Identification of a T Linea Progenitor in Adult Blood

et al., 1997). In the adult thymus, progenitors from the bonemarrow are recruited via the blood stream. However, the nature of thymic immigrants has remained elusive. Based on phenotypic similarity to the early T cell progen-itors (ETPs), multipotent LSK cells in blood were assumed to represent the most effective thymic immigrants in adult mice (Allman et al., 2003; Benz and Bleul, 2005; Schwarz and Bhandoola, 2004). However, immigration of these cells into the thymus has not been directly shown, and cell potential. Subdivision of DN1 cells according to c-kit and heat-stable antigen (HSA) revealed the most potent T cell progenitors in the DN1a and b subsets that are likely linked by a precursor-product relationship (Porritt et al., 2004). Progressive loss of B cell potential (Benz and Bleul, 2005; Sambandam et al., 2005) and clonal analysis of the most immature ETPs (Benz and Bleul, 2005) is best com-patible with the notion that T and B lineages diverge intra-thymically, although this is disputed (Balciunaite et al.,Articl