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

Knowledge From London and Berlin: Finding Threads to a Functional HIV Cure

Despite the ability of combination antiretroviral therapy (cART) to increase the life expectancy of patients infected with human immunodeficiency virus (HIV), viral reservoirs persist during life-long treatment. Notably, two cases of functional cure for HIV have been reported and are known as the "Berlin Patient" and the "London Patient". Both patients received allogeneic hematopoietic stem cell transplantation from donors with homozygous CCR5 delta32 mutation for an associated hematological malignancy. Therefore, there is growing interest in creating an HIV-resistant immune system through the use of gene-modified autologous hematopoietic stem cells with non-functional CCR5. Moreover, studies in CXCR4-targeted gene therapy for HIV have also shown great promise. Developing a cure for HIV infection remains a high priority. In this review, we discuss the increasing progress of coreceptor-based hematopoietic stem cell gene therapy, cART, milder conditioning regimens, and shock and kill strategies that have important implications for designing potential strategies aiming to achieve a functional cure for the majority of people with HIV.

Shocking HIV-1 with immunomodulatory latency reversing agents

The "shock-and-kill" strategy is one of the most explored HIV-1 cure approaches to eliminate latent virus. This strategy is based on HIV-1 reactivation using latency reversing agents (LRAs) to reactivate latent proviruses (the "shock" phase) and to induce subsequent elimination of the reactivated cells by immune responses or virus-induced cytopathic effects (the "kill" phase). Studies using immunomodulatory LRAs such as blockers of immune checkpoint molecules, toll-like receptor agonists, cytokines and CD8⁺ T cell depleting antibodies showed promising potential as LRAs inducing directly or indirectly cellular pathways known to control HIV transcription. However, the precise molecular mechanisms by which these immunomodulatory LRAs reverse latency remain incompletely understood. Together with the heterogenous nature of HIV-1 latency, this lack of understanding complicates efforts to develop more efficient and safer cure strategies. Hence, deciphering those mechanisms is pivotal in designing approaches to eliminate latent HIV infection.

A "Drug-Dependent" Immune System Can Compromise Protection against Infection: The Relationships between Psychostimulants and HIV

Psychostimulant use is a major comorbidity in people living with HIV, which was initially explained by them adopting risky behaviors that facilitate HIV transmission. However, the effects of drug use on the immune system might also influence this phenomenon. Psychostimulants act on peripheral immune cells even before they reach the central nervous system (CNS) and their effects on immunity are likely to influence HIV infection. Beyond their canonical activities, classic neurotransmitters and neuromodulators are expressed by peripheral immune cells (e.g., dopamine and enkephalins), which display immunomodulatory properties and could be influenced by psychostimulants. Immune receptors, like Toll-like receptors (TLRs) on microglia, are modulated by cocaine and amphetamine exposure. Since peripheral immunocytes also express TLRs, they may be similarly affected by psychostimulants. In this review, we will summarize how psychostimulants are currently thought to influence peripheral immunity, mainly focusing on catecholamines, enkephalins and TLR4, and shed light on how these drugs might affect HIV infection. We will try to shift from the classic CNS perspective and adopt a more holistic view, addressing the potential impact of psychostimulants on the peripheral immune system and how their systemic effects could influence HIV infection.

Natural killer cells play an important role in virus infection control: Antiviral mechanism, subset expansion and clinical application

With the global spread of coronavirus disease 2019 (COVID-19), the important role of natural killer (NK) cells in the control of various viral infections attracted more interest, via non-specific activation, such as antibody-dependent cell-mediated cytotoxicity (ADCC) and activating receptors, as well as specific activation, such as memory-like NK generation. In response to different viral infections, NK cells fight viruses in different ways, and different NK subsets proliferate. For instance, cytomegalovirus (CMV) induces NKG2C + CD57 + KIR+ NK cells to expand 3-6 months after hematopoietic stem cell transplantation (HSCT), but human immunodeficiency virus (HIV) induces KIR3DS1+/KIR3DL1 NK cells to expand in the acute phase of infection. However, the similarities and differences among these processes and their molecular mechanisms have not been fully discussed. In this article, we provide a summary and comparison of antiviral mechanisms, unique subset expansion and time periods in peripheral blood and tissues under different conditions of CMV, HIV, Epstein-Barr virus (EBV), COVID-19 and hepatitis B virus (HBV) infections. Accordingly, we also discuss current clinical NK-associated antiviral applications, including cell therapy and NK-related biological agents, and we state the progress and future prospects of NK cell antiviral treatment.

Latency Reversal 2.0: Giving the Immune System a Seat at the Table

PURPOSE OF REVIEW

For most people living with HIV (PLWH), treatment with effective antiretroviral therapy (ART) results in suppression of viremia below the limit of detection of clinical assays, immune reconstitution, reduced immune activation, avoidance of opportunistic infections, and progression to AIDS. However, ART alone is not curative, and HIV persists in a non-replicating, latent form. In this review, we provide a historical perspective on non-specific latency reversal approaches (LRA 1.0) and summarize recent advances in latency reversal strategies that target specific signaling pathways within CD4+ T cells or other immune cells to induce expression of latent HIV (immune-based latency reversal, or LRA 2.0).

RECENT FINDINGS

The HIV reservoir is primarily composed of latently infected CD4+ T cells carrying integrated, replication-competent provirus that can give rise to rebound viremia if ART is stopped. Myeloid lineage cells also contribute to HIV latency in certain tissues; we focus here on CD4+ T cells as a sufficient body of evidence regarding latency reversal in myeloid cells is lacking. The immunomodulatory LRA 2.0 approaches we describe include pattern recognition receptor agonists, immune checkpoint inhibitors, non-canonical NF-kB stimulation, and transient CD8+ lymphocyte depletion, along with promising combination strategies. We highlight recent studies demonstrating robust latency reversal in nonhuman primate models. While significant strides have been made in terms of virus reactivation from latency, initial hopes for latency reversal alone to result in a reduction of infected cells, through viral cytopathic effect or an unboosted immune system, have not been realized and it seems clear that even effective latency reversal strategies will need to be paired with an approach that facilitates immune recognition and clearance of cells containing reactivated virus.

Multiply spliced HIV RNA is a predictive measure of virus production ex vivo and in vivo following reversal of HIV latency

BACKGROUND

One strategy being pursued to clear latently infected cells that persist in people living with HIV (PLWH) on antiretroviral therapy (ART) is to activate latent HIV infection with a latency reversing agent (LRA). Surrogate markers that accurately measure virus production following an LRA are needed.

METHODS

We quantified cell-associated unspliced (US), multiply spliced (MS) and supernatant (SN) HIV RNA by qPCR from total and resting CD4+ T cells isolated from seven PLWH on ART before and after treatment ex vivo with different LRAs, including histone deacetylase inhibitors (HDACi). MS and plasma HIV RNA were also quantified from PLWH on ART (n-11) who received the HDACi panobinostat.

FINDINGS

In total and resting CD4+ T cells from PLWH on ART, detection of US RNA was common while detection of MS RNA was infrequent. Primers used to detect MS RNA, in contrast to US RNA, bound sites of the viral genome that are commonly mutated or deleted in PLWH on ART. Following ex vivo stimulation with LRAs, we identified a strong correlation between the fold change increase in SN and MS RNA, but not the fold change increase in SN and US RNA. In PLWH on ART who received panobinostat, MS RNA was significantly higher in samples with detectable compared to non0detectable plasma HIV RNA.

INTERPRETATION

Following administration of an LRA, quantification of MS RNA is more likely to reflect an increase in virion production and is therefore a better indicator of meaningful latency reversal.

FUNDING

NHMRC, NIH DARE collaboratory.

