Our results showed that high AID expression is almost exclusively restricted to the subpopulation of tumoral cells having an ongoing CSR process and more important, the presence of this subpopulation in CLL is closely related to an aggressive course of the disease.57, 59 This small clonal subset having achieved CSR and expressing either IgG at the membrane or both IgM and IgG, displays higher levels of AID, and higher levels of proliferation and anti-apoptotic molecules like Ki-67, c-myc and Bcl-2. This evidence concerns the gene BCL2 and B-cell chronic lymphocytic leukemia.