Present and future clinical relevance of interleukin 3.

Interleukin 3 (IL-3) is a hematopoietic growth factor with a pronounced thrombopoietic activity as well as a broad spectrum of activities on multipotent, committed and mature cells of different lineages. Available for clinical trials since 1989, IL-3 has been used in well over two thousand patients. In numerous phase I-II clinical trials, the tolerability profile and the various biologic activities have been defined, and ongoing phase III trials will finally establish its clinical relevance. Doses between 2.5 and 10 micrograms/kg/d given subcutaneously are well tolerated, cause low grade fever, occasional flu-like symptoms and headache. At these doses IL-3 enhances platelet and neutrophil recovery after cycles of myelotoxic chemotherapy, resulting in better adherence to the planned chemotherapy doses and schedules and a decrease in the need for platelet transfusions. Accelerated engraftment of platelets and neutrophils is seen with IL-3 also after bone marrow transplantation. The effect on neutrophil recovery can be enhanced by the use of a myeloid growth factor such as granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte (G)-CSF after five to 10 days of IL-3. Treatment enhancement is related to the effect of IL-3 on the proliferation of hematopoietic progenitors, which leads to an increase in target cells for GM- or G-CSF. Because of the increase in bone marrow proliferation, IL-3 is being used to increase the mobilization of progenitor cells to the blood and in bone marrow failure.(ABSTRACT TRUNCATED AT 250 WORDS)