Effects of Syngeneic Bone Marrow Cells on Mice Given a Leukemogenic Treatment with Urethan

A leukemogenic treatment with urethan in infant (SWR x C57BL)F₁ mice (1 mg/g body weight, 5 times, once every second day) induced a marked reduction of the thymus and spleen weight, of the number of RBC, WBC, and bone marrow cells, with an inverted lymphoid/myeloid cell ratio in the bone marrow. An analysis of the bone marrow population showed that the carcinogen acted selectively on the lymphoid cells and, to a lesser extent, on the erythroblastic ones, while the myeloid cells did not appear to be involved. The damage was still present 10 days after the end of treatment. A single intracardiac inoculum of 15–20 × 10⁶ syngeneic normal bone marrow cells, 3 days after the last urethan injection, determined a recovery of the spleen weight and of the cell ratio in the bone marrow, whereas the thymus weight and the blood and bone marrow cell counts were uneffected. Moreover the bone marrow inoculum failed to inhibit the induction of thymic lymphosarcomas.