Reversal of HIV-1 latency with anti-microRNA inhibitors

HibeRNAtion: HIV-1 RNA Metabolism and Viral Latency

HIV-1 infection remains non-curative due to the latent reservoir, primarily a small pool of resting memory CD4+ T cells bearing replication-competent provirus. Pharmacological reversal of HIV-1 latency followed by intrinsic or extrinsic cell killing has been proposed as a promising strategy to target and eliminate HIV-1 viral reservoirs. Latency reversing agents have been extensively studied for their role in reactivating HIV-1 transcription in vivo, although no permanent reduction of the viral reservoir has been observed thus far. This is partly due to the complex nature of latency, which involves strict intrinsic regulation at multiple levels at transcription and RNA processing. Still, the molecular mechanisms that control HIV-1 latency establishment and maintenance have been almost exclusively studied in the context of chromatin remodeling, transcription initiation and elongation and most known LRAs target LTR-driven transcription by manipulating these. RNA metabolism is a largely understudies but critical mechanistic step in HIV-1 gene expression and latency. In this review we provide an update on current knowledge on the role of RNA processing mechanisms in viral gene expression and latency and speculate on the possible manipulation of these pathways as a therapeutic target for future cure studies.

Biological differentiation of traditional Chinese medicine from excessive to deficient syndromes in AIDS: Comparative microRNA microarray profiling and syndrome-specific biomarker identification

Traditional Chinese medicine (TCM) has been widely applied as a supplementary therapy of human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) in China. TCM has a positive effect on improving the quality of life, prolonging life, and ameliorating the symptoms of HIV/AIDS patients. Yang deficiency of spleen and kidney (YDSK) syndrome is a typical deficient TCM syndrome in AIDS patients, and accumulation of heat-toxicity (AHT) syndrome is a common excessive syndrome in the earlier stage of AIDS. Thus, accurate diagnosis of these two syndromes can improve the targeted treatment effect, and predict the prognosis of the disease. However, the scientific basis of TCM syndromes remains lacking, greatly hindering the accuracy of diagnosis and effectiveness of treatment. In this research, microRNA (miRNA) microarray and quantitative real-time polymerase chain reaction combined with bioinformatics were used for comparative analysis between YDSK and AHT patients. Significantly differential expressed miRNAs (SDE-miRNAs) of each TCM syndrome were identified, including hsa-miR-766-3p and hsa-miR-1260a and so on, as well hsa-miR-6124, hsa-let-7g-5p and so on, for YDSK and AHT, respectively. Biological differences were found between their SDE-miRNAs based on bioinformatics analyses, for example, ErbB signaling pathway mainly linked to AHT, while focal adhesion dominated in YDSK. Syndrome-specific SDE-miRNAs were further identified as potential biomarkers, including hsa-miR-30e-5p, hsa-miR-144-5p for YDSK and hsa-let-7g-5p, hsa-miR-126-3p for AHT, respectively. All of them have laid biological and clinical bases for TCM diagnosis and treatment of AIDS syndrome at the miRNA level, offering potential diagnostic indicators of immune reconstitution.

An insight on promising strategies hoping to cure HIV-1 infection by targeting Rev protein-short review

Human immunodeficiency virus-1 (HIV-1) infection remains to be one of the major threats throughout the world. Many researchers are working in this area to find a cure for HIV-1. The group of the FDA approved drugs which are currently used against HIV-1 in the clinical practice include nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), integrase inhibitors (InIs), and protease inhibitors (PIs). Fixed dose combinations (FDCs) of these drugs are available and are used as per the anti-retroviral therapy (ART) guidelines. Despite these, unfortunately, there is no cure for HIV1 infection to date. The present review is focused upon describing the importance of a post-transcriptional regulatory protein "Rev", responsible for latent HIV-1 infection as a possible, and promising therapeutic target against HIV-1.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of “shock and kill” to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current “shock and kill” strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

Strategies to eradicate HIV from infected patients: elimination of latent provirus reservoirs