Replicate Aptima Assay for Quantifying Residual Plasma Viremia in Individuals on Antiretroviral Therapy

Detection of residual plasma viremia in antiretroviral therapy (ART)-suppressed HIV-infected individuals is critical for characterizing the latent reservoir and evaluating the impact of cure interventions. Ultracentrifugation-based single-copy assays are sensitive but labor intensive. Fully automated replicate testing using a standard clinical viral load assay was evaluated as a high-throughput alternative for the quantification of low-level viremia. Four plasma samples from blood donors with acute HIV-1 infection and one viral culture supernatant were serially diluted into 25-ml samples to nominal viral loads ranging from 39 to <0.

Detection of residual plasma viremia in antiretroviral therapy (ART)-suppressed HIV-infected individuals is critical for characterizing the latent reservoir and evaluating the impact of cure interventions. Ultracentrifugation-based single-copy assays are sensitive but labor intensive. Fully automated replicate testing using a standard clinical viral load assay was evaluated as a high-throughput alternative for the quantification of low-level viremia. Four plasma samples from blood donors with acute HIV-1 infection and one viral culture supernatant were serially diluted into 25-ml samples to nominal viral loads ranging from 39 to <0.5 copies (cp)/ml. Each dilution was tested with 45 replicates (reps) using 0.5 ml/rep with the Aptima HIV-1 Quant assay. The nominal and estimated viral loads based on the single-hit Poisson model were compared, and a hybrid Poisson digital model for calibrated viral load estimation was derived. Testing performed using 45 reps on longitudinal plasma samples from 50 ART-suppressed individuals in the Reservoir Assay Validation and Evaluation Network (RAVEN) study cohort (range of 1 to 19 years of continuous ART suppression) showed a median viral load of 0.54 cp/ml (interquartile range [IQR], 0.22 to 1.46 cp/ml) and a 14% (95% confidence interval [CI], 9% to 19%) decline in viral load for each additional year in duration suppressed. Within the RAVEN cohort, the expected false-negative rate for detection at lower rep numbers using 9 and 18 reps was 26% and 14%, respectively. Residual plasma viremia levels positively correlated with cell-associated HIV RNA and DNA. The performance characteristics of the replicate Aptima assay support its use for quantifying residual plasma viremia to study the latent HIV reservoir and cure interventions.

The Role of Toll-Like Receptors in Retroviral Infection

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

Brief Report: Toll-like Receptor 9-1635A/G Polymorphism Is Associated With HIV-1 Rebound After Four Weeks of Interruption of Antiretroviral Therapy

OBJECTIVES

This study aims to analyze the association of the presence of common polymorphisms [single nucleotide polymorphisms (SNPs)] on Toll-like receptors (TLRs), such as TLR9-1635A/G, TLR2-1892A/C, TLR2-2258G/A, TLR4-899A/G, and TLR4-1196C/T, with the viral rebound after stopping antiretroviral treatment (ART). CCR5-Δ32 deletion and HLA-A/HLA-B alleles were also analyzed.

DESIGN

Interruption of ART may be required to investigate the outcome of strategies aimed to achieve drug-free HIV remission or cure. However, interruption of ART is currently not indicated. This was a retrospective longitudinal study that included 57 long-term suppressed HIV-1-infected individuals.

METHODS

TLR SNPs were detected by real-time polymerase chain reaction (PCR). CCR5-Δ32 was analyzed by conventional PCR and HLA-A and HLA-B alleles by PCR-SSOP Luminex.

RESULTS

HIV-1 RNA rebound at week 4 after treatment interruption positively correlated with pre-ART HIV-1 load (P = 0.025). The TLR9-1635AA genotype was independently associated with a higher HIV-1 rebound compared with those with AG + GG genotype (multivariate stepwise regression analysis, P = 0.004). Women had lower HIV-1 RNA load both at rebound and during the 72 weeks of follow-up compared with men (P < 0.05 at all time-points), whereas CD4 nadir and CD4 count set-point were similar according to sex. The pre-ART viral load was independently associated with the viral set-point (P = 0.001), whereas the presence of the HLA-A01 allele (P = 0.027) and the CD4 nadir (P = 0.001) were associated with the CD4 count set-point.

CONCLUSIONS

The association of the TLR9-1635AA genotype with a higher HIV-1 rebound suggests that this SNP may affect the results from strategies requiring interruption of ART aimed to cure HIV-1 infection.

A randomized trial of vorinostat with treatment interruption after initiating antiretroviral therapy during acute HIV-1 infection

OBJECTIVE AND DESIGN

A randomized, open-label pilot study in individuals treated with antiretroviral therapy (ART) since acute HIV infection (AHI) with a regimen including a histone deacetylase inhibitor to induce HIV from latency and control HIV replication during subsequent treatment interruption (TI).

METHODS

Fifteen participants who initiated ART at AHI were randomized to vorinostat/hydroxychloroquine/maraviroc (VHM) plus ART (n ​= ​10) or ART alone (n ​= ​5). The VHM arm received three 14-day vorinostat cycles within 10 weeks before TI. ART was resumed for plasma viral load (VL) ​> ​1,000 HIV RNA copies/mL. Primary outcome was proportion of participants on VHM ​+ ​ART versus ART only with VL ​< ​50 copies/mL for 24 weeks after TI.

RESULTS

Fifteen participants on ART (median: 178 weeks: range 79-295) enrolled. Two on VHM ​+ ​ART experienced serious adverse events. Fourteen participants underwent TI; all experienced VL rebound with no difference in time between arms: VHM ​+ ​ART (n ​= ​9) median: 4 weeks and ART only (n ​= ​5) median: 5 weeks. VHM induced a 2.2-fold increase in VL (p ​= ​0.008) by single-copy HIV RNA assay after the first cycle. Neopterin levels increased significantly following the first two cycles. After VHM treatment, the frequencies of peripheral blood mononuclear cells harboring total HIV DNA and cell-associated RNA were unchanged. All participants achieved VL suppression following ART re-initiation.

CONCLUSIONS

Administration of VHM increased HIV VL in plasma, but this was not sustained. VHM did not impact time to viral rebound following TI and had no impact on the size of the HIV reservoir, suggesting that HIV reservoir elimination will require alternative treatment strategies.

Interferon-α alters host glycosylation machinery during treated HIV infection

Background

A comprehensive understanding of host factors modulated by the antiviral cytokine interferon-α (IFNα) is imperative for harnessing its beneficial effects while avoiding its detrimental side-effects during HIV infection. Cytokines modulate host glycosylation which plays a critical role in mediating immunological functions. However, the impact of IFNα on host glycosylation has never been characterized.

Methods

We assessed the impact of pegylated IFNα2a on IgG glycome, as well as CD8⁺ T and NK cell-surface glycomes, of 18 HIV-infected individuals on suppressive antiretroviral therapy. We linked these glycomic signatures to changes in inflammation, CD8⁺ T and NK cell phenotypes, and HIV DNA.

Findings

We identified significant interactions that support a model in which a) IFNα increases the proportion of pro-inflammatory, bisecting GlcNAc glycans (known to enhance FcγR binding) within the IgG glycome, which in turn b) increases inflammation, which c) leads to poor CD8⁺ T cell phenotypes and poor IFNα-mediated reduction of HIV DNA. Examining cell-surface glycomes, IFNα increases levels of the immunosuppressive GalNAc-containing glycans (T/Tn antigens) on CD8⁺ T cells. This induction is associated with lower HIV-gag-specific CD8⁺ T cell functions. Last, IFNα increases levels of fucose on NK cells. This induction is associated with higher NK functions upon K562 stimulation.

Interpretation

IFNα causes host glycomic alterations that are known to modulate immunological responses. These alterations are associated with both detrimental and beneficial consequences of IFNα. Manipulating host glycomic interactions may represent a strategy for enhancing the positive effects of IFNα while avoiding its detrimental side-effects.

Funding

NIH grants R21AI143385, U01AI110434.

