DNA-PK activity in CLL samples. Whole cell extracts (50 μg) derived from CLL lymphocytes obtained either from untreated or treated-resistant patients were tested for DNA-PK activity using standard DNA-PK microfractionation/peptide assays in the presence of wild-type (▪) or mutated (▨) p53 peptide as indicated in Materials and Methods. The panel represents the mean activity (±SE) for the two groups of samples. *P value as determined by using an unpaired Student's t-test.