Phase I study of recombinant human interleukin-3 in patients with bone marrow failure.

Interleukin-3 (IL-3) is a T-cell-derived colony-stimulating factor (CSF) whose primary targets include relatively early, multipotential, hematopoietic progenitor cells. In this trial, we treated 24 patients with recombinant human IL-3 given by a daily 4-hour intravenous infusion for 28 days. The dose levels were 30, 60, 125, 250, 500, 750, and 1,000 micrograms/m2/d. At least three patients were entered at every dose level. Each participant suffered from bone marrow failure, with the underlying diagnosis being myelodysplastic syndrome (13 patients), aplastic anemia (eight patients), or aplasia after prolonged high-dose chemotherapy (three patients) for multiple myeloma, breast cancer, or acute myelogenous leukemia. Most patients tolerated therapy well, with the most frequent side effects being low-grade fever and headaches. Hematopoietic changes included modest increases in neutrophil counts (eight patients), eosinophil counts (six patients), platelet counts (three patients), and reticulocyte counts (two patients). An increase in blasts occurred in one patient who had refractory anemia with excess blasts in transformation and was reversible once IL-3 was discontinued. In addition, one patient with chronic myelomonocytic leukemia showed an increase in monocytes (and granulocytes). Progression to acute leukemia did not occur. Pharmacokinetic analyses showed a rapid clearance with a mean half-life of 18.8 minutes at the 60 micrograms/m2/d dose, and 52.9 minutes at the 250 micrograms/m2/d dose. Serum concentrations of 10 to 20 ng/mL of IL-3 were achievable at the 250 micrograms/m2/d dose. Our observations indicate that recombinant human IL-3 can be given safely at doses of 1,000 micrograms/m2/d or less. In addition, on the basis of preclinical data and the biologic activity observed in this study, further trials of this molecule, alone and in combination with other growth factors, are warranted in patients with pancytopenia.