[In vitro effects and possible clinical relevance of interleukin 3]

Cytokines are mainly produced by monocytes and lymphocytes and influence a broad spectrum of physiological processes within the hematopoietic and the immune system. Clinical trials have mainly been initiated with a subgroup of cytokines namely the hematopoietic growth factors. Interleukin 3 (IL-3) was recently introduced into phase I and II trials. This factor was also termed "multipoietin" because of its ability to stimulate in vitro the hematopoietic stem cell and thus all three hematopoietic cell lines. The latest in vivo data, however, demonstrate that IL-3 stimulates leukopoiesis and megakaryopoieis with only marginal effects on erythropoiesis. In large clinical trials the therapeutic effect of this factor is investigated in patients with myelodysplastic syndromes. Further indications will be other primary bone marrow failures and aplasia caused by bone marrow transplantation, aggressive chemotherapy and radiation. Potential applications offered by combinations with other cytokines can hardly be foreseen.