Variable differentiation patterns of acute myelogenous leukaemia blasts in liquid suspension cultures

To study the ability of acute myelogenous leukaemia blasts to spontaneously differentiate in vitro, bone marrow and/or blood mononuclear cells from 63 patients with acute myelogenous leukaemia were incubated in liquid suspension cultures containing human serum, without addition of chemical inducers of differentiation. Cultures were examined weekly for disappearance or persistence of blasts, and for appearance of morphologically recognizable granulocytes and macrophages. Culture outcomes were extremely variable, ranging from lack of appearance of differentiated cells to complete disappearance of blasts with replacement by mature cells. In 50 cases an increase (25-185%) in the absolute number of differentiated cells in culture was noted during the culture period. Full differentiation was seen exclusively in cultures from 13/48 (27.1%) patients studied at diagnosis, as compared to 0/20 patients studied at relapse (P less than 0.01). The ability to fully or partially differentiate in culture was lost to a significant degree at relapse (13/20 patients) as compared to diagnosis (48/48 patients, P = 0.0001). At diagnosis full differentiation in culture was associated with a significantly higher remission rate than partial differentiation (89% versus 40%, P less than 0.02). Origination of mature cells from leukaemic rather than normal precursors was suggested by the appearance of Auer rods in mature cells in seven cases, by the correlation of types of differentiated cells seen in culture with the FAB class of leukaemia and by cytogenetic data in one case.