Engineering CAR T Cells to Target the HIV Reservoir

The HIV reservoir remains to be a difficult barrier to overcome in order to achieve a therapeutic cure for HIV. Several strategies have been developed to purge the reservoir, including the “kick and kill” approach, which is based on the notion that reactivating the latent reservoir will allow subsequent elimination by the host anti-HIV immune cells. However, clinical trials testing certain classes of latency reactivating agents (LRAs) have so far revealed the minimal impact on reducing the viral reservoir. A robust immune response to reactivated HIV expressing cells is critical for this strategy to work. A current focus to enhance anti-HIV immunity is through the use of chimeric antigen receptors (CARs). Currently, HIV-specific CARs are being applied to peripheral T cells, NK cells, and stem cells to boost recognition and killing of HIV infected cells. In this review, we summarize current developments in engineering HIV directed CAR-expressing cells to facilitate HIV elimination. We also summarize current LRAs that enhance the “kick” strategy and how new generation and combinations of LRAs with HIV specific CAR T cell therapies could provide an optimal strategy to target the viral reservoir and achieve HIV clearance from the body.

The Use of Toll-Like Receptor Agonists in HIV-1 Cure Strategies

Toll-like receptors (TLRs) are a family of pattern recognition receptors and part of the first line of defense against invading microbes. In humans, we know of 10 different TLRs, which are expressed to varying degrees in immune cell subsets. Engaging TLRs through their specific ligands leads to activation of the innate immune system and secondarily priming of the adaptive immune system. Because of these unique properties, TLR agonists have been investigated as immunotherapy in cancer treatment for many years, but in recent years there has also been growing interest in the use of TLR agonists in the context of human immunodeficiency virus type 1 (HIV-1) cure research. The primary obstacle to curing HIV-1 is the presence of a latent viral reservoir in transcriptionally silent immune cells. Due to the very limited transcription of the integrated HIV-1 proviruses, latently infected cells cannot be targeted and cleared by immune effector mechanisms. TLR agonists are very interesting in this context because of their potential dual effects as latency reverting agents (LRAs) and immune modulatory compounds. Here, we review preclinical and clinical data on the impact of TLR stimulation on HIV-1 latency as well as antiviral and HIV-1-specific immunity. We also focus on the promising role of TLR agonists in combination strategies in HIV-1 cure research. Different combinations of TLR agonists and broadly neutralizing antibodies or TLRs agonists as adjuvants in HIV-1 vaccines have shown very encouraging results in non-human primate experiments and these concepts are now moving into clinical testing.

Plasmacytoid Dendritic Cells as Cell-Based Therapeutics: A Novel Immunotherapy to Treat Human Immunodeficiency Virus Infection?

Dendritic cells (DCs) play a critical role in mediating innate and adaptive immune responses. Since their discovery in the late 1970's, DCs have been recognized as the most potent antigen-presenting cells (APCs). DCs have a superior capacity for acquiring, processing, and presenting antigens to T cells and they express costimulatory or coinhibitory molecules that determine immune activation or anergy. For these reasons, cell-based therapeutic approaches using DCs have been explored in cancer and infectious diseases but with limited success. In humans, DCs are divided into heterogeneous subsets with distinct characteristics. Two major subsets are CD11c⁺ myeloid (m)DCs and CD11c⁻ plasmacytoid (p)DCs. pDCs are different from mDCs and play an essential role in the innate immune system via the production of type I interferons (IFN). However, pDCs are also able to take-up antigens and effectively cross present them. Given the rarity of pDCs in blood and technical difficulties in obtaining them from human blood samples, the understanding of human pDC biology and their potential in immunotherapeutic approaches (e.g. cell-based vaccines) is limited. However, due to the recent advancements in cell culturing systems that allow for the generation of functional pDCs from CD34⁺ hematopoietic stem and progenitor cells (HSPC), studying pDCs has become easier. In this mini-review, we hypothesize about the use of pDCs as a cell-based therapy to treat HIV by enhancing anti-HIV-immune responses of the adaptive immune system and enhancing the anti-viral responses of the innate immune system. Additionally, we discuss obstacles to overcome before this approach becomes clinically applicable.

Pattern Recognition Receptor Ligands as an Emerging Therapeutic Agent for Latent HIV-1 Infection

Toll-like receptors (TLRs) were first identified as molecular sensors that transduce signals from specific structural patterns derived from pathogens; their underlying molecular mechanisms of recognition and signal transduction are well-understood. To date, more than 20 pattern-recognition receptors (PRRs) have been reported in humans, some of which are membrane-bound, similar to TLRs, whereas others are cytosolic, including retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), and stimulator of interferon genes (STING). Clinically, PRR ligands have been developed as vaccine adjuvants to activate innate immunity and enhance subsequent antigen-specific immune responses. Recently, PRR ligands have been used as direct immunostimulators to enhance immune responses against infectious diseases and cancers. HIV-1 remains one of the world's most significant public health challenges. Without the elimination of HIV-1 latently infected cells, patients require lifelong combination antiretroviral therapy (cART), while research aimed at a functional cure for HIV-1 infection continues. Based on the concept of "shock and kill," a latency-reversing agent (LRA) has been developed to reactivate latently infected cells and induce cell death. However, previous research has shown that LRAs have limited efficacy in the eradication of these reservoirs in vivo. Besides, PRR ligands with anti-retroviral drugs have been developed for use in HIV treatment for these years. This mini-review summarizes the current understanding of the role of PRR ligands in AIDS research, suggests directions for future research, and proposes potential clinical applications.

Pathways towards human immunodeficiency virus elimination

Antiretroviral therapy (ART) suppresses human immunodeficiency virus (HIV) infection. Research seeking to transform viral suppression into elimination has generated novel immune, chemical and molecular antiviral agents. However, none, to date, have excised latent integrated proviral DNA or removed infected cells from infected persons. These efforts included, but are not limited to, broadly neutralizing antibodies, "shock" and "kill" latency-reversing agents, innate immune regulators, and sequential long-acting antiretroviral nanoformulated prodrugs and CRISPR-Cas9 gene editing. While, the latter, enabled the complete excision of latent HIV-1 from the host genome success was so far limited. We contend that improvements in antiretroviral delivery, potency, agent specificity, or combinatorial therapies can provide a pathway towards complete HIV elimination.

Diverse effects of interferon alpha on the establishment and reversal of HIV latency

HIV latency is the major barrier to a cure for people living with HIV (PLWH) on antiretroviral therapy (ART) because the virus persists in long-lived non-proliferating and proliferating latently infected CD4⁺ T cells. Latently infected CD4⁺ T cells do not express viral proteins and are therefore not visible to immune mediated clearance. Therefore, identifying interventions that can reverse latency and also enhance immune mediated clearance is of high interest. Interferons (IFNs) have multiple immune enhancing effects and can inhibit HIV replication in activated CD4⁺ T cells. However, the effects of IFNs on the establishment and reversal of HIV latency is not understood. Using an in vitro model of latency, we demonstrated that plasmacytoid dendritic cells (pDC) inhibit the establishment of HIV latency through secretion of type I IFNα, IFNβ and IFNω but not IFNε or type III IFNλ1 and IFNλ3. However, once latency was established, IFNα but no other IFNs were able to efficiently reverse latency in both an in vitro model of latency and CD4⁺ T cells collected from PLWH on suppressive ART. Binding of IFNα to its receptor expressed on primary CD4⁺ T cells did not induce activation of the canonical or non-canonical NFκB pathway but did induce phosphorylation of STAT1, 3 and 5 proteins. STAT5 has been previously demonstrated to bind to the HIV long terminal repeat and activate HIV transcription. We demonstrate diverse effects of interferons on HIV latency with type I IFNα; inhibiting the establishment of latency but also reversing HIV latency once latency is established.

Antiretroviral therapy (ART) cannot cure HIV or eliminate infection from long-lived and proliferating latently infected CD4⁺ T cells. Plasmacytoid dendritic cells (pDC) are major producers of interferons (IFNs), which have multiple effects on viral replication and immunity including suppression of viral expression that could favor HIV latency. Van Der Sluis et al. show that type I IFNs inhibit the establishment of HIV latency, however, once established, latency can be reversed by IFNα but not by other type I or type III IFNs. These observations demonstrate that pDC through type I IFNs are important in HIV latency and can potentially be manipulated to eliminate latent infection.

