Molecular characterization, reactivation, and depletion of latent HIV

HIV Reservoirs and Treatment Strategies toward Curing HIV Infection

Combination antiretroviral therapy (cART) has significantly improved the prognosis of individuals living with human immunodeficiency virus (HIV). Acquired immunodeficiency syndrome has transformed from a fatal disease to a treatable chronic infection. Currently, effective and safe anti-HIV drugs are available. Although cART can reduce viral production in the body of the patient to below the detection limit, it cannot eliminate the HIV provirus integrated into the host cell genome; hence, the virus will be produced again after cART discontinuation. Therefore, research into a cure (or remission) for HIV has been widely conducted. In this review, we focus on drug development targeting cells latently infected with HIV and assess the progress including our current studies, particularly in terms of the "Shock and Kill", and "Block and Lock" strategies.

Examining Chronic Inflammation, Immune Metabolism, and T Cell Dysfunction in HIV Infection

Chronic Human Immunodeficiency Virus (HIV) infection remains a significant challenge to global public health. Despite advances in antiretroviral therapy (ART), which has transformed HIV infection from a fatal disease into a manageable chronic condition, a definitive cure remains elusive. One of the key features of HIV infection is chronic immune activation and inflammation, which are strongly associated with, and predictive of, HIV disease progression, even in patients successfully treated with suppressive ART. Chronic inflammation is characterized by persistent inflammation, immune cell metabolic dysregulation, and cellular exhaustion and dysfunction. This review aims to summarize current knowledge of the interplay between chronic inflammation, immune metabolism, and T cell dysfunction in HIV infection, and also discusses the use of humanized mice models to study HIV immune pathogenesis and develop novel therapeutic strategies.

Soluble CD4 and low molecular weight CD4-mimetic compounds sensitize cells to be killed by anti-HIV cytotoxic immunoconjugates

IMPORTANCE

HIV infection can be effectively treated to prevent the development of AIDS, but it cannot be cured. We have attached poisons to anti-HIV antibodies to kill the infected cells that persist even after years of effective antiviral therapy. Here we show that the killing of infected cells can be markedly enhanced by the addition of soluble forms of the HIV receptor CD4 or by mimics of CD4.

Ponatinib Represses Latent HIV-1 by Inhibiting AKT-mTOR

Although antiretroviral therapy (ART) is effective in suppressing viral replication, it does not cure HIV-1 infection due to the presence of the viral latent reservoir. Rather than reactivating the latent viruses, the "block and lock" strategy aims to shift the viral reservoir to a deeper state of transcriptional silencing, thus preventing viral rebound after ART interruption. Although some latency-promoting agents (LPAs) have been reported, none of them have been approved for clinical application due to cytotoxicity and limited efficacy; therefore, it is important to search for novel and effective LPAs. Here, we report an FDA-approved drug, ponatinib, that can broadly repress latent HIV-1 reactivation in different cell models of HIV-1 latency and in primary CD4+ T cells from ART-suppressed individuals ex vivo. Ponatinib does not change the expression of activation or exhaustion markers on primary CD4+ T cells and does not induce severe cytotoxicity and cell dysfunction. Mechanistically, ponatinib suppresses proviral HIV-1 transcription by inhibiting the activation of the AKT-mTOR pathway, which subsequently blocks the interaction between key transcriptional factors and the HIV-1 long terminal repeat (LTR). In summary, we discovered a novel latency-promoting agent, ponatinib, which could have promising significance for future applications of HIV-1 functional cure.

Identification of Anti-gp41 Monoclonal Antibodies That Effectively Target Cytotoxic Immunoconjugates to Cells Infected with Human Immunodeficiency Virus, Type 1

We are developing cytotoxic immunoconjugates (CICs) targeting the envelope protein (Env) of the Human Immunodeficiency Virus, type 1 (HIV) to purge the persistent reservoirs of viral infection. We have previously studied the ability of multiple monoclonal antibodies (mAbs) to deliver CICs to an HIV-infected cell. We have found that CICs targeted to the membrane-spanning gp41 domain of Env are most efficacious, in part because their killing is enhanced in the presence of soluble CD4. The ability of a mAb to deliver a CIC does not correlate with its ability to neutralize nor mediate Ab-dependent cellular cytotoxicity. In the current study, we seek to define the most effective anti-gp41 mAbs for delivering CICs to HIV-infected cells. To do this, we have evaluated a panel of human anti-gp41 mAbs for their ability to bind and kill two different Env-expressing cell lines: persistently infected H9/NL4-3 and constitutively transfected HEK293/92UG. We measured the binding and cytotoxicity of each mAb in the presence and absence of soluble CD4. We found that mAbs to the immunodominant helix-loop-helix region (ID-loop) of gp41 are most effective, whereas neutralizing mAbs to the fusion peptide, gp120/gp41 interface, and the membrane proximal external region (MPER) are relatively ineffective at delivering CICs. There was only a weak correlation between antigen exposure and killing activity. The results show that the ability to deliver an effective IC and neutralization are distinct functions of mAbs.

Genome-wide CRISPR screens identify combinations of candidate latency reversing agents for targeting the latent HIV-1 reservoir

Reversing HIV-1 latency promotes killing of infected cells and is essential for cure strategies; however, no single latency reversing agent (LRA) or LRA combination have been shown to reduce HIV-1 latent reservoir size in persons living with HIV-1 (PLWH). Here, we describe an approach to systematically identify LRA combinations to reactivate latent HIV-1 using genome-wide CRISPR screens. Screens on cells treated with suboptimal concentrations of an LRA can identify host genes whose knockout enhances viral gene expression. Therefore, inhibitors of these genes should synergize with the LRA. We tested this approach using AZD5582, an activator of the noncanonical nuclear factor κB (ncNF-κB) pathway, as an LRA and identified histone deacetylase 2 (HDAC2) and bromodomain-containing protein 2 (BRD2), part of the bromodomain and extra-terminal motif (BET) protein family targeted by BET inhibitors, as potential targets. Using CD4⁺ T cells from PLWH, we confirmed synergy between AZD5582 and several HDAC inhibitors and between AZD5582 and the BET inhibitor, JQ1. A reciprocal screen using suboptimal concentrations of an HDAC inhibitor as an LRA identified BRD2 and ncNF-κB regulators, especially BIRC2, as synergistic candidates for use in combination with HDAC inhibition. Moreover, we identified and validated additional synergistic drug candidates in latency cell line cells and primary lymphocytes isolated from PLWH. Specifically, the knockout of genes encoding CYLD or YPEL5 displayed synergy with existing LRAs in inducing HIV mRNAs. Our study provides insights into the roles of host factors in HIV-1 reactivation and validates a system for identifying drug combinations for HIV-1 latency reversal.

Pharmacological Targeting of Sphingosine Kinases Impedes HIV-1 Infection of CD4 T Cells through SAMHD1 Modulation

Sphingosine-1-phosphate (S1P) is a sphingolipid modulator of a myriad of cellular processes, and therapeutic targeting of S1P signaling is utilized clinically to treat multiple sclerosis. We have previously shown that functional antagonism of S1P receptors reduces cell-free, cell-to-cell, and latent HIV-1 infection in primary CD4 T cells. In this work, we examined whether targeting sphingosine kinase 1 or 2 (SPHK1/2) to inhibit S1P production would prevent infection using multiple HIV-1 primary isolates and infectious molecular clones. SPHK inhibition reduced HIV transmission between primary CD4 T cells in both cell-to-cell transmission and pretreatment coculture models. Mechanistically, pharmacological inhibition of SPHK reduced susceptibility to infection primarily by downregulating phosphorylated SAMHD1 (pSAMHD1), enhancing the activity of this innate HIV-1 restriction factor. Furthermore, genetic disruption of either SPHK1 or SPHK2 by CRISPR/Cas9 reduced phosphorylation of SAMHD1, demonstrating the role of these kinases in modulation of SAMHD1 activity. The effect of SPHK inhibition on limiting HIV-1 infection in CD4 T cells was observed irrespective of the biological sex or age of the donor, with neither variable significantly influencing the effectiveness of SPHK inhibition. Our results demonstrate that targeting SPHK inhibits transmission of HIV-1 via modulation of SAMHD1 phosphorylation to decrease permissiveness to infection in CD4 T cells and suggests that therapeutic targeting of this pathway early in infection enables development of strategies to prevent establishment of infection and hinder cell-to-cell transmission of HIV-1.

