SPONTANEOUS MEGAKARYOCYTE COLONY FORMATION IN MYELOPROLIFERATIVE DISORDERS IS NOT NEUTRALIZABLE BY ANTIBODIES AGAINST IL3, IL6, AND GM-CSF

Megakaryocyte progenitor growth in 42 patients with myeloproliferative disorders (MPD), including 23 essential thrombocythaemia (ET), eight polycythaemia vera (PV), six chronic myelogenous leukaemia (CML) and a ve primary myelofibrosis (PMF), was studied in vitro using plasma clot assay and serum-free agar culture. Spontaneous megakaryocyte colonies (CFU-MK) were found in 34/40 (80%) blood and 14/18 (77.8%) bone marro w plasma clot cultures, and also observed in 27/35 (77.1%) blood and 1 0/18 (55.6%) bone marrow serum-free agar cultures. In the blood of 27 patients with MPD (15 ET, four PV, four CML and four PMF) and the bone marrow of 10 patients (five ET, four CML and one PV), spontaneous col ony formation was observed in both plasma clot and serum-free agar cul tures. However, spontaneous CFU-MK was only found in plasma clot cultu re, but not in agar culture in two blood (one ET and one CML) and four bone marrow cultures (one ET, two PV, one CML). The colony numbers we re greatly increased in the presence of aplastic anaemia serum (AAS) u nder both conditions. In 17 patients (12 ET, two CML and three PV) wit h spontaneous megakaryocyte colonies, anti-cytokine antibody neutraliz ing experiments were carried out in blood cultures. Anti-IL3, anti-IL6 and anti-GM-CSF antibody, alone or in combination, at different conce ntrations (1, 5 and 10 mu/ml), were added into plasma clot or agar cul tures without exogenous stimulating growth factors. The results showed that the numbers of spontaneous megakaryocyte colonies were not signi ficantly decreased in the presence of these monoclonal antibodies in t he cultures. The data indicated that the megakaryocyte progenitor grow th in MPD under in vitro conditions was heterogenous, and independent of exogenous stimulatory factors in most patients and that optimal meg akaryocyte colony development in MPD still requires exogenous growth f actors. Three possibilities are discussed with regard to the phenomeno n that the spontaneous colony formation was not decreased with the add ition of anti-IL3, anti-IL6 and anti-GM-CSF antibodies.