Sensitivity of acute myeloid leukaemia cells to colony stimulating activity: relation to response to chemotherapy.

Agar cultures of acute myeloid leukaemia (AML) cells were used to determine the sensitivity of AML clone forming cells to the specific regulator granulocyte-macrophage colony stimulating activity (CSA). The mean CSA threshold (amount of CSA required to stimulate 0.5 of the clone forming cells) of 27 different AML cell samples varied from normal to an approximately nine-fold increase in CSA requirement. The degree of sensitivity to CSA at presentation was found to be closely correlated to the response to induction chemotherapy in 15 patients. There was a highly significant correlation (P less than 0.001) between the mean CSA threshold and the number of courses of chemotherapy required to induce remission. Also, an increased mean CSA threshold at presentation was associated with a significantly slower decline of marrow blasts following the first course of chemotherapy and a reduced remission rate. Sensitivity to CSA was closely related to the clone size achieved in maximally stimulated cultures of AML cells and this in turn also related to the remission rate and ease with which remission was achieved (presentation marrows, 39 patients). Possible reasons for the linking of these two functional properties of AML cells and their relation to response to chemotherapy will be discussed.