[In vitro and in vivo effects of recombinant human interleukin-3 on hematopoietic progenitor cells].

As part of a phase I/II clinical trial with recombinant human Interleukin-3 (rhIL-3), bone marrow and peripheral blood cells from patients treated with rhIL-3 were assessed in vitro for effects on the cycling status and frequencies of erythroid, myelomonocytic and multilineage progenitor cells. Treatment with rhIL-3 induced a pronounced increase in S-phase rate of BFU-E, CFU-GEMM and day 14 CFU