Suha Saleh

An in-depth comparison of latent HIV-1 reactivation in multiple cell model systems and resting CD4+ T cells from aviremic patients

The possibility of HIV-1 eradication has been limited by the existence of latently infected cellular reservoirs. Studies to examine control of HIV latency and potential reactivation have been hindered by the small numbers of latently infected cells found in vivo. Major conceptual leaps have been facilitated by the use of latently infected T cell lines and primary cells. However, notable differences exist among cell model systems. Furthermore, screening efforts in specific cell models have identified drug candidates for “anti-latency” therapy, which often fail to reactivate HIV uniformly across different models. Therefore, the activity of a given drug candidate, demonstrated in a particular cellular model, cannot reliably predict its activity in other cell model systems or in infected patient cells, tested ex vivo. This situation represents a critical knowledge gap that adversely affects our ability to identify promising treatment compounds and hinders the advancement of drug testing into relevant animal models and clinical trials. To begin to understand the biological characteristics that are inherent to each HIV-1 latency model, we compared the response properties of five primary T cell models, four J-Lat cell models and those obtained with a viral outgrowth assay using patient-derived infected cells. A panel of thirteen stimuli that are known to reactivate HIV by defined mechanisms of action was selected and tested in parallel in all models. Our results indicate that no single in vitro cell model alone is able to capture accurately the ex vivo response characteristics of latently infected T cells from patients. Most cell models demonstrated that sensitivity to HIV reactivation was skewed toward or against specific drug classes. Protein kinase C agonists and PHA reactivated latent HIV uniformly across models, although drugs in most other classes did not.

Establishment of HIV-1 latency in resting CD4+ T cells depends on chemokine-induced changes in the actin cytoskeleton

Eradication of HIV-1 with highly active antiretroviral therapy (HAART) is not possible due to the persistence of long-lived, latently infected resting memory CD4+ T cells. We now show that HIV-1 latency can be established in resting CD4+ T cells infected with HIV-1 after exposure to ligands for CCR7 (CCL19), CXCR3 (CXCL9 and CXCL10), and CCR6 (CCL20) but not in unactivated CD4+ T cells. The mechanism did not involve cell activation or significant changes in gene expression, but was associated with rapid dephosphorylation of cofilin and changes in filamentous actin. Incubation with chemokine before infection led to efficient HIV-1 nuclear localization and integration and this was inhibited by the actin stabilizer jasplakinolide. We propose a unique pathway for establishment of latency by direct HIV-1 infection of resting CD4+ T cells during normal chemokine-directed recirculation of CD4+ T cells between blood and tissue.

Expression and reactivation of HIV in a chemokine induced model of HIV latency in primary resting CD4+ T cells

BackgroundWe recently described that HIV latent infection can be established in vitro following incubation of resting CD4+ T-cells with chemokines that bind to CCR7. The main aim of this study was to fully define the post-integration blocks to virus replication in this model of CCL19-induced HIV latency.ResultsHigh levels of integrated HIV DNA but low production of reverse transcriptase (RT) was found in CCL19-treated CD4+ T-cells infected with either wild type (WT) NL4.3 or single round envelope deleted NL4.3 pseudotyped virus (NL4.3- Δenv). Supernatants from CCL19-treated cells infected with either WT NL4.3 or NL4.3- Δenv did not induce luciferase expression in TZM-bl cells, and there was no expression of intracellular p24. Following infection of CCL19-treated CD4+ T-cells with NL4.3 with enhanced green fluorescent protein (EGFP) inserted into the nef open reading frame (NL4.3- Δnef-EGFP), there was no EGFP expression detected. These data are consistent with non-productive latent infection of CCL19-treated infected CD4+ T-cells. Treatment of cells with phytohemagluttinin (PHA)/IL-2 or CCL19, prior to infection with WT NL4.3, resulted in a mean fold change in unspliced (US) RNA at day 4 compared to day 0 of 21.2 and 1.1 respectively (p = 0.01; n = 5), and the mean expression of multiply spliced (MS) RNA was 56,000, and 5,000 copies/million cells respectively (p = 0.01; n = 5). In CCL19-treated infected CD4+ T-cells, MS-RNA was detected in the nucleus and not in the cytoplasm; in contrast to PHA/IL-2 activated infected cells where MS RNA was detected in both. Virus could be recovered from CCL19-treated infected CD4+ T-cells following mitogen stimulation (with PHA and phorbyl myristate acetate (PMA)) as well as TNFα, IL-7, prostratin and vorinostat.ConclusionsIn this model of CCL19-induced HIV latency, we demonstrate HIV integration without spontaneous production of infectious virus, detection of MS RNA in the nucleus only, and the induction of virus production with multiple activating stimuli. These data are consistent with ex vivo findings from latently infected CD4+ T-cells from patients on combination antiretroviral therapy, and therefore provide further support of this model as an excellent in vitro model of HIV latency.

