Failure of HIV-exposed CD4+ T cells to activate dendritic cells is reversed by restoration of CD40/CD154 interactions

CD40 ligand preferentially modulates immune response and enhances protection against influenza virus

CD40L, a key regulator of the immune system, was studied as both a targeting ligand and a molecular adjuvant in nucleoprotein (NP)-based host defense against influenza in mouse models with different genetic backgrounds. Adenoviral vectors secreting NP-CD40L fusion protein (denoted as rAd-SNP40L) afforded full protection of immunocompetent and immunocompromised mice (CD40L(-/-) and CD4(-/-)) against lethal influenza infection. Mechanistically, rAd-SNP40L preferentially induced early and persistent B cell germinal center formation, and accelerated Ig isotype-switching and Th1-skewed, NP-specific Ab response. Moreover, it drastically augmented primary and memory NP-specific CTL activity and polyfunctional CD8(+) T cells. The markedly enhanced nonneutralizing Abs and CTLs significantly reduced viral burdens in the lungs of mice upon lethal virus challenge. Data generated from CD40L(-/-) and CD4(-/-) mice revealed that the protection was indeed CD40L mediated but CD4(+) T cell independent, demonstrating the viability of the fusion Ags in protecting immunodeficient hosts. Notably, a single dose of rAd-SNP40L completely protected mice from lethal viral challenge 4 mo after immunization, representing the first report, to our knowledge, on NP in conjunction with a molecular adjuvant inducing a robust and long-lasting memory immune response against influenza. This platform is characterized by an increased in vivo load of CD40-targeted Ag upon the secretion of the fusion protein from adenovirus-infected cells and may represent a promising strategy to enhance the breadth, durability, and potency of Ag-specific immune responses.

Differential impact of PD-1 and/or interleukin-10 blockade on HIV-1-specific CD4 T cell and antigen-presenting cell functions

Antigen persistence in chronic infections and cancer upregulates inhibitory networks, such as the PD-1 and interleukin-10 (IL-10) pathways, that impair immunity and lead to disease progression. These pathways are attractive targets for immunotherapy, as demonstrated by recent clinical trials of PD-1/PD-L1 blockade in cancer patients. However, in HIV-1 infection not all subjects respond to inhibition of either pathway and the mechanistic interactions between these two networks remain to be better defined. Here we demonstrate that in vitro blockade of PD-L1 and/or IL-10Rα results in markedly different profiles of HIV-1-specific CD4 T cell restoration. Whereas PD-L1 blockade leads to balanced increase in gamma interferon (IFN-γ), IL-2, and IL-13 secretion, IL-10Rα blockade preferentially restores IFN-γ production. In viremic subjects, combined PD-L1/IL-10Rα blockade results in a striking 10-fold increase in IFN-γ secretion by HIV-1-specific CD4 T cells that is not observed in subjects with spontaneous (elite controllers) or therapy-induced control of viral replication. In contrast to the dramatic increase in IFN-γ production, concurrent blockade has a marginal additive effect on IL-2 production, IL-13 secretion, and HIV-1-specific CD4 T cell proliferation. IFN-γ produced by Thelper cells upregulates PD-L1, HLA I/II, and IL-12 expression by monocytes. The effect of combined blockade on IFN-γ was dependent on reciprocal reinforcement through IL-12. These studies provide crucial information on the different immunoregulatory qualities of PD-1 and IL-10 in progressive disease and link exhausted virus-specific CD4 T cells and monocytes in the regulation of IFN-γ and IL-12 secretion.

IMPORTANCE

Infection with HIV results in most people in uncontrolled viral replication and progressive weakening of the body defenses. In the absence of antiviral therapy, this process results in clinical disease, or AIDS. An important reason why HIV continues to multiply is that a population of white blood cells called CD4 T cells that targets the virus fails to work properly. At least part of this impairment is under the control of inhibitory mechanisms that can be blocked to improve the function of these CD4 T cells. In this report, we show that blocking one or two of the molecules involved, called PD-1 and IL-10, has different effects on the individual functions of these cells and that one is strongly improved. We investigate how these effects are caused by interactions between CD4 T cells and antigen-presenting cells. These observations can have implications for new therapeutic approaches in HIV infection.