Reduce and Control: A Combinatorial Strategy for Achieving Sustained HIV Remissions in the Absence of Antiretroviral Therapy

Human immunodeficiency virus (HIV-1) indefinitely persists, despite effective antiretroviral therapy (ART), within a small pool of latently infected cells. These cells often display markers of immunologic memory and harbor both replication-competent and -incompetent proviruses at approximately a 1:100 ratio. Although complete HIV eradication is a highly desirable goal, this likely represents a bridge too far for our current and foreseeable technologies. A more tractable goal involves engineering a sustained viral remission in the absence of ART––a “functional cure.” In this setting, HIV remains detectable during remission, but the size of the reservoir is small and the residual virus is effectively controlled by an engineered immune response or other intervention. Biological precedence for such an approach is found in the post-treatment controllers (PTCs), a rare group of HIV-infected individuals who, following ART withdrawal, do not experience viral rebound. PTCs are characterized by a small reservoir, greatly reduced inflammation, and the presence of a poorly understood immune response that limits viral rebound. Our goal is to devise a safe and effective means for replicating durable post-treatment control on a global scale. This requires devising methods to reduce the size of the reservoir and to control replication of this residual virus. In the following sections, we will review many of the approaches and tools that likely will be important for implementing such a “reduce and control” strategy and for achieving a PTC-like sustained HIV remission in the absence of ART.

Combination Immune Checkpoint Blockade to Reverse HIV Latency

In people living with HIV on antiretroviral therapy, HIV latency is the major barrier to a cure. HIV persists preferentially in CD4⁺ T cells expressing multiple immune checkpoint (IC) molecules, including programmed death (PD)-1, T cell Ig and mucin domain-containing protein 3 (TIM-3), lymphocyte associated gene 3 (LAG-3), and T cell immunoreceptor with Ig and ITIM domains (TIGIT). We aimed to determine whether these and other IC molecules have a functional role in maintaining HIV latency and whether blocking IC molecules with Abs reverses HIV latency. Using an in vitro model that establishes latency in both nonproliferating and proliferating human CD4⁺ T cells, we show that proliferating cells express multiple IC molecules at high levels. Latent infection was enriched in proliferating cells expressing PD-1. In contrast, nonproliferating cells expressed IC molecules at significantly lower levels, but latent infection was enriched in cells expressing PD-1, TIM-3, CTL-associated protein 4 (CTLA-4), or B and T lymphocyte attenuator (BTLA). In the presence of an additional T cell-activating stimulus, staphylococcal enterotoxin B, Abs to CTLA-4 and PD-1 reversed HIV latency in proliferating and nonproliferating CD4⁺ T cells, respectively. In the absence of staphylococcal enterotoxin B, only the combination of Abs to PD-1, CTLA-4, TIM-3, and TIGIT reversed latency. The potency of latency reversal was significantly higher following combination IC blockade compared with other latency-reversing agents, including vorinostat and bryostatin. Combination IC blockade should be further explored as a strategy to reverse HIV latency.

Role of Dendritic Cells in Exposing Latent HIV-1 for the Kill

The development of effective yet nontoxic strategies to target the latent human immunodeficiency virus-1 (HIV-1) reservoir in antiretroviral therapy (ART)-suppressed individuals poses a critical barrier to a functional cure. The ‘kick and kill’ approach to HIV eradication entails proviral reactivation during ART, coupled with generation of cytotoxic T lymphocytes (CTLs) or other immune effectors equipped to eliminate exposed infected cells. Pharmacological latency reversal agents (LRAs) that have produced modest reductions in the latent reservoir ex vivo have not impacted levels of proviral DNA in HIV-infected individuals. An optimal cure strategy incorporates methods that facilitate sufficient antigen exposure on reactivated cells following the induction of proviral gene expression, as well as the elimination of infected targets by either polyfunctional HIV-specific CTLs or other immune-based strategies. Although conventional dendritic cells (DCs) have been used extensively for the purpose of inducing antigen-specific CTL responses in HIV-1 clinical trials, their immunotherapeutic potential as cellular LRAs has been largely ignored. In this review, we discuss the challenges associated with current HIV-1 eradication strategies, as well as the unharnessed potential of ex vivo-programmed DCs for both the ‘kick and kill’ of latent HIV-1.

Why and where an HIV cure is needed and how it might be achieved

Despite considerable global investment, only 60% of people who live with HIV currently receive antiretroviral therapy. The sustainability of current programmes remains unknown and key incidence rates are declining only modestly. Given the complexities and expenses associated with lifelong medication, developing an effective curative intervention is now a global priority. Here we review why and where a cure is needed, and how it might be achieved. We argue for expanding these efforts from resource-rich regions to sub-Saharan Africa and elsewhere: for any intervention to have an effect, region-specific biological, therapeutic and implementation issues must be addressed.

Pattern recognition receptors as potential drug targets in inflammatory disorders

Pattern recognition receptors (PRRs) are a key part of the innate immune system, the body's first line of defense against infection and tissue damage. This superfamily of receptors including Toll-like receptors (TLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs) and RIG-like receptors (RLRs) are responsible for initiation of the inflammatory response by their recognition of molecular patterns present in invading microorganisms (such as bacteria, viruses or fungi) during infection or in molecules released following tissue damage during acute or chronic disease states (such as sepsis or arthritis). These receptors are widely expressed and located on the cell surface, in intracellular compartments or in the cytoplasm can detect a single or subset of molecules including lipoproteins, carbohydrates or nucleic acids. In response, they initiate an intracellular signaling cascade that culminates in the synthesis and release of cytokines, chemokines and vasoactive molecules. These steps are necessary to maintain tissue homeostasis and remove potentially dangerous pathogens. However, during extreme or acute responses or during chronic disease, this can be damaging and even lead to death. Therefore, it is thought that targeting such receptors may offer a therapeutic approach in chronic inflammatory diseases or in cases of acute infection leading to sepsis. Herein, the current knowledge on the molecular biology of PRRs is reviewed along with their association with inflammatory and infectious diseases. Finally, the testing of therapeutic compounds and their future merit as targets is discussed.

Targeting Cellular and Tissue HIV Reservoirs With Toll-Like Receptor Agonists

The elimination of both cellular and tissue latent reservoirs is a challenge toward a successful HIV cure. "Shock and Kill" are among the therapeutic strategies that have been more extensively studied to target these reservoirs. These strategies are aimed toward the reactivation of the latent reservoir using a latency-reversal agent (LRA) with the subsequent killing of the reactivated cell either by the cytotoxic arm of the immune system, including NK and CD8 T cells, or by viral cytopathic mechanisms. Numerous LRAs are currently being investigated in vitro, ex vivo as well as in vivo for their ability to reactivate and reduce latent reservoirs. Among those, several toll-like receptor (TLR) agonists have been shown to reactivate latent HIV. In humans, there are 10 TLRs that recognize different pathogen-associated molecular patterns. TLRs are present in several cell types, including CD4 T cells, the cell compartment that harbors the majority of the latent reservoir. Besides their ability to reactivate latent HIV, TLR agonists also increase immune activation and promote an antiviral response. These combined properties make TLR agonists unique among the different LRAs characterized to date. Additionally, some of these agonists have shown promise toward finding an HIV cure in animal models. When in combination with broadly neutralizing antibodies, TLR-7 agonists have shown to impact the SIV latent reservoir and delay viral rebound. Moreover, there are FDA-approved TLR agonists that are currently being investigated for cancer therapy and other diseases. All these has prompted clinical trials using TLR agonists either alone or in combination toward HIV eradication approaches. In this review, we provide an extensive characterization of the state-of-the-art of the use of TLR agonists toward HIV eradication strategies and the mechanism behind how TLR agonists target both cellular and tissue HIV reservoirs.

