title: Adult T-cell progenitors retain myeloid potential.
abstract: During haematopoiesis, pluripotent haematopoietic stem cells are sequentially restricted to give rise to a variety of lineage-committed progenitors. The classical model of haematopoiesis postulates that, in the first step of differentiation, the stem cell generates common myelo-erythroid progenitors and common lymphoid progenitors (CLPs). However, our previous studies in fetal mice showed that myeloid potential persists even as the lineage branches segregate towards T and B cells. We therefore proposed the 'myeloid-based' model of haematopoiesis, in which the stem cell initially generates common myelo-erythroid progenitors and common myelo-lymphoid progenitors. T-cell and B-cell progenitors subsequently arise from common myelo-lymphoid progenitors through myeloid-T and myeloid-B stages, respectively. However, it has been unclear whether this myeloid-based model is also valid for adult haematopoiesis. Here we provide clonal evidence that the early cell populations in the adult thymus contain progenitors that have lost the potential to generate B cells but retain substantial macrophage potential as well as T-cell, natural killer (NK)-cell and dendritic-cell potential. We also show that such T-cell progenitors can give rise to macrophages in the thymic environment in vivo. Our findings argue against the classical dichotomy model in which T cells are derived from CLPs; instead, they support the validity of the myeloid-based model for both adult and fetal haematopoiesis.
authors.affiliation: Laboratory for Lymphocyte Development, RIKEN Research Center for Allergy and Immunology, Yokohama 230-0045, Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Wada
authors.forename: Kyoko
authors.initials: K
authors.lastname: Masuda
authors.forename: Rumi
authors.initials: R
authors.lastname: Satoh
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Kakugawa
authors.forename: Tomokatsu
authors.initials: T
authors.lastname: Ikawa
authors.forename: Yoshimoto
authors.initials: Y
authors.lastname: Katsura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawamoto
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology; D019070:Cell Lineage; D002478:Cells, Cultured; D018920:Coculture Techniques; D003713:Dendritic Cells / Q000166:cytology; D005333:Fetus; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D007694:Killer Cells, Natural / Q000166:cytology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D022423:Myeloid Cells / Q000166:cytology* / Q000378:metabolism; D017154:Stromal Cells / Q000166:cytology; D013601:T-Lymphocytes / Q000166:cytology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000196:embryology / Q000637:transplantation