Neutrophils are the body's critical phagocytic cells for defense against bacterial and
fungal infections; bone marrow must produce approximately 10 x 10(9) neutrophils/kg/d to maintain normal blood neutrophil counts. Production of neutrophils depends on myeloid
growth factors, particularly
granulocyte colony-stimulating factor (
G-CSF). After the original phase of development, researchers modified these
growth factors to increase their size and delay renal clearance, increase their
biologic potency, and create unique molecules for business purposes. Pegylated
G-CSF is a successful product of these efforts. Researchers have also tried to identify small molecules to serve as oral agents that mimic the parent molecules, but these programs have been less successful. In 2006, the European Medicines Agency established guidelines for the introduction of new
biologic medicinal products claimed to be similar to reference products that had previously been granted marketing authorization in the European community, called bio-similars. Globally, new and copied versions of
G-CSF and other myeloid
growth factors are now appearing. Some properties of the myeloid
growth factors are similar to other agents, offering opportunities for the development of alternative drugs and treatments. For example, recent research shows that hematopoietic progenitor cells can be mobilized with a
chemokine receptor antagonist,
chemotherapy,
G-CSF, and
granulocyte macrophage colony-stimulating factor. Advances in neutrophil biology coupled with better understanding and development of myeloid
growth factors offer great promise for improving the care of patients with
cancer and many other disorders.