These time points were chosen for the following reasons: (a) at 12 weeks of age, CD5+ B cells represent a large fraction of splenic B cells in dnRAG1 and DTG mice, but only a small fraction of splenic B cells in WT and Eμ-TCL1 mice; and (b) the 36 week time point represents the approximate median life span of DTG mice where CLL onset is evident [18]. The gene discussed is CD5; the disease is B-cell chronic lymphocytic leukemia.