Entinostat is a histone deacetylase inhibitor selective for class 1 histone deacetylases and activates HIV production from latently infected primary T cells

Objectives:To compare the potency, toxicity and mechanism of action of multiple histone deacetylase inhibitors (HDACi) in activating HIV production from latency. Design:In-vitro analysis of HDACi in a primary T-cell model of HIV latency and latently infected cell lines. Methods:Latently infected chemokine ligand 19 (CCL19)-treated CD4+ T cells and the latently infected cell lines ACH2 and J-Lat were treated with a panel of HDACi, including entinostat, vorinostat, panonbinostat and MCT3. Viral production and cell viability were compared. Expression of cellular HDACs was measured by western blot and PCR. Association of HDACs with the HIV long-terminal repeat (LTR) using latently infected CCL19-treated primary CD4+ T cells in the presence and absence of specific HDACi was determined by chromatin immunoprecipitation (ChIP). Results:We demonstrated considerable variation in the potency and toxicity of HDACi in latently infected primary CD4+ T cells and cell lines. All HDACi tested activated HIV production in latently infected primary T cells with greatest potency demonstrated with entinostat and vorinostat and greatest toxicity with panobinostat. Following the addition of HDACi in vitro, there were no changes in markers of T-cell activation or expression of the HIV coreceptors chemokine (C-X-C motif) receptor 4 (CXCR4) or chemokine (C-C motif) receptor type 5 (CCR5). ChIP analysis of latently infected CCL19-treated primary CD4+ T cells showed binding by HDAC1, HDAC2 and HDAC3 to the LTR with removal of HDAC1 and HDAC2 following treatment with the HDACi vorinostat and HDAC1 only following treatment with entinostat. Conclusion:The HDACi entinostat, selective for inhibition of class I HDACs, induced virus expression in latently infected primary CD4+ T cells making this compound an attractive novel option for future clinical trials.

Coinfection of Hepatic Cell Lines with Human Immunodeficiency Virus and Hepatitis B Virus Leads to an Increase in Intracellular Hepatitis B Surface Antigen

ABSTRACT Liver-related mortality is increased in the setting of HIV-hepatitis B virus (HBV) coinfection. However, interactions between HIV and HBV to explain this observation have not been described. We hypothesized that HIV infection of hepatocytes directly affects the life cycle of HBV. We infected human hepatic cell lines expressing HBV (Hep3B and AD38 cells) or not expressing HBV (Huh7, HepG2, and AD43 cells) with laboratory strains of HIV (NL4-3 and AD8), as well as a vesicular stomatitis virus (VSV)-pseudotyped HIV expressing enhanced green fluorescent protein (EGFP). Following HIV infection with NL4-3 or AD8 in hepatic cell lines, we observed a significant increase in HIV reverse transcriptase activity which was infectious. Despite no detection of surface CD4, CCR5, and CXCR4 by flow cytometry, AD8 infection of AD38 cells was inhibited by maraviroc and NL4-3 was inhibited by AMD3100, demonstrating that HIV enters AD38 hepatic cell lines via CCR5 or CXCR4. High-level infection of AD38 cells (50%) was achieved using VSV-pseudotyped HIV. Coinfection of the AD38 cell line with HIV did not alter the HBV DNA amount or species as determined by Southern blotting or nucleic acid signal amplification. However, coinfection with HIV was associated with a significant increase in intracellular HBsAg when measured by Western blotting, quantitative HBsAg, and fluorescence microscopy. We conclude that HIV infection of HBV-infected hepatic cell lines significantly increased intracellular HBsAg but not HBV DNA synthesis and that increased intrahepatic HBsAg secondary to direct infection by HIV may contribute to accelerated liver disease in HIV-HBV-coinfected individuals.

