TCL1, also known asT-cell leukemia/lymphoma protein 1A, protein p14 TCL1 and oncogene TCL-1,is a 14kD beta-barrel protein that was originallyidentified on the basis of its association with T-cell prolymphocytic leukemia (T-PLL). Activated by the T-cell receptor enhancer through inv(14)(q11;q32.1) or t(14;14)(q11;q32.1), TCL1 is normally expressed in immature cortical thymocytes, activated peripheral T-cells, pro-B cells, andnaive mantle zone B cells of peripheral lymphoid tissues,but notin post-germinal center (GC) memory B cells and plasma cells. Akt and TCL1 interact via Akt’s pleckstrin homology domain to form hetero-oligomers at the leaflet of the inner plasma membrane stimulating the protein kinase C-mitogen activated protein kinase-extracellular signal-related kinase (PKC-MAPK-ERK) signal transduction pathway. TCL1 also inhibits activation-induced cell death in T-cells by blocking PKCtheta. In addition to T-PLL dysregulation is implicated in such B-cell neoplasias as lymphoblastic lymphoma, chronic lymphocytic leukemia (CLL) and Burkitt lymphoma.