IMPORTANCE HIV-1 infection, once established, requires lifelong treatment due to the ability of the virus to maintain latent infection in its host and become reactivated during an interruption in antiretroviral treatment (ART). Although preventing transmission and acquisition of HIV is an important goal, no ART thus far have exploited harnessing a component of the host immune system to combat transmission of the virus. We have previously shown that inhibition of sphingosine-1-phosphate (S1P) receptors, a component of S1P signaling, reduces HIV-1 infection in human CD4 T cells. We therefore investigated inhibition of sphingosine kinases, another element of this signaling system, in this work. We found that inhibition of sphingosine kinases 1 and 2 (SPHK1/2) could reduce HIV-1 transmission, both among CD4 T cells and between macrophages and CD4 T cells. Our research therefore suggests that therapeutic targeting of SPHK or S1P receptors may aid in the development of strategies to prevent establishment and transmission of HIV-1 infection among immune cells.

Multiparameter immunohistochemistry analysis of HIV DNA, RNA and immune checkpoints in lymph node tissue

The main barrier to a cure for HIV is the persistence of long-lived and proliferating latently infected CD4+ T-cells despite antiretroviral therapy (ART). Latency is well characterized in multiple CD4+ T-cell subsets, however, the contribution of regulatory T-cells (Tregs) expressing FoxP3 as well as immune checkpoints (ICs) PD-1 and CTLA-4 as targets for productive and latent HIV infection in people living with HIV on suppressive ART is less well defined. We used multiplex detection of HIV DNA and RNA with immunohistochemistry (mIHC) on formalin-fixed paraffin embedded (FFPE) cells to simultaneously detect HIV RNA and DNA and cellular markers. HIV DNA and RNA were detected by in situ hybridization (ISH) (RNA/DNAscope) and IHC was used to detect cellular markers (CD4, PD-1, FoxP3, and CTLA-4) by incorporating the tyramide system amplification (TSA) system. We evaluated latently infected cell lines, a primary cell model of HIV latency and excisional lymph node (LN) biopsies collected from people living with HIV (PLWH) on and off ART. We clearly detected infected cells that coexpressed HIV RNA and DNA (active replication) and DNA only (latently infected cells) in combination with IHC markers in the in vitro infection model as well as LN tissue from PLWH both on and off ART. Combining ISH targeting HIV RNA and DNA with IHC provides a platform to detect and quantify HIV persistence within cells identified by multiple markers in tissue samples from PLWH on ART or to study HIV latency.

A widely distributed HIV-1 provirus elimination assay to evaluate latency-reversing agents in vitro

Persistence of HIV-1 latent reservoir cells during antiretroviral therapy (ART) is a major obstacle for curing HIV-1. Even though latency-reversing agents (LRAs) are under development to reactivate and eradicate latently infected cells, there are few useful models for evaluating LRA activity in vitro. Here, we establish a long-term cell culture system called the "widely distributed intact provirus elimination" (WIPE) assay. It harbors thousands of different HIV-1-infected cell clones with a wide distribution of HIV-1 provirus similar to that observed in vivo. Mathematical modeling and experimental results from this in vitro infection model demonstrates that the addition of an LRA to ART shows a latency-reversing effect and contributes to the eradication of replication-competent HIV-1. The WIPE assay can be used to optimize therapeutics against HIV-1 latency and investigate mechanistic insights into the clonal selection of heterogeneous HIV-1-infected cells.

In Vivo Dynamics of the Latent Reservoir for HIV-1: New Insights and Implications for Cure

Although antiretroviral therapy (ART) can reduce viremia to below the limit of detection and allow persons living with HIV-1 (PLWH) to lead relatively normal lives, viremia rebounds when treatment is interrupted. Rebound reflects viral persistence in a stable latent reservoir in resting CD4⁺ T cells. This reservoir is now recognized as the major barrier to cure and is the focus of intense international research efforts. Strategies to cure HIV-1 infection include interventions to eliminate this reservoir, to prevent viral rebound from the reservoir, or to enhance immune responses such that viral replication is effectively controlled. Here we consider recent developments in understanding the composition of the reservoir and how it can be measured in clinical studies. We also discuss exciting new insights into the in vivo dynamics of the reservoir and the reasons for its remarkable stability. Finally we discuss recent discoveries on the complex processes that govern viral rebound. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Low Inducibility of Latent Human Immunodeficiency Virus Type 1 Proviruses as a Major Barrier to Cure

The latent reservoir for human immunodeficiency virus type 1 (HIV-1) in resting CD4+ T cells is a major barrier to cure. The dimensions of the reservoir problem can be defined with 2 assays. A definitive minimal estimate of the frequency of latently infected cells is provided by the quantitative viral outgrowth assay (QVOA), which detects cells that can be induced by T-cell activation to release infectious virus. In contrast, the intact proviral DNA assay (IPDA) detects all genetically intact proviruses and provides a more accurate upper limit on reservoir size than standard single-amplicon polymerase chain reaction assays which mainly detect defective proviruses. The frequency of cells capable of initiating viral rebound on interruption of antiretroviral therapy lies between the values produced by the QVOA and the IPDA. We argue here that the 1-2-log difference between QVOA and IPDA values in part reflects that the fact that many replication-competent proviruses are not readily induced by T-cell activation. Findings of earlier studies suggest that latently infected cells can be activated to proliferate in vivo without expressing viral genes. The proliferating cells nevertheless retain the ability to produce virus on subsequent stimulation. The low inducibility of latent proviruses is a major problem for the shock-and-kill strategy for curing HIV-1 infection, which uses latency-reversing agents to induce viral gene expression and render infected cells susceptible to immune clearance. The latency-reversing agents developed to date are much less effective at reversing latency than T-cell activation. Taken together, these results indicate that HIV-1 eradication will require the discovery of much more effective ways to induce viral gene expression.

Evaluation of the expression pattern of 4 microRNAs and their correlation with cellular/viral factors in PBMCs of Long Term non-progressors and HIV infected naïve Individuals

BACKGROUND

Long-term non-progressors (LTNPs) are small subsets of HIV-infected subjects that can control HIV-1 replication for several years without receiving ART. The exact mechanism of HIV-1 suppression has not yet been completely elucidated. Although the modulatory role of microRNAs (miRNAs) in HIV-1 replication has been reported, their importance in LTNPs is unclear.

OBJECTIVE

The aim of this cross-sectional study was to assess the expression pattern of miR-27b, -29, -150, and -221, as well as their relationship with CD4+ T-cell count, HIV-1 viral load, and nef gene expression in peripheral blood mononuclear cells (PBMCs) of untreated viremic patients and in LTNPs.

METHODS

MiRNAs expression levels were evaluated with real-time PCR assay using RNA isolated from PBMCs of LTNPs, HIV-1 infected naive patients, and healthy people. Moreover, CD4 T-cell count, HIV viral load, and nef gene expression were assessed.

RESULTS

The expression level of all miRNAs significantly decreased in the HIV-1 patient group compared to the control group, while the expression pattern of miRNAs in the LNTPs group was similar to that in the healthy subject group. In addition, there were significant correlations between some miRNA expression with viral load, CD4+ T-cell count, and nef gene expression.

