Toll-like receptor agonists are potent inhibitors of human immunodeficiency virus-type 1 replication in peripheral blood mononuclear cells

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

The Role of Extracellular Traps in HIV Infection

Human immunodeficiency virus (HIV) infection is still an important public health problem, which justifies the research of new therapies to combat it. Recent studies show that Extracellular Traps (ETs) are cellular mechanisms useful in the capture and destruction of some viruses, such as the HIV. Here, we show that neutrophils from peripheral blood, genital tissues, and placenta are activated when exposed to human immunodeficiency virus type 1 (HIV-1) and release Neutrophil Extracellular Traps (NETs). The NETs can capture, neutralize, and inactivate the virus and, also, protect other target cells from HIV infection, as long as the DNA and other constituents of the NETs remain intact. Further, the review indicates that the immunoprotective role of NETs in the context of HIV-1 infection is a promising finding for the development of new antiviral therapies. It is necessary, however, the development of studies that evaluate the tissue injury that NETs can cause and the biological relationships with other cells to improve them as therapeutic targets.

MiR-155 Negatively Regulates Anti-Viral Innate Responses among HIV-Infected Progressors

HIV infection impairs host immunity, leading to progressive disease. An anti-retroviral treatment efficiently controls viremia but cannot completely restore the immune dysfunction in HIV-infected individuals. Both host and viral factors determine the rate of disease progression. Among the host factors, innate immunity plays a critical role; however, the mechanism(s) associated with dysfunctional innate responses are poorly understood among HIV disease progressors, which was investigated here. The gene expression profiles of TLRs and innate cytokines in HIV-infected (LTNPs and progressors) and HIV-uninfected individuals were examined. Since the progressors showed a dysregulated TLR-mediated innate response, we investigated the role of TLR agonists in restoring the innate functions of the progressors. The stimulation of PBMCs with TLR3 agonist-poly:(I:C), TLR7 agonist-GS-9620 and TLR9 agonist-ODN 2216 resulted in an increased expression of IFN-α, IFN-β and IL-6. Interestingly, the expression of IFITM3, BST-2, IFITM-3, IFI-16 was also increased upon stimulation with TLR3 and TLR7 agonists, respectively. To further understand the molecular mechanism involved, the role of miR-155 was explored. Increased miR-155 expression was noted among the progressors. MiR-155 inhibition upregulated the expression of TLR3, NF-κB, IRF-3, TNF-α and the APOBEC-3G, IFITM-3, IFI-16 and BST-2 genes in the PBMCs of the progressors. To conclude, miR-155 negatively regulates TLR-mediated cytokines as wel l as the expression of host restriction factors, which play an important role in mounting anti-HIV responses; hence, targeting miR-155 might be helpful in devising strategic approaches towards alleviating HIV disease progression.

Toll-like Receptor Response to Human Immunodeficiency Virus Type 1 or Co-Infection with Hepatitis B or C Virus: An Overview

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that play important roles in the early detection of pathogen-associated molecular patterns and shaping innate and adaptive immune responses, which may influence the consequences of infection. Similarly to other viral infections, human immunodeficiency virus type 1 (HIV-1) also modulates the host TLR response; therefore, a proper understanding of the response induced by human HIV-1 or co-infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), due to the common mode of transmission of these viruses, is essential for understanding HIV-1 pathogenesis during mono- or co-infection with HBV or HCV, as well as for HIV-1 cure strategies. In this review, we discuss the host TLR response during HIV-1 infection and the innate immune evasion mechanisms adopted by HIV-1 for infection establishment. We also examine changes in the host TLR response during HIV-1 co-infection with HBV or HCV; however, this type of study is extremely scarce. Moreover, we discuss studies investigating TLR agonists as latency-reverting agents and immune stimulators towards new strategies for curing HIV. This understanding will help develop a new strategy for curing HIV-1 mono-infection or co-infection with HBV or HCV.

The synthetic opioid fentanyl increases HIV replication and chemokine co-receptor expression in vitro

The US is experiencing a major public health crisis that is fueled by the illicit use of synthetic opioids including fentanyl. While several drugs of abuse can enhance viral replication and/or antagonize immune responses, the impact of specific synthetic opioids on HIV pathogenesis is poorly understood. Thus, we evaluated the effects of fentanyl on HIV replication in vitro. HIV-susceptible or HIV-expressing cell lines were incubated with fentanyl. HIV p24 synthesis and chemokine receptor levels were quantified by ELISA in culture supernatants and cell lysates, respectively. Addition of fentanyl resulted in a dose-dependent increase in HIV replication. Fentanyl enhanced expression of the HIV chemokine co-receptors CXCR4 and CCR5 and caused a dose-dependent decrease in cell viability. The opioid antagonist naltrexone blocked the effect of fentanyl on HIV replication and CCR5 receptor levels but not CXCR4 receptor levels. TLR9 expression was induced by HIV; however, fentanyl inhibited TLR9 expression in a dose-dependent manner. These data demonstrate that the synthetic opioid fentanyl can promote HIV replication in vitro. As increased HIV levels are associated with accelerated disease progression and higher likelihood of transmission, additional research is required to enhance the understanding of opioid-virus interactions and to develop new and/or optimized treatment strategies for persons with HIV and opioid use disorder.