35 years since identification of HIV as the causative agent of AIDS, and 35 million deaths associated with this disease, significant effort is now directed towards the development of potential cures. Current anti-retroviral (ART) therapies for HIV/AIDS can suppress virus replication to undetectable levels, and infected individuals can live symptom free so long as treatment is maintained. However, removal of therapy allows rapid re-emergence of virus from a highly stable reservoir of latently infected cells that exist as a barrier to elimination of the infection with current ART. Prospects of a cure for HIV infection are significantly encouraged by two serendipitous cases where individuals have entered remission following stem cell transplantation from compatible HIV-resistant donors. However, development of a routine cure that could become available to millions of infected individuals will require a means of specifically purging cells harboring latent HIV, preventing replication of latent provirus, or destruction of provirus genomes by gene editing. Elimination of latently infected cells will require a means of exposing this population, which may involve identification of a natural specific biomarker or therapeutic intervention to force their exposure by reactivation of virus expression. Accordingly, the proposed "Shock and Kill" strategy involves treatment with latency-reversing agents (LRA) to induce HIV provirus expression thus exposing these cells to killing by cellular immunity or apoptosis. Current efforts to enable this strategy are directed at developing improved combinations of LRA to produce broad and robust induction of HIV provirus and enhancing the elimination of cells where replication has been reactivated by targeted immune modulation. Alternative strategies may involve preventing re-emergence virus from latently infected cells by "Lock and Block" intervention, where transcription of provirus is inhibited to prevent virus spread or disruption of the HIV provirus genome by genome editing.

RNAa Induced by TATA Box-Targeting MicroRNAs

Recent studies reveal that some nuclear microRNAs (miRNA) and synthesized siRNAs target gene promoters to activate gene transcription (RNAa). Interestingly, our group identified a novel HIV-1-encoded miRNA, miR-H3, which targets specifically the core promoter TATA box of HIV-1 and activates viral gene expression. Depletion of miR-H3 significantly impaired the replication of HIV-1. miR-H3 mimics could activate viruses from CD4⁺ T cells isolated from patients receiving suppressive highly active antiretroviral therapy, which is very intriguing for reducing HIV-1 latent reservoir. Further study revealed that many cellular miRNAs also function like miR-H3. For instance, let-7i targets the TATA box of the interleukin-2 (IL-2) promoter and upregulates IL-2 expression in T-lymphocytes. In RNAa induced by TATA box-targeting miRNAs, Argonaute (AGO) proteins are needed, but there is no evidence for the involvement of promoter-associated transcripts or epigenetic modifications. We propose that the binding of small RNA-AGO complex to TATA box could facilitate the assembly of RNA Polymerase II transcription preinitiation complex. In addition, synthesized small RNAs targeting TATA box can also efficiently activate transcription of interested genes, such as insulin, IL-2, and c-Myc. The discovery of RNAa induced by TATA box-targeting miRNA provides an easy-to-use tool for activating gene expression.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of "shock and kill" to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current "shock and kill" strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

Non-coding RNAs and retroviruses

Retroviruses can cause severe diseases such as cancer and acquired immunodeficiency syndrome. A unique feature in the life cycle of retroviruses is that their RNA genome is reverse transcribed into double-stranded DNA, which then integrates into the host genome to exploit the host machinery for their benefits. The metazoan genome encodes numerous non-coding RNAs (ncRNA), which act as key regulators in essential cellular processes such as antiviral response. The development of next-generation sequencing technology has greatly accelerated the detection of ncRNAs from viruses and their hosts. ncRNAs have been shown to play important roles in the retroviral life cycle and virus–host interactions. Here, we review recent advances in ncRNA studies with special focus on those have changed our understanding of retroviruses or provided novel strategies to treat retrovirus-related diseases. Many ncRNAs such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are involved in the late phase of the retroviral life cycle. However, their roles in the early phase of viral replication merit further investigations.

Two cellular microRNAs, miR-196b and miR-1290, contribute to HIV-1 latency

Understanding the mechanism of HIV-1 latency is crucial to the viral reservoir eradication. Human cellular miRNAs can modulate HIV-1 expression by targeting of viral RNAs or host gene transcripts. To identify miRNAs modulating HIV-1 latency, we determined the miRNA expression profiles of HIV-1 latently infected and productively infected cells by microarray and qRT-PCR. Among the differentially expressed miRNAs, miR-196b and miR-1290 targeted the 3' untranslated region of HIV-1 and affected its expression. Ectopic expression of these two miRNAs efficiently suppressed HIV-1 production and infectivity. Specific inhibitors of these miRNAs substantially counteracted their effects on HIV-1, as measured either as viral production and infectivity in HEK-293T cells or as HIV-1 RNA expression or viral production in cells isolated from HIV-1-infected individuals. Our study emphasizes the role of cellular miRNAs in HIV-1 latency regulation, and it suggests that inhibitors of miR-196b and miR-1290 could be used to activate latent HIV-1.

Sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1)-facilitated HIV restriction in astrocytes is regulated by miRNA-181a

Background

Although highly active antiretroviral therapy (HAART) has significantly reduced the morbidity and mortality in HIV patients, virus continues to reside in the central nervous system (CNS) reservoir. Hence, a complete eradication of virus remains a challenge. HIV productively infects microglia/macrophages, but astrocytes are generally restricted to HIV infection. The relative importance of the possible replication blocks in astrocytes, however, is yet to be delineated. A recently identified restriction factor, sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1), restricts HIV infection in resting CD4⁺T cells and in monocyte-derived dendritic cells. However, SAMHD1 expression and HIV-1 restriction activity regulation in the CNS cells are unknown. Though, certain miRNAs have been implicated in HIV restriction in resting CD4⁺T cells, their role in the CNS HIV restriction and their mode of action are not established. We hypothesized that varying SAMHD1 expression would lead to restricted HIV infection and host miRNAs would regulate SAMHD1 expression in astrocytes.

Results

We found increased SAMHD1 expression and decreased miRNA expression (miR-181a and miR-155) in the astrocytes compared to microglia. We report for the first time that miR-155 and miR-181a regulated the SAMHD1 expression. Overexpression of these cellular miRNAs increased viral replication in the astrocytes, through SAMHD1 modulation. Reactivation of HIV replication was accompanied by decrease in SAMHD1 expression.

Conclusions

Here, we provide a proof of concept that increased SAMHD1 in human astrocytes is in part responsible for the HIV restriction, silencing of which relieves this restriction. At this time, this concept is of theoretical nature. Further experiments are needed to confirm if HIV replication can be reactivated in the CNS reservoir.

miR-28-3p is a cellular restriction factor that inhibits human T cell leukemia virus, type 1 (HTLV-1) replication and virus infection

Human T cell leukemia virus, type 1 (HTLV-1) replication and spread are controlled by different viral and cellular factors. Although several anti-HIV cellular microRNAs have been described, such a regulation for HTLV-1 has not been reported. In this study, we found that miR-28-3p inhibits HTLV-1 virus expression and its replication by targeting a specific site within the genomic gag/pol viral mRNA. Because miR-28-3p is highly expressed in resting T cells, which are resistant to HTLV-1 infection, we investigated a potential protective role of miR-28-3p against de novo HTLV-1 infection. To this end, we developed a new sensitive and quantitative assay on the basis of the detection of products of reverse transcription. We demonstrate that miR-28-3p does not prevent virus receptor interaction or virus entry but, instead, induces a post-entry block at the reverse transcription level. In addition, we found that HTLV-1, subtype 1A isolates corresponding to the Japanese strain ATK-1 present a natural, single-nucleotide polymorphism within the miR-28-3p target site. As a result of this polymorphism, the ATK-1 virus sequence was not inhibited by miR-28. Interestingly, genetic studies on the transmission of the virus has shown that the ATK-1 strain, which carries a Thr-to-Cys transition mutation, is transmitted efficiently between spouses, suggesting that miR-28 may play an important role in HTLV-1 transmission.

The emerging role of miRNAs in inflammatory bowel disease: a review

Inflammatory bowel disease (IBD), comprised of ulcerative colitis and Crohn's disease, is believed to develop as a result of a deregulated inflammatory response to environmental factors in genetically susceptible individuals. Despite advances in understanding the genetic risks of IBD, associated single nucleotide polymorphisms have low penetrance, monozygotic twin studies suggest a low concordance rate, and increasing worldwide IBD incidence leave gaps in our understanding of IBD heritability and highlight the importance of environmental influences. Operating at the interface between environment and heritable molecular and cellular phenotypes, microRNAs (miRNAs) are a class of endogenous, small noncoding RNAs that regulate gene expression. Studies to date have identified unique miRNA expression profile signatures in IBD and preliminary functional analyses associate these deregulated miRNAs to canonical pathways associated with IBD pathogenesis. In this review, we summarize and discuss the miRNA expression signatures associated with IBD in tissue and peripheral blood, highlight miRNAs with potential future clinical applications as diagnostic and therapeutic targets, and provide an outlook on how to develop miRNA based therapies.

