The past decade has witnessed the cloning and characterization of several hematopoietic growth factors. Many of these have already assumed a role in medical treatment. However, since these factors typically have more than one action, some of these actions may be undesirable in a given case. For example, some cytokines used to ameliorate chemotherapy-induced neutropenia may have the undesirable effect of stimulating the growth of tumor cells or of activating mature neutrophils. Hence, growth factors alone provide insufficiently precise control of the hematopoietic system.
Growth factors are only a part of a complex system regulating hematopoiesis.
For each growth factor there is a receptor, signal transducers, and responsive genetic elements. Much current work focuses on signal transduction. Intervention via signal transducers may be complicated by the fact that some signal transducers are common to several pathways serving different functions. Studies in several animal and cell culture systems support the idea that tyrosine kinase receptors, Ras and protein kinase C are part of a common signaling pathway. Thus, identification of responsive genetic elements for growth factors may be the best approach to obtain the specificity required for therapeutic intervention.