Telomeres are shorter in B-CLL cells, particularly in those with unmutated IgV_Hgenes. (A) Telomere lengths of negatively selected B cells from 70 B-CLL patients and 33 age-matched healthy donors were determined by Flow-FISH. Telomeres of B cells from healthy donors were significantly longer than those from B-CLL patients (P < .0001). The 70 B-CLL patients were also segregated based on Ig V gene mutation. B cells from the unmutated subgroup expressed significantly shorter telomeres than those from the mutated subgroup (P < .0001). Both unmutated and mutated cells in B-CLL patients displayed significantly reduced (P < .0001) telomere lengths compared independently with telomere lengths of age-matched healthy donors. (B) Mean telomere lengths of fluorescence-activated cell sorter (FACS) B-cell subsets (CD19⁺CD5⁺ and CD19⁺CD5^–) from 8 aging healthy subjects compared with B cells from unmutated and mutated cells of B-CLL patients (n = 35 each). B cells from unmutated subsets show significantly shorter telomeres compared with normal B-cell subsets (P < .001) and with mutated cells (P < .0001). Horizontal bars indicate mean values for each set of data points. (C) The positive correlation (r = 0.51; P < .001) between mean telomere length and percentage Ig V gene mutation in the 70 B-CLL patients is illustrated in a scatter plot.