An immunomodulating motif of the HIV-1 fusion protein is chirality-independent: implications for its mode of action

An immunosuppressive motif was recently found within the HIV-1 gp41 fusion protein (termed immunosuppressive loop-associated determinant core motif (ISLAD CM)). Peptides containing the motif interact with the T-cell receptor (TCR) complex; however, the mechanism by which the motif exerts its immunosuppressive activity is yet to be determined. Recent studies showed that interactions between protein domains in the membrane milieu are not always sterically controlled. Therefore, we utilized the unique membrane leniency toward association between D- and L-stereoisomers to investigate the detailed mechanism by which ISLAD CM inhibits T-cell activation. We show that a D-enantiomer of ISLAD CM (termed ISLAD D-CM) inhibited the proliferation of murine myelin oligodendrocyte glycoprotein (MOG)-(35-55)-specific line T-cells to the same extent as the l-motif form. Moreover, the D- and L-forms preferentially bound spleen-derived T-cells over B-cells by 13-fold. Furthermore, both forms of ISLAD CM co-localized with the TCR on activated T-cells and interacted with the transmembrane domain of the TCR. FRET experiments revealed the importance of basic residues for the interaction between ISLAD CM forms and the TCR transmembrane domain. Ex vivo studies demonstrated that ISLAD D-CM administration inhibited the proliferation (72%) and proinflammatory cytokine secretion of pathogenic MOG(35-55)-specific T-cells. This study provides insights into the immunosuppressive mechanism of gp41 and demonstrates that chirality-independent interactions in the membrane can take place in diverse biological systems. Apart from HIV pathogenesis, the D-peptide reported herein may serve as a potential tool for treating T-cell-mediated pathologies.

HIV-1 fusion protein exerts complex immunosuppressive effects

One of the routes by which HIV-1 is able to escape the immune response is by immunosuppression. The gp41 fusion protein of the HIV-1 envelope mediates virus entry by membrane fusion and also functions as an inhibitor of T cell activation. Here, we review the recent studies suggesting that some of the gp41 immunosuppressive processes are initiated by novel motifs, located within the hydrophobic regions of the protein. This indicates that the immunosuppressive process mediated by gp41 is much more complex than initially thought. Additionally, we propose a model illustrating the interactions and interferences of these regions with the T cell receptor complex.

A highly conserved sequence associated with the HIV gp41 loop region is an immunomodulator of antigen-specific T cells in mice

Modulation of T-cell responses by HIV occurs via distinct mechanisms, 1 of which involves inactivation of T cells already at the stage of virus-cell fusion. Hydrophobic portions of the gp41 protein of the viral envelope that contributes to membrane fusion may modulate T-cell responsiveness. Here we found a highly conserved sequence (termed "ISLAD") that is associated with the membranotropic gp41 loop region. We showed that ISLAD has the ability to bind the T-cell membrane and to interact with the T-cell receptor (TCR) complex. Furthermore, ISLAD inhibited T-cell proliferation and interferon-γ secretion that resulted from TCR engagement through antigen-presenting cells. Moreover, administering ISLAD (10 µg per mouse) to an experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis reduced the severity of the disease. This was related to the inhibition of pathogenic T-cell proliferation and to reduced pro-inflammatory cytokine secretion in the lymph nodes of ISLAD-treated EAE mice. The data suggest that T-cell inactivation by HIV during membrane fusion may lie in part in this conserved sequence associated with the gp41 loop region.

A GxxxG-like motif within HIV-1 fusion peptide is critical to its immunosuppressant activity, structure, and interaction with the transmembrane domain of the T-cell receptor

To thrive in the human body, HIV fuses to its target cell and evades the immune response via several mechanisms. The fusion cascade is initiated by the fusion peptide (FP), which is located at the N-terminal of gp41, the transmembrane protein of HIV. Recently, it has been shown that the HIV-1 FP, particularly its 5-13 amino acid region (FP(5-13)), suppresses T-cell activation and interacts with the transmembrane domain (TMD) of the T-cell receptor (TCR) complex. Specific amino acid motifs often contribute to such interactions in TMDs of membrane proteins. Using bioinformatics and experimental studies, we report on a GxxxG-like motif (AxxxG), which is conserved in the FP throughout different clades and strains of HIV-1. Biological activity studies and FTIR spectroscopy revealed that HIV FP(5-13)-derived peptides, in which the motif was altered either by randomization or by a single amino acid shift, lost their immunosuppressive activity concomitant with a loss of the β-sheet structure in a membranous environment. Furthermore, fluorescence studies revealed that the inactive mutants lost their ability to interact with their target site, namely, the TMD of TCRα, designated CP. Importantly, lipotechoic acid activated macrophages (lacking TCR) were not affected by FP, further demonstrating the specificity of the immunosuppressant activity of CP. Finally, although the AxxxG WT and the GxxxG analog both associated with the CP and immunosuppressed T-cells, the AxxxG WT but not the GxxxG analog induced lipid mixing. Overall, the data support an important role for the AxxxG motif in the function of FP and might explain the natural selection of the AxxxG motif rather than the classical GxxxG motif in FP.

