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Latency-reversing agents are a novel way to help the immune system find and kill the HIV virus.
Although antiretroviral drugs effectively suppress HIV in patients, the virus still hides within their cells. Scientists are trying out new molecules that can make it a visible target for the immune system.
In 10 seconds? ‘Latency-reversing agents’ are promising compounds in the battle against HIV. Scientists have managed to use them to tackle ‘latency’, one of the key tricks that HIV uses to hide from immune cells trying to clear the virus from the body.
So what exactly is latency? It’s the ability of the virus to stop replicating and lie dormant in a subset of immune cells called CD4+ T. In HIV-infected people who are on antiretroviral therapy (ART), the virus is suppressed to very low levels, but it still lurks around unseen by the immune system.
And what’s the news on this front? Scientists have managed to reactivate HIV in its usual hiding place – cells known as the viral reservoir – using chemicals called ‘latency reversal agents’, or LRAs. This is important because the active virus becomes a visible target for killer immune cells, so it can be destroyed. Researchers call this the ‘kick and kill’ method.
How did they do it? In a recent study of 20 HIV patients on ART, researchers found that a drug called maraviroc led to an increase in HIV transcription in resting CD4+ T cells. Transcription is part of how the virus replicates – and this activity gives away the HIV’s hiding place. This supports the idea that LRAs could be used to eliminate virus reservoirs in HIV patients.
And is this already effective? It still needs fine-tuning. Sole ‘agents’ are less effective, but researchers using computational models discovered that pairs of LRAs can significantly reverse HIV latency, so this is a promising path for further research.
Is anything else being tried? Absolutely – scientists are looking into how our genes can affect HIV latency. One previously unrecognised ‘instruction’ regulating genes is called histone crotonylation. Researchers used an enzyme boosting crotonylation in HIV-infected lab monkeys and managed to reactivate the latent virus in their gut cells. The next step is to repeat this in humans, which can lead to new drugs and possibly, a cure.
Researchers experiment with traditional medicine to fight latency
Scientists have studied plant extracts from traditional medications to see if their compounds could help reverse HIV latency.
They used a plant called Croton megalobotrys, which has been long known for its medicinal properties in South-East Asia, Africa and South America.
The extracts appeared to reverse latency in lab conditions, and when added to the diets of a small number of HIV patients, they reported improved health – but of course, further research is needed!
Abstract: HIV infection requires lifelong antiretroviral therapy because of the persistence of latently infected CD4+ T cells. Induction of viral expression from latently infected cells occurs following T cell receptor (TCR) activation but not all latently infected cells respond to TCR stimulation. We compared two models of latently infected cells using an enhanced green fluorescent protein (EGFP) reporter virus to infect CCL19 treated resting CD4+ (rCD4) T cells (pre-activation latency) or activated CD4+ T cells that returned to a resting state (post-activation latency). We isolated latently infected cells by sorting for EGFP- cells after infection. These cells were cultured with antivirals and stimulated with anti-CD3/anti-CD28, mitogens, latency reversing agents (LRA) as well as co-cultured with monocytes and anti-CD3. Spontaneous EGFP expression was more frequent in post-activation than pre-activation latency. Stimulation of latently infected cells with monocytes/anti-CD3 resulted in an increase in EGFP expression compared to unstimulated controls using the pre-activation latency model but led to a reduction in EGFP expression in the post-activation latency model. The reduced EGFP expression was not associated with a reduction in viral DNA or the levels of T cell proliferation but depended on direct contact between monocytes and T cells. Monocytes added to the post-activation latency model during the establishment of latency reduced spontaneous viral expression suggesting that monocyte-T cell interactions at an early time point post infection can maintain HIV latency. This direct comparison of pre- and post- activation latency suggests that effective strategies needed to reverse latency will depend on how latency is established. One strategy being evaluated to eliminate latently infected cells that persist in HIV-infected individuals on antiretroviral therapy (ART) is to activate HIV expression or production with the goal of inducing virus mediated cytolysis or immune mediated clearance of the infected cells. The gold standard for activation of latent virus is T cell receptor stimulation with anti-CD3/anti-CD28. However, this stimulus only activates a small proportion of latently infected cells. We show clear differences in the response of latently infected cells to activating stimuli based on how latent infection is established, an observation that may potentially explain the persistence of non-induced intact proviruses in HIV-infected individuals on ART. Copyright © 2018 American Society for Microbiology.