Statistical analysis of single-copy assays when some observations are zero

Observational and interventional studies for HIV cure research often use single-copy assays to quantify rare entities in blood or tissue samples. Statistical analysis of such measurements presents challenges due to tissue sampling variability and frequent findings of 0 copies in the sample analysed. We examined four approaches to analysing such studies, reflecting different ways of handling observations of 0 copies: (A) replace observations of 0 copies with 1 copy; (B) add 1 to all observed numbers of copies; (C) treat observations of 0 copies as left-censored at 1 copy; and (D) leave the data unaltered and apply a method for count data, negative binomial regression. Because research seeks to estimate general patterns rather than individuals' values, we argue that unaltered use of 0 copies is suitable for research purposes and that altering those observations can introduce bias. When applied to a simulated study comparing preintervention to postintervention measurements within 12 participants, methods A-C showed more attenuation than method D in the estimated intervention effect, less chance of finding P < 0.05 for the intervention effect and a lower chance of including the true intervention effect within the 95% confidence interval. Application of the methods to actual data from a study comparing multiply-spliced HIV RNA among men and women estimated smaller differences by methods A-C than by method D. We recommend that negative binomial regression, which is readily available in many statistical software packages, be considered for analysis of studies of rare entities that are measured by single-copy assays.

Potential of the NKG2D/NKG2DL Axis in NK Cell-Mediated Clearance of the HIV-1 Reservoir

Viral persistency in latently infected CD4⁺ T cells despite antiretroviral therapy (ART) represents a major drawback in the fight against HIV-1. Efforts to purge latent HIV-1 have been attempted using latency reversing agents (LRAs) that activate expression of the quiescent virus. However, initial trials have shown that immune responses of ART-treated patients are ineffective at clearing LRA-reactivated HIV-1 reservoirs, suggesting that an adjuvant immunotherapy is needed. Here we overview multiple lines of evidence indicating that natural killer (NK) cells have the potential to induce anti-HIV-1 responses relevant for virus eradication. In particular, we focus on the role of the NKG2D activating receptor that crucially enables NK cell-mediated killing of HIV-1-infected cells. We describe recent data indicating that LRAs can synergize with HIV-1 at upregulating ligands for NKG2D (NKG2DLs), hence sensitizing T cells that exit from viral latency for recognition and lysis by NK cells; in addition, we report in vivo and ex vivo data showing the potential benefits and drawbacks that LRAs may have on NKG2D expression and, more in general, on the cytotoxicity of NK cells. Finally, we discuss how the NKG2D/NKG2DLs axis can be exploited for the development of effective HIV-1 eradication strategies combining LRA-induced virus reactivation with recently optimized NK cell-based immunotherapies.

Impacts of HIV Cure Interventions on Viral Reservoirs in Tissues

HIV reservoirs persist in infected individuals despite combination antiretroviral therapy and can be identified in secondary lymphoid tissues, in intestinal tissues, in the central nervous system as well as in blood. Clinical trials have begun to explore effects of small molecule interventions to perturb the latent viral infection, but only limited information is available regarding the impacts of HIV cure-related clinical interventions on viral reservoirs found in tissues. Of the 14 HIV cure-related clinical trials since 2012 that have evaluated the effects of small molecule interventions in vivo, four trials have examined the impacts of the interventions in peripheral blood as well as other tissues that harbor persistent HIV. The additional tissues examined include cerebral spinal fluid, intestines and lymph nodes. We provide a comparison contrast analyses of the data across anatomical compartments tested in these studies to reveal where peripheral blood analyses reflect outcomes in other tissues as well as where the data reveal differences between tissue outcomes. We also summarize the current knowledge on these topics and highlight key open questions that need to be addressed experimentally to move the HIV cure research field closer to the development of an intervention strategy capable of eliciting long-term antiretroviral free remission of HIV disease.

A broad drug arsenal to attack a strenuous latent HIV reservoir

HIV cure is impeded by the persistence of a strenuous reservoir of latent but replication competent infected cells, which remain unsusceptible to c-ART and unrecognized by the immune system for elimination. Ongoing progress in understanding the molecular mechanisms that control HIV transcription and latency has led to the development of strategies to either permanently inactivate the latent HIV infected reservoir of cells or to stimulate the virus to emerge out of latency, coupled to either induction of death in the infected reactivated cell or its clearance by the immune system. This review focuses on the currently explored and non-exclusive pharmacological strategies and their molecular targets that 1. stimulate reversal of HIV latency in infected cells by targeting distinct steps in the HIV-1 gene expression cycle, 2. exploit mechanisms that promote cell death and apoptosis to render the infected cell harboring reactivated virus more susceptible to death and/or elimination by the immune system, and 3. permanently inactivate any remaining latently infected cells such that c-ART can be safely discontinued.

TLR9 agonist MGN1703 enhances B cell differentiation and function in lymph nodes

Background

TLR9 agonists are being developed as immunotherapy against malignancies and infections. TLR9 is primarily expressed in B cells and plasmacytoid dendritic cells (pDCs). TLR9 signalling may be critically important for B cell activity in lymph nodes but little is known about the in vivo impact of TLR9 agonism on human lymph node B cells. As a pre-defined sub-study within our clinical trial investigating TLR9 agonist MGN1703 (lefitolimod) treatment in the context of developing HIV cure strategies (NCT02443935), we assessed TLR9 agonist-mediated effects in lymph nodes.

Methods

Participants received MGN1703 for 24 weeks concurrent with antiretroviral therapy. Seven participants completed the sub-study including lymph node resection at baseline and after 24 weeks of treatment. A variety of tissue-based immunologic and virologic parameters were assessed.

Findings

MGN1703 dosing increased B cell differentiation; activated pDCs, NK cells, and T cells; and induced a robust interferon response in lymph nodes. Expression of Activation-Induced cytidine Deaminase, an essential regulator of B cell diversification and somatic hypermutation, was highly elevated. During MGN1703 treatment IgG production increased and antibody glycosylation patterns were changed.

Interpretation

Our data present novel evidence that the TLR9 agonist MGN1703 modulates human lymph node B cells in vivo. These findings warrant further considerations in the development of TLR9 agonists as immunotherapy against cancers and infectious diseases.

Fund

This work was supported by Aarhus University Research Foundation, the Danish Council for Independent Research and the NovoNordisk Foundation. Mologen AG provided study drug free of charge.

Effects of 24-week Toll-like receptor 9 agonist treatment in HIV type 1+ individuals

DESIGN

This was an exploratory, single-arm clinical trial that tested the immune enhancement effects of 24-weeks of Toll-like receptor 9 (TLR9) agonist (MGN1703; Lefitolimod; 60 mg × 2 weekly) therapy.

METHODS

We enrolled HIV-1-infected individuals on suppressive combination antiretroviral therapy. Safety was assessed throughout the study. The primary outcome was reduction in total CD4 T-cell viral DNA levels. Secondary outcomes included safety, detailed immunological and virological analyses, and time to viral rebound (viral load > 5000 copies/ml) after randomization into an analytical treatment interruption (ATI).

RESULTS

A total of 12 individuals completed the treatment phase and nine completed the ATI. Adverse events were limited and consistent with previous reports for MGN1703. Although the dosing regimen led to potent T-cell activation and increased HIV-1-specific T-cell responses, there were no cohort-wide changes in persistent virus (total CD4 T cells viral DNA; P = 0.34). No difference in time to rebound was observed between the ATI arms (log rank P = 0.25). One of nine ATI participants, despite harboring a large replication-competent reservoir, controlled viremia for 150 days via both HIV-1-specific cellular and antibody-mediated immune responses.

CONCLUSION

A period of 24 weeks of MGN1703 treatment was safe and improved innate as well as HIV-1-specific adaptive immunity in HIV-1+ individuals. These findings support the incorporation of TLR9 agonism into combination HIV-1 cure strategies.

TRIAL NAME AND REGISTRATION

TLR9 Enhancement of antiviral immunity in chronic HIV-1 infection: a phase 1B/2A trial; ClinicalTrials.gov NCT02443935.

