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

Abstract

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.