HIV-1 impairs in vitro priming of naïve T cells and gives rise to contact-dependent suppressor T cells

HIV-1 induction of tolerogenic dendritic cells is mediated by cellular interaction with suppressive T cells

HIV-1 infection gives rise to a multi-layered immune impairment in most infected individuals. The chronic presence of HIV-1 during the priming and activation of T cells by dendritic cells (DCs) promotes the expansion of suppressive T cells in a contact-dependent manner. The mechanism behind the T cell side of this HIV-induced impairment is well studied, whereas little is known about the reverse effects exerted on the DCs. Herein we assessed the phenotype and transcriptome profile of mature DCs that have been in contact with suppressive T cells. The HIV exposed DCs from cocultures between DCs and T cells resulted in a more tolerogenic phenotype with increased expression of e.g., PDL1, Gal-9, HVEM, and B7H3, mediated by interaction with T cells. Transcriptomic analysis of the DCs separated from the DC-T cell coculture revealed a type I IFN response profile as well as an activation of pathways involved in T cell exhaustion. Taken together, our data indicate that the prolonged and strong type I IFN signaling in DCs, induced by the presence of HIV during DC-T cell cross talk, could play an important role in the induction of tolerogenic DCs and suppressed immune responses seen in HIV-1 infected individuals.

MAVS Genetic Variation Is Associated with Decreased HIV-1 Replication In Vitro and Reduced CD4+ T Cell Infection in HIV-1-Infected Individuals

The mitochondrial antiviral protein MAVS is a key player in the induction of antiviral responses; however, human immunodeficiency virus 1 (HIV-1) is able to suppress these responses. Two linked single nucleotide polymorphisms (SNPs) in the MAVS gene render MAVS insensitive to HIV-1-dependent suppression, and have been shown to be associated with a lower viral load at set point and delayed increase of viral load during disease progression. Here, we studied the underlying mechanisms involved in the control of viral replication in individuals homozygous for this MAVS genotype. We observed that individuals with the MAVS minor genotype had more stable total CD4⁺ T cell counts during a 7-year follow up and had lower cell-associated proviral DNA loads. Genetic variation in MAVS did not affect immune activation levels; however, a significantly lower percentage of naïve CD4⁺ but not CD8⁺ T cells was observed in the MAVS minor genotype. In vitro HIV-1 infection of peripheral blood mononuclear cells (PBMCs) from healthy donors with the MAVS minor genotype resulted in decreased viral replication. Although the precise underlying mechanism remains unclear, our data suggest that the protective effect of the MAVS minor genotype may be exerted by the initiation of local innate responses affecting viral replication and CD4⁺ T cell susceptibility.

SAMHD1 Functions and Human Diseases

Deoxynucleoside triphosphate (dNTP) molecules are essential for the replication and maintenance of genomic information in both cells and a variety of viral pathogens. While the process of dNTP biosynthesis by cellular enzymes, such as ribonucleotide reductase (RNR) and thymidine kinase (TK), has been extensively investigated, a negative regulatory mechanism of dNTP pools was recently found to involve sterile alpha motif (SAM) domain and histidine-aspartate (HD) domain-containing protein 1, SAMHD1. When active, dNTP triphosphohydrolase activity of SAMHD1 degrades dNTPs into their 2'-deoxynucleoside (dN) and triphosphate subparts, steadily depleting intercellular dNTP pools. The differential expression levels and activation states of SAMHD1 in various cell types contributes to unique dNTP pools that either aid (i.e., dividing T cells) or restrict (i.e., nondividing macrophages) viral replication that consumes cellular dNTPs. Genetic mutations in SAMHD1 induce a rare inflammatory encephalopathy called Aicardi-Goutières syndrome (AGS), which phenotypically resembles viral infection. Recent publications have identified diverse roles for SAMHD1 in double-stranded break repair, genome stability, and the replication stress response through interferon signaling. Finally, a series of SAMHD1 mutations were also reported in various cancer cell types while why SAMHD1 is mutated in these cancer cells remains to investigated. Here, we reviewed a series of studies that have begun illuminating the highly diverse roles of SAMHD1 in virology, immunology, and cancer biology.

Regulation of Virus Replication and T Cell Homeostasis by N6-Methyladenosine

RNA modifications are abundant in eukaryotes, bacteria, and archaea. N⁶-methyladenosine (m⁶A), a type of RNA modification mainly found in messenger RNA (mRNA), has significant effects on the metabolism and function of mRNAs. This modification is governed by three types of proteins, namely methyltransferases as "writers", demethylases as "erasers", and specific m⁶A-binding proteins (YTHDF1-3) as "readers". Further, it is important for the regulation of cell fate and has a critical function in many biological processes including virus replication, stem cell differentiation, and cancer development, and exerts its effect by controlling gene expression. Herein, we summarize recent advances in research on m⁶A in virus replication and T cell regulation, which is a rapidly emerging field that will facilitate the development of antiviral therapies and the study of innate immunity.