The HIV Reservoir in Monocytes and Macrophages

In people living with HIV (PLWH) who are failing or unable to access combination antiretroviral therapy (cART), monocytes and macrophages are important drivers of pathogenesis and progression to AIDS. The relevance of the monocyte/macrophage reservoir in PLWH receiving cART is debatable as in vivo evidence for infected cells is limited and suggests the reservoir is small. Macrophages were assumed to have a moderate life span and lack self-renewing potential, but recent discoveries challenge this dogma and suggest a potentially important role of these cells as long-lived HIV reservoirs. This, combined with new HIV infection animal models, has led to a resurgence of interest in monocyte/macrophage reservoirs. Infection of non-human primates with myeloid-tropic SIV implicates monocyte/macrophage activation and infection in the brain with neurocognitive disorders, and infection of myeloid-only humanized mouse models are consistent with the potential of the monocyte/macrophage reservoir to sustain infection and be a source of rebound viremia following cART cessation. An increased resistance to HIV-induced cytopathic effects and a reduced susceptibility to some antiretroviral drugs implies macrophages may be relevant to residual replication under cART and to rebound viremia. With a reappraisal of monocyte circulation dynamics, and the development of techniques to differentiate between self-renewing tissue-resident, and monocyte-derived macrophages in different tissues, a new framework exists to contextualize and evaluate the significance and relevance of the monocyte/macrophage HIV reservoir. In this review, we discuss recent developments in monocyte and macrophage biology and appraise current and emerging techniques to quantify the reservoir. We discuss how this knowledge influences our evaluation of the myeloid HIV reservoir, the implications for HIV pathogenesis in both viremic and virologically-suppressed PLWH and the need to address the myeloid reservoir in future treatment and cure strategies.

Polymorphisms in Toll-Like Receptors (TLRs)-7 and 9 Genes in Indian Population with Progressive and Nonprogressive HIV-1 Infection

The polymorphisms in Toll-like receptor (TLR) 7 and 9 genes are shown to influence HIV-1 infection. We studied HIV-1-infected Indian individuals for presence and association of TLR7 and 9 gene polymorphism with different disease outcomes. Genomic DNA from 65 HIV-infected individuals (35 long-term nonprogressors and 30 progressors) and 89 uninfected healthy donors was isolated, amplified, and sequenced for the reported polymorphisms in TLR7 [Gln11Leu (A/T); rs179008] and TLR9 (1635A/G; rs352140) genes. Of these, only the reported TLR9 single-nucleotide polymorphism [SNP; p = .017, odds ratio (OR) = 0.20] and its allele A frequency (p = .038, OR = 0.41) were found to be associated with slow disease progression. Of the new SNPs observed (three TLR7 and two TLR9), the TLR7 rs2074109 G allele showed less likely association with HIV-1 acquisition (p = .019, OR = 0.27). These findings indicate that TLR7 SNP (rs2074109) could be one of the factors for predisposition to HIV-1 and TLR9 1635A/G genotype and allele might have a role in HIV-1 disease progression in Indian population.

Adaptive NK cell responses in HIV/SIV infections: A roadmap to cell-based therapeutics?

NK cells play a critical role in antiviral and antitumor responses. Although current NK cell immune therapies have focused primarily on cancer biology, many of these advances can be readily applied to target HIV/simian immunodeficiency virus (SIV)-infected cells. Promising developments include recent reports that CAR NK cells are capable of targeted responses while producing less off-target and toxic side effects than are associated with CAR T cell therapies. Further, CAR NK cells derived from inducible pluripotent stem cells or cell lines may allow for more rapid "off-the-shelf" access. Other work investigating the IL-15 superagonist ALT-803 (now N803) may also provide a recourse for enhancing NK cell responses in the context of the immunosuppressive and inflammatory environment of chronic HIV/SIV infections, leading to enhanced control of viremia. With a broader acceptance of research supporting adaptive functions in NK cells it is likely that novel immunotherapeutics and vaccine modalities will aim to generate virus-specific memory NK cells. In doing so, better targeted NK cell responses against virus-infected cells may usher in a new era of NK cell-tuned immune therapy.

Barriers and strategies to achieve a cure for HIV

9 years since the report of a cure for HIV after C-C chemokine receptor type 5 Δ32 stem cell transplantation, no other case of HIV cure has been reported, despite much research. However, substantial progress has been made in understanding the biology of the latent HIV reservoir, and in measuring the amount of virus that persists after antiretroviral therapy (ART) with increasingly sophisticated approaches. This knowledge is being translated into a long pipeline of clinical trials seeking to reduce viral persistence in participants on suppressive treatment and ultimately to allow safe cessation of ART. In this Review, we discuss the main barriers preventing the development of an HIV cure, methods used to measure HIV persistence in individuals on ART, clinical strategies that aim to cure HIV, and future directions for studies in the field of HIV cure research.

Between a shock and a hard place: challenges and developments in HIV latency reversal

Latently infected cells that persist in HIV-infected individuals on antiretroviral therapy (ART) are a major barrier to cure. One strategy to eliminate latency is by activating viral transcription, commonly called latency reversal. Several small non-randomised clinical trials of latency reversing agents (LRAs) in HIV-infected individuals on ART increased viral production, but disappointingly did not reduce the number of latently infected cells or delay time to viral rebound following cessation of ART. More recent approaches aimed at reversing latency include compounds that both activate virus and also modulate immunity to enhance clearance of infected cells. These immunomodulatory LRAs include toll-like receptor agonists, immune checkpoint inhibitors and some cytokines. Here, we provide a brief review of the rationale for transcription-activating and immunomodulatory LRAs, discuss recent clinical trials and some suggestions for combination approaches and research priorities for the future.

Characterization of Intact Proviruses in Blood and Lymph Node from HIV-Infected Individuals Undergoing Analytical Treatment Interruption

The role of lymphoid tissue as a potential source of HIV-1 rebound following interruption of antiretroviral therapy (ART) is uncertain. To address this issue, we compared the latent viruses obtained from CD4+ T cells in peripheral blood and lymph nodes to viruses emerging during treatment interruption. Latent viruses were characterized by sequencing near-full-length (NFL) proviral DNA and env from viral outgrowth assays (VOAs). Five HIV-1-infected individuals on ART were studied, four of whom participated in a clinical trial of a TLR9 agonist that included an analytical treatment interruption. We found that 98% of intact or replication-competent clonal sequences overlapped between blood and lymph node. In contrast, there was no overlap between 205 latent reservoir and 125 rebound sequences in the four individuals who underwent treatment interruption. However, rebound viruses could be accounted for by recombination. The data suggest that CD4+ T cells carrying latent viruses circulate between blood and lymphoid tissues in individuals on ART and support the idea that recombination may play a role in the emergence of rebound viremia.IMPORTANCE HIV-1 persists as a latent infection in CD4+ T cells that can be found in lymphoid tissues in infected individuals during ART. However, the importance of this tissue reservoir and its contribution to viral rebound upon ART interruption are not clear. In this study, we sought to compare latent HIV-1 from blood and lymph node CD4+ T cells from five HIV-1-infected individuals. Further, we analyzed the contribution of lymph node viruses to viral rebound. We observed that the frequencies of intact proviruses were the same in blood and lymph node. Moreover, expanded clones of T cells bearing identical proviruses were found in blood and lymph node. These latent reservoir sequences did not appear to be the direct origin of rebound virus. Instead, latent proviruses were found to contribute to the rebound compartment by recombination.

STING agonists activate latently infected cells and enhance SIV-specific responses ex vivo in naturally SIV controlled cynomolgus macaques

To achieve a functional cure for HIV, treatment regimens that eradicate latently HIV-infected cells must be established. For this, many groups have attempted to reactivate latently-infected cells to induce cytopathic effects and/or elicit cytotoxic T lymphocyte (CTL)/NK cell-mediated immune responses to kill these cells. We believe that not only the reactivation of latently-infected cells, but also the induction of strong CTL responses, would be required for this. Here, we used typical immune activators that target pattern recognition receptors (PRRs). For our experimental model, we identified eight SIV-infected cynomolgus monkeys that became natural controllers of viremia. Although plasma viral loads were undetectable, we could measure SIV-DNA by qPCR in peripheral blood mononuclear cells (PBMCs). Using these PBMCs, we screened 10 distinct PRR ligands to measure IFN-α and IFN-γ production. Among these, STING ligands, cGAMP and c-di-AMP, and the TLR7/8 agonist R848 markedly increased cytokine levels. Both R848 and STING ligands could reactivate latently-infected cells in both cynomolgus monkeys and human PBMCs in vitro. Furthermore, c-di-AMP increased the frequency of SIV Gag-specific CD8⁺ T cells including polyfunctional CD8⁺ T cells, as compared to that in untreated control or R848-treated cells. Together, STING ligands might be candidates for HIV treatment.

