Fig. 5B indicates that a marked reduction of the formation of ROS was observed when Antho 50-treated CLL cells were pre-incubated with the membrane-permeant analog of catalase (PEG-catalase). In contrast neither native SOD nor catalase had such an effect (Fig. 5B). Exposure of cells to the intracellular antioxidant PEG-catalase significantly prevented the Antho 50-induced reduction in cell viability (Fig. 5C) and apoptosis (Fig. 5D) whereas native SOD and catalase had only slight effects. This evidence concerns the gene CAT and B-cell chronic lymphocytic leukemia.