Quantification of TIF in CLL cells according to their in vitro sensitivity to apoptosis. (A) FISH with a telomere-specific (C₃TA₂)₃–Cy3-labeled peptide nucleic acid probe (PNA; red fluorescence) and immunostaining of TRF2 or TRF1 used to control for the telomere position in the interphase nuclei of CLL cells. (B) Double immunostaining of γ-H2AX and 53BP1 in CLL cells after 2 Gy or 10 Gy irradiations used to label DNA DSBs in interphase nuclei. (C) Double immunostaining of γ-H2AX and TRF2 in CLL-R and CLL-S cells. Arrows indicate the γ-H2AX/TRF2 colocalizations. (D) Double immunostaining of 53BP1 and TRF2. Their colocalization is indicated by arrows. (E) Double immunostaining of γ-H2AX and TRF1. Their colocalization is indicated by arrows. (F) Comparisons of γ-H2AX/TRF2-positive cells between CLL-S and CLL-R. Positivity was assigned when more than or equal to 50% γ-H2AX foci colocalized with TRF2 in one cell. Bars represent the mean percentage ± SD. (G) Comparison of 53BP1/TRF2-positive cells between CLL-S and CLL-R. Bars represent the mean percentage ± SD. (H) Comparison of γ-H2AX/TRF1–positive cells between CLL-S and CLL-R and comparison of γ-H2AX–positive cells between γ-H2AX/TRF2 and γ-H2AX/TRF1 in CLL-S and CLL-R. Bars represent the mean percentage ± SD. The Mann-Whitney U test was used to assess statistical significance: *P < .01; ***P < .001