TAG HIV Basic Science, Vaccines, and Cure Project Blog

By Richard Jefferys, Project Director at Treatment Action Group (TAG).

recent posts

  • Studying HIV Persistence in Liver Macrophages

    The major reservoir of HIV that persists despite ART is contained in long-lived memory CD4 T cells. Whether other cell types, particularly macrophages, can harbor a reservoir of replication-competent HIV—and thus contribute to viral load rebound if ART is interrupted—remains uncertain, and a matter of some controversy among scientists. The question is important, because identifying and eliminating virus reservoirs is a central plank of the research effort to cure HIV infection. In a new paper in the Journal of Clinical Investigation (available open access), Abraham J. Kandathil and colleagues investigate whether human liver macrophages—which they note comprise up to 90% of all tissue macrophages—can sequester infectious HIV in people on ART.

    The researchers obtained liver tissue samples from eight people with HIV on ART who had undetectable viral loads in blood (seven were undergoing liver transplantation, and one was sampled at the time of death). HIV DNA could be detected in most samples, but it wasn’t possible to assess whether this represented unintegrated or integrated DNA in the liver macrophages due to the limited numbers of cells available.

    Importantly, in only one case could infectious HIV be propagated from purified liver tissue macrophages into susceptible target cells, leading to the detection of HIV RNA. This individual had been on ART for the shortest period prior to sampling (8 months) and also represented the only instance in which low-level contamination by T cells was detectable in the liver macrophage sample.

    The findings suggest that tissue macrophages may not represent a significant contributor to the long-term reservoir of replication-competent HIV in people on ART. The authors offer several reasons why that might be the case, including expression of the HIV restriction factor SAMHD1 in this cell population and the lifespan of HIV-infected macrophages, which could conceivably cause them to decay much faster during ART than memory CD4 T cells.

    Several possible caveats to the study are also noted, such as the relatively small number of participants and the possibility that inflammatory liver disease (which had prompted the need for transplantation in most cases) influenced that makeup of the liver macrophage population, i.e. increasing the number of recently-generated versus longer-lived macrophages.

    Despite these limitations, the study adds novel evidence to the debate regarding the role of macrophages in HIV persistence.

  • HIV Cure-Related Research at AIDS 2018

    Workshops, sessions and presentations related to HIV cure research at the upcoming AIDS 2018 conference in Amsterdam. 

    HIV Cure Research with the Community Workshop 
    Pre-Conference Meeting
    Room E105–108, RAI, Amsterdam, Netherlands
    Saturday July 21, 2018, 9:00-18:00

    Strategies for diagnosing and managing acute HIV infection in the context of PrEP and immediate ART
    Code: MOSA52
    Session Type: Non-Commercial Satellite
    Venue: Hall 11B
    Monday July 23, 17:00 – 19:00

    17:20 MOSA5203 
    Acute HIV infection and HIV cure
    Thumbi Ndung’u, Africa Health Research Institute, University of KwaZulu-Natal, South Africa 

    Biomedical research innovations in the prevention, remission and cure of HIV/AIDS
    Code: MOSA48
    Session Type: Major Industry Sponsor Satellite
    Venue: Elicium 2
    Monday July 23, 17:00 – 19:00

    17:05 MOSA4802
    30 years of progress in the field of HIV/AIDS
    Anthony Fauci, National Institutes of Health (NIH), United States 

    18:05 MOSA4802
    Passive immunization/bNAbs monoclonals both for prevention and treatment
    Penny Moore, University of the Witwatersrand / National Institute for Communicable Diseases, South Africa 

    18:25 MOSA4802
    Remission and cure efforts
    Javier Martinez-Picado, AIDS Research Institute irsiCaixa, Spain 

    Besieging the reservoir and kicking it where it hurts
    Code: TUPDA01
    Session Type: Oral Poster Discussion Session Track A – Basic and translational research
    Venue: G104-105
    Tuesday July 24, 13:00 – 14:00

    13:00 TUPDA0101 
    Association between immunogenetic factors and post-treatment control of HIV-1 infection. ANRS VISCONTI and PRIMO studies
    Asier Saéz-Cirion, Insitut Pasteur, France

    13:05 TUPDA0102 
    HCV treatment with direct-acting antivirals (DAAs) in HIV/HCV coinfected subjects affects the dynamics of the HIV-1 reservoir 
    Natalia Laufer, INBIRS Institute (UBA-CONICET), Argentina 

    13:10 TUPDA0103
    IL-10 contributes to, and is a biomarker for, viral persistence in ART-treated, SIV-infected rhesus macaques 
    Mirko Paiardini, Emory University, United States

    13:15 TUPDA0104
    Follicular CD8+ T-cells in gut-associated lymphoid tissue are associated with lower HIV-1 reservoir in the terminal ileum after ART initiated during primary HIV infection 
    John Patrick Thornhill, Imperial College London, United Kingdom

    13:20 TUPDA0105
    HIV-1 reservoir diversity and genetic compartmentalization in blood and testis
    Rosalie Ponte, The Research Institute of the McGill University Health Centre, Canada

    13:25 TUPDA0106LB
    Ixazomib reduces HIV-1 reservoir size in a Casp8p41-dependent manner
    Nathan Cummins, Mayo Clinic, United States
     
    Strategies for cure: Pitfalls, possibilities and promise
    Code: TUAA02
    Session Type: Oral Abstract Session Track A – Basic and translational research
    Venue: E102
    Tuesday July 24, 16:30 – 18:00

    16:30 TUAA0201
    Therapeutic Vaccines for Cure 
    Steven Deeks, University of California, United States

    16:45 TUAA0202LB
    A randomised controlled trial comparing the impact of antiretroviral therapy (ART) with a 'Kick-and-Kill' approach to ART alone on HIV reservoirs in individuals with primary HIV infection (PHI); RIVER trial
    Sarah Fidler, Imperial College London, United Kingdom

    17:00 TUAA0203
    Dominant HIV DNA populations present in different T-cell subsets before stem cell transplantation persist in tissues early after transplantation with CCR5Δ32 stem cells 
    Annemarie Wensing, University Medical Center Utrecht, Netherlands

    17:15 TUAA0204
    Rapid rebound of a highly replication competent preexisting CXCR4-tropic HIV variant after allogeneic stem cell transplantation with CCR5Δ32 stem cells 
    Monique Nijhuis, University Medical Center Utrecht, Netherlands

    17:30 TUAA0205
    Modular gene therapy vectors for gene therapy cure in resting immune cells 
    Andrew Wong, The University Of New South Wales Sydney, Australia

    17:45 TUAA0206LB
    Evaluation of an antibody to Alpha4Beta7 in the control of SIV infection
    Michele Di Mascio, National Institute of Allergy and Infectious Diseases, United States

    Building bridges from scientific innovation to implementation 
    Code: WEPL01 
    Plenary Session 
    Venue: Hall 12 
    Wednesday July 25, 08:45 – 10:30 