The Role of Innate Immunity in Natural Elite Controllers of HIV-1 Infection

The natural process of human immunodeficiency virus type 1(HIV-1) infection is characterized by high viral load, immune cell exhaustion, and immunodeficiency, which eventually leads to the stage of acquired immunodeficiency syndrome (AIDS) and opportunistic infections. Rapidly progressing HIV-1 individuals often die of AIDS several years after infection without treatment. The promotion of ART greatly prolongs the survival time of HIV-infected persons. However, some patients have incomplete immune function reconstruction after ART due to latent storage of HIV-infected cells. Therefore, how to achieve a functional cure has always been the focus and hot spot of global AIDS research. Fortunately, the emergence of ECs/LTNPs who can control virus replication naturally has ignited new hope for realizing a functional cure for AIDS. Recently, a special category of infected individuals has attracted attention that can delay the progression of the disease more rigorously than the natural progression of HIV-1 infection described above. These patients are characterized by years of HIV-1 infection, long-term asymptomatic status, and normal CD4+T cell count without ART, classified as HIV-infected long-term nonprogressors (LTNPs) and elite controllers (ECs). Numerous studies have shown that the host and virus jointly determine the progression of HIV-1 infection, in which the level of innate immunity activation plays an important role. As the first line of defense against pathogen invasion, innate immunity is also a bridge to induce adaptive immunity. Compared with natural progressors, innate immunity plays an antiviral role in HIV-1 infection by inducing or activating many innate immune-related factors in the natural ECs. Learning the regulation of ECs immunity, especially the innate immunity in different characteristics, and thus studying the mechanism of the control of disease progression naturally, will contribute to the realization of the functional cure of AIDS. Therefore, this review will explore the relationship between innate immunity and disease progression in ECs of HIV-1 infection from the aspects of innate immune cells, signaling pathways, cytokines, which is helpful to provide new targets and theoretical references for the functional cure, prevention and control of AIDS, and development of a vaccine.

Nucleic acid nanoparticles (NANPs) as molecular tools to direct desirable and avoid undesirable immunological effects

Nucleic acid nanoparticles (NANPs) represent a highly versatile molecular platform for the targeted delivery of various therapeutics. However, despite their promise, further clinical translation of this innovative technology can be hindered by immunological off-target effects. All human cells are equipped with an arsenal of receptors that recognize molecular patterns specific to foreign nucleic acids and understanding the rules that guide this recognition offer the key rationale for the development of therapeutic NANPs with tunable immune stimulation. Numerous recent studies have provided increasing evidence that in addition to NANPs' physicochemical properties and therapeutic effects, their interactions with cells of the immune system can be regulated through multiple independently programmable architectural parameters. The results further suggest that defined immunomodulation by NANPs can either support their immunoquiescent delivery or be used for conditional stimulation of beneficial immunological responses.

The Role of Toll-Like Receptors in Retroviral Infection

Toll-like receptors (TLRs) are key pathogen sensing receptors that respond to diverse microbial ligands, and trigger both innate and adaptive immune responses to infection. Since their discovery, a growing body of evidence has pointed to an important role for TLRs in retroviral infection and pathogenesis. These data suggest that multiple TLRs contribute to the anti-retroviral response, and that TLR engagement by retroviruses can have complex and divergent outcomes for infection. Despite this progress, numerous questions remain about the role of TLRs in retroviral infection. In this review, I summarize existing evidence for TLR-retrovirus interactions and the functional roles these receptors play in immunity and pathogenesis, with particular focus on human immunodeficiency virus (HIV).

HIV infection suppresses TLR3 activation-mediated antiviral immunity in microglia and macrophages

Monocytic-lineage cells in the central nervous system (CNS), including microglia and brain resident macrophages, are the key players in the CNS innate immunity against viral infections, including human immunodeficiency virus (HIV). However, these cells also serve as the major targets and reservoirs for HIV in the CNS. To address the question of how HIV can establish persistent infection in the target cells in the CNS, we examined whether HIV has the ability to counteract Toll-like receptor 3 (TLR3) activation-mediated antiviral immunity in microglia and macrophages. We observed that HIV latently infected microglial cells (HC69·5) expressed reduced levels of TLR3 and TLR3 activation-mediated interferons (IFN-α/β and IFN-λ) as compared with the uninfected control cells (C20). In addition, HIV infection of primary human macrophages suppressed the expression of TLR3 and the IFNs. HIV infection also inhibited the expression of the antiviral IFN-stimulated genes (ISGs) and the HIV-restriction miRNAs. Mechanistically, HIV infection inhibited the phosphorylation of IFN regulatory factors (IRF3 and IRF7) and signal transducer and activator of transcription proteins (STAT1 and STAT3) in both HIV latently infected microglia and acutely infected macrophages. These findings provide previously unrecognized and sound mechanisms for HIV infection and persistence in the primary target and reservoir cells in the brain.

