A previous study compared clonality of malignant B cells in the Eμ-TCL1 model at 4 and 8 months of age and detected several clonotypes at the earlier time point, whereas one major BCR rearrangement was observed in 8-month-old mice suggesting monoclonal expansion of CLL cells during progressive disease [51]. Here, BCR is linked to B-cell chronic lymphocytic leukemia.