T-CELL DEVELOPMENT - NEW APPROACHES

The differentiation of T lymphocyte precursors into functionally matur e progeny procedes in distinct stages. Since these are identified by c haracteristic constellations of phenotypic markers, the effects of exp erimental manipulations on T cell development can be readly monitored. In order to complete their developmental program, thymocytes must int eract with stromal elements, which positively and negatively select th e functional T cell receptor (TCR) repertoire (1-6). This process norm ally assures self tolerance and immunocompetence. Disturbances are of practical importance for clinical disorders including immunodeficienci es and autoimmune phenomena (7), raising a particular interest in huma n T cell development and repertoire formation. Here, we discuss result s and possible applications of a culture system for human thymocytes. Further, we describe an in vitro approach addressing the requirements for a crucial step in T cell development; the transition from the imma ture CD4 CD8 double positive (DP) to the mature CD4 single positive (S P) stage.