Assessment of BCR-ABL expression in leukemic colonies grown in different experimental conditions. In 26 of the 35 patients reported in Table 4 we randomly selected 48 single colonies (12 for each treatment condition). (A) RNA extracted from each colony was used to perform a 1-step RT-PCR for BCR-ABL. Negative RT-PCR reactions were subjected to a nested PCR for BCR-ABL. Colonies that again scored negative were further analyzed for the ubiquitously expressed gene NCOA4 to verify the quality of the RNA obtained. Each PCR reaction included a negative (-) and positive (+) control. One representative patient (UPN 30) is shown here. (B) Average number of BCR-ABL-positive colonies in the 4 experimental conditions (NT is represented by ○; IM, ▵; LMB, ⋄; and I+L, ▪). Data are presented as percentage of variations with 12 positive colonies set at 100%. Horizontal bars indicate the average number of BCR-ABL-positive colonies in each experimental condition.