    08:55 WEPL0105
    The newest science in the search for a cure and vaccine 
    Brad Jones, Weill Cornell Medicine and The George Washington University, United States

    Poking, prodding and purging the final reservoir frontier
    Code: WEAA01
    Session Type: Oral Abstract Session Track A – Basic and translational research
    Venue: G104-105
    Wednesday July 25, 11:00 – 12:30

    11:00 WEAA0101
    Chidamide reactivates and diminishes latent HIV-1 DNA in patients on suppressive antiretroviral therapy 
    Wen Kang, Tangdu Hospital affiliated to The Fourth Military Medical University, China

    11:15 WEAA0102
    The antiretroviral CCR5-inhibitor maraviroc effectively reverses HIV latency by phosphorylation of Nf-κB 
    Jori Symons, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Australia

    11:30 WEAA0103
    Activation of latent HIV and SIV RNA transcription in vitro and in vivo in ART suppressed SIV-infected rhesus macaques by the Ingenol-based protein kinase C agonist, GSK445A 
    Afam Okoye, Oregon Health and Science University, United States

    11:45 WEAA0104
    The RNA-binding proteins, SRP14 and HMGB3 play a crucial role in controlling HIV replication and latency 
    Georges Khoury, Peter Doherty Institute, Australia

    12:00 WEAA0105
    Using the PPARg antagonism to block/lock HIV reactivation in Th17 cells 
    Petronela Ancuta, Universite de Montreal and CHUM Research Centre, Canada

    12:15 WEAA0108LB
    The majority of the replication-competent virus in the latent reservoir originates from viruses circulating near the time of ART initiation
    Sarah B. Joseph, University of North Carolina at Chapel Hill, United States

    Durable control of HIV infections in the absence of antiretroviral therapy: Opportunities and obstacles and Jonathan Mann Memorial Lecture: Data to drive equity
    Code: WESS01
    Session Type: Special Session
    Venue: Hall 12
    Wednesday 25 July, 13:00 – 14:00

    13:05 WESS0102
    Durable control of HIV infection in the absence of antiretroviral therapy: Opportunities and obstacles
    Anthony Fauci, National Institutes of Health (NIH), United States

    Acute infection and viral reservoir
    Code: WEPDB01
    Session Type: Oral Poster Discussion Session Track B – Clinical research
    Venue: E102
    Wednesday July 25, 13:00 – 14:00

    13:00 WEPDB0101
    Validation of Alere TM q HIV-1/2 detect for detection of acute HIV infection at Anonymous Clinic, The Thai Red Cross AIDS Research Centre 
    Irin Srila-Or, The Thai Red Cross AIDS Research Centre, Thailand

    13:05 WEPDB0102
    Favorable clinical phenotype reached in less than half of people treated in acute HIV infection 
    Jintanat Ananworanich, The Henry M. Jackson Foundation for the Advancement of Military Medicine, United States

    13:10 WEPDB0103
    Increasing contribution of integrated forms to total HIV1-DNA in blood, in primary infection during natural history – ANRS PRIMO and SEROCO cohorts 
    Véronique Avettand-Fenoel, Université Paris Descartes, France

    13:15 WEPDB0104
    Intermittent viremia after treatment interruption increased risk of ART resumption in post-treatment HIV-1 controllers. ANRS VISCONTI study 
    Laurent Hocqueloux, CHR d'Orléans – La Source, France

    13:20 WEPDB0105
    Auranofin plus nicotinamide impact HIV reservoir among ART suppressed HIV individuals 
    Ricardo Sobhie Diaz, Federal University of Sao Paulo, Brazil

    All fired up: Tackling inflammation
    Code: WEPDA01 
    Session Type: Oral Poster Discussion Session Track A – Basic and translational research 
    Venue: Hall 11B 
    Wednesday July 25, 13:00 – 14:00 

    13:10 WEPDA0103
    Persistence of myeloid cell-associated inflammation in HIV-infected children after 8 years on early initiated therapy – the key role players in HIV persistence? 
    Shalena Naidoo, Stellenbosch University, South Africa 

    Killers or helpers: The double life of T cells
    Code: WEAA02
    Session Type: Oral Abstract Session Track A – Basic and translational research
    Venue: Hall 11B
    Wednesday July 25, 14:30 – 16:00

    14:30 WEAA0201
    Increase in restriction factor expression in response to viral rebound after analytical treatment interruption in HIV-infected patients
    Marie-Angélique De Scheerder, UZ Gent, Belgium 

    14:45 WEAA0202
    RhCMV-induced, SIV-specific MHC-E-restricted T cells recognize SIV through the T cell receptor 
    Shaheed Abdulhaqq, Oregon Health and Science University, United States

    15:00 WEAA0203
    Genetic factors leading to loss of viral control in HIV elite controller patients 
    José M. Benito, Instituto de Investigación Sanitaria Fundación Jiménez Díaz, Universidad Autónoma de Madrid (IIS-FJD, UAM), Spain 

    15:15 WEAA0204
    Frequent generation of HIV broadly neutralizing antibodies in infected children is associated with both increased help and regulation within germinal centers 
    Julia Roider, University of Oxford, South Africa

    15:30 WEAA0205
    Initiation of antiretroviral therapy during hyperacute HIV infection preserves germinal center T follicular (GCTfh) helper cell function
    Zaza Ndhlovu, University of KwaZulu Natal, South Africa

    Eliminating HIV latency: Shock and kill or block and lock?
    Code: WESY09
    Session Type: Symposia Session
    Venue: Hall 11B
    Wednesday July 25, 16:30 – 18:00

    16:44 WESY0902 
    Introductory comments 
    Maureen Goodenow, U.S. DHHS National Institutes of Health, Office of AIDS Research, United States

    16:49 WESY0903
    Understanding HIV persistence – do defective viruses matter? 
    Ya-Chi Ho, Yale University School of Medicine, United States

    17:06 WESY0904
    Low level transcript
    ion on ART – implications for latency elimination 
    Steve Yukl, University of California, United States

    17:23 WESY0905 
    TLR agonists and latency reversal: can they both shock and kill? 
    Martin Tolstrup, Aarhus University, Denmark

    17:40 WESY0906
    Block and lock using gene silencing 
    Anthony Kelleher, The University of New South Wales (UNSW), Australia

    17:57 WESY0907 
    Understanding community participation in cure studies: what scientists need to know 
    Cipriano Martinez, National Association for People Living with HIV in Australia, Australia
     
    Broadly neutralizing antibodies (bNabs): Towards a cure and vaccine
    Code: THSY04
    Session Type: Symposia Session
    Venue: G104-105
    Thursday July 26, 11:00 – 12:30

    11:05 THSY0402
    Factors determining bNab elicitation in HIV-infected individuals during natural infection: Challenges a vaccine has to overcome
    Alexandra Trkola, Leiterin Group Trkola, Switzerland