Increased SAMHD1 transcript expression correlates with interferon-related genes in HIV-1-infected patients

PURPOSE

To investigate the contribution of SAMHD1 to HIV-1 infection in vivo and its relationship with IFN response, the expression of SAMHD1 and IFN-related pathways was evaluated in HIV-1-infected patients.

METHODS

Peripheral blood mononuclear cells (PBMC) from 388 HIV-1-infected patients, both therapy naïve (n = 92) and long-term HAART treated (n = 296), and from 100 gender and age-matched healthy individuals were examined. CD4+ T cells, CD14+ monocytes and gut biopsies were also analyzed in HIV-1-infected subjects on suppressive antiretroviral therapy. Gene expression levels of SAMDH1, ISGs (MxA, MxB, HERC5, IRF7) and IRF3 were evaluated by real-time RT-PCR assays.

RESULTS

SAMHD1 levels in HIV-1-positive patients were significantly increased compared to those in healthy donors. SAMHD1 expression was enhanced in treated patients compared to naïve patients (p < 0.0001) and healthy donors (p = 0.0038). Virologically suppressed treated patients exhibited higher SAMHD1 levels than healthy donors (p = 0.0008), viraemic patients (p = 0.0001) and naïve patients (p < 0.0001). SAMHD1 levels were also increased in CD4+ T cells compared to those in CD14+ monocytes and in PBMC compared to those of GALT. Moreover, SAMHD1 was expressed more strongly than ISGs in HIV-1-infected patients and positive correlations were found between SAMHD1, ISGs and IRF3 levels.

CONCLUSIONS

SAMHD1 is more strongly expressed than the classical IFN-related genes, increased during antiretroviral therapy and correlated with ISGs and IRF3 in HIV-1-infected patients.

Human Endogenous Retroviruses Are Ancient Acquired Elements Still Shaping Innate Immune Responses

About 8% of our genome is composed of sequences with viral origin, namely human Endogenous Retroviruses (HERVs). HERVs are relics of ancient infections that affected the primates' germ line along the last 100 million of years, and became stable elements at the interface between self and foreign DNA. Intriguingly, HERV co-evolution with the host led to the domestication of activities previously devoted to the retrovirus life cycle, providing novel cellular functions. For example, selected HERV envelope proteins have been coopted for pregnancy-related purposes, and proviral Long Terminal Repeats participate in the transcriptional regulation of various cellular genes. Given the HERV persistence in the host genome and its basal expression in most healthy tissues, it is reasonable that human defenses should prevent HERV-mediated immune activation. Despite this, HERVs and their products (including RNA, cytosolic DNA, and proteins) are still able to modulate and be influenced by the host immune system, fascinatingly suggesting a central role in the evolution and functioning of the human innate immunity. Indeed, HERV sequences had been major contributors in shaping and expanding the interferon network, dispersing inducible genes that have been occasionally domesticated in various mammalian lineages. Also the HERV integration within or near to genes encoding for critical immune factors has been shown to influence their activity, or to be responsible for their polymorphic variation in the human population, such as in the case of an HERV-K(HML10) provirus in the major histocompatibility complex region. In addition, HERV expressed products have been shown to modulate innate immunity effectors, being therefore often related on the one side to inflammatory and autoimmune disorders, while on the other side to the control of excessive immune activation through their immunosuppressive properties. Finally, HERVs have been proposed to establish a protective effect against exogenous infections. The present review summarizes the involvement of HERVs and their products in innate immune responses, describing how their intricate interplay with the first line of human defenses can actively contribute either to the host protection or to his damage, implying a subtle balance between the persistence of HERV expression and the maintenance of a basal immune alert.

Recent advances in the discovery and development of TLR ligands as novel therapeutics for chronic HBV and HIV infections

INTRODUCTION

Toll-like receptor (TLR) ligands remain as promising antiviral drug candidates for the treatment of chronic viral infections. Basic research on the mechanisms of antiviral activity of TLR ligands in preclinical animal models and clinical testing of drug candidates have been carried out in recent years. Areas covered: This review provides an overview of the preclinical and clinical testing of TLR ligands in two major viral infections: hepatitis B virus (HBV) and human immunodeficiency virus (HIV). Recent results have further demonstrated the potent antiviral activity of various TLR ligands . A TLR7 agonist is in clinical trials for the treatment of chronic HBV infection while a HBV vaccine using a TLR9 ligand as an adjuvant has proven to be superior to conventional HBV vaccines and has been approved for clinical use. Generally, TLR activation may achieve viral control mainly by promoting adaptive immunity to viral proteins. Expert opinion: Recent research in this field indicates that TLR ligands could be developed as clinically effective drugs if the obstacles concerning toxicity and application routes are overcome. TLR-mediated promotion of adaptive immunity is a major issue for future studies and will determine the future development of TLR ligands as drugs for immunomodulation.

Short-Course Toll-Like Receptor 9 Agonist Treatment Impacts Innate Immunity and Plasma Viremia in Individuals With Human Immunodeficiency Virus Infection

Background.

Treatment with latency reversing agents (LRAs) enhances human immunodeficiency virus type 1 (HIV-1) transcription in vivo but leads to only modest reductions in the size of the reservoir, possibly due to insufficient immune-mediated elimination of infected cells. We hypothesized that a single drug molecule-a novel Toll-like receptor 9 (TLR9) agonist, MGN1703-could function as an enhancer of innate immunity and an LRA in vivo.

