Activation of HIV-1 expression in latently infected CD4+ T cells by the small molecule PKC412

A Canadian Survey of Research on HIV-1 Latency-Where Are We Now and Where Are We Heading?

Worldwide, almost 40 million people are currently living with HIV-1. The implementation of cART inhibits HIV-1 replication and reduces viremia but fails to eliminate HIV-1 from latently infected cells. These cells are considered viral reservoirs from which HIV-1 rebounds if cART is interrupted. Several efforts have been made to identify these cells and their niches. There has been little success in diminishing the pool of latently infected cells, underscoring the urgency to continue efforts to fully understand how HIV-1 establishes and maintains a latent state. Reactivating HIV-1 expression in these cells using latency-reversing agents (LRAs) has been successful, but only in vitro. This review aims to provide a broad view of HIV-1 latency, highlighting Canadian contributions toward these aims. We will summarize the research efforts conducted in Canadian labs to understand the establishment of latently infected cells and how this informs curative strategies, by reviewing how HIV latency is established, which cells are latently infected, what methodologies have been developed to characterize them, how new compounds are discovered and evaluated as potential LRAs, and what clinical trials aim to reverse latency in people living with HIV (PLWH).

Irreversible Loss of HIV-1 Proviral Competence in Myeloid Cells upon Suppression of NF-κB Activity

Although antiretroviral therapy (ART) sustains potent suppression of plasma viremia in people with HIV-1 infection (PWH), reservoirs of viral persistence rekindle viral replication and viremia if ART is halted. Understanding the nature of viral reservoirs and their persistence mechanisms remains fundamental to further research aiming to eliminate them and achieve ART-free viral remission or virological cure. CD4+ T-cell models have helped to define the mechanisms that regulate HIV-1 latency as well as to identify potential latency manipulators, and we similarly hoped to extend this understanding to macrophages given the increasing evidence of a role for myeloid cells in HIV-1 persistence under ART (T. Igarashi, C. R. Brown, Y. Endo, A. Buckler-White, et al., Proc Natl Acad Sci U S A 98:658-663, 2001, https://doi.org/10.1073/pnas.98.2.658; J. M. Orenstein, C. Fox, and S. M. Wahl, Science 276:1857-1861, 1997, https://doi.org/10.1126/science.276.5320.1857). In the pursuit of a primary cell model of macrophage latency using monocyte-derived macrophages (MDMs), we observed that NF-κB inhibition, originally intended to promote synchronous entry into a latent state, led to an irreversible loss of proviral competence. Proviruses were refractory to latency reversal agents (LRAs), yet host cell functions such as phagocytic capacity and cytokine production remained intact. Even after NF-κB inhibition was relieved and NF-κB action was restored, proviruses remained refractory to reactivation. Agents that interfere with the NF-κB-HIV-1 axis in myeloid cells may provide an approach with which to render myeloid cell reservoirs inert. IMPORTANCE Although HIV-1 infection can be suppressed using antiretroviral therapy, it cannot yet be cured. This is because HIV-1 integrates itself into host cells and may become dormant but also remains ready to emerge from such reservoirs when antiretroviral therapy stops. The CD4+ T cell has been the most actively investigated cell type in reservoir research due to its prominent role in hosting HIV-1; however, HIV-1 can infect and fall latent in myeloid cells, and therefore, their role must also be assessed in pursuit of a cure. Here, we show that caffeic acid and resveratrol, two nontoxic chemicals, both of which interfere with the same set of host mechanisms, can each prevent HIV-1 reactivation from latency in myeloid cells even after either chemical is removed and previous cell functionality is restored. Strategies to interfere with latency underlie the future of HIV-1 cure research, and our findings help to focus such strategies on an important but often neglected cell type.

A novel selective histone deacetylase I inhibitor CC-4a activates latent HIV-1 through NF-κB pathway

AIMS

The fact that HIV-1 inside human bodies can perform reverse transcription and integrate resultant DNA into host chromosome remains a challenge in AIDS treatment. "Shock and kill" strategy was proposed to achieve the functional cure, which requested latency reactivating agents (LRAs) to reactivate latent HIV-1 and then extirpate viruses and infected cells with antiviral agents and the immune system. However, there are no feasible LRAs clinically applied. Herein, we examined a synthesized HDAC I inhibitor, CC-4a, in reactivating latent HIV-1 and investigated its mechanisms.

MATERIALS AND METHODS

Two HIV-1 infected cell models and human PBMCs were used in this study. Flow cytometry, ELISA, luciferase, and RT-PCR assay were used to analyze the expression of viral protein and mRNA. The mechanisms were explored by using cytoplasmic nuclear protein isolation and western blotting assays.

