The HPV16(+) subjects with high-grade lesions had an increased number of circulating peripheral blood CD56^bright NK cells with reduced functionality and IFN-γ secretion. The expression levels of the inhibitory molecules TIGIT and KLRG1 on CD56^bright NK cells increased in parallel with increasing CIN grade. In addition, TIGIT and KLRG1 related ligands, Poliovirus receptor (PVR), N-Cadherin and E-Cadherin expression level was also elevated with increasing CIN grade.

CONCLUSIONS

Our results suggest that up-regulation of the inhibitory TIGIT, KLRG1 and their ligands may negatively regulate cervical CD56^bright NK-mediated immunity to HPV16 and contribute to the progression of CIN. These results may facilitate the development of early-warning immune predictors and therapeutic strategies for HPV16(+) CIN based on the TIGIT and KLRG1 inhibitory pathways of NK cells.

Lipid Interactions Between Flaviviruses and Mosquito Vectors

Mosquito-borne flaviviruses, such as dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses, threaten a large part of the human populations. In absence of therapeutics and effective vaccines against each flaviviruses, targeting viral metabolic requirements in mosquitoes may hold the key to new intervention strategies. Development of metabolomics in the last decade opened a new field of research: mosquito metabolomics. It is now clear that flaviviruses rely on mosquito lipids, especially phospholipids, for their cellular cycle and propagation. Here, we review the biosyntheses of, biochemical properties of and flaviviral interactions with mosquito phospholipids. Phospholipids are structural lipids with a polar headgroup and apolar acyl chains, enabling the formation of lipid bilayer that form plasma- and endomembranes. Phospholipids are mostly synthesized through the de novo pathway and remodeling cycle. Variations in headgroup and acyl chains influence phospholipid physicochemical properties and consequently the membrane behavior. Flaviviruses interact with cellular membranes at every step of their cellular cycle. Recent evidence demonstrates that flaviviruses reconfigure the phospholipidome in mosquitoes by regulating phospholipid syntheses to increase virus multiplication. Identifying the phospholipids involved and understanding how flaviviruses regulate these in mosquitoes is required to design new interventions.

Phosphatidylserine-Targeting Monoclonal Antibodies Exhibit Distinct Biochemical and Cellular Effects on Anti-CD3/CD28-Stimulated T Cell IFN-γ and TNF-α Production

Phosphatidylserine (PS)-targeting monoclonal Abs (mAbs) that directly target PS and target PS via β2-gp1 (β2GP1) have been in preclinical and clinical development for over 10 y for the treatment of infectious diseases and cancer. Although the intended targets of PS-binding mAbs have traditionally included pathogens as well as stressed tumor cells and its associated vasculature in oncology, the effects of PS-targeting mAbs on activated immune cells, notably T cells, which externalize PS upon Ag stimulation, is not well understood. Using human T cells from healthy donor PBMCs activated with an anti-CD3 + anti-CD28 Ab mixture (anti-CD3/CD28) as a model for TCR-mediated PS externalization and T cell stimulation, we investigated effects of two different PS-targeting mAbs, 11.31 and bavituximab (Bavi), on TCR activation and TCR-mediated cytokine production in an ex vivo paradigm. Although 11.31 and Bavi bind selectivity to anti-CD3/28 activated T cells in a PS-dependent manner, surprisingly, they display distinct functional activities in their effect on IFN-γ and TNF-ɑ production, whereby 11.31, but not Bavi, suppressed cytokine production. This inhibitory effect on anti-CD3/28 activated T cells was observed on both CD4⁺ and CD8⁺ cells and independently of monocytes, suggesting the effects of 11.31 were directly mediated by binding to externalized PS on activated T cells. Imaging showed 11.31 and Bavi bind at distinct focal depots on the cell membrane. Collectively, our findings indicate that PS-targeting mAb 11.31 suppresses cytokine production by anti-CD3/28 activated T cells.

Update on Fc-Mediated Antibody Functions Against HIV-1 Beyond Neutralization

Antibodies (Abs) are the major component of the humoral immune response and a key player in vaccination. The precise Ab-mediated inhibitory mechanisms leading to in vivo protection against HIV have not been elucidated. In addition to the desired viral capture and neutralizing Ab functions, complex Ab-dependent mechanisms that involve engaging immune effector cells to clear infected host cells, immune complexes, and opsonized virus have been proposed as being relevant. These inhibitory mechanisms involve Fc-mediated effector functions leading to Ab-dependent cellular cytotoxicity, phagocytosis, cell-mediated virus inhibition, aggregation, and complement inhibition. Indeed, the decreased risk of infection observed in the RV144 HIV-1 vaccine trial was correlated with the production of non-neutralizing inhibitory Abs, highlighting the role of Ab inhibitory functions besides neutralization. Moreover, Ab isotypes and subclasses recognizing specific HIV envelope epitopes as well as pecular Fc-receptor polymorphisms have been associated with disease progression. These findings further support the need to define which Fc-mediated Ab inhibitory functions leading to protection are critical for HIV vaccine design. Herein, based on our previous review Su & Moog Front Immunol 2014, we update the different inhibitory properties of HIV-specific Abs that may potentially contribute to HIV protection.

Sera of patients with systemic lupus erythematosus cross-neutralizes dengue viruses

Dengue is the most prevalent mosquito-borne disease in Southeast Asia, where the incidence of systemic lupus erythematosus (SLE) is approximately 30 to 53 per 100,000. Severe dengue, however, is rarely reported among individuals with SLE. Here, whether sera of patients with SLE cross-neutralize dengue virus (DENV) was investigated. Serum samples were obtained from individuals with SLE who were dengue IgG and IgM serology negative. Neutralization assays were performed against the three major DENV serotypes. Of the dengue serology negative sera of individuals with SLE, 60%, 61% and 52% of the sera at 1/320 dilution showed more than 50% inhibition against dengue type-1 virus (DENV-1), DENV-2 and DENV-3, respectively. The neutralizing capacity of the sera was significantly greater against DENV-1 (P < 0.001) and DENV-3 (P < 0.01) than against DENV-2 (P < 0.05). Neutralization against the DENV correlated with dengue-specific IgG serum titers below the cut-off point for dengue positivity. Depletion of total IgG from the sera of patients with SLE resulted in significant decreases of up to 80% in DENV inhibition, suggesting that IgG plays an important role. However, some of the SLE sera was still able to neutralize DENV, even with IgG titers <0.1 OD absorbance. Our findings suggest that sera of patients with SLE contain IgG, and possibly other type of antibodies, that can cross-neutralize DENV, which may explain the rarity of severe dengue in individuals with SLE. Further studies, are needed to further substantiate this finding and to elucidate the specific neutralizing epitopes recognized by the sera of individuals with SLE.