Recent advances on T-cell exhaustion in malaria infection

T-cell exhaustion reportedly leads to dysfunctional immune responses of antigen-specific T cells. Investigations have revealed that T cells expand into functionally defective phenotypes with poor recall/memory abilities to parasitic antigens. The exploitation of co-inhibitory pathways represent a highly viable area of translational research that has very well been utilized against certain cancerous conditions. Malaria, at times, evolve into a sustained chronic state where T cells express several co-inhibitory molecules (negative immune checkpoints) facilitating parasite escape and sub-optimal protective responses. Experimental evidence suggests that blockade of co-inhibitory molecules on T cells in malaria could result in the sustenance of protective responses together with dramatic parasite clearance. The role of several co-inhibitory molecules in malaria infection largely remain unclear, and here we discussed the potential applicability of co-inhibitory molecules in the management of malaria with a view to harness protective host responses against chronic disease and associated consequences.

Complement-Opsonized HIV-1 Alters Cross Talk Between Dendritic Cells and Natural Killer (NK) Cells to Inhibit NK Killing and to Upregulate PD-1, CXCR3, and CCR4 on T Cells

Dendritic cells (DCs), natural killer (NK) cells, and T cells play critical roles during primary HIV-1 exposure at the mucosa, where the viral particles become coated with complement fragments and mucosa-associated antibodies. The microenvironment together with subsequent interactions between these cells and HIV at the mucosal site of infection will determine the quality of immune response that ensues adaptive activation. Here, we investigated how complement and immunoglobulin opsonization influences the responses triggered in DCs and NK cells, how this affects their cross talk, and what T cell phenotypes are induced to expand following the interaction. Our results showed that DCs exposed to complement-opsonized HIV (C-HIV) were less mature and had a poor ability to trigger IFN-driven NK cell activation. In addition, when the DCs were exposed to C-HIV, the cytotolytic potentials of both NK cells and CD8 T cells were markedly suppressed. The expression of PD-1 as well as co-expression of negative immune checkpoints TIM-3 and LAG-3 on PD-1 positive cells were increased on both CD4 as well as CD8 T cells upon interaction with and priming by NK–DC cross talk cultures exposed to C-HIV. In addition, stimulation by NK–DC cross talk cultures exposed to C-HIV led to the upregulation of CD38, CXCR3, and CCR4 on T cells. Together, the immune modulation induced during the presence of complement on viral surfaces is likely to favor HIV establishment, dissemination, and viral pathogenesis.

DDX3 in HIV-1 infection and sensing: A paradox

HIV-1 sensors and their signaling features have been an ongoing topic of intense research over the last decade, as these mechanisms fail to establish protective immunity against HIV-1. Here, we discuss how HIV-1 infects dendritic cells (DCs) and which sensors play a role in recognizing viral DNA and RNA in these specialized immune cells. We will elaborate on the RNA helicase DDX3, which is crucial in translation initiation of HIV-1 mRNA, but also fulfills an important role as RNA sensor and inducer of antiviral immunity in DCs. As DDX3 is indispensable for HIV-1 replication, the virus cannot escape sensing by DDX3, which is an important aspect of its function. Last but not least, we will discuss how HIV-1 suppresses DDX3 sensing and how this impacts the viral load in HIV-1-infected individuals.

The Dynamic Interplay between HIV-1, SAMHD1, and the Innate Antiviral Response

The innate immune response constitutes the first cellular line of defense against initial HIV-1 infection. Immune cells sense invading virus and trigger signaling cascades that induce antiviral defenses to control or eliminate infection. Professional antigen-presenting cells located in mucosal tissues, including dendritic cells and macrophages, are critical for recognizing HIV-1 at the site of initial exposure. These cells are less permissive to HIV-1 infection compared to activated CD4⁺ T-cells, which is mainly due to host restriction factors that serve an immediate role in controlling the establishment or spread of viral infection. However, HIV-1 can exploit innate immune cells and their cellular factors to avoid detection and clearance by the host immune system. Sterile alpha motif and HD-domain containing protein 1 (SAMHD1) is the mammalian deoxynucleoside triphosphate triphosphohydrolase responsible for regulating intracellular dNTP pools and restricting the replication of HIV-1 in non-dividing myeloid cells and quiescent CD4⁺ T-cells. Here, we review and analyze the latest literature on the antiviral function of SAMHD1, including the mechanism of HIV-1 restriction and the ability of SAMHD1 to regulate the innate immune response to viral infection. We also provide an overview of the dynamic interplay between HIV-1, SAMHD1, and the cell-intrinsic antiviral response to elucidate how SAMHD1 modulates HIV-1 infection in non-dividing immune cells. A more complete understanding of SAMHD1’s role in the innate immune response to HIV-1 infection may help develop stratagems to enhance its antiviral effects and to more efficiently block HIV-1 replication and avoid the pathogenic result of viral infection.