Poly-ICLC, a TLR3 Agonist, Induces Transient Innate Immune Responses in Patients With Treated HIV-Infection: A Randomized Double-Blinded Placebo Controlled Trial

Objective: Toll-like receptor-3 agonist Poly-ICLC has been known to activate immune cells and induce HIV replication in pre-clinical experiments. In this study we investigated if Poly-ICLC could be used for disrupting HIV latency while simultaneously enhancing innate immune responses.

Design: This was a randomized, placebo-controlled, double-blinded trial in aviremic, cART-treated HIV-infected subjects. Participants (n = 15) were randomized 3:1 to receive two consecutive daily doses of Poly-ICLC (1.4 mg subcutaneously) vs. placebo. Subjects were observed for adverse events, immune activation, and viral replication.

Methods: Besides primary outcomes of safety and tolerability, several longitudinal immune parameters were evaluated including immune cell phenotype and function via flowcytometry, ELISA, and transcriptional profiling. PCR assays for plasma HIV-1 RNA, CD4⁺ T cell-associated HIV-1 RNA, and proviral DNA were performed to measure HIV reservoirs and latency.

Results: Poly-ICLC was overall safe and well-tolerated. Poly-ICLC-related adverse events were Grade 1/2, with the exception of one Grade 3 neutropenia which was short-lived. Mild Injection site reactions were observed in nearly all participants in the Poly-ICLC arm. Transcriptional analyses revealed upregulation of innate immune pathways in PBMCs following Poly-ICLC treatment, including strong interferon signaling accompanied by transient increases in circulating IP-10 (CXCL10) levels. These responses generally peaked by 24–48 h after the first injection and returned to baseline by day 8. CD4⁺ T cell number and phenotype were unchanged, plasma viral control was maintained and no significant effect on HIV reservoirs was observed.

Conclusions: These finding suggest that Poly-ICLC could be safely used for inducing transient innate immune responses in treated HIV⁺ subjects indicating promise as an adjuvant for HIV therapeutic vaccines.

Trial Registration:www.ClinicalTrials.gov, identifier: NCT02071095.

Type 1-programmed dendritic cells drive antigen-specific latency reversal and immune elimination of persistent HIV-1

Background

Despite the success of antiretroviral therapy (ART), latent HIV-1 continues to persist in a long-lived population of resting memory CD4⁺ T cells within those who are infected. Finding a safe and effective means to induce latency reversal (LR) during ART to specifically expose this latent HIV-1 cellular reservoir for immune elimination has been a major barrier to a functional cure.

Methods

In this study, we test the use of antigen-presenting type 1-polarized, monocyte-derived dendritic cells (MDC1) generated from chronic HIV-1-infected individuals on ART as a means to induce HIV-1 latency reversal in autologous CD4⁺ T cells harboring replication-competent provirus. We use the same MDC1 for ex-vivo generation of autologous HIV-1 antigen-specific CD8⁺ cytotoxic T cells (CTL) and test their effector responses against the MDC1-exposed HIV-1- infected CD4⁺ T cell targets.

Findings

MDC1 presentation of either HIV-1 or cytomegalovirus (CMV) antigens to CD4⁺ T cells facilitated HIV-1 LR. This antigen-driven MDC1-mediated LR was sharply diminished with blockade of the CD40L/CD40 ‘helper’ signaling pathway. Importantly, these antigen-presenting MDC1 also activated the expansion of CTL capable of killing the exposed HIV-1-infected targets.

Interpretation

Inclusion of virus-associated MHC class II ‘helper’ antigens in MDC1-based HIV-1 immunotherapies could serve both as a targeted means to safely unmask antigen-specific CD4⁺ T cells harboring HIV-1, and to support CTL responses that can effectively target the MDC1-exposed HIV-1 cellular reservoir as a functional cure strategy.

Fund

This study was supported by the NIH-NAID grants R21-AI131763, U01-AI35041, UM1-AI126603, and T32-AI065380.

HIV "shock and kill" therapy: In need of revision

The implementation of antiretroviral therapy 23 years ago has rendered HIV infection clinically manageable. However, the disease remains incurable, since it establishes latent proviral reservoirs, which in turn can stochastically begin reproducing viral particles throughout the patient's lifetime. Viral latency itself depends in large part on the silencing environment of the infected host cell, which can be chemically manipulated. "Shock and kill" therapy intends to reverse proviral quiescence by inducing transcription with pharmaceuticals and allowing a combination of antiretroviral therapy, host immune clearance and HIV-cytolysis to remove latently infected cells, leading to a complete cure. Over 160 compounds functioning as latency-reversing agents (LRAs) have been identified to date, but none of the candidates has yet led to a promising functional cure. Furthermore, fundamental bioinformatic and clinical research from the past decade has highlighted the complexity and highly heterogeneous nature of the proviral reservoirs, shedding doubt on the "shock and kill" concept. Alternative therapies such as the HIV transcription-inhibiting "block and lock" strategy are therefore being considered. In this review we describe the variety of existing classes of LRAs, discuss their current drawbacks and highlight the potential for combinatorial "shocktail" therapies for potent proviral reactivation. We also suggest investigating LRAs with lesser-known mechanisms of action, and examine the feasibility of "block and lock" therapy.

Hexamethylene bisacetamide impairs NK cell-mediated clearance of acute T lymphoblastic leukemia cells and HIV-1-infected T cells that exit viral latency

The hexamethylene bisacetamide (HMBA) anticancer drug was dismissed due to limited efficacy in leukemic patients but it may re-enter into the clinics in HIV-1 eradication strategies because of its recently disclosed capacity to reactivate latent virus. Here, we investigated the impact of HMBA on the cytotoxicity of natural killer (NK) cells against acute T lymphoblastic leukemia (T-ALL) cells or HIV-1-infected T cells that exit from latency. We show that in T-ALL cells HMBA upmodulated MICB and ULBP2 ligands for the NKG2D activating receptor. In a primary CD4⁺ T cell-based latency model, HMBA did not reactivate HIV-1, yet enhanced ULBP2 expression on cells harboring virus reactivated by prostratin (PRO). However, HMBA reduced the expression of NKG2D and its DAP10 adaptor in NK cells, hence impairing NKG2D-mediated cytotoxicity and DAP10-dependent response to IL-15 stimulation. Alongside, HMBA dampened killing of T-ALL targets by IL-15-activated NK cells and impaired NK cell-mediated clearance of PRO-reactivated HIV-1⁺ cells. Overall, our results demonstrate a dominant detrimental effect of HMBA on the NKG2D pathway that crucially controls NK cell-mediated killing of tumors and virus-infected cells, providing one possible explanation for poor clinical outcome in HMBA-treated cancer patients and raising concerns for future therapeutic application of this drug.