Efferocytosis of dying cells differentially modulate immunological outcomes in tumor microenvironment

Programmed cell death (apoptosis) is an integral part of tissue homeostasis in complex organisms, allowing for tissue turnover, repair, and renewal while simultaneously inhibiting the release of self antigens and danger signals from apoptotic cell-derived constituents that can result in immune activation, inflammation, and autoimmunity. Unlike cells in culture, the physiological fate of cells that die by apoptosis in vivo is their rapid recognition and engulfment by phagocytic cells (a process called efferocytosis). To this end, apoptotic cells express specific eat-me signals, such as externalized phosphatidylserine (PS), that are recognized in a specific context by receptors to initiate signaling pathways for engulfment. The importance of carefully regulated recognition and clearance pathways is evident in the spectrum of inflammatory and autoimmune disorders caused by defects in PS receptors and signaling molecules. However, in recent years, several additional cell death pathways have emerged, including immunogenic cell death, necroptosis, pyroptosis, and netosis that interweave different cell death pathways with distinct innate and adaptive responses from classical apoptosis that can shape long-term host immunity. In this review, we discuss the role of different cell death pathways in terms of their immune potential outcomes specifically resulting in specific cell corpse/phagocyte interactions (phagocytic synapses) that impinge on host immunity, with a main emphasis on tolerance and cancer immunotherapy.

Antibody targeting of phosphatidylserine for the detection and immunotherapy of cancer

Phosphatidylserine (PS) is a negatively charged phospholipid in all eukaryotic cells that is actively sequestered to the inner leaflet of the cell membrane. Exposure of PS on apoptotic cells is a normal physiological process that triggers their rapid removal by phagocytic engulfment under noninflammatory conditions via receptors primarily expressed on immune cells. PS is aberrantly exposed in the tumor microenvironment and contributes to the overall immunosuppressive signals that antagonize the development of local and systemic antitumor immune responses. PS-mediated immunosuppression in the tumor microenvironment is further exacerbated by chemotherapy and radiation treatments that result in increased levels of PS on dying cells and necrotic tissue. Antibodies targeting PS localize to tumors and block PS-mediated immunosuppression. Targeting exposed PS in the tumor microenvironment may be a novel approach to enhance immune responses to cancer.

Human immunodeficiency virus type-1 (HIV-1) evades antibody-dependent phagocytosis

Fc gamma receptor (FcyR)-mediated antibody functions play a crucial role in preventing HIV infection. One such function, antibody-dependent phagocytosis (ADP), is thought to be involved in controlling other viral infections, but its role in HIV infection is unknown. We measured the ability of HIV-specific polyclonal and monoclonal antibodies (mAbs) to mediate the internalization of HIV-1 virions and HIV-1-decorated cells by phagocytes. To measure ADP of virions, we primarily used a green-fluorescent protein-expressing molecular clone of HIV-1JRFL, an R5, clinical isolate, in combination with polyclonal HIVIG or mAbs known to capture and/or neutralize HIV-1. THP-1 and U937 cells, as well as freshly isolated primary monocytes from healthy individuals, were used as phagocytic effector cells, and uptake of virions was measured by cytometry. We surprisingly found minimal or no ADP of virions with any of the antibodies. However, after coating virions with gp41 or with gp41-derived peptides, gp41- (but not gp120-) specific mAbs efficiently mediated phagocytosis. We estimated that a minimum of a few hundred gp41 molecules were needed for successful phagocytosis, which is similar to the number of envelope spikes on viruses that are readily phagocytosed (e.g. influenza virus). Furthermore, by employing fluorescence correlation spectroscopy, a well-established technique to measure particle sizes and aggregation phenomena, we found a clear association between virus aggregation and ADP. In contrast to virions themselves, virion-decorated cells were targets for ADP or trogocytosis in the presence of HIV-specific antibodies. Our findings indicate that ADP of virions may not play a role in preventing HIV infection, likely due to the paucity of trimers and the consequent inability of virion-bound antibody to cross-link FcyRs on phagocytes. However, ADP or trogocytosis could play a role in clearing HIV-infected cells and cells on the verge of infection.

Protective Effect of Anti-Phosphatidylserine Antibody in a Guinea Pig Model of Advanced Hemorrhagic Arenavirus Infection

Objective

Host derived markers on virally infected cells or virions may provide targets for the generation of antiviral agents. Recently, we identified phosphatidylserine (PS) as a host marker of virions and virally-infected cells.

Methods and Materials

Under normal physiological conditions, PS is maintained on the inner leaflet of the plasma membrane facing the cytosol. Following viral infection, activation or pre-apoptotic changes cause PS to become externalized. We have previously shown that bavituximab, a chimeric human-mouse antibody that binds PS complexed with β2-glycoprotein I (β2GP1), protected rodents against lethal Pichinde virus and cytomegalovirus infections.

Results

Here, we determined the antiviral activity of a fully human monoclonal antibody, PGN632, that directly binds to PS. Treatment with PGN632 protected 20% of guinea pigs with advanced infections of the hemorrhagic arenavirus, Pichinde, from death. Combining PGN632 with ribavirin improved the antiviral activity of both agents, such that the combination rescued 50% of animals from death.

Conclusion

The major mechanisms of action of PGN632 appear to be opsonization of virus and antibody-dependent cellular cytotoxicity of virally-infected cells. PS-targeting agents may have utility in the treatment of viral diseases.

Immunologic characteristics of HIV-infected individuals who make broadly neutralizing antibodies

Induction of broadly neutralizing antibodies (bnAbs) capable of inhibiting infection with diverse variants of human immunodeficiency virus type 1 (HIV‐1) is a key, as‐yet‐unachieved goal of prophylactic HIV‐1 vaccine strategies. However, some HIV‐infected individuals develop bnAbs after approximately 2‐4 years of infection, enabling analysis of features of these antibodies and the immunological environment that enables their induction. Distinct subsets of CD4⁺ T cells play opposing roles in the regulation of humoral responses: T follicular helper (Tfh) cells support germinal center formation and provide help for affinity maturation and the development of memory B cells and plasma cells, while regulatory CD4⁺ (Treg) cells including T follicular regulatory (Tfr) cells inhibit the germinal center reaction to limit autoantibody production. BnAbs exhibit high somatic mutation frequencies, long third heavy‐chain complementarity determining regions, and/or autoreactivity, suggesting that bnAb generation is likely to be highly dependent on the activity of CD4⁺ Tfh cells, and may be constrained by host tolerance controls. This review discusses what is known about the immunological environment during HIV‐1 infection, in particular alterations in CD4⁺ Tfh, Treg, and Tfr populations and autoantibody generation, and how this is related to bnAb development, and considers the implications for HIV‐1 vaccine design.