Acute Malaria Induces PD1+CTLA4+ Effector T Cells with Cell-Extrinsic Suppressor Function

In acute Plasmodium falciparum (P. falciparum) malaria, the pro- and anti-inflammatory immune pathways must be delicately balanced so that the parasitemia is controlled without inducing immunopathology. An important mechanism to fine-tune T cell responses in the periphery is the induction of coinhibitory receptors such as CTLA4 and PD1. However, their role in acute infections such as P. falciparum malaria remains poorly understood. To test whether coinhibitory receptors modulate CD4+ T cell functions in malaria, blood samples were obtained from patients with acute P. falciparum malaria treated in Germany. Flow cytometric analysis showed a more frequent expression of CTLA4 and PD1 on CD4+ T cells of malaria patients than of healthy control subjects. In vitro stimulation with P. falciparum-infected red blood cells revealed a distinct population of PD1+CTLA4+CD4+ T cells that simultaneously produced IFNγ and IL10. This antigen-specific cytokine production was enhanced by blocking PD1/PDL1 and CTLA4. PD1+CTLA4+CD4+ T cells were further isolated based on surface expression of PD1 and their inhibitory function investigated in-vitro. Isolated PD1+CTLA4+CD4+ T cells suppressed the proliferation of the total CD4+ population in response to anti-CD3/28 and plasmodial antigens in a cell-extrinsic manner. The response to other specific antigens was not suppressed. Thus, acute P. falciparum malaria induces P. falciparum-specific PD1+CTLA4+CD4+ Teffector cells that coproduce IFNγ and IL10, and inhibit other CD4+ T cells. Transient induction of regulatory Teffector cells may be an important mechanism that controls T cell responses and might prevent severe inflammation in patients with malaria and potentially other acute infections.

HIV-1 and hijacking of the host immune system: the current scenario

Human immunodeficiency virus (HIV) infection is a major health burden across the world which leads to the development of acquired immune deficiency syndrome (AIDS). This review article discusses the prevalence of HIV, its major routes of transmission, natural immunity, and evasion from the host immune system. HIV is mostly prevalent in Sub-Saharan Africa and low income countries. It is mostly transmitted by sharing syringe needles, blood transfusion, and sexual routes. The host immune system is categorized into three main types; the innate, the adaptive, and the intrinsic immune system. Regarding the innate immune system against HIV, the key players are mucosal membrane, dendritic cells (DCs), complement system, interferon, and host Micro RNAs. The major components of the adaptive immune system exploited by HIV are T cells mainly CD4+ T cells and B cells. The intrinsic immune system confronted by HIV involves (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G) APOBEC3G, tripartite motif 5-α (TRIM5a), terherin, and (SAM-domain HD-domain containing protein) SAMHD1. HIV-1 efficiently interacts with the host immune system, exploits the host machinery, successfully replicates and transmits from one cell to another. Further research is required to explore evasion strategies of HIV to develop novel therapeutic approaches against HIV.

Cervical HPV infection in Romanian women infected with HIV during early childhood

Human papillomavirus (HPV) is the most common cause of cervical cancer worldwide, and Romania has the highest rate of cervical cancer in Europe. Sixty-five young Romanian women infected with HIV during early childhood and 25 control subjects were evaluated for the presence of cervical HPV infection and for cytologic abnormalities. HPV infection was evaluated longitudinally in 42 HIV-infected individuals. Overall 28/65 (43.1%) of HIV-infected and 8/25 (32.0%) of uninfected subjects were infected with HPV, and 21/65 (32.3%) and 6/25 (24%) had high-risk subtypes, respectively. In HIV-infected women, those maintaining or acquiring a new subtype in follow-up were more likely to have a lower nadir (p = 0.04) and current (p = 0.01) CD4 cell counts. The incidence rate for HPV acquisition events was 0.69 per subject per year, and 0.52 for high-risk subtypes. In the HIV-infected group, 9/13 (69.2%) individuals with abnormal cytology progressed at follow-up. Although HPV prevalence was similar to controls, the rate of Pap smear abnormalities was much higher, possibly due to the decreased ability to mount new immune responses. Given the high rate of incident detection of vaccine preventable strains and cytologic progression in this cohort, HPV vaccination may be beneficial at any age in co-infected women.

Short Communication: Low Expression of Activation and Inhibitory Molecules on NK Cells and CD4(+) T Cells Is Associated with Viral Control

Chronic HIV-1 infection induces severe immune alterations, including hyperactivation, exhaustion, and apoptosis. In fact, viral control has been associated with low frequencies of these processes. Here, we evaluated the expression of activation and inhibitory molecules on natural killer (NK) and CD4(+) T cells and plasma levels of proinflammatory cytokines in individuals exhibiting viral control: a cohort of HIV-1-exposed-seronegative individuals (HESN) and a cohort of HIV controllers. There was lower expression of CD69, LAG-3, PD-1, and TIM-3 in both cohorts when compared to a low-risk population or HIV progressors. In addition, HIV controllers exhibited lower plasma levels of proinflamatory molecules TNF-α and IP-10. These findings suggest that individuals exhibiting viral control have lower basal expression of markers associated with cellular activation and particularly immune exhaustion.

