No abstract

Ionizing radiation kills hematopoietic stem and progenitor cells. However, several cytokines, including tumor necrosis factor‐α (TNF‐α), protect the murine hematopoietic system if they are introduced before or immediately after irradiation. We examined the in vitro capacity of TNF‐α to protect human hematopoietic stem cells and early progenitor cells from x‐ray‐induced death. Human CD34+ cells obtained from normal bone marrow were highly enriched for stem and progenitor cells. Pulse exposure of these cells to human TNF‐α during the first hour immediately after x irradiation (doses of 0.45 Gy to 9 Gy) significantly improved further survival of true hematopoietic stem cells and early progenitors and the ability of CD34+ cells to produce mature hematopoietic cells in liquid culture with hematopoietic growth factors. The radioprotective effect of TNF‐α was stronger at lower doses, when complete restoration of hematopoiesis was often observed. In contrast, the radioprotective effect of TNF‐α was moderate at higher doses, with neither complete restoration of the number of stem and progenitor cells nor the production of mature cells. Our data suggest that TNF‐α can protect human hematopoietic stem and early progenitor cells from ionizing radiation. Stem Cells 1997; 15(suppl 2): 95‐102