Phosphatidylserine Sensing by TAM Receptors Regulates AKT-Dependent Chemoresistance and PD-L1 Expression

Tyro3, Axl, and Mertk (collectively TAM receptors) are three homologous receptor tyrosine kinases that bind vitamin K-dependent endogenous ligands, Protein S (ProS), and growth arrest-specific factor 6 (Gas6), and act as bridging molecules to promote phosphatidylserine (PS)-mediated clearance of apoptotic cells (efferocytosis). TAM receptors are overexpressed in a vast array of tumor types, whereby the level of expression correlates with the tumor grade and the emergence of chemo- and radioresistance to targeted therapeutics, but also have been implicated as inhibitory receptors on infiltrating myeloid-derived cells in the tumor microenvironment that can suppress host antitumor immunity. In the present study, we utilized TAM-IFNγR1 reporter lines and expressed TAM receptors in a variety of epithelial cell model systems to show that each TAM receptor has a unique pattern of activation by Gas6 or ProS, as well as unique dependency for PS on apoptotic cells and PS liposomes for activity. In addition, we leveraged this system to engineer epithelial cells that express wild-type TAM receptors and show that although each receptor can promote PS-mediated efferocytosis, AKT-mediated chemoresistance, as well as upregulate the immune checkpoint molecule PD-L1 on tumor cells, Mertk is most dominant in the aforementioned pathways. Functionally, TAM receptor-mediated efferocytosis could be partially blocked by PS-targeting antibody 11.31 and Annexin V, demonstrating the existence of a PS/PS receptor (i.e., TAM receptor)/PD-L1 axis that operates in epithelial cells to foster immune escape. These data provide a rationale that PS-targeting, anti-TAM receptor, and anti-PD-L1-based therapeutics will have merit as combinatorial checkpoint inhibitors.Implications: Many tumor cells are known to upregulate the immune checkpoint inhibitor PD-L1. This study demonstrates a role for PS and TAM receptors in the regulation of PD-L1 on cancer cells. Mol Cancer Res; 15(6); 753-64. ©2017 AACR.

Efferocytosis of Pathogen-Infected Cells

The prompt and efficient clearance of unwanted and abnormal cells by phagocytes is termed efferocytosis and is crucial for organism development, maintenance of tissue homeostasis, and regulation of the immune system. Dying cells are recognized by phagocytes through pathways initiated via "find me" signals, recognition via "eat me" signals and down-modulation of regulatory "don't eat me" signals. Pathogen infection may trigger cell death that drives phagocytic clearance in an immunologically silent, or pro-inflammatory manner, depending on the mode of cell death. In many cases, efferocytosis is a mechanism for eliminating pathogens and pathogen-infected cells; however, some pathogens have subverted this process and use efferocytic mechanisms to avoid innate immune detection and assist phagocyte infection. In parallel, phagocytes can integrate signals received from infected dying cells to elicit the most appropriate effector response against the infecting pathogen. This review focuses on pathogen-induced cell death signals that drive infected cell recognition and uptake by phagocytes, and the outcomes for the infected target cell, the phagocyte, the pathogen and the host.

Neutralizing antibodies in patients with chronic hepatitis C and correlation to liver cirrhosis and estimated duration of infection

Although chronic hepatitis C virus (HCV) infection accounts for 30% of individuals with cirrhotic livers worldwide, factors influencing disease progression are far from elucidated. The aim of this study was to determine whether the level of neutralizing antibodies (NAbs) correlated with the development of cirrhosis in patients with chronic HCV infection, genotype 1, when adjusting for estimated duration of infection. Thirty-nine patients with chronic hepatitis C, with either no/mild fibrosis (n = 23) or cirrhosis (n = 16), were enrolled from two university hospitals in Denmark. Duration of HCV infection was estimated based on patient information and/or anti-HCV seroconversion. Serial dilutions of purified serum/plasma derived IgGs were tested for their ability to neutralize six HCV-genotype 1 cell-culture strains. The results were expressed as the lowest IgG concentration yielding ≥50% neutralization (NAb50 -titer). A significant difference in HCV NAb50 -titers among the six genotype 1a/1b recombinants was found. In patients with cirrhosis, a tendency for higher level of NAbs was observed compared to patients with no/mild fibrosis, although not statistical significant. Stratifying the two groups revealed that being infected >25 years resulted in higher levels of NAbs in both. Furthermore, by correlating estimated duration of HCV infection to NAb50 -titers a significant result was found against two recombinants. The NAb titer does not differ significantly between HCV patients with either no/mild fibrosis or cirrhosis but show a tendency for increasing level with increased duration of infection. NAbs might contribute as a biological marker to increase the accuracy of patient based information on duration of HCV infection. J. Med. Virol. 88:1791-1803, 2016. © 2016 Wiley Periodicals, Inc.

Phosphatidylserine (PS) Is Exposed in Choroidal Neovascular Endothelium: PS-Targeting Antibodies Inhibit Choroidal Angiogenesis In Vivo and Ex Vivo

PURPOSE

Choroidal neovascularization (CNV) accounts for 90% of cases of severe vision loss in patients with advanced age-related macular degeneration. Identifying new therapeutic targets for CNV may lead to novel combination therapies to improve outcomes and reduce treatment burden. Our goal was to test whether phosphatidylserine (PS) becomes exposed in the outer membrane of choroidal neovascular endothelium, and whether this could provide a new therapeutic target for CNV.

METHODS

Choroidal neovascularization was induced in C57BL/6J mice using laser photocoagulation. Choroidal neovascularization lesions costained for exposed PS and for intercellular adhesion molecule 2 (or isolectin B4) were imaged in flat mounts and in cross sections. The laser CNV model and a choroidal sprouting assay were used to test the effect of PS-targeting antibodies on choroidal angiogenesis. Choroidal neovascularization lesion size was determined by intercellular adhesion molecule 2 (ICAM-2) staining of flat mounts.

RESULTS

We found that PS was exposed in CNV lesions and colocalized with vascular endothelial staining. Treatment with PS-targeting antibodies led to a 40% to 80% reduction in CNV lesion area when compared to treatment with a control antibody. The effect was the same as that seen using an equal dose of an anti-VEGF antibody. Results were confirmed using the choroid sprouting assay, an ex vivo model of choroidal angiogenesis.

CONCLUSIONS

We demonstrated that PS is exposed in choroidal neovascular endothelium. Furthermore, targeting this exposed PS with antibodies may be of therapeutic value in CNV.

Phosphatidylserine is a global immunosuppressive signal in efferocytosis, infectious disease, and cancer

Apoptosis is an evolutionarily conserved and tightly regulated cell death modality. It serves important roles in physiology by sculpting complex tissues during embryogenesis and by removing effete cells that have reached advanced age or whose genomes have been irreparably damaged. Apoptosis culminates in the rapid and decisive removal of cell corpses by efferocytosis, a term used to distinguish the engulfment of apoptotic cells from other phagocytic processes. Over the past decades, the molecular and cell biological events associated with efferocytosis have been rigorously studied, and many eat-me signals and receptors have been identified. The externalization of phosphatidylserine (PS) is arguably the most emblematic eat-me signal that is in turn bound by a large number of serum proteins and opsonins that facilitate efferocytosis. Under physiological conditions, externalized PS functions as a dominant and evolutionarily conserved immunosuppressive signal that promotes tolerance and prevents local and systemic immune activation. Pathologically, the innate immunosuppressive effect of externalized PS has been hijacked by numerous viruses, microorganisms, and parasites to facilitate infection, and in many cases, establish infection latency. PS is also profoundly dysregulated in the tumor microenvironment and antagonizes the development of tumor immunity. In this review, we discuss the biology of PS with respect to its role as a global immunosuppressive signal and how PS is exploited to drive diverse pathological processes such as infection and cancer. Finally, we outline the rationale that agents targeting PS could have significant value in cancer and infectious disease therapeutics.

