Latency reversal and viral clearance to cure HIV-1

Raman-Enhanced Spectroscopy Distinguishes Anal Squamous Intraepithelial Lesions in Human Immunodeficiency Virus-Serodiscordant Couples

HIV-positive individuals are at increased risk for precancerous anal squamous intraepithelial lesions (SILs). Anal cytology and digital rectal examination are performed as screening tools, but extensive training and appropriate instruments are required to follow up on an abnormal anal cytology. Thus, novel approaches to SIL evaluation could improve better health care follow-up by efficient and timely diagnosis to offer treatment options. Recently, Raman-enhanced spectroscopy (RESpect) has emerged as a potential new tool for early identification of SIL. RESpect is a noninvasive, label-free, laser-based technique that identifies molecular composition of tissues and cells. HIV-serodiscordant couples had anal biopsies obtained during high-resolution anoscopy. RESpect was performed on the specimens. Principal component analysis of the data identified differences between normal and abnormal tissue as well as HIV-positive and HIV-negative individuals of each couple even with similar pathologies. RESpect has the potential to change the paradigm of anal pathology diagnosis and could provide insight into different pathways leading to SIL in HIV-serodiscordant couples.

Hybrid nanocarriers incorporating mechanistically distinct drugs for lymphatic CD4+ T cell activation and HIV-1 latency reversal

A proposed strategy to cure HIV uses latency-reversing agents (LRAs) to reactivate latent proviruses for purging HIV reservoirs. A variety of LRAs have been identified, but none has yet proven effective in reducing the reservoir size in vivo. Nanocarriers could address some major challenges by improving drug solubility and safety, providing sustained drug release, and simultaneously delivering multiple drugs to target tissues and cells. Here, we formulated hybrid nanocarriers that incorporate physicochemically diverse LRAs and target lymphatic CD4+ T cells. We identified one LRA combination that displayed synergistic latency reversal and low cytotoxicity in a cell model of HIV and in CD4+ T cells from virologically suppressed patients. Furthermore, our targeted nanocarriers selectively activated CD4+ T cells in nonhuman primate peripheral blood mononuclear cells as well as in murine lymph nodes, and substantially reduced local toxicity. This nanocarrier platform may enable new solutions for delivering anti-HIV agents for an HIV cure.

Pharmacokinetic stability of macrocyclic peptide triazole HIV-1 inactivators alone and in liposomes

Previously, we reported the discovery of macrocyclic peptide triazoles (cPTs) that bind to HIV-1 Env gp120, inhibit virus cell infection with nanomolar potencies, and cause irreversible virion inactivation. Given the appealing virus-killing activity of cPTs and resistance to protease cleavage observed in vitro, we here investigated in vivo pharmacokinetics of the cPT AAR029b. AAR029b was investigated both alone and encapsulated in a PEGylated liposome formulation that was designed to slowly release inhibitor. Pharmacokinetic analysis in rats showed that the half-life of FITC-AAR029b was substantial both alone and liposome-encapsulated, 2.92 and 8.87 hours, respectively. Importantly, liposome-encapsulated FITC-AAR029b exhibited a 15-fold reduced clearance rate from serum compared with the free FITC-cPT. This work thus demonstrated both the in vivo stability of cPT alone and the extent of pharmacokinetic enhancement via liposome encapsulation. The results obtained open the way to further develop cPTs as long-acting HIV-1 inactivators against HIV-1 infection.

Inhibitors of Signaling Pathways That Block Reversal of HIV-1 Latency

Signaling pathways play a key role in HIV-1 latency. In this study, we used the 24ST1NLESG cell line of HIV-1 latency to screen a library of structurally diverse, medicinally active, cell permeable kinase inhibitors, which target a wide range of signaling pathways, to identify inhibitors of HIV-1 latency reversal. The screen was carried out in the absence or presence of three mechanistically distinct latency-reversing agents (LRAs), namely, prostratin, panobinostat, and JQ-1. We identified inhibitors that only blocked the activity of a specific LRA, as well as inhibitors that blocked the activity of all LRAs. For example, we identified 12 inhibitors targeted toward protein kinase C or downstream kinases that blocked the activity of prostratin. We also identified 12 kinase inhibitors that blocked the reversal of HIV-1 latency irrespective of the LRA used in the screen. Of these, danusertib, an Aurora kinase inhibitor, and PF-3758309, a PAK4 inhibitor, were the most potent. The 50% inhibitory concentrations in the 24ST1NLESG cells ranged from 40 to 147 nM for danusertib (selectivity indices, >150) and from 0.1 to 1 nM for PF-3758309 (selectivity indices, >3,300). Both danusertib and PF-3758309 inhibited latency reversal in CD4⁺ T cells isolated from HIV-1-infected donors. Collectively, our study describes a chemical approach that can be applied to elucidate the role of signaling pathways involved in LRA activity or the maintenance of HIV-1 latency and also identifies inhibitors of latent HIV-1 reactivation that could be used with antiretroviral therapy to reduce residual viremia.

Reiterative Enrichment and Authentication of CRISPRi Targets (REACT) identifies the proteasome as a key contributor to HIV-1 latency

The establishment of HIV-1 latency gives rise to persistent chronic infection that requires life-long treatment. To reverse latency for viral eradiation, the HIV-1 Tat protein and its associated ELL2-containing Super Elongation Complexes (ELL2-SECs) are essential to activate HIV-1 transcription. Despite efforts to identify effective latency-reversing agents (LRA), avenues for exposing latent HIV-1 remain inadequate, prompting the need to identify novel LRA targets. Here, by conducting a CRISPR interference-based screen to reiteratively enrich loss-of-function genotypes that increase HIV-1 transcription in latently infected CD4⁺ T cells, we have discovered a key role of the proteasome in maintaining viral latency. Downregulating or inhibiting the proteasome promotes Tat-transactivation in cell line models. Furthermore, the FDA-approved proteasome inhibitors bortezomib and carfilzomib strongly synergize with existing LRAs to reactivate HIV-1 in CD4⁺ T cells from antiretroviral therapy-suppressed individuals without inducing cell activation or proliferation. Mechanistically, downregulating/inhibiting the proteasome elevates the levels of ELL2 and ELL2-SECs to enable Tat-transactivation, indicating the proteasome-ELL2 axis as a key regulator of HIV-1 latency and promising target for therapeutic intervention.

To cure chronic HIV-1 infection requires reversal of HIV-1 latency from latently infected CD4⁺ T cells. A key step in HIV latency reversal is the recruitment of Super Elongation Complexes (SECs) that contain ELL2 by an HIV-encoded protein, Tat, to activate proviral transcription. To identify novel drug targets, we conducted a CRISPRi-based screen to enrich the sgRNAs that increase HIV transcription in latently infected CD4⁺ T cells. Three of the six most prominent hits in our screen are proteasome subunits. We further proved that antagonizing the proteasome promotes Tat-induced HIV-1 transcription in cell line-based latency models. Furthermore, we found that two FDA-approved proteasome inhibitors strongly synergize with existing LRAs ex vivo without inducing cell activation or proliferation. We further found that antagonizing the proteasome elevates the levels of ELL2 and ELL2-containing SECs in the cells, thus enabling Tat-transactivation. These results indicate that the proteasome-ELL2 axis is a key regulator of HIV-1 latency could potentially be targeted for therapeutic interventions.