    11:25 THSY0403
    Maturation of bNabs in HIV-1 infected patients (specifics of B-cell maturation), what is different from other infections?
    Michel Nussenzweig, The Rockefeller University, United States

    11:45 THSY0404
    Induction of bNabs by vaccines: where do we stand, what is being needed for success
    Rogier Sanders, AMC, Netherlands

    12:05 THSY0405
    bNabs for clinical use: antiviral activity and effector functions other than neutralization
    Lynn Morris, University of the Witwatersrand, South Africa

    How Far are We from HIV Remission? 
    Code: THSA14 
    Session Type: Non-Commercial Satellite 
    Venue: Hall 11A 
    Thursday July 26, 18:30 – 20:30

    18:35 THSA1402 
    An Update on Post-Treatment Controllers in France and Worldwide 
    Laurent Hocqueloux, CHR d'Orléans – La Source, France

    18:50 THSA1403 
    Insights on Mechanisms of Post-Treatment Control 
    Asier Saéz-Cirion, Insitut Pasteur, France

    19:10 THSA1405
    Lessons from Research Interventions aiming at HIV Remission

    19:30 THSA1406
    Very early ART Initiation during "Hyperacute" HIV Infection 
    Timothy Henrich, University of California at San Francisco ( UCSF), United States

    19:45 THSA1407
    Stem Cell Transplantations: ICISTEM 
    Monique Nijhuis, University Medical Center Utrecht, Netherlands

    20:00 THSA1408
    Interventions with broadly neutralizing antibodies (bNAb)
    Michel Nussenszweig, Howard Hughes Institute, The Rockefeller University, United States

    20:15 THSA1409
    HIV Remission Research: Expectations and Questioning
    Alain Volny-Anne, France

    20:45 THSA1411
    Concluding Remarks
    Françoise Barré-Sinoussi, Institut Pasteur, France

  • Elite Controllers: Sex Differences and Factors Associated with Loss of Immune Control

    Over the past few months, several interesting papers addressing elite control of HIV infection have seen publication. The ability of elite controllers to maintain undetectable viral loads and relatively preserved CD4 T cell counts in the absence of ART has led them to be proposed as a model for a functional cure of HIV infection. But there is also evidence that many elite controllers exhibit elevated levels of inflammation compared to HIV-negative counterparts, and eventually experience disease progression, leading some researchers to call this proposition into question. The uncertain relevance of elite control to HIV cure research is prompting studies that attempt to parse the factors distinguishing individuals who preserve elite controller status from those who ultimately progress.

    In the journal eBioMedcine, Wang Zhang and colleagues explore the expression of a variety of genes and proteins in a cohort of 19 elite controllers, compared to 32 individuals with progressive HIV infection and 23 healthy HIV-negative controls. Of particular note, nearly half the elite controllers (9) were women, allowing the researchers to compare results based on sex. The authors point out that several previous studies have reported that women tend to be overrepresented among elite controllers (e.g. see Crowell et al and de Azevedo et al).

    A potentially important finding is that the gene expression profiles of female elite controllers were similar to HIV-negative females, but there were significant differences between male elite controllers and HIV-negative male controls. A potential implication is that women will be more likely to maintain elite controller status over time compared to men—this possibility will need to be investigated further. 

    Among the differences observed in elite controllers compared to individuals with progressive HIV infection were downregulation of the genes for CXCR6 and SIGLEC1. The authors explain that these differences could be associated with decreased susceptibility of CD4 T cells for HIV entry and reduced cell-to-cell virus transmission mediated by myeloid cells.

    Levels of the chemokine CCL4 (MIP-1β) were found to be higher among elite controllers versus progressors, consistent with a previous study. Conversely, levels of the inhibitory immune cell receptor PD-1 (and its ligand PD1-L2) were significantly lower, echoing another recent paper reporting lower levels of multiple inhibitory receptors in elite controllers.

    BMC Medicine has published an analysis by José Benito and colleagues that looks at possible contributors to loss of elite control. The researchers evaluated 36 elite controllers followed for approximately a decade on average, comparing multiple immunological parameters between those with stable CD4 T cell counts (n=22) and those exhibiting significant CD4 T cell decline during the follow up period (n=14). Interestingly, women made up 67% of the former group but only 31% of the latter, a statistically significant difference (p=0.04). The authors don’t offer any comment on this apparent overrepresentation of women in the group of elite controllers with stable CD4 T counts.

    Many immunological variables were found to differ between elite controllers and HIV-negative healthy controls, as well as between stable elite controllers and those experiencing CD4 T cell declines. Distinctions between elite controllers and HIV-negative healthy controls included lower levels of several T cell subsets: naïve, recent thymic emigrant, stem cell memory, and regulatory. Expression of the T cell costimulatory receptor CD28 was lower, whereas CD95—involved in apoptotic cell death—was increased.

    Comparisons between the stable elite controllers and progressors revealed that the latter group had lower levels of naïve and recent thymic emigrant CD8 T cells, as well as higher levels of CD8 T cells with effector memory and senescent phenotypes. The finding suggests that CD8 T cells may have been differentiating at a higher rate in this group—in other words, naïve CD8 T cells were more frequently becoming activated and transitioning into memory cells (perhaps reflective of a more strenuous battle to keep HIV contained). The progressor group also showed increased expression levels of PD-1 in both total CD4 T cells and the central memory CD4 T cell subset.

    In a separate study published in the Journal of Virology earlier this month, María Pernas and colleagues conducted a retrospective, longitudinal analysis of factors contributing to loss of viral load suppression in a cohort of elite controllers. A total of 31 elite controllers were included, defined based on having viral load below detectable levels (50 copies/ml) on three consecutive measures over a year of follow up.

    Fourteen of these individuals subsequently experienced increases in viral load (two consecutive measures above the detection limit within a year), and were classified as transient controllers. The remaining 17 maintained undetectable viral loads and were classified as persistent controllers. Sex differences were not apparent in this study, with women making up 43% of the former group and 41% of the latter. The only significant differences were for time since diagnosis (averaging 8 years and 18 years, respectively) and sexual transmission as mode of HIV acquisition (71% vs. 35%).

    The availability of samples prior to the viral load increases in the transient controller group allowed several factors associated with the loss of HIV suppression to be identified. CD8 T cells targeting the HIV Gag protein were found to be significantly less polyfunctional (assessed based on production of the cytokines IFN-γ, TNF-α and IL-2) and displayed a more activated phenotype a year prior to viral load becoming detectable. HIV genetic diversity within the env gene was also significantly higher, with a similar trend observed for the gag gene. In contrast, persistent controllers showed little or no evidence of ongoing viral evolution.

    Inflammatory biomarkers were elevated in the transient controllers. and an analysis of 70 different cytokines and chemokines in plasma samples revealed that increased levels of RANTES and Platelet Derived Growth Factor (PDGF) AA were the best predictors of subsequent loss of elite controller status. RANTES in particular showed a strong association, being an average of four-fold higher in transient controllers.

