TAG HIV Basic Science, Vaccines, and Cure Project Blog

Mapping the HIV Integration Landscape: “Cancer Genes” and the Persistence of the Latent Reservoir

Several presentations at last year’s CROI offered evidence that the proliferation and persistence of latently infected CD4 T cells is associated with HIV integration into certain genes that have also been implicated in the development of cancers. The results prompted the investigators to hypothesize that HIV integration into cancer-associated genes plays a causative role in sustaining the reservoir of latently infected CD4 T cells by promoting their survival. Some of the scientists involved in the research went so far as to suggest that the findings might somehow contribute to explaining the elevated risk of cancer in HIV-positive people (see the CROI 2014 summary on the blog). The studies were eventually published in Science last July, along with a commentary by David Margolis and Frederic Bushman pointing out that “most HIV-related malignancies are not T cell cancers, and even most HIV-related lymphomas are of B cell origin” and gently noting: “alternative interpretations of the data are possible." 

Recently, in the journal Cell, a comprehensive analysis of HIV integration sites was published and the data argues against the idea that HIV targets cancer-associated genes as a means to persist; rather, integration into these genes is shown to be consistent with HIV’s well-documented preference for integrating into genes that are active in the cell it has infected. A separate but complementary paper in Nature provides a topological explanation for HIV’s integration preferences.

To start with the study published in Cell (led by Lillian B. Cohn from the laboratory of Michel Nussenzweig at Rockefeller University), it identified a staggering 6,719 unique HIV integration sites in CD4 T cells from 13 individuals. Three participants provided samples before and after starting ART, two were already on ART, four were untreated and the remaining four were viremic controllers (viral loads less than 2000 copies in the absence of ART). In all cases, there was evidence of proliferation of CD4 T cells containing integrated HIV DNA. Termed “clonal expansions,” these cells are identifiable because the HIV DNA they contain is integrated into the same exact location in the genome.

Consistent with previous studies, clonal expansions of CD4 T cells containing integrated HIV DNA were more common in participants in whom HIV replication was suppressed by ART compared to those with ongoing virus replication (perhaps because homeostatic proliferation of CD4 T cells contributes to immune reconstitution after ART initiation). There was also a bias for clonal expansions to involve HIV integrated into genes with lower expression levels compared to single, non-expanded HIV integrations, which more often occurred in highly expressed genes.

Based on this finding, the authors suggest that the latent HIV in clonally expanded CD4 T cells is less likely to be capable of expression and may not contribute substantially to the replication-competent HIV reservoir.  In additional support for this argument, they note that all 75 of the clonally expanded HIV genomes they tested were defective, consistent with two previously published reports demonstrating homeostatic proliferation of CD4 T cells containing integrated HIV DNA; in both of those studies the viruses were also grossly defective (see Imamichi et al., 2014 and Josefsson et al., 2013). However they acknowledge: “we cannot rule out the possibility that a rare clone of cells contains an active virus,” and this proved a wise caveat because at CROI 2015 several presentations described examples of clonally expanded HIV DNA that appeared replication-competent (e.g. Sarah Palmer, who showed that in one participant in a clinical trial of panobinostat, a clonally expanded HIV contributed to viral load rebound after an ART interruption).  

The Cell paper addresses the issue of HIV integration into cancer-associated genes in several ways. An analysis of all HIV integration sites confirms that these genes are overrepresented, but the authors explain: “this preference does not seem to be significant because it is similar to the overall preference for integration into highly expressed genes.” Importantly, there were no associations between HIV integrations into cancer-associated genes and persistence or clonal expansion, and a longitudinal study involving three participants who initiated ART demonstrated a significant decrease in integrations into these genes over time.

A logical interpretation is that HIV’s preference for integrating into active genes causes the virus to frequently end up located in genes that are being expressed in the CD4 T cells it is infecting; these genes inevitably include those involved in the cell cycle and proliferation because HIV primarily replicates in activated CD4 T cells. And it is cell cycle and proliferation genes that commonly go awry in cancer, hence the association between HIV integration sites and cancer-associated genes.

