FdUMP[10] induces less toxicity than either 5-FU or Ara-C plus Dox. (A) H&E staining of organs from mice treated with either FdUMP[10], 5-FU, or Ara/Dox. Mice were treated in the same manner as in Figure 6 and killed 72 hours after the last dose, and organs were harvested, fixed, paraffin-embedded, sectioned, and stained. Slides were imaged with a Nikon Eclipse 50i light microscope, magnification as indicated. Photographs of tissues were taken with the NIS Elements D3.10 camera and software system. (B) BM transplantation. Donor mice were treated with 5-FU, FdUMP[10], or Ara-C/Dox as in panel A, and 72 hours after last doses animals were killed and b/l femur cells were harvested. Ly5.1⁺ C57/Bl6 recipient mice were irradiated to 8 Gy and injected with donor cells. After 3 weeks recipients were harvested, and degree of femur engraftment by donor cells was determined by staining with Ly5.2 Ab and analyzed by flow cytometry. *P < .0001 and #P = .0827.