    In discussing their results, the authors emphasize the importance of focusing on examples of strict, persistent control of HIV if the goal is to identify “the right model of functional remission.” They also suggest that factors strongly predictive of future viral load rebound—such as RANTES levels—might have the potential to help discriminate elite controllers likely to benefit from ART from those who may not require it.

    Similar points are made in a commentary in EBioMedicine by Laura Tarancon-Diez and colleagues. The commentary accompanies a paper describing an elite controller who has maintained extremely low levels of HIV RNA and HIV DNA for a decade, without fully seroconverting on the Western Blot antibody assay. Evidence of polyfunctional HIV-specific CD8 T cell responses and strong antibody-mediated cellular cytotoxicity (ADCC) by natural killer cells is reported. The individual acquired HIV from a partner who was not able to control the same CRF02_AG virus variant. Neither partner possesses known favorable HLA alleles although both are heterozygous for the CCR5Δ32 mutation.

    The commentary also cites work published last year from the French CODEX cohort, which described a subset of HIV controllers in whom viral load had never been detectable using routine assays during an average of 18 years of follow up. In a comparison with controllers who had experienced viral load blips, T cell counts were reported to be stable (as opposed to progressively declining), and this was accompanied by lower T cell activation and HIV DNA measurements. This study also showed a trend toward an overrepresentation of women in the persistently undetectable group (34 out of 52, 65%) versus the viral load blips group (90 out of 178, 51%, p=0.06).

    Tarancon-Diez and colleagues advocate concentrating on “this very scarce proportion of individuals that are able to persistently control the virus” in order to inform the design of cure strategies aiming to induce long-term remission in the absence of ongoing ART.

    Whether there might be particular features of the immune response (or other factors) in women that increase the likelihood of persistent elite control needs to be elucidated. Ongoing work is investigating possible differences related to HIV persistence in women receiving ART, with Eileen Scully presenting the latest findings from her research as a poster at the CROI 2018 conference. Scully has uncovered a number of significant sex-based associations, including higher expression of several antiviral genes.

    As Zhang and colleagues argue in the closing section of their EBioMedicine paper: "Despite extensive data on the male and female difference on disease outcome, research does not sufficiently take gender into account. Altogether, our study showed that it would be important to carefully consider gender in cohort design for future transcriptomic and intervention studies on HIV-1 patients."

  • Assessing Antiretroviral Therapy Interruptions in HIV Cure Research

    Last month, researchers from the Laboratory of Immunoregulation at the National Institute of Allergy and Infectious Diseases (NIAID) published a paper in PLoS Pathogens addressing the use of antiretroviral therapy (ART) interruptions in HIV cure research. The joint lead authors were Katherine E. Clarridge and Jana Blazkova, and the focus of the study was on the effects of an analytical treatment interruption (ATI) performed during a clinical trial of the broadly neutralizing antibody VRC01. The main results offer reassurance that the ATI had no long-term negative effects for participants—as articulated in an accompanying NIAID press release titled NIH Study Supports Use of Short-Term HIV Treatment Interruption in Clinical Trials—but there are some possible safety concerns that the data does not address.

    Results of the VRC01 trial were published in 2016 in the New England Journal of Medicine. The protocol design involved an initial VRC01 infusion upon entering the study, followed by an ATI three days later. VRC01 infusions were subsequently administered every four weeks until week 24. Criteria for restarting ART included:

    • A confirmed >30% decline in baseline CD4 cell count or an absolute CD4 cell count <350 cells/mm3
    • A sustained (≥4 weeks) HIV RNA level of >5,000 copies/mL
    • Any HIV-related symptoms

    Ten participants were enrolled. VRC01 only led to a slight delay in viral load rebound, so ART was restarted in all cases with the duration of the ATI ranging from 22 to 115 days (median 57 days). Nine of the individuals restarted ART due to meeting the criteria for a sustained viral load increase to over 5,000 copies/mL, while the remaining participant experienced a confirmed >30% decline in baseline CD4 cell count. No participant had a CD4 T cell drop to less than 350 cells/mm3.

    The researchers evaluated multiple HIV reservoir measures as well as biomarkers of immune activation and inflammation, comparing results obtained prior to the ATI with those observed after viral load was re-suppressed by ART. In almost all cases, there were no significant differences pre- and post-ATI. The lone exception was the chemokine RANTES, a potential inflammatory biomarker, which remained significantly elevated after ART resumption (at least at the time point measured, which was a median of 363 days after restarting).

    Several parameters were evaluated during the ATI, revealing that there were increases in measures of the HIV reservoir and immune activation that subsequently declined to baseline levels after ART was resumed. However, data on inflammatory biomarkers during the ATI are not reported, making it unclear to what extent inflammation may have been temporarily elevated—it seems likely that it was, given the transient spike in markers of immune activation. The relationship between short-term inflammation and risk of clinical events is uncertain but potentially of concern, so this is an aspect of ATIs that deserves additional study. Among the steps taken to maximize safety in the trial, the exclusion criteria included evidence of heart disease, which might render an individual particularly susceptible to inflammation-related risks.

    Another question that has been raised regarded the safety of ATIs—particularly by longtime treatment activist Jules Levin of the National AIDS Treatment Advocacy Project (NATAP)—is whether HIV levels in the central nervous system (CNS) might increase and have the potential to cause harm. CNS samples were not taken in this NIAID study.

    Overall, the trial results are consistent with the idea that short-term ATIs can be performed safely in the context of HIV cure research, but they do not necessarily represent the last word on the topic. There was a robust dialogue regarding the use of ATIs at the recent Regulation of Clinical Research Related to HIV Cure meeting that took place in Bethesda on January 25, and a webcast of the session should soon be available on the Forum for Collaborative Research website. TAG has also received support from the Elizabeth Taylor AIDS Foundation to survey community-based treatment activists regarding their views on ATIs, and a report will be published in the fall of 2018.

    The Laboratory of Immunoregulation at NIAID has recently published a different study involving an ATI that highlights another important consideration in this type of HIV cure research: the inclusion of a placebo arm. The researchers conducted a clinical trial of a combination therapeutic HIV vaccine approach (DNA primes followed by a vesicular stomatitis virus vector boost) administered to individuals who initiated ART soon after infection. The vaccines were found to induce HIV-specific T cell responses, but this did not lead to superior control of viral load rebound during an ATI compared to placebo immunization.

    The researchers noted that, perhaps surprisingly, there were four cases of post-ATI control of viral load to low levels that occurred in the placebo arm of the trial. The finding emphasizes that a subset of early-treated individuals can exhibit prolonged viral load suppression after an ATI, and that this needs to be considered when designing trials of therapeutic interventions. In the absence of a placebo arm, spontaneous control of HIV replication could be misinterpreted as evidence of a therapeutic effect. The authors specifically cite the open-label trial of therapeutic vaccination plus romidepsin that was presented by Beatriz Mothe at CROI 2017, pointing out that a similar proportion of participants in the placebo arm of their study maintained viral loads below 2000 copies/ml for at least 16 weeks.

