The aim of our project is to determine the overall characteristics of naive T cell repertoires directed against various viral or tumoral antigens in humans as well as parameters influencing these repertoires both qualitatively and quantitatively. An in depth understanding of these mechanisms would provide important insights into the ability of a given individual to develop a subsequent efficient immune response against tumors, infectious pathogens or after vaccination. To this end we have set up a strategy allowing ex vivo quantification and phenotypic analysis of antigen-specific T lymphocytes present even at very low frequencies in biological samples (detection threshold : 10-7). Our results obtained with different peptide/MHC class I (pMHC-I) complexes have already shown that T cell repertoires specific for several viral and tumoral immunodominant antigens are differentially affected by both the expression of the HLA restricting-allele and the inherent reactivity of the TCRs found in those repertoires. During this analysis, we have also formally documented the presence of CD4+CD8- T cells reactive against pMHC-I complexes, while clearly selected against MHC class II molecules. Using the same approach, pMHC specific B cells have also been detected at significant frequencies (10-5 - 10-4). We thus have unique opportunity to dissect the parameters governing the overall pMHC antigenicity towards immune adaptive receptors. In particular we will address the role of thymic selection processes on both the quantity and quality of Ag specific T cell repertoires, determined the structural bases of TCR crossreactivity, peptide-dependency and biased usage of particular variable gene segment for recognition of particular pMHC, and investigate the role of pMHC class I specific B cells in immune responses and possible fallout for the production of highly specific antibodies against pMHC. This project is based on a multidisciplinary approach, combining molecular and cellular immunology and structural biology, that relies on the competences of two teams acknowledged by numerous publications in the field of immunobiology of human lymphocytes in healthy, tumor or infectious situations and in the structural basis of TCR antigen recognition. The work program will provide key information about the mechanisms contributing to the shaping of the preimmune peripheral T cell repertoire in humans. This knowledge is a prerequisite for identifying predictive clues of an efficient immune response in a variety of physiopathological and vaccinal situations. The investigations on pMHC specific B cells may lead to a very promising alternative technique to identify antibodies with sufficient affinity and peptide specificity for a given pMHC and that will be extremely beneficial for diagnostic and therapeutic purposes.

Bone diseases such as osteoporosis represent one of the major health care problems in the elderly. Osteoporosis results in a severe reduction in bone mass and weakening of bone micro-structure predisposing a person to an increased risk of spontaneous fractures at a relatively late stage of the pathology. Therefore, the determination of revealing risk factors is essential to identify patients at risk and to handle the disease preventively. For the clinician, predicting fracture risk for individual patients is nearly restricted to the quantitative analysis of bone density. However, bone which is a 'living biomaterial', adapts to strains by a redistribution of trabeculae by the remodeling process. It is now fully recognized that bone strength reflects the integration of two main features: bone density and bone quality. A good estimation of bone quality has to take into account critical parameters such as trabecular and cortical microarchitecture, bone remodeling, the degree of mineral content of the collagen and other proteins bone matrix, and the amount of microdamage present. Thus, detecting the micro-structural changes and their impact in the pathogenesis of bone fragility is a crucial point to better identify the risk of fractures and improve the rationale for specific treatment of bone fragility which is at the moment mainly related on bone remodelling blockage by biphosphonates therapy. The main purpose of this research project is to develop a predicting tool for giving early, accurate and reliable diagnosis of bone quality in presence of different pathologies in order to identify persons at risk for fracture, to choose and to evaluate the efficacy of the treatment. This project, which is an interdisciplinary collaborative effort of three teams, is organized around 3 highly interrelated objectives and phases, (i) Effect of pathology and treatment on mechanical and biological properties of bone (ii) Prediction of remodelling process at the representative volume elementary (RVE) scale (iii) Development of bone adaptation model based on topology optimization They are sketched right now: 1. Effect of pathology and treatment on mechanical and biological properties of bone. This part is based on analysis of architectural (microscaner, SEM, ulstrasound), biological (Mineral content, collagen properties) and mechanical (Elastic properties) properties of bone at various levels of the structural organization. 2. Prediction of remodelling process at the RVE scale. This part is based on experimental analysis of local damage and numerical model of bone remodelling of a set of Basic Multicellular Unit for typical RVE. Experimental results will provide local criterion damage to set up signal involve in resorption phase used in numerical model. 3. Development of bone adaptation model based on topology optimization able to understand and monitor pathologic states of bone at both macroscopic and microscopic scales over time in its changing environment. The major expected result of this project is to develop a diagnostic tool of bone quality to prevent fracture risk, based on bone adaptation model validate by advanced mechanical tests to different bone samples normal, pathological or remodelled.