The novel histone deacetylase inhibitors metacept-1 and metacept-3 potently increase HIV-1 transcription in latently infected cells.

We investigated the ability of several novel class I histone deacetylase inhibitors to activate HIV-1 transcription in latently infected cell lines. Oxamflatin, metacept-1 and metacept-3 induced high levels of HIV-1 transcription in latently infected T cell and monocytic cells lines, were potent inhibitors of histone deacetylase activity and caused preferential cell death in transcriptionally active cells. Although these compounds had potent in-vitro activity, their cytotoxicity may limit their use in patients.

Myeloid dendritic cells induce HIV-1 latency in non-proliferating CD4+ T cells.

Latently infected resting CD4+ T cells are a major barrier to HIV cure. Understanding how latency is established, maintained and reversed is critical to identifying novel strategies to eliminate latently infected cells. We demonstrate here that co-culture of resting CD4+ T cells and syngeneic myeloid dendritic cells (mDC) can dramatically increase the frequency of HIV DNA integration and latent HIV infection in non-proliferating memory, but not naïve, CD4+ T cells. Latency was eliminated when cell-to-cell contact was prevented in the mDC-T cell co-cultures and reduced when clustering was minimised in the mDC-T cell co-cultures. Supernatants from infected mDC-T cell co-cultures did not facilitate the establishment of latency, consistent with cell-cell contact and not a soluble factor being critical for mediating latent infection of resting CD4+ T cells. Gene expression in non-proliferating CD4+ T cells, enriched for latent infection, showed significant changes in the expression of genes involved in cellular activation and interferon regulated pathways, including the down-regulation of genes controlling both NF-κB and cell cycle. We conclude that mDC play a key role in the establishment of HIV latency in resting memory CD4+ T cells, which is predominantly mediated through signalling during DC-T cell contact.

HIV persistence: Chemokines and their signalling pathways

Latently infected resting CD4+ T cells are the major barrier to curing HIV. We have recently demonstrated that chemokines, which bind to the chemokine receptors CCR7, CXCR3 and CCR6, facilitate efficient HIV nuclear localisation and integration in resting CD4+ T cells, leading to latency. As latently infected cells are enriched in lymphoid tissues, where chemokines are highly concentrated, this may provide a mechanism for the generation of latently infected cells in vivo. Here we review the role of chemokines in HIV persistence; the main signalling pathways that are involved; and how these pathways may be exploited to develop novel strategies to reduce or eliminate latently infected cells.

The antibody response to Plasmodium falciparum Merozoite Surface Protein 4: comparative assessment of specificity and growth inhibitory antibody activity to infection-acquired and immunization-induced epitopes

BackgroundMalaria remains a global public health challenge. It is widely believed that an effective vaccine against malaria will need to incorporate multiple antigens from the various stages of the parasites complex life cycle. Plasmodium falciparum Merozoite Surface Protein 4 (MSP4) is a vaccine candidate that has been selected for development for inclusion in an asexual stage subunit vaccine against malaria.MethodsNine monoclonal antibodies (Mabs) were produced against Escherichia coli-expressed recombinant MSP4 protein and characterized. These Mabs were used to develop an MSP4-specific competition ELISA to test the binding specificity of antibodies present in sera from naturally P. falciparum-infected individuals from a malaria endemic region of Vietnam. The Mabs were also tested for their capacity to induce P. falciparum growth inhibition in vitro and compared against polyclonal rabbit serum raised against recombinant MSP4ResultsAll Mabs reacted with native parasite protein and collectively recognized at least six epitopes. Four of these Mabs recognize reduction-sensitive epitopes within the epidermal growth factor-like domain found near the C-terminus of MSP4. These sera were shown to contain antibodies capable of inhibiting the binding of the six Mabs indicating infection-acquired responses to the six different epitopes of MSP4. All of the six epitopes were readily recognized by human immune sera. Competition ELISA titres varied from 20 to 640, reflecting heterogeneity in the intensity of the humoral response against the protein among different individuals. The IgG responses during acute and convalescent phases of infection were higher to epitopes in the central region than to other parts of MSP4. Immunization with full length MSP4 in Freunds adjuvant induced rabbit polyclonal antisera able to inhibit parasite growth in vitro in a manner proportionate to the antibody titre. By contrast, polyclonal antisera raised to individual recombinant fragments rMSP4A, rMSP4B, rMSP4C and rMSP4D gave negligible inhibition. Similarly, murine Mabs alone or in combination did not inhibit parasite growth.ConclusionsThe panel of MSP4-specific Mabs produced were found to recognize six distinct epitopes that are also targeted by human antibodies during natural malaria infection. Antibodies directed to more than three epitope regions spread across MSP4 are likely to be required for P. falciparum growth inhibition in vitro.