KEY FINDINGS

CC-4a could successfully reactivate latent HIV-1 at the protein and gene levels with low cytotoxicity. Intriguingly, CC-4a showed the ability to induce apoptosis in HIV-1 infected cell models. CC-4a exerted a synergistic activation effect with prostratin without triggering global T cell activation and inflammatory factor storm. It was further found that CC-4a down-regulated the expressions of CCR5 and CD4. Moreover, CC-4a together with antiviral drugs was proved to antagonize HIV-1 without mutual interference. Finally, the enhanced histone acetylation and activated NF-κB pathway were detected in CC-4a mechanisms.

SIGNIFICANCE

The results suggested that CC-4a activated latent HIV-1 and showed promising clinical applications, demonstrating that CC-4a played a role in HIV-1 eradication in "shock and kill" strategy.

Low-Level Ionizing Radiation Induces Selective Killing of HIV-1-Infected Cells with Reversal of Cytokine Induction Using mTOR Inhibitors

HIV-1 infects 39.5 million people worldwide, and cART is effective in preventing viral spread by reducing HIV-1 plasma viral loads to undetectable levels. However, viral reservoirs persist by mechanisms, including the inhibition of autophagy by HIV-1 proteins (i.e., Nef and Tat). HIV-1 reservoirs can be targeted by the “shock and kill” strategy, which utilizes latency-reversing agents (LRAs) to activate latent proviruses and immunotarget the virus-producing cells. Yet, limitations include reduced LRA permeability across anatomical barriers and immune hyper-activation. Ionizing radiation (IR) induces effective viral activation across anatomical barriers. Like other LRAs, IR may cause inflammation and modulate the secretion of extracellular vesicles (EVs). We and others have shown that cells may secrete cytokines and viral proteins in EVs and, therefore, LRAs may contribute to inflammatory EVs. In the present study, we mitigated the effects of IR-induced inflammatory EVs (i.e., TNF-α), through the use of mTOR inhibitors (mTORi; Rapamycin and INK128). Further, mTORi were found to enhance the selective killing of HIV-1-infected myeloid and T-cell reservoirs at the exclusion of uninfected cells, potentially via inhibition of viral transcription/translation and induction of autophagy. Collectively, the proposed regimen using cART, IR, and mTORi presents a novel approach allowing for the targeting of viral reservoirs, prevention of immune hyper-activation, and selectively killing latently infected HIV-1 cells.

Diversity of small molecule HIV-1 latency reversing agents identified in low- and high-throughput small molecule screens

The latency phenomenon produced by human immunodeficiency virus (HIV-1) prevents viral clearance by current therapies, and consequently development of a cure for HIV-1 disease represents a formidable challenge. Research over the past decade has resulted in identification of small molecules that are capable of exposing HIV-1 latent reservoirs, by reactivation of viral transcription, which is intended to render these infected cells sensitive to elimination by immune defense recognition or apoptosis. Molecules with this capability, known as latency-reversing agents (LRAs) could lead to realization of proposed HIV-1 cure strategies collectively termed "shock and kill," which are intended to eliminate the latently infected population by forced reactivation of virus replication in combination with additional interventions that enhance killing by the immune system or virus-mediated apoptosis. Here, we review efforts to discover novel LRAs via low- and high-throughput small molecule screens, and summarize characteristics and biochemical properties of chemical structures with this activity. We expect this analysis will provide insight toward further research into optimized designs for new classes of more potent LRAs.

The landscape of alternative splicing in HIV-1 infected CD4 T-cells

Background

Elucidating molecular mechanisms that are altered during HIV-1 infection may provide a better understanding of the HIV-1 life cycle and how it interacts with infected T-cells. One such mechanism is alternative splicing (AS), which has been studied for HIV-1 itself, but no systematic analysis has yet been performed on infected T-cells. We hypothesized that AS patterns in infected T-cells may illuminate the molecular mechanisms underlying HIV-1 infection and identify candidate molecular markers for specifically targeting infected T-cells.

Methods

We downloaded previously published raw RNA-seq data obtained from HIV-1 infected and non-infected T-cells. We estimated percent spliced in (PSI) levels for each AS exon, then identified differential AS events in the infected cells (FDR < 0.05, PSI difference > 0.1). We performed functional gene set enrichment analysis on the genes with differentially expressed AS exons to identify their functional roles. In addition, we used RT-PCR to validate differential alternative splicing events in cyclin T1 (CCNT1) as a case study.