Stochastic population switch may explain the latent reservoir stability and intermittent viral blips in HIV patients on suppressive therapy

Highly active antiretroviral therapy can suppress plasma viral loads of HIV-1 infected individuals to below the detection limit of standard clinical assays. However, low-level viremia still persists. Many patients also have transient viral load measurements above the detection limit (the so-called "viral blips"). The latent reservoir consisting of latently infected CD4+ T cells represents a major obstacle to HIV-1 eradication. These cells can be activated to produce virions but the size of the latent reservoir is relatively stable. The mechanisms underlying low viral load persistence, emergence of intermittent viral blips and stability of the latent reservoir are not well understood. Cellular and viral transcription factors play an important role in the establishment and maintenance of HIV-1 latency. Infected cells with intermediate transcriptional activities may either revert to a latent state or become highly activated and produce virions due to intracellular perturbations. Here we develop a mathematical model that includes such stochastic population switch. We demonstrate that the model can generate a stable latent reservoir, intermittent viral blips, as well as low-level viremia persistence. Latently infected cells with intermediate transcription activities may maintain their size through a high level of homeostatic proliferation, while cells with low transcriptional activities are likely to be maintained through the reversion from cells with intermediate transcription activities. Simulations also suggest that treatment intensification or activation therapy may not help to eradicate the latent reservoir. Blocking the proliferation of latently infected cells might be a good strategy. These results provide more insights into the long-term dynamics of virus and latently infected cells in HIV patients on suppressive therapy and may help to develop novel treatment strategies.

HIV-1 latency in monocytes/macrophages

Human immunodeficiency virus type 1 (HIV-1) targets CD4⁺ T cells and cells of the monocyte/macrophage lineage. HIV pathogenesis is characterized by the depletion of T lymphocytes and by the presence of a population of cells in which latency has been established called the HIV-1 reservoir. Highly active antiretroviral therapy (HAART) has significantly improved the life of HIV-1 infected patients. However, complete eradication of HIV-1 from infected individuals is not possible without targeting latent sources of infection. HIV-1 establishes latent infection in resting CD4⁺ T cells and findings indicate that latency can also be established in the cells of monocyte/macrophage lineage. Monocyte/macrophage lineage includes among others, monocytes, macrophages and brain resident macrophages. These cells are relatively more resistant to apoptosis induced by HIV-1, thus are important stable hideouts of the virus. Much effort has been made in the direction of eliminating HIV-1 resting CD4⁺ T-cell reservoirs. However, it is impossible to achieve a cure for HIV-1 without considering these neglected latent reservoirs, the cells of monocyte/macrophage lineage. In this review we will describe our current understanding of the mechanism of latency in monocyte/macrophage lineage and how such cells can be specifically eliminated from the infected host.

Host microRNA regulation of human cytomegalovirus immediate early protein translation promotes viral latency

Reactivation of human cytomegalovirus (HCMV) is a significant cause of disease and death in immunocompromised patients, underscoring the need to understand how latency is controlled. Here we demonstrate that HCMV has evolved to utilize cellular microRNAs (miRNAs) in cells that promote latency to regulate expression of a viral protein critical for viral reactivation. Our data reveal that hsa-miR-200 miRNA family members target the UL122 (immediate early protein 2) 3' untranslated region, resulting in repression of this viral protein. Utilizing recombinant viruses that mutate the miRNA-binding site compared to the sequence of the wild-type virus results in lytic rather than latent infections in ex vivo infections of primary CD34+ cells. Cells permissive for lytic replication demonstrate low levels of these miRNAs. We propose that cellular miRNA regulation of HCMV is critical for maintenance of viral latency.

IMPORTANCE

Human cytomegalovirus (HCMV) is a herpesvirus that infects a majority of the population. Once acquired, individuals harbor the virus for life, where the virus remains, for the most part, in a quiet or latent state. Under weakened immune conditions, the virus can reactivate, which can cause severe disease and often death. We have found that members of a family of small RNAs, termed microRNAs, encoded by human myeloid progenitor cells are capable of repressing a key viral protein, thus enabling the virus to ensure a quiet/latent state. As these progenitor cells mature further down the myeloid lineage toward cells that support active viral replication, the levels of these microRNAs decrease. Together, our data suggest that host cell microRNA regulation of HCMV is important for the quiet/latent state of this pathogen.