The BET bromodomain inhibitor apabetalone induces apoptosis of latent HIV-1 reservoir cells following viral reactivation

The persistence of latent HIV-1 reservoirs throughout combination antiretroviral therapy (cART) is a major barrier on the path to achieving a cure for AIDS. It has been shown that bromodomain and extra-terminal (BET) inhibitors could reactivate HIV-1 latency, but restrained from clinical application due to their toxicity and side effects. Thus, identifying a new type of BET inhibitor with high degrees of selectivity and safety is urgently needed. Apabetalone is a small-molecule selective BET inhibitor specific for second bromodomains, and has been evaluated in phase III clinical trials that enrolled patients with high-risk cardiovascular disorders, dyslipidemia, and low HDL cholesterol. In the current study, we examined the impact of apabetalone on HIV-1 latency. We showed that apabetalone (10-50 μmol/L) dose-dependently reactivated latent HIV-1 in 4 types of HIV-1 latency cells in vitro and in primary human CD4⁺ T cells ex vivo. In ACH2 cells, we further demonstrated that apabetalone activated latent HIV-1 through Tat-dependent P-TEFB pathway, i.e., dissociating bromodomain 4 (BDR4) from the HIV-1 promoter and recruiting Tat for stimulating HIV-1 elongation. Furthermore, we showed that apabetalone (10-30 μmol/L) caused dose-dependent cell cycle arrest at the G₁/G₀ phase in ACH2 cells, and thereby induced the preferential apoptosis of HIV-1 latent cells to promote the death of reactivated reservoir cells. Notably, cardiovascular diseases and low HDL cholesterol are known as the major side effects of cART, which should be prevented by apabetalone. In conclusion, apabetalone should be an ideal bifunctional latency-reversing agent for advancing HIV-1 eradication and reducing the side effects of BET inhibitors.

Safety, tolerability and impact on viral reservoirs of the addition to antiretroviral therapy of ABX464, an investigational antiviral drug, in individuals living with HIV-1: a Phase IIa randomised controlled study

OBJECTIVES

To assess the safety and tolerability as well as antiretroviral impact of ABX464, an oral investigational drug with a novel mechanism of HIV-1 inhibition (ClinicalTrials.gov NCT02735863).

METHODS

Randomised, double-blind, placebo-controlled, Phase IIa study in individuals living with HIV-1 on antiretroviral therapy at six clinical centres in Spain, France and Belgium. ABX464 was administered once a day to 22 fully controlled HIV-1-positive participants at two doses (50 mg, n=6 and 150 mg, n=16) versus placebo, which was given to eight participants for 28 days in combination with a boosted protease inhibitor (darunavir/ritonavir or darunavir/cobicistat). The primary objective of the study was to assess ABX464 safety and tolerability when used in combination with darunavir boosted therapy. The secondary objective was to study antiretroviral efficacy on viral reservoirs using time to viral rebound following treatment interruption. The impact of ABX464 on HIV-1 reservoirs was further assessed by measuring levels of total HIV-1 in peripheral blood mononuclear cells (PBMCs) in the intervention arm versus placebo. A positive response was defined as an absolute reduction in HIV-1 DNA of at least 50 copies/10⁶ PBMCs and a relative decrease >25% of HIV-1 DNA level.

RESULTS

Twenty-six of the 30 randomly allocated participants completed the study according to the study protocol. ABX464 was found to be safe and well tolerated with the majority of adverse events (AEs) being mild or moderate. Of the participants, 22 (73.3%) experienced treatment-associated AEs (93.8%, 66.7%, 37.5% in the ABX464 150-mg, 50-mg dose and placebo arms, respectively). Percentages for combined grade 3/4 AEs for the three arms were 6.3%, 0% and 12.5%, respectively. Median time (Kaplan-Meier estimates) to viral rebound for ABX464 150-mg, 50-mg and placebo arms were 12.0 (95% confidence interval [CI]: 10-15), 15.5 (95% CI 14-22) and 15.5 (95% CI 1-22) days, respectively with no significant difference between the 150-mg treatment arm and placebo. Median changes in total HIV-1 DNA copies/10⁶ PBMCs for ABX464 150-mg, 50-mg and placebo arms after 28 days of treatment were -40 (range -434 to +194), -115 (range -116 to -114) and 25 (range -35 to +218), respectively, showing a decrease in the intervention arms. There were 6/14, 2/2, and 0/4 responders for ABX464 150 mg, 50 mg and placebo, respectively. No significant difference was seen between treatment arms and placebo with respect to these virological parameters.

CONCLUSIONS

This small controlled study confirmed the good safety and tolerability of ABX464 and provides some evidence of a potential reduction of the HIV-1 reservoir in terms of HIV-1 DNA levels in PBMCs when it was added to an HIV-1 protease inhibitor-based regimen. These results will need to be confirmed in a larger study.

Small Molecule Targeting of Specific BAF (mSWI/SNF) Complexes for HIV Latency Reversal

The persistence of a pool of latently HIV-1-infected cells despite combination anti-retroviral therapy treatment is the major roadblock for a cure. The BAF (mammalian SWI/SNF) chromatin remodeling complex is involved in establishing and maintaining viral latency, making it an attractive drug target for HIV-1 latency reversal. Here we report a high-throughput screen for inhibitors of BAF-mediated transcription in cells and the subsequent identification of a 12-membered macrolactam. This compound binds ARID1A-specific BAF complexes, prevents nucleosomal positioning, and relieves transcriptional repression of HIV-1. Through this mechanism, these compounds are able to reverse HIV-1 latency in an in vitro T cell line, an ex vivo primary cell model of HIV-1 latency, and in patient CD4+ T cells without toxicity or T cell activation. These macrolactams represent a class of latency reversal agents with unique mechanism of action, and can be combined with other latency reversal agents to improve reservoir targeting.

Structural mechanism for HIV-1 TAR loop recognition by Tat and the super elongation complex

Promoter-proximal pausing by RNA polymerase II (Pol II) is a key regulatory step in human immunodeficiency virus-1 (HIV-1) transcription and thus in the reversal of HIV latency. By binding to the nascent transactivating response region (TAR) RNA, HIV-1 Tat recruits the human super elongation complex (SEC) to the promoter and releases paused Pol II. Structural studies of TAR interactions have been largely focused on interactions between the TAR bulge and the arginine-rich motif (ARM) of Tat. Here, the crystal structure of the TAR loop in complex with Tat and the SEC core was determined at a 3.5-Å resolution. The bound TAR loop is stabilized by cross-loop hydrogen bonds. It makes structure-specific contacts with the side chains of the Cyclin T1 Tat-TAR recognition motif (TRM) and the zinc-coordinating loop of Tat. The TAR loop phosphate backbone forms electrostatic and VDW interactions with positively charged side chains of the CycT1 TRM. Mutational analysis showed that these interactions contribute importantly to binding affinity. The Tat ARM was present in the crystallized construct; however, it was not visualized in the electron density, and the TAR bulge was not formed in the RNA construct used in crystallization. Binding assays showed that TAR bulge-Tat ARM interactions contribute less to TAR binding affinity than TAR loop interactions with the CycT1 TRM and Tat core. Thus, the TAR loop evolved to make high-affinity interactions with the TRM while Tat has three roles: scaffolding and stabilizing the TRM, making specific interactions through its zinc-coordinating loop, and making electrostatic interactions through its ARM.

Quantitation of Integrated HIV Provirus by Pulsed-Field Gel Electrophoresis and Droplet Digital PCR

We utilized pulsed-field gel electrophoresis (PFGE) to purify high-molecular-weight DNA from HIV-infected cells. This purification, in combination with our previously described droplet digital PCR (ddPCR) assay, was used to develop a method to quantify proviral integrated HIV DNA free of lower-molecular-weight species of HIV DNA. Episomal 2-long-terminal-repeat (2-LTR) circles were completely cleared from HIV DNA samples. Technical replicates of the complete assay, starting with the same specimens, resulted in no statistical differences in quantification of integrated HIV gag sequences in cellular DNA from cells from HIV-infected subjects after prolonged treatment with antiretroviral therapy (ART). The PFGE ddPCR assay was compared to the Alu-gag quantitative PCR (qPCR) assay, the most widely used assay to measure proviral integrated HIV DNA. Spearman's rho nonparametric correlation determined PFGE ddPCR results to be positively correlated with Alu-gag qPCR results (r = 0.7052; P = 0.0273). In summary, PFGE ddPCR is a sensitive, reproducible, and robust method to measure proviral integrated HIV DNA and is theoretically more accurate than previously described assays, because it is a direct measure of integrated HIV DNA.

Bispecific antibodies: Potential immunotherapies for HIV treatment

Bispecific (bs) antibodies (Abs, bsAbs) are engineered immunoglobulins that contain two different antigen-binding sites in one molecule. bsAbs can be divided in two molecular formats; the IgG-like and non-IgG like. The structural elements of each format have implications for engaging the immune system. Elimination of HIV will need sophisticated approaches with immunotherapies being one of the strategies under investigation. Furthermore, HIV genetic variability and functional compromise of the adaptive CTL response complicate the potential usefulness of some immunotherapeutic strategies. Inclusion of novel HIV neutralizing Abs with high potency and breadth as components of bsAbs could represent alternative strategies for virus elimination by harnessing the adaptive immune response in vivo.