The paper in Nature, by Bruna Marini and colleagues, offers a relatively prosaic explanation for HIV’s integration site preferences, albeit one that required complex experiments to reveal. Essentially, it appears that the three-dimensional composition of a cell’s nucleus dictates the gene regions that are most rapidly reachable by HIV and, upon entry into the nucleus, the virus plumps for the nearest options. These areas are on the periphery of the nucleus, and there is a strong bias against integration into genes located more centrally. In addition to the location, the genes also need to be accessible for integration, and because genes that are not being expressed are cloaked in chromatin, this means the genes have to be active to some extent. The authors’ suggestion is: “the virus simply integrates into the first open chromatin regions it meets along its route into the nucleus.”

While these recent papers offer some evidence contrary to the notion that HIV integrates into cancer-associated genes as a strategy to facilitate its persistence, it appears likely that the topic will continue to be the subject of debate, at least until more data become available. A senior author of one of the Science papers, Stephen Hughes from the National Cancer Institute (NCI), continued to argue the original hypothesis in a plenary presentation at CROI 2015. Hughes showed a slide with the following bullet point: “Data from several labs show that there are genes in which HIV integration can cause clonal expansion (MKL2 and BACH2).” But a causative relationship between HIV integration into these genes and clonal expansion of CD4 T cells is not established; the reported data only supports an association. Rather than reflecting cause, the association could be an effect of these genes being active in CD4 T cells differentiating into a long-lived memory phenotype (BACH2 is known to have a role in CD4 T cell differentiation).   

Additionally, the last bullet point of Hughes’s presentation states: “There are reports of HIV integrations into human cancers, including a report of a tumor with an integration in BACH2 (Mack et al.).” Hughes’s Science paper includes a similar statement: “there are reports of a small number of lymphomas with HIV proviruses integrated at defined sites; one lymphoma had a provirus integrated in BACH2 (15, 29, 30).” The three numbered cites are all from the same laboratory (of Michael McGrath), and are dated 2003, 1994 and 1992 respectively. To the best of my knowledge, no other similar findings have been reported. The Mack et al citation is #15 (full text PDF is available free), and the problem is that it does not show that “one lymphoma had a provirus integrated in BACH2.” The paper clearly states: "The integration assay used had a relatively low sensitivity, indicating that identified integration sites were from multiple clonal cell populations. Some of these HIV-infected clonal cell populations may be associated with induction of pathogenesis in these tissues." Nowhere does it confirm that the HIV integration was in the lymphoma.

Although it’s understandable that the low sensitivity of the assay used in the study might lead someone to assume that the integration must have been in the cancer cells (because those cells would be present at high frequency), that is not the only potential explanation. An alternative possibility is that the HIV integration was in the genome of a clonally expanded CD4 T cell population infiltrating the cancerous tissue. Coincidentally, a study reporting exactly that phenomenon was presented at CROI 2015 by Francesco Simonetti from NCI. Simonetti demonstrated the clonal expansion of a latently infected CD4 T cell in tumor tissue—perhaps due to the CD4 T cell specifically responding to a cancer antigen—in an HIV-positive individual with squamous cell carcinoma. 

At this point, it appears that the specter of an additional cause of cancer in HIV-positive people has been raised with no compelling supporting evidence. And the most recent of the three papers that have been cited as offering inferential evidence was miscited. When you consider how many people are living with HIV and the amount of HIV integration events occurring in those individuals, contrasted with the relative rarity of T cell cancers, it never seemed a very plausible idea to begin with—as David Margolis and Frederic Bushman imply in their Science commentary. This issue is not only relevant to HIV-positive people, but also for gene therapy researchers using HIV-based vectors to modify T cell receptors as a means to target cancers for immune-mediated destruction (an approach that has had considerable success in clinical trials).