Methods.

We conducted a single-arm, open-label study in which 15 virologically suppressed HIV-1-infected individuals on antiretroviral therapy received 60 mg MGN1703 subcutaneously twice weekly for 4 weeks. We characterized plasmacytoid dendritic cell, natural killer (NK), and T-cell activation using flow cytometry on baseline and after 4 weeks of treatment. HIV-1 transcription was quantified by measuring plasma HIV-1 RNA during MGN1703 administration.

Results.

In accordance with the cell type-specific expression of TLR9, MGN1703 treatment led to pronounced activation of plasmacytoid dendritic cells and substantial increases in plasma interferon-α2 levels (P < .0001). Consistently, transcription of interferon-stimulated genes (eg, OAS1, ISG15, Mx1; each P < .0001) were upregulated in CD4+ T cells as demonstrated by RNA sequencing. Further, proportions of activated cytotoxic NK cells and CD8+ T cells increased significantly during MGN1703 dosing, suggesting an enhancement of cellular immune responses. In 6 of 15 participants, plasma HIV-1 RNA increased from <20 copies/mL to >1500 copies/mL (range, 21-1571 copies/mL) during treatment.

Conclusions.

TLR9 agonist treatment in HIV infection has a dual potential by increasing HIV-1 transcription and enhancing cytotoxic NK cell activation, both of which are key outcomes in HIV-1 eradication therapy.

Clinical Trials Registration.

NCT02443935.

Interferons: Reprogramming the Metabolic Network against Viral Infection

Viruses exploit the host and induce drastic metabolic changes to ensure an optimal environment for replication and the production of viral progenies. In response, the host has developed diverse countermeasures to sense and limit these alterations to combat viral infection. One such host mechanism is through interferon signaling. Interferons are cytokines that enhances the transcription of hundreds of interferon-stimulated genes (ISGs) whose products are key players in the innate immune response to viral infection. In addition to their direct targeting of viral components, interferons and ISGs exert profound effects on cellular metabolism. Recent studies have started to illuminate on the specific role of interferon in rewiring cellular metabolism to activate immune cells and limit viral infection. This review reflects on our current understanding of the complex networking that occurs between the virus and host at the interface of cellular metabolism, with a focus on the ISGs in particular, cholesterol-25-hydroxylase (CH25H), spermidine/spermine acetyltransferase 1 (SAT1), indoleamine-2,3-dioxygenase (IDO1) and sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1), which were recently discovered to modulate specific metabolic events and consequently deter viral infection.

Clinical Interventions in HIV Cure Research

Research over the past decade has resulted in a much-improved understanding of how and where HIV persists in patients on otherwise suppressive antiretroviral therapy (ART). It has become clear that the establishment of a latent infection in long-lived cells is the key barrier to curing HIV or allowing for sustained ART-free remission. Informed by in vitro and ex vivo studies, several therapeutic approaches aimed at depleting the pool of latently infected cells have been tested in small-scale experimental clinical trials including studies of ART intensification, genome editing, ART during acute/early infection and latency reversal. Many studies have focused on the use of latency-reversing agents (LRAs) to induce immune- or virus-mediated elimination of virus-producing cells. These trials have been instrumental in establishing safety and have shown that it is possible to impact the state HIV latency in patients on suppressive ART. However, administration of LRAs alone has thus far not demonstrated an effect on the frequency of latently infected cells or the time to virus rebound during analytical interruption of ART. More recently, there has been an enhanced focus on immune-based therapies in the onwards search for an HIV cure including therapeutic vaccines, toll-like receptor agonists, broadly neutralising antibodies, immune checkpoint inhibitors, interferon-α and interleukin therapy. In ongoing studies immunotherapy interventions are also tested in combination with latency reversal. In this chapter, the overall results of these clinical interventions ultimately aimed at a cure for HIV are presented and discussed.

Interferons and beyond: Induction of antiretroviral restriction factors

Antiviral restriction factors are structurally and functionally diverse cellular proteins that play a key role in the first line of defense against viral pathogens. Although many cell types constitutively express restriction factors at low levels, their induction in response to viral exposure and replication is often required for potent control and repulse of the invading pathogens. It is well established that type I IFNs efficiently induce antiviral restriction factors. Accumulating evidence suggests that other types of IFN, as well as specific cytokines, such as IL-27, and other activators of the cell are also capable of enhancing the expression of restriction factors and hence to establish an antiviral cellular state. Agents that efficiently induce restriction factors, increase their activity, and/or render them resistant against viral antagonists without causing general inflammation and significant side effects hold some promise for novel therapeutic or preventive strategies. In the present review, we summarize some of the current knowledge on the induction of antiretroviral restriction factors and perspectives for therapeutic application.