Short Communication: Exploring Antibody Potential as Prophylactic/Therapeutic Strategies for Prevention of Early Mucosal HIV-1 Infection

Mucosal tissues are the predominant sites for genital HIV-1 transmission. We investigated the mechanisms by which broadly neutralizing antibodies (bNAbs) inhibit HIV-1 replication in a coculture model including primary mucosal dendritic cells (DCs), such as Langerhans cells, interstitial dendritic cells, and CD4(+) T lymphocytes. We show that bNAbs efficiently prevent HIV-1 infection by inhibiting HIV-1 transmission to CD4(+) T lymphocytes. This inhibition of cell-to-cell transmission was observed with equal potency as the inhibition of cell-free infection of primary CD4(+) T lymphocytes. In addition, a decrease in HIV-1 replication in DCs and the induction of DC maturation were detected. This additional inhibition was Fc mediated as it was blocked by the use of specific anti-FcγR monoclonal Abs. The DC maturation by bNAbs during HIV transmission may contribute to mucosal protection. Therefore, multiple antibody-mediated inhibitory functions should be combined for the improvement of future preventive/therapeutic strategies to cure HIV.

The Biology and Disease Relevance of CD300a, an Inhibitory Receptor for Phosphatidylserine and Phosphatidylethanolamine

The CD300a inhibitory receptor belongs to the CD300 family of cell surface molecules that regulate a diverse array of immune cell processes. The inhibitory signal of CD300a depends on the phosphorylation of tyrosine residues embedded in ITIMs of the cytoplasmic tail. CD300a is broadly expressed on myeloid and lymphoid cells, and its expression is differentially regulated depending on the cell type. The finding that CD300a recognizes phosphatidylserine and phosphatidylethanolamine, two aminophospholipids exposed on the outer leaflet of dead and activated cells, has shed new light on its role in the modulation of immune functions and in its participation in the host response to several diseases states, such as infectious diseases, cancer, allergy, and chronic inflammatory diseases. This review summarizes the literature on CD300a expression, regulation, signaling pathways, and ligand interaction, as well as its role in fine tuning immune cell functions and its clinical relevance.

Human Non-neutralizing HIV-1 Envelope Monoclonal Antibodies Limit the Number of Founder Viruses during SHIV Mucosal Infection in Rhesus Macaques

HIV-1 mucosal transmission begins with virus or virus-infected cells moving through mucus across mucosal epithelium to infect CD4+ T cells. Although broadly neutralizing antibodies (bnAbs) are the type of HIV-1 antibodies that are most likely protective, they are not induced with current vaccine candidates. In contrast, antibodies that do not neutralize primary HIV-1 strains in the TZM-bl infection assay are readily induced by current vaccine candidates and have also been implicated as secondary correlates of decreased HIV-1 risk in the RV144 vaccine efficacy trial. Here, we have studied the capacity of anti-Env monoclonal antibodies (mAbs) against either the immunodominant region of gp41 (7B2 IgG1), the first constant region of gp120 (A32 IgG1), or the third variable loop (V3) of gp120 (CH22 IgG1) to modulate in vivo rectal mucosal transmission of a high-dose simian-human immunodeficiency virus (SHIV-BaL) in rhesus macaques. 7B2 IgG1 or A32 IgG1, each containing mutations to enhance Fc function, was administered passively to rhesus macaques but afforded no protection against productive clinical infection while the positive control antibody CH22 IgG1 prevented infection in 4 of 6 animals. Enumeration of transmitted/founder (T/F) viruses revealed that passive infusion of each of the three antibodies significantly reduced the number of T/F genomes. Thus, some antibodies that bind HIV-1 Env but fail to neutralize virus in traditional neutralization assays may limit the number of T/F viruses involved in transmission without leading to enhancement of viral infection. For one of these mAbs, gp41 mAb 7B2, we provide the first co-crystal structure in complex with a common cyclical loop motif demonstrated to be critical for infection by other retroviruses.

Avanti lipid tools: connecting lipids, technology, and cell biology

Lipid research is challenging owing to the complexity and diversity of the lipidome. Here we review a set of experimental tools developed for the seasoned lipid researcher, as well as, those who are new to the field of lipid research. Novel tools for probing protein-lipid interactions, applications for lipid binding antibodies, enhanced systems for the cellular delivery of lipids, improved visualization of lipid membranes using gold-labeled lipids, and advances in mass spectrometric analysis techniques will be discussed. Because lipid mediators are known to participate in a host of signal transduction and trafficking pathways within the cell, a comprehensive lipid toolbox that aids the science of lipidomics research is essential to better understand the molecular mechanisms of interactions between cellular components. This article is part of a Special Issue entitled Tools to study lipid functions.

Neutralizing antibodies inhibit HIV-1 infection of plasmacytoid dendritic cells by an FcγRIIa independent mechanism and do not diminish cytokines production

Plasmacytoid dendritic cells (pDC) expressing FcγRIIa are antigen-presenting cells able to link innate and adaptive immunity and producing various cytokines and chemokines. Although highly restricted, they are able to replicate HIV-1. We determined the activity of anti-HIV-1 neutralizing antibodies (NAb) and non-neutralizing inhibitory antibodies (NNIAb) on the infection of primary pDC by HIV-1 primary isolates and analyzed cytokines and chemokines production. Neutralization assay was performed with primary pDC in the presence of serial antibodies (Ab) concentrations. In parallel, we measured the release of cytokines and chemokines by ELISA and CBA Flex assay. We found that NAb, but not NNIAb, inhibit HIV-1 replication in pDC. This inhibitory activity was lower than that detected for myeloid dendritic cells (mDC) infection and independent of FcγRIIa expressed on pDC. Despite the complete protection, IFN-α production was detected in the supernatant of pDC treated with NAb VRC01, 4E10, PGT121, 10-1074, 10E8, or polyclonal IgG44 but not with NAb b12. Production of MIP-1α, MIP-1β, IL-6, and TNF-α by pDC was also maintained in the presence of 4E10, b12 and VRC01. These findings suggest that pDC can be protected from HIV-1 infection by both NAb and IFN-α release triggered by the innate immune response during infection.

Which Antibody Functions are Important for an HIV Vaccine?

