High spontaneous granulocyte/macrophage-colony formation in patients with myelofibrosis.

Unstimulated methylcellulose cultures in 25 myelofibrosis (MF) patients were performed to better understand the role of cytokines in the proliferation of MF cells. Compared to controls MF patients show a variable but highly increased spontaneous CFU-GM formation (66 vs 4.8/10(5) PBMNC). There was a marked reduction of autonomous CFU-GM growth by the cytokine-synthesis-inhibiting molecule IL-10 as well as by antibodies against GM-CSF whereas antibodies against IL-3, G-CSF, M-CSF and IL-1β showed heterogeneous effects. Spontaneous CFU-GM growth >100/10(5) PBMNC predicted shorter survival. Constitutive release of GM-CSF seems to contribute to proliferation of MF cells in vitro and possibly in vivo.