TCL1B and B-cell chronic lymphocytic leukemia: Furthermore, TCL1 family gene members have oncogenic ability, as clearly demonstrated by four different transgenic animal models in which overexpression of these genes, in either T or B cells, causes T-PLL, B-chronic lymphocytic leukaemia (B-CLL) or mature B-cell lymphoma (Gritti et al, 1998; Virgilio et al, 1998; Bichi et al, 2002; Hoyer et al, 2002).