SAMHD1 degradation enhances active suppression of dendritic cell maturation by HIV-1

A hallmark of HIV-1 infection is the lack of sterilizing immunity. Dendritic cells (DCs) are crucial in the induction of immunity, and lack of DC activation might underlie the absence of an effective anti-HIV-1 response. We have investigated how HIV-1 infection affects maturation of DCs. Our data show that even though DCs are productively infected by HIV-1, infection does not induce DC maturation. HIV-1 infection actively suppresses DC maturation, as HIV-1 infection inhibited TLR-induced maturation of DCs and thereby decreased the immune stimulatory capacity of DCs. Interfering with SAMHD1 restriction further increased infection of DCs, but did not lead to DC maturation. Notably, higher infection observed with SAMHD1 depletion correlated with a stronger suppression of maturation. Furthermore, blocking reverse transcription rescued TLR-induced maturation. These data strongly indicate that HIV-1 replication does not trigger immune activation in DCs, but that HIV-1 escapes immune surveillance by actively suppressing DC maturation independent of SAMHD1. Elucidation of the mechanism of suppression can lead to promising targets for therapy or vaccine design.

Autologous aldrithiol-2-inactivated HIV-1 combined with polyinosinic-polycytidylic acid-poly-L-lysine carboxymethylcellulose as a vaccine platform for therapeutic dendritic cell immunotherapy

Therapeutic interventions for HIV-1 that successfully augment adaptive immunity to promote killing of infected cells may be a requisite component of strategies to reduce latent cellular reservoirs. Adoptive immunotherapies utilizing autologous monocyte-derived dendritic cells (DCs) that have been activated and antigen loaded ex vivo may serve to circumvent defects in DC function that are present during HIV infection in order to enhance adaptive immune responses. Here we detail the clinical preparation of DCs loaded with autologous aldrithiol-2 (AT-2)-inactivated HIV that have been potently activated with the viral mimic, Polyinosinic-polycytidylic acid-poly-l-lysine carboxymethylcellulose (Poly-ICLC). HIV is first propagated from CD4+ T cells from HIV-infected donors and then rendered non-replicative by chemical inactivation with aldrithiol-2 (AT-2), purified, and quantified. Viral inactivation is confirmed through measurement of Tat-regulated β-galactosidase reporter gene expression following infection of TZM-bl cells. In-process testing for sterility, mycoplasma, LPS, adventitious agents, and removal of AT-2 is performed on viral preparations. Autologous DCs are generated and pulsed with autologous AT-2-inactivated virus and simultaneously stimulated with Poly-ICLC to constitute the final DC vaccine product. Phenotypic identity, maturation, and induction of HIV-specific adaptive immune responses are confirmed via flow cytometric analysis of DCs and cocultured autologous CD4+ and CD8+ T cells. Lot release criteria for the DC vaccine have been defined in accordance with Good Manufacturing Practice (GMP) guidelines. The demonstrated feasibility of this approach has resulted in approval by the FDA for investigational use in antiretroviral (ART) suppressed individuals. We discuss how this optimized DC formulation may enhance the quality of anti-HIV adaptive responses beyond what has been previously observed during DC immunotherapy trials for HIV infection.

Late-emerging strains of HIV induce T-cell homeostasis failure by promoting bystander cell death and immune exhaustion in naïve CD4 and all CD8 T-cells

The mechanisms involved in the decline of CD4 and CD8 T-cells that lead to HIV-induced immune dysregulation are not clearly understood. We hypothesize that late-emerging strains of HIV, such as CXCR4-tropic (X4) virions, induce T-cell homeostasis failure by promoting significantly more bystander cell death, and immune exhaustion in naïve CD4 and all CD8 T-cells, when compared to strain of HIV, such as CCR5-tropic (R5) virions, found early during the course of infection. In the reported study, inactivated X4 virions induced greater bystander cell death in sort-purified naïve CD4 T-cells compared to R5 virions, which was significant (p=0.013), and in memory CD8 T-cells, though the latter was not significant. A clearer understanding of the mechanisms involved in HIV-induced depletion of T-cell numbers and function could lead to therapies that prevent T-cell death and restore immune function. These therapies could improve current anti-retroviral and cure-related treatments by boosting the immune system's own ability to combat the virus.

HIV-Mycobacterium tuberculosis co-infection: a 'danger-couple model' of disease pathogenesis

Tuberculosis (TB) and human immunodeficiency virus (HIV) infection interfere and impact the pathogenesis phenomena of each other. Owing to atypical clinical presentations and diagnostic complications, HIV/TB co-infection continues to be a menace for healthcare providers. Although the increased access to highly active antiretroviral therapy (HAART) has led to a reduction in HIV-associated opportunistic infections and mortality, the concurrent management of HIV/TB co-infection remains a challenge owing to adverse effects, complex drug interactions, overlapping toxicities and tuberculosis -associated immune reconstitution inflammatory syndrome. Several hypotheses have been put forward for the exacerbation of tuberculosis by HIV and vice versa supported by immunological studies. Discussion on the mechanisms produced by infectious cofactors with impact on disease pathology could shed light on how to design potential interventions that could decelerate disease progression. With no vaccine for HIV and lack of an effective vaccine for tuberculosis, it is essential to design strategies against HIV-TB co-infection.