    The inclusion of placebo control arms in trials is not necessarily as simple as it might sound, because there are cost and logistical issues that are prohibitive for some research groups. However, it is clearly a necessary step for establishing that a candidate intervention has had a genuine effect, and results from open-label trials should be interpreted with caution until confirmed in a randomized controlled context. 

  • Recruiting Natural Killer Cells to Target HIV Persistence

    An important goal in HIV cure research is the identification of immune responses that might be induced or enhanced to promote clearance of virus-infected cells. The main focus of this work has been on adaptive immunity—components of the immune system that can specifically recognize HIV, which include CD4 T cells, CD8 T cells, B cells and antibodies. But there is growing interest in cells considered part of the innate immune system, particularly natural killer (NK) cells. NK cells have the potential to destroy virus-infected cells by several mechanisms, including the identification of generic signs of cellular distress or infection, or via antibody-mediated recruitment to a target cell (known as antibody-dependent cellular cytotoxicity/ADCC).

    Over the past few months a number of studies have been published that support the idea that NK cells can play an important role in controlling virus replication. In the journal Nature Medicine, Nicolas Huot and colleagues describe evidence that NK cells contribute to suppression of SIV replication in the lymph nodes of African Green Monkeys (AGMs), a host species that does not experience pathogenic consequences from the infection.

    In experiments comparing nonpathogenic SIV infection of AGMs to pathogenic infection in macaques, NK cells were found to localize within and around lymph node B cell follicles—the major site of virus replication and persistence—in AGMs, but were scattered randomly in macaques, with no accumulation in follicles. NK cell numbers in lymph nodes also progressively declined in macaques, while being maintained at pre-infection levels in AGMs.

    Additional analyses found that these differences were associated with an increased frequency of NK cells expressing CXCR5 (a receptor governing homing into follicles) and localized production of the cytokine IL-15 in the follicles of AGMs. The role of IL-15 was further confirmed by administration of an anti-IL-15 antibody, which depleted NK cells from the lymph nodes of the AGMs and led to a significant increase in SIV replication.

    The authors write in their conclusion: “On the basis of our results, we anticipate that better comprehension of NK cell biology in lymphoid tissues, as provided here, will endorse the search for new NK cell–based immunotherapies for HIV infection.”

    A review published in the journal AIDS in November covers some of the potential NK cell–based immunotherapies that are under investigation. A panoply of clinical trials are testing broadly neutralizing antibodies (bNAbs), which may have the ability to promote NK cell-mediated ADCC. In some cases bNAbs are being evaluated in tandem with latency-reversing agents, with the aim of depleting the HIV reservoir.

    Also cited is the toll-like receptor 9 (TLR9) agonist MGN1703, which researchers at the University of Aarhus have shown can promote NK cell activation in HIV-positive people on ART. The same research group has also reported that NK cell responses may have been linked to an HIV DNA decline in some participants in a trial of the latency-reversing agent panobinostat.

    Other NK cell–based immunotherapies in clinical trials include ALT-803, a modified version of the cytokine IL-15. The research group of Timothy Schacker at the University of Minnesota is conducting a small study involving ALT-803 administration to HIV-positive individuals on ART. A paper published in the Journal of Virology late last year describes a transient anti-SIV effect of the compound in macaques that were not receiving ART. Schacker and colleagues have also recently launched a trial in which individuals will receive infusions of NK cells from matched donors in combination with the cytokine IL-2.

    The effects of the cytokine alpha interferon on HIV persistence are a major topic of interest at the newly-funded BEAT-HIV Collaboratory led by Luis Montaner at the Wistar Institute in Philadelphia. Last month in Clinical Infectious Diseases, Stéphane Hua and colleagues presented evidence that NK cell activation associates with a decline in HIV DNA levels in HIV-positive individuals receiving alpha interferon for the treatment of hepatitis C.

    In sum, after a long period in the shadow of the better-known components of the adaptive immune system, NK cells are now emerging as potentially important players in HIV cure research. Results from the ongoing trials should soon shed additional light on how they might be able to contribute.

  • New Data on Identifying and Targeting the Latent HIV Reservoir

    Several recently presented and published studies offer potentially important new data relevant to efforts to identify cells containing latent HIV and target them for elimination.

    At the 8th International Workshop on HIV Persistence held in Miami last December, multiple research groups reported on their attempts to confirm a newly published—and widely publicized—claim that the cell surface molecule CD32a is preferentially expressed on latently infected cells. The results indicate that the picture is considerably more complicated: the original findings could not be verified and instead it appears that expression of CD32a may be driven by other factors, including cell activation and active HIV transcription. Summaries of these studies can be found in the published abstracts from the workshop (see abstract numbers OP 1.5, OP 2.4, OP 2.6 and OP 4.2).

    While disappointing, this work does not end hopes that markers of latently infected cells can be identified – other candidates that are being examined are CCR5, when expressed by resting memory CD4 T cells (see the study from the laboratory of Robert Siliciano published late last year), and CD30, a cell surface molecule better known for its association with lymphoma that is being investigated by Tim Henrich and colleagues.

    One of the reasons why markers of latently infected cells would be a boon to the cure research field is that they might facilitate elimination strategies akin to those now being used successfully against cancers. A number of effective cancer immunotherapies involve equipping T cells with receptors that target cell surface molecules on malignant cells, such as CD19, CD22, and CD30. It is conceivable that this “chimeric antigen receptor” (CAR) T cell approach could be adapted to target latently infected cells if appropriate markers could be identified.

    CAR T cells are also being developed that target HIV antigens, with a recent paper in PLoS Pathogens from Scott Kitchen colleagues reporting some encouraging results obtained with stem cell-derived CAR T cells in macaques. However, in order for the approach to work against latently infected cells, it would be necessary to activate the latent HIV first to trigger production of viral antigens. An article in STAT News by Sharon Begley provides an accurate and nuanced perspective on Kitchen’s paper, offering the appropriately cautious headline: “Preliminary study hints that genetically modified T cells might fight HIV.” In contrast, coverage in The Daily Beast unfortunately opts for misleading hype, with their piece titled: “This Doctor's Revolutionary Stem Cell Treatments Could Eradicate HIV.”

    The research group of Jonathan Angel in Canada is pursuing a novel method for targeting latently infected cells: an oncolytic rhabdovirus named MG1, which is primarily being developed for its ability to preferentially infect and destroy cancer cells. Angel and colleagues have published a study in the Journal of Infectious Diseases demonstrating that MG1 also appears capable of targeting cells latently infected with HIV, while sparing uninfected cells (the paper is open access).