Determinants of the efficacy of HIV latency-reversing agents and implications for drug and treatment design

HIV eradication studies have focused on developing latency-reversing agents (LRAs). However, it is not understood how the rate of latent reservoir reduction is affected by different steps in the process of latency reversal. Furthermore, as current LRAs are host-directed, LRA treatment is likely to be intermittent to avoid host toxicities. Few careful studies of the serial effects of pulsatile LRA treatment have yet been done. This lack of clarity makes it difficult to evaluate the efficacy of candidate LRAs or predict long-term treatment outcomes. We constructed a mathematical model that describes the dynamics of latently infected cells under LRA treatment. Model analysis showed that, in addition to increasing the immune recognition and clearance of infected cells, the duration of HIV antigen expression (i.e., the period of vulnerability) plays an important role in determining the efficacy of LRAs, especially if effective clearance is achieved. Patients may benefit from pulsatile LRA exposures compared with continuous LRA exposures if the period of vulnerability is long and the clearance rate is high, both in the presence and absence of an LRA. Overall, the model framework serves as a useful tool to evaluate the efficacy and the rational design of LRAs and combination strategies.

Stochastic Dynamics of the Latently Infected Cell Reservoir During HIV Infection

The presence of cells latently infected with HIV is currently considered to be a major barrier to viral eradication within a patient. Here, we consider birth-death-immigration models for the latent cell population in a single patient, and present analytical results for the size of this population in the absence of treatment. We provide results both at steady state (viral set point), and during the non-equilibrium setting of early infection. We obtain semi-analytic results showing how latency-reversing drugs might be expected to affect the size of the latent pool over time. We also analyze the probability of rare mutant viral strains joining the latent cell population, allowing for steady-state and dynamic viral populations within the host.

Pharmaceutical Approaches to HIV Treatment and Prevention

Human immunodeficiency virus (HIV) infection continues to pose a major infectious disease threat worldwide. It is characterized by the depletion of CD4+ T cells, persistent immune activation, and increased susceptibility to secondary infections. Advances in the development of antiretroviral drugs and combination antiretroviral therapy have resulted in a remarkable reduction in HIV-associated morbidity and mortality. Antiretroviral therapy (ART) leads to effective suppression of HIV replication with partial recovery of host immune system and has successfully transformed HIV infection from a fatal disease to a chronic condition. Additionally, antiretroviral drugs have shown promise for prevention in HIV pre-exposure prophylaxis and treatment as prevention. However, ART is unable to cure HIV. Other limitations include drug-drug interactions, drug resistance, cytotoxic side effects, cost, and adherence. Alternative treatment options are being investigated to overcome these challenges including discovery of new molecules with increased anti-viral activity and development of easily administrable drug formulations. In light of the difficulties associated with current HIV treatment measures, and in the continuing absence of a cure, the prevention of new infections has also arisen as a prominent goal among efforts to curtail the worldwide HIV pandemic. In this review, the authors summarize currently available anti-HIV drugs and their combinations for treatment, new molecules under clinical development and prevention methods, and discuss drug delivery formats as well as associated challenges and alternative approaches for the future.

Visualization of HIV-1 RNA Transcription from Integrated HIV-1 DNA in Reactivated Latently Infected Cells

We have recently developed the first microscopy-based strategy that enables simultaneous multiplex detection of viral RNA (vRNA), viral DNA (vDNA), and viral protein. Here, we used this approach to study the kinetics of latency reactivation in cells infected with the human immunodeficiency virus (HIV). We showed the transcription of nascent vRNA from individual latently integrated and reactivated vDNA sites appearing earlier than viral protein. We further demonstrated that this method can be used to quantitatively assess the efficacy of a variety of latency reactivating agents. Finally, this microscopy-based strategy was augmented with a flow-cytometry-based approach, enabling the detection of transcriptional reactivation of large numbers of latently infected cells. Hence, these approaches are shown to be suitable for qualitative and quantitative studies of HIV-1 latency and reactivation.

Neuropathogenesis of human immunodeficiency virus infection

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) remain a common end-organ manifestation of viral infection. Subclinical and mild symptoms lead to neurocognitive and behavioral abnormalities. These are associated, in part, with viral penetrance and persistence in the central nervous system. Infections of peripheral blood monocytes, macrophages, and microglia are the primary drivers of neuroinflammation and neuronal impairments. While current antiretroviral therapy (ART) has reduced the incidence of HIV-associated dementia, milder forms of HAND continue. Depression, comorbid conditions such as infectious liver disease, drugs of abuse, antiretroviral drugs themselves, age-related neurodegenerative diseases, gastrointestinal maladies, and concurrent social and economic issues can make accurate diagnosis of HAND challenging. Increased life expectancy as a result of ART clearly creates this variety of comorbid conditions that often blur the link between the virus and disease. With the discovery of novel biomarkers, neuropsychologic testing, and imaging techniques to better diagnose HAND, the emergence of brain-penetrant ART, adjunctive therapies, longer life expectancy, and better understanding of disease pathogenesis, disease elimination is perhaps a realistic possibility. This review focuses on HIV-associated disease pathobiology with an eye towards changing trends in the face of widespread availability of ART.

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.

Influence of Biological Sex, Age, and HIV Status in an In Vitro Primary Cell Model of HIV Latency Using a CXCR4 Tropic Virus

Primary cell models of human immunodeficiency virus (HIV) latency have become tools to both understand the mechanisms involved in establishment of latency and test preclinical strategies toward HIV-1 cure. These models rely on infection of CD4 T cells from healthy donors. As such, these models provide an opportunity to explore the role of biological sex, age, and HIV status on establishment and reactivation of latent HIV in vitro. We have used an established primary cell model of latency based on the generation of latently infected central memory CD4 T cells with the CXCR4 strain HIV-1_NL4-3 to address whether these variables influence (i) HIV-1_NL4-3 replication, (ii) establishment of latency, and (iii) latency reversal in CD4 T cells. Our results indicate that replication of HIV-1_NL4-3, but not establishment of latency, is influenced by the age of female, but not male, donors. Moreover, the frequency of latently infected cells in this model is directly correlated with levels of productive infection in both male and female donors independent of age. We did not find differences in the ability of five different latency-reversing agents to reactivate latent HIV-1_NL4-3. Finally, we have found that this model can be generated using cells from aviremic participants. In conclusion, we have further characterized the central memory T cell model of latency regarding biological sex and age and demonstrated that this model is suitable for use with cells isolated from aviremic participants, opening the opportunity to use this primary cell model to address cure approaches, including shock and kill, in HIV-infected individuals.

A defucosylated bispecific multivalent molecule exhibits broad HIV-1-neutralizing activity and enhanced antibody-dependent cellular cytotoxicity against reactivated HIV-1 latently infected cells

OBJECTIVE

Current treatments cannot completely eradicate HIV-1 owing to the presence of latently infected cells, which harbor transcriptionally silent HIV-1. However, defucosylated antibodies can readily kill latently infected cells after their activation to express envelope glycoprotein (Env) through antibody-dependent cellular cytotoxicity (ADCC). We herein aimed to test a defucosylated bispecific multivalent molecule consisting of domain-antibody and single-domain CD4, LSEVh-LS-F, for its HIV-1 neutralizing activity and ADCC against the reactivated latently infected cells, compared with the nondefucosylated molecule LSEVh-LS.

METHODS

LSEVh-LS-F's neutralizing activity against a panel of newly characterized Chinese HIV-1 clinical isolates was assessed by using TZM-bl-based and PBMC-based assays. LSEVh-LS-F-mediated ADCC in the presence of natural killer cells against cell lines that stably express Env proteins, HIV-1-infected cells and LRA-reactivated HIV-1 latent cells, was measured using a lactate dehydrogenase (LDH) cytotoxicity assay or flow cytometry.