HIV-1 Tat protein induces the production of IDO in human monocyte derived-dendritic cells through a direct mechanism: effect on T cells proliferation

During HIV-1 infection, an increase of indoleamine 2,3 dioxygenase (IDO) expression, and dendritic cells (DC) dysfunction were often associated with AIDS disease progression. In this work, we investigated the effect of HIV-1 Tat protein on the expression of IDO, in MoDCs. We show that Tat induces IDO protein expression and activity in a dose dependent manner by acting at the cell membrane. Using Tat-mutants, we show that the N-Terminal domain, Tat 1–45, but not the central region, Tat 30–72, is sufficient to induce the expression of active IDO. Tat protein is also able to induce several cytokines in MoDCs, including IFN-γ, a strong inducer of IDO. In order to understand whether IDO is induced directly by Tat protein or indirectly following IFN-γ production, complementary experiments were performed and showed that: i) at the kinetic level, Tat induced IDO expression before the production of IFN-γ ii) treatment of MoDCs with Tat-conditioned medium was unable to stimulate IDO expression, iii) coculture of MoDCs in a transwell cell system did not allow IDO expression in MoDCs not previously treated by Tat, iv) direct contact between Tat-treated and untreated MoDCs was not sufficient to induce IDO expression in a Tat-independent manner, and v) treatment of MoDCs in the presence of IFN-γ pathway inhibitors, Jak I and Ly294002, inhibited IFN-γ-induced IDO but had no effect on Tat-induced IDO. At the functional level, our data showed that treatment of MoDCs with Tat led to the inhibition of their capacity to stimulate T cell proliferation. This impairement was totally abolished when the stimulation was performed in the presence of 1MT, an inhibitor of IDO activity, arguing for the implication of the kynurenine pathway. By inducing IDO, Tat protein may be considered, as a viral pathogenic factor, in the dysregulation of the DC functions during HIV-1 infection.

Complement opsonization of HIV-1 results in a different intracellular processing pattern and enhanced MHC class I presentation by dendritic cells

Induction of optimal HIV-1-specific T-cell responses, which can contribute to controlling viral infection in vivo, depends on antigen processing and presentation processes occurring in DCs. Opsonization can influence the routing of antigen processing and pathways used for presentation. We studied antigen proteolysis and the role of endocytic receptors in MHC class I (MHCI) and II (MHCII) presentation of antigens derived from HIV-1 in human monocyte-derived immature DCs (IDCs) and mature DCs, comparing free and complement opsonized HIV-1 particles. Opsonization of virions promoted MHCI presentation by DCs, indicating that complement opsonization routes more virions toward the MHCI presentation pathway. Blockade of macrophage mannose receptor (MMR) and β7-integrin enhanced MHCI and MHCII presentation by IDCs and mature DCs, whereas the block of complement receptor 3 decreased MHCI and MHCII presentation. In addition, we found that IDC and MDC proteolytic activities were modulated by HIV-1 exposure; complement-opsonized HIV-1 induced an increased proteasome activity in IDCs. Taken together, these findings indicate that endocytic receptors such as MMR, complement receptor 3, and β7-integrin can promote or disfavor antigen presentation probably by routing HIV-1 into different endosomal compartments with distinct efficiencies for degradation of viral antigens and MHCI and MHCII presentation, and that HIV-1 affects the antigen-processing machinery.

Molecular signatures of T-cell inhibition in HIV-1 infection

Cellular immune responses play a crucial role in the control of viral replication in HIV-infected individuals. However, the virus succeeds in exploiting the immune system to its advantage and therefore, the host ultimately fails to control the virus leading to development of terminal AIDS. The virus adopts numerous evasion mechanisms to hijack the host immune system. We and others recently described the expression of inhibitory molecules on T cells as a contributing factor for suboptimal T-cell responses in HIV infection both in vitro and in vivo. The expression of these molecules that negatively impacts the normal functions of the host immune armory and the underlying signaling pathways associated with their enhanced expression need to be discussed. Targets to restrain the expression of these molecular markers of immune inhibition is likely to contribute to development of therapeutic interventions that augment the functionality of host immune cells leading to improved immune control of HIV infection. In this review, we focus on the functions of inhibitory molecules that are expressed or secreted following HIV infection such as BTLA, CTLA-4, CD160, IDO, KLRG1, LAG-3, LILRB1, PD-1, TRAIL, TIM-3, and regulatory cytokines, and highlight their significance in immune inhibition. We also highlight the ensemble of transcriptional factors such as BATF, BLIMP-1/PRDM1, FoxP3, DTX1 and molecular pathways that facilitate the recruitment and differentiation of suppressor T cells in response to HIV infection.

Innate immune sensing of HIV-1 by dendritic cells

HIV-1-specific antibodies and CD8(+) cytotoxic T cells are detected in most HIV-1-infected people, yet HIV-1 infection is not eradicated. Contributing to the failure to mount a sterilizing immune response may be the inability of antigen-presenting dendritic cells (DCs) to sense HIV-1 during acute infection, and thus the inability to effectively prime naive, HIV-1-specific T cells. Recent findings related to DC-expressed innate immune factors including SAMHD1, TREX1, and TRIM5 provide a molecular basis for understanding why DCs fail to adequately sense invasion by this deadly pathogen and suggest experimental approaches to improve T cell priming to HIV-1 in prophylactic vaccination protocols.

