Mohamed El-Far

HIV reservoir size and persistence are driven by T cell survival and homeostatic proliferation

HIV persists in a reservoir of latently infected CD4+ T cells in individuals treated with highly active antiretroviral therapy (HAART). Here we identify central memory (TCM) and transitional memory (TTM) CD4+ T cells as the major cellular reservoirs for HIV and find that viral persistence is ensured by two different mechanisms. HIV primarily persists in TCM cells in subjects showing reconstitution of the CD4+ compartment upon HAART. This reservoir is maintained through T cell survival and low-level antigen-driven proliferation and is slowly depleted with time. In contrast, proviral DNA is preferentially detected in TTM cells from aviremic individuals with low CD4+ counts and higher amounts of interleukin-7–mediated homeostatic proliferation, a mechanism that ensures the persistence of these cells. Our results suggest that viral eradication might be achieved through the combined use of strategic interventions targeting viral replication and, as in cancer, drugs that interfere with the self renewal and persistence of proliferating memory T cells.

Programmed death-1–induced interleukin-10 production by monocytes impairs CD4 + T cell activation during HIV infection

Viral replication and microbial translocation from the gut to the blood during HIV infection lead to hyperimmune activation, which contributes to the decline in CD4+ T cell numbers during HIV infection. Programmed death-1 (PD-1) and interleukin-10 (IL-10) are both upregulated during HIV infection. Blocking interactions between PD-1 and programmed death ligand-1 (PD-L1) and between IL-10 and IL-10 receptor (IL-10R) results in viral clearance and improves T cell function in animal models of chronic viral infections. Here we show that high amounts of microbial products and inflammatory cytokines in the plasma of HIV-infected subjects lead to upregulation of PD-1 expression on monocytes that correlates with high plasma concentrations of IL-10. Triggering of PD-1 expressed on monocytes by PD-L1 expressed on various cell types induced IL-10 production and led to reversible CD4+ T cell dysfunction. We describe a new function for PD-1 whereby microbial products inhibit T cell expansion and function by upregulating PD-1 levels and IL-10 production by monocytes after binding of PD-1 by PD-L1.

Peripheral Blood CCR4+CCR6+ and CXCR3+CCR6+ CD4+ T Cells Are Highly Permissive to HIV-1 Infection

There is limited knowledge on the identity of primary CD4+ T cell subsets selectively targeted by HIV-1 in vivo. In this study, we established a link between HIV permissiveness, phenotype/homing potential, and lineage commitment in primary CD4+ T cells. CCR4+CCR6+, CCR4+CCR6−, CXCR3+CCR6+, and CXCR3+CCR6− T cells expressed cytokines and transcription factors specific for Th17, Th2, Th1Th17, and Th1 lineages, respectively. CCR4+CCR6+ and CXCR3+CCR6+ T cells expressed the HIV coreceptors CCR5 and CXCR4 and were permissive to R5 and X4 HIV replication. CCR4+CCR6− T cells expressed CXCR4 but not CCR5 and were permissive to X4 HIV only. CXCR3+CCR6− T cells expressed CCR5 and CXCR4 but were relatively resistant to R5 and X4 HIV in vitro. Total CCR6+ T cells compared with CCR6− T cells harbored higher levels of integrated HIV DNA in treatment-naive HIV-infected subjects. The frequency of total CCR6+ T cells and those of CCR4+CCR6+ and CXCR3+CCR6+ T cells were diminished in chronically infected HIV-positive subjects, despite viral-suppressive therapy. A high-throughput analysis of cytokine profiles identified CXCR3+CCR6+ T cells as a major source of TNF-α and CCL20 and demonstrated a decreased TNF-α/IL-10 ratio in CXCR3+CCR6− T cells. Finally, CCR4+CCR6+ and CXCR3+CCR6+ T cells exhibited gut- and lymph node-homing potential. Thus, we identified CCR4+CCR6+ and CXCR3+CCR6+ T cells as highly permissive to HIV replication, with potential to infiltrate and recruit more CCR6+ T cells into anatomic sites of viral replication. It is necessary that new therapeutic strategies against HIV interfere with viral replication/persistence in discrete CCR6+ T cell subsets.

CD160 and PD-1 Co-Expression on HIV-Specific CD8 T Cells Defines a Subset with Advanced Dysfunction

Chronic viral infections lead to persistent CD8 T cell activation and functional exhaustion. Expression of programmed cell death-1 (PD-1) has been associated to CD8 T cell dysfunction in HIV infection. Herein we report that another negative regulator of T cell activation, CD160, was also upregulated on HIV-specific CD8 T lymphocytes mostly during the chronic phase of infection. CD8 T cells that expressed CD160 or PD-1 were still functional whereas co-expression of CD160 and PD-1 on CD8 T cells defined a novel subset with all the characteristics of functionally exhausted T cells. Blocking the interaction of CD160 with HVEM, its natural ligand, increased HIV-specific CD8 T cell proliferation and cytokine production. Transcriptional profiling showed that CD160−PD-1+CD8 T cells encompassed a subset of CD8+ T cells with activated transcriptional programs, while CD160+PD-1+ T cells encompassed primarily CD8+ T cells with an exhausted phenotype. The transcriptional profile of CD160+PD-1+ T cells showed the downregulation of the NFκB transcriptional node and the upregulation of several inhibitors of T cell survival and function. Overall, we show that CD160 and PD-1 expressing subsets allow differentiating between activated and exhausted CD8 T cells further reinforcing the notion that restoration of function will require multipronged approaches that target several negative regulators.

