Human CD34(+) thymocyte maturation: pre-T and NK cell differentiation on neonatal thymic stromal cell culture

The development of a simple assay for studying human T and NK lymphopoiesis from CD34 progenitors is of great interest. T and NK cells arise from a common CD34(+) immature precursor. While T cell maturation is dependent on interactions and cytokines provided by thymic stromal cells. NK maturation does not require the thymic microenvironment and primarily takes place extrathymically. In addition to models using a mouse thymic microenvironment, in vitro assays based on coculture on human fetal thymic stroma have been described. As an alternative source of fetal thymic tissue we studied the capacity of neonatal thymic epithelial cell enriched stroma to support T and NK cell differentiation. While in the fetal-based assays on NK cells were observed under the conditions used for T cell differentiation, neonatal stroma can generate CD3/TcR+ as well as CD56(+)3(-)8(+)NKR-P1(+)NK cells from both CD34(+)1(-) and CD34(+)1(+) thymocyte precursors. However, following acquisition of CD3/TcR, T-lineage cells disappeared from the culture after 2-3 weeks as a consequence of the outgrowth of the NK cells. These CD56(+)3(-) NK cells appeared to be functionally immature as they required incubation with IL2 or IL15 to lyse K562 target cells. Our data offer a simple and reliable assay for studying the reconstitution potential of T and NK cell progenitors on a monolayer of thymic epithelial cells.