RESULTS

LSEVh-LS-F and LSEVh-LS were equally effective in neutralized infection of all HIV-1 isolates tested with IC50 and IC90 values 3∼4-fold lower than those of VRC01. LSEVh-LS-F was more effective in natural killer-mediated killing of HIV-1 Env-expressing cell lines, HIV-1-infected cells, latency reactivation agents-reactivated ACH2 cells and reactivated latently infected resting CD4+ T cell line as well as resting CD4+ T lymphocytes isolated from patients receiving HAART.

CONCLUSION

LSEVh-LS-F exhibits broad HIV-1 neutralizing activity and enhanced ADCC against HIV-1-infected cells, reactivated latently infected cell lines and primary CD4+ T cells, thus being a promising candidate therapeutic for eradicating the HIV-1 reservoir.

TSC1 and DEPDC5 regulate HIV-1 latency through the mTOR signaling pathway

The latent reservoir of HIV-1 presents a major barrier to viral eradication. The mechanism of the establishment and maintenance of the latent viral reservoir is not yet fully understood, which hinders the development of effective curative strategies. In this study, we identified two inhibitory genes, TSC1 and DEPDC5, that maintained HIV-1 latency by suppressing the mTORC1 pathway. We first adapted a genome-wide CRISPR screening approach to identify host factors required for HIV latency in a T-cell-based latency model and discovered two inhibitory genes, TSC1 and DEPDC5, which are potentially involved in HIV-1 latency. Knockout of either TSC1 or DEPDC5 led to enhanced HIV-1 reactivation in both a T-cell line (C11) and a monocyte cell line (U1), and this enhancement could be antagonized by the mTORC1 inhibitor rapamycin. Further evaluation of the mechanism revealed that TSC1 suppresses AKT-mTORC1-S6 via downregulation of Rheb, whereas DEPDC5 inhibits AKT-mTORC1-S6 through RagA. Overall, both TSC1 and DEPDC5 negatively regulate the AKT-mTORC1 pathway, and thus their agonists could be used in the development of new therapeutic approaches for activating HIV-1 latency.

SAMHD1 Impairs HIV-1 Gene Expression and Negatively Modulates Reactivation of Viral Latency in CD4+ T Cells

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) restricts human immunodeficiency virus type 1 (HIV-1) replication in nondividing cells by degrading intracellular deoxynucleoside triphosphates (dNTPs). SAMHD1 is highly expressed in resting CD4+ T cells, which are important for the HIV-1 reservoir and viral latency; however, whether SAMHD1 affects HIV-1 latency is unknown. Recombinant SAMHD1 binds HIV-1 DNA or RNA fragments in vitro, but the function of this binding remains unclear. Here we investigate the effect of SAMHD1 on HIV-1 gene expression and reactivation of viral latency. We found that endogenous SAMHD1 impaired HIV-1 long terminal repeat (LTR) activity in monocytic THP-1 cells and HIV-1 reactivation in latently infected primary CD4+ T cells. Overexpression of wild-type (WT) SAMHD1 suppressed HIV-1 LTR-driven gene expression at a transcriptional level. Tat coexpression abrogated SAMHD1-mediated suppression of HIV-1 LTR-driven luciferase expression. SAMHD1 overexpression also suppressed the LTR activity of human T-cell leukemia virus type 1 (HTLV-1), but not that of murine leukemia virus (MLV), suggesting specific suppression of retroviral LTR-driven gene expression. WT SAMHD1 bound to proviral DNA and impaired reactivation of HIV-1 gene expression in latently infected J-Lat cells. In contrast, a nonphosphorylated mutant (T592A) and a dNTP triphosphohydrolase (dNTPase) inactive mutant (H206D R207N [HD/RN]) of SAMHD1 failed to efficiently suppress HIV-1 LTR-driven gene expression and reactivation of latent virus. Purified recombinant WT SAMHD1, but not the T592A and HD/RN mutants, bound to fragments of the HIV-1 LTR in vitro These findings suggest that SAMHD1-mediated suppression of HIV-1 LTR-driven gene expression potentially regulates viral latency in CD4+ T cells.IMPORTANCE A critical barrier to developing a cure for HIV-1 infection is the long-lived viral reservoir that exists in resting CD4+ T cells, the main targets of HIV-1. The viral reservoir is maintained through a variety of mechanisms, including regulation of the HIV-1 LTR promoter. The host protein SAMHD1 restricts HIV-1 replication in nondividing cells, but its role in HIV-1 latency remains unknown. Here we report a new function of SAMHD1 in regulating HIV-1 latency. We found that SAMHD1 suppressed HIV-1 LTR promoter-driven gene expression and reactivation of viral latency in cell lines and primary CD4+ T cells. Furthermore, SAMHD1 bound to the HIV-1 LTR in vitro and in a latently infected CD4+ T-cell line, suggesting that the binding may negatively modulate reactivation of HIV-1 latency. Our findings indicate a novel role for SAMHD1 in regulating HIV-1 latency, which enhances our understanding of the mechanisms regulating proviral gene expression in CD4+ T cells.

Sex Differences in HIV Infection: Mystique Versus Machismo

Biological sex is a determinant of both susceptibility to and pathogenesis of multiple infections, including HIV. These differences have effects on the spectrum of HIV disease from acquisition to eradication, with diverse mechanisms including distinct chromosomal complements, variation in microbiota composition, hormonal effects on transcriptional profiles, and expression of different immunoregulatory elements. With a comparative biology approach, these sex differences can be used to highlight protective and detrimental immune activation pathways, to identify strategies for effective prevention, treatment, and curative interventions.

Role of Host Factors on the Regulation of Tat-Mediated HIV-1 Transcription

BACKGROUND

The viral transactivator Tat protein is a key modulator of HIV-1 replication, as it regulates transcriptional elongation from the integrated proviral genome. Tat recruits the human transcription elongation factor b, and other host proteins, such as the super elongation complex, to activate the cellular RNA polymerase II, normally stalled shortly after transcription initiation at the HIV promoter. By means of a complex set of interactions with host cellular factors, Tat determines the fate of viral activity within the infected cell. The virus will either actively replicate to promote dissemination in blood and tissues, or become dormant mostly in memory CD4+ T cells, as part of a small but long-living latent reservoir, the main obstacle for HIV eradication.

OBJECTIVE

In this review, we summarize recent advances in the understanding of the multi-step mechanism that regulates Tat-mediated HIV-1 transcription and RNA polymerase II release, to promote viral transcription elongation. Early events of the human transcription elongation factor b release from the inhibitory 7SK small nuclear ribonucleoprotein complex and its recruitment to the HIV promoter will be discussed. Specific roles of the super elongation complex subunits during transcription elongation, and insight on recently identified cellular factors and mechanisms regulating HIV latency will be detailed.

CONCLUSION

Understanding the complexity of HIV transcriptional regulation by host factors may open the door for development of novel strategies to eradicate the resilient latent reservoir.

Short-Term Pegylated Interferon α2a Treatment Does Not Significantly Reduce the Viral Reservoir of Simian Immunodeficiency Virus-Infected, Antiretroviral Therapy-Treated Rhesus Macaques

The major obstacle to human immunodeficiency type 1 (HIV-1) eradication is a reservoir of latently infected cells that persists despite long-term antiretroviral therapy (ART) and causes rapid viral rebound if treatment is interrupted. Type I interferons are immunomodulatory cytokines that induce antiviral factors and have been evaluated for the treatment of HIV-infected individuals, resulting in moderate reduction of viremia and inconclusive data about their effect on reservoir size. Here, we assessed the potential of pegylated IFN-α2a (pIFN-α2a) to reduce the viral reservoir in simian immunodeficiency virus (SIV)-infected, ART-treated rhesus macaques (RMs). We found that pIFN-α2a treatment of animals in which virus replication is effectively suppressed with ART is safe and well tolerated, as no major clinical side effects were observed. By monitoring the cellular immune response during this intervention, we established that pIFN-α2a administration is not associated with either CD4⁺ T cell depletion or increased immune activation. Importantly, we found that interferon-stimulated genes (ISGs) were significantly upregulated in IFN-treated RMs compared to control animals, confirming that pIFN-α2a is bioactive in vivo To evaluate the effect of pIFN-α2a administration on the viral reservoir in CD4⁺ T cells, we performed cell-associated proviral SIV DNA measurements in multiple tissues and assessed levels of replication-competent virus by a quantitative viral outgrowth assay (QVOA). These analyses failed to reveal any significant difference in reservoir size between IFN-treated and control animals. In summary, our data suggest that short-term type I interferon treatment in combination with suppressive ART is not sufficient to induce a significant reduction of the viral reservoir in SIV-infected RMs.IMPORTANCE The potential of type I interferons to reduce the viral reservoir has been recently studied in clinical trials in HIV-infected humans. However, given the lack of mechanistic data and the potential for safety concerns, a more comprehensive testing of IFN treatment in vivo in SIV-infected RMs is critical to provide rationale for further development of this intervention in humans. Utilizing the SIV/RM model in which virus replication is suppressed with ART, we addressed experimental limitations of previous human studies, in particular the lack of a control group and specimen sampling limited to blood. Here, we show by rigorous testing of blood and lymphoid tissues that virus replication and reservoir size were not significantly affected by pIFN-α2a treatment in SIV-infected, ART-treated RMs. This suggests that intensified and/or prolonged IFN treatment regimens, possibly in combination with other antilatency agents, are necessary to effectively purge the HIV/SIV reservoir under ART.