Chronic immune activation in HIV-1 infection contributes to reduced interferon alpha production via enhanced CD40:CD40 ligand interaction

Although a signature of increased interferon (IFN-)alpha production is observed in HIV-1 infection, the response of circulating plasmacytoid dendritic cells (PDC) to Toll-like receptor ligand stimulation is substantially impaired. This functional PDC deficit, which we specifically observed in HIV-1 infected individuals with less than 500 CD4+ T cells/µl, is not well understood. We provide evidence that the peripheral IFN-alpha production in HIV-1 infection is actively suppressed by the enhanced interaction of CD40 ligand (CD40L), a member of the tumor necrosis factor family, and its receptor CD40, which are both upregulated upon immune activation. Plasma levels of soluble CD40L were significantly higher in untreated HIV-1 infected individuals (n = 52) than in subjects on long-term antiretroviral therapy (n = 62, p<0.03) and in uninfected control donors (n = 16, p<0.001). Concomitantly, cell-associated CD40L and the expression of the receptor CD40 on the PDC were significantly upregulated in HIV-1 infection (p<0.05). Soluble and cell-associated CD40L inhibited the PDC-derived IFN-alpha production by CpG oligodeoxynucleotides dose-dependently. This suppressive effect was observed at much lower, physiological CD40L concentrations in peripheral blood mononuclear cells (PBMC) of HIV-1 infected individuals compared to controls (p<0.05). The CpG-induced IFN-alpha production in PBMC of HIV-1 infected donors was directly correlated with PDC and CD4+ T cell counts, and inversely correlated with the viral loads (p<0.001). In HIV-1 infected donors with less than 500 CD4+ T cells/µl, the CpG-induced IFN-alpha production was significantly correlated with the percentage of CD40-expressing PDC and the level of CD40 expression on these cells (p<0.05), whereas CD40L plasma levels played a minor role. In addition, low-dose CD40L contributed to the enhanced production of interleukin 6 and 8 in PBMC of HIV-1 infected donors compared to controls. Our data support the conclusion that the chronic immune activation in HIV-1 infection impairs peripheral PDC innate immune responses at least in part via enhanced CD40:CD40L interactions.

Highly active antiretroviral therapy in patients infected with human immunodeficiency virus increases CD40 ligand expression and IL-12 production in cells ex vivo

Highly active anti-retroviral therapy (HAART) restores CD4(+) T-cell numbers in the periphery; however, its efficacy in restoring functional immunity is not fully elucidated. Here we evaluated longitudinal changes in the expression of several key markers of T-cell activation, namely CD40 ligand (CD154), OX40 (CD134), or CD69, after anti-CD3/CD28 activation, as well as levels of IL-12 production after Staphylococcus aureus Cowan stimulation in 28 HIV-infected adult patients. Patients were followed up to 12 mo post-HAART initiation. Viral burdens and CD4 cell counts were measured at the same time points. A control group of 15 HIV-uninfected adult subjects was included for comparison. Significant increases in CD40L and OX40 expression, but not of CD69 expression, were observed over time in the overall patient population, and more particularly in patients with baseline CD4 counts lower than or equal to 200 cells/μL, or those with baseline viral loads lower than or equal to 10(5) RNA copies/mL. Similar increases were seen for IL-12 production. Viral loads were inversely associated with CD40L expression or IL-12 production in a mixed linear model analysis, while CD4 counts were directly associated. CD40L expression and IL-12 production were significantly correlated. In conclusion, HAART-mediated control of viral replication led to partial restoration of CD40L upregulation/expression, and to increased IL-12 production, but the magnitude of the response depended on the baseline characteristics of the treated patients.

