MicroRNAs are a recently discovered class of small (22nt) translational repressor RNAs that play key roles in many cellular pathways. In this project, we want to obtain novel insights in the role of miRNA expression in both normal and malignant T-cell development. For the T-ALL study, we will use EORTC patient material and the EORTC database for treatment of childhood ALL (Prof. Y. Benoit, study supervisor EORTC), which contains clinical, immuno-phenotypical, karyotypic and molecular-cytogenetic information on a very large cohort of T-ALL patients. Concerning the study of miRNA expression during normal T-cell development, we will initiate a close collaboration with the Department of Immunology from the Unicersity Hosptital Ghent (Prof. J. Plum). This department has great experience into the molecular signaling pathways involved in human T-cell development.