title: A new mechanism shapes the naïve CD8+T cell repertoire: the selection for full diversity.
abstract: During thymic T cell differentiation, TCR repertoires are shaped by negative, positive and agonist selection. In the thymus and in the periphery, repertoires are also shaped by strong inter-clonal and intra-clonal competition to survive death by neglect. Understanding the impact of these events on the T cell repertoire requires direct evaluation of TCR expression in peripheral naïve T cells. Several studies have evaluated TCR diversity, with contradictory results. Some of these studies had intrinsic technical limitations since they used material obtained from T cell pools, preventing the direct evaluation of clonal sizes. Indeed with these approaches, identical TCRs may correspond to different cells expressing the same receptor, or to several amplicons from the same T cell. We here overcame this limitation by evaluating TCRB expression in individual naïve CD8+T cells. Of the 2269 Tcrb sequences we obtained from 13 mice, 99% were unique. Mathematical analysis of the data showed that the average number of naïve peripheral CD8+T cells expressing the same TCRB is 1.1 cell. Since TCRA co-expression studies could only increase repertoire diversity, these results reveal that the number of naïve T cells with unique TCRs approaches the number of naïve cells. Since thymocytes undergo multiple rounds of divisions after TCRB rearrangement and 3-5% of thymocytes survive thymic selection events the number of cells expressing the same TCRB was expected to be much higher. Thus, these results suggest a new repertoire selection mechanism, which strongly selects for full TCRB diversity.
authors.affiliation: Lymphocyte Population Biology Unit, CNRS URA 196, Institut Pasteur, Paris, France; INSERM, U1151, CNRS, UMR8253, Faculté de Médecine Paris Descartes, Paris, France. Electronic address: pedro.goncalves@pasteur.fr.
authors.forename: Pedro
authors.initials: P
authors.lastname: Gonçalves
authors.affiliation: Department of Applied Mathematics, University of Leeds, Leeds LS29JT, UK.
authors.forename: Marco
authors.initials: M
authors.lastname: Ferrarini
authors.affiliation: Department of Applied Mathematics, University of Leeds, Leeds LS29JT, UK.
authors.forename: Carmen
authors.initials: C
authors.lastname: Molina-Paris
authors.affiliation: Department of Applied Mathematics, University of Leeds, Leeds LS29JT, UK.
authors.forename: Grant
authors.initials: G
authors.lastname: Lythe
authors.affiliation: Lymphocyte Population Biology Unit, CNRS URA 196, Institut Pasteur, Paris, France; INSERM, U1151, CNRS, UMR8253, Faculté de Médecine Paris Descartes, Paris, France.
authors.forename: Florence
authors.initials: F
authors.lastname: Vasseur
authors.affiliation: Lymphocyte Population Biology Unit, CNRS URA 196, Institut Pasteur, Paris, France.
authors.forename: Annik
authors.initials: A
authors.lastname: Lim
authors.affiliation: Lymphocyte Population Biology Unit, CNRS URA 196, Institut Pasteur, Paris, France; INSERM, U1151, CNRS, UMR8253, Faculté de Médecine Paris Descartes, Paris, France. Electronic address: benedita.rocha@inserm.fr.
authors.forename: Benedita
authors.initials: B
authors.lastname: Rocha
authors.affiliation: INSERM, U1151, CNRS, UMR8253, Faculté de Médecine Paris Descartes, Paris, France.
authors.forename: Orly
authors.initials: O
authors.lastname: Azogui
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002469:Cell Separation; D051379:Mice; D008810:Mice, Inbred C57BL; D060885:Multiplex Polymerase Chain Reaction; D016133:Polymerase Chain Reaction; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics / Q000276:immunology*
chemical_list: D016693:Receptors, Antigen, T-Cell, alpha-beta
keywords: CD8(+) T cells; CDR3 sequences; Mice TCR repertoires; TCR cross-reactivity; TCR diversity