Two members of the tumor necrosis factor (TNF) family, BAFF (B cell activating factor of the TNF family) and APRIL (a proliferation-inducing ligand), are already known for their crucial roles in normal B cell survival, differentiation and apoptosis and have recently been shown to be expressed by B-CLL cells [10]. This evidence concerns the gene TNFSF13B and B-cell chronic lymphocytic leukemia.