In Vitro Exposure to Prostratin but Not Bryostatin-1 Improves Natural Killer Cell Functions Including Killing of CD4+ T Cells Harboring Reactivated Human Immunodeficiency Virus

In the attempt of purging the HIV-1 reservoir through the “shock-and-kill” strategy, it is important to select latency-reversing agents (LRAs) devoid of deleterious effects on the antiviral function of immune effector cells. Here, we investigated two LRAs with PKC agonist activity, prostratin (PRO) and bryostatin-1 (BRY), for their impact on the function of natural killer (NK) cells, the major effectors of innate immunity whose potential in HIV-1 eradication has emerged in recent clinical trials. Using NK cells of healthy donors, we found that exposure to either PRO or BRY potently activated NK cells, resulting in upmodulation of NKG2D and NKp44 activating receptors and matrix metalloprotease-mediated shedding of CD16 receptor. Despite PRO and BRY affected NK cell phenotype in the same manner, their impact on NK cell function was diverse and showed considerable donor-to-donor variation. Altogether, in most tested donors, the natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) of NK cells were either improved or maintained by PRO, while both activities were impaired by BRY. Moreover, we analyzed the effect of these drugs on the capacity of treated NK cells to kill autologous latently infected CD4⁺ T cells reactivated via the same treatment. First, we found that PRO but not BRY increased upmodulation of the ULBP2 ligand for NKG2D on reactivated p24⁺ cells. Importantly, we showed that clearance of reactivated p24⁺ cells by NK cells was enhanced when both targets and effectors were exposed to PRO but not to BRY. Overall, PRO had a superior potential compared with BRY as to the impact on key NK cell functions and on NK-cell-mediated clearance of the HIV-1 reservoir. Our results emphasize the importance of considering the effects on NK cells of candidate “shock-and-kill” interventions. With respect to combinative approaches, the impact on NK cells of each LRA should be re-evaluated upon combination with a second LRA, which may have analogous or opposite effects, or with immunotherapy targeting NK cells. In addition, avoiding co-administration of LRAs that negatively impact ADCC activity by NK cells might be essential for successful application of antibodies or vaccination to “shock-and-kill” strategies.

Diverse Impacts of HIV Latency-Reversing Agents on CD8+ T-Cell Function: Implications for HIV Cure

Antiretroviral therapy regimens durably suppress HIV replication, but do not cure infection. This is partially attributable to the persistence of long-lived pools of resting CD4+ T-cells harboring latent replication-competent virus. Substantial clinical and pre-clinical research is currently being directed at purging this viral reservoir by combining pharmacological latency reversal with immune effectors, such as HIV-specific CD8+ T-cells, capable of eliminating reactivated targets-the so-called "shock-and-kill" approach. However, several studies indicate that the latency-reversing agents (LRAs) may affect CD8+ T-cell function. The current review aims to frame recent advances, and ongoing challenges, in implementing "shock-and-kill" strategies from the perspective of effectively harnessing CD8+ T-cells. We review and contextualize findings indicating that LRAs often have unintended impacts on CD8+ T-cell function, both detrimental and beneficial. We identify and attempt to bridge the gap between viral reactivation, as measured by the detection of RNA or protein, and bona fide presentation of viral antigens to CD8+ T-cells. Finally, we highlight factors on the effector (CD8+) and target (CD4+) cell sides that contribute to whether or not infected-cell recognition results in killing/elimination. These perspectives may contribute to an integrated view of "shock-and-kill," with implications for therapeutic development.

γδ T cells: an immunotherapeutic approach for HIV cure strategies

Current strategies aimed to cure HIV infection are based on combined efforts to reactivate the virus from latency and improve immune effector cell function to clear infected cells. These strategies are primarily focused on CD8+ T cells and approaches are challenging due to insufficient HIV antigen production from infected cells and poor HIV-specific CD8+ T cells. γδ T cells represent a unique subset of effector T cells that can traffic to tissues, and selectively target cancer or virally infected cells without requiring MHC presentation. We analyzed whether γδ T cells represent a complementary/alternative immunotherapeutic approach towards HIV cure strategies. γδ T cells from HIV-infected virologically suppressed donors were expanded with bisphosphonate pamidronate (PAM) and cells were used in autologous cellular systems ex vivo. These cells (a) are potent cytotoxic effectors able to efficiently inhibit HIV replication ex vivo, (b) degranulate in the presence of autologous infected CD4+ T cells, and (c) specifically clear latently infected cells after latency reversal with vorinostat. This is the first proof of concept to our knowledge showing that γδ T cells target and clear autologous HIV reservoirs upon latency reversal. Our results open potentially new insights into the immunotherapeutic use of γδ T cells for current interventions in HIV eradication strategies.

Cumulative Antiretroviral Exposure Measured in Hair Is Not Associated With Measures of HIV Persistence or Inflammation Among Individuals on Suppressive ART

Data on the relationship of antiretroviral exposure to measures of human immunodeficiency virus (HIV) persistence are limited. To address this gap, multiple viral, immunologic, and pharmacologic measures were analyzed from individuals with sustained virologic suppression on therapy (median 7 years) in the AIDS Clinical Trials Group A5321 cohort. Among 110 participants on tenofovir-(TFV)-disoproxil-fumarate (TDF)/emtricitabine (FTC)-containing regimens, we found no significant correlation between hair concentrations of individual antiretrovirals (ARVs) in the regimen and measures of HIV persistence (plasma HIV-1 RNA by single copy assay, cell-associated-DNA, cell-associated RNA) or soluble markers of inflammation. These findings suggest that higher systemic ARV exposure may not impact HIV persistence or inflammation.

Coloring hidden viruses

An improved dual-color reporter reveals how the fate of latent HIV-1 depends on where it integrates in the human genome.

Cyclin-dependent kinase 7 (CDK7)-mediated phosphorylation of the CDK9 activation loop promotes P-TEFb assembly with Tat and proviral HIV reactivation

The HIV trans-activator Tat recruits the host transcription elongation factor P-TEFb to stimulate proviral transcription. Phosphorylation of Thr-186 on the activation loop (T-loop) of cyclin-dependent kinase 9 (CDK9) is essential for its kinase activity and assembly of CDK9 and cyclin T1 (CycT1) to form functional P-TEFb. Phosphorylation of a second highly conserved T-loop site, Ser-175, alters the competitive binding of Tat and the host recruitment factor bromodomain containing 4 (BRD4) to P-TEFb. Here, we investigated the intracellular mechanisms that regulate these key phosphorylation events required for HIV transcription. Molecular dynamics simulations revealed that the CDK9/CycT1 interface is stabilized by intramolecular hydrogen bonding of pThr-186 by an arginine triad and Glu-96 of CycT1. Arginine triad substitutions that disrupted CDK9/CycT1 assembly accumulated Thr-186-dephosphorylated CDK9 associated with the cytoplasmic Hsp90/Cdc37 chaperone. The Hsp90/Cdc37/CDK9 complex was also present in resting T cells, which lack CycT1. Hsp90 inhibition in primary T cells blocked P-TEFb assembly, disrupted Thr-186 phosphorylation, and suppressed proviral reactivation. The selective CDK7 inhibitor THZ1 blocked CDK9 phosphorylation at Ser-175, and in vitro kinase assays confirmed that CDK7 activity is principally responsible for Ser-175 phosphorylation. Mutation of Ser-175 to Lys had no effect on CDK9 kinase activity or P-TEFb assembly but strongly suppressed both HIV expression and BRD4 binding. We conclude that the transfer of CDK9 from the Hsp90/Cdc37 complex induced by Thr-186 phosphorylation is a key step in P-TEFb biogenesis. Furthermore, we demonstrate that CDK7-mediated Ser-175 phosphorylation is a downstream nuclear event essential for facilitating CDK9 T-loop interactions with Tat.

