Human GM-CSF Carrier-Free Recombinant Protein, eBioscience?. GM-CSF (Granulocyte-Macrophage colony-stimulating factor) is a 14.6kDa hematopoietic growth factor that exists in glycosylated and non-glycosylated biologically active forms, and stimulates the development of granulocytes, macrophages, early megakaryocytes and eosinophil progenitor cells. The active form of the GM-CSF protein is found extracellularly as a homodimer and the GM-CSF gene has been localized to a cluster of related genes at chromosome region 5q31, which is known to be associated with interstitial deletions in the 5q-syndrome and acute myelogenous leukemia. Other genes in the cluster include those encoding interleukins 4, 5, and 13. The ability of recombinant GM-C