Proliferative Effect of Human Granulocyte Colony‐stimulating Factor on Blast Cells of Acute Promyelocytic Leukemia

The effect of human granulocyte colony‐stimulating factor (G‐CSF) on leukemic cells of acute promyelocytic leukemia (APL) was examined. Mononuclear cells obtained from bone marrow cells containing more than 90% blasts from seven APL patients were incubated in the presence of G‐CSF using semisolid and liquid culture systems. On day 7, the cells from all the patients produced many clusters consisting of 8–40 cells. These cells appeared to be promyelocyte‐like blast cells in four patients and had differentiated to more mature neutrophils in three patients. On day 14, the number of clusters decreased except for two patiens. Blast cells from the two patients showing the increase of blast clusters could proliferate in a liquid culture containing G‐CSF. Blast cells cultured for 14 days formed many secondary cultures after replating on a methylcellulose medium. Moreover, chromosomal analyses of blasts cultivated in the presence of G‐CSF for 7 days showed t(15;17) in all metaphases in one patient. It appears that the leukemic cells from APL patients could proliferate in the presence of G‐CSF.