Kinetic characteristics of de novo and secondary AML cells influence their response to haemopoietic growth factor (HGF) priming and correlate with clinical outcome

This study has assessed the effect of in vitro haemopoietic growth factor (HGF) priming on the S phase activity of cells from patients with de novo AML and AML secondary to MDS. The occurrence of receptors for G-CSF, GM-CSF, IL-3 and SCF on marrow cells was assessed using immunofluorescent ligand binding assays. Additionally, patients responses to first phase induction chemotherapy was recorded to examine whether in vitro kinetic data might correlate with clinical outcome. All kinetic and receptor assays were performed in normal marrow cells to ascertain their response to priming. Incubation of AML cells in serum free medium (SFM)±G+GM-CSF, IL-3, SCF, G+GM-CSF+SCF or IL-3+SCF prior to S phase assessment revealed that priming permutations inclusive of SCF were most effective but also that the baseline level of S phase activity with SFM alone influenced the subsequent response to priming. Regardless of AML group, samples with low baseline S phase activity (10%) SFM S phase levels. However there was no corresponding difference in the percentages of cells bearing receptors. In both AML groups, low baseline S phase activity was observed more frequently in samples from patients who achieved CR. Normal samples possessed receptors for all HGFs and were responsive to all priming permutations except SCF alone. This study raises four points: (a) it may be prudent to reserve the use of priming HGFs for those patients with low baseline S phase activity whose cells respond in vitro and to use SCF in these priming cocktails; (b) the presence of receptors capable of ligand binding in AML samples did not guarantee kinetic response; (c) normal progenitors were responsive to priming which may have implications for haemopoietic reconstitution post therapy; and (d) the kinetic characteristics of AML progenitors may influence clinical outcome regardless of whether treatment includes HGFs.