EBV LMP1, a viral mimic of CD40, activates dendritic cells and functions as a molecular adjuvant when incorporated into an HIV vaccine

HIV-1 does not significantly activate cellular immunity, which has made it difficult to use attenuated forms of HIV-1 as a vaccine. In contrast, EBV induces robust T cell responses in most infected individuals, perhaps as this virus contains LMP1, a viral mimic of CD40, which is a key activating molecule for DCs and macrophages. Consequently, studies were conducted using LMP1 and LMP1-CD40, a related construct formed by replacing the intracellular signaling domain of LMP1 with that of CD40. Upon electroporation into DCs, LMP1 and LMP1-CD40 mRNAs were sufficient to up-regulate costimulatory molecules and proinflammatory cytokines, indicating that these molecules can function in isolation as adjuvant-like molecules. As a first step toward an improved HIV vaccine, LMP1 and LMP1-CD40 were introduced into a HIV-1 construct to produce virions encoding these proteins. Transduction of DCs and macrophages with these viruses induced morphological changes and up-regulated costimulatory molecules and cytokine production by these cells. HIV-LMP1 enhanced the antigen-presenting function of DCs, as measured in an in vitro immunization assay. Taken together, these data show that LMP1 and LMP1-CD40 are portable gene cassettes with strong adjuvant properties that can be introduced into viruses such as HIV, which by themselves, are insufficient to induce protective cellular immunity.

FOXP3 expression is upregulated in CD4T cells in progressive HIV-1 infection and is a marker of disease severity

Background

Understanding the role of different classes of T cells during HIV infection is critical to determining which responses correlate with protective immunity. To date, it is unclear whether alterations in regulatory T cell (Treg) function are contributory to progression of HIV infection.

Methodology

FOXP3 expression was measured by both qRT-PCR and by flow cytometry in HIV-infected individuals and uninfected controls together with expression of CD25, GITR and CTLA-4. Cultured peripheral blood mononuclear cells were stimulated with anti-CD3 and cell proliferation was assessed by CFSE dilution.

Principal Findings

HIV infected individuals had significantly higher frequencies of CD4⁺FOXP3⁺ T cells (median of 8.11%; range 1.33%–26.27%) than healthy controls (median 3.72%; range 1.3–7.5%; P = 0.002), despite having lower absolute counts of CD4⁺FOXP3⁺ T cells. There was a significant positive correlation between the frequency of CD4⁺FOXP3⁺ T cells and viral load (rho = 0.593 P = 0.003) and a significant negative correlation with CD4 count (rho = −0.423 P = 0.044). 48% of our patients had CD4 counts below 200 cells/µl and these patients showed a marked elevation of FOXP3 percentage (median 10% range 4.07%–26.27%). Assessing the mechanism of increased FOXP3 frequency, we found that the high FOXP3 levels noted in HIV infected individuals dropped rapidly in unstimulated culture conditions but could be restimulated by T cell receptor stimulation. This suggests that the high FOXP3 expression in HIV infected patients is likely due to FOXP3 upregulation by individual CD4⁺ T cells following antigenic or other stimulation.

Conclusions/Significance

FOXP3 expression in the CD4⁺ T cell population is a marker of severity of HIV infection and a potential prognostic marker of disease progression.

Incorporation of CD40 ligand into SHIV virus-like particles (VLP) enhances SHIV-VLP-induced dendritic cell activation and boosts immune responses against HIV

Engagement of CD40 with CD40L induces dendritic cell (DC) maturation and activation, thereby promoting immune responses. The objective of this study was to investigate whether immunization with chimeric CD40L/SHIV virus-like particles (CD40L/SHIV-VLP) could enhance immune responses to SIV Gag and HIV Env proteins by directly activating DCs. We found that CD83, CD40, and CD86 were significantly up-regulated and significantly increased cytokines production were observed after hCD40L/SHIV-VLP treatment in human CD14(+) monocyte-derived DCs as compared to SHIV-VLP treatment. Mice immunized with mCD40L/SHIV-VLP showed more than a two-fold increase in HIV Env-specific IgG antibody production, an increase in SIV Gag and HIV Env-specific IFN-gamma and IL-4 producing cells, and an increase in HIV Env-specific cytotoxic activity compared to that in SHIV-VLP immunized mice. Furthermore, multifunctional CD4(+) Th1 cells, which simultaneously produce IFN-gamma, IL-2 and TNF-alpha triple cytokines, and CD8(+) T-cells, which produce IFN-gamma were elevated in the mCD40L/SHIV-VLP immunized group. These data demonstrate that chimeric CD40L/SHIV-VLP potently induce DC activation and enhance the magnitude of both humoral and cellular immune responses to the SIV Gag and HIV Env proteins in the mouse model. Therefore, incorporation of CD40L into VLP may represent a novel strategy to develop effective HIV vaccines.