RNA viruses and microRNAs: challenging discoveries for the 21st century

RNA viruses represent the predominant cause of many clinically relevant viral diseases in humans. Among several evolutionary advantages acquired by RNA viruses, the ability to usurp host cellular machinery and evade antiviral immune responses is imperative. During the past decade, RNA interference mechanisms, especially microRNA (miRNA)-mediated regulation of cellular protein expression, have revolutionized our understanding of host-viral interactions. Although it is well established that several DNA viruses express miRNAs that play crucial roles in their pathogenesis, expression of miRNAs by RNA viruses remains controversial. However, modulation of the miRNA machinery by RNA viruses may confer multiple benefits for enhanced viral replication and survival in host cells. In this review, we discuss the current literature on RNA viruses that may encode miRNAs and the varied advantages of engineering RNA viruses to express miRNAs as potential vectors for gene therapy. In addition, we review how different families of RNA viruses can alter miRNA machinery for productive replication, evasion of antiviral immune responses, and prolonged survival. We underscore the need to further explore the complex interactions of RNA viruses with host miRNAs to augment our understanding of host-virus interplay.

miRNAs: small molecules with a big impact on HIV infection and pathogenesis

miRNAs belong to a class of small noncoding RNAs that regulate gene expression at the post-transcriptional level. These are approximately 22-nt long sequences and control expression of 30–60% of all human genes, which has considerable significance in HIV infection, especially the way in which host–virus interaction occurs in vivo. Over the course of human evolution, viruses too have evolved, but there is still controversy surrounding the presence of miRNAs encoded by HIV. Considering the wide involvement of miRNAs in host gene regulation during infection and their association with HIV, this review provides insights into miRNAs encoded by the host and their role in host–virus interactions in addition to controlling host gene expression.

Epigenetic regulation of HIV-1 persistence and evolving strategies for virus eradication

Despite the intense effort put by researchers globally to understand Human Immunodeficiency Virus (HIV-1) pathogenesis since its discovery 30 years ago, the acquired knowledge till date is not good enough to eradicate HIV-1 from an infected individual. HIV-1 infects cells of the human immune system and integrates into the host cell genome thereby leading to persistent infection in these cells. Based on the activation status of the cells, the infection could be productive or result in latent infection. The current regimen used to treat HIV-1 infection in an AIDS patient includes combination of antiretroviral drugs called Highly Active Anti-Retroviral Therapy (HAART). A major challenge for the success of HAART has been these latent reservoirs of HIV which remain hidden and pose major hurdle for the eradication of virus. Combination of HAART therapy with simultaneous activation of latent reservoirs of HIV-1 seems to be the future of anti-retroviral therapy; however, this will require a much better understanding of the mechanisms and regulation of HIV-1 latency. In this chapter, we have tried to elaborate on HIV-1 latency, highlighting the strategies employed by the virus to ensure persistence in the host with specific focus on epigenetic regulation of latency. A complete understanding of HIV-1 latency will be extremely essential for ultimate eradication of HIV-1 from the human host.

Nanoparticle-based therapy in an in vivo microRNA-155 (miR-155)-dependent mouse model of lymphoma

MicroRNA-155 (miR-155) is an oncogenic microRNA that regulates several pathways involved in cell division and immunoregulation. It is overexpressed in numerous cancers, is often correlated with poor prognosis, and is thus a key target for future therapies. In this work we show that overexpression of miR-155 in lymphoid tissues results in disseminated lymphoma characterized by a clonal, transplantable pre-B-cell population of neoplastic lymphocytes. Withdrawal of miR-155 in mice with established disease results in rapid regression of lymphadenopathy, in part because of apoptosis of the malignant lymphocytes, demonstrating that these tumors are dependent on miR-155 expression. We show that systemic delivery of antisense peptide nucleic acids encapsulated in unique polymer nanoparticles inhibits miR-155 and slows the growth of these "addicted" pre-B-cell tumors in vivo, suggesting a promising therapeutic option for lymphoma/leukemia.

Achieving a cure for HIV infection: do we have reasons to be optimistic?

The introduction of highly active antiretroviral therapy (HAART) in 1996 has transformed a lethal disease to a chronic pathology with a dramatic decrease in mortality and morbidity of AIDS-related symptoms in infected patients. However, HAART has not allowed the cure of HIV infection, the main obstacle to HIV eradication being the existence of quiescent reservoirs. Several other problems have been encountered with HAART (such as side effects, adherence to medication, emergence of resistance and cost of treatment), and these motivate the search for new ways to treat these patients. Recent advances hold promise for the ultimate cure of HIV infection, which is the topic of this review. Besides these new strategies aiming to eliminate the virus, efforts must be made to improve current HAART. We believe that the cure of HIV infection will not be attained in the short term and that a strategy based on purging the reservoirs has to be associated with an aggressive HAART strategy.