Toll-Like Receptor-3 Mediates HIV-1-Induced Interleukin-6 Expression in the Human Brain Endothelium via TAK1 and JNK Pathways: Implications for Viral Neuropathogenesis

HIV-1-associated neurocognitive disorders (HAND) is associated with blood-brain-barrier (BBB) inflammation, and inflammation involves toll-like receptors (TLRs) signaling. It is not known whether primary human brain microvascular endothelial cells (HBMEC), the major BBB component, express TLRs or whether TLRs are involved in BBB dysfunction and HAND. We demonstrate that HBMEC express TLR3, 4, 5, 7, 9, and 10, and TLR3 was the most abundant. HIV-1 and TLR3 activation increased endothelial TLR3 transcription and expression. HIV-1-positive human subjects showed significantly higher TLR3 expression in brain tissues and blood vessels, with higher TLR3 levels in subjects with HAND. HIV-1 and TLR3 activation increased endothelial IL6 expression by 6-to-127-fold (P < 0.001), activated c-jun(serine-63) and SAPK/JNK(Thr183/Tyr185). HIV-1 upregulated IL6 through interleukin-1 receptor-associated-kinase (IRAK)-1/4/TAK1/JNK pathways, via ATP-dependent JNK activation. TLR3 activation upregulated IL6 through TAK1/JNK pathways, via ATP-dependent or -independent JNK activation. HIV-1 and TLR3 activation also upregulated transcription factors associated with IL6 and TAK1/JNK pathways (Jun, CEBPA, STAT1). Blocking TLR3 activation prevented HIV-1- and TLR3 ligands-induced upregulation of these transcription factors, prevented IL6 transcription and expression, c-jun and JNK activation. HIV-1 and TLR3 ligands significantly increased monocytes adhesion and migration through the BBB, and decreased endothelial claudin-5 expression. Blocking TLR3 and JNK activation prevented HIV-1- and TLR3 ligands-induced claudin-5 downregulation, monocytes adhesion and transendothelial migration. These data suggest that viral immune recognition via endothelial TLR3 is involved in endothelial inflammation and BBB dysfunction in HIV/AIDS and HAND. Our data provides novel insights into the molecular basis of these HIV-1- and TLR3-mediated effects.

Opiate use inhibits TLR9 signaling pathway in vivo: possible role in pathogenesis of HIV-1 infection

The molecular mechanism of opiate use promoting HIV-1 infection is not fully understood. TLR9 is expressed in many immune cells, including monocytes, macrophages, which can recognize viruses and viral products and consequently induce the production of antiviral factors and initiate immune responses. Previous studies have shown that chronic viral infections can overcome and impair TLR9 pathway. We aimed to explore whether opiate use enhances HIV infection through inhibition of TLR9 pathway via a population-based study. A total of 200 subjects were enrolled and divided into four groups as follows: Opiate+ HIV+ (50), Opiate- HIV+ (50), Opiate+ HIV- (50), and healthy control (Opiate- HIV-, 50). All HIV-infected subjects did not receive antiretroviral therapy while they were enrolled in the study. The results showed that opiate use was associated with higher viral load and lower CD4+ T cell count. Opiate use alone led to lower expression of TLR9, IRF7, and IFN-α at the protein level in PBMCs. Combined with HIV-1 infection, opiate use resulted in lower expression of MyD88, ISG56, and MxA. In addition, morphine treatment promoted HIV-1 replication in macrophages via inhibition of TLR9 pathway. Our data reveal that opiate use plays a cofactor role in pathogenesis of HIV-1 infection through inhibition of TLR9 pathway.

Cancer therapies in HIV cure research

PURPOSE OF REVIEW

This article provides an overview of anticancer therapies in various stages of clinical development as potential interventions to target HIV persistence.

RECENT FINDINGS

Epigenetic drugs developed for cancer have been investigated in vitro, ex vivo and in clinical trials as interventions aimed at reversing HIV latency and depleting the amount of virus that persists on antiretroviral therapy. Treatment with histone deacetylase inhibitors induced HIV expression in patients on antiretroviral therapy but did not reduce the frequency of infected cells. Other interventions that may accelerate the decay of latently infected cells, in the presence or absence of latency-reversing therapy, are now being explored. These include apoptosis-promoting agents, nonhistone deacetylase inhibitor compounds to reverse HIV latency and immunotherapy interventions to enhance antiviral immunity such as immune checkpoint inhibitors and Toll-like receptor agonists.

SUMMARY

A curative strategy in HIV will likely need to both reduce the amount of virus that persists on antiretroviral therapy and improve anti-HIV immune surveillance. Although we continue to explore advances in the field of oncology including cancer immunotherapy, there are major differences in the risk-benefit assessment between HIV-infected individuals and patients with malignancies. Drug development specifically targeting HIV persistence will be the key to developing effective interventions with an appropriate safety profile.