CONCLUSION

The significant similarity and difference of the miRNA expression pattern between LNTPs and healthy individuals as well as between elite controllers and HIV-infected patients, respectively, showed that these miRNAs could be used as diagnostic biomarkers. Further, positive and negative correlations between miRNAs expression and viral/cellular factors could justify the role of these miRNAs in HIV-1 disease monitoring.

Tracking HIV Rebound following Latency Reversal Using Barcoded HIV

HIV latency prevents cure of infection with antiretroviral therapy (ART) alone. One strategy for eliminating latently infected cells involves the induction of viral protein expression via latency-reversing agents (LRAs), allowing killing of host cells by viral cytopathic effects or immune effector mechanisms. Here, we combine a barcoded HIV approach and a humanized mouse model to study the effects of a designed, synthetic protein kinase C modulating LRA on HIV rebound. We show that administration of this compound during ART results in a delay in rebound once ART is stopped. Furthermore, the rebounding virus appears composed of a smaller number of unique barcoded viruses than occurs in control-treated animals, suggesting that some reservoir cells that would have contributed virus to the rebound process are eliminated by LRA administration. These data support the use of barcoded virus to study rebound and suggest that LRAs may be useful in HIV cure efforts.

Pharmacological Inhibition of PPARy Boosts HIV Reactivation and Th17 Effector Functions, While Preventing Progeny Virion Release and de novo Infection

The frequency and functions of Th17-polarized CCR6⁺RORyt⁺CD4⁺ T cells are rapidly compromised upon HIV infection and are not restored with long-term viral suppressive antiretroviral therapy (ART). In line with this, Th17 cells represent selective HIV-1 infection targets mainly at mucosal sites, with long-lived Th17 subsets carrying replication-competent HIV-DNA during ART. Therefore, novel Th17-specific therapeutic interventions are needed as a supplement of ART to reach the goal of HIV remission/cure. Th17 cells express high levels of peroxisome proliferator-activated receptor gamma (PPARy), which acts as a transcriptional repressor of the HIV provirus and the rorc gene, which encodes for the Th17-specific master regulator RORyt. Thus, we hypothesized that the pharmacological inhibition of PPARy will facilitate HIV reservoir reactivation while enhancing Th17 effector functions. Consistent with this prediction, the PPARy antagonist T0070907 significantly increased HIV transcription (cell-associated HIV-RNA) and RORyt-mediated Th17 effector functions (IL-17A). Unexpectedly, the PPARy antagonism limited HIV outgrowth from cells of ART-treated people living with HIV (PLWH), as well as HIV replication in vitro. Mechanistically, PPARy inhibition in CCR6⁺CD4⁺ T cells induced the upregulation of transcripts linked to Th17-polarisation (RORyt, STAT3, BCL6 IL-17A/F, IL-21) and HIV transcription (NCOA1-3, CDK9, HTATIP2). Interestingly, several transcripts involved in HIV-restriction were upregulated (Caveolin-1, TRIM22, TRIM5α, BST2, miR-29), whereas HIV permissiveness transcripts were downregulated (CCR5, furin), consistent with the decrease in HIV outgrowth/replication. Finally, PPARy inhibition increased intracellular HIV-p24 expression and prevented BST-2 downregulation on infected T cells, suggesting that progeny virion release is restricted by BST-2-dependent mechanisms. These results provide a strong rationale for considering PPARy antagonism as a novel strategy for HIV-reservoir purging and restoring Th17-mediated mucosal immunity in ART-treated PLWH.

Fingolimod inhibits multiple stages of the HIV-1 life cycle

Antiretroviral drugs that target various stages of the Human Immunodeficiency Virus (HIV) life cycle have been effective in curbing the AIDS epidemic. However, drug resistance, off-target effects of antiretroviral therapy (ART), and varying efficacy in prevention underscore the need to develop novel and alternative therapeutics. In this study, we investigated whether targeting the signaling molecule Sphingosine-1-phosphate (S1P) would inhibit HIV-1 infection and generation of the latent reservoir in primary CD4 T cells. We show that FTY720 (Fingolimod), an FDA-approved functional antagonist of S1P receptors, blocks cell-free and cell-to-cell transmission of HIV and consequently reduces detectable latent virus. Mechanistically, FTY720 impacts the HIV-1 life cycle at two levels. Firstly, FTY720 reduces the surface density of CD4, thereby inhibiting viral binding and fusion. Secondly, FTY720 decreases the phosphorylation of the innate HIV restriction factor SAMHD1 which is associated with reduced levels of total and integrated HIV, while reducing the expression of Cyclin D3. In conclusion, targeting the S1P pathway with FTY720 could be a novel strategy to inhibit HIV replication and reduce the seeding of the latent reservoir.

Prodrugs of PKC modulators show enhanced HIV latency reversal and an expanded therapeutic window

AIDS is a pandemic disease caused by HIV that affects 37 million people worldwide. Current antiretroviral therapy slows disease progression but does not eliminate latently infected cells, which resupply active virus, thus necessitating lifelong treatment with associated compliance, cost, and chemoexposure issues. Latency-reversing agents (LRAs) activate these cells, allowing for their potential clearance, thus presenting a strategy to eradicate the infection. Protein kinase C (PKC) modulators-including prostratin, ingenol esters, bryostatin, and their analogs-are potent LRAs in various stages of development for several clinical indications. While LRAs are promising, a major challenge associated with their clinical use is sustaining therapeutically meaningful levels of the active agent while minimizing side effects. Here we describe a strategy to address this problem based on LRA prodrugs, designed for controllable release of the active LRA after a single injection. As intended, these prodrugs exhibit comparable or superior in vitro activity relative to the parent compounds. Selected compounds induced higher in vivo expression of CD69, an activation biomarker, and, by releasing free agent over time, significantly improved tolerability when compared to the parent LRAs. More generally, selected prodrugs of PKC modulators avoid the bolus toxicities of the parent drug and exhibit greater efficacy and expanded tolerability, thereby addressing a longstanding objective for many clinical applications.

Benefits and limitations of humanized mice in HIV persistence studies

Significant advances in the treatment of HIV infection have been made in the last three decades. Antiretroviral therapy (ART) is now potent enough to prevent virus replication and stop disease progression. However, ART alone does not cure the infection, primarily because HIV can persist in stable long-term reservoir cells including latently-infected CD4 + T cells. A central goal of the HIV research field is to devise strategies to eliminate these reservoirs and thereby develop a cure for HIV. This requires robust in vivo model systems to facilitate both the further characterization of persistent HIV reservoirs and evaluation of methods for eliminating latent virus. Humanized mice have proven to be versatile experimental models for studying many basic aspects of HIV biology. These models consist of immunodeficient mice transplanted with human cells or tissues, which allows development of a human immune system that supports robust infection with HIV. There are many potential applications for new generations of humanized mouse models in investigating HIV reservoirs and latency, but these models also involve caveats that are important to consider in experimental design and interpretation. This review briefly discusses some of the key strengths and limitations of humanized mouse models in HIV persistence studies.

The Establishment of an In Vivo HIV-1 Infection Model in Humanized B-NSG Mice

Suitable animal models for human immunodeficiency virus type 1 (HIV-1) infection are important for elucidating viral pathogenesis and evaluating antiviral strategies in vivo. The B-NSG (NOD-PrkdcscidIl2rgtm1/Bcge) mice that have severe immune defect phenotype are examined for the suitability of such a model in this study. Human peripheral blood mononuclear cells (PBMCs) were engrafted into B-NSG mice via mouse tail vein injection, and the repopulated human T-lymphocytes were observed at as early as 3-weeks post-transplantation in mouse peripheral blood and several tissues. The humanized mice could be infected by HIV-1, and the infection recapitulated features of T-lymphocyte dynamic observed in HIV-1 infected humans, meanwhile the administration of combination antiretroviral therapy (cART) suppressed viral replication and restored T lymphocyte abnormalities. The establishment of HIV-1 infected humanized B-NSG mice not only provides a model to study virus and T cell interplays, but also can be a useful tool to evaluate antiviral strategies.

