Human chronic lymphocytic leukemia modeled in mouse by targeted TCL1 expression

TheTCL1gene at 14q32.1 is involved in chromosomal translocations and inversions in mature T cell leukemias. These leukemias are classified either as T prolymphocytic leukemias, which occur very late in life, or as T chronic lymphocytic leukemias, which often arise in patients with ataxia telangiectasia (AT) at a young age. In transgenic animals, the deregulated expression ofTCL1leads to mature T cell leukemia, demonstrating the role ofTCL1in the initiation of malignant transformation in T cell neoplasia. Expression of high levels of Tcl1 have also been found in a variety of human tumor-derived B cell lines ranging from pre-B cell to mature B cell. Here we describe the phenotype of transgenic mice, Eμ-TCL1, established withTCL1under the control of a VHpromoter-IgH-Eμ enhancer to targetTCL1expression to immature and mature B cells. Flow cytometric analysis reveals a markedly expanded CD5+population in the peritoneal cavity of Eμ-TCL1mice starting at 2 mo of age that becomes evident in the spleen by 3–5 mo and in the bone marrow by 5–8 mo. Analysis of Ig gene rearrangements indicates monoclonality or oligoclonality in these populations, suggesting a preneoplastic expansion of CD5+B cell clones, with the elder mice eventually developing a chronic lymphocytic leukemia (CLL)-like disorder resembling human B-CLL. Our findings provide an animal model for CLL, the most common human leukemia, and demonstrate that deregulation of the Tcl1 pathway plays a crucial role in CLL pathogenesis.