Human blood granulocyte macrophage progenitors (GM-CFU) during extended field radiation therapy.

The rate of the clonogenicity of granulocyte macrophage forming cells (GM-CFU) in agar was analysed using mononuclear cells from the peripheral blood of cancer patients undergoing total body irradiation (TBI, 5 patients, 1.5 Gy in 15 days) or hemicorporal irradiation of the lower (LHBI, 5 patients, 15 Gy in 15 days) or upper (UHBI, 4 patients, 15 Gy in 15 days) part of the body. Although the GM-CFU level in the blood is low compared with that in the bone marrow, and shows considerable variability, the preliminary results demonstrated that in most cases the GM-CFU level was increased around the 10th day after the beginning of irradiation, followed by a return to base level within a few days, for LHBI and TBI but not for UHBI. The question of whether the observed peak for the clonogenicity was due to stem cells leaving a radiation-injured compartment of the bone marrow or to vicarious stem cells migrating from non-irradiated regions, or was the result of enhanced activity of colony-stimulating factors, remains to be investigated.