HIV antibody (Ab) functions capable of preventing mucosal cell-free or cell-to-cell HIV transmission are critical for the development of effective prophylactic and therapeutic vaccines. In addition to CD4(+) T cells, other potential HIV-target cell types including antigen-presenting cells (APCs) (dendritic cells, macrophages) residing at mucosal sites are infected. Moreover, the interactions between APCs and HIV lead to HIV cell-to-cell transmission. Recently discovered broadly neutralizing antibodies (NAbs) are able to neutralize a broad spectrum of HIV strains, inhibit cell-to-cell transfer, and efficiently protect from infection in the experimentally challenged macaque model. However, the 31% protection observed in the RV144 vaccine trial in the absence of detectable NAbs in blood samples pointed to the possible role of additional Ab inhibitory functions. Increasing evidence suggests that IgG Fcγ receptor (FcγR)-mediated inhibition of Abs present at the mucosal site may play a role in protection against HIV mucosal transmission. Moreover, mucosal IgA Abs may be determinant in protection against HIV sexual transmission. Therefore, defining Ab inhibitory functions that could lead to protection is critical for further HIV vaccine design. Here, we review different inhibitory properties of HIV-specific Abs and discuss their potential role in protection against HIV sexual transmission.

Multi-Parameter Exploration of HIV-1 Virus-Like Particles as Neutralizing Antibody Immunogens in Guinea Pigs, Rabbits and Macaques

Virus-like particles (VLPs) offer a platform to test the hypothesis that, since antibody binding to native envelope glycoprotein (Env) trimers results in HIV-1 neutralization, that native Env trimers presented in membranes may be useful for inducing neutralizing antibodies (nAbs) in a vaccine setting. So far, VLPs have not fulfilled this potential. Here, using a "shotgun" approach, we evaluated a wide cross-section of variables in a series of VLP immunizations. We identified 3 tentative leads. First, that VLP doses may not have been sufficient for optimal nAb induction. Second, that dampening the antigenicity of non-functional Env (for example uncleaved gp160) using either protease digests or IgG masking may be useful. Third, that guinea pig sera preferentially target non-conserved epitopes and exhibit relatively high background activity, suggesting that rabbits may be preferable as small animal vaccine models. Recent immunogenicity studies in rabbits appear to bear out all 3 of these leads.

Detection of HIV-1 neutralizing antibodies in a human CD4⁺/CXCR4⁺/CCR5⁺ T-lymphoblastoid cell assay system

Sensitive assays are needed to meaningfully assess low levels of neutralizing antibodies (NAbs) that may be important for protection against the acquisition of HIV-1 infection in vaccine recipients. The current assay of choice uses a non-lymphoid cell line (TZM-bl) that may lack sensitivity owing to over expression of CD4 and CCR5. We used transfection of a human CD4+/CXCR4+/α4β7+ T-lymphoblastoid cell line (A3.01) with a CMV IE promoter-driven CCR5neo vector to stably express CCR5. The resulting line, designated A3R5, is permissive to a wide range of CCR5-tropic circulating strains of HIV-1, including HIV-1 molecular clones containing a Tat-inducible Renilla luciferase reporter gene and expressing multiple Env subtypes. Flow cytometric analysis found CCR5 surface expression on A3R5 cells to be markedly less than TZM-bl but similar to CD3.8 stimulated PBMC. More importantly, neutralization mediated by a diverse panel of monoclonal antibodies, HIV-1 positive polyclonal sera and sCD4 was consistently greater in A3R5 compared to TZM-bl cells. The A3R5 cell line provides a novel approach to guide the development and qualification of promising new HIV-1 vaccine immunogens.

Tenascin-C is an innate broad-spectrum, HIV-1-neutralizing protein in breast milk

Achieving an AIDS-free generation will require elimination of postnatal transmission of HIV-1 while maintaining the nutritional and immunologic benefits of breastfeeding for infants in developing regions. Maternal/infant antiretroviral prophylaxis can reduce postnatal HIV-1 transmission, yet toxicities and the development of drug-resistant viral strains may limit the effectiveness of this strategy. Interestingly, in the absence of antiretroviral prophylaxis, greater than 90% of infants exposed to HIV-1 via breastfeeding remain uninfected, despite daily mucosal exposure to the virus for up to 2 y. Moreover, milk of uninfected women inherently neutralizes HIV-1 and prevents virus transmission in animal models, yet the factor(s) responsible for this anti-HIV activity is not well-defined. In this report, we identify a primary HIV-1-neutralizing protein in breast milk, Tenascin-C (TNC). TNC is an extracellular matrix protein important in fetal development and wound healing, yet its antimicrobial properties have not previously been established. Purified TNC captured and neutralized multiclade chronic and transmitted/founder HIV-1 variants, and depletion of TNC abolished the HIV-1-neutralizing activity of milk. TNC bound the HIV-1 Envelope protein at a site that is induced upon engagement of its primary receptor, CD4, and is blocked by V3 loop- (19B and F39F) and chemokine coreceptor binding site-directed (17B) monoclonal antibodies. Our results demonstrate the ability of an innate mucosal host protein found in milk to neutralize HIV-1 via binding to the chemokine coreceptor site, potentially explaining why the majority of HIV-1-exposed breastfed infants are protected against mucosal HIV-1 transmission.

Phosphatidylserine exposure on the surface of Leishmania amazonensis amastigotes modulates in vivo infection and dendritic cell function

Leishmania amazonensis parasites can cause diverse forms of leishmaniasis in humans and persistent lesions in most inbred strains of mice. In both cases, the infection is characterized by a marked immunosuppression of the host. We previously showed that amastigote forms of the parasite make use of surface-exposed phosphatidylserine (PS) molecules to infect host cells and promote alternative macrophage activation, leading to uncontrolled intracellular proliferation of the parasites. In this study, we demonstrated that treatment of infected mice with a PS-targeting monoclonal antibody ameliorated parasite loads and lesion development, which correlated with increased proliferative responses by lymphocytes. In addition, we observed an enhanced dendritic cell (DC) activation and antigen presentation in vitro. Our data imply that the recognition of PS exposed on the surface of amastigotes plays a role in down-modulating DC functions, in a matter similar to that of apoptotic cell clearance. This study provides new information regarding the mechanism of immune suppression in Leishmania infection.

Multiantibody strategies for HIV

Vaccination strategies depend entirely on the appropriate responsiveness of our immune system against particular antigens. For this active immunization to be truly effective, neutralizing antibodies (nAbs) need to efficiently counter the infectivity or propagation of the pathogen. Some viruses, including HIV, are able to take advantage of this immune response in order to evade nAbs. This review focuses on viral immune evasion strategies that result directly from a robust immune response to infection or vaccination. A rationale for multi-Ab therapy to circumvent this phenomenon is discussed. Progress in the formulation, production, and regulatory approval of monoclonal antibodies (mAbs) is presented.