Pub.: 13 Apr '18, Pinned: 26 Apr '18
Abstract: Eradication of HIV-1 (HIV) is hindered by stable viral reservoirs. Viral latency is epigenetically regulated. While the effects of histone acetylation and methylation at the HIV long-terminal repeat (LTR) have been described, our knowledge of the proviral epigenetic landscape is incomplete. We report that a previously unrecognized epigenetic modification of the HIV LTR, histone crotonylation, is a regulator of HIV latency. Reactivation of latent HIV was achieved following the induction of histone crotonylation through increased expression of the crotonyl-CoA-producing enzyme acyl-CoA synthetase short-chain family member 2 (ACSS2). This reprogrammed the local chromatin at the HIV LTR through increased histone acetylation and reduced histone methylation. Pharmacologic inhibition or siRNA knockdown of ACSS2 diminished histone crotonylation-induced HIV replication and reactivation. ACSS2 induction was highly synergistic in combination with either a protein kinase C agonist (PEP005) or a histone deacetylase inhibitor (vorinostat) in reactivating latent HIV. In the SIV-infected nonhuman primate model of AIDS, the expression of ACSS2 was significantly induced in intestinal mucosa in vivo, which correlated with altered fatty acid metabolism. Our study links the HIV/SIV infection-induced fatty acid enzyme ACSS2 to HIV latency and identifies histone lysine crotonylation as a novel epigenetic regulator for HIV transcription that can be targeted for HIV eradication.
Pub.: 20 Feb '18, Pinned: 25 Apr '18
Abstract: Maraviroc is a CCR5 antagonist used in the treatment of HIV-1 infection. We and others have suggested that maraviroc could reactivate latent HIV-1. To test the latency reversing potential of maraviroc and the mechanisms involved, we performed a phase-II, single-center, open-label study in which maraviroc was administered for 10 days to 20 HIV-1-infected individuals on suppressive antiretroviral therapy (Eudra CT: 2012-003215-66). All patients completed full maraviroc dosing and follow up. The primary endpoint was to study whether maraviroc may reactivate HIV-1 latency, eliciting signalling pathways involved in the viral reactivation. An increase in HIV-1 transcription in resting CD4T-cells, estimated by HIV-1 unspliced RNA, was observed. Moreover, activation of the NF-κB transcription factor was observed in these cells. In contrast, AP-1 and NFAT activity was not detected. To elucidate the mechanism of NF-κB activation by maraviroc, we have evaluated in HeLa P4 C5 cells, which stably express CCR5, if maraviroc could be acting as a partial CCR5-agonist, with no other mechanisms or pathways involved. Our results show that maraviroc can induce NF-κB activity and NF-κB target genes expression by CCR5 binding, since the use of TAK779, a CCR5 inhibitor, blocked NF-κB activation and functionality. Taken together, we show that maraviroc may have a role in the activation of latent virus transcription through the activation of NF-κB as a result of binding CCR5. Our results strongly support a novel use of maraviroc as a potential latency reversal agent in HIV-1-infected patients.HIV-1 persistence in a small pool of long-lived latently infected resting CD4T-cells is a major barrier to viral eradication in HIV-1-infected patients on antiretroviral therapy. A potential strategy to cure HIV-1-infection is the use of latency reversing agents to eliminate the reservoirs established in resting CD4T-cells. As no drug has been shown to be completely effective so far, the search for new drugs and combinations remains a priority in the HIV cure. We examined the ability of maraviroc, a CCR5-antagonist used as an antiretroviral drug, to activate latent HIV-1 in infected-individuals on antiretroviral therapy. The study showed that maraviroc can activate NF-κB and, subsequently, induce latent HIV-1-transcription in resting CD4T-cells from HIV-1-infected individuals on suppressive antiretroviral therapy. Additional interventions will be needed to eliminate latent HIV-1 infection. Our results suggest that maraviroc may be a new latency reversing agent to interfere with HIV-1 persistence during antiretroviral therapy. Copyright © 2018 American Society for Microbiology.