Crossroads of Cancer and HIV-1: Pathways to a Cure for HIV

Recently, a second individual (the “London patient”) with HIV-1 infection and concomitant leukemia was cured of both diseases by a conditioning myeloablative regimen followed by transplantation of stem cells bearing the homozygous CCR5 Δ32 mutation. The substantial risks and cost associated with this procedure render it unfeasible on a large scale. This strategy also indicates that a common pathway toward a cure for both HIV and cancer may exist. Successful approaches to curing both diseases should ideally possess three components, i.e., (1) direct targeting of pathological cells (neoplastic cells in cancer and the HIV-infected reservoir cells), (2) subsequent impediment to reconstitution of the pool of pathological cells and (3) sustained, immunologic control of the disease (both diseases are characterized by detrimental immune hyper-activation that hinders successful establishment of immunity). In this review, we explore medications that are either investigational or FDA-approved anticancer treatments that may be employed to achieve the goal of curing HIV-1. These include: thioredoxin reductase inhibitors (phases 1–3), immune checkpoint inhibitors (phases 1, 3), Jak inhibitors (FDA approved for arthritis and multiple cancer indications, summarized in Table 1). Of note, some of these medications such as arsenic trioxide and Jak inhibitors may also reversibly down regulate CCR5 expression on CD4⁺ T-cells, thus escaping the ethical issues of inducing or transferring mutations in CCR5 that are presently the subject of interest as it relates to HIV-1 cure strategies.

The inhibitor apoptosis protein antagonist Debio 1143 Is an attractive HIV-1 latency reversal candidate

Antiretroviral therapy (ART) suppresses HIV replication, but does not cure the infection because replication-competent virus persists within latently infected CD4+ T cells throughout years of therapy. These reservoirs contain integrated HIV-1 genomes and can resupply active virus. Thus, the development of strategies to eliminate the reservoir of latently infected cells is a research priority of global significance. In this study, we tested efficacy of a new inhibitor of apoptosis protein antagonist (IAPa) called Debio 1143 at reversing HIV latency and investigated its mechanisms of action. Debio 1143 activates HIV transcription via NF-kB signaling by degrading the ubiquitin ligase baculoviral IAP repeat-containing 2 (BIRC2), a repressor of the non-canonical NF-kB pathway. Debio 1143-induced BIRC2 degradation results in the accumulation of NF-κB-inducing kinase (NIK) and proteolytic cleavage of p100 into p52, leading to nuclear translocation of p52 and RELB. Debio 1143 greatly enhances the binding of RELB to the HIV-1 LTR. These data indicate that Debio 1143 activates the non-canonical NF-kB signaling pathway by promoting the binding of RELB:p52 complexes to the HIV-1 LTR, resulting in the activation of the LTR-dependent HIV-1 transcription. Importantly, Debio 1143 reverses viral latency in HIV-1 latent T cell lines. Using knockdown (siRNA BIRC2), knockout (CRIPSR NIK) and proteasome machinery neutralization (MG132) approaches, we found that Debio 1143-mediated HIV latency reversal is BIRC2 degradation- and NIK stabilization-dependent. Debio 1143 also reverses HIV-1 latency in resting CD4+ T cells derived from ART-treated patients or HIV-1-infected humanized mice under ART. Interestingly, daily oral administration of Debio 1143 in cancer patients at well-tolerated doses elicited BIRC2 target engagement in PBMCs and induced a moderate increase in cytokines and chemokines mechanistically related to NF-kB signaling. In conclusion, we provide strong evidences that the IAPa Debio 1143, by initially activating the non-canonical NF-kB signaling and subsequently reactivating HIV-1 transcription, represents a new attractive viral latency reversal agent (LRA).

Repurposing medications for use in treating HIV infection: A focus on valproic acid as a latency-reversing agent

WHAT IS KNOWN AND OBJECTIVE

Combined antiretroviral therapy (ART) reduces human immunodeficiency virus type 1 (HIV-1) RNA plasma levels below the limit of detection. However, HIV-1 persists in latently infected CD4+ T cells, which is currently the barrier to curing HIV-1. Novel mechanisms are being explored to target HIV-1 latent reservoirs. The purpose of this review was to critically evaluate the available literature on innovative use of valproic acid (VPA) for the agent's therapeutic effects on reversing latent human immunodeficiency virus (HIV) reservoirs.

METHODS

A search of PubMed (1996-December 2017) and International Pharmaceutical Abstracts (1970-December 2017) was conducted using the MeSH terms HIV, valproic acid and latency. Free text searches included the terms latency-reversing agents, HIV therapy and valproic acid.

RESULTS

Six clinical trials and one case report were critically evaluated on VPA's therapeutic effects on reversing HIV reservoirs. Only one study reported that VPA therapy has a significant effect on reversing HIV-1 latent reservoirs; all other studies reviewed and did not demonstrate an appreciable effect of VPA on reversing HIV latent reservoirs.

WHAT IS NEW AND CONCLUSION

Current literature does not support the use of VPA as adjunctive therapy to reverse HIV-1 latent reservoirs. Sample sizes were small, and overall studies were not sufficiently powered. Further studies are needed to make informed conclusions on the use of VPA as an HIV-1 latency-reversing agent.

Epigenetic Modulation of CD8⁺ T Cell Function in Lentivirus Infections: A Review

CD8⁺ T cells are critical for controlling viremia during human immunodeficiency virus (HIV) infection. These cells produce cytolytic factors and antiviral cytokines that eliminate virally- infected cells. During the chronic phase of HIV infection, CD8⁺ T cells progressively lose their proliferative capacity and antiviral functions. These dysfunctional cells are unable to clear the productively infected and reactivated cells, representing a roadblock in HIV cure. Therefore, mechanisms to understand CD8⁺ T cell dysfunction and strategies to boost CD8⁺ T cell function need to be investigated. Using the feline immunodeficiency virus (FIV) model for lentiviral persistence, we have demonstrated that CD8⁺ T cells exhibit epigenetic changes such as DNA demethylation during the course of infection as compared to uninfected cats. We have also demonstrated that lentivirus-activated CD4⁺CD25⁺ T regulatory cells induce forkhead box P3 (Foxp3) expression in virus-specific CD8⁺ T cell targets, which binds the interleukin (IL)-2, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ promoters in these CD8⁺ T cells. Finally, we have reported that epigenetic modulation reduces Foxp3 binding to these promoter regions. This review compares and contrasts our current understanding of CD8⁺ T cell epigenetics and mechanisms of lymphocyte suppression during the course of lentiviral infection for two animal models, FIV and simian immunodeficiency virus (SIV).

