Granulocyte/macrophage colony-stimulating factor and accessory cells modulate radioprotection by purified hematopoietic cells.

Granulocyte/macrophage colony-stimulating factor (GM-CSF) promotes the survival, proliferation, and differentiation of myeloid lineage cells and regulates chemotaxis and adhesion. However, mice in which the genes encoding GM-CSF (Gmcsf) or the beta common subunit of the GM-CSF receptor (betac) are inactivated display normal steady-state hematopoiesis. Here, we show that host GM-CSF signaling strongly modulates the ability of donor hematopoietic cells to radioprotect lethally irradiated mice. Although bone marrow mononuclear cells efficiently rescue Gmcsf mutant recipients, fetal liver cells and Sca1(+) lin(-/dim) marrow cells are markedly impaired. This defect is partially attributable to accessory cells that are more prevalent in bone marrow. In contrast, Gmcsf-deficient hematopoietic stem cells demonstrate normal proliferative potentials. Short-term survival is also impaired in irradiated betac mutant recipients transplanted with fetal liver or bone marrow. These data demonstrate a nonredundant function of GM-CSF in radioprotection by donor hematopoietic cells that may prove relevant in clinical transplantation.