SHORT-TERM EFFECTS OF EARLY-ACTING AND MUTILINEAGE HEMATOPOIETIC GROWTH-FACTORS ON THE REPAIR AND PROLIFERATION OF IRRADIATED PURE CORD-BLOOD (CB) CD34(+) HEMATOPOIETIC PROGENITOR CELLS

Purpose: Hematopoietic growth factor(s) (GF) may exert positive effect s in vitro or in vivo on the survival of hematopoietic stem and progen itor cells after accidental or therapeutic total body irradiation. Met hods and Materials: We studied the clonogenic survival and DNA repair of irradiated (0.36, 0.73, and 1.46 Gy) CD34(+) cord blood (CB) cells after short-term incubation (24 h) with GFs. CD34(+) cells were stimul ated with basic fibroblast growth factor (bFGF), stem cell factor/c-ki t ligand (SCF), interleukin-3 (IL-3), IL-6, leukemia inhibitory factor (LIF), and granulocyte-monocyte colony stimulating factor (GM-CSF) al one or in combination in short-term serum-free liquid suspension cultu res (LSC) immediately after irradiation and then assayed for clonogeni c progenitors. DNA repair was evaluated by analysis of DNA strand brea ks using the comet assay. Survival of CFU-GM, BFU-E, and CPU-Mix was d etermined and dose-response curves were fitted to the data. Results: T he radiobiological parameters (D-0 and n) showed significant GF(s) eff ects. Combination of IL-3 with IL-6, SCF or GM-CSF resulted in best su rvival for CFU-GM BFU-E and CFU-Mix, respectively. Combinations of thr ee or more GFs did not increase the survival of clonogenic CD34(+) cel ls compared to optimal two-factor combinations. The D-0 values for CFU -GR I, BFU-E, and CFU-Mix ranged between 0.56-1.15, 0.31-2.24, and 0.5 6-1.29 Gy, respectively. As for controls, the curves remained strictly exponential, i.e., all survival curves were strictly exponential with out any shoulder (extrapolation numbers n = 1 for all tested GF(s). DN A repair capacity of CD34(+) cells determined by comet assay, was meas ured before, immediately after irradiation, as well as 30 and 120 min after irradiation at 1 Gy. Notably, after irradiation the 2-h repair o f cytokine-stimulated and unstimulated CD34(+) cells was similar. Conc lusion: Our data indicate that increased survival of irradiated CB CD3 4(+) cells after short-term GF treatment is mediated through prolifera tive GF effects on the surviving fraction but not through improved DNA repair capacity. (C) 1998 Elsevier Science Inc.