Th2-Th1 shift with the multiantigenic formulation TERAVAC-HIV-1 in Balb/c mice

In chronic HIV infection a progressive Th1 to Th2/Th0 cytokine-profile shift is related to disease progression. One of the possible benefits of a therapeutic vaccination might be to counterbalance this phenomenon to allow viral replication control under a Th1-type immune response. TERAVAC-HIV-1 is a multiantigenic formulation vaccine candidate against HIV-1 which comprises the recombinant protein CR3 that contains T cell epitopes and the surface and nucleocapsid antigens of Hepatitis B Virus (HBV). Previous studies showed that such virus like particles of the HBV provide a Th1 adjuvant effect. The present studies examined the capacity of TERAVAC to elicit a Th1 response in the presence of an ongoing HIV-specific Th2-type response in Balb/c mice. To examine this issue, we injected subcutaneously the animals with CR3 or viral lysate in alum which resulted in a Th2-type response. The CR3-specific Th2-type response was verified by induction of IL-4 and IL-10 secretion in ex vivo stimulated splenocytes without secretion of IFN-γ and IgG2a antibodies in serum. Further subcutaneous and simultaneous subcutaneous-nasal immunizations of the same mice with TERAVAC promoted IFN-γ secretion and production of IgG2a antibodies in accordance with a Th1-type response. This result suggests a therapeutic benefit of this vaccine candidate in the restoration of the Th1-type HIV-specific cellular response in seropositive patients.

p38 Mitogen-activated protein kinase/signal transducer and activator of transcription-3 pathway signaling regulates expression of inhibitory molecules in T cells activated by HIV-1-exposed dendritic cells

Human immunodeficiency virus type 1 (HIV-1) infection enhances the expression of inhibitory molecules on T cells, leading to T-cell impairment. The signaling pathways underlying the regulation of inhibitory molecules and subsequent onset of T-cell impairment remain elusive. We showed that both autologous and allogeneic T cells exposed to HIV-pulsed dendritic cells (DCs) upregulated cytotoxic T-lymphocyte antigen (CTLA-4), tumor-necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), lymphocyte-activation gene-3 (LAG3), T-cell immunoglobulin mucin-3 (TIM-3), CD160 and certain suppression-associated transcription factors, such as B-lymphocyte induced maturation protein-1 (BLIMP-1), deltex homolog 1 protein (DTX1) and forkhead box P3 (FOXP3), leading to T-cell suppression. This induction was regulated by p38 mitogen-activated protein kinase/signal transducer and activator of transcription-3 (P38MAPK/STAT3) pathways, because their blockade significantly abrogated expression of all the inhibitory molecules studied and a subsequent recovery in T-cell proliferation. Neither interleukin-6 (IL-6) nor IL-10 nor growth factors known to activate STAT3 signaling events were responsible for STAT3 activation. Involvement of the P38MAPK/STAT3 pathways was evident because these proteins had a higher level of phosphorylation in the HIV-1-primed cells. Furthermore, blockade of viral CD4 binding and fusion significantly reduced the negative effects DCs imposed on primed T cells. In conclusion, HIV-1 interaction with DCs modulated their functionality, causing them to trigger the activation of the P38MAPK/STAT3 pathway in T cells, which was responsible for the upregulation of inhibitory molecules.

HIV-1, interferon and the interferon regulatory factor system: an interplay between induction, antiviral responses and viral evasion

Thirty years after the first isolation of the etiological agent of AIDS, the virus HIV-1 is still a major threat worldwide with millions of individuals currently infected. Although current combination therapies allow viral replication to be controlled, HIV-1 is not eradicated and persists in drug- and immune system-insensitive reservoirs and a cure is still lacking. Pathogens such as HIV-1 that cause chronic infections are able to adapt to the host in a manner that ensures long term residence and survival, via the evolution of numerous mechanisms that evade various aspects of the innate and adaptive immune response. One such mechanism is targeted to members of the interferon (IFN) regulatory factor (IRF) family of proteins. These transcription factors regulate a variety of biological processes including interferon induction, immune cell activation and downstream pattern recognition receptors (PRRs). HIV-1 renders IRFs harmless and hijacks them to its own advantage in order to facilitate its replication and evasion of immune responses. Type I interferon (IFN), the canonical antiviral innate response, can be induced in both acute and chronic HIV-1 infection in vivo, but in the majority of individuals this initial response is not protective and can contribute to disease progression. Type I IFN expression is largely inhibited in T cells and macrophages in order to successfully establish productive infection, whereas sustained IFN production by plasmacytoid dendritic cells is considered an important source of chronic immune activation, a hallmark to AIDS progression.

Loss of CD127 & increased immunosenescence of T cell subsets in HIV infected individuals

Background & objectives:

HIV infection is characterized by a perturbation in T cell homeostasis, leading to alteration in T cell subsets. In addition to alteration in differentiation, HIV infection also leads to change in T cell survival and regenerative capacity, as suggested by differential expression of CD127 and CD57. We evaluated the expression patterns of CD127 and CD57 on CD4 and CD8 effector, memory and naïve T cell subsets in HIV-infected and uninfected individuals.