Results

We identified 427 candidate genes with differentially expressed AS exons in infected T-cells, including 20 genes related to cell surface, 35 to kinases, and 121 to immune-related genes. In addition, protein-protein interaction analysis identified six essential subnetworks related to the viral life cycle, including Transcriptional regulation by TP53, Class I MHC mediated antigen, G2/M transition, and late phase of HIV life cycle. CCNT1 exon 7 was more frequently skipped in infected T-cells, leading to loss of the key Cyclin_N motif and affecting HIV-1 transcriptional elongation.

Conclusions

Our findings may provide new insight into systemic host AS regulation under HIV-1 infection and may provide useful initial candidates for the discovery of new markers for specifically targeting infected T-cells.

Characterization of the Role of Host Cellular Factor Histone Deacetylase 10 during HIV-1 Replication

To date, a series of histone deacetylases have been documented to restrict HIV-1 replication at different steps. In this study, we identified histone deacetylase 10 (HDAC10) as an inhibitory factor against HIV-1 replication. Our results showed that endogenous HDAC10 is downregulated at the transcriptional level during HIV-1 replication. By knocking down HDAC10 in CD4+ T cells with specific shRNAs, we observed that the downregulation of HDAC10 significantly facilitates viral replication. Moreover, RQ-PCR analysis revealed that the downregulation of HDAC10 increased viral integrated DNA. Further, we identified that HDAC10 interacts with the HIV-1 integrase (IN) and that the region of residues from 55 to 165 in the catalytic domain of IN is required for HDAC10 binding. Interestingly, we found that the interaction between HDAC10 and IN specifically decreases the interaction between IN and cellular protein lens epithelium-derived growth factor (LEDGF/p75), which consequently leads to the inhibition of viral integration. In addition, we have investigated the role of HDAC10 in the late stage of viral replication by detecting the infectiousness of progeny virus produced from HDAC10 knockdown cells or HDAC10 overexpressing cells and revealed that the progeny virus infectivity is increased in the HDAC10 downregulated cells, but decreased in the HDAC10 overexpressed cells. Overall, these findings provide evidence that HDAC10 acts as a cellular inhibitory factor at the early and late stages of HIV-1 replication.

Incorporation of Ebola glycoprotein into HIV particles facilitates dendritic cell and macrophage targeting and enhances HIV-specific immune responses

The development of an effective vaccine against HIV infection remains a global priority. Dendritic cell (DC)-based HIV immunotherapeutic vaccine is a promising approach which aims at optimizing the HIV-specific immune response using primed DCs to promote and enhance both the cellular and humoral arms of immunity. Since the Ebola virus envelope glycoprotein (EboGP) has strong DC-targeting ability, we investigated whether EboGP is able to direct HIV particles towards DCs efficiently and promote potent HIV-specific immune responses. Our results indicate that the incorporation of EboGP into non-replicating virus-like particles (VLPs) enhances their ability to target human monocyte-derived dendritic cells (MDDCs) and monocyte-derived macrophages (MDMs). Also, a mucin-like domain deleted EboGP (EboGPΔM) can further enhanced the MDDCs and MDMs-targeting ability. Furthermore, we investigated the effect of EboGP on HIV immunogenicity in mice, and the results revealed a significantly stronger HIV-specific humoral immune response when immunized with EboGP-pseudotyped HIV VLPs compared with those immunized with HIV VLPs. Splenocytes harvested from mice immunized with EboGP-pseudotyped HIV VLPs secreted increased levels of macrophage inflammatory proteins-1α (MIP-1α) and IL-4 upon stimulation with HIV Env and/or Gag peptides compared with those harvested from mice immunized with HIV VLPs. Collectively, this study provides evidence for the first time that the incorporation of EboGP in HIV VLPs can facilitate DC and macrophage targeting and induce more potent immune responses against HIV.

