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In vitro evaluation of the haemopoietic defect of CD34+ cells from patients with acute myeloid leukaemia in first remission

Haemopoietic cells from patients with acute myeloid leukaemia (AML) in first complete remission (CR1) show in vitro a haemopoietic defect and a decreased expansion potential. To better characterize this haemopoietic defect, CR1 AML and normal CD34+ cells were analysed for immunophenotype, viability, cell cycle and progenitor content before and during expansion culture in stroma‐conditioned medium supplemented with cytokines. The production of haemopoiesis inhibitor by patient cells and the influence of high concentrations of stem cell factor (SCF) and Flt3‐ligand (FL) on cell survival and ex vivo expansion potential were also studied. Before expansion, patient CD34+ cells showed viability and cell‐cycle phase distribution similar to normal but lower percentages of CD34+DR− or CD34+CD38− cells and lower progenitor content. After 48 h of culture ±30% of patient cells had died regardless of the cytokine combination used, whereas only 15% of normal cells died. After 7 d of culture, viability and cell cycle analyses showed comparable data for normal and patient samples. Co‐culture of patient and normal cells did not show any evidence for haemopoiesis inhibitor production by patient cells. Even at high cytokine concentrations, a low progenitor expansion and a decrease in CD34+ cell numbers was observed for patient samples in contrast to normal samples. In conclusion, CR1 AML CD34+ cells showed excessive early cell mortality. No evidence for cell‐cycle arrest or haemopoiesis inhibitor production was shown. SCF and FL used at high concentrations did not correct the patient cell expansion defect.