1
Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA. petrieh@mskcc.org
2
Departments of Immunology and Molecular Biology, Leiden University Medical Center, Leiden, the Netherlands. vanewijk@lumc.nl
The identity of the thymic epithelium precursor has been elusive.A marker is now shown to identify a population of cells that can give rise to a functional thymus.