For cure research, a central issue is whether latently infected memory CD4 T cells behave any differently from other memory CD4 T cells. Certainly, long-term persistence and homeostatic proliferation are completely normal facets of memory CD4 T cell biology; this is why, for example, smallpox-specific memory CD4 T cells remain detectable for decades after vaccination despite the absence of any exposure to smallpox antigens. Also, if HIV integration into specific genes exerts some kind of control over memory CD4 T cell behavior, it does not lead to notable growth of the latent HIV reservoir—longitudinal studies show that the reservoir decays slowly with a half-life of around 43-44 months. The latest longitudinal study was just published in the Journal of Infectious Diseases by David Margolis’s research group and, as is noted in an accompanying commentary by Bob and Janet Siliciano, the estimated half-life of 43 months matches previous data almost exactly (the prior estimate was 44 months).  

Because the techniques that allow comprehensive analyses of HIV integration sites are new, it’s perhaps inevitable that there is some wrangling over how to interpret the data. The confusion is likely to resolve as more results become available, and there is clearly room for larger longitudinal studies to track clonally expanded latently infected CD4 T cells and their HIV integration sites over time, and better define what proportion of these expanded virus genomes are replication-competent. 

Science. 2014 Jul 10. pii: 1256304. [Epub ahead of print]

Proliferation of cells with HIV integrated into cancer genes contributes to persistent infection. (open access)

Wagner TA, McLaughlin S, Garg K, Cheung CY, Larsen BB, Styrchak S, Huang HC, Edlefsen PT, Mullins JI, Frenkel LM.

Abstract

Antiretroviral treatment (ART) of HIV infection suppresses viral replication. Yet if ART is stopped, virus re-emerges due to the persistence of infected cells. We evaluated the contribution of infected-cell proliferation and sites of proviral integration to HIV persistence. 534 HIV integration sites (IS) and 63 adjacent HIV env sequences were derived from three study participants over 11.3 to 12.7 years of ART. Each participant had identical viral sequences integrated at the same position in multiple cells, demonstrating infected-cell proliferation. Integrations were overrepresented in genes associated with cancer and favored in 12 genes across multiple participants. Over time on ART, a greater proportion of persisting proviruses were in proliferating cells. HIV integration into specific genes may promote proliferation of HIV-infected cells, slowing viral decay during ART. 

Science. 2014 Jul 11;345(6193):179-83. doi: 10.1126/science.1254194. Epub 2014 Jun 26.

HIV latency. Specific HIV integration sites are linked to clonal expansion and persistence of infected cells. (open access)

Maldarelli F, Wu X, Su L, Simonetti FR, Shao W, Hill S, Spindler J, Ferris AL, Mellors JW, Kearney MF, Coffin JM, Hughes SH.

Abstract

The persistence of HIV-infected cells in individuals on suppressive combination antiretroviral therapy (cART) presents a major barrier for curing HIV infections. HIV integrates its DNA into many sites in the host genome; we identified 2410 integration sites in peripheral blood lymphocytes of five infected individuals on cART. About 40% of the integrations were in clonally expanded cells. Approximately 50% of the infected cells in one patient were from a single clone, and some clones persisted for many years. There were multiple independent integrations in several genes, including MKL2 and BACH2; many of these integrations were in clonally expanded cells. Our findings show that HIV integration sites can play a critical role in expansion and persistence of HIV-infected cells.

Science. 2014 Jul 11;345(6193):143-4. doi: 10.1126/science.1257426.

HIV/AIDS. Persistence by proliferation? (open access)

Margolis D, Bushman F.

Cell. 2015 Jan 29;160(3):420-32. doi: 10.1016/j.cell.2015.01.020.

HIV-1 Integration Landscape during Latent and Active Infection.

Cohn LB, Silva IT, Oliveira TY, Rosales RA, Parrish EH, Learn GH, Hahn BH, Czartoski JL, McElrath MJ, Lehmann C, Klein F, Caskey M, Walker BD, Siliciano JD, Siliciano RF, Jankovic M, Nussenzweig MC.

