In vivo effect of ZOL on the emergence of leukemic cells in the blood of engrafted mice. Ten weeks after leukemic cell engraftment, all untreated NOD/SCID mice (group 1) had human leukemic cells (A), whereas none of the ZOL-treated mice (groups 2 and 3) had human leukemic cells in their PB (B). Fluorescein in situ hybridization analysis revealed that the human cells in the untreated mice had 2 Bcr-Abl fusion genes (arrow), indicating they were Ph⁺ leukemic cells (C). Original magnification × 400. The data shown are representative of 6 mice.