HIV Replication and Latency in a Humanized NSG Mouse Model during Suppressive Oral Combinational Antiretroviral Therapy

Although current combinatorial antiretroviral therapy (cART) is therapeutically effective in the majority of HIV patients, interruption of therapy can cause a rapid rebound in viremia, demonstrating the existence of a stable reservoir of latently infected cells. HIV latency is therefore considered a primary barrier to HIV eradication. Identifying, quantifying, and purging the HIV reservoir is crucial to effectively curing patients and relieving them from the lifelong requirement for therapy. Latently infected transformed cell models have been used to investigate HIV latency; however, these models cannot accurately represent the quiescent cellular environment of primary latently infected cells in vivo For this reason, in vivo humanized murine models have been developed for screening antiviral agents, identifying latently infected T cells, and establishing treatment approaches for HIV research. Such models include humanized bone marrow/liver/thymus mice and SCID-hu-thy/liv mice, which are repopulated with human immune cells and implanted human tissues through laborious surgical manipulation. However, no one has utilized the human hematopoietic stem cell-engrafted NOD/SCID/IL2rγ^null (NSG) model (hu-NSG) for this purpose. Therefore, in the present study, we used the HIV-infected hu-NSG mouse to recapitulate the key aspects of HIV infection and pathogenesis in vivo Moreover, we evaluated the ability of HIV-infected human cells isolated from HIV-infected hu-NSG mice on suppressive cART to act as a latent HIV reservoir. Our results demonstrate that the hu-NSG model is an effective surgery-free in vivo system in which to efficiently evaluate HIV replication, antiretroviral therapy, latency and persistence, and eradication interventions.IMPORTANCE HIV can establish a stably integrated, nonproductive state of infection at the level of individual cells, known as HIV latency, which is considered a primary barrier to curing HIV. A complete understanding of the establishment and role of HIV latency in vivo would greatly enhance attempts to develop novel HIV purging strategies. An ideal animal model for this purpose should be easy to work with, should have a shortened disease course so that efficacy testing can be completed in a reasonable time, and should have immune correlates that are easily translatable to humans. We therefore describe a novel application of the hematopoietic stem cell-transplanted humanized NSG model for dynamically testing antiretroviral treatment, supporting HIV infection, establishing HIV latency in vivo The hu-NSG model could be a facile alternative to humanized bone marrow/liver/thymus or SCID-hu-thy/liv mice in which laborious surgical manipulation and time-consuming human cell reconstitution is required.

Receptor-targeted aptamer-siRNA conjugate-directed transcriptional regulation of HIV-1

Gene-based therapies represent a promising therapeutic paradigm for the treatment of HIV-1, as they have the potential to maintain sustained viral inhibition with reduced treatment interventions. Such an option may represent a long-term treatment alternative to highly active antiretroviral therapy.

Methods: We previously described a therapeutic approach, referred to as transcriptional gene silencing (TGS), whereby small noncoding RNAs directly inhibit the transcriptional activity of HIV-1 by targeting sites within the viral promoter, specifically the 5' long terminal repeat (LTR). TGS differs from traditional RNA interference (RNAi) in that it is characterized by concomitant silent-state epigenetic marks on histones and DNA. To deliver TGS-inducing RNAs, we developed functional RNA conjugates based on the previously reported dual function of the gp120 (A-1) aptamer conjugated to 27-mer Dicer-substrate anti-HIV-1 siRNA (dsiRNA), LTR-362.

Results: We demonstrate here that high levels of processed guide RNAs localize to the nucleus in infected T lymphoblastoid CEM cell line and primary human CD4+ T-cells. Treatment of the aptamer-siRNA conjugates induced TGS with an ~10-fold suppression of viral p24 levels as measured at day 12 post infection. To explore the silencing efficacy of aptamer-siRNA conjugates in vivo, HIV-1-infected humanized NOD/SCID/IL2 rγ^null mice (hu-NSG) were treated with the aptamer-siRNA conjugates. Systemic delivery of the A-1-stick-LTR-362 27-mer siRNA conjugates suppressed HIV-1 infection and protected CD4+ T cell levels in viremia hu-NSG mice.

Principle conclusions: Collectively these data suggest that the gp120 aptamer-dsiRNA conjugate design is suitable for systemic delivery of small RNAs that can be used to suppress HIV-1.

In Vitro Transduction and Target-Mutagenesis Efficiency of HIV-1 pol Gene Targeting ZFN and CRISPR/Cas9 Delivered by Various Plasmids and/or Vectors: Toward an HIV Cure

Efficiency of artificial restriction enzymes toward curing HIV has only been separately examined, using differing delivery vehicles. We compared the in vitro transduction and target-mutagenesis efficiency of consortium plasmid and adenoviral vector delivered HIV-1 pol gene targeting zinc finger nuclease (ZFN) with CRISPR/Cas, Custom-ZFN, CRISPR-Cas-9, and plasmids and vectors (murCTSD_pZFN, pGS-U-gRNA, pCMV-Cas-D01A, Ad5-RGD); cell lines (TZM-bl and ACH-2/J-Lat cells); and the latency reversing agents prostratin, suberoylanilide hydroxamic acid, and phorbol myristate acetate. Cell lines were grown in either Dulbecco's modified Eagle's medium or Roswell Park Memorial Institute with the antibiotics kanamycin, zeocin, and efavirenz. Efficiency was assayed by GFP/luciferase activity and/or validated by yeast MEL1 reporter assay, CEL1 restriction fragment assay, and quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Ad5-RGD vectors had better transduction efficiency than murCTSD and pGS-U-gRNA/pCMV-Cas-D01A plasmids. CRISPR/Cas9 exhibited better target-mutagenesis efficiency relative to ZFN (delivered by either plasmid or Ad5 vector) based on gel electrophoresis of pol gene amplicons within ACH-2 and J-Lat cells. Ad-5-RGD vectors enhanced target mutagenesis of ZFN, relative to murCTSD_pZFN plasmids, to levels of CRISPR/Cas9 plasmids. Similar reduction of luciferase activity among TZM-bl treated with Ad5-ZFN vectors relative to CRISPR/Cas-9 and murCTSD_pZFN plasmids was observed on challenge with HIV-1. qRT-PCR of HIV-1 pol gene transcripts affirmed that Ad5 (RGD) vectors enhanced target mutagenesis of ZFN. Whereas CRISPR/Cas-9 may possess inherent superior target-mutagenesis efficiency; the efficiency of ZFN (off-target toxicity withstanding) can be enhanced by altering delivery vehicle from plasmid to Ad5 (RGD) vectors.

In vivo activation of latent HIV with a synthetic bryostatin analog effects both latent cell "kick" and "kill" in strategy for virus eradication

The ability of HIV to establish a long-lived latent infection within resting CD4+ T cells leads to persistence and episodic resupply of the virus in patients treated with antiretroviral therapy (ART), thereby preventing eradication of the disease. Protein kinase C (PKC) modulators such as bryostatin 1 can activate these latently infected cells, potentially leading to their elimination by virus-mediated cytopathic effects, the host's immune response and/or therapeutic strategies targeting cells actively expressing virus. While research in this area has focused heavily on naturally-occurring PKC modulators, their study has been hampered by their limited and variable availability, and equally significantly by sub-optimal activity and in vivo tolerability. Here we show that a designed, synthetically-accessible analog of bryostatin 1 is better-tolerated in vivo when compared with the naturally-occurring product and potently induces HIV expression from latency in humanized BLT mice, a proven and important model for studying HIV persistence and pathogenesis in vivo. Importantly, this induction of virus expression causes some of the newly HIV-expressing cells to die. Thus, designed, synthetically-accessible, tunable, and efficacious bryostatin analogs can mediate both a "kick" and "kill" response in latently-infected cells and exhibit improved tolerability, therefore showing unique promise as clinical adjuvants for HIV eradication.

Humanized Mouse Models for Human Immunodeficiency Virus Infection

Human immunodeficiency virus (HIV) remains a significant source of morbidity and mortality worldwide. No effective vaccine is available to prevent HIV transmission, and although antiretroviral therapy can prevent disease progression, it does not cure HIV infection. Substantial effort is therefore currently directed toward basic research on HIV pathogenesis and persistence and developing methods to stop the spread of the HIV epidemic and cure those individuals already infected with HIV. Humanized mice are versatile tools for the study of HIV and its interaction with the human immune system. These models generally consist of immunodeficient mice transplanted with human cells or reconstituted with a near-complete human immune system. Here, we describe the major humanized mouse models currently in use, and some recent advances that have been made in HIV research/therapeutics using these models.

