Hematopoietic effects of a granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein.

The common functional characteristics of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) may be explained by the presence of a subpopulation of cell surface receptors capable of binding both growth hormones. A GM-CSF/IL-3 fusion protein (pIXY 321) was produced in a yeast expression host. Receptor binding studies with HL-60, JM-1, AML-193, and KG-1 cell lines suggested that the GM-CSF and IL-3 regions had adopted a native conformation within the fusion protein. The fusion protein also exhibited enhanced biologic activity compared with GM-CSF or IL-3 in assays of normal, primary human hematopoietic progenitor cells. pIXY 321 may offer significant clinical advantages over the individual cytokines.