Residual damage of lymphohematopoietic repopulating cells after irradiation of mice at different stages of development

Objective. The purpose of this study was to evaluate the repopulating prope rties of bone marrow (BM) from mice irradiated during embryonic and adult s tages of development. Materials and Methods. Four-day-old embryos, 17-day-old fetuses, and 12-wee k-old mice were irradiated with of 1 or 3 Gy of x-rays, At 3 and 9 months p ostirradiation, the effects generated within the different compartments of repopulating cells (RCs) were evaluated by determining, in a BM competition assay, the contribution of the irradiated precursors to the lymphohematopo iesis of recipients at different times posttransplantation (3, 9, and 15 mo nths). Results. The irradiation of 4-day-old embryos with either 1 or 3 Gy did not produce residual repopulation or differentiation effects within the differ ent RCs assayed, However, significant impairments in RC functionality were observed in mice irradiated on the 17th day postconception or at the 12th w eek of age. Whereas irradiation of these animals with 1 Gy did not impair t he long-term functionality of the very primitive 15-month-old RCs, irradiat ion with 3 Gy generated sustained impairment in all tested types of hematop oietic progenitors and RCs, Moreover, repopulation data derived from the an alysis of recipient BM and thymus strongly suggested that the observed effe cts were produced within the multipotent pool of lymphohematopoietic RCs. Conclusions. Our data show the generation of long-term effects in the multi potent RCs of mice irradiated at fetal and adult stages of growth and revea ls the normal functionality of the RCs from animals irradiated during the e arly stages of embryonic development, (C) 2000 International Society for Ex perimental Hematology. Published by Elsevier Science Inc.