Effect of Radiation Exposures on Fetal Hematopoietic Cells

Purpose of this Review It has generally been thought that fetuses are highly sensitive to radiation-induced cancer. Epidemiologic case-control studies indicated that X-ray exposures given to pregnant women (on the order of 1 cGy) could have increased the risk of developing childhood leukemia and solid cancers in the offspring. The authors wished to re-consider this observation. Recent Findings Atomic bomb survivors who were exposed in utero were found to show almost no increase in the frequency of translocations in their blood lymphocytes when the survivors were examined at around 40 years of age. Subsequent animal studies revealed that tissue stem cells in embryos/fetuses may or may not retain radiation-induced chromosome damage depending on the developmental stage at the time of irradiation. Summary Our data are compatible with the model that radiation effects can be recorded only when an exposure occurs after the stem cells have settled in their appropriate niche, and that a small fraction of fetal hematopoietic stem cells began making long-term contributions to the lymphoid cell pool in both mice and humans. It remains to be established whether or not the increased risk of childhood leukemia and other childhood cancers was caused by fetal X-ray exposures of about 1 cGy.