Blast colony‐forming cell binding from CML bone marrow, or blood, on stromal layers pretreated with G‐CSF or SCF

. Blast colony‐forming cells (CFU‐BL) represent a specific subpopulation of special primitive progenitors characterized by colony formation only in close contact with a preformed stromal layer. CFU‐BL derived from bone marrow of chronic myeloid leukaemia (CML) patients have been proved to adhere poorly to bone marrow derived stromal layers suggesting that the appearance of progenitors and precursors in the circulation is due to a defective adhesion of these cells to the bone marrow microenvironment. In the present experiments the effect of short‐term incubation of preformed normal bone marrow stroma on the adherence of CML derived CFU‐BL was studied. For stroma cultures bone marrow cells were cultured in microplates in the presence of hydrocortisone. Cultures were used when stromal layers became confluent and no sign of haemopoiesis could be observed. CFU‐BL were studied by panning plastic non‐adherent mononuclear (PNAMNC) bone marrow or blood cells. 8.9 ± 2.4 colonies/10 3 PNAMNC (six experiments) were formed from normal bone marrow on stromal layers and 4.8 ± 2.1 colonies/10 3 PNAMNC (five experiments) from CML bone marrow. Colony formation from normal bone marrow was not increased if stromal layers were incubated with 100 ng/mL granulocyte colony‐stimulating factor (G‐CSF) or stem cell factor (SCF). Incubation of stroma with G‐CSF or SCF, however, increased the colony formation of PNAMNC from CML bone marrow or blood significantly. These findings suggest that local concentration of haemopoietic growth factors at the time of panning may influence the attachment of CML progenitors to the stroma.