Amgen Inc.'s Neupogen granulocyte-colony stimulating factor and Epogen erythropoietin work extremely well to stimulate production of blood cells. But subsequent efforts to develop other blood cell boosters have met with more limited success.

Genetics Institute Inc.'s Neumega IL-11 and AMGN's Stemgen stem cell factor both received lukewarm FDA advisory committee recommendations based on what the panelists saw as equivocal data (see BioCentury Extra, July 31, and July 25, 1997). Neumega has received marketing approval while Stemgen is still under review. Other compounds, including AMGN's megakaryocyte growth and development factor (also being developed by Genentech Inc. (GNE) as thrombopoietin), have experienced problems in the clinic.