Thus, the differences in mutational status between CLL cells would be unsurprising if (i) unmutated CLL B-cells are derived from less “antigen-experienced” IgM memory B-cells with little or no SHM [accounting for around 10% of IgM memory B-cells (9, 13)], and (ii) mutated CLL B-cells are derived from well “antigen-experienced” IgM memory B-cells with a high SHM frequency. The gene discussed is CD40LG; the disease is B-cell chronic lymphocytic leukemia.