    In an analysis of the effects of MG1 on memory CD4 T cells isolated from 14 HIV-positive individuals on ART, both total and integrated HIV DNA levels declined in 12 out of the 14 samples. The mechanism for MG1’s preferential targeting is unclear, but may relate to changes in latently infected cells that affect their response to the cytokine interferon. The authors note that clinical trials are already underway in cancer, which should help discern if the approach can be safely studied in HIV infection. In an interview with MD Magazine, Angel notes MG1 that can cause fever and malaise, and adverse events may be dose-dependent.

    Another paper in PLoS Pathogens that has drawn attention comes from Christina Gavegnano and colleagues, who show that a class of drugs called Jak inhibitors can inhibit the maintenance of latently infected cells, and prevent them spreading infection when latent HIV is reactivated. Jak inhibitors target a pathway involved in the survival and proliferation of memory CD4 T cells, and have been found safe in the treatment of certain inflammatory diseases and myelofibrosis. The authors note that an ongoing clinical trial is evaluating the effects of the Jak inhibitor ruxolitinib in HIV-positive people on ART.

  • Update on AAV Vectors as Delivery Vehicles for Broadly Neutralizing Antibodies: Ron Desrosiers and the Miami Macaque

    The idea of using adeno-associated virus (AAV) as a vehicle to deliver genes encoding anti-HIV broadly neutralizing antibodies (bNAbs) has been around for some time, and has been covered a number of times previously on the blog (e.g. see posts from May 2009 and January 2013). The approach was first developed by Phil Johnson as a possible way of circumventing the challenges associated with inducing broadly neutralizing antibodies using traditional vaccines. AAVs primarily take up residence in muscle tissue and can act as a factory for producing proteins encoded by genes inserted into the AAV genome. This past Tuesday evening at the HIV Persistence Workshop in Miami, the researcher Ron Desrosiers presented an update on efforts to deliver bNAbs with AAV, including the intriguing tale of a macaque in which the method appeared to have a profound therapeutic effect.

    Many years ago Desrosiers, then at the New England Primate Research Center, collaboratored with Phil Johnson on the first study to demonstrate that anti-SIV antibodies delivered by AAV could protect macaques against a highly pathogenic SIV challenge. Desrosiers has since moved to the University of Miami and is now exploring the potential of AAV to deliver the more recently discovered potent bNAbs.

    At the workshop, Desrosiers described a preliminary study in which four macaques were infected with a SHIV AD8 challenge virus and, 86 weeks later, given three AAV vectors encoding the bNAbs 10E8, 3BNC117 and 10-1074, respectively. Because they originated in humans, the bNAbs were modified to make them compatible with rhesus macaque antibodies (rhesusized, to use Desrosiers term). No antiretroviral therapies were employed in the experiment.

    Evaluations of bNAb levels after AAV administration produced disappointing results: 10E8 was very low or undetectable in all cases, 3BNC117 was delivered successfully in just one out of four animals and 10-1074 achieved significant levels in three out of four. As Desrosiers and colleagues explained in a paper published in Molecular Therapy last year, the problem was caused by the generation of antibodies against the AAV-encoded bNAbs (anti-antibody responses). This problem was also seen in SIV prevention experiments.

    There was a more encouraging finding, however. One macaque developed sustained levels of both 3BNC117 and 10-1074, and this was associated with a persistent decline in SHIV AD8 viral load to undetectable levels – below 15 copies/mL in 26 samples taken over a 24-month period (viral load analyses were conducted by Jeff Lifson at the National Cancer Institute). Virus reservoirs also became undetectable: 62 weeks after AAV administration, no SHIV AD8 could be recovered from 180 million peripheral blood mononuclear cells (PBMC) using a quantitative virus outgrowth assay (QVOA).

    Several additional experiments were conducted in an attempt to ascertain if a cure of the challenge virus might have been achieved. Cells from an entire lymph node sampled after 74 weeks were transferred into an uninfected macaque, without causing SHIV AD8 infection. A follow up five weeks later, in which approximately 140 million cells derived from an extracted cluster of lymph nodes were transferred, also failed to establish SHIV AD8 infection. Desrosiers presented these results earlier this year in a talk that is available on Youtube (thanks to @DanWilliamsVisa on twitter for sharing it with me).

    On Tuesday, Desrosiers reported that 87 weeks after AAV was given, SHIV AD8 was finally recovered at very low levels on three occasions by QVOA, with the frequency of infected cells estimated to be ~1 in 50 million PBMC (depleted of CD8 cells). While this ends hopes that the virus may have been entirely eradicated, Desrosiers noted that the animal—dubbed the Miami monkey by some of his colleagues—might legitimately be described as functionally cured, although he acknowledged the major caveat: it is just one case.

    Desrosiers’s research group is now focused on circumventing the problem of anti-bNAb antibodies. The AAV variant used in studies to date has been AAV1, and he showed evidence that AAV8 appears less prone to inducing anti-antibodies. This may be because AAV8 is tropic for the liver, a site in the body where immune responses against vector-encoded bNAbs are less likely to be induced (a phenomenon known as the “liver tolerance effect”).

    Experiments in which AAV8 administration was followed later by AAV1 have suggested the combination might further reduce anti-antibody levels; in essence a type of “prime-boost” in which the booster is enhancing immunological tolerance rather than enhancing immune responses. An additional strategy involves including a piece of genetic code in the AAV vector that is designed to shut down antigen presentation by cells (e.g. dendritic cells) that might otherwise promote the development of anti-antibodies.

    Plans are now underway to conduct a study in which 12 macaques infected with SHIV AD8 will be divided into two groups and receive either AAV8 vectors encoding 3BNC117 and 10-1074 (possibly with an AAV1 boost) or antiretroviral therapy.

    There is one ongoing trial of an AAV1 vector encoding a bNAb (PG9) in humans, launched several years ago by a collaboration involving Phil Johnson and the International AIDS Vaccine Initiative (IAVI). The trial population is HIV-negative men. Results were initially due in January 2016 and have been eagerly anticipated. In his presentation at the Persistence Workshop, Desrosiers stated that he recently attended a meeting at the Gates Foundation at which preliminary data were presented and obtained permission to disclose them.

    According to his description, what the results revealed is that the anti-antibody problem is not limited to macaques: nine trial participants that were analyzed did not have detectable PG9 levels, but seven out of the nine had readily detectable anti-PG9 antibodies. There may be subtleties to the findings that could not be conveyed in a brief aside, but it sounds like the promise of the AAV approach—both in the preventive and therapeutic contexts—will only be realized if a means to avoid anti-antibodies can be developed.

    Update 12/18/17: The National Institute of Allergy and Infectious Diseases (NIAID) has just opened a clinical trial investigating the delivery of the bNAb VRCO7 by an AAV8 vector in HIV-positive individuals on ART. The trial is taking place at the National Institutes of Health Clinical Center in Bethesda.

    Abstracts from the Eighth International Workshop on HIV Persistence during Therapy are now available from the Journal of Virus Eradication. 

