Ogie biologique, Hopital Cochin), ML ^ Gougeon (Unite ?Immunite virale, biotherapie et vaccins ? Institut ???Pasteur).Author ContributionsConceived and designed the experiments: OL CC V. Tsatsaris YV JMT FG. Performed the experiments: AK V. Epigenetics Truster V. Tsatsaris JL YV FR FA FG. Analyzed the data: OL AK CA TA FG. Contributed reagents/ materials/analysis tools: AK V. Truster FA. Wrote the paper: OL AK CA TA FG.Pandemic Influenza 2009 Vaccine and Pregnancy
T cell development Epigenetics occurs mainly in the thymus [1]. However, by the time T cell precursors reach this primary lymphoid organ, they are not fully committed, and only later receive the cues that engage them on a T cell fate [1,2,3]. Thus, the thymic microenvironment is thought to provide appropriate signals that maintain a balance between thymocyte selection, proliferation and cell death [4,5]. These signals are dependent on thymocyte receptors and their cognate ligands, 
either soluble or membrane bound, which are obtained from the thymic 
microenvironment. Determinant factors to T cell precursor development have a mesenchymal or hematopoietic cell origin and are believed to trigger a gene expression program leading to specific cell fates [1,2,3]. Among major known molecular players in T cell development are Notch-Delta and TCR-MHC interactions [6,7]. However, identification of additional regulators of thymocyte development is still an unmet need in T cell biology. Although recent advances have added into the complexity of T cell developmental stages, the latter can still be defined based on the expression of the T cell receptor (TCR) and the co-receptors CD4 and CD8 [2,4,8]. Initially, immature (CD32) thymocytes are double-negative (DN) CD42CD82, then develop into doublepositive (DP) CD4+CD8+ thymocytes through an immature CD8+CD32 (ImmCD8) intermediate 23977191 stage, and ultimately areselected into CD4+CD3+ or CD8+CD3+ mature compartments [2,8]. T cell development starts in embryonic life [4,9]. Seeding of the embryonic thymus occurs around E13.5 and few thymocytes are beyond DN stage until E16.5 [4]. Full maturation of ab T cells is residual before E19.5, but some unique cd T cell populations are produced exclusively at defined foetal stages [2,4]. Previous studies showed expression of neurotrophic factors of the glial cell-line derived neurotrophic factor (GDNF) family (GFLs) in the thymus [10,11]. Productive signalling by GFLs is dependent on their association to a co-receptor (GFRa1 to 4), which also confers a degree of specificity to each GFL. Thus, GFRa1 is required to GDNF signalling, GFRa2 to NRTN, GFRa3 to ARTN and GFRa4 to PSPN [12]. GFRa molecules cooperate mainly with the transmembrane tyrosine kinase receptor RET for downstream signalling [12]. Activating mutations of Ret have been linked to cancer, i.e., somatic chromosomal rearrangements result in Papillary Thyroid Carcinoma, point mutations of RET lead to Multiple Endocrine Neoplasia 2 syndrome and RET is also differentially expressed in acute myeloid leukaemia [13,14]. Thus, RET inhibitors were recently developed for specific human cancer therapies [15,16]. RET signalling axes are critical to the neuronal system and kidney [12], but recent evidence indicates that RET signals are also key to intestinal lymphoid organ development [17,18].RET Signalling and T Cell DevelopmentInterestingly, it was shown that RET is expressed by mature lymphocytes [19] and GDNF promotes DN thymocytes survival in vitro [11]; thus, raising the exciting po.Ogie biologique, Hopital Cochin), ML ^ Gougeon (Unite ?Immunite virale, biotherapie et vaccins ? Institut ???Pasteur).Author ContributionsConceived and designed the experiments: OL CC V. Tsatsaris YV JMT FG. Performed the experiments: AK V. Truster V. Tsatsaris JL YV FR FA FG. Analyzed the data: OL AK CA TA FG. Contributed reagents/ materials/analysis tools: AK V. Truster FA. Wrote the paper: OL AK CA TA FG.Pandemic Influenza 2009 Vaccine and Pregnancy
T cell development occurs mainly in the thymus [1]. However, by the time T cell precursors reach this primary lymphoid organ, they are not fully committed, and only later receive the cues that engage them on a T cell fate [1,2,3]. Thus, the thymic microenvironment is thought to provide appropriate signals that maintain a balance between thymocyte selection, proliferation and cell death [4,5]. These signals are dependent on thymocyte receptors and their cognate ligands, either soluble or membrane bound, which are obtained from the thymic microenvironment. Determinant factors to T cell precursor development have a mesenchymal or hematopoietic cell origin and are believed to trigger a gene expression program leading to specific cell fates [1,2,3]. Among major known molecular players in T cell development are Notch-Delta and TCR-MHC interactions [6,7]. However, identification of additional regulators of thymocyte development is still an unmet need in T cell biology. Although recent advances have added into the complexity of T cell developmental stages, the latter can still be defined based on the expression of the T cell receptor (TCR) and the co-receptors CD4 and CD8 [2,4,8]. Initially, immature (CD32) thymocytes are double-negative (DN) CD42CD82, then develop into doublepositive (DP) CD4+CD8+ thymocytes through an immature CD8+CD32 (ImmCD8) intermediate 23977191 stage, and ultimately areselected into CD4+CD3+ or CD8+CD3+ mature compartments [2,8]. T cell development starts in embryonic life [4,9]. Seeding of the embryonic thymus occurs around E13.5 and few thymocytes are beyond DN stage until E16.5 [4]. Full maturation of ab T cells is residual before E19.5, but some unique cd T cell populations are produced exclusively at defined foetal stages [2,4]. Previous studies showed expression of neurotrophic factors of the glial cell-line derived neurotrophic factor (GDNF) family (GFLs) in the thymus [10,11]. Productive signalling by GFLs is dependent on their association to a co-receptor (GFRa1 to 4), which also confers a degree of specificity to each GFL. Thus, GFRa1 is required to GDNF signalling, GFRa2 to NRTN, GFRa3 to ARTN and GFRa4 to PSPN [12]. GFRa molecules cooperate mainly with the transmembrane tyrosine kinase receptor RET for downstream signalling [12]. Activating mutations of Ret have been linked to cancer, i.e., somatic chromosomal rearrangements result in Papillary Thyroid Carcinoma, point mutations of RET lead to Multiple Endocrine Neoplasia 2 syndrome and RET is also differentially expressed in acute myeloid leukaemia [13,14]. Thus, RET inhibitors were recently developed for specific human cancer therapies [15,16]. RET signalling axes are critical to the neuronal system and kidney [12], but recent evidence indicates that RET signals are also key to intestinal lymphoid organ development [17,18].RET Signalling and T Cell DevelopmentInterestingly, it was shown that RET is expressed by mature lymphocytes [19] and GDNF promotes DN thymocytes survival in vitro [11]; thus, raising the exciting po.