IL-23 and IL-12p70 production by monocytes and dendritic cells in primary HIV-1 infection

IL-12 enhances protective responses against HIV replication. Its production after in vitro stimulation is defective in chronic HIV infection, but higher responses can be found. IL-23 shares the p40 chain and some properties with IL-12 and enhances Th17 responses, but its role in HIV infection is unknown. The production of IL-12 and IL-23 and the respective contribution of monocytes and myeloid conventional DC (cDCs) during primary HIV infection were determined. Sixteen patients included in the French PRIMO-ANRS Cohort without antiretroviral treatment were followed prospectively and compared with uninfected donors. Intracellular p40 expression by monocytes and cDCs, analyzed by flow cytometry, was transiently increased in monocytes and cDCs in response to LPS and more consistently, in monocytes in response to LPS + IFN-gamma. IL-23 production, measured by ELISA after PBMC stimulation, was induced by LPS in strong correlation with VLs. IL-12p70 production required the addition of IFN-gamma and was transiently increased in patients compared with controls in correlation with VLs, whereas IL-23 was increased sustainedly. Therefore, an apparent domination of IL-23 over IL-12 responses occurred throughout primary HIV infection, and a potential restoration of IL-12 responses might be expected from a treatment mimicking activated T cell signals.

Dendritic cell differentiation and maturation in the presence of HIV type 2 envelope

Dendritic cells (DCs) are fundamental for the initiation of immune responses and are important players in AIDS immunopathogenesis. Impairment of DC function may result from bystander effects of HIV-1 envelope proteins independently of direct HIV-1 infection. HIV-2 envelope proteins are thought to interact with a broader range of receptors than those of HIV-1, and have been shown to have T cell immunosuppressive properties mediated by monocytes. The effects of HIV-2 envelope on DC differentiation and maturation were investigated. The modulatory properties of the HIV-2 envelope on DC generated from monocytes were assessed using both recombinant proteins (HIV-2(ROD) and HIV-2(ALI)) and whole chemically inactivated virus (aldrithiol-2-treated HIV-2(ROD)). DC phenotype was assessed by flow cytometry and DC function by their ability to stimulate allogeneic T cells and to produce cytokines. We demonstrate that HIV-2 Env had no effects upon DC differentiation and maturation despite its broad receptor usage and ability to modulate monocyte function. It is plausible to speculate that a reduced ability of the HIV-2 Env to impair myeloid DC function could represent a contributory factor to the relatively benign course of HIV-2 disease.

Antiphospholipid antibodies: paradigm in transition

OBJECTIVES

This is a critical review of anti-phospholipid antibodies (aPL). Most prior reviews focus on the aPL syndrome (APS), a thrombotic condition often marked by neurological disturbance. We bring to attention recent evidence that aPL may be equally relevant to non-thrombotic autoimmune conditions, notably, multiple sclerosis and ITP.

ORGANIZATION

After a brief history, the recent proliferation of aPL target antigens is reviewed. The implication is that many more exist. Theories of aPL in thrombosis are then reviewed, concluding that all have merit but that aPL may have more diverse pathological consequences than now recognized. Next, conflicting results are explained by methodological differences. The lupus anticoagulant (LA) is then discussed. LA is the best predictor of thrombosis, but why this is true is not settled. Finally, aPL in non-thrombotic disorders is reviewed.

CONCLUSION

The current paradigm of aPL holds that they are important in thrombosis, but they may have much wider clinical significance, possibly of special interest in neurology.

