Flt-3 ligand does not induce the growth of peripheral blood granulocyte-macrophage colony-forming cells in myeloproliferative disorders

Flt-3 ligand (FL) is a growth factor (GF) which might have clinical use as a mobilizer of stem and progenitor cells into peripheral blood (PB) in auto logous transplantations of various malignant haematological diseases, unles s FL stimulates the growth of malignant cells in these diseases. The presen t study evaluated the effects of FL on the proliferation of granulocyte-mac rophage (GM) progenitor cells collected from PB of 24 patients with chronic myeloproliferative disorders (MPDs) by using a methylcellulose assay in se rum-free culture conditions. It was shown that FL as a single factor had no stimulatory effect on GM colony formation either in the whole MPD group or in the MPD subgroups, which comprised 9 patients with essential thrombocyt haemia, 7 with polycythaemia vera and 8 with chronic myelogenous leukaemia. No increase in GM colony formation was observed, either, when FL was used in combination with other GFs, such as mast cell growth factor (MGF), granu locyte-colony stimulating factor (G-CSF), GM-CSF or interleukin-3 (IL-3). G M-CSF and IL-3 were the only single GFs which significantly increased GM co lony formation in the whole MPD group. As a conclusion, FL does not seem to induce GM colony formation of MPDs alone or in combination with G-CSF in i n vitro colony assays.