Pattern of leukemia induction in BC3F1 mice transplanted with irradiated lymphohemopoietic tissues

(C57BL/Cne X C3H/Cne)F1 male mice spontaneously develop reticulum cell sarcoma (RCS) with an average final incidence of 56%; neither myeloid leukemia (ML) nor thymic lymphoma (TL) has been observed in intact animals. X rays (4Gy, 250 kV) induce a few cases of ML but no TL. In increasing the dose to 6 Gy, we observed a few cases of TL, no ML, and a drastic reduction (8%) of RCS. The same dose of 6 Gy fractionated into four weekly doses of 1.5 Gy induced 24% of TL. By transplanting cells into appropriately preirradiated (4 Gy) syngeneic recipients we found evidence that four weekly doses of 1.5 Gy to donor animals caused an excess of ML and drastic changes of both TL and RCS incidences and rates in recipients as a function of time postirradiation at which the lymphohemopoietic tissues are transplanted. Furthermore, the same transplanted animals showed an evident acceleration of time of appearance of RCS and an enhanced incidence of NL; the latter effect is significant 10 days after the last X-ray fraction, but not thereafter. These data are in line with the hypothesis that committed cells for these two types of systemic tumors may be present among the irradiated transplanted tissues