Overexpression of the TCL1 gene in humans has been implicated in the development of mature T cell leukemia, in which chromosomal rearrangements bring the TCL1 gene in close proximity to the T-cell antigen receptor (TCR)-alpha (MIM 186880) or TCR-beta (MIM 186930) regulatory elements (summarized by Virgilio et al., 1998 [PubMed 9520462]). In normal T cells TCL1 is expressed in CD4-/CD8- cells, but not in cells at later stages of differentiation. TCL1 functions as a coactivator of the cell survival kinase AKT (MIM 164730) (Laine et al., 2000 [PubMed 10983986]).[supplied by OMIM, Jul 2010].