title: Differentiation of human thymic regulatory T cells at the double positive stage.
abstract: Treg cells, best identified by the expression of the transcription factor FOXP3, play a crucial role in maintaining self-tolerance. Natural Treg cells constitute an independent thymus-derived T-cell lineage whose developmental program in humans is still ill-defined. Here, we provide evidence of a Treg-cell differentiation pathway at the double positive (DP) stage, prior to commitment to the CD4(+)  or CD8(+)  lineage, in pediatric thymuses. FOXP3(+)  DP cells displayed a functional IL-7 receptor and increased Bcl-2 levels that may protect them from cell death/negative selection, and an activated/suppressive phenotype that was lost as CD4 single positive (SP) cells matured and acquired egress markers. A subpopulation of FOXP3(+)  DP thymocytes expressing CD103 likely represents the precursor of FOXP3(+)  CD8SP cells, which homogeneously expressed this mucosal-homing molecule. Finally, co-cultures of DP thymocytes with primary thymic epithelial cells and multiple linear regression analyses support that FOXP3(+)  SP cells are largely derived from FOXP3(+)  DP thymocytes. Overall, our data suggest that human Treg-cell lineage commitment significantly occurs at the DP stage with possible implications for the diversity and autoreactivity of the natural Treg-cell repertoire.
authors.affiliation: Unidade de Imunologia Clínica, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Helena
authors.initials: H
authors.lastname: Nunes-Cabaço
authors.forename: Iris
authors.initials: I
authors.lastname: Caramalho
authors.forename: Nuno
authors.initials: N
authors.lastname: Sepúlveda
authors.forename: Ana E
authors.initials: AE
authors.lastname: Sousa
mesh_terms: D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D019070:Cell Lineage; D018920:Coculture Techniques / Q000379:methods; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D020395:Receptors, Interleukin-7 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D060168:Thymocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism
chemical_list: D015703:Antigens, CD; C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors; D019253:Proto-Oncogene Proteins c-bcl-2; D020395:Receptors, Interleukin-7