Abstract

The barrier to curing HIV-1 is thought to reside primarily in CD4(+) T cells containing silent proviruses. To characterize these latently infected cells, we studied the integration profile of HIV-1 in viremic progressors, individuals receiving antiretroviral therapy, and viremic controllers. Clonally expanded T cells represented the majority of all integrations and increased during therapy. However, none of the 75 expanded T cell clones assayed contained intact virus. In contrast, the cells bearing single integration events decreased in frequency over time on therapy, and the surviving cells were enriched for HIV-1 integration in silent regions of the genome. Finally, there was a strong preference for integration into, or in close proximity to, Alu repeats, which were also enriched in local hotspots for integration. The data indicate that dividing clonally expanded T cells contain defective proviruses and that the replication-competent reservoir is primarily found in CD4(+) T cells that remain relatively quiescent.

Nature (2015) doi:10.1038/nature14226

Nuclear architecture dictates HIV-1 integration site selection

Bruna Marini, Attila Kertesz-Farkas, Hashim Ali, Bojana Lucic, Kamil Lisek, Lara Manganaro, Sandor Pongor, Roberto Luzzati, Alessandra Recchia, Fulvio Mavilio, Mauro Giacca & Marina Lusic

Abstract

Long-standing evidence indicates that human immunodeficiency virus type 1 (HIV-1) preferentially integrates into a subset of transcriptionally active genes of the host cell genome1, 2, 3, 4. However, the reason why the virus selects only certain genes among all transcriptionally active regions in a target cell remains largely unknown. Here we show that HIV-1 integration occurs in the outer shell of the nucleus in close correspondence with the nuclear pore. This region contains a series of cellular genes, which are preferentially targeted by the virus, and characterized by the presence of active transcription chromatin marks before viral infection. In contrast, the virus strongly disfavours the heterochromatic regions in the nuclear lamin-associated domains5 and other transcriptionally active regions located centrally in the nucleus. Functional viral integrase and the presence of the cellular Nup153 and LEDGF/p75 integration cofactors are indispensable for the peripheral integration of the virus. Once integrated at the nuclear pore, the HIV-1 DNA makes contact with various nucleoporins; this association takes part in the transcriptional regulation of the viral genome. These results indicate that nuclear topography is an essential determinant of the HIV-1 life cycle.

J Infect Dis. first published online April 15, 2015 doi: 10.1093/infdis/jiv218

Precise Quantitation of the Latent HIV-1 Reservoir: Implications for Eradication Strategies (open access)

A.M. Crooks, R. Bateson, A.B. Cope, N.P. Dahl, M.K. Griggs, J.D. Kuruc, C.L. Gay, J.J. Eron, D.M. Margolis, R.J. Bosch and N.M. Archin

Abstract

The quantitative viral outgrowth assay (QVOA) provides a precise minimal estimate of the reservoir of resting CD4+ T cell infection (RCI). However, the variability of RCI over time on ART, relevant to assess potential effects of latency-reversing agents or other interventions, has not been fully described. We performed QVOA on resting CD4+ T cells obtained via leukapheresis from 37 HIV+ patients, on stable suppressive ART over a period of 6 years. Patients who started ART in acute HIV infection (AHI, n=17) or in chronic infection (CHI, n=20) were studied once HIV RNA was <50 copies/mL for≥6 months. Using random effects analysis of 160 RCI measurements, we found that RCI declined significantly over time (p<0.001) with estimated mean half-life of 3.6 (95% CI: 2.3-8.1) years, remarkably consistent with prior studies. There was no evidence of more rapid decay for AHI vs. CHI (p=0.99) in patients suppressed for≥6 months. RCI was reliably estimated with longitudinal measurements generally showing <2-fold variation from the previous measure. When QVOA is performed in this format, RCI decreases >6 fold were rare. We suggest that a 6-fold decline is a relevant threshold to reliably identify effects of anti-latency therapeutics on RCI.

