Blood cells are vital to life: they transport oxygen and carbon dioxide, contribute to host immunity, and facilitate blood clotting. An intricate, multistep pro-cess allows immature precursor cells in the bone marrow to differentiate, mature, and become func-tional blood cells. Ordinarily, this well-regulated process allows for replacement of cells lost through daily physiologic activities. The process is also capable of producing adequate and appropriate cells for fighting infection and for replacing cell losses due to hemorrhaging or destruction. The process of production and maturation of blood cells is called hematopoiesis.
In the early 1900s, scientists recognized the presence of circulating factors that regulate hemato-poiesis. It took approximately 50 years, until cell culture systems were developed that could sustain cell colonies in vitro, to definitively prove the activity of these proteins. The growth and survival of early blood cells required the presence of specific factors, called colony-stimulating factors (CSF). However, hematopoietic growth factor (HGF) is the preferredterm because it is more precise than the term based on laboratory observations of the effects of these factors.
Efforts to purify HGFs progressed throughout the 1970s and early 1980s. Blood and other materials (e.g., bone marrow and urine) contain extremely small amounts of growth factors. The presence of many growth factors confounded the search for a single growth factor with a specific activity. Scientific progress was slow until it became possible to purify sufficient quantities to fully evaluate the character-istics and biologic potential of the isolated materials. The introduction of recombinant DNA technology triggered a flurry of studies and an information explosion. Many HGFs have been isolated; some have been studied extensively, and a few have been made for clinical or commercial use.