Roles of SAMHD1 in antiviral defense, autoimmunity and cancer

The enzyme, sterile α motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1) diminishes infection of human immunodeficiency virus type 1 (HIV-1) by hydrolyzing intracellular deoxynucleotide triphosphates (dNTPs) in myeloid cells and resting CD4+ T cells. This dNTP degradation reduces the dNTP concentration to a level insufficient for viral cDNA synthesis, thereby inhibiting retroviral replication. This antiviral enzymatic activity can be inhibited by viral protein X (Vpx). The HIV-2/SIV Vpx causes degradation of SAMHD1, thus interfering with the SAMHD1-mediated restriction of retroviral replication. Recently, SAMHD1 has been suggested to restrict HIV-1 infection by directly digesting genomic HIV-1 RNA through a still controversial RNase activity. Here, we summarize the current knowledge about structure, antiviral mechanisms, intracellular localization, interferon-regulated expression of SAMHD1. We also describe SAMHD1-deficient animal models and an antiviral drug on the basis of disrupting proteasomal degradation of SAMHD1. In addition, the possible roles of SAMHD1 in regulating innate immune sensing, Aicardi-Goutières syndrome and cancer are discussed in this review.

TLR7/8 agonist induces a post-entry SAMHD1-independent block to HIV-1 infection of monocytes

Background

Monocytes, the primary myeloid cell-type in peripheral blood, are resistant to HIV-1 infection as a result of the lentiviral restriction factor SAMHD1. Toll-like receptors recognize microbial pathogen components, inducing the expression of antiviral host proteins and proinflammatory cytokines. TLR agonists that mimic microbial ligands have been found to have activity against HIV-1 in macrophages. The induction of restriction factors in monocytes by TLR agonist activation has not been well studied. To analyze restriction factor induction by TLR activation in monocytes, we used the imidazoquinoline TLR7/8 agonist R848 and infected with HIV-1 reporter virus that contained packaged viral accessory protein Vpx, which allows the virus to escape SAMHD1-mediated restriction. 

Results

R848 prevented the replication of Vpx-containing HIV-1 and HIV-2 in peripheral blood mononuclear cells and monocytes. The block was post-entry but prior to reverse transcription of the viral genomic RNA. The restriction was associated with destabilization of the genomic RNA molecules of the in-coming virus particle. R848 treatment of activated T cells did not protect them from infection but treated monocytes produced high levels of proinflammatory cytokines, including type-I IFN that protected bystander activated T cells from infection.

Conclusion

The activation of TLR7/8 induces two independent restrictions to HIV-1 replication in monocytes: a cell-intrinsic block that acts post-entry to prevent reverse transcription; and a cell-extrinsic block, in which monocytes produce high levels of proinflammatory cytokines (primarily type-I IFN) that protects bystander monocytes and T lymphocytes. The cell-intrinsic block may result from the induction of a novel restriction factor, which can be termed Lv5 and acts by destabilizing the in-coming viral genomic RNA, either by the induction of a host ribonuclease or by disrupting the viral capsid. TLR agonists are being developed for therapeutic use to diminish the size of the latent provirus reservoir in HIV-1 infected individuals. Such drugs may both induce latent provirus expression and restrict virus replication during treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-016-0316-3) contains supplementary material, which is available to authorized users.

HIV-1-neutrophil interactions trigger neutrophil activation and Toll-like receptor expression

Although neutrophils are the first-line of host defense against infection and express a wide number of pattern recognition receptors (PRRs), the function of these PRRs, including Toll-like receptors (TLRs), in HIV-1 infection remains unclear. TLRs play an important role in innate immunity, and while their involvement in viral immune pathogenesis was recently proposed, little is known about their expression and function during the neutrophil response to HIV-1 exposure. Here, we have shown that freshly isolated human neutrophils from healthy donors exhibited altered TLR expression, which may affect their function, after being challenged with HIV-1, alone or in the presence of TLR agonists. TLRs may promote neutrophil activation, pro-inflammatory cytokine secretion, and the production of reactive oxygen species. To our knowledge, this study is the first demonstration of functional TLR expression on neutrophils in response to HIV-1 treatment, suggesting a possible neutrophil/HIV-1 interaction through TLRs. Although additional studies are required to confirm the function of TLRs in neutrophils, our data clearly suggest that they play a role in the regulation of innate immunity by neutrophils, which could be engaged in HIV-1 pathogenesis or host defense.

Interferon regulatory factor 3 is a key regulation factor for inducing the expression of SAMHD1 in antiviral innate immunity

SAMHD1 is a type I interferon (IFN) inducible host innate immunity restriction factor that inhibits an early step of the viral life cycle. The underlying mechanisms of SAMHD1 transcriptional regulation remains elusive. Here, we report that inducing SAMHD1 upregulation is part of an early intrinsic immune response via TLR3 and RIG-I/MDA5 agonists that ultimately induce the nuclear translocation of the interferon regulation factor 3 (IRF3) protein. Further studies show that IRF3 plays a major role in upregulating endogenous SAMHD1 expression in a mechanism that is independent of the classical IFN-induced JAK-STAT pathway. Both overexpression and activation of IRF3 enhanced the SAMHD1 promoter luciferase activity, and activated IRF3 was necessary for upregulating SAMHD1 expression in a type I IFN cascade. We also show that the SAMHD1 promoter is a direct target of IRF3 and an IRF3 binding site is sufficient to render this promoter responsive to stimulation. Collectively, these findings indicate that upregulation of endogenous SAMHD1 expression is attributed to the phosphorylation and nuclear translocation of IRF3 and we suggest that type I IFN induction and induced SAMHD1 expression are coordinated.