J Infect Dis. first published online April 15, 2015 doi:10.1093/infdis/jiv219

Editorial

The remarkable stability of the latent reservoir for HIV-1 in resting memory CD4+ T cells (open access)

Janet M. Siliciano and Robert F. Siliciano

Combining Latency-Reversing Agents, and Reviewing Methods of Measuring the Latent HIV Reservoir

At CROI last year, Gregory Laird presented results from a laboratory study that tested the activity of several candidate HIV latency-reversing agents (LRAs) on latently infected CD4 T cells isolated from HIV-positive individuals on ART. The results were disappointing: only one LRA showed a very modest effect on HIV gene expression and none induced significant production of HIV virions (the study was later published in Nature Medicine). Laird concluded his CROI talk by offering a glimpse at more hopeful preliminary data suggesting that combinations of LRAs could perform better, and these experiments have since been completed and were published recently in the Journal of Clinical Investigation (the paper is open access).

The nub of the results is that pairings of LRAs from different classes can show synergistic or additive effects, depending on the combination. In particular, HDAC inhibitors—several of which are undergoing evaluation in clinical trials—showed evidence of synergy with the PKC agonists bryostatin-1 and prostratin. The researchers used the extent of latency reversal achieved with maximal CD4 T cell activation as the benchmark for judging the activity of LRA combinations and, as an example, bryostatin-1 and the HDAC inhibitor panobinostat prompted an induction of HIV gene expression that averaged around 50% of that obtained with T cell activation. Although there are concerns about the potential toxicity of bryostatin-1, it is being evaluated in a small trial in Spain and other PKC agonists—most notably an extract from a tropical shrub named Ingenol B—are being considered for clinical testing. Laird’s study found that low doses of bryostatin-1 worked synergistically with the HDAC inhibitor romidepsin, suggesting a means to try and minimize the risk of adverse effects.

The paper also presents data derived from mathematical models indicating that, in clinical trials, effective LRAs or LRA combinations should produce bursts of HIV production of sufficient magnitude to be detected with standard viral load assays. The authors note that so far evidence of this effect has only been reported for the HDAC inhibitor romidepsin (see the AIDS 2014 conference presentation by Dr. Ole Schmeltz Søgaard).

The senior author of the study is latency expert Robert Siliciano from Johns Hopkins University. In a separate open access review just published in Trends in Microbiology, Siliciano and colleagues describe the current tools available to measure the latent HIV reservoir in vivo. The pros and cons of each are delineated, and the need for improved technologies highlighted in the concluding remarks: “Without a high-throughput, sensitive, and well-validated assay, it will remain difficult for researchers to identify novel LRAs, move forward with clinical trials, and develop strategies to eradicate HIV-1.”

J Clin Invest. doi:10.1172/JCI80142.

Research Article

Ex vivo analysis identifies effective HIV-1 latency–reversing drug combinations

Gregory M. Laird1, C. Korin Bullen1, Daniel I.S. Rosenbloom2, Alyssa R. Martin3,Alison L. Hill4, Christine M. Durand1, Janet D. Siliciano1 and Robert F. Siliciano1,5

Authorship note: Gregory M. Laird and C. Korin Bullen contributed equally to this work. 

Published March 30, 2015

Submitted: November 21, 2014; Accepted: February 6, 2015.

