PRIMARY PROLIFERATING IMMATURE MYELOID CELLS FROM CML PATIENTS ARE NOT RESISTANT TO INDUCTION OF APOPTOSIS BY DNA-DAMAGE AND GROWTH-FACTOR WITHDRAWAL

Induction of apoptosis by growth factor deprivation or gamma-irradiati on-induced DNA damage was directly studied in proliferating primary ha emopoietic cells derived from CD34-positive cells of 13 CML patients a nd 12 normal controls, CD34-positive cells were cultured in the presen ce of appropriate concentrations of SCF and G-CSF for 5-7 d. After gam ma irradiation with 500 rad or growth factor deprivation, the fraction of apoptotic cells was assessed by two independent methods applying e ither measurement of cells incorporating FITC-labelled dUTP by termina l transferase or assessment of the fraction of cells with a less than 2N DNA content in flow cytometry. Proliferating CML cells were not res istant to the induction of apoptosis either after gamma irradiation or subsequent to growth factor deprivation. A similar fraction of normal and CML cells underwent apoptosis 48 h after withdrawal of growth fac tors. CML cells displayed an increased susceptibility to induction of apoptosis after DNA damage. A significantly higher proportion of apopt otic cells were detected in samples derived from CML patients after ir radiation with 0.5 Gy. These results, in conjunction with conflicting observations by other investigators, on the induction of apoptosis by gamma irradiation in various bcr-abl positive cells, suggest that bcr- abl-dependent effects on apoptosis strongly depend on the cells used, Our observations in CML cells derived exclusively from newly diagnosed CML patients demonstrate that bcr-abl expression per se is not suffic ient to induce resistance to apoptosis.