In Vivo Models of Human Immunodeficiency Virus Persistence and Cure Strategies

Current HIV therapy is not curative regardless of how soon after infection it is initiated or how long it is administered, and therapy interruption almost invariably results in robust viral rebound. Human immunodeficiency virus persistence is therefore the major obstacle to a cure for AIDS. The testing and implementation of novel yet unproven approaches to HIV eradication that could compromise the health status of HIV-infected individuals might not be ethically warranted. Therefore, adequate in vitro and in vivo evidence of efficacy is needed to facilitate the clinical implementation of promising strategies for an HIV cure. Animal models of HIV infection have a strong and well-documented history of bridging the gap between laboratory discoveries and eventual clinical implementation. More recently, animal models have been developed and implemented for the in vivo evaluation of novel HIV cure strategies. In this article, we review the recent progress in this rapidly moving area of research, focusing on the two most promising model systems: humanized mice and nonhuman primates.

Promising Role of Toll-Like Receptor 8 Agonist in Concert with Prostratin for Activation of Silent HIV

The persistence of latently HIV-infected cells in patients under combined antiretroviral treatment (cART) remains the major hurdle for HIV eradication. Thus far, individual compounds have not been sufficiently potent to reactivate latent virus and guarantee its elimination in vivo. Thus, we hypothesized that transcriptional enhancers, in concert with compounds triggering the innate immune system, are more efficient in reversing latency by creating a Th1 supportive milieu that acts against latently HIV-infected cells at various levels. To test our hypothesis, we screened six compounds on a coculture of latently infected cells (J-lat) and monocyte-derived dendritic cells (MDDCs). The protein kinase C (PKC) agonist prostratin, with a Toll-like receptor 8 (TLR8) agonist, resulted in greater reversion of HIV latency than any single compound. This combinatorial approach led to a drastic phenotypic and functional maturation of the MDDCs. Tumor necrosis factor (TNF) and cell-cell interactions were crucial for the greater reversion observed. Similarly, we found a greater potency of the combination of prostratin and TLR8 agonist in reversing HIV latency when applying it to primary cells of HIV-infected patients. Thus, we demonstrate here the synergistic interplay between TLR8-matured MDDCs and compounds acting directly on latently HIV-infected cells, targeting different mechanisms of latency, by triggering various signaling pathways. Moreover, TLR8 triggering may reverse exhaustion of HIV-specific cytotoxic T lymphocytes that might be essential for killing or constraining the latently infected cells.

IMPORTANCE

Curing HIV is the Holy Grail. The so-called "shock and kill" strategy relies on drug-mediated reversion of HIV latency and the subsequent death of those cells under combined antiretroviral treatment. So far, no compound achieves efficient reversal of latency or eliminates this latent reservoir. The compounds may not target all of the latency mechanisms in all latently infected cells. Moreover, HIV-associated exhaustion of the immune system hinders the efficient elimination of the reactivated cells. In this study, we demonstrated synergistic latency reversion by combining agonists for protein kinase C and Toll-like receptor 8 in a coculture of latently infected cells with myeloid dendritic cells. The drug prostratin stimulates directly the transcriptional machinery of latently infected cells, and the TLR8 agonist acts indirectly by maturing dendritic cells. These findings highlight the importance of the immune system and its activation, in combination with direct-acting compounds, to reverse latency.

Identification of Human Anti-HIV gp160 Monoclonal Antibodies That Make Effective Immunotoxins

The envelope (Env) glycoprotein of HIV is the only intact viral protein expressed on the surface of both virions and infected cells. Env is the target of neutralizing antibodies (Abs) and has been the subject of intense study in efforts to produce HIV vaccines. Therapeutic anti-Env Abs can also exert antiviral effects via Fc-mediated effector mechanisms or as cytotoxic immunoconjugates, such as immunotoxins (ITs). In the course of screening monoclonal antibodies (MAbs) for their ability to deliver cytotoxic agents to infected or Env-transfected cells, we noted disparities in their functional activities. Different MAbs showed diverse functions that did not correlate with each other. For example, MAbs against the external loop region of gp41 made the most effective ITs against infected cells but did not neutralize virus and bound only moderately to the same cells that they killed so effectively when they were used in ITs. There were also differences in IT-mediated killing among transfected and infected cell lines that were unrelated to the binding of the MAb to the target cells. Our studies of a well-characterized antigen demonstrate that MAbs against different epitopes have different functional activities and that the binding of one MAb can influence the interaction of other MAbs that bind elsewhere on the antigen. These results have implications for the use of MAbs and ITs to kill HIV-infected cells and eradicate persistent reservoirs of HIV infection.

IMPORTANCE

There is increased interest in using antibodies to treat and cure HIV infection. Antibodies can neutralize free virus and kill cells already carrying the virus. The virus envelope (Env) is the only HIV protein expressed on the surfaces of virions and infected cells. In this study, we examined a panel of human anti-Env antibodies for their ability to deliver cell-killing toxins to HIV-infected cells and to perform other antiviral functions. The ability of an antibody to make an effective immunotoxin could not be predicted from its other functional characteristics, such as its neutralizing activity. Anti-HIV immunotoxins could be used to eliminate virus reservoirs that persist despite effective antiretroviral therapy.

Design and In Vivo Characterization of Immunoconjugates Targeting HIV gp160

The envelope (Env) glycoprotein of HIV is expressed on the surface of productively infected cells and can be used as a target for cytotoxic immunoconjugates (ICs), in which cell-killing moieties, including toxins, drugs, or radionuclides, are chemically or genetically linked to monoclonal antibodies (MAbs) or other targeting ligands. Such ICs could be used to eliminate persistent reservoirs of HIV infection. We have found that MAbs which bind to the external loop of gp41, e.g., MAb 7B2, make highly effective ICs, particularly when used in combination with soluble CD4. We evaluated the toxicity, immunogenicity, and efficacy of the ICs targeted with 7B2 in mice and in simian-human immunodeficiency virus-infected macaques. In the macaques, we tested immunotoxins (ITs), consisting of protein toxins bound to the targeting agent. ITs were well tolerated and initially efficacious but were ultimately limited by their immunogenicity. In an effort to decrease immunogenicity, we tested different toxic moieties, including recombinant toxins, cytotoxic drugs, and tubulin inhibitors. ICs containing deglycosylated ricin A chain prepared from ricin toxin extracted from castor beans were the most effective in killing HIV-infected cells. Having identified immunogenicity as a major concern, we show that conjugation of IT to polyethylene glycol limits immunogenicity. These studies demonstrate that cytotoxic ICs can target virus-infected cells in vivo but also highlight potential problems to be addressed.

IMPORTANCE

It is not yet possible to cure HIV infection. Even after years of fully effective antiviral therapy, a persistent reservoir of virus-infected cells remains. Here we propose that a targeted conjugate consisting of an anti-HIV antibody bound to a toxic moiety could function to kill the HIV-infected cells that constitute this reservoir. We tested this approach in HIV-infected cells grown in the lab and in animal infections. Our studies demonstrated that these immunoconjugates are effective both in vitro and in test animals. In particular, ITs constructed with the deglycosylated A chain prepared from native ricin were the most effective in killing cells, but their utility was blunted because they provoked immune reactions that interfered with the therapeutic effects. We then demonstrated that coating of the ITs with polyethylene glycol minimized the immunogenicity, as has been demonstrated with other protein therapies.

Development of real-time PCR for quantitation of simian immunodeficiency virus 2-LTR circles

BACKGROUND

Non-human primates infected with simian immunodeficiency virus (SIV) represent a robust model to evaluate pre-clinical efficacy of HIV-1 preventive strategies and to determine the size of reservoir.

METHODS

We developed a real-time qPCR assay to specifically quantify episomal 2-LTR circular DNA in peripheral blood mononuclear cells and brain tissues from SIV-infected macaques.

