Radiation sensitivity of megakaryocyte colony-forming cells in human placental and umbilical cord blood

The in vitro radiation sensitivity of CPU-Meg isolated from human placental and umbilical cord blood was evaluated in plasma clot cultures stimulated by recombinant human cytokines, including thrombopoietin, the FLT3 ligand ( FLT3LG), interleukin-3, interleukin-11 and stem cell factor. The CD34(+) ce lls were irradiated with X rays at a dose rate of 73 cGy/min, The megakaryo cyte colonies were identified by using an FITC-conjugated antibody to glyco protein IIbIIIa and were classified into two groups based on colony size: l arge colonies (immature CPU-Meg) and small colonies (mature CPU-Meg), Treat ment with thrombopoietin alone or in combination with FLT3LG and/or interle ukin-11 gave exponential radiation survival curves (D-0 for immature CFU-Me g = 56-77 cGy, D-0 for mature CPU-Meg = 86 cGy-1.12 Gy), while marked shoul ders were observed on the survival curves for colonies supported by the com bination of thrombopoietin, interleukin-3 and stem cell factor (D-0 for imm ature CFU-Meg = 89-98 cGy; D-0 for mature CFU-Meg = 1.25-1.31 Gy). Our resu lts showed that the immature CPU-Meg were more radiosensitive than the matu re CPU-Meg and that the combination of cytokines, including thrombopoietin, interleukin-3 and stem cell factor, affected the radiation sensitivity of CFU-Meg to the same extent as with thrombopoietin alone or in combination w ith FLT3LG and/or interleukin-11. (C) 2000 by Radiation Research Society.