Unit: Immunorégulation

Director: Rogge, Lars

The Immunoregulation Group pursues three projects:

Epigenetic control of human T helper cell differentiation

We study how signals originating at the T cell receptor and at cytokine receptors are integrated to shape a T helper subset-specific gene expression program. We focus in particular on the interplay of transcription factors and chromatin remodeling complexes to induce epigenetic changes and gene transcription during T helper type 1 (Th1) cell development.

Analysis of the long-term effects of IL-2 therapy on CD4+ T lymphocytes in HIV patients

We characterize at the molecular level a novel subset of CD4+ T cells expressing high levels of the IL-2 receptor alpha chain (CD25) that appears during IL-2 therapy of HIV patients and compare it to a subset of "natural" CD4+CD25+ regulatory T cells from healthy controls, which plays a critical role in the control of autoimmunity.

A novel regulator of ubiquitination processes: the COP9 signalosome

We analyze the biochemical and molecular functions of the human COP9 signalosome and its role in regulating the ubiquitination processes that control cell proliferation and gene expression in normal and transformed cells.

Epigenetic Control of Human T Helper Cell Differentiation

Functional distinct subsets of CD4+ T lymphocytes are essential to orchestrate efficient immune responses against different types of pathogens. T helper type 1 (Th1) cells promote cell-mediated immunity and are necessary to clear the organism from intracellular pathogens whereas Th2 responses are essential to combat extracellular pathogens. On the other hand, uncontrolled Th1 responses are associated with inflammatory or autoimmune pathologies such as rheumatoid arthritis, insulin-dependent diabetes mellitus, or psoriasis and excessive Th2 responses are associated with allergies and asthma. This indicates that the development of Th1 and Th2 cells must be tightly controlled and that therapeutic modulation of immune responses may have an impact on human diseases.

The main interest of my laboratory for the past years has been to analyze the mechanisms that control the differentiation of naive CD4+ T lymphocytes into polarized Th1 and Th2 effector cells. We have established an in vitro cell culture system based on human cord blood leukocytes that allowed us to generate Th1 and Th2 subsets with strongly polarized cytokine profiles. Using this system, we identified the first cell surface marker for Th1 cells (the signaling subunit of the IL-12 receptor, IL-12Rβ2) and demonstrated IL-12Rβ2 expression on T cells purified from tissues of patients with Th1-mediated inflammatory diseases. Our laboratory further demonstrated that IFN-α/β, through activation of the transcription factor STAT4, induce Th1 differentiation in human T cells.

Naive T lymphocytes are characterized by small and extremely compact nuclei with dense heterochromatin. This "closed" chromatin structure poses a physical challenge to gene transcription and naive lymphocytes have barely detectable rates of transcription. Antigenic stimulation starts the differentiation process and results in the rapid appearance of euchromatin. Cytokines present at the time of priming play a critical role to determine the T helper cell fate. Work over the past years has established that T helper cell differentiation results in dramatic changes in the chromatin structure of genes associated with terminal differentiation (such as IFN-γ or the genes at the so-called Th2 cytokine locus, IL-4, IL-5, and IL-13). These "epigenetic" modifications are stably maintained and propagated to daughter cells and may explain the stability of the cytokine secretion profile of differentiated Th1 and Th2 cells. It is at present not known how signals from the environment (such as cytokines and TCR ligands) can induce the modifications of the chromatin structure in developing T helper cells. Ongoing studies in the laboratory address how signals originating at T cell receptor (TCR) and at cytokine receptors are integrated to determine a T helper subset-specific gene expression program. We focus our studies in particular on the interplay of transcription factors and chromatin remodeling machines in the induction of IL-12Rβ2 during Th1 cell development. Our most recent data show that chromatin remodeling by the SWI/SNF-like BAF complex and STAT4 activation synergistically induce IL-12Rβ2 expression during human Th1 cell differentiation.

Cellular and Molecular Characterization of a Novel CD4+ T Lymphocyte Subset Induced by IL-2 Immunotherapy

HIV infection results in a severe loss of CD4+ T cell number and function, which is largely responsible for the pathological features of the disease and HIV-related mortality. Recent studies have established that intermittent interleukin-2 (IL-2) therapy in combination with highly active antiretroviral therapy (HAART) leads to a substantial increase of CD4+ T cell numbers in HIV-infected individuals. IL-2 immunotherapy induces a novel subset of CD4+ T cells expressing high levels of the IL-2 receptor alpha chain (CD25) in the peripheral blood of patients. This subset can account for up to 70% of the total CD4+ T cell pool of treated patients and persists for a long time after IL-2 treatment. The phenotype of the IL-2-induced CD4+CD25+ T cell subset in HIV patients is similar to a subpopulation of CD4+ T cells that acts in a dominant way to suppress immune activation and plays a critical role in the control of autoimmunity. These cells were initially characterized by high-level expression of CD25 and have been called "natural" CD4+CD25+ T regulatory cells (Treg).

It is of paramount interest (both from a clinical and "basic science" perspective) to know whether IL-2 therapy induces T cells with regulatory properties in humans. We therefore intend to analyze the IL-2-induced CD4+CD25+ T cell subset in HIV patients in more detail. In order to get access to blood samples from IL-2-treated HIV patients, we have integrated this project as a nested study of a clinical trial organized by the ANRS (ANRS 118). The design of this trial gives us the unique opportunity to perform a longitudinal analysis of CD4+ T cell subsets during IL-2 therapy in humans. This project is part of a " Grand Programme Horizontale " at Institut Pasteur and is performed in collaboration with the teams of Jacques Thèze at Institut Pasteur and Yves Levy at the Hôpital Henri Mondor.

A Novel Regulator of Ubiquitination Processes: the COP9 Signalosome

Ubiquitin-mediated proteolysis plays an important role in many fundamental cellular processes, including cell cycle regulation, differentiation, modulation of growth factor receptors, and gene transcription. It is therefore not surprising that alterations in this pathway contribute to the pathogenesis of several diseases, among which several malignancies. The COP9 signalosome (CSN) complex has been recently identified as a novel upstream regulator of ubiquitination processes. Studies in vitro and in model organisms (yeast, plants) have indicated that the CSN may control the activity of the SCF complex, an ubiquitin ligase responsible for the degradation of many cell-cycle and transcriptional regulators (such as inhibitors of cell-cycle dependent kinases, p27Kip1 and p21, cyclins and the inhibitor of NF-kB, IkB). The CSN is conserved in mammalian cells: our laboratory and others have established a role for the human CSN in signal transduction and transcriptional control. However, the mechanisms and the targets of CSN activity in mammalian cells are still largely unknown.

We propose to study the biochemical and molecular functions of the human CSN and its role in regulating the ubiquitination processes that control cell proliferation and gene expression in normal and transformed cells. In Arabidopsis the CSN functionally interacts with the transcriptional repressor atCOP1. We have recently cloned the human COP1 orthologue and have demonstrated that huCOP1 is a novel ubiquitin-ligase that represses c-Jun transcriptional activity. We will further investigate the molecular basis of huCOP1 function and its relationship to the CSN in mammalian cells. The aim of our studies is to provide a comprehensive map of the cellular pathways that are controlled at the transcriptional level by the CSN and to broaden our comprehension of how ubiquitination processes are regulated.

Keywords: T helper cell differentiation, chromatin remodeling, HIV, regulatory T cells, Interleukin-2, ubiquitination, transcription, COP9 signalosome


Activity Reports 2005 - Institut Pasteur
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