Haemopoietic growth factors

The growth and development of mature blood cells in vitro is supported by a series of glycoproteins with a range of biological activities. Many of these growth factors have been molecularly cloned, purified to homogeneity, and their biological effects determined on various target cells. Some of these growth factors promote the proliferation and differentiation of multipotent stem cells; others are more restricted in their action and, when used alone, can support only the development of lneage-restricted progenitor cells. When used in combinations however, the spectrum of target cells supported by these growth factors can be considerably enlarged. Furthermore, other molecules (which are not themselves growth promoters for multipotent stem cells) can synergise with these growth factors and permit primitive cells to undergo proliferation and development. These findings are likely to have major therapeutic implications.