Methods:

We characterized T cell subsets based on expression of these markers, and compared their expression pattern in HIV infected subjects and uninfected controls. We further assessed therapy generated changes in these subsets and expression of CD127 and CD57 on them.

Results:

There was a generalized decrease in naïve CD4 and CD8 T cells in HIV infected subjects. These changes in T cell subset distribution were related to antigen load. CD127 expression was significantly reduced in T cells from HIV infected subject. In association to this, HIV infected subjects had higher percentage of T cell subsets expressing CD57. Increased CD57 and reduced CD127 expression correlated with plasma viraemia and CD8 T cell activation state. Incomplete restoration of T cell subset proportions was observed, despite suppression of viral replication and increase in CD4 T cell counts. Further, the improvement was more pronounced in CD127 expression.

Interpretation & conclusions:

HIV infected subjects have reduced T cell regenerative capacity along with increased senescence, highlighting decreased proliferation and effector activities.

HIV-induced T-cell activation/exhaustion in rectal mucosa is controlled only partially by antiretroviral treatment

Peripheral blood T-cells from untreated HIV-1-infected patients exhibit reduced immune responses, usually associated with a hyperactivated/exhausted phenotype compared to HAART treated patients. However, it is not clear whether HAART ameliorates this altered phenotype of T-cells in the gastrointestinal-associated lymphoid tissue (GALT), the main site for viral replication. Here, we compared T-cells from peripheral blood and GALT of two groups of chronically HIV-1-infected patients: untreated patients with active viral replication, and patients on suppressive HAART. We characterized the T-cell phenotype by measuring PD-1, CTLA-4, HLA-DR, CD25, Foxp3 and granzyme A expression by flow cytometry; mRNA expression of T-bet, GATA-3, ROR-γt and Foxp3, and was also evaluated in peripheral blood mononuclear cells and rectal lymphoid cells. In HIV-1+ patients, the frequency of PD-1⁺ and CTLA-4⁺ T-cells (both CD4+ and CD8+ T cells) was higher in the GALT than in the blood. The expression of PD-1 by T-cells from GALT was higher in HIV-1-infected subjects with active viral replication compared to controls. Moreover, the expression per cell of PD-1 and CTLA-4 in CD4⁺ T-cells from blood and GALT was positively correlated with viral load. HAART treatment decreased the expression of CTLA-4 in CD8⁺ T cells from blood and GALT to levels similar as those observed in controls. Frequency of Granzyme A⁺ CD8⁺ T-cells in both tissues was low in the untreated group, compared to controls and HAART-treated patients. Finally, a switch towards Treg polarization was found in untreated patients, in both tissues. Together, these findings suggest that chronic HIV-1 infection results in an activated/exhausted T-cell phenotype, despite T-cell polarization towards a regulatory profile; these alterations are more pronounced in the GALT compared to peripheral blood, and are only partiality modulated by HAART.

Innate immunity in acute HIV-1 infection

PURPOSE OF REVIEW

Acute HIV-1 infection (AHI) is composed of the eclipse phase, during which the transmitted virus struggles to avoid eradication and achieve amplification/spread; the expansion phase when virus disseminates and undergoes exponential replication associated with extensive CD4⁺ T-cell destruction; and the containment phase when set-point levels of viremia and immune activation are established. The importance of interactions between HIV-1 and innate responses in determining events throughout AHI is increasingly recognized, and is reviewed here.

RECENT FINDINGS

During the eclipse phase, HIV-1 subverts dendritic cell functions to promote its replication at mucosal sites and employs multiple strategies to minimize control by type 1 interferons. Systemic virus dissemination is associated with widespread activation of innate responses which fuels HIV-1 replication. To minimize the protective effects of innate responses, HIV-1 resists control by natural killer cells and may impair innate regulation of adaptive responses. Innate responses remain chronically activated after HIV-1 containment which is thought to drive HIV-1 pathogenesis.

SUMMARY

Innate responses are pivotal determinants of events at all stages of AHI. Increased understanding of mechanisms involved in innate control of HIV-1 and pathways regulating innate activation during HIV-1 infection could facilitate development of novel approaches to combating this infection.

Myeloid dendritic cells in HIV-1 infection

PURPOSE OF REVIEW

Myeloid dendritic cells (mDCs) are pivotal players in HIV-1 infection. They promote transmission and spread and at the same time are critical for recognizing HIV-1 and initiating immune responses to fight infection. Notably, their immunostimulatory capabilities can be harnessed to design better HIV-1 vaccines. In this review, advances in these areas of mDC-HIV-1 interactions are summarized.

RECENT FINDINGS

New insights into HIV-1-induced dysfunction of mDCs and dysfunctional mDC effects on other cell types, as well as novel mechanisms of viral sensing by mDCs and their evasion by HIV-1, have been uncovered. These results emphasize the importance of mDCs in protection against HIV-1 infection. Targeting mDCs with vaccines and tailored adjuvants may improve the quality and anatomical location of elicited immune responses.

SUMMARY

Understanding the multiplicity of HIV-1-dendritic cell interactions together with the numerous advances in targeted therapy and vaccination will help in the rational design of approaches to treat and block infection.