HIV exposed seronegative individuals show antibodies specifically recognizing native HIV envelope glycoprotein

BACKGROUND

Susceptibility to HIV transmission by sexual intercourse has been associated with cellular anti-HIV responses. We aimed to also evaluate potential systemic humoral responses against HIV in a group of HIV-exposed seronegative individuals (HESN) in stable relationship with HIV-infected partners.

METHODS

We recruited 27 serodiscordant couples. HESN were classified according to HIV exposure into very low/low and moderate/high risk. Plasma from HESN and HIV partners were tested for neutralizing capacity and for the recognition of cell-surface expressed and recombinant forms of HIV envelope glycoproteins (Env). Healthy individuals (healthy control, n=11) were used as controls.

RESULTS

Recognition of cell-surface expressed Env by both immunoglobulin (Ig)G and IgA was higher in plasma samples from HESN than in healthy controls (P=0.0062 and P=0.0144, respectively). IgG binding to Env was significantly increased in HESN after unmasking CD4-induced epitopes (P=0.001), suggesting a wide range of targeted epitopes. Remarkably, ELISA assays using trimeric gp140 or monomeric gp120 failed to detect significant differences in reactivity between groups. Neutralization analysis showed residual activity in only three HESN samples (11%), whereas 70% of HIV-infected partners showed neutralizing activity. Although anti-Env humoral responses were found in 85% of HESN, their magnitude was not associated with the estimated level of exposure or the detection of HIV-specific cellular immune responses.

CONCLUSION

A high proportion of HESN show detectable plasma IgG or IgA recognizing different exposed and cryptic Env native epitopes unrelated to neutralizing capacity. Therefore, low but persistent HIV exposure induces new virus-specific systemic humoral responses or boosts preexisting natural antibodies.

A monoclonal antibody against lymphocyte function-associated antigen-1 decreases HIV-1 replication by inducing the secretion of an antiviral soluble factor

Background

Lymphocyte Function-Associated Antigen-1 (LFA-1) likely plays a role in the pathogenesis of against HIV-1 and is known to facilitate cell-to-cell transmission of the virus. A monoclonal antibody specific for LFA-1 (Cytolin®) was evaluated as a potential therapeutic in pilot studies performed in the mid-1990s. These uncontrolled human studies suggested that administration of this anti-LFA-1 antibody to HIV-1 infected individuals could provide a modest benefit by decreasing circulating HIV-1 RNA and increasing CD4+ T cell counts. At the time, it was proposed that when bound to cytolytic T cells, the antibody inhibited lysis of activated CD4+ T cells. Given the renewed interest in monoclonal antibody therapy for HIV-1 infected individuals, we investigated possible mechanisms of action of this antibody in vitro.

Methods

To assess whether this anti-LFA-1 antibody binds to HIV-1, a virus capture assay was performed. Binding of the antibody to cells was assessed using flow cytometry. Inhibition of HIV-1 replication was determined in culture by measuring the amount of p24 produced by ELISA. After co-culture of the antibody with peripheral blood mononuclear cells, supernatants were assayed for cytokines and chemokines using various immunoassays.

Results

Our experiments demonstrate that anti-LFA-1 antibody binds to CCR5 and CXCR4 utilizing strains of HIV-1. It also binds to CD8+ T cells and dendritic cells. When bound to virus prior to infection, there is no decrease in HIV-1 replication, suggesting it does not directly inhibit viral replication via virus binding. When bound to cells, it does not inhibit lysis of CD4+ T cells, as was originally hypothesized. Binding to cells does appear to induce the production of a soluble factor that inhibits HIV-1 replication. We determined that this soluble factor was not any of the cytokines or chemokines with known anti-HIV-1 activity. Further, the antibody does not appear to induce any common immune modulating cytokines or chemokines.

Conclusions

These results suggest that one possible mechanism of action of this anti-LFA-1 antibody is to inhibit HIV-1 replication via the production of a soluble antiviral factor that is induced upon binding to cells.

CD4 binding determinant mimicry for HIV vaccine design

The immunodominant epitopes expressed by the HIV-1 envelope protein gp120 are hypermutable, defeating attempts to develop an effective HIV vaccine. Targeting the structurally conserved gp120 determinant that binds host CD4 receptors (CD4BD) and initiates infection is a more promising route to vaccination, but this has proved difficult because of the conformational flexibility of gp120 and immune evasion mechanisms used by the virus. Mimicking the outer CD4BD conformational epitopes is difficult because of their discontinuous nature. The CD4BD region composed of residues 421–433 (CD4BD^core) is a linear epitope, but this region possesses B cell superantigenic character. While superantigen epitopes are vulnerable to a small subset of spontaneously produced neutralizing antibodies present in humans without infection (innate antibodies), their non-covalent binding to B cell receptors (BCRs) does not stimulate an effective adaptive response from B cells. Covalent binding at naturally occurring nucleophilic sites of the BCRs by an electrophilic gp120 (E-gp120) analog is a promising solution. E-gp120 induces the synthesis of neutralizing antibodies the CD4BD^core. The highly energetic covalent reaction is hypothesized to convert the abortive superantigens–BCR interaction into a stimulatory signal, and the binding of a spatially distinct epitope at the traditional combining site of the BCRs may furnish a second stimulatory signal. Flexible synthetic peptides can detect pre-existing CD4BD^core-specific neutralizing antibodies. However, induced-fit conformational transitions of the peptides dictated by the antibody combining site structure may induce the synthesis of non-neutralizing antibodies. Successful vaccine targeting of the CD4BD will require a sufficiently rigid immunogen that mimics the native epitope conformation and bypasses B cell checkpoints restricting synthesis of the neutralizing antibodies.

Antibodies to a superantigenic glycoprotein 120 epitope as the basis for developing an HIV vaccine

Failure to induce synthesis of neutralizing Abs to the CD4 binding determinant (CD4BD) of gp120, a central objective in HIV vaccine research, has been alternately ascribed to insufficient immunogen binding to Abs in their germline V region configuration expressed as BCRs, insufficient adaptive mutations in Ab V regions, and conformational instability of gp120. We employed peptide analogs of gp120 residues 421-433 within the CD4BD (CD4BD(core)) to identify Abs produced without prior exposure to HIV (constitutive Abs). The CD4BD(core) peptide was recognized by single-chain Fv fragments from noninfected humans with lupus that neutralized genetically diverse strains belonging to various HIV subtypes. Replacing the framework region (FR) of a V(H)4-family single-chain Fv with the corresponding V(H)3-family FRs from single-chain Fv JL427 improved the CD4BD(core) peptide-binding activity, suggesting a CD4BD(core) binding site outside the pocket formed by the CDRs. Replacement mutations in the FR site vicinity suggested the potential for adaptive improvement. A very small subset of serum CD4BD(core)-specific serum IgAs from noninfected humans without autoimmune disease isolated by epitope-specific chromatography neutralized the virus potently. A CD4BD(core)-specific, HIV neutralizing murine IgM with H and L chain V regions (V(H) and V(L) regions) free of immunogen-driven somatic mutations was induced by immunization with a CD4BD(core) peptide analog containing an electrophilic group that binds B cells covalently. The studies indicate broad and potent HIV neutralization by constitutive Abs as an innate, germline-encoded activity directed to the superantigenic CD4BD(core) epitope that is available for amplification for vaccination against HIV.