MicroRNAs and their potential involvement in HIV infection

Treatment and cure of HIV-1 infection remain one of the greatest therapeutic challenges owing to its persistent infection, which often leads to AIDS. Although it has been 28 years since the discovery of the virus, the development of an effective vaccine is still years away. Relatively newly discovered miRNAs are a family of small noncoding RNAs that can regulate gene expression primarily by binding to the 3' untranslated region of targeted transcripts. An understanding of how HIV-1 infection affects the host miRNA pathway could generate new insights into the basic mechanisms underlying HIV-1-mediated pathologies and T-lymphocyte depletion. Here, we review literature on the biogenesis of HIV-1-encoded miRNAs, cellular miRNAs that can directly target HIV-1 or essential cellular factors required for HIV-1 replication. We also discuss the feasibility of using miRNAs for HIV-1 therapy.

RNAi and cellular miRNAs in infections by mammalian viruses

MicroRNAs (miRNAs) play an essential role in the regulation of eukaryotic gene expression. Recent studies demonstrate that miRNAs can also strongly affect the replication of pathogenic viruses. For example, cellular miRNAs can target and repress the expression of viral mRNAs, but there is also at least one example of a cellular miRNA that stimulates virus replication. Furthermore, viruses can encode their own miRNAs, trigger changes in cellular miRNA expression or encode RNA silencing suppressor factors that inhibit cellular miRNAs. These interactions together form a complex regulatory network that controls both viral and host gene expression, which ultimately determines the outcome of viral infection at the cellular level and disease progression in the host. Here, we summarize the literature data on such virus–cell interactions in mammals and discuss how miRNAs can be used as research tools or targets in the development of novel antiviral therapeutics.

Immune reconstitution under antiretroviral therapy: the new challenge in HIV-1 infection

Although highly active antiretroviral therapy has enabled constant progress in reducing HIV-1 replication, in some patients who are "aviremic" during treatment, the problem of insufficient immune restoration remains, and this exposes them to the risk of immune deficiency-associated pathologies. Various mechanisms may combine and account for this impaired immunologic response to treatment. A first possible mechanism is immune activation, which may be because of residual HIV production, microbial translocation, co-infections, immunosenescence, or lymphopenia per se. A second mechanism is ongoing HIV replication. Finally, deficient thymus output, sex, and genetic polymorphism influencing apoptosis may impair immune reconstitution. In this review we will discuss the tools at our disposal to identify the various mechanisms at work in a given patient and the specific therapeutic strategies we could propose based on this etiologic diagnosis.

Molecular control of HIV-1 postintegration latency: implications for the development of new therapeutic strategies

The persistence of HIV-1 latent reservoirs represents a major barrier to virus eradication in infected patients under HAART since interruption of the treatment inevitably leads to a rebound of plasma viremia. Latency establishes early after infection notably (but not only) in resting memory CD4⁺ T cells and involves numerous host and viral trans-acting proteins, as well as processes such as transcriptional interference, RNA silencing, epigenetic modifications and chromatin organization. In order to eliminate latent reservoirs, new strategies are envisaged and consist of reactivating HIV-1 transcription in latently-infected cells, while maintaining HAART in order to prevent de novo infection. The difficulty lies in the fact that a single residual latently-infected cell can in theory rekindle the infection. Here, we review our current understanding of the molecular mechanisms involved in the establishment and maintenance of HIV-1 latency and in the transcriptional reactivation from latency. We highlight the potential of new therapeutic strategies based on this understanding of latency. Combinations of various compounds used simultaneously allow for the targeting of transcriptional repression at multiple levels and can facilitate the escape from latency and the clearance of viral reservoirs. We describe the current advantages and limitations of immune T-cell activators, inducers of the NF-κB signaling pathway, and inhibitors of deacetylases and histone- and DNA- methyltransferases, used alone or in combinations. While a solution will not be achieved by tomorrow, the battle against HIV-1 latent reservoirs is well- underway.

HIV interactions with monocytes and dendritic cells: viral latency and reservoirs

HIV is a devastating human pathogen that causes serious immunological diseases in humans around the world. The virus is able to remain latent in an infected host for many years, allowing for the long-term survival of the virus and inevitably prolonging the infection process. The location and mechanisms of HIV latency are under investigation and remain important topics in the study of viral pathogenesis. Given that HIV is a blood-borne pathogen, a number of cell types have been proposed to be the sites of latency, including resting memory CD4⁺ T cells, peripheral blood monocytes, dendritic cells and macrophages in the lymph nodes, and haematopoietic stem cells in the bone marrow. This review updates the latest advances in the study of HIV interactions with monocytes and dendritic cells, and highlights the potential role of these cells as viral reservoirs and the effects of the HIV-host-cell interactions on viral pathogenesis.