Preleukemic change in the bone marrow of whole-body irradiated RFM/Up mice.

In the whole-body irradiated mouse, various late effects of radiation are observed after the recovery from acute radiation injury. Some of these account for the familiar proneness of certain mouse strains to develop leukemias. The two experiments described below were designed to (a) identify such preleukemic changes in blood-forming tissues and (b) to find ways to manipulate them experimentally with the purpose of preventing leukemia. Preleukemic change of the bone marrow appears to be a mere quantitative departure from normal in a qualitatively non-malignant tissue. It entails increased proneness of immature (precursor) cells to react with latent virus. Our data are consistent with the assumption that this proneness is enhanced (or brought about) by removal of a controlling influence exerted by the mature cells over their precursors (feed-back inhibition). Re-irradiation combined with intravenous bone marrow substitution offsets the leukemogenic influence of an earlier radiation exposure. The effect of re-irradiation on bone marrow displaying preleukemic lesions corroborates conclusions from earlier experiments on the nature of these lesions.