Distinct chromatin functional states correlate with HIV latency reactivation in infected primary CD4+ T cells

Human immunodeficiency virus (HIV) infection is currently incurable, due to the persistence of latently infected cells. The 'shock and kill' approach to a cure proposes to eliminate this reservoir via transcriptional activation of latent proviruses, enabling direct or indirect killing of infected cells. Currently available latency-reversing agents (LRAs) have however proven ineffective. To understand why, we used a novel HIV reporter strain in primary CD4+ T cells and determined which latently infected cells are reactivatable by current candidate LRAs. Remarkably, none of these agents reactivated more than 5% of cells carrying a latent provirus. Sequencing analysis of reactivatable vs. non-reactivatable populations revealed that the integration sites were distinguishable in terms of chromatin functional states. Our findings challenge the feasibility of 'shock and kill', and suggest the need to explore other strategies to control the latent HIV reservoir.

The KAT5-Acetyl-Histone4-Brd4 axis silences HIV-1 transcription and promotes viral latency

The bromodomain protein Brd4 promotes HIV-1 latency by competitively inhibiting P-TEFb-mediated transcription induced by the virus-encoded Tat protein. Brd4 is recruited to the HIV LTR by interactions with acetyl-histones3 (AcH3) and AcH4. However, the precise modification pattern that it reads and the writer for generating this pattern are unknown. By examining a pool of latently infected proviruses with diverse integration sites, we found that the LTR characteristically has low AcH3 but high AcH4 content. This unusual acetylation profile attracts Brd4 to suppress the interaction of Tat with the host super elongation complex (SEC) that is essential for productive HIV transcription and latency reversal. KAT5 (lysine acetyltransferase 5), but not its paralogs KAT7 and KAT8, is found to promote HIV latency through acetylating H4 on the provirus. Antagonizing KAT5 removes AcH4 and Brd4 from the LTR, enhances the SEC loading, and reverses as well as delays, the establishment of latency. The pro-latency effect of KAT5 is confirmed in a primary CD4+ T cell latency model as well as cells from ART-treated patients. Our data thus indicate the KAT5-AcH4-Brd4 axis as a key regulator of latency and a potential therapeutic target to reactivate latent HIV reservoirs for eradication.

A major impediment to the cure of HIV/AIDS is the viral latency. Previous studies have identified the bromodomain protein Brd4 as a promoter of HIV latency by binding to the viral LTR to inhibit Tat-induced transcription. Here, we discover that the LTR of latent HIV has low acetylated histone H3 (AcH3) but high AcH4 content, which recruits Brd4 to inhibit Tat-transactivation. Furthermore, the lysine acetyltransferase KAT5 but not the paralogs KAT7 and KAT8 promotes latency through acetylating H4 on the provirus. Antagonizing KAT5 removes AcH4 and Brd4 from the LTR, enhances loading of the Super Elongation Complex, and interferes with the establishment of latency. Thus, the KAT5-AcH4-Brd4 axis is a key regulator of HIV latency and a potential therapeutic target for eradicating latent HIV reservoirs.

Ethics of treatment interruption trials in HIV cure research: addressing the conundrum of risk/benefit assessment

Though antiretroviral therapy is the standard of care for people living with HIV, its treatment limitations, burdens, stigma and costs lead to continued interest in HIV cure research. Early-phase cure trials, particularly those that include analytic treatment interruption (ATI), involve uncertain and potentially high risk, with minimal chance of clinical benefit. Some question whether such trials should be offered, given the risk/benefit imbalance, and whether those who choose to participate are acting rationally. We address these questions through a longitudinal decision-making study nested in a Thai acute HIV research cohort.In-depth interviews revealed central themes about decisions to join. Participants felt they possessed an important identity as members of the acute cohort, viewing their bodies as uniquely suited to both testing and potentially benefiting from HIV cure approaches. While acknowledging risks of ATI, most perceived they were given an opportunity to interrupt treatment, to test their own bodies and increase normalcy in a safe, highly monitored circumstance. They were motivated by potential benefits to themselves, the investigators and larger acute cohort, and others with HIV. They believed their own trial experiences and being able to give back to the community were sufficient to offset participation risks.These decisions were driven by the specific circumstances experienced by our participants. Judging risk/benefit ratios without appreciating these lived experiences can lead to false determinations of irrational decision- making. While this does not minimise vital oversight considerations about risk reduction and protection from harm, it argues for inclusion of a more participant-centered approach.

Comparative Proteomic Profiling and Biomarker Identification of Traditional Chinese Medicine-Based HIV/AIDS Syndromes

Given the challenges in exploring lifelong therapy with little side effect for human immunodeficiency virus infection and acquired immune deficiency syndrome (HIV/AIDS) cases, there is increasing interest in developing traditional Chinese medicine (TCM) treatments based on specific TCM syndrome. However, there are few objective and biological evidences for classification and diagnosis of HIV/AIDS TCM syndromes to date. In this study, iTRAQ-2DLC-MS/MS coupled with bioinformatics were firstly employed for comparative proteomic profiling of top popular TCM syndromes of HIV/AIDS: accumulation of heat-toxicity (AHT) and Yang deficiency of spleen and kidney (YDSK). It was found that for the two TCM syndromes, the identified differential expressed proteins (DEPs) as well as their biological function distributions and participation in signaling pathways were significantly different, providing biological evidence for the classification of HIV/AIDS TCM syndromes. Furthermore, the TCM syndrome-specific DEPs were confirmed as biomarkers based on western blot analyses, including FN1, GPX3, KRT10 for AHT and RBP4, ApoE, KNG1 for YDSK. These biomarkers also biologically linked with the specific TCM syndrome closely. Thus the clinical and biological basis for differentiation and diagnosis of HIV/AIDs TCM syndromes were provided for the first time, providing more opportunities for stable exertion and better application of TCM efficacy and superiority in HIV/AIDS treatment.

Control of HIV infection by IFN-α: implications for latency and a cure

Viral infections, including HIV, trigger the production of type I interferons (IFNs), which in turn, activate a signalling cascade that ultimately culminates with the expression of anti-viral proteins. Mounting evidence suggests that type I IFNs, in particular IFN-α, play a pivotal role in limiting acute HIV infection. Highly active anti-retroviral treatment reduces viral load and increases life expectancy in HIV positive patients; however, it fails to fully eliminate latent HIV reservoirs. To revisit HIV as a curable disease, this article reviews a body of literature that highlights type I IFNs as mediators in the control of HIV infection, with particular focus on the anti-HIV restriction factors induced and/or activated by IFN-α. In addition, we discuss the relevance of type I IFN treatment in the context of HIV latency reversal, novel therapeutic intervention strategies and the potential for full HIV clearance.

