EVIDENCE FOR INTERNAL AUTOCRINE REGULATION OF GROWTH IN ACUTE MYELOBLASTIC-LEUKEMIA CELLS

Blast cells from 70% of patients with acute myeloid leukemia (AML) sho w some evidence of in vitro autonomous growth, which appears to be rel ated to the autocrine secretion of growth factors, particularly granul ocyte-macrophage colony-stimulating factor (GM-CSF). In the majority o f cases, the growth factors appear to be involved in classical extrace llular autocrine or paracrine loops with neutralizing antibodies to th e relevant cytokine inhibiting growth despite evidence of secretion of the cytokine. There is evidence for intracellular autocrine loops in murine leukemic cell lines. In this study, we wished to investigate fo r the presence of such intracellular loops involving GM-CSF in AML bla st cells. Blast cells from 11 patients with AML were cultured in the p resence of either neutralizing GM-CSF antibody or an antisense oligonu cleotide directed against GM-CSF. We also studied the effect of the ol igonucleotide on the autonomous growth of cells whose production of GM -CSF had been apparently abolished by either interleukin-1 receptor an tagonist (IL-1Ra) or following blast cell purification using the CD34 antigen. The autonomous growth of the blast cells from nine of the 11 patients was inhibited by the antisense oligonucleotide (but not by th e control sense oligonucleotide). However, only six of the nine were i nhibited by the anti-GM-CSF antibody. Similarly, in one patient whose CD34 purified blast cells continued to show a high degree of autonomou s growth but did not produce detectable GM-CSF, growth was inhibited b y the antisense oligonucleotide but not by antibody, while in another patient whose cells were inhibited by IL-1Ra with, again, loss of dete ctable GM-CSF, growth could be further inhibited by the addition of th e oligonucleotide but not the antibody. These studies provide evidence that intracellular autocrine loops involving GM-CSF are involved in t he autonomous growth of some AML blast cells.