Antiproliferative effect of BIBR1532 in primary CLL cells. (A) Primary CLL cells were cultured in complete RPMI for 14 days supplemented with 80 μM BIBR1532. As previously reported,³⁴  viability was determined using the DiOC₆/PI assay at indicated time points and is expressed as percentage of the controls. Values are means ± SEM (n = 20). (B) FSC/SSC pattern is shown for a representative CLL patient sample measured by day 14 using FACS analysis. Gated cells represent the viable cells at the end of culture. (C) The mean telomere length was measured using flow-FISH technique.³⁵  Representative telomere fluorescence histograms of one CLL patient sample are demonstrated following treatment of BIBR1532 and of DMSO (control cells) for 14 days. Telomere fluorescence intensity was calculated by subtracting the mean background fluorescence (gray) from the corresponding mean fluorescence provided by the telomere-specific probe (black).