| Abstract: |
The effects of different dose rates of in vitro irradiation on the proliferative capacity of marrow stromal, hematopoietic and leukemic colony-forming cells (CFC) are described. Marrow cell suspensions, HL-60 cells and trypsin-dispersed fibroblasts were irradiated at 5 or 45 cGy/min and then assayed for CFC. Irradiation at low (5 cGy/min) compared to high (45 cGy/min) dose rate showed a significant difference in survival of stromal and of HL-60 cells, but not of hematopoietic progenitors: the respective D0 values were 170 and 120 (p = 0.003) for marrow fibroblastic progenitors (CFU-F); 145 and 110 (p = 0.005) for passaged marrow fibroblasts (CFU-F); 170 and 140 (p = 0.045) for HL-60 cells; 85 and 85 for multipotential CFC (CFU-mix); 125 and 120 for erythroid progenitors (BFU-E); and 115 and 120 for granulomonopoietic progenitors (CFU-GM) (p = 0.5 for hematopoietic clonogenic cells). Marrow suspensions did not establish confluent stromal layers in long-term marrow cultures following irradiation with 600 cGy at 45 cGy/min, whereas after 840 cGy at 5 cGy/min confluent stromal layers were obtained. This indicates that low dose rate-sparing effect applies to all stromal cell progenitors. Confluent stromal layers derived from progenitors surviving irradiation sustained hematopoiesis as well as controls when co-cultured with fresh hematopoietic cells. Adherent layers in long-term marrow cultures irradiated after establishment with doses less than or equal to 1500 cGy at 5 or 45 cGy/min also showed normal hematopoietic supportive function when co-cultured with freshly isolated hematopoietic cells.(ABSTRACT TRUNCATED AT 250 WORDS) |
