THE EFFECT OF RECOMBINANT HUMAN STEM-CELL FACTOR AND BASIC FIBROBLASTGROWTH-FACTOR ON THE IN-VITRO RADIOSENSITIVITY OF CD34(-CORD BLOOD() HEMATOPOIETIC PROGENITORS FROM HUMAN UMBILICAL)

Human umbilical cord blood (CB) cells selected by immunomagnetic beads for expression of the CD34 antigen were irradiated with increasing do ses of x-rays (72 cGy/min). Clonogenic survival of the hematopoietic p rogenitors, including mixed colony-forming cells (Mix-CFC), erythroid burst-forming units (BFU-E), and granulocyte-macrophage colony-forming cells (GM-CFC), was determined in methylcellulose cultures containing placenta conditioned medium (PCM) and erythropoietin (Epo). Exponenti al survival curves were fitted to the data of all the colonies, result ing in D-0 = 95 cGy for Mix-CFC, 136 cGy for BFU-E, and 136 cGy for GM -CFC. Additionally, the radiosensitivity of CD34(+) cells was studied employing cultures containing either recombinant human stem cell facto r (rhSCF) or basic fibroblast growth factor (b-FGF) in combination wit h PCM and Epo. It was found that the colony-forming efficiency (CFE) o f nonirradiated CD34(+) cells of 5.5% (range 1.4 to 14.4%) did not inc rease after the addition of SCF or b-FGF to the culture. The radiation response characteristics showed, however, that in the presence of SCF , the D-0 value and the extrapolation number n increased significantly . This suggests the stimulation of what operationally is termed ''reco very from potentially lethal damage.'' In contrast, no response modify ing effect could be seen for b-FGF.