  • Additional Remission Cases Published

    Two recent case reports of temporary HIV remission, first presented at this year’s CROI and IAS conferences, have now been published in the open access journal PLoS Medicine.

    Tim Henrich and colleagues from UCSF report on an adult male diagnosed with HIV and started on ART unusually early, due to acquiring the infection during a short window between a screening visit for a pre-exposure prophylaxis (PrEP) demonstration project and the day on which Truvada PrEP was initiated. Truvada was switched to a full ART regimen as soon as the test result confirming the HIV diagnosis became available. The time from infection to PrEP initiation was estimated to be 10 days, and ART was begun seven days later. As first reported by Hiroyu Hatano at CROI in 2014, HIV rapidly became undetectable by multiple assays, including measures of the viral reservoir.

    ART was eventually interrupted and the individual did not experience an HIV viral load rebound until 225 days afterward. Henrich’s talk at the IAS 2017 conference is available on youtube and was covered on the blog in a report from the meeting.

    The new paper adds information on analyses of possible predictors of the viral load rebound, noting that expression of CD30 (a lymphoma tumor marker and member of the tumor necrosis factor super-receptor family) increased on the surface of both CD4 and CD8 T cells months before the HIV viral load rebound occurred. A similar increase in CD30 expression was observed in one of the Boston patients, who experienced a very similar period of HIV remission resulting from a stem cell transplant procedure for cancer. As mentioned on the blog previously, Henrich’s research group has a longstanding interest in CD30 as a possible biomarker of the HIV reservoir and is continuing to pursue investigations in this area.

    The paper also describes results obtained using a relatively new approach to HIV reservoir measurement, the murine virus outgrowth assay (mVOA). The mVOA involves transferring large numbers of sampled CD4 T cells into multiple immunodeficient mice and monitoring for evidence of the emergence of HIV RNA (the methodology is described in detail in a recent open access review by Kelly A. Metcalf Pate and Joel N. Blankson in the open access journal Retrovirology). After 18 months on ART (prior to the interruption), approximately 530 million CD4 T cells were sampled from the individual and divided among ten mice. One of the mice displayed a low HIV RNA level of 201 copies/mL in plasma after receiving an anti-CD3 antibody to activate the T cells, around five weeks after the transfer. Efforts to genetically sequence the virus in order to confirm the finding were unsuccessful, however.

    In discussing the mVOA result, the authors note that it may have represented the only evidence that HIV was still present, and go on to write: “our study suggests that sampling of hundreds of millions of PBMCs may, at times, be more sensitive than tissue-based studies for the detection of residual HIV infection since a much larger number of cells can be interrogated. Further studies comparing mVOAs with traditional ex vivo co-culture assays utilizing rigorous positive and negative controls are certainly warranted.”

    The researchers also provide information on a second individual diagnosed under similar circumstances—between screening for a PrEP demonstration project and starting Truvada. The timing was slightly later, with HIV infection estimated to have been acquired approximately 12 days before starting Truvada PrEP, and the switch to ART occurring after another 12 days. ART has not been interrupted in this study participant, and HIV RNA was more readily detected in the mVOA, with three of eight mice displaying viral loads of 1,000, 5,000, and 11,000 copies/mL, respectively (from a total of 50 million CD4 T cells transferred into each mouse).

    A key takeaway highlighted in the paper is that PrEP programs represent an opportunity to catch individuals at the very earliest stages of HIV infection and study the impact of rapid ART initiation. The authors recommend that PrEP programs conduct HIV RNA testing before starting PrEP, as well as prior to restarting if there is an interruption, and immediately switch to a full ART regimen if an individual is found to be infected.

    The second paper is by Nathan Cummins and colleagues and features a case of temporary HIV remission that was presented as a poster at CROI 2017. Similar to the Boston patients, the individual in question underwent a stem cell transplant for the treatment of a cancer (acute lymphoblastic leukemia) and measures of the HIV reservoir subsequently declined to undetectable levels while ART was maintained.

    Permission was ultimately obtained to conduct an analytical treatment interruption, which took place at day 784 post-transplant. Viral load remained undetectable for 288 days, at which point a rebound to 60 copies/mL was detected. Five days later the level had risen to 1,640 HIV-1 copies/mL and ART was restarted. Genetic sequencing of the rebounding virus indicated it emerged from a source that was not detected in blood samples prior to transplantation, and the authors write that it “may have originated from sanctuary tissue sites harboring archived viral species seeded during the extensive HIV-1 disease process preceding the patient’s oncologic history.”

    The report adds to the evidence that stem cell transplantation can significantly reduce the size of the HIV reservoir, but the researchers note that the estimated decline was approximately 200-fold at most, considerably short of the 10,000-fold reduction that mathematical modeling studies have indicated may be needed to prevent HIV rebound for a lifetime.

  • HIV Latency: Trapped in Transition, Lurking in Treg

    The question of how HIV latency is typically established in long-lived memory CD4 T cells has yet to be fully resolved. One theory is that latency occurs when HIV infects a CD4 T cell that is in the process of transitioning from an activated state to a resting state, but direct evidence has been lacking. A new paper from the research group of Robert Siliciano, published in the journal Immunity, provides experimental support for this model of HIV latency initiation.

    For background, HIV preferentially targets activated CD4 T cells because their genetic code (the genome) is very busy transcribing the proteins required to for the cell to go about its work, and the virus is able to hijack this process by integrating its own DNA into the cell’s DNA in order to generate new virions (which can then go on to infect other cells). Resting CD4 T cells are less amenable to HIV replication because their genome is largely shut down, and the virus has difficulty coopting it for the production of new viruses.

    Siliciano’s research offers evidence that HIV latency occurs when the virus’s DNA essentially becomes entrapped in the genome of an activated CD4 T cell as it is in the process of shutting down, due to the transition of the cell into a resting state. An example of when these transitions normally occur is after a CD4 T cell has responded to an infection—when the responsible pathogen is cleared or controlled, a proportion of the activated responding CD4 T cells return to a resting memory state, ready to react again should the same pathogen cause further trouble.

    The experiments described in the new paper mimicked the transition process in the laboratory by activating CD4 T cells (modified with a gene, Bcl-2, that enhances their survival in the lab dish) and then allowing them to return to rest. A key finding was that latent infection occurred most frequently when activated CD4 T cells were infected with HIV at a time when analyses showed the transcriptional activity of their genome was shutting down—on days 6, 9 or 15 after receiving an activating stimulus. Studies of CCR5 co-receptor expression found that, at these timepoints, the CD4 T cells were displaying enough CCR5 on their surface to facilitate infection by R5-tropic HIV.

    The results contrasted with those obtained when CD4 T cells were infected with R5-tropic HIV immediately after activation, or when they were already in a resting state. In these experiments, essentially no establishment of viral latency could be detected.