Reversal of HIV-1 latency by small molecules is a potential cure strategy. This approach will likely require effective drug combinations to achieve high levels of latency reversal. Using resting CD4+ T cells (rCD4s) from infected individuals, we developed an experimental and theoretical framework to identify effective latency-reversing agent (LRA) combinations. Utilizing ex vivo assays for intracellular HIV-1 mRNA and virion production, we compared 2-drug combinations of leading candidate LRAs and identified multiple combinations that effectively reverse latency. We showed that protein kinase C agonists in combination with bromodomain inhibitor JQ1 or histone deacetylase inhibitors robustly induce HIV-1 transcription and virus production when directly compared with maximum reactivation by T cell activation. Using the Bliss independence model to quantitate combined drug effects, we demonstrated that these combinations synergize to induce HIV-1 transcription. This robust latency reversal occurred without release of proinflammatory cytokines by rCD4s. To extend the clinical utility of our findings, we applied a mathematical model that estimates in vivo changes in plasma HIV-1 RNA from ex vivo measurements of virus production. Our study reconciles diverse findings from previous studies, establishes a quantitative experimental approach to evaluate combinatorial LRA efficacy, and presents a model to predict in vivo responses to LRAs.

Trends Microbiol. 2015 Apr;23(4):192-203. doi: 10.1016/j.tim.2015.01.013. Epub 2015 Mar 5.

Towards an HIV-1 cure: measuring the latent reservoir.

Bruner KM, Hosmane NN, Siliciano RF.

Abstract

The latent reservoir (LR) of HIV-1 in resting memory CD4+ T cells serves as a major barrier to curing HIV-1 infection. While many PCR- and culture-based assays have been used to measure the size of the LR, correlation between results of different assays is poor and recent studies indicate that no available assay provides an accurate measurement of reservoir size. The discrepancies between assays are a hurdle to clinical trials that aim to measure the efficacy of HIV-1 eradication strategies. Here we describe the advantages and disadvantages of various approaches to measuring the LR.

Broadly Neutralizing Antibody Suppresses HIV in Clinical Trial

The past decade has seen a boom in the identification of antibodies capable of potently neutralizing a broad array of different HIV isolates (broadly neutralizing antibodies or bNAbs). New technologies that allow antibodies to be fished from huge numbers of individual B cells and tested for activity have spurred this rapid acceleration of discovery. There is now intense interest in learning whether the blossoming array of bNAbs can be put to therapeutic and preventive use. A paper published yesterday in Nature describes encouraging results from a phase I trial involving the bNAb 3BNC117. Reflecting the level of interest in the topic, the paper has attracted extensive press coverage.

Led by Marina Caskey from Rockefeller University, the study enrolled 12 HIV-negative and 17 HIV-positive individuals (including two on ART) who received a single infusion of 3BNC117 at various doses (1, 3, 10 or 30 mg kg⁻¹). The infusions were well tolerated; there were no grade 3 or greater adverse events and no laboratory abnormalities. HIV-positive participants receiving the two highest doses showed significant declines in viral load, with the exception of one individual whose virus turned out to be resistant to 3BNC117 at baseline. The eight recipients of the 30 mg kg⁻¹ dose experienced reductions in viral load ranging from 0.8 to 2.5 logs, with four remaining below baseline at the last reported follow-up (day 56 post-infusion). Evidence of HIV evolving resistance to 3BNC117 was documented, particularly in the lowest dose groups. Assessments of whether anti-3BNC117 immune responses were invoked in any participants are not yet complete, but will be reported in the near future. 

The study confirms that bNAbs are active against HIV in humans, consistent with humanized mice and macaque experiments. A number of pathways toward the therapeutic and preventive use of bNAbs can now be explored, but could still prove challenging to navigate. As the authors of the paper note, bNAbs will likely need to be used in combination to maximize activity and prevent resistance; they may also benefit from additional modifications to enhance their potency and persistence in the body.

On the therapeutic side, there is the potential to combine bNAbs with latency-reversing agents with the aim of promoting clearance of the viral reservoir via antibody-mediated cellular cytotoxicity (ADCC). Another approach is to test whether combination bNAbs could provide a long-acting alternative or supplement to daily ART. A trial involving the combination of the bNAb VRC01 plus ART is due to start later this year in individuals with acute HIV infection in Thailand (see Jintanat Ananworanich’s presentation at last year’s Forum for Collaborative HIV Research cure research meeting for background). Dan Barouch has plans to study the bNAb PGT121 in several different populations, as outlined in his talk at CROI 2015. 

