Coculture of CLL cells with CD31-transfected fibroblasts does not result in an altered expression profile of apoptosis-regulating genes. CLL samples were cocultured for 3 days with 3T3, 3T31, or 3T40L cells (CD38^low n = 2; CD38^high n = 4 for 3T3; 3T31 and n = 3 for 3T40L). The relative expression level of indicated genes, as assessed by RT-MLPA, was related to the average expression in the CLL samples cocultured with 3T3 cells. The resulting matrix was imported into the program MultiExperiment Viewer, and values were assigned green or red colors: green for values between 0 and 1, indicating down-regulation, and red for values greater than 1, indicating up-regulation. The CLL samples are ordered as indicated below the matrix. In the right column, the genes are ordered by functional category (HKG = housekeeping genes; β2M = β-2-microglobulin). A significant change in expression level was defined as a 2-fold up- or down-regulation of the average expression of a gene in samples cocultured with 3T31 or 3T40L cells compared with samples cocultured with 3T3 cells and a statistical significant difference with a P value less than .05 (2-sided Student t test for 5 paired samples). No significant differences were found after coculture with 3T3 or 3T31 cells; genes with a significant differential expression level after coculture with 3T40L are denoted with *. To exclude the possibility that variations in gene expression occur at time points earlier or later than 72 hours, additional RNA of 2 CD38^high CLL patients was isolated after 24 and 120 hours of coculture. At these additional time points, no differences were found (data not shown).