    The researchers found that X4-tropic HIV was more promiscuous in its ability to cause latent infection in CD4 T cells—whether activated, resting, or in transition—which they note is “probably due to the universal expression pattern of CXCR4 on CD4 T cells.” However, analyses of latently infected CD4 T cells isolated directly from HIV-positive individuals on ART demonstrated that the majority contained R5-tropic virus, implying that the mechanism involving infection of activated CD4 T cells transitioning to a resting state is predominant in creating the latent reservoir.

    Interestingly, the laboratory studies revealed that while most of the activated CD4 T cells downregulated CCR5 expression as they transitioned into a resting state, a subset continued to display the molecule. Subsequent assessments of samples from the individuals on ART found that levels of HIV DNA were 10- to 100-fold higher in these CCR5-expressing resting memory CD4 T cells compared to CCR5-negative subsets. The CCR5-expressing resting memory CD4 T cells also harbored a greater proportion of replication-competent HIV, suggesting that CCR5 should be included among the candidate biomarkers for identifying latently infected cells.

    In a final set of experiments, the researchers showed that functional HIV-specific CD8 T cells have the potential to recognize and destroy virus-infected activated CD4 T cells that are transitioning to a resting state, thereby reducing the frequency of latent infection. These results indicate that effective HIV-specific CD8 T cell responses have the potential to inhibit the formation of the latent reservoir.

    The model of HIV latency described by Siliciano and colleagues differs from some other proposed scenarios. For example, a recent paper identifying CD32a as a biomarker of latently infected CD4 T cells reported that the finding was consistent with direct HIV infection of resting memory CD4 T cells as the initiator of latency. The research group of Sharon Lewin in Australia has also demonstrated that certain chemokines and myeloid dendritic cells can facilitate HIV infection of resting memory CD4 T cells and generate latently infected cells.

    Evidence in support of the in vivo relevance of Siciliano’s results may come from studies of the specific locations in the genome of CD4 T cells into which HIV commonly integrates – at the IAS 2017 meeting earlier this year, Jori Symons from Sharon Lewin’s laboratory noted that HIV DNA is more commonly found integrated into cellular genes that would be predicted to be active in activated CD4 T cells (a video of the presentation is available, and the slides can be downloaded).

    It may not be an either-or proposition, as both mechanisms might conceivably contribute to the formation of the latent HIV reservoir.

    Another recent theory to explain HIV latency involves the virus having specifically evolved the strategy in order to facilitate crossing the mucosal barrier at the time of initial infection. In the discussion section of their paper, Siliciano and colleagues argue that their data supports a simpler explanation: "latency results from infection of cells in a narrow time window after activation when cells are permissive for infection but not for prolonged HIV-1 gene expression."

    Treg and Latent HIV

    In the same issue of Immunity, Colleen S. McGary and colleagues report that a previously obscure subset of memory CD4 T cells that express the immune checkpoint receptor CTLA-4, but not PD-1, contribute significantly to the latent virus reservoir. The findings are largely derived from SIV-infected macaques but the researchers also documented the presence of these cells in lymphoid tissue samples from HIV-positive individuals on ART. The majority of the CTLA-4+PD-1- CD4 T cells were found to be of a regulatory (Treg) phenotype, a subset typically involved in dampening down immune activation. Several previous studies have reported that Treg can harbor latent HIV (e.g. Jiao YM et al and Tran TA et al), and a cellular gene that has been identified as a common HIV integration site—BACH2—is known to be involved in Treg differentiation.

    The researchers suggest that immune checkpoint inhibitors that target CTLA-4, such as the licensed anticancer antibody ipilimumab, may be able to reverse HIV latency in the CTLA-4+PD-1- CD4 T cell population; in support of this suggestion, they cite a published case report regarding an HIV-positive individual receiving ipilimumab for the treatment of cancer, which documented an increase in cell-associated HIV-1 RNA. Further exploration of this possibility is likely to focus on the SIV/macaque model, at least initially, because ipilimumab has a number of potentially serious side effects.

  • Locking Down Latent HIV

    Strategies for dealing with the reservoir of latent HIV that persists despite antiretroviral therapy (ART) have primarily focused on awakening the virus from its dormant state. But Susana Valente and colleagues from the Scripps Research Institute in Florida are taking a different tack, flipping the idea of latency reversal on its head. Their approach—which they have dubbed block and lock—involves trying to imprison latent HIV in a way that prevents it from ever reactivating. The latest work by Valente’s group was published recently in the open access journal Cell Reports.

    The intervention Valente and colleagues are testing is Didehydro-Cortistatin A (dCA), an analogue of a natural substance isolated from the marine sponge Corticium simplex. Previous studies have shown that dCA inhibits the HIV Tat protein, and can have the effect of pushing the virus into a deep state of latency that is not reversed by T cell activation or latency-reversing agents in laboratory tests.

    The new paper extends these results by testing the longer-term effects of dCA on latently infected CD4 T cells isolated from five HIV-positive individuals on suppressive ART. An initial evaluation found that the combination of dCA+ART led to greater suppression of HIV RNA production by the cells during prolonged culture when compared to just ART.

    Another experiment maintained the cells for a 35-day period in culture in the presence of either ART or dCA+ART, then withdrew the treatments and stimulated the cells with the latency-reversing agent prostratin. HIV rebound occurred immediately in cultures that had been treated with ART, but viral reactivation was inhibited by an average of 99% in the cultures exposed to dCA+ART, with two participant samples showing 100% inhibition. The difference was statistically significant. Several other similar experiments found HIV rebound was significantly delayed and reduced as a result of dCA, including after activating cells with the mitogen PHA.

    To gain insight into the potential in vivo relevance of the findings, studies were also performed in humanized mice infected with HIV. Treatment with dCA+ART was associated with 10.5-fold lower levels of HIV RNA in lymph nodes and seven-fold lower levels in brain tissue compared to ART, but differences in the spleen, bone marrow and peripheral blood mononuclear cells (PBMC) were not statistically significant.  

    A subsequent test also demonstrated that dCA+ART delayed HIV viral load rebound in HIV-infected humanized mice after treatment was interrupted, compared to ART. The latter group displayed evidence of recrudescing viral load at day three after interruption, extending to all eight animals by day 10. In contrast, among the dCA recipients, six out of 10 still had undetectable viral load at day 10. Viremia eventually became detectable in all the animals in the dCA group at day 19.

    The researchers propose that dCA or similar Tat inhibitor compounds could have a role in providing additional suppression of HIV and limiting the formation of the viral reservoir if given in combination with early ART. They also suggest that, while dCA delayed rather then prevented HIV rebound after ART withdrawal in the current study, a greater duration of treatment might lead to more prolonged repression of viral reactivation from latency. The hope is that: “over time (in combination or not with other inhibitors), transcriptional repression could be pushed past a certain threshold where viral reactivation from latency is extremely difficult to overcome, blocking and locking HIV into sustained latency.” Additional studies are planned in macaque models, with the goal of advancing the approach into clinical trials.