Entry of HIV in primary human resting CD4(+) T cells pretreated with the chemokine CCL19.

Resting CD4+ T cells latently infected with HIV are a major barrier to a cure and therefore antiretroviral therapy is required life-long. There are two major potential pathways leading to the establishment of latency. One pathway, which we refer to as postactivation latency, occurs with the reversion of an activated infected CD4+ T cell to the resting memory state with an integrated silenced provirus. The other pathway, preactivation latency, occurs via direct infection of resting CD4+ T cells. The relative contribution in vivo of preactivation and postactivation latency is unclear, but latency can be established in vitro via both pathways.1 We have previously demonstrated that although unstimulated resting CD4+ T cells are relatively resistant to HIV infection, incubation of resting CD4+ T cells with chemokines that bind the chemokine receptors, CCR7, CXCR3, and CCR6, which are all highly expressed on resting CD4+T cells, facilitates latent infection in vitro.2,3 Pretreatment with the chemokine CCL19, the ligand for CCR7, facilitated rapid nuclear localization and efficient integration. This was in part mediated via CCL19-induced changes in the actin cytoskeleton.3 Our aim here was to visualize the early events following HIV entry into a resting CD4+ T cell. We used fluorescent HIV to infect CCL19-treated resting CD4+ T cells to track the migration of virus to the nucleus. Resting CD4+ T cells were incubated with 30 nM CCL19 and infected at an MOI of 0.1 with HIVNL4.3 that was dual labeled with green fluorescent protein (GFP) fused to HIV Vpr and S15tomato fused to the viral membrane. GFPVpr associates with HIV cores and tracks HIV complexes in the cytoplasm of target cells. S15tomato is a fluorescent variant of S15mCherry that is no longer visible when virus particles fuse to target cells.4 Therefore, HIV that has fused and entered a cell can be identified as GFPVpr+ S15tomato−.4 Two hours after the addition of virus, cells were fixed and filamentous actin (F-actin) was stained using Alexa Fluor 350.phalloidin (Molecular Probes). The cells were placed in a Labtek II chamber slide and images were captured in a z series using a CoolSNAP camera (Photometrics) on a DeltaVision microscope (100×1.4 numerical aperture oil immersion lens, Applied Precision). Images were deconvolved using softWoRx deconvolution software (Applied Precision). A single z section of a deconvolved image is shown. Cells were also cultured for 4 days and quantification of integrated DNA was performed using Alu-LTR real time PCR.3 Reverse transcriptase (RT) was quantified in supernatant. The frequency of integrated HIV was 92,000 copies/106 CD4+ T cells and there was minimal RT production consistent with latent infection. In the image shown in Fig. 1, fused HIV complexes (GFPVpr+ S15tomato−) that have penetrated cortical F-actin at the cell periphery and are located in the resting CD4+ T cell cytoplasm can be seen. We are now examining how HIV interacts with other components of the cell cytoskeleton and defining key cellular proteins required for rapid transit of HIV to the nucleus in CCL19-treated resting CD4+ T cells. FIG. 1. Fused HIV in the cytoplasm of CCL19-treated resting CD4+ T cells. Resting CD4+ T cells pretreated with 30 nM CCL19 were infected for 2 h with HIVNL4.3 dual labeled with GFPVpr (yellow) and S15tomato (majenta). Fixed cells were stained ...