The local environment orchestrates mucosal decidual macrophage differentiation and substantially inhibits HIV-1 replication

Macrophages from the decidua basalis (dM), the main uterine mucosa during pregnancy, are weakly permissive to HIV-1 infection. Here, we investigated the mechanisms underlying this natural control. We show, by using freshly purified decidual macrophages and ex vivo human decidual explants, that the local decidual environment influences dM differentiation and naturally protects these cells from HIV-1 infection. Interferon (IFN)-γ, present in the decidual tissue, contributes to maintenance of the dM phenotype and restricts HIV-1 infection by mechanisms involving the cyclin-dependent kinase inhibitor p21Cip1/Waf1. We also found that activation of Toll-like receptors 7 and 8 expressed by dM reinforces the low permissivity of dM to HIV-1 by restricting viral replication and inducing secretion of cytokines in the decidual environment, including IFN-γ, that shape dM plasticity. A major challenge for HIV-1 eradication is to control infection of tissue-resident macrophages in the female reproductive tract. Our findings provide clues to the development of novel strategies to prevent HIV-1 macrophage infection.

Gut immune dysfunction through impaired innate pattern recognition receptor expression and gut microbiota dysbiosis in chronic SIV infection

HIV targets the gut mucosa early in infection, causing immune and epithelial barrier dysfunction and disease progression. However, gut mucosal sensing and innate immune signaling through mucosal pattern recognition receptors (PRRs) during HIV infection and disease progression are not well defined. Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model of AIDS, we found a robust increase in PRRs and inflammatory cytokine gene expression during the acute SIV infection in both peripheral blood and gut mucosa, coinciding with viral replication. PRR expression remained elevated in peripheral blood following the transition to chronic SIV infection. In contrast, massive dampening of PRR expression was detected in the gut mucosa, despite the presence of detectable viral loads. Exceptionally, expression of Toll-like receptor 4 (TLR4) and TLR8 was downmodulated and diverged from expression patterns for most other TLRs in the gut. Decreased mucosal PRR expression was associated with increased abundance of several pathogenic bacterial taxa, including Pasteurellaceae members, Aggregatibacter and Actinobacillus, and Mycoplasmataceae family. Early antiretroviral therapy led to viral suppression but only partial maintenance of gut PRRs and cytokine gene expression. In summary, SIV infection dampens mucosal innate immunity through PRR dysregulation and may promote immune activation, gut microbiota changes, and ineffective viral clearance.

Toll-like receptor-3 mediates HIV-1 transactivation via NFκB and JNK pathways and histone acetylation, but prolonged activation suppresses Tat and HIV-1 replication

TLR3 has been implicated in the pathogenesis of several viral infections, including SIV- and HIV-1-induced inflammation and AIDS. However the molecular mechanisms of these TLR3-mediated effects are not known, and it is not known whether HIV interacts with cellular TLR3 to affect disease process. Here we investigate the effects of TLR3 ligands on HIV-1 transactivation using both primary human macrophages and cells containing integrated copies of the HIV-1 promoter. We demonstrate that TLR3 activation induced upregulation of transcription factors such as c-Jun, CCAAT/enhancer-binding protein alpha (CEBPA), signal transducer and activator of transcription (STAT)-1, STAT-2, RELB, and nuclear factor kappa-B1 (NFκB1), most of which are known to regulate the HIV promoter activity. We also demonstrate that TLR3 activation increased HIV-1 transactivation via the c-Jun N-terminal kinase (JNK) and NFκB pathways. This was associated with epigenetic modifications, including decreased histone deacetylase activity, increased histone acetyl transferase (HAT) activity, and increased acetylation of histones H3 and H4 at lysine residues in the nucleosome-0 and nucleosome-1 of the HIV-1 promoter. However, prolonged TLR3 activation decreased HIV-1 transactivation, decreased HAT activity and Tat transcription, and suppressed viral replication. Overall, data suggests that TLR3 can act as viral sensor to mediate viral transactivation, cellular signaling, innate immune response, and inflammation in HIV-infected humans. Our study provides novel insights into the molecular basis for these TLR3-mediated effects.

Interplay between HIV-1 and Toll-like receptors in human myeloid cells: friend or foe in HIV-1 pathogenesis?

The Toll-like receptors are the first line of the host response to pathogens, representing an essential component of the innate and adaptive immune response. They recognize different pathogens and trigger responses directed at eliminating the invader and at developing immunologic long-term memory, ultimately affecting viral pathogenesis. In viral infections, sensing of nucleic acids and/or viral structural proteins generally induces a protective immune response. Thus, it is not surprising that many viruses have developed strategies to evade or counteract signaling through the Toll-like receptor pathways, to survive the host defense machinery and ensure propagation. Thus, Toll-like receptor engagement can also be part of viral pathogenic mechanisms. Evidence for a direct interaction of Toll-like receptors with human immunodeficiency virus type 1 (HIV-1) structures has started to be achieved, and alterations of their expression and function have been described in HIV-1-positive subjects. Furthermore, Toll-like receptor triggering by bacterial and viral ligands have been described to modulate HIV-1 replication and host response, leading to protective or detrimental effects. This review covers major advances in the field of HIV-1 interplay with Toll-like receptors, focusing on human myeloid cells (e.g., monocytes/macrophages and dendritic cells). The role of this interaction in the dysregulation of myeloid cell function and in dictating aspects of the multifaceted pathogenesis of acquired immunodeficiency syndrome will be discussed.