On the preventive side, there is interest in evaluating the efficacy of passive immunization (either intravenous or subcutaneous) with bNAbs in both high risk adults and infants exposed to HIV via breastfeeding (see the webcast of Barney Graham’s presentation at the 2014 R4P conference for additional information).

While this research is likely to move forward, there are many lingering uncertainties regarding passive immunization: the need for repeated injections raises the concern of practicality (particularly in the prevention context), and another issue that has to be considered is the complexity and cost of bNAb manufacture (for an informative excursion into the industry of bNAb production, see Michael Dumiak’s 2014 IAVI Report article, “Making it to Manufacturing”). As has been covered previously on the blog, there is at least one alternative, potentially simpler method of bNAb delivery: gene transfer with adeno-associated virus (AAV), which is being tested in an ongoing phase I trial in the UK. But it is not yet known if AAV can deliver bNAb levels high enough to be efficacious.  

To discuss the prospects for passive immunization against HIV, AVAC is hosting a webinar on Tuesday, April 21 at 11am EDT with Dr. Sarah Schlesinger from Rockefeller University (click here to register). 

Nature (2015) doi:10.1038/nature14411

Viraemia suppressed in HIV-1-infected humans by broadly neutralizing antibody 3BNC117

Marina Caskey, Florian Klein, Julio C. C. Lorenzi, Michael S. Seaman, Anthony P. West Jr, Noreen Buckley, Gisela Kremer, Lilian Nogueira, Malte Braunschweig, Johannes F. Scheid, Joshua A. Horwitz, Irina Shimeliovich, Sivan Ben-Avraham, Maggi Witmer-Pack, Martin Platten, Clara Lehmann, Leah A. Burke, Thomas Hawthorne, Robert J. Gorelick, Bruce D. Walker, Tibor Keler, Roy M. Gulick, Gerd Fätkenheuer, Sarah J. Schlesinger & Michel C. Nussenzweig

HIV-1 immunotherapy with a combination of first generation monoclonal antibodies was largely ineffective in pre-clinical and clinical settings and was therefore abandoned. However, recently developed single-cell-based antibody cloning methods have uncovered a new generation of far more potent broadly neutralizing antibodies to HIV-1. These antibodies can prevent infection and suppress viraemia in humanized mice and nonhuman primates, but their potential for human HIV-1 immunotherapy has not been evaluated. Here we report the results of a first-in-man dose escalation phase 1 clinical trial of 3BNC117, a potent human CD4 binding site antibody, in uninfected and HIV-1-infected individuals. 3BNC117 infusion was well tolerated and demonstrated favourable pharmacokinetics. A single 30 mg kg−1 infusion of 3BNC117 reduced the viral load in HIV-1-infected individuals by 0.8–2.5 log10 and viraemia remained significantly reduced for 28 days. Emergence of resistant viral strains was variable, with some individuals remaining sensitive to 3BNC117 for a period of 28 days. We conclude that, as a single agent, 3BNC117 is safe and effective in reducing HIV-1 viraemia, and that immunotherapy should be explored as a new modality for HIV-1 prevention, therapy and cure.

Nature News

doi:10.1038/nature.2015.17260

Antibody shows promise as treatment for HIV

Erika Check Hayden

Souped-Up IL-15 Sparks Natural Killer Cell Activity Against HIV

The cytokine interleukin-15 (IL-15) can exert a range of effects on the immune system, but is particularly important for promoting the proliferation and function of natural killer (NK) cells and CD8 T cells. Some observational studies in HIV have suggested salutary effects of higher IL-15 levels, in one case finding an association with delayed viral load rebound after ART interruption. But attempts at therapeutic administration of the cytokine to SIV-infected macaques have generally produced deleterious effects, including CD4 T cell depletion. More recently, IL-15 has been reexamined in the context of cure research, with laboratory studies demonstrating it can induce latently infected CD4 T cells to produce HIV. There is also increasing interest in therapeutic manipulation of NK cell responses as a means to eliminate the HIV reservoir, a task for which IL-15 may be well suited. A paper published last week in the Journal of Virology reports that an optimized form of IL-15 promoted potent inhibition of HIV by NK cells in humanized mice.  

