T-cell Development, Doing It in a Dish

The thymus provides a unique environment for the development of T lymphocytes from bone marrow-derived progenitor cells. Several environmental factors have been identified that influence the development of T cells in the thymus. In particular, the Notch pathway has emerged as critical for the induction of T-lineage commitment and differentiation. Until recently, however, the precise nature of the thymus-derived signals that drive T-cell development were unclear, and the only reliable in vitro culture system that supported T-cell differentiation required the use of thymus organ cultures. Here, we discuss recent advances in the identification of critical Notch receptor ligands that have facilitated the development of a simple in vitro model for the differentiation of T cells 'in a dish', providing an alternate approach for studying T lymphopoiesis.