Dual effect of the broad spectrum kinase inhibitor midostaurin in acute and latent HIV-1 infection

Midostaurin is a multi-kinase inhibitor with antineoplastic activity. We assessed the capacity of midostaurin to affect early and late steps of HIV-1 infection and to reactivate HIV-1 latently infected cells, alone or in combination with histone deacetylase inhibitors (HDACi) known to act as latency-reversing agents (LRA). Acute HIV-1 infection was assessed by flow cytometry in three cell types treated with midostaurin in the presence or absence of SAMHD1. Non-infected cells were treated with midostaurin and harvested for Western blot analysis. Macrophage infections were also measured by quantitative RT-PCR. HIV-1 latency reactivation was assessed in several latency models. Midostaurin induced G2/M arrest and inhibited CDK2, preventing the phosphorylation of SAMHD1 associated to inhibition of its dNTPase activity. In the presence of SAMHD1, midostaurin blocked HIV-1 DNA formation and viral replication. However, following Vpx-mediated SAMHD1 degradation, midostaurin increased viral transcripts and virus replication. In three out of four HIV-1 latency models, including primary CD4⁺ T cells, midostaurin effectively reversed HIV-1 latency and was synergistic in combination with LRA vorinostat and panobinostat. Our study describes a dual effect for midostaurin in HIV-1 infection, antiviral or proviral depending on SAMHD1 activation, and highlights a role for active SAMHD1 in regulating the activity of potential HIV-1 latency reversal agents.

N6-Methyladenosine and Viral Infection

N⁶-methyladenosine (m⁶A), as a dynamic posttranscriptional RNA modification, recently gave rise to the field of viral epitranscriptomics. The interaction between virus and host is affected by m⁶A. Multiple m⁶A-modified viral RNAs have been observed. The epitranscriptome of m⁶A in host cells are altered after viral infection. The expression of viral genes, the replication of virus and the generation of progeny virions are influenced by m⁶A modifications in viral RNAs during virus infection. Meanwhile, the decorations of m⁶A in host mRNAs can make viral infections more likely to happen or can enhance the resistance of host to virus infection. However, the mechanism of m⁶A regulation in viral infection and host immune response has not been thoroughly elucidated to date. With the development of sequencing-based biotechnologies, transcriptome-wide mapping of m⁶A in viruses has been achieved, laying the foundation for expanding its functions and corresponding mechanisms. In this report, we summarize the positive and negative effects of m⁶A in distinct viral infection. Given the increasingly important roles of m⁶A in diverse viruses, m⁶A represents a novel potential target for antiviral therapy.

New approaches for the enhancement of chimeric antigen receptors for the treatment of HIV

HIV infection continues to be a life-long chronic disease in spite of the success of antiretroviral therapy (ART) in controlling viral replication and preventing disease progression. However, because of the high cost of treatment, severe side effects, and inefficiency in curing the disease with ART, there is a call for alternative therapies that will provide a functional cure for HIV. Cytotoxic T lymphocytes (CTLs) are vital in the control and clearance of viral infections and therefore immune-based therapies have attempted to engineer HIV-specific CTLs that would be able to clear the infection from the body. The development of chimeric antigen receptors (CARs) provides an opportunity to engineer superior HIV-specific CTLs that will be independent of the major histocompatibility complex for target recognition. A CD4-based CAR has been previously tested in clinical trials to test the antiviral efficacy of peripheral T cells armed with this CD4-based CAR. The results from these clinical trials showed the safety and feasibility of CAR T cell therapy for HIV infection; however, minimal antiviral efficacy was seen. In this review, we will discuss the various strategies being developed to enhance the therapeutic potency of anti-HIV CARs with the goal of generating superior antiviral responses that will lead to life-long HIV immunity and clearance of the virus from the body.

Midostaurin: a novel therapeutic agent for patients with FLT3-mutated acute myeloid leukemia and systemic mastocytosis

The development of FLT3-targeted inhibitors represents an important paradigm shift in the management of patients with highly aggressive fms-like tyrosine kinase 3-mutated (FLT3-mut) acute myeloid leukemia (AML). Midostaurin is an orally administered type III tyrosine kinase inhibitor which in addition to FLT3 inhibits c-kit, platelet-derived growth factor receptors, src, and vascular endothelial growth factor receptor. Midostaurin is the first FLT3 inhibitor that has been shown to significantly improve survival in younger patients with FLT3-mut AML when given in combination with standard cytotoxic chemotherapy based on the recently completed RATIFY study. Its role for maintenance therapy after allogeneic transplantation and use in combination with hypomethylating agents for older patients with FLT3-mut has not yet been defined. Midostaurin also has recently been shown to have significant activity in systemic mastocytosis and related disorders due to its inhibitory effect on c-kit bearing a D816V mutation. Activation of downstream pathways in both of these myeloid malignancies likely plays an important role in the development of resistance, and strategies to inhibit these downstream targets may be synergistic. Incorporating patient factors and tumor characteristics, such as FLT3 mutant to wild-type allele ratios and resistance mutations, likely will be important in the optimization of midostaurin and other FLT3 inhibitors in the treatment of myeloid neoplasms.