The version of IL-15 used in the study is described as a superagonist, comprising the cytokine bound to part of the receptor with which it interacts. This modified IL-15 is being developed as a cancer therapeutic under the name ALT-803 and, in mice, it has been shown to have superior biological activity (~25-fold greater) and a much longer half-life (~25 hours vs. ~40 minutes) compared to the unaltered cytokine. The new Journal of Virology paper reports that in a humanized mouse model, administration of ALT-803 either one or three days after HIV challenge reduced subsequent virus levels by over 90% (measured up to 21 days later). However, there was no significant effect if the delay in ALT-803 administration was extended to five days after challenge. The researchers used cell transfer experiments to confirm that NK cells, and not CD8 T cells, mediated the inhibition of acute HIV infection in this model. Discussing the results, they state: “to our knowledge, this study is the first reported demonstration that in vivo activation of NK cells can inhibit acute HIV-1 infection.” They also note that the poor outcomes seen previously in the SIV model could be due to unmodified IL-15 producing less antiviral activity and more unwanted effects (e.g. CD4 T cell activation), or might reflect differential responsiveness in macaque compared to human cells. 

A dose-escalation pilot trial of ALT-803 in HIV-positive individuals on ART is due to start soon at the University of Minnesota. The primary aim is to evaluate safety and tolerability, but the study will also measure HIV reservoir levels as a secondary endpoint. Due to evidence from animal studies that ALT-803 may be able to invoke NK cell activity against tumors, several phase I trials are already ongoing in people with cancers.

J Virol. 2015 Apr 1. pii: JVI.00563-15. [Epub ahead of print]

In Vivo Activation of Human NK cells by Treatment with an IL-15 Superagonist Potently Inhibits Acute In Vivo HIV-1 Infection in Humanized Mice.

Seay K, Church C, Zheng JH, Deneroff K, Ochsenbauer C, Kappes JC, Liu B, Jeng EK, Wong HC, Goldstein H.

Abstract

Natural killer (NK) cells with anti-HIV-1 activity may inhibit HIV-1 replication and dissemination during acute HIV-1 infection. We hypothesized that the NK cell capacity to suppress acute in vivo HIV-1 infection would be augmented by activating them via treatment with an IL-15 superagonist, IL-15 bound to soluble IL-15Rα, an approach that potentiates human NK cell-mediated killing of tumor cells. In vitro stimulation of human NK cells with a recombinant IL-15 superagonist significantly induced their expression of cytotoxic effector molecules granzyme B and perforin, their degranulation upon exposure to K562 cells as indicated by cell-surface expression of CD107a and their capacity to lyse K562 cells and HIV-1-infected T cells. The impact of IL-15 superagonist-induced activation of human NK cells on acute in vivo HIV-1 infection was investigated using hu-spl-PBMC-NSG mice, NOD-SCID-IL2rγ-/- mice intrasplenically injected with human PBMCs, which develop productive in vivo infection after intrasplenic inoculation with HIV-1. IL-15 superagonist treatment potently inhibited acute HIV-1 infection in hu-spl-PBMC-NSG mice even when delayed until three days after intrasplenic HIV-1 inoculation. Removal of NK cells from the human PBMCs prior to intrasplenic injection into NSG mice completely abrogated IL-15 superagonist-mediated suppression of in vivo HIV-1 infection. Thus, the in vivo activation of NK cells, integral mediators of the innate immune response, by treatment with an IL-15 superagonist increases their anti-HIV activity and enables them to potently suppress acute in vivo HIV-1 infection. These results indicate that in vivo activation of NK cells may represent a new immunotherapeutic approach to suppress acute HIV-1 infection.