RESULTS

This assay has sensitivity, accuracy and reproducibility over seven orders of magnitude. High copy numbers of SIV 2-LTR circles were correlated to high proviral DNA levels in brains of two SIV encephalitic animals. In contrast, no 2-LTR circles were detectable in two SIV-infected animals with no sign of encephalitis or two animals that had mild encephalitis with low levels of proviral DNA.

CONCLUSIONS

These results suggest that simultaneous application of total proviral DNA and 2-LTR circle assays provides quantitative evaluation of pathogenesis and outcome of SIV infection in macaques.

Humanized mice for HIV and AIDS research

HIV has a very limited species tropism that prevents the use of most conventional small animal models for AIDS research. The in vivo analysis of HIV/AIDS has benefited extensively from novel chimeric animal models that accurately recapitulate key aspects of the human condition. Specifically, immunodeficient mice that are systemically repopulated with human hematolymphoid cells offer a viable alternative for the study of a multitude of highly relevant aspects of HIV replication, pathogenesis, therapy, transmission, prevention, and eradication. This article summarizes some of the multiple contributions that humanized mouse models of HIV infection have made to the field of AIDS research. These models have proven to be highly informative and hold great potential for accelerating multiple aspects of HIV research in the future.

Blocking CXCL9 Decreases HIV-1 Replication and Enhances the Activity of Prophylactic Antiretrovirals in Human Cervical Tissues

OBJECTIVES

The interferon-gamma-induced chemokine CXCL9 is expressed in a wide range of inflammatory conditions including those affecting the female genital tract. CXCL9 promotes immune cell recruitment, activation, and proliferation. The role of CXCL9 in modulating HIV-1 infection of cervicovaginal tissues, a main portal of viral entry, however, has not been established. We report a link between CXCL9 and HIV-1 replication in human cervical tissues and propose CXCL9 as a potential target to enhance the anti-HIV-1 activity of prophylactic antiretrovirals.

DESIGN

Using ex vivo infection of human cervical tissues as a model of mucosal HIV-1 acquisition, we described the effect of CXCL9 neutralization on HIV-1 gene expression and mucosal CD4 T-cell activation. The anti-HIV-1 activity of tenofovir, the leading mucosal pre-exposure prophylactic microbicide, alone or in combination with CXCL9 neutralization was also studied.

METHODS

HIV-1 replication was evaluated by p24 ELISA. HIV-1 DNA and RNA, and CD4, CCR5, and CD38 transcription were evaluated by quantitative real-time polymerase chain reaction. Frequency of activated cervical CD4 T cells was quantified using fluorescence-activated cell sorting.

RESULTS

Antibody blocking of CXCL9 reduced HIV-1 replication by decreasing mucosal CD4 T-cell activation. CXCL9 neutralization in combination with suboptimal concentrations of tenofovir, possibly present in the cervicovaginal tissues of women using the drug inconsistently, demonstrated an earlier and greater decrease in HIV-1 replication compared with tissues treated with tenofovir alone.

CONCLUSIONS

CXCL9 neutralization reduces HIV-1 replication and may be an effective target to enhance the efficacy of prophylactic antiretrovirals.

Using animal models to overcome temporal, spatial and combinatorial challenges in HIV persistence research

Research challenges associated with understanding HIV persistence during antiretroviral therapy can be categorized as temporal, spatial and combinatorial. Temporal research challenges relate to the timing of events during establishment and maintenance of HIV persistence. Spatial research challenges regard the anatomical locations and cell subsets that harbor persistent HIV. Combinatorial research challenges pertain to the order of administration, timing of administration and specific combinations of compounds to be administered during HIV eradication therapy. Overcoming these challenges will improve our understanding of HIV persistence and move the field closer to achieving eradication of persistent HIV. Given that humanized mice and non-human primate HIV models permit rigorous control of experimental conditions, these models have been used extensively as in vivo research platforms for directly addressing these research challenges. The aim of this manuscript is to provide a comprehensive review of these recent translational advances made in animal models of HIV persistence.

A Simple Mouse Model for the Study of Human Immunodeficiency Virus

Humanized mouse models derived from immune-deficient mice have been the primary tool for studies of human infectious viruses, such as human immunodeficiency virus (HIV). However, the current protocol for constructing humanized mice requires elaborate procedures and complicated techniques, limiting the supply of such mice for viral studies. Here, we report a convenient method for constructing a simple HIV-1 mouse model. Without prior irradiation, NOD/SCID/IL2Rγ-null (NSG) mice were intraperitoneally injected with 1 × 10(7) adult human peripheral blood mononuclear cells (hu-PBMCs). Four weeks after PBMC inoculation, human CD45(+) cells, and CD3(+)CD4(+) and CD3(+)CD8(+) T cells were detected in peripheral blood, lymph nodes, spleen, and liver, whereas human CD19(+) cells were observed in lymph nodes and spleen. To examine the usefulness of hu-PBMC-inoculated NSG (hu-PBMC-NSG) mice as an HIV-1 infection model, we intravenously injected these mice with dual-tropic HIV-1DH12 and X4-tropic HIV-1NL4-3 strains. HIV-1-infected hu-PBMC-NSG mice showed significantly lower human CD4(+) T cell counts and high HIV viral loads in the peripheral blood compared with noninfected hu-PBMC-NSG mice. Following highly active antiretroviral therapy (HAART) and neutralizing antibody treatment, HIV-1 replication was significantly suppressed in HIV-1-infected hu-PBMC-NSG mice without detectable viremia or CD4(+) T cell depletion. Moreover, the numbers of human T cells were maintained in hu-PBMC-NSG mice for at least 10 weeks. Taken together, our results suggest that hu-PBMC-NSG mice may serve as a relevant HIV-1 infection and pathogenesis model that could facilitate in vivo studies of HIV-1 infection and candidate HIV-1 protective drugs.

Recent developments in the effort to cure HIV infection: going beyond N = 1

Combination antiretroviral therapy (ART) can suppress plasma HIV to undetectable levels, allowing HIV-infected individuals who are treated early a nearly normal life span. Despite the clear ability of ART to prevent morbidity and mortality, it is not curative. Even in individuals who have full suppression of viral replication on ART, there are resting memory CD4+ T cells that harbor stably integrated HIV genomes, which are capable of producing infectious virus upon T cell activation. This latent viral reservoir is considered the primary obstacle to the development of an HIV cure, and recent efforts in multiple areas of HIV research have been brought to bear on the development of strategies to eradicate or develop a functional cure for HIV. Reviews in this series detail progress in our understanding of the molecular and cellular mechanisms of viral latency, efforts to accurately assess the size and composition of the latent reservoir, the characterization and development of HIV-targeted broadly neutralizing antibodies and cytolytic T lymphocytes, and animal models for the study HIV latency and therapeutic strategies.

In vivo platforms for analysis of HIV persistence and eradication

HIV persistence in patients undergoing antiretroviral therapy is a major impediment to the cure of HIV/AIDS. The molecular and cellular mechanisms underlying HIV persistence in vivo have not been fully elucidated. This lack of basic knowledge has hindered progress in this area. The in vivo analysis of HIV persistence and the implementation of curative strategies would benefit from animal models that accurately recapitulate key aspects of the human condition. This Review summarizes the contribution that humanized mouse models of HIV infection have made to the field of HIV cure research. Even though these models have been shown to be highly informative in many specific areas, their great potential to serve as excellent platforms for discovery in HIV pathogenesis and treatment has yet to be fully developed.