An anti-phosphoinositide-specific monoclonal antibody that neutralizes HIV-1 infection of human monocyte-derived macrophages

HIV-1 entry into cells requires the interaction of both HIV-1 envelope proteins and membrane lipids. We investigated the mechanism of neutralization of HIV-1 infection of primary monocyte-derived macrophages (MDM) by a murine monoclonal antibody (mAb) WR321. WR321 specifically binds phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate. These phosphoinositides are present not only on the inner surface of the plasma membranes of cells but also on the surface of virions. HIV-1 acquires these lipids during the budding process. Pre-incubation of WR321 with the virus but not with MDM neutralized HIV-1 infection of MDM. Our results demonstrate that WR321 was internalized only when it was bound to HIV-1. WR321 did not prevent the entry of HIV-1 into MDM. However, once WR321 was internalized along with HIV-1 the mAb acted intracellulary to prevent the release of virions from MDM and also triggered the release of β-chemokines.

Isolation of HIV-1-neutralizing mucosal monoclonal antibodies from human colostrum

Background

Generation of potent anti-HIV antibody responses in mucosal compartments is a potential requirement of a transmission-blocking HIV vaccine. HIV-specific, functional antibody responses are present in breast milk, and these mucosal antibody responses may play a role in protection of the majority of HIV-exposed, breastfeeding infants. Therefore, characterization of HIV-specific antibodies produced by B cells in milk could guide the development of vaccines that elicit protective mucosal antibody responses.

Methods

We isolated B cells from colostrum of an HIV-infected lactating woman with a detectable neutralization response in milk and recombinantly produced and characterized the resulting HIV-1 Envelope (Env)-specific monoclonal antibodies (mAbs).

Results

The identified HIV-1 Env-specific colostrum mAbs, CH07 and CH08, represent two of the first mucosally-derived anti-HIV antibodies yet to be reported. Colostrum mAb CH07 is a highly-autoreactive, weakly-neutralizing gp140-specific mAb that binds to linear epitopes in the gp120 C5 region and gp41 fusion domain. In contrast, colostrum mAb CH08 is a nonpolyreactive CD4-inducible (CD4i) gp120-specific mAb with moderate breadth of neutralization.

Conclusions

These novel HIV-neutralizing mAbs isolated from a mucosal compartment provide insight into the ability of mucosal B cell populations to produce functional anti-HIV antibodies that may contribute to protection against virus acquisition at mucosal surfaces.

The role of natural killer (NK) cells and NK cell receptor polymorphisms in the assessment of HIV-1 neutralization

The importance of innate immune cells in HIV-1 pathogenesis and protection has been highlighted by the role of natural killer (NK) cells in the containment of viral replication. Use of peripheral blood mononuclear cells (PBMC) in immunologic studies provides both HIV-1 target cells (ie. CD4+ T cells), as well as anti-HIV-1 effector cells, such as NK cells. In this study, NK and other immune cell populations were analyzed in HIV-negative donor PBMC for an impact on the anti-HIV activity of polyclonal and monoclonal antibodies. NK cell percentages were significantly higher in donor PBMC that supported lower levels of viral replication. While the percentage of NK cells was not directly associated with neutralization titers, NK cell-depletion significantly diminished the antiviral antibody activity by up to three logs, and polymorphisms in NK killer immunoglobulin receptor (KIR) and FcγRIIIa alleles appear to be associated with this affect. These findings demonstrate that NK cells and NK cell receptor polymorphisms may influence assessment of traditional HIV-1 neutralization in a platform where antibody is continuously present. This format appears to simultaneously assess conventional entry inhibition (neutralization) and non-neutralizing antibody-dependent HIV inhibition, which may provide the opportunity to delineate the dominant antibody function(s) in polyclonal vaccine responses.

Transmembrane domain membrane proximal external region but not surface unit-directed broadly neutralizing HIV-1 antibodies can restrict dendritic cell-mediated HIV-1 trans-infection

BACKGROUND

Although broadly neutralizing antibodies (bNAbs) have been shown to block a diverse array of cell-free human immunodeficiency type 1 (HIV-1) infections, it remains unclear whether these antibodies exhibit similar potency against mature dendritic cell (mDC)-mediated HIV-1 trans-infection.

METHODS

Sensitivity to bNAbs targeting HIV-1 envelope surface unit gp120 (VRCO1, PG16, b12, and 2G12) and transmembrane domain gp41 (4E10 and 2F5) was examined for both cell-free and mDC-mediated infections of TZM-bl and CD4(+) T cells.

RESULTS

Compared with cell-free infection, mDC-mediated infection was significantly less susceptible to gp120-directed bNAbs for the majority of virus isolates. A b12 antigen-binding fragment blocked both cell-free and mDC-mediated infection with equal efficiency. In contrast, cell-free and mDC-associated viruses were equally sensitive to gp41-directed bNAbs. Anti-gp41 bNAbs bound to the surface of mDCs and localized at the mDC-T cell synaptic junctions in the absence of virus.

CONCLUSIONS

Anti-gp41 bNAbs have the potential to inhibit mDC-mediated HIV-1 infection because they bind plasma membranes prior to the formation of an infectious synapse, positioning them to neutralize subsequent virus transfer. As opposed to gp120-directed antibodies, anti-gp41 bNAbs might prevent HIV-1 infection if transmission or spread at the initial site of invasion occurs from a DC-associated source.

Development of bavituximab, a vascular targeting agent with immune-modulating properties, for lung cancer treatment

Bavituximab is a chimeric monoclonal antibody directed against the membrane phospholipid phosphatidylserine. Phosphatidylserine exposure is increased on endothelial cells and apoptotic cancer cells in solid tumors, allowing tumor-specific targeting of bavituximab. Bavituximab binding results in tumor vessel occlusion and enhanced antitumor immunity. Preclinical investigations have demonstrated efficacy as monotherapy and in combination with other modalities against multiple cancer types. Phase I clinical trials of bavituximab monotherapy and in combination with chemotherapy in adults with refractory solid tumors have been completed. Phase II trials of bavituximab in combination with chemotherapy for the first- and second-line treatment of advanced non-small-cell lung cancer are currently ongoing. This article summarizes the preclinical development and clinical experience with bavituximab in non-small-cell lung cancer.

Immunotherapeutic restoration in HIV-infected individuals

While the development of combined active antiretroviral therapy (cART) has dramatically improved life expectancies and quality of life in HIV-infected individuals, long-term clinical problems, such as metabolic complications, remain important constraints of life-long cART. Complete immune restoration using only cART is normally unattainable even in cases of sufficient plasma viral suppression. The need for immunologic adjuncts that complement cART remains, because while cART alone may result in the complete recovery of peripheral net CD4+ T lymphocytes, it may not affect the reservoir of HIV-infected cells. Here, we review current immunotherapies for HIV infection, with a particular emphasis on recent advances in cytokine therapies, therapeutic immunization, monoclonal antibodies, immune-modulating drugs, nanotechnology-based approaches and radioimmunotherapy.