Trade-off between synergy and efficacy in combinations of HIV-1 latency-reversing agents

Eradicating HIV-1 infection is difficult because of the reservoir of latently infected cells that gets established soon after infection, remains hidden from antiretroviral drugs and host immune responses, and retains the capacity to reignite infection following the cessation of treatment. Drugs called latency-reversing agents (LRAs) are being developed to reactivate latently infected cells and render them susceptible to viral cytopathicity or immune killing. Whereas individual LRAs have failed to induce adequate reactivation, pairs of LRAs have been identified recently that act synergistically and hugely increase reactivation levels compared to individual LRAs. The maximum synergy achievable with LRA pairs is of clinical importance, as it would allow latency-reversal with minimal drug exposure. Here, we employed stochastic simulations of HIV-1 transcription and translation in latently infected cells to estimate this maximum synergy. We incorporated the predominant mechanisms of action of the two most promising classes of LRAs, namely, protein kinase C agonists and histone deacetylase inhibitors, and quantified the activity of individual LRAs in the two classes by mapping our simulations to corresponding in vitro experiments. Without any adjustable parameters, our simulations then quantitatively captured experimental observations of latency-reversal when the LRAs were used in pairs. Performing simulations representing a wide range of drug concentrations, we estimated the maximum synergy achievable with these LRA pairs. Importantly, we found with all the LRA pairs we considered that concentrations yielding the maximum synergy did not yield the maximum latency-reversal. Increasing concentrations to increase latency-reversal compromised synergy, unravelling a trade-off between synergy and efficacy in LRA combinations. The maximum synergy realizable with LRA pairs would thus be restricted by the desired level of latency-reversal, a constrained optimum we elucidated with our simulations. We expect this trade-off to be important in defining optimal LRA combinations that would maximize synergy while ensuring adequate latency-reversal.

HIV-1 infection typically requires lifelong treatment because a class of infected cells called latently infected cells remains hidden from drugs and host immune responses and can reignite infection when treatment is stopped. Massive efforts are ongoing to devise ways to eliminate latently infected cells. The most advanced of the strategies developed for this purpose involves using drugs called latency-reversing agents (LRAs), which reactivate latently infected cells, effectively bringing them out of their hiding. Multiple mechanisms are involved in the establishment of latency. Pairs of LRAs targeting distinct mechanisms have been found to synergize and induce significantly higher latency-reversal than individual LRAs. If this synergy can be maximized, latency-reversal can be achieved with minimal drug exposure. Using stochastic simulations of HIV-1 latency, we unraveled a trade-off between synergy and efficacy in LRA pairs. Drug concentrations that maximized synergy did not also maximize latency-reversal. Drug concentrations that yielded higher latency-reversal compromised synergy and vice versa. This trade-off would constrain the synergy realizable between LRAs and guide the identification of optimal LRA combinations that would maximize synergy while ensuring adequate latency-reversal.

Epigenetic regulation of HIV-1 latency: focus on polycomb group (PcG) proteins

HIV-1 latency allows the virus to persist until reactivation, in a transcriptionally silent form in its cellular reservoirs despite the presence of effective cART. Such viral persistence represents a major barrier to HIV eradication since treatment interruption leads to rebound plasma viremia. Polycomb group (PcG) proteins have recently got a considerable attention in regulating HIV-1 post-integration latency as they are involved in the repression of proviral gene expression through the methylation of histones. This epigenetic regulation plays an important role in the establishment and maintenance of HIV-1 latency. In fact, PcG proteins act in complexes and modulate the epigenetic signatures of integrated HIV-1 promoter. Key role played by PcG proteins in the molecular control of HIV-1 latency has led to hypothesize that PcG proteins may represent a valuable target for future HIV-1 therapy in purging HIV-1 reservoirs. In this regard, various small molecules have been synthesized or explored to specifically block the epigenetic activity of PcG. In this review, we will highlight the possible therapeutic approaches to achieve either a functional or sterilizing cure of HIV-1 infection with special focus on histone methylation by PcG proteins together with current and novel pharmacological approaches to reactivate HIV-1 from latency that could ultimately lead towards a better clearance of viral latent reservoirs.

Beyond the replication-competent HIV reservoir: transcription and translation-competent reservoirs

Recent years have seen a substantial increase in the number of tools available to monitor and study HIV reservoirs. Here, we discuss recent technological advances that enable an understanding of reservoir dynamics beyond classical assays to measure the frequency of cells containing provirus able to propagate a spreading infection (replication-competent reservoir). Specifically, we focus on the characterization of cellular reservoirs containing proviruses able to transcribe viral mRNAs (so called transcription-competent) and translate viral proteins (translation-competent). We suggest that the study of these alternative reservoirs provides complementary information to classical approaches, crucially at a single-cell level. This enables an in-depth characterization of the cellular reservoir, both following reactivation from latency and, importantly, directly ex vivo at baseline. Furthermore, we propose that the study of cellular reservoirs that may not contain fully replication-competent virus, but are able to produce HIV mRNAs and proteins, is of biological importance. Lastly, we detail some of the key contributions that the study of these transcription and translation-competent reservoirs has made thus far to investigations into HIV persistence, and outline where these approaches may take the field next.

The HIV-1 accessory proteins Nef and Vpu downregulate total and cell surface CD28 in CD4+ T cells

Background

The HIV-1 accessory proteins Nef and Vpu alter cell surface levels of multiple host proteins to modify the immune response and increase viral persistence. Nef and Vpu can downregulate cell surface levels of the co-stimulatory molecule CD28, however the mechanism of this function has not been completely elucidated.

Results

Here, we provide evidence that Nef and Vpu decrease cell surface and total cellular levels of CD28. Moreover, using inhibitors we implicate the cellular degradation machinery in the downregulation of CD28. We shed light on the mechanisms of CD28 downregulation by implicating the Nef LL₁₆₅ and DD₁₇₅ motifs in decreasing cell surface CD28 and Nef DD₁₇₅ in decreasing total cellular CD28. Moreover, the Vpu LV₆₄ and S_52/56 motifs were required for cell surface CD28 downregulation, while, unlike for CD4 downregulation, Vpu W₂₂ was dispensable. The Vpu S_52/56 motif was also critical for Vpu-mediated decreases in total CD28 protein level. Finally, the ability of Vpu to downregulate CD28 is conserved between multiple group M Vpu proteins and infection with viruses encoding or lacking Nef and Vpu have differential effects on activation upon stimulation.

Conclusions

We report that Nef and Vpu downregulate cell surface and total cellular CD28 levels. We identified inhibitors and mutations within Nef and Vpu that disrupt downregulation, shedding light on the mechanisms utilized to downregulate CD28. The conservation and redundancy between the abilities of two HIV-1 proteins to downregulate CD28 highlight the importance of this function, which may contribute to the development of latently infected cells.

Electronic supplementary material

The online version of this article (10.1186/s12977-018-0388-3) contains supplementary material, which is available to authorized users.

Optimization and comparison of CD4-targeting lipid-polymer hybrid nanoparticles using different binding ligands

Monoclonal antibodies and peptides are conjugated to the surface of nanocarriers (NCs) for targeting purposes in numerous applications. However, targeting efficacy may vary with their specificity, affinity, or avidity when linked to NCs. The physicochemical properties of NCs may also affect targeting. We compared the targeting efficacy of the CD4 binding peptide BP4 and an anti-CD4 monoclonal antibody (CD4 mAb) and its fragments, when conjugated to lipid-coated poly(lactic-co-glycolic) acid nanoparticles (LCNPs). Negatively charged LCNPs with cholesteryl butyrate in the lipid layer (cbLCNPs) dramatically reduced nonspecific binding, leading to higher targeting specificity, compared to neutral or positively charged LCNPs with DOTAP (dtLCNP). cbLCNPs surface conjugated with a CD4 antibody (CD4-cbLCNPs) or its fragments (fCD4-cbLCNPs), but not BP4, showed high binding in vitro to the human T cell line 174xCEM, and preferential binding to CD3+ CD14-CD8- cells from pigtail macaque peripheral blood mononuclear cells. CD4-cbLCNPs showed 10-fold higher binding specificity for CD4+ than CD8+ T cells, while fCD4-cbLCNPs demonstrated the highest binding level overall, but only three-fold higher binding specificity. This study demonstrates the importance of ζ-potential on NC targeting and indicates that CD4 mAb and its fragments are the best candidates for delivery of therapeutic agents to CD4+ T cells. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1177-1188, 2018.

