Most B-CLL cells express CD5 and IgM/IgD and thus have a mantle zone-like phenotype of naive cells, which, in normal conditions express UM Ig genes.17 However, 50–70% of CLL harbor somatic mutations of IgVH genes25 as if they had matured in a lymphoid follicle. Here, CD5 is linked to B-cell chronic lymphocytic leukemia.