In the murine system, Notch2 is implicated in the development of marginal zone (MZ) B2 B-cells and of Cd5+ (B-1a) B-lymphocytes [24], and is indispensable for CLL initiation in Cd5+ (B-1a) B-cells [25]. This evidence concerns the gene NOTCH2 and B-cell chronic lymphocytic leukemia.