Population Pharmacokinetics and Pharmacodynamics of Disulfiram on Inducing Latent HIV-1 Transcription in a Phase IIb Trial

Disulfiram (DSF) was well tolerated and activated viral transcription (cell-associated unspliced (CA-US) and plasma human immunodeficiency virus (HIV) RNA) in a phase II dose-escalation trial in HIV+ antiretroviral therapy (ART)-suppressed participants. Here, we investigated whether exposure to DSF and its metabolites predicted these changes in HIV transcription. Participants were administered 500 (N = 10), 1,000 (N = 10), or 2,000 (N = 10) mg of DSF for 3 consecutive days. DSF and four metabolites were measured by ultraperformance liquid chromatography-tandem mass spectrometry. Changes in CA-US and plasma HIV RNA were quantified by polymerase chain reaction (PCR) and analyzed in NONMEM. A seven-compartment pharmacokinetic (PK) model demonstrated nonlinear elimination kinetics. The fitted median area under the curve values for 72 hours (AUC0-72 ) were 3,816, 8,386, and 22,331 mg*hour/L, respectively. Higher exposure predicted greater increases in CA-US (maximum effect (Emax ) = 78%, AUC50  = 1,600 μg*hour/L, P = 0.013) but not plasma HIV RNA. These results provide support for further development of DSF as an important drug for future HIV cure strategies.

Toll-Like Receptor 7 (TLR-7) and TLR-9 Agonists Improve Hepatitis C Virus Replication and Infectivity Inhibition by Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) are innate immune cells with high antiviral activity triggered by Toll-like receptor 7 (TLR-7) and TLR-9 stimulation. Moreover, they are important mediators between innate and adaptive immunity. Although nowadays there is available an effective therapeutic arsenal against hepatitis C virus (HCV), a protective vaccine is not available. We have analyzed the pDCs' response to HCV infection in a hepatitis C virus (HCV)-Huh7.5 virus-cell system, which allows completion of the virus infectious cycle. pDCs were cocultured following human immunodeficiency virus (HIV) aldrithiol-2 (AT-2 [TLR-7 agonist]) inactivation and CpG (TLR-9 agonist) stimulation. We employed three virus derivatives-wild-type Jc1, interferon (IFN)-resistant virus IR, and high-replicative-fitness virus P100-in order to explore additional IFN-α-related virus inhibition mechanisms. pDCs inhibited HCV infectivity and replication and produced IFN-α. After TLR-7 and TLR-9 stimulation, inhibition of infectivity and IFN-α production by pDCs were enhanced. TLR-7 stimulation drove higher TNF-related apoptosis-inducing ligand (TRAIL) expression in pDCs. Additionally, TLR-7- and TLR-9-stimulated pDCs exhibited a mature phenotype, improving the antigen presentation and lymph node homing-related markers. In conclusion, pDCs could serve as a drug target against HCV in order to improve antiviral activity and as an enhancer of viral immunization.IMPORTANCE We implemented a coculture system of pDCs with HCV-infected hepatoma cell line, Huh7.5. We used three HCV derivatives in order to gain insight into pDCs' behavior against HCV and associated antiviral mechanisms. The results with this cell coculture system support the capacity of pDCs to inhibit HCV replication and infectivity mainly via IFN-α, but also through additional mechanisms associated with pDC maturation. We provided evidence that TLR agonists can enhance antiviral pDCs' function and can induce phenotypic changes that may facilitate the interplay with other immune cells. These findings suggest the possibility of including TLR agonists in the strategies of HCV vaccine development.

Implications of HIV-1 Nef for "Shock and Kill" Strategies to Eliminate Latent Viral Reservoirs

Finding a cure for HIV is challenging because the virus is able to integrate itself into the host cell genome and establish a silent state, called latency, allowing it to evade antiviral drugs and the immune system. Various “shock and kill” strategies are being explored in attempts to eliminate latent HIV reservoirs. The goal of these approaches is to reactivate latent viruses (“shock”), thereby exposing them to clearance by viral cytopathic effects or immune-mediated responses (“kill”). To date, there has been limited clinical success using these methods. In this review, we highlight various functions of the HIV accessory protein Nef and discuss their double-edged effects that may contribute to the limited effectiveness of current “shock and kill” methods to eradicate latent HIV reservoirs in treated individuals.

HIV control: Is getting there the same as staying there?

In this brief review and perspective, we address the question of whether the immune responses that bring about immune control of acute HIV infection are the same as, or distinct from, those that maintain long-term viral suppression once control of viremia has been achieved. To this end, we describe the natural history of elite and post-treatment control, noting the lack of data regarding what happens acutely. We review the evidence suggesting that the two clinical phenotypes may differ in terms of the mechanisms required to achieve and maintain control, as well as the level of inflammation that persists once a steady state is achieved. We then describe the evidence from longitudinal studies of controllers who fail and studies of biologic sex (male versus female), age (children versus adults), and simian immunodeficiency virus (SIV) (pathogenic/experimental versus nonpathogenic/natural infection). Collectively, these studies demonstrate that the battle between the inflammatory and anti-inflammatory pathways during acute infection has long-term consequences, both for the degree to which control is maintained and the health of the individual. Potent and stringent control of HIV may be required acutely, but once control is established, the chronic inflammatory response can be detrimental. Interventional approaches designed to bring about HIV cure and/or remission should be nuanced accordingly.

Synthetic Ingenols Maximize Protein Kinase C-Induced HIV-1 Latency Reversal

Antiretroviral therapy (ART) does not cure HIV-1 infection due to the persistence of proviruses in long-lived resting T cells. Strategies targeting these latently infected cells will be necessary to eradicate HIV-1 in infected individuals. Protein kinase C (PKC) activation is an effective mechanism to reactivate latent proviruses and allows for recognition and clearance of infected cells by the immune system. Several ingenol compounds, naturally occurring PKC agonists, have been described to have potent latency reversal activity. We sought to optimize this activity by synthesizing a library of novel ingenols via esterification of the C-3 hydroxyl group of the ingenol core, which itself is inactive for latency reversal. Newly synthesized ingenol derivatives were evaluated for latency reversal activity, cellular activation, and cytotoxicity alongside commercially available ingenols (ingenol-3,20-dibenzoate, ingenol 3-hexanoate, and ingenol-3-angelate) in HIV latency cell lines and resting CD4⁺ T cells from aviremic participants. Among the synthetic ingenols that we produced, we identified several compounds that demonstrate high efficacy and represent promising leads as latency reversal agents for HIV-1 eradication.

Dual TLR2 and TLR7 agonists as HIV latency-reversing agents

The presence of a reservoir of latently infected cells in HIV-infected patients is a major barrier towards finding a cure. One active cure strategy is to find latency-reversing agents that induce viral reactivation, thus leading to immune cell recognition and elimination of latently infected cells, known as the shock-and-kill strategy. Therefore, the identification of molecules that reactivate latent HIV and increase immune activation has the potential to further these strategies into the clinic. Here, we characterized synthetic molecules composed of a TLR2 and a TLR7 agonist (dual TLR2/7 agonists) as latency-reversing agents and compared their activity with that of the TLR2 agonist Pam2CSK4 and the TLR7 agonist GS-9620. We found that these dual TLR2/7 agonists reactivate latency by 2 complementary mechanisms. The TLR2 component reactivates HIV by inducing NF-κB activation in memory CD4+ T cells, while the TLR7 component induces the secretion of TNF-α by monocytes and plasmacytoid dendritic cells, promoting viral reactivation in CD4+ T cells. Furthermore, the TLR2 component induces the secretion of IL-22, which promotes an antiviral state and blocks HIV infection in CD4+ T cells. Our study provides insight into the use of these agonists as a multipronged approach targeting eradication of latent HIV.

Barriers for HIV Cure: The Latent Reservoir

Thirty-five years after the identification of HIV-1 as the causative agent of AIDS, we are still in search of vaccines and treatments to eradicate this devastating infectious disease. Progress has been made in understanding the molecular pathogenesis of this infection, which has been crucial for the development of the current therapy regimens. However, despite their efficacy at limiting active viral replication, these drugs are unable to purge the latent reservoir: a pool of cells that harbor transcriptionally inactive, but replication-competent HIV-1 proviruses, and that represent the main barrier to eradicate HIV-1 from affected individuals. In this review, we discuss advances in the field that have allowed a better understanding of HIV-1 latency, including the diverse cell types that constitute the latent reservoir, factors influencing latency, tools to study HIV-1 latency, as well as current and prospective therapeutic approaches to target these latently infected cells, so a functional cure for HIV/AIDS can become a reality.