CD4+ cells are required for chronic eosinophilic lung inflammation but not airway remodeling

The contribution of CD4 T cells and other CD4+ cells to lung inflammation and airway remodeling remains unclear during bouts of chronic exposure to airborne allergen. Previously, murine models have shown that CD4 T cells are required for initiation of acute inflammation and the remodeling process. However, it is unknown whether CD4 T cells or other CD4+ cells continue to be required for remodeling during ongoing allergen challenges after the development of acute eosinophilic lung inflammation. To test this, mice were sensitized and challenged with ovalbumin (OVA). After acute airway inflammation was established, a CD4 depleting antibody was administered for 4 wk during a period of chronic exposure to intranasal OVA, resulting in effective depletion of CD4+ cells from all organs, including the lung, lung-draining lymph nodes, and spleen. In these mice, levels of peribronchial inflammation, bronchoalveolar (BAL) eosinophils, and lung CD11c+, CD8+, and Siglec-F+CD11c- cells were significantly reduced. However, mucus metaplasia, peribronchial subepithelial fibrosis, and smooth muscle mass were not affected. Additionally, depletion of CD4+ cells before the last week of chronic allergen challenges also led to significant reductions in BAL eosinophils, peribronchial inflammation, and lung CD11c+, CD8+, and Siglec-F+CD11c- cells. These results show that CD4 T cells, and other CD4+ cells including subsets of dendritic cells, iNKT cells, and LTi cells, play a role in ongoing eosinophilic lung inflammation during periods of chronic allergen challenge, but are not required for progressive airway remodeling that develops after initial acute inflammation.

Altered bone marrow dendritic cell cytokine production to toll-like receptor and CD40 ligation during chronic feline immunodeficiency virus infection

Impaired dendritic cell (DC) function is thought to be central to human immunodeficiency virus-associated immunodeficiency. In this study, we examined the effect of chronic feline immunodeficiency virus (FIV) infection on DC cytokine production in response to microbial and T-cell stimulation. Cytokine production after either Toll-like receptor (TLR) or CD40 ligation in bone marrow-derived DCs (BM-DCs) was measured in naïve and chronically FIV-infected cats. The BM-DCs were stimulated with ligands to TLR-2, -3, -4, -7 and -9 or cocultured with 3T3 cells expressing feline CD40 ligand. Ligation of TLR-4 and TLR-9 in BM-DCs from infected cats resulted in a significant decrease in the ratio of interleukin-12 (IL-12) to IL-10. Conversely, TLR-7 ligation produced a significant increase in the IL-12 : IL-10 ratio in BM-DCs from infected cats. No difference was noted for TLR-3 ligation. RNA expression levels of TLR-2, -3, -4, -7 and -9 were not significantly altered by FIV infection. CD40 ligation significantly elevated both IL-10 and IL-12 messenger RNA production but did not alter the IL-12 : IL-10 ratio. Chronic FIV infection alters the ratio of immunoregulatory cytokines produced by BM-DCs in response to certain pathogen-derived signals, which is probably relevant to the increased risk of opportunistic infections seen in lentiviral infection.

Chimpanzee CD4+ T cells are relatively insensitive to HIV-1 envelope-mediated inhibition of CD154 up-regulation

CD40-CD154 interaction forms a key event in regulation of crosstalk between dendritic cells and CD4 T cells. In human immunodeficiency virus (HIV)-1 infected patients CD154 expression is impaired, and the resulting loss of immune responsiveness by CD4+ T cells contributes to a progressive state of immunodeficiency in humans. Although chimpanzees are susceptible to chronic HIV-1/SIVcpz infection, they are relatively resistant to the onset of AIDS. This relative resistance is characterized by maintenance of CD4+ T cell populations and function, which is highly compromised in human patients. In our cohort of chronically HIV-1- and SIVcpz-infected chimpanzees, we demonstrated the capacity to produce IL-2, following CD3/CD28 stimulation, as well as preserved CD154 up-regulation. Cross-linking of CD4 with mAb was found to inhibit CD3/CD28-induced up-regulation of CD154 equally in chimpanzees and humans. However, specific cross-linking with trimeric recombinant HIV-1 gp140 revealed reduced sensitivity for inhibition of CD154 up-regulation in chimpanzees, requiring fourfold higher concentrations of viral protein. Chimpanzee CD4+ T cells are thus less sensitive to the immune-suppressive effect of low-dose HIV-1 envelope protein than human CD4+ T cells.

