One has previously characterized two different hematopoietic cell populations (obtained by negative-selection) from normal bone marrow. Population I was enriched for CD34+ Lin- cells, whereas Population II was enriched for CD34+ CD38- Lin- cells. Both populations showed elevated proliferation and expansion potentials in serum-free liquid cultures, supplemented with a combination of eight different cytokines, with the latter displaying more immature features than the former. One has also characterized the chronic myeloid leukemia (CML) counterparts of these two populations and demonstrated functional deficiencies in terms of their growth in culture. In keeping with this line of research, the goal of the present study was to obtain the same two populations (Populations I and II) from acute myeloid leukemia (AML) bone marrow and to characterize their biological behavior under the same culture conditions. The results demonstrated that AML-derived Populations I and II were unable to proliferate in culture conditions that allowed significant proliferation of Populations I and II from normal marrow. Population I from AML also showed a deficient expansion capacity; in contrast, Population II cells were able to expand to a similar extent to the one observed for Population II from normal marrow. Both normal and AML populations were highly sensitive to the inhibitory effects of TNF-alpha; interestingly, whereas in normal fractions TNF-alpha showed a more pronounced inhibitory effect on more mature cells (Population I), this cytokine inhibited proliferation and expansion of AML Populations I and II in a similar degree. It is noteworthy that the functional deficiencies observed in AML cells were even more pronounced than those previously reported for cultures of CML cells. The results reported here may be of relevance considering the interest by several groups in developing methods for the in vitro purging of leukemic cells, as part of protocols for autologous transplantation of hematopoietic cells in leukemic patients.
In the present study, we have assessed the effects of recombinant human Granulocyte-Macrophage Colony-Stimulating Factor (rhGM-CSF) in Dexter-type long-term marrow cultures (LTMC) from patients with acute myelogenous leukemia (AML). Addition of rhGM-CSF to AML LTMC resulted in a significant increase in the number of total nucleated cells (1.3-4.3-fold, as compared to untreated cultures). However, a simultaneous decrease in the numbers of myeloid progenitor cells (CFU) was observed. Interestingly, there was a selective stimulation of the growth of leukemic progenitors (AML-CFU). Indeed, whereas on day 0 these cells were detected in only 2 patients, between weeks 1 and 5 they were detected in 10 of the 14 patients included in the study. It is noteworthy that around 50% of the cells detected in the non-adherent fraction of rhGM-CSF-treated AML LTMC were blasts, whereas in untreated cultures, blasts corresponded to only 23% of the non-adherent cells, and the majority corresponded to cells of the monocyte-macrophage lineage. These results indicate that rhGM-CSF is a cytokine with a significant stimulatory activity for the in vitro growth of AML progenitor andblast cells, and, together with previous reports in the literature, suggest that the use of rhGM-CSF in clinical settings must be taken with caution since this cytokine, although beneficial in reducing the risk of infections after chemotherapy, may induce the reappearance of the disease after treatment. Further studies should be encouraged to understand in greater detail the effects of rhGM-CSF, and other cytokines, on the hematopoietic system of AML patients.
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