Animal Models for HIV Cure Research

The HIV-1/AIDS pandemic continues to spread unabated worldwide, and no vaccine exists within our grasp. Effective antiretroviral therapy (ART) has been developed, but ART cannot clear the virus from the infected patient. A cure for HIV-1 is badly needed to stop both the spread of the virus in human populations and disease progression in infected individuals. A safe and effective cure strategy for human immunodeficiency virus (HIV) infection will require multiple tools, and appropriate animal models are tools that are central to cure research. An ideal animal model should recapitulate the essential aspects of HIV pathogenesis and associated immune responses, while permitting invasive studies, thus allowing a thorough evaluation of strategies aimed at reducing the size of the reservoir (functional cure) or eliminating the reservoir altogether (sterilizing cure). Since there is no perfect animal model for cure research, multiple models have been tailored and tested to address specific quintessential questions of virus persistence and eradication. The development of new non-human primate and mouse models, along with a certain interest in the feline model, has the potential to fuel cure research. In this review, we highlight the major animal models currently utilized for cure research and the contributions of each model to this goal.

Modulation of apoptosis and viral latency - an axis to be well understood for successful cure of human immunodeficiency virus

Human immunodeficiency virus (HIV) is the causative agent of the deadly disease AIDS, which is characterized by the progressive decline of CD4(+)T-cells. HIV-1-encoded proteins such as envelope gp120 (glycoprotein gp120), Tat (trans-activator of transcription), Nef (negative regulatory factor), Vpr (viral protein R), Vpu (viral protein unique) and protease are known to be effective in modulating host cell signalling pathways that lead to an alteration in apoptosis of both HIV-infected and uninfected bystander cells. Depending on the stage of the virus life cycle and host cell type, these viral proteins act as mediators of pro- or anti-apoptotic signals. HIV latency in viral reservoirs is a persistent phenomenon that has remained beyond the control of the human immune system. To cure HIV infections completely, it is crucial to reactivate latent HIV from cellular pools and to drive these apoptosis-resistant cells towards death. Several previous studies have reported the role of HIV-encoded proteins in apoptosis modulation, but the molecular basis for apoptosis evasion of some chronically HIV-infected cells and reactivated latently HIV-infected cells still needs to be elucidated. The current review summarizes our present understanding of apoptosis modulation in HIV-infected cells, uninfected bystander cells and latently infected cells, with a focus on highlighting strategies to activate the apoptotic pathway to kill latently infected cells.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

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.

Double trouble: HIV latency and CTL escape

HIV can enter a state of latency that allows it to persist for decades in antiretroviral drug-treated patients. In a recent Nature paper, Deng et al. (2015) show that this latent reservoir also contains a large number of cytotoxic T lymphocyte escape mutants, presenting another challenge to HIV cure efforts.

Studies of retroviral infection in humanized mice

Many important aspects of human retroviral infections cannot be fully evaluated using only in vitro systems or unmodified animal models. An alternative approach involves the use of humanized mice, which consist of immunodeficient mice that have been transplanted with human cells and/or tissues. Certain humanized mouse models can support robust infection with human retroviruses including different strains of human immunodeficiency virus (HIV) and human T cell leukemia virus (HTLV). These models have provided wide-ranging insights into retroviral biology, including detailed information on primary infection, in vivo replication and pathogenesis, latent/persistent reservoir formation, and novel therapeutic interventions. Here we describe the humanized mouse models that are most commonly utilized to study retroviral infections, and outline some of the important discoveries that these models have produced during several decades of intensive research.

Experimental Approaches for Eliminating Latent HIV

Antiretroviral therapy (ART) can reduce HIV viral loads to undetectable levels and prevent disease progression. However, HIV persists in rare cellular reservoirs within ART-treated patients and rapidly reemerges if ART is stopped. Latently infected CD4⁺ T cells represent a major reservoir of HIV that persists during ART. Therefore, a cure for HIV must include methods that either permanently inactivate or eliminate latent virus. Experimental methods under investigation for eliminating latently infected cells include transplantation/gene therapy approaches intended to deplete the infected cells and replace them with HIV-resistant ones, and DNA editing strategies that are capable of damaging or excising non-expressing HIV proviruses. Alternatively, "activation-elimination," also known as "shock and kill," approaches aim to induce expression of latent virus, allowing the virus to be eliminated by viral cytopathic effects, immune effector mechanisms, or additional cells/antibodies that specifically target and kill cells expressing HIV proteins. Here, we describe these experimental approaches for eliminating latent HIV along with other recent advances in HIV cure research.

Finding a cure for human immunodeficiency virus-1 infection

Remarkable advances have been made in the treatment of human immunodeficiency virus (HIV)-1 infection, but in the entire history of the epidemic, only 1 patient has been cured. Herein we review the fundamental mechanisms that render HIV-1 infection difficult to cure and then discuss recent clinical and experimental situations in which some form of cure has been achieved. Finally, we consider approaches that are currently being taken to develop a general cure for HIV-1 infection.

Recent developments in the search for a cure for HIV-1 infection: targeting the latent reservoir for HIV-1

HIV-1 infection can now be readily controlled with combination antiretroviral therapy. However, the virus persists indefinitely in a stable latent reservoir in resting CD4(+) T cells. This reservoir generally prevents cure of the infection with combination antiretroviral therapy alone. However, several recent cases of potential HIV-1 cure have generated renewed optimism. Here we review these cases and consider new developments in our understanding of the latent reservoir. In addition, we consider clinical aspects of curative strategies to provide a more realistic picture of what a generally applicable cure for HIV-1 infection is likely to entail.

An integrated overview of HIV-1 latency

Despite significant advances in our understanding of HIV, a cure has not been realized for the more than 34 million infected with this virus. HIV is incurable because infected individuals harbor cells where the HIV provirus is integrated into the host's DNA but is not actively replicating and thus is not inhibited by antiviral drugs. Similarly, these latent viruses are not detected by the immune system. In this Review, we discuss HIV-1 latency and the mechanisms that allow this pathogenic retrovirus to hide and persist by exploiting the cellular vehicles of immunological memory.

Gag-positive reservoir cells are susceptible to HIV-specific cytotoxic T lymphocyte mediated clearance in vitro and can be detected in vivo [corrected]

Resting CD4+ T cells infected with HIV persist in the presence of suppressive anti-viral therapy (ART) and are barriers to a cure. One potential curative approach, therapeutic vaccination, is fueled by recognition of the ability of a subset of elite controllers (EC) to control virus without therapy due to robust anti-HIV immune responses. Controllers have low levels of integrated HIV DNA and low levels of replication competent virus, suggesting a small reservoir. As our recent data indicates some reservoir cells can produce HIV proteins (termed GPR cells for Gag-positive reservoir cells), we hypothesized that a fraction of HIV-expressing resting CD4+ T cells could be efficiently targeted and cleared in individuals who control HIV via anti-HIV cytotoxic T lymphocytes (CTL). To test this we examined if superinfected resting CD4+ T cells from EC express HIV Gag without producing infectious virus and the susceptibility of these cells to CTL. We found that resting CD4+ T cells expressed HIV Gag and were cleared by autologous CD8+ T cells from EC. Importantly, we found the extent of CTL clearance in our in vitro assay correlates with in vivo reservoir size and that a population of Gag expressing resting CD4+ T cells exists in vivo in patients well controlled on therapy.

T-Cell Signaling in HIV-1 Infection

HIV exploits the T-cell signaling network to gain access to downstream cellular components, which serves as effective tools to break the cellular barriers. Multiple host factors and their interaction with viral proteins contribute to the complexity of HIV-1 pathogenesis and disease progression. HIV-1 proteins gp120, Nef, Tat and Vpr alter the T-cell signaling pathways by activating multiple transcription factors including NF-ĸB, Sp1 and AP-1. HIV-1 evades the immune system by developing a multi-pronged strategy. Additionally, HIV-1 encoded proteins influence the apoptosis in the host cell favoring or blocking T-cell apoptosis. Thus, T-cell signaling hijacked by viral proteins accounts for both viral persistence and immune suppression during HIV-1 infection. Here, we summarize past and present studies on HIV-1 T-cell signaling with special focus on the possible role of T cells in facilitating viral infection and pathogenesis