Multi-Envelope HIV-1 Vaccine Development: Two Targeted Immune Pathways, One Desired Protective Outcome

In 2016, there were more than 30 million individuals living with HIV-1, ∼1.8 million new HIV-1 infections, and ∼1 million HIV-1-related deaths according to UNAIDS ( unaids.org ). Hence, a preventive HIV-1 vaccine remains a global priority. The variant envelopes of HIV-1 present a significant obstacle to vaccine development and the vaccine field has realized that immunization with a single HIV-1 envelope protein will not be sufficient to generate broadly neutralizing antibodies. Here we describe two nonmutually exclusive, targeted pathways with which a multi-envelope HIV-1 vaccine may generate protective immune responses against variant HIV-1. Pathways include (i) the induction of a polyclonal immune response, comprising a plethora of antibodies with subset-reactive and cross-reactive specificities, together able to neutralize diverse HIV-1 (termed Poly-nAb in this report) and (ii) the induction of one or a few monoclonal antibodies, each with a broadly neutralizing specificity (bnAb). With each pathway in mind, we describe challenges and strategies that may ultimately support HIV-1 vaccine success.

"We Need to Deploy Them Very Thoughtfully and Carefully": Perceptions of Analytical Treatment Interruptions in HIV Cure Research in the United States-A Qualitative Inquiry

Strategies to control HIV in the absence of antiretroviral therapy are needed to cure HIV. However, such strategies will require analytical treatment interruptions (ATIs) to determine their efficacy. We investigated how U.S. stakeholders involved in HIV cure research perceive ATIs. We conducted 36 in-depth interviews with three groups of stakeholders: 12 people living with HIV, 11 clinician-researchers, and 13 policy-makers/bioethicists. Qualitative data revealed several themes. First, there was little consensus on when ATIs would be ethically warranted. Second, the most frequent perceived hypothetical motivators for participating in research on ATIs were advancing science and contributing to society. Third, risks related to viral rebound were the most prevalent concerns related to ATIs. Stakeholders suggested ways to minimize the risks of ATIs in HIV cure research. Increased cooperation between scientists and local communities may be useful for minimizing risk. Further ethics research is necessary.

Design, synthesis, and biological evaluation of AV6 derivatives as novel dual reactivators of latent HIV-1

The “shock and kill” strategy might be a promising therapeutic approach for HIV/AIDS due to the existence of latent viral reservoirs. A major challenge of the “shock and kill” strategy arises from the general lack of clinically effective latency-reversing agents (LRAs). The 2-methylquinoline derivative, antiviral 6 (AV6) has been reported to induce latent HIV-1 expression and act synergistically with a HDAC inhibitor VA to reverse HIV latency. We report herein the design and identification of AV6 analogues which possess the zinc-binding group of HDAC inhibitors and have dual acting mechanism for the reactivation of HIV-1 from latency. Evaluation of compounds for the reactivation of HIV-1 latency identified two excellent active compounds 12c and 12d. Further bioassays revealed that these two compounds reactivated latent HIV-1 through dual mechanism, the inhibition of HDACs and NFAT-required for early HIV-1 gene expression. Additionally, it was found that 12c and 12d could reactivate HIV-1 transcription by releasing P-TEFb from the inactive complex 7SK snRNP. At last, molecular docking identified their orientation and binding interactions at the active site of HDAC2. This experimental data suggests that 12c and 12d can be served as effective HIV-1 LRAs which can be taken up for further studies.

As dual-acting HIV LRAs, compounds 12c and 12d could activate latent HIV-1 via the NFAT-required mechanism and as histone deacetylase (HDAC) inhibitors.

Antiviral Immunotoxin Against Bovine herpesvirus-1: Targeted Inhibition of Viral Replication and Apoptosis of Infected Cell

Bovine herpesvirus 1 (BoHV-1) is a highly contagious viral pathogen which causes infectious bovine rhinotracheitis in cattle worldwide. Currently, there is no antiviral prophylactic treatment available capable of mitigating the disease impact and facilitating recovery from latent infection. In this study, we have engineered a novel recombinant anti-BoHV-1 immunotoxin construct termed "BoScFv-PE38" that consists of a single-chain monoclonal antibody fragment (scFv) fused with an active domain of Pseudomonas exotoxin A as a toxic effector (PE38). The recombinant BoScFv-PE38 immunotoxin expressed in a prokaryotic expression system has specific binding affinity for BoHV-1 glycoprotein D (gD) with a dissociation constant (Kd) of 12.81 nM and for BoHV-1 virus particles with a Kd value of 97.63 nM. We demonstrate that the recombinant BoScFv-PE38 is internalized into MDBK cell compartments that inhibit BoHV-1 replication with a half-maximal inhibitory concentration (IC₅₀) of 4.95 ± 0.33 nM and a selective index (SI) of 456 ± 31. Furthermore, the BoScFv-PE38 exerted a cytotoxic effect through the induction of ATP and ammonia, leading to apoptosis of BoHV-1-infected cells and the inhibition of BoHV-1 replication in MDBK cells. Collectively, we show that BoScFv-PE38 can potentially be employed as a therapeutic agent for the treatment of BoHV-1 infection.

HIV Latency Gets a New Histone Mark

Transcriptional latency of integrated HIV-1 provirus represents a major obstacle to curing HIV. In this issue of Cell Host & Microbe, Boehm et al. (2017) identify a new lysine methyltransferase that writes a repressive histone mark associated with HIV-1 latency. The results are important for strategies to pharmacologically reverse HIV-1 latency.

eCD4-Ig promotes ADCC activity of sera from HIV-1-infected patients

Antibody-dependent cell-mediated cytotoxity (ADCC) can eliminate HIV-1 infected cells, and may help reduce the reservoir of latent virus in infected patients. Sera of HIV-1 positive individuals include a number of antibodies that recognize epitopes usually occluded on HIV-1 envelope glycoprotein (Env) trimers. We have recently described eCD4-Ig, a potent and exceptionally broad inhibitor of HIV-1 entry that can be used to protect rhesus macaques from multiple high-dose challenges with simian-human immunodeficiency virus AD8 (SHIV-AD8). Here we show that eCD4-Ig bearing an IgG1 Fc domain (eCD4-IgG1) can mediate efficient ADCC activity against HIV-1 isolates with differing tropisms, and that it does so at least 10-fold more efficiently than CD4-Ig, even when more CD4-Ig molecules bound cell surface-expressed Env. An ADCC-inactive IgG2 form of eCD4-Ig (eCD4-IgG2) exposes V3-loop and CD4-induced epitopes on cell-expressed trimers, and renders HIV-1-infected cells susceptible to ADCC mediated by antibodies of these classes. Moreover, eCD4-IgG2, but not IgG2 forms of the broadly neutralizing antibodies VRC01 and 10-1074, enhances the ADCC activities of serum antibodies from patients by 100-fold, and significantly enhanced killing of two latently infected T-cell lines reactivated by vorinostat or TNFα. Thus eCD4-Ig is qualitatively different from CD4-Ig or neutralizing antibodies in its ability to mediate ADCC, and it may be uniquely useful in treating HIV-1 infection or reducing the reservoir of latently infected cells.

Bovine single chain Fv antibody inhibits bovine herpesvirus-1 infectivity by targeting viral glycoprotein D

Glycoprotein D (gD) of bovine herpesvirus-1 (BoHV-1) is essential for attachment and penetration of cells during infection and is a major target for neutralizing antibodies during an adaptive immune response. Currently there are no recombinant antibodies capable of binding gD epitopes for use in treating BoHV-1 infection. In this study, a bovine scFv gene derived from a hybridoma secreting monoclonal antibodies (McAbs) against the amino acid motif MEESKGYEPP of gD was expressed in E. coli. Molecular modeling, western blot and ELISA analysis showed that this scFv had a high affinity for BoHV-1 gD, with a Kd of 161.2 ± 37.58 nM and for whole BoHV-1 virus, with a Kd of 67.44 ± 16.99 nM. In addition, this scFv displayed a high affinity for BoHV-1 antigen in an ELISA and competed with BoHV-1 anti-serum in a competitive ELISA. Immunofluorescence assay (IFA) and laser confocal microscopy showed that this scFv could efficiently bind to and be internalized by BoHV-1 infected Madin-Darby bovine kidney (MDBK) cells. Importantly, this scFv was shown to inhibit BoHV-1 infectivity and to reduce the number of viral plaques by blocking viral attachment to MDBK cells. Our study suggests that this bovine single-chain antibody could be developed for use as a diagnostic and therapeutic agent against BoHV-1 infection in cattle.