Activation of TLR3/interferon signaling pathway by bluetongue virus results in HIV inhibition in macrophages

Bluetongue virus (BTV), a nonenveloped double-stranded RNA virus, is a potent inducer of type Ι interferons in multiple cell systems. In this study, we report that BTV16 treatment of primary human macrophages induced both type I and III IFN expression, resulting in the production of multiple antiviral factors, including myxovirus resistance protein A, 2',5'-oligoadenylate synthetase, and the IFN-stimulated gene 56. Additionally, BTV-treated macrophages expressed increased HIV restriction factors (apolipoprotein B mRNA-editing enzyme catalytic polypeptide 3 G/F/H) and CC chemokines (macrophage inflammatory protein 1-α, macrophage inflammatory protein 1-β, regulated on activation of normal T cell expressed and secreted), the ligands for HIV entry coreceptor CC chemokine receptor type 5. BTV16 also induced the expression of tetherin, which restricts HIV release from infected cells. Furthermore, TLR3 signaling of macrophages by BTV16 resulted in the induction of several anti-HIV microRNAs (miRNA-28, -29a, -125b, -150, -223, and -382). More importantly, the induction of antiviral responses by BTV resulted in significant suppression of HIV in macrophages. These findings demonstrate the potential of BTV-mediated TLR3 activation in macrophage innate immunity against HIV.

Enhancing Interferon Regulatory Factor 7 Mediated Antiviral Responses and Decreasing Nuclear Factor Kappa B Expression Limit HIV-1 Replication in Cervical Tissues

Establishment of a productive HIV-1 infection in the female reproductive tract likely depends on the balance between anti-viral and pro-inflammatory responses leading to activation and proliferation of HIV target cells. Immune modulators that boost anti-viral and depress pro-inflammatory immune responses may decrease HIV-1 infection or replication. Polyinosinic:polycytidylic [Poly (I:C)] has been reported to down-regulate HIV-1 replication in immune cell subsets and lymphoid tissues, yet the scope and mechanisms of poly (I:C) regulation of HIV-1 replication in the cervicovaginal mucosa, the main portal of viral entry in women remain unknown. Using a relevant, underexplored ex vivo cervical tissue model, we demonstrated that poly (I:C) enhanced Interferon Regulatory Factor (IRF)7 mediated antiviral responses and decreased tissue Nuclear Factor Kappa B (NFκB) RNA expression. This pattern of cellular transcription factor expression correlated with decreased HIV-1 transcription and viral release. Reducing IRF7 expression up-regulated HIV-1 and NFκB transcription, providing proof of concept for the critical involvement of IRF7 in cervical tissues. By combining poly (I:C) with a suboptimal concentration of tenofovir, the leading anti-HIV prophylactic microbicide candidate, we demonstrated an earlier and greater decrease in HIV replication in poly (I:C)/tenofovir treated tissues compared with tissues treated with tenofovir alone, indicating overall improved efficacy. Poly (I:C) decreases HIV-1 replication by stimulating IRF7 mediated antiviral responses while reducing NFκB expression. Early during the infection, poly (I:C) improved the anti-HIV-1 activity of suboptimal concentrations of tenofovir likely to be present during periods of poor adherence i.e. inconsistent or inadequate drug use. Understanding interactions between anti-viral and pro-inflammatory immune responses in the genital mucosa will provide crucial insights for the identification of targets that can be harnessed to develop preventative combination strategies to improve the efficacy of topical or systemic antiviral prophylactic agents and protect women from HIV-1 and other sexually transmitted infections.

Toll-like receptor 3 signaling inhibits simian immunodeficiency virus replication in macrophages from rhesus macaques

Toll-like receptor 3 (TLR3) recognizes double-stranded RNA and induces multiple intracellular events responsible for innate antiviral immunity against viral infections. Here we demonstrate that TLR3 signaling of monocyte-derived macrophages (MDM) from rhesus monkeys by poly I:C inhibited simian immunodeficiency virus (SIV) infection and replication. Investigation of the mechanisms showed that TLR3 activation resulted in the induction of type I and type III interferons (IFNs) and IFN-inducible antiviral factors, including APOBEC3G (A3G), tetherin and SAMHD1. In addition, poly I:C-treated macaque macrophages expressed increased levels of CC chemokines including CCL3, CCL4 and CCL5, the ligands for HIV or SIV coreceptor CCR5. Furthermore, TLR3 signaling of macaque macrophages induced the expression of cellular microRNAs (miR-29a, -29b, -146a and -9), the newly identified intracellular SIV restriction factors. TLR3 activation-mediated anti-SIV effect could be compromised by the knockdown of IRF3 and IRF7. These findings indicate that TLR3-mediated induction of multiple viral restriction factors contribute to the inhibition of SIV infection in macaque macrophages, which support future preclinical studies using rhesus macaques to determine whether in vivo TLR3 activation is safe and beneficial for treating people infected with HIV.