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Haemopoietic growth factors, the cell cycle of acute myeloblastic leukaemia progenitors and sensitivity to cytosine arabinoside.

We describe an 'in vitro' model which permits assessment of acute myeloblastic leukaemia (AML) progenitor cells' response to Ara-C alone and in conjunction with recombinant human (rh) cytokines by evaluating cell cycle characteristics of purified AML blast progenitors and their chemosensitivity in clonogenic culture before and after cytokine priming. Parallel investigation of Ara-C/cytokine treatment on normal CFU-GM progenitors was included as these cells are important for post-therapeutic reconstitution of haemopoiesis. Kinetic and clonogenic findings for AML marrows were extremely variable with G+GM-CSF or IL-3 priming. However, inclusion of rhSCF and resultant synergism with the other cytokines, introduced a pronounced element of consistency in AML results. Normal CFU-GM responded to rhG+GM-CSF or IL-3 with increased kinetic activity and sensitivity to Ara-C. rhSCF synergised strongly with the other factors, causing increased cell cycling and attainment of maximal chemosensitivity 'in vitro'. No correlation was evident between 'in vitro' findings for AML samples, patient FAB types or clinical outcome. This study highlights the fact that both normal and AML cells can be targeted by rh cytokines, particularly when rhSCF is included in priming cocktails.