Pub.: 16 Feb '18, Pinned: 25 Apr '18
Abstract: Eradicating HIV-1 infection is difficult because of the reservoir of latently infected cells that gets established soon after infection, remains hidden from antiretroviral drugs and host immune responses, and retains the capacity to reignite infection following the cessation of treatment. Drugs called latency-reversing agents (LRAs) are being developed to reactivate latently infected cells and render them susceptible to viral cytopathicity or immune killing. Whereas individual LRAs have failed to induce adequate reactivation, pairs of LRAs have been identified recently that act synergistically and hugely increase reactivation levels compared to individual LRAs. The maximum synergy achievable with LRA pairs is of clinical importance, as it would allow latency-reversal with minimal drug exposure. Here, we employed stochastic simulations of HIV-1 transcription and translation in latently infected cells to estimate this maximum synergy. We incorporated the predominant mechanisms of action of the two most promising classes of LRAs, namely, protein kinase C agonists and histone deacetylase inhibitors, and quantified the activity of individual LRAs in the two classes by mapping our simulations to corresponding in vitro experiments. Without any adjustable parameters, our simulations then quantitatively captured experimental observations of latency-reversal when the LRAs were used in pairs. Performing simulations representing a wide range of drug concentrations, we estimated the maximum synergy achievable with these LRA pairs. Importantly, we found with all the LRA pairs we considered that concentrations yielding the maximum synergy did not yield the maximum latency-reversal. Increasing concentrations to increase latency-reversal compromised synergy, unravelling a trade-off between synergy and efficacy in LRA combinations. The maximum synergy realizable with LRA pairs would thus be restricted by the desired level of latency-reversal, a constrained optimum we elucidated with our simulations. We expect this trade-off to be important in defining optimal LRA combinations that would maximize synergy while ensuring adequate latency-reversal.
Pub.: 17 Feb '18, Pinned: 25 Apr '18
Abstract: The definitive cure for human immunodeficiency virus type-1 (HIV) infection is represented by the eradication of the virus from the patient's body. To reach this result, cells that are infected but do not produce the virus must become recognizable to be killed by the immune system. For this purpose, drugs defined "latency reverting agents" (LRA) that reactivate viral production are under investigation. A few clinical studies have been performed in HIV-infected patients treated with LRA and combined antiretroviral therapy (cART). The strategy is thus to combine cART and LRA to reactivate the virus and unmask latently infected cells that, because of cART, cannot produce a fully competent form of the virus. Unmasked cells can present viral antigens to the immune system, that ultimately recognizes and kills such latently infected cells. This review reports and discusses recent studies that have been published on this topic.