Identification of a strongly activating human anti-CD40 antibody that suppresses HIV type 1 infection

We characterized the functional properties of a novel set of human anti-CD40 monoclonal antibodies originating from a human phage display library and identified an antibody that strongly activates cells via the CD40 receptor for potential use in HIV therapy. The anti-CD40 antibodies were converted from a single chain antibody fragment format (scFv) to an IgG format and produced in HEK293 cells, and the binding characteristics were evaluated. Next, their ability to (1) rescue a human B cell line from induced apoptosis, (2) stimulate B cell proliferation, and (3) block the CD40-CD40L interaction was determined. Finally, the most activating anti-CD40 antibody was tested for its ability to block HIV-1 infection in a monocyte-derived cell line. The different anti-CD40 antibodies, A24, B44, E30, F33, and A2-54, displayed a wide variety of binding and functional properties. In particular, B44 showed a very strong ability to activate normal human B cells and, in addition, did not block the CD40-CD40L interaction. This antibody was able to suppress HIV-1 infection in a human cell line (MonoMac 1) and may be a potential therapeutic candidate in HIV infection.

Characterization of human immunodeficiency virus type 1 replication in immature and mature dendritic cells reveals dissociable cis- and trans-infection

Dendritic cells (DCs) transmit human immunodeficiency virus type 1 (HIV-1) to CD4(+) T cells through the trans- and cis-infection pathways; however, little is known about the relative efficiencies of these pathways and whether they are interdependent. Here we compare cis- and trans-infections of HIV-1 mediated by immature DCs (iDCs) and mature DCs (mDCs), using replication-competent and single-cycle HIV-1. Monocyte-derived iDCs were differentiated into various types of mDCs by lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), and CD40 ligand (CD40L). iDCs and CD40L-induced mDCs were susceptible to HIV-1 infection and mediated efficient viral transmission to CD4(+) T cells. Although HIV-1 cis-infection was partially restricted in TNF-alpha-induced mDCs and profoundly blocked in LPS-induced mDCs, these cells efficiently promoted HIV-1 trans-infection of CD4(+) T cells. The postentry restriction of HIV-1 infection in LPS-induced mDCs was identified at the levels of reverse transcription and postintegration, using real-time PCR quantification of viral DNA and integration. Furthermore, nucleofection of DCs with HIV-1 proviral DNA confirmed that impaired gene expression of LPS-induced mDCs was responsible for the postentry restriction of HIV-1 infection. Our results suggest that various DC subsets in vivo may differentially contribute to HIV-1 dissemination via dissociable cis- and trans-infections.

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

HIV inhibits CD4+ T-cell proliferation by inducing indoleamine 2,3-dioxygenase in plasmacytoid dendritic cells

Infection with the human immunodeficiency virus type-1 (HIV) results in acute and progressive numeric loss of CD4(+) T-helper cells and functional impairment of T-cell responses. The mechanistic basis of the functional impairment of the surviving cells is not clear. Indoleamine 2,3-dioxygenase (IDO) is an immunosuppressive enzyme that inhibits T-cell proliferation by catabolizing the essential amino acid tryptophan (Trp) into the kynurenine (kyn) pathway. Here, we show that IDO mRNA expression is elevated in peripheral blood mononuclear cells (PBMCs) from HIV(+) patients compared with uninfected healthy controls (HCs), and that in vitro inhibition of IDO with the competitive blocker 1-methyl tryptophan (1-mT) results in increased CD4(+) T-cell proliferative response in PBMCs from HIV-infected patients. We developed an in vitro model in which exposure of PBMCs from HCs to either infectious or noninfectious, R5- or X4-tropic HIV induced IDO in plasmacytoid dendritic cells (pDCs). HIV-induced IDO was not inhibited by blocking antibodies against interferon type I or type II, which, however, induced IDO in pDCs when added to PBMC cultures. Blockade of gp120/CD4 interactions with anti-CD4 Ab inhibited HIV-mediated IDO induction. Thus, induction of IDO in pDCs by HIV may contribute to the T-cell functional impairment observed in HIV/AIDS by a non-interferon-dependent mechanism.

