Specific binding of radioiodinated human GM-CSF to the blast cells of acute myeloblastic leukemia

We describe here the presence of two classes of binding sites for GM-CSF expressed on blasts freshly isolated from five AML patients and one patient with CML in blastic phase: one of high-affinity (38-177 per cell, KD 8-150 pM) and one of low-affinity (121-806 per cell, KD 503-2683 pM). No correlation is observed between the receptor number, receptor affinity, and the growth stimulatory effect of GM-CSF on leukemic blast progenitors. Blasts from two cases showed no or negligible response to GM-CSF but expressed comparable numbers of receptors when compared with the numbers expressed by the sensitive blasts. Our data suggest that significant proliferative effects of GM-CSF can occur at low levels of high-affinity receptor occupancy. Lack of responsiveness to GM-CSF in some AML patients is not correlated to the absence of GM-CSF receptors on leukemic cells. Reduction in the growth of blast progenitors at high concentrations of GM-CSF may be attributed to the differentiating activity of GM-CSF via low-affinity receptors on leukemic cells.