ABSTRACT
Leukemias and lymphomas appear as the result of an uncontrolled proliferation of cells from the hematopoietic system at large. The Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) activity, as indicated by the formation of GM colonies from bone marrow, spleen, or cord cells, was the first hematopoietic factor to be identified in the supernatants of cultures of phytohemagglutinin-stimulated T-lymphocytes and some human tumor cell lines. CSF-1 is a factor required for the survival, proliferation, and differentiation of cells of the monocytic lineage; it was shown to act on monocyte precursors, monocytes, and mature macrophages. Normal hematopoiesis represents a complex process, in which the functional and mature cells are continuously produced from progenitor cells. This process is precisely regulated by a network of growth factors and inhibitors and by various cellular interactions. The potential relevance of growth factors to the leukemic process is suggested by the fact that growth factors induce the proliferation and clonal expansion of malignant cells in vitro.
