From the Department of Immunology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan; Department of Immunology and Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan; Laboratory for Lymphocyte Development, RIKEN Research Center for Allergy and Immunology, Yokohama, Japan; and Division of Cell Regeneration and Transplantation, Advanced Medical Research Center, Nihon University School of Medicine, Tokyo, Japan.
During murine fetal development, hemato-poietic progenitors start to colonize the thymic anlage at day 11 of gestation via blood stream. The present study aims at identifying the earliest prethymic progenitors in circulation. Here, we show that the interleukin-7 receptor–positive (IL-7R+) cells in Lin– c-kit+ population are circulating exclusively between days 11 and 14 of fetal age. Clonal analysis revealed that these IL-7R+ cells mostly contain T-cell lineage–restricted progenitors (p-Ts). The proportion of circulating p-Ts reaches 30% of the total p-Ts during these fetal ages, whereas virtually all B-cell lineage–restricted progenitors stay in the fetal liver, suggesting that the p-Ts are selectively released to the circulation. The circulating p-Ts retain the potential to generate natural killer cells and dendritic cells and exhibit extensive proliferation before the occurrence of T-cell receptor 
(TCR) chain gene rearrangement. We propose that the wave of p-Ts in fetal blood disclosed by this study represents the ontogenically earliest thymic immigrants.
Identification of a Small Molecular Anti-HIV-1 Compound that Interferes with Formation of the Fusion -active gp41 Core
Metabolomic Identification of Novel Biomarkers of Myocardial Ischemia
Identification and Characterization of Two Genes (MIP-1;, VE-CADHERIN) Implicated in Acute Rejection in Human Heart Transplantation
Identification of Penumbra and Infarct in Acute Ischemic Stroke Using Computed Tomography Perfusion–Derived Blood Flow and Blood Volume Measurements
Identification of Culprit Lesions After Transient Ischemic Attack by Combined 18F Fluorodeoxyglucose Positron-Emission Tomography and High-Resolution Magnetic Resonance Imaging
Significance of Susceptibility Vessel Sign on T2-Weighted Gradient Echo Imaging for Identification of Stroke Subtypes
Identification of Embolic Stroke Patterns by Diffusion-Weighted MRI in Clinically Defined Lacunar Stroke Syndromes
Helical CT with CT Angiography in Assessing Periampullary Neoplasms: Identification of Vascular Invasion
Identification of Attenuated Variants of HIV-1 Circulating Recombinant Form 01_AE That Are Associated with Slow Disease Progression Due to Gross Genetic Alterations in the nef/Long Terminal Repeat Seq
Identification of the Optimal Structure Required for a Shiga Toxin Neutralizer with Oriented Carbohydrates to Function in the Circulation