Biologic Properties In Vitro of a Recombinant Human Granulocyte-Macrophage Colony-Stimulating Factor

stimulating factor (rH GM-CSF) was purified to homogene-ity from medium conditioned by COS cells transfected with a cloned human GM-CSF cDNA and shown to be an effective proliferative stimulus in human marrow cultures for GM and eosinophil colony formation. The specific activity of purified rH GM-CSF in human marrow cultures was calculated to be at least 4 x iO U/mg protein. Clone transfer experiments showed that this proliferation was due to direct stimulation of responding clonogenic cells. Acting alone, rH GM-CSF did not stimulate erythroid colony formation. but in combination with erythropoietin. increased erythroid and multipotential colony formation in cultures of peripheral blood cells. rH GM-CSF had no T HE granulocyte-macrophage colony-stimulating factors (CSFs) are specific glycoproteins that control the pro