Distinct roles of CD4+ T cell subpopulations in retroviral immunity: lessons from the Friend virus mouse model

It is well established that CD4⁺ T cells play an important role in immunity to infections with retroviruses such as HIV. However, in recent years CD4⁺ T cells have been subdivided into several distinct populations that are differentially regulated and perform widely varying functions. Thus, it is important to delineate the separate roles of these subsets, which range from direct antiviral activities to potent immunosuppression. In this review, we discuss contributions from the major CD4⁺ T cell subpopulations to retroviral immunity. Fundamental concepts obtained from studies on numerous viral infections are presented along with a more detailed analysis of studies on murine Friend virus. The relevance of these studies to HIV immunology and immunotherapy is reviewed.

Expression of PD-L1 and PD-L2 on human macrophages is up-regulated by HIV-1 and differentially modulated by IL-10

PD-1 plays an important role in T cell exhaustion during HIV infection. PD-1 has two ligands: PD-L1, expressed on hematopoietic and nonhematopoietic cells, and PD-L2, limited to DCs and macrophages. Little is known about PD-L1 expression and regulation in human macrophages. Previous reports have found few immediate effects of macrophage exposure to HIV, suggesting that macrophages lack PRRs for this virus. Using quantitative confocal microscopy and a multiplexed cytokine bead array, we measured induction of PD-L1, PD-L2, and innate response cytokines in human MDMs in response to chemically inactivated HIV virions. Consistent with previous reports, no cytokines were induced by HIV virion exposure. Whereas PD-L1 and PD-L2 had low baseline expression, TLR ligands (LPS and CL097) up-regulated PD-L1 but not PD-L2. Unlike what we found for cytokine expression, PD-L1 and PD-L2 were up-regulated in response to exposure with inactivated HIV virions or with replication-competent HIV. Expression of PD-L1 was differentially modulated by IL-10, which induced up-regulation of PD-L1 but not of PD-L2, and IL-10 blockade enhanced only PD-L2 expression. We discuss implications for innate recognition of HIV by macrophages and potential, different roles for PD-L1 and PD-L2 in immunity and pathogenesis.

Expression of a broad array of negative costimulatory molecules and Blimp-1 in T cells following priming by HIV-1 pulsed dendritic cells

Accumulating evidence indicates that immune impairment in persistent viral infections could lead to T-cell exhaustion. To evaluate the potential contribution of induction of negative costimulatory molecules to impaired T-cell responses, we primed naïve T cells with mature monocyte-derived dendritic cells (MDDCs) pulsed with HIV-1 in vitro. We used quantitative real-time polymerase chain reaction and flow cytometry, respectively, to compare the gene and surface-protein expression profiles of naïve T cells primed with HIV-pulsed or mock-pulsed DCs. We detected elevated expressions of negative costimulatory molecules, including lymphocyte activation gene-3 (LAG-3), CD160, cytolytic T-lymphocyte antigen-4 (CTLA-4), T-cell immunoglobulin mucin-containing domain-3 (TIM-3), programmed death-1 (PD-1) and TRAIL (tumor necrosis-factor-related apoptosis-inducing ligand) in T cells primed by HIV-pulsed DCs. The PD-1(+) T-cell population also coexpressed TIM-3, LAG-3, and CTLA-4. Interestingly, we also found an increase in gene expression of the transcriptional repressors Blimp-1 (B-lymphocyte-induced maturation protein-1) and Foxp3 (forkhead transcription factor) in T-cells primed by HIV-pulsed DCs; Blimp-1 expression was directly proportional to the expression of the negative costimulatory molecules. Furthermore, levels of the effector cytokines interleukin-2, tumor necrosis factor-α and interferon-γ, and perforin and granzyme B were decreased in T-cell populations primed by HIV-pulsed DCs. In conclusion, in vitro priming of naïve T-cells with HIV-pulsed DC leads to expansion of T cells with coexpression of a broad array of negative costimulatory molecules and Blimp-1, with potential deleterious consequences for T-cell responses.

Multi-analyte profiling of ten cytokines in South African HIV-infected patients with Immune Reconstitution Inflammatory Syndrome (IRIS)

Background

Immune reconstitution inflammatory syndrome (IRIS) is an important complication of HAART in sub-Saharan Africa, where opportunistic infections (OIs) including mycobacteria and cryptococcus are common. The immune system's role in HIV infected patients is complex with cytokine expression strongly influencing HIV infection and replication.

Methods

We determined the expression patterns of 10 cytokines by Luminex multi-analyte profiling in 17 IRIS nested case-control pairs participating in a prospective South African cohort initiating anti-retroviral therapy.

Results

Interferon-gamma (IFN-γ) expression was significantly elevated in IRIS cases compared to controls (median 9.88 pg/ml versus 2.68 pg/ml, respectively, P = 0.0057), while other cytokines displayed non-significant differences in expression. Significant correlation was observed between IL-6, IL-10, and IFN-γ expression in the IRIS patients.

Conclusions

Significantly increased expression levels of IFN-γ suggest that this cytokine possibly plays a role in IRIS pathology and is a potential diagnostic marker.