Recombination activating genes and CD3-TCR molecules are coexpressed in a subset of human T-cell acute lymphoblastic leukemias.

The V-(D) -J recombination that occurs during lymphoid differentiation is the basic event which settles the diversity of antigen receptors. Two recently cloned genes, RAG1 and RAG2, are sufficient to induce rearrangements of synthetic substrates when transfected into fibroblasts. In order to determine at which differentiation steps where the human RAG are expressed and in order to investigate the possible impairment of their expression by the leukemic process, we have recently studied a large series of B and T lymphoid neoplasias. We show that RAG are expressed in almost all sIg- B-ALL but not in the sIg+ B cell proliferations we have tested. Furthermore, we show that RAG can be expressed not only by CD3-TCR negative but also by CD3-TCRab or gd positive T-ALL cells. We conclude that the recombinase activity is not turned off by the expression of a functionnal T-cell receptor on the cell surface. This observation is in line with recent studies on RAG expression in human thymus and are of major interest to understand the set up of the TCR repertoire.