Heterogeneity of radiation sensitivity of hemopoietic stem cell subsets.

Immature hemopoietic cells are heterogeneous with respect to repopulating capacity following exposure to ionizing radiation, growth factor receptor and surface marker phenotype as well as cycling state. In the present paper, the evidence from studies in subhuman primates and mice is reviewed, which demonstrates that the heterogeneity of immature stem cells is also reflected by a differential sensitivity to radiation, the most immature stem cells with long-term repopulating capacity being less sensitive to radiation than assumed on the basis of 50% lethal dose (LD50) data, and the radiation sensitivity of immature hemopoietic cells measured by the spleen-colony test. In addition, these immature cells appear to have a considerable repair capacity. These findings have a direct bearing on future strategies for the treatment of patients after accidental exposure to ionizing radiation, either by transplantation of (subsets of) stem cells or by administration of a specific combination of hemopoietic growth factors.