Expansion of CD5+/CD19+ CLL cells could be detected in the peripheral blood after 4 weeks in Lynwt/wt and chLyn−/− mice, but not in tLyn−/− mice (Fig. 1b), reproducing the failure of leukemic engraftment observed before in aged global Lyn−/− mice20. This evidence concerns the gene LYN and B-cell chronic lymphocytic leukemia.