B cell responses to HIV-1 infection and vaccination: pathways to preventing infection

The B cell arm of the immune response becomes activated soon after HIV-1 transmission, yet the initial antibody response does not control HIV-1 replication, and it takes months for neutralizing antibodies to develop against the autologous virus. Antibodies that can be broadly protective are made only in a minority of subjects and take years to develop--too late to affect the course of disease. New studies of the earliest stages of HIV-1 infection, new techniques to probe the human B cell repertoire, the modest degree of efficacy in a vaccine trial and new studies of human monoclonal antibodies that represent the types of immune responses an HIV-1 vaccine should induce are collectively illuminating paths that a successful HIV-1 vaccine might take.

Multivalent dendrimeric compounds containing carbohydrates expressed on immune cells inhibit infection by primary isolates of HIV-1

Specific glycosphingolipids (GSL), found on the surface of target immune cells, are recognized as alternate cell surface receptors by the human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein. In this study, the globotriose and 3'-sialyllactose carbohydrate head groups found on two GSL were covalently attached to a dendrimer core to produce two types of unique multivalent carbohydrates (MVC). These MVC inhibited HIV-1 infection of T cell lines and primary peripheral blood mononuclear cells (PBMC) by T cell line-adapted viruses or primary isolates, with IC(50)s ranging from 0.1 to 7.4 μg/ml. Inhibition of Env-mediated membrane fusion by MVC was also observed using a dye-transfer assay. These carbohydrate compounds warrant further investigation as a potential new class of HIV-1 entry inhibitors. The data presented also shed light on the role of carbohydrate moieties in HIV-1 virus-host cell interactions.

Inhibition of HIV-1 infection of peripheral blood mononuclear cells by a monoclonal antibody that binds to phosphoinositides and induces secretion of β-chemokines

A murine IgG mAb, WR321, selected for the ability to bind to phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate, but an inability to bind to any of 17 other lipids, including phosphatidylinositol, was examined as a probe for studying interactions of HIV-1 with primary human peripheral blood mononuclear cells. The WR321 mAb broadly neutralized CCR5-tropic strains of HIV-1 to prevent infection of the cells. The mAb also exhibited direct interaction with cells in the culture, resulting in secretion of chemokines that interfered with the interaction of HIV-1 virions with CCR5, the coreceptor for HIV-1 on the susceptible cells, leading to inhibition of infection by HIV-1. Phosphoinositides that are recognized by WR321 do not exist on the external surface of cells, but are concentrated on the inner surface (cytoplasmic leaflet) of the plasma membrane. Murine anti-phosphoinositide mAbs similar to WR321 have previously been directly microinjected into a variety of cultured cells, resulting in important changes in the functions of the cells. The present results suggest that binding of a mAb to phosphoinositides, resulting in secretion of β-chemokines into the culture medium and neutralization of infection by CCR5-tropic HIV-1 of nearby susceptible cells, occurred by uptake and binding of the mAb at an intracellular location in the cultured cells that then led to secretion of HIV-1-inhibitory β-chemokines.

The effect of sCD4 on the binding and accessibility of HIV-1 gp41 MPER epitopes to human monoclonal antibodies

Two human monoclonal anti-HIV-1 antibodies, 2F5 and 4E10, were utilized to investigate the accessibility and conservation of gp41 MPER epitopes on five different clades of HIV-1 in the absence and presence of sCD4. The binding of human monoclonal antibodies (mAbs) to HIV-1 was dependent upon the virus clade. Soluble CD4 significantly increased the accessibility of gp41 MPER-binding epitopes on several isolates that previously showed little or no binding with 2F5 and 4E10 mAbs as determined by a modified ELISA-based virus capture assay and surface plasmon resonance. Studies on the relationship between virus binding and neutralization in a TZM-bl pseudovirus assay indicated that in most cases, mAbs that exhibited neutralization also bound the virus. However, neither binding per se nor the total envelope content per virion was a predictor of neutralization. The hidden or conformational gp41 MPER epitopes unmasked by sCD4 may provide additional targets for vaccine design.

Replication competent molecular clones of HIV-1 expressing Renilla luciferase facilitate the analysis of antibody inhibition in PBMC

Effective vaccine development for human immunodeficiency virus type 1 (HIV-1) will require assays that ascertain the capacity of vaccine immunogens to elicit neutralizing antibodies (NAb) to diverse HIV-1 strains. To facilitate NAb assessment in peripheral blood mononuclear cell (PBMC)-based assays, we developed an assay-adaptable platform based on a Renilla luciferase (LucR) expressing HIV-1 proviral backbone. LucR was inserted into pNL4-3 DNA, preserving all viral open reading frames. The proviral genome was engineered to facilitate expression of diverse HIV-1 env sequences, allowing analysis in an isogenic background. The resulting Env-IMC-LucR viruses are infectious, and LucR is stably expressed over multiple replications in PBMC. HIV-1 neutralization, targeting TZM-bl cells, was highly correlative comparing virus (LucR) and cell (firefly luciferase) readouts. In PBMC, NAb activity can be analyzed either within a single or multiple cycles of replication. These results represent advancement toward a standardizable PBMC-based neutralization assay for assessing HIV-1 vaccine immunogen efficacy.

Strategies for eliciting HIV-1 inhibitory antibodies

PURPOSE OF REVIEW

Major roadblocks persist in the development of vaccines that elicit potent neutralizing antibodies targeting diverse HIV-1 strains, similar to known broadly neutralizing HIV-1 human monoclonal antibodies. Alternatively, other types of anti-HIV-1 envelope antibodies that may not neutralize HIV-1 in traditional neutralization assays but have other anti-HIV-1 activities (hereafter termed HIV-1 inhibitory antibodies) can be elicited by current vaccine strategies, and numerous studies are exploring their roles in preventing HIV-1 acquisition. We review examples of strategies for eliciting potentially protective HIV-1 inhibitory antibodies.

RECENT FINDINGS

Heterologous prime-boost strategies can yield anti-HIV immune responses, although only one (canarypox prime, Env protein boost) has been tested and shown positive results in an efficacy trial (RV144). Although the immune correlates of protection are as yet undefined, the reduced rate of acquisition without a significant effect on initial viral loads or CD4 T-cell counts, have raised the hypothesis of an RV144 vaccine-elicited transient protective B-cell response.

SUMMARY

In light of the RV144 trial, there is a critical need to define the entire functional spectrum of anti-HIV-1 antibodies, how easily each can be elicited, and how effective different types of antibody effector mechanisms can be in prevention of HIV-1 transmission.