Effect of cytokines on growth and differentiation of leukaemic cells with translocation t(6;9)(p23;q34).

The translocation t(6;9)(p23;q34) is detected infrequently in subtypes of haematological malignancies including acute myelogenous leukaemia (AML) and myelodysplastic syndrome (MDS). Although the t(6;9) leukaemia is commonly associated with bone marrow basophilia, the cytological characteristics of leukaemic cells are unclear. In the current study, we examined the in vitro effects of several cytokines on growth and differentiation of t(6;9) leukaemic cells. Isolated bone marrow mononuclear cells from four patients with t(6;9) (two MDS and two AML) were cultured for 14 d in the presence or absence of each cytokine. At the end of culture, viable cells were counted, and their histology was examined. Bone marrow cells obtained from 22 patients (10 AML, six AML from MDS, six MDS) lacking t(6;9) were used as controls. Compared with control cultures, significantly higher numbers of blasts appeared in the culture of bone marrow cells from t(6;9)-positive patients in response to stimulation with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF) or interleukin 3 (IL-3). Stem cell factor (SCF) had little effect. Neutrophil counts were also significantly increased in the presence of G-CSF or IL-3. SCF and IL-3 were potent in increasing basophil counts from t(6;9)-positive cultures. These findings suggest that bone marrow cells obtained from t(6;9) patients are highly sensitive to growth- and/or differentiation-promoting cytokines. Special attention should be paid to the use of "therapeutic" cytokines in these patients.