granulocyte-macrophage colony-stimulating factor

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A naturally occurring protein that stimulates the production of granulocytes and macrophages by stem cells and is used as a drug by some immunosuppressed individuals.

Wiktionary

1. n. A cytokine protein secreted by macrophages, T cells, mast cells, endothelial cells and fibroblasts.