The immunoregulatory effects of HIV‐1 Nef on dendritic cells and the pathogenesis of AIDS

Dendritic cells (DC) play a crucial role in the generation and regulation of immunity, and their interaction with HIV is relevant in the pathogenesis of AIDS favoring both the initial establishment and spread of the infection and the development of antiviral immunity. HIV-1 Nef is an essential factor for efficient viral replication and pathogenesis, and several studies have been addressed to assess the possible influence of endogenous or exogenous Nef on DC biology. Our findings and other reported data described in this review demonstrate that Nef subverts DC biology interfering with phenotypical, morphological, and functional DC developmental programs, thus representing a viral tool underlying AIDS pathogenesis. This review provides an overview on the mechanism by which Nef, hijacking DC functional activity, may favor both the replication of HIV-1 and the escape from immune surveillance. Overall, the findings described here may contribute to the understanding of Nef function, mechanism of action, and cellular partners. Further elucidation of genes induced through Nef signaling in DC could reveal pathways used by DC to drive HIV spread and will be critical to identify therapeutic strategies to bias the DC system toward activation of antiviral immunity instead of facilitating virus dissemination.

Role of gp120 in dendritic cell dysfunction in HIV infection

Only a limited fraction of circulating virions are demonstrably infectious; therefore, exposure to inactivated viruses may mimic the most frequent type of CD4-HIV interactions that occur in vivo. Several studies have recently underscored the crucial role that those noninfectious viruses could play in defective immune function in HIV-infected individuals and in particular, in the dysregulation of dendritic cell (DC) function. In this review, we discuss how interactions between DC and HIV gp120 or inactivated virus, which harbor intact surface gp120, lead to impaired DC function through direct (direct contact) or indirect mechanisms (as a consequence of primary CD4+ T cell dysregulation, followed by defective CD4-DC interactions). It is important that these functionally impaired DCs fail to give optimal signal to T cells but appear to favor the emergence of regulatory T cells. gp120-mediated impairment of DC function could therefore play an important role in the pathogenesis of HIV disease.

HIV-1-driven regulatory T-cell accumulation in lymphoid tissues is associated with disease progression in HIV/AIDS

Regulatory T (Treg) cells accumulate in the lymphoid tissues of human immunodeficiency virus (HIV)-infected individuals, contributing to the inability of the immune system to control virus replication. We investigate here Treg-cell numbers and functional markers (FOXP3, CTLA-4, IDO, and TGF-beta1) in lymphoid tissues from untreated infected hosts with progressive or nonprogressive disease (HIV-infected humans and simian immunodeficiency virus [SIV]-infected macaques). We found that increased numbers of FOXP3(+) T cells as well as increased expression of Treg-cell-associated functional markers were detected only during progressive disease. Such increases were not correlated with immune activation. Of importance, a high-perforin/FOXP3 ratio was associated with nonprogressive disease, suggesting that the immune control of virus replication represents a balance between cell-mediated immune responses and Treg-cell-mediated counter regulation of such responses. Furthermore, using an in vitro model of Treg-cell-HIV interactions, we showed that exposure of Treg cells to HIV selectively promoted their survival via a CD4-gp120-dependent pathway, thus providing an underlying mechanism for the accumulation of Treg cells in infected hosts with active viral replication. Considered together, our findings imply that therapeutic manipulation of Treg-cell number and/or function could improve immune control of HIV infection.

The promise and challenge of anti-HIV cellular immunity

PURPOSE OF REVIEW

We discuss recent studies giving insight into the promise of cell-mediated immunity for prophylactic HIV vaccine strategies, and challenges to be overcome for this approach to succeed.

RECENT FINDINGS

Advances in understanding of events in very early HIV infection and their importance in viral pathogenesis emphasize the rapidity with which vaccine-induced T-cell responses must act to modulate CD4 cell destruction, but also reveal an early window of opportunity when foci of infection are limited and could potentially be eliminated. Super-infection with diverse HIV strains is now appreciated to be relatively common, indicating that cell-mediated responses in most infected individuals do not confer protection. Recent studies suggest that T-cell correlates of good control of HIV replication may be a consequence rather than a cause of containment of viraemia. Analysis of features of HIV-specific T-cell responses restricted by human leukocyte antigen alleles associated with differential prognosis of infection is giving insight into correlates of protection. The importance of efficacious responses, escape from which incurs high fitness costs, is increasingly appreciated.

SUMMARY

There are many challenges to be overcome before the promise of cell-mediated immunity for HIV vaccines is realized.