Pub.: 11 Feb '18, Pinned: 25 Apr '18
Abstract: Antiretroviral therapy (ART) has rendered HIV-1 infection a treatable illness; however, ART is not curative owing to the persistence of replication-competent, latent proviruses in long-lived restingTcells. Strategies that target these latently infected cells and allow immune recognition and clearance of this reservoir will be necessary to eradicate HIV-1 in infected individuals. This review describes current pharmacologic approaches to reactivate the latent reservoir so that infected cells can be recognized and targeted, with the ultimate goal of achieving an HIV-1 cure. Expected final online publication date for the Annual Review of Medicine Volume 69 is January 29, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Pub.: 04 Nov '17, Pinned: 25 Apr '18
Abstract: Current HIV therapies do not act on latent cellular HIV reservoirs; hence they are not curative. While experimental latency reversal agents (LRAs) can promote HIV expression in these cells, thereby exposing them to immune recognition, existing LRAs exhibit limited clinical efficacy and high toxicity. We previously described a traditional 3-step medicinal plant regimen used for HIV/AIDS management in Northern Botswana that inhibits HIV replication in vitro. Here we describe use of one component of the regimen that additionally contains novel phorbol esters possessing HIV latency-reversal properties.We sought to document experiences of traditional medicine users, assess the ability of traditional medicine components to reverse HIV latency in vitro, and identify pure compounds that conferred these activities.Experiences of two HIV-positive traditional medicine users (patients) were documented using qualitative interview techniques. Latency reversal activity was assessed using a cell-based model (J-Lat, clone 9.2). Crude plant extracts were fractionated by open column chromatography and reverse-phase HPLC. Compound structures were elucidated using NMR spectroscopy and mass spectrometry.Patients using the 3-step regimen reported improved health over several years despite no reported use of standard HIV therapies. Crude extracts from Croton megalobotrys Müll Arg. ("Mukungulu"), the third component of the 3-step regimen, induced HIV expression in J-lat cells to levels comparable to the known LRA prostratin. Co-incubation with known LRAs and pharmacological inhibitors indicated that the active agent(s) in C. megalobotrys were likely to be protein kinase C (PKC) activator(s). Consistent with these results, two novel phorbol esters (Namushen 1 and 2) were isolated as abundant components of C. megalobotrys and were sufficient to confer HIV latency reversal in vitro.We have identified novel LRAs of the phorbol ester class from a medicinal plant used in HIV/AIDS management. These data, combined with self-reported health effects and previously-described in vitro anti-HIV activities of this traditional 3-step regimen, support the utility of longitudinal observational studies of patients undergoing this regimen to quantify its effects on plasma viral loads and HIV reservoir size in vivo.
Pub.: 04 Oct '17, Pinned: 25 Apr '18
Abstract: We report the identification of 67 previously undescribed histone modifications, increasing the current number of known histone marks by about 70%. We further investigated one of the marks, lysine crotonylation (Kcr), confirming that it represents an evolutionarily-conserved histone posttranslational modification. The unique structure and genomic localization of histone Kcr suggest that it is mechanistically and functionally different from histone lysine acetylation (Kac). Specifically, in both human somatic and mouse male germ cell genomes, histone Kcr marks either active promoters or potential enhancers. In male germinal cells immediately following meiosis, Kcr is enriched on sex chromosomes and specifically marks testis-specific genes, including a significant proportion of X-linked genes that escape sex chromosome inactivation in haploid cells. These results therefore dramatically extend the repertoire of histone PTM sites and designate Kcr as a specific mark of active sex chromosome-linked genes in postmeiotic male germ cells.
Pub.: 20 Sep '11, Pinned: 25 Apr '18
Abstract: Acetylation of histones at DNA regulatory elements plays a critical role in transcriptional activation. Histones are also modified by other acyl moieties, including crotonyl, yet the mechanisms that govern acetylation versus crotonylation and the functional consequences of this "choice" remain unclear. We show that the coactivator p300 has both crotonyltransferase and acetyltransferase activities, and that p300-catalyzed histone crotonylation directly stimulates transcription to a greater degree than histone acetylation. Levels of histone crotonylation are regulated by the cellular concentration of crotonyl-CoA, which can be altered through genetic and environmental perturbations. In a cell-based model of transcriptional activation, increasing or decreasing the cellular concentration of crotonyl-CoA leads to enhanced or diminished gene expression, respectively, which correlates with the levels of histone crotonylation flanking the regulatory elements of activated genes. Our findings support a general principle wherein differential histone acylation (i.e., acetylation versus crotonylation) couples cellular metabolism to the regulation of gene expression.
Pub.: 31 Mar '15, Pinned: 25 Apr '18