Memory CCR6+CD4+ T Cells Are Preferential Targets for Productive HIV Type 1 Infection Regardless of Their Expression of Integrin β7

HIV type 1 infection is associated with a rapid depletion of Th17 cells from the GALT. The chemokine receptor CCR6 is a marker for Th17 lineage polarization and HIV permissiveness in memory CD4+ T cells. CCR6+ T cells have the potential to migrate into the GALT via the gut-homing integrin α4β7, a newly identified HIV-gp120 binding receptor. In this study, we investigated whether memory T cells coexpressing CCR6 and integrin β7 are selective HIV targets and whether retinoic acid (RA)-induced imprinting for gut-homing selectively increases CCR6+ T cell permissiveness to infection. We demonstrated that β7−R6+ and β7+R6+ compared with β7−R6− and β7+R6− T cells were highly permissive to HIV, produced Th17 cytokines, and their frequency was decreased in the peripheral blood of HIV-infected subjects. RA upregulated integrin α4 and β7 coexpression in both CCR6+ and CCR6− T cells, but increased HIV permissiveness selectively in CCR6+ T cells via entry (CCR5 upregulation) and postentry mechanisms. In conclusion, these results demonstrate that CCR6, but not the integrin β7, is a discriminative marker for memory T cells imprinted with a transcriptional program favorable to HIV replication. Nevertheless, given the ability of integrin β7 to regulate cell migration into the GALT and bind HIV-gp120, CCR6+ T cells coexpressing integrin β7 and CCR5 might have an extraordinary ability to disseminate HIV from the portal sites of entry. Understanding the molecular mechanisms of memory CCR6+ T cell differentiation is critical for the design of new therapeutic strategies that should interfere with viral permissiveness but not Th17 lineage commitment and gut-homing potential in CCR6+ T cells.

Immunosuppressive tryptophan catabolism and gut mucosal dysfunction following early HIV infection

BACKGROUND Tryptophan (Trp) catabolism into kynurenine (Kyn) contributes to immune dysfunction in chronic human immunodeficiency virus (HIV) infection. To better define the relationship between Trp catabolism, inflammation, gut mucosal dysfunction, and the role of early antiretroviral therapy (ART), we prospectively assessed patients early after they acquired HIV. METHODS Forty patients in the early phase of infection were longitudinally followed for 12 months after receiving a diagnosis of HIV infection; 24 were untreated, and 16 were receiving ART. Kyn/Trp ratio, regulatory T-cells (Tregs) frequency, T-cell activation, dendritic cell counts, and plasma levels of gut mucosal dysfunction markers intestinal-type fatty acid-binding protein, soluble suppression of tumorigenicity 2, and lipopolysaccharide were assessed. RESULTS Compared with healthy subjects, patients in the early phase of infection presented with elevated Kyn/Trp ratios, which further increased in untreated patients but normalized in ART recipients. Accordingly, in untreated subjects, the elevated Treg frequency observed at baseline continued to increase over time. The highest CD8(+) T-cell activation was observed during the early phase of infection and decreased in untreated patients, whereas activation normalized in ART recipients. The Kyn/Trp ratio was positively associated with CD8(+) T-cell activation and levels of inflammatory cytokines (interleukin 6, interferon γ-inducible protein 10, interleukin 18, and tumor necrosis factor α) and negatively associated with dendritic cell frequencies at baseline and in untreated patients. However, ART did not normalize plasma levels of gut mucosal dysfunction markers. CONCLUSIONS Early initiation of ART normalized enhanced Trp catabolism and immune activation but did not improve plasma levels of gut mucosal dysfunction markers.

Programmed death 1: a critical regulator of T-cell function and a strong target for immunotherapies for chronic viral infections.

Purpose of reviewThe intricate balance between positive and negative signals delivered by accessory molecules is crucial to generate efficient immune responses while maintaining tolerance and preventing autoimmunity. Of these molecules, programmed death 1 has been described as a negative regulator of T-cell activation. This review will focus on current knowledge about PD-1 regulation in different diseases and discuss its potential benefits for the development of novel immune therapies. Recent findingsPD-1 has recently been shown to be upregulated on HIV-specific CD8 T cells, whereas the PD-1 expression level was significantly correlated with viral load. Blockade of the PD-1/PD-L1 interaction enhanced the capacity of HIV-specific CD8 and CD4 T cells to proliferate or secrete cytokines and cytotoxic molecules. Future manipulations of this pathway could rescue the function of exhausted CD8 and CD4 T cells. SummaryThe engagement of PD-1 with its ligands induces inhibitory signals as it blocks T-cell receptor-induced T-cell proliferation and cytokine production. The PD-1 pathway plays a crucial role in the maintenance of peripheral tolerance and the pathogenesis of cancer and chronic viral infections. Understanding the mechanisms by which PD-1 interferes with T-cell functions will pave the way for novel therapeutic immune interventions to treat these diseases.

Current topics in HIV-1 pathogenesis: The emergence of deregulated immuno-metabolism in HIV-infected subjects.

HIV-1 infection results in long-lasting activation of the immune system including elevated production of pro-inflammatory cytokine/chemokines, and bacterial product release from gut into blood and tissue compartments, which are not fully restored by antiretroviral therapies. HIV-1 has also developed numerous strategies via viral regulatory proteins to hijack cell molecular mechanisms to enhance its own replication and dissemination. Here, we reviewed the relationship between viral proteins, immune activation/inflammation, and deregulated metabolism occurring in HIV-1-infected patients that ultimately dampens the protective innate and adaptive arms of immunity. Defining precisely the molecular mechanisms related to deregulated immuno-metabolism during HIV-1 infection could ultimately help in the development of novel clinical approaches to restore proper immune functions in these patients.

Current topics in HIV pathogenesis, part 2: Inflammation drives a Warburg-like effect on the metabolism of HIV-infected subjects

HIV-1 infection leads to a depletion of CD4 T-cells associated with a persistent immune inflammation and changes in cellular metabolism. Most effort of managing HIV infection with combination of antiretroviral therapies (ART) has been focused on CD4 T-cell recovery, while control of persistent immune inflammation and metabolism were relatively underappreciated in the past. Recent discoveries on the interplay between innate immunity, inflammation (especially the inflammasome) and metabolic changes in the context of cancer and autoimmunity provide an emerging field for chronic viral infections including HIV-1. In a previous review, we described the deregulated metabolism contributing to immune dysfunctions such as alteration of memory T-cell responses, mucosal protection, and dendritic cell-related antigen presentation. Here, we summarize the latest knowledge on the detrimental influence of long-lasting inflammation and inflammasome activation induced by HIV-1, gut dysbiosis, and bacterial translocation, on metabolism during the course of viral infection. We also report on the inability of ART to fully counteract inflammation, resulting in partial metabolic improvement and leading to an insufficient decrease in the risk of non-AIDS events. Further advances in our understanding of the relationship between inflammation, altered metabolism, and long-term ART is warranted. Additionally, there is a critical need for developing new strategies to regulate the pro-inflammatory signals to enhance cellular metabolism and immune functions in order to improve the quality of life of individuals living with HIV-1.

Identification of novel HIV-1 dependency factors in primary CCR4+CCR6+Th17 cells via a genome-wide transcriptional approach

AbstractBackgroundThe HIV-1 infection is characterized by profound CD4+ T cell destruction and a marked Th17 dysfunction at the mucosal level. Viral suppressive antiretroviral therapy restores Th1 but not Th17 cells. Although several key HIV dependency factors (HDF) were identified in the past years via genome-wide siRNA screens in cell lines, molecular determinants of HIV permissiveness in primary Th17 cells remain to be elucidated.ResultsIn an effort to orient Th17-targeted reconstitution strategies, we investigated molecular mechanisms of HIV permissiveness in Th17 cells. Genome-wide transcriptional profiling in memory CD4+ T-cell subsets enriched in cells exhibiting Th17 (CCR4+CCR6+), Th1 (CXCR3+CCR6−), Th2 (CCR4+CCR6−), and Th1Th17 (CXCR3+CCR6+) features revealed remarkable transcriptional differences between Th17 and Th1 subsets. The HIV-DNA integration was superior in Th17 versus Th1 upon exposure to both wild-type and VSV-G-pseudotyped HIV; this indicates that post-entry mechanisms contribute to viral replication in Th17. Transcripts significantly enriched in Th17 versus Th1 were previously associated with the regulation of TCR signaling (ZAP-70, Lck, and CD96) and Th17 polarization (RORγt, ARNTL, PTPN13, and RUNX1). A meta-analysis using the NCBI HIV Interaction Database revealed a set of Th17-specific HIV dependency factors (HDFs): PARG, PAK2, KLF2, ITGB7, PTEN, ATG16L1, Alix/AIP1/PDCD6IP, LGALS3, JAK1, TRIM8, MALT1, FOXO3, ARNTL/BMAL1, ABCB1/MDR1, TNFSF13B/BAFF, and CDKN1B. Functional studies demonstrated an increased ability of Th17 versus Th1 cells to respond to TCR triggering in terms of NF-κB nuclear translocation/DNA-binding activity and proliferation. Finally, RNA interference studies identified MAP3K4 and PTPN13 as two novel Th17-specific HDFs.ConclusionsThe transcriptional program of Th17 cells includes molecules regulating HIV replication at multiple post-entry steps that may represent potential targets for novel therapies aimed at protecting Th17 cells from infection and subsequent depletion in HIV-infected subjects.