Research project P7/39 (Research action P7)
The major objective of the present proposal is to gain insights into the mechanism whereby antigen-stimulated T lymphocytes acquire and express adequate effector function during an immune response. The long term goal of our project is to devise novel and efficient strategies for the immunotherapy of cancer. The identification of a series of tumour-specific antigens by one of the members of our consortium has paved the way to immune-based cancer therapies. To be effective, these “cancer vaccines” need to address two major challenges: (i) vaccination needs to stimulate the clonal expansion and differentiation of tumour-specific effector lymphocytes toward the desired phenotype (cytotoxic / inflammatory) and (ii) suppressor mechanisms limiting immunotherapy need to be overcome.
This long term goal requires therefore a better understanding of the molecular linguistics governing immune cells interactions, i.e. (i) the identification of molecules (costimulatory factors, cytokines and others) used by cells of the immune system to communicate and (ii) the sequence of molecular events initiated by these molecules in responsive cells and finally (iii) the evaluation of “cellular autonomous” (i.e. intrinsic) and “infectious“ (i.e. imposed by a distinct cellular subset) regulatory mechanisms opposing the development of an immune response. The project, reuniting nine different teams with both overlapping and complementary expertise in fundamental and clinical immunology will be structured around 5 work packages (WPs), as briefly summarized below:
WP1 Differentiation and function of Thelper subsets
The focus of this WP will be to characterize newly emerging subsets of lymphocytes, characterized by the secretion of selected panels of cytokines. In particular, Th2 cells, often considered as a homogenous cell population, have recently found to comprise cells displaying distinct functional characteristics. Some Th2 population bear some resemblance with follicular helper T cells (TFH), a subset of cells known to induce humoral responses characterized by the presence of long-lived plasma cells secreting high affinity antibodies. Whether TFH represent a distinct T cell subset or a transient differentiation state of cells otherwise committed to become classical Th2 (or even Th1, to be explored) is still a matter of debate and will be examined. Similarly, cells producing IL-9 (originally a bona fide Th2 cytokine) have been recognized (in particular within our consortium) as a separate subset of cells whose function will be explored within the frame of this project. Finally, groups of cytokines previously thought to be regulated in a concerted fashion (IL-17 and IL-22 in particular) have also been shown to be produced by multiple cellular sources that we wish to further characterize. Relevant in vivo models will be developed to better understand the molecular details governing the expression of these cytokines and their physiological role.
WP2 Mechanisms of immune suppression by regulatory T cells
The goal of WP2 is to dissect the molecular mechanisms of immune suppression by regulatory T cells (Tregs) in mouse models and to begin to translate this knowledge into the human context. This workpackage builds upon work of the consortium partners in identifying three major molecular mediators – TGFβ, CD27 and adenosine – and will identify the molecular mediators by which these immunosuppressive molecules function. The workpackage will also investigate the recently identified “subsets” of regulatory T cells, to determine whether they are stable lineages or alternative activation states and whether the differential activity is caused by the unique expression of suppressive molecules or by unique migration capacity. Finally, the workpackage will start to translate these murine advances into humans, by analysis of suppressive mechanisms in human Tregs, and profiling of Tregs in individuals that have broken tolerance towards self.
WP3 Understanding and reverting functional impairment of effector T cells
T cells chronically stimulated by persistent antigen often become functionally exhausted and do not respond appropriately to therapeutic vaccination. Therefore, understanding the biology of T cells chronically stimulated by persistent antigens is a prerequisite to the development of therapeutic vaccine strategies aimed at boosting more effectively endogenous T cell responses against chronic viral infections and cancers. The specific aim of WP3 is to gain knowledge on the immune mechanisms that allow the concomitant persistence of specific T cells and their antigen. We will first take advantage of a murine model of T cell exhaustion that has been previously developed within this consortium and identify a molecular signature (transcriptome analysis) in the signalling cascade of dysfunctional cells. A similar functional defect has been identified in human T cells isolated from CMV infected infants, a subset of T cells characterized by the loss of expression of the CD28 marker, and work will be performed to confirm a signalling defect in these cells. Notably, cells lacking CD28 have been recently identified within our consortium in multiple sclerosis patients, a clinical situation whereby self antigen specific T cells are under chronic stimulation. Finally, a signalling defect in tumour specific T cells has been also recently described in one of the participating teams, revealing again a clinical situation in which continuous presence of an antigen causes unresponsiveness in specific T cells. The long term objective of this WP is to devise strategies to revive function in exhausted cells during infection or in cancer patients, while reinforcing this unresponsive state in autoimmune diseases.
WP4 Interplay between innate immunity and T cell responses
Innate antigen-presenting cells (APCs), with dendritic cells (DCs) and macrophages being their most potent representatives, are essential components of the immune system through their roles at the interface between innate immunity and adaptive T cell responses. Yet, the mechanisms by which diverse APCs shape the vast array of responses of the adaptive immune system remain incompletely understood. Here, using comparative epigenetic profiling, genetic engineering of key transcriptional regulators, in vitro modeling of APC-T cell interaction and in vivo models, we will aim at characterizing phenotypic and functional specializations of APCs, deciphering their developmental programs, and dissecting molecular mechanisms implicated in their effects on the orientation of T cell responses. Specifically, we will exploit these lines of research in our domains of expertise, which include the regulation of cytokine expression in APCs, the study of novel APC subsets and their interaction in the lung and the dissection of the cellular and molecular mechanisms of action of vaccine adjuvants. This work package will lead to novel insights into the control of adaptive immune responses by innate APCs in the aforementioned domains that should be generalizable to many (patho)physiological conditions.
WP5 Novel strategies for the induction of anti-tumour T cells
In this WP we will explore novel strategies to harness the immune system to fight cancers. Relevant murine models of induced melanoma or transplanted lung cancer will be used as preclinical platforms for the evaluation of clinically relevant immunotherapeutic approaches. Approaches aimed at better exploiting the innate immune system to develop immunotherapeutic approaches will be evaluated, including the evaluation of the antigen-presenting machinery of tumour antigens and the possibility to develop mRNA-based vaccination protocols against well-established tumour antigens. Finally, the possibility to exploit a subset of T cells with innate-like characteristics (the TcR-expressing cells) will be evaluated. The ability of these cells to home to selected peripheral tissues, their propensity to differentiate by default toward a cytotoxic/inflammatory effector cell and their lack of MHC restriction render this cell population an attractive target for guided immunotherapy. Building upon recent work performed within our consortium both in human and mouse models, we will undertake the identification of the molecular target recognized on several tumour cell lines by a subset of T cells recently identified within our consortium, and by analysing the anti-melanoma potential of skin resident T cells.
The overall objective of our project is to devise strategies that would enable us to selectively induce, in clinical settings, the differentiation of antigen-specific T cells toward a pre-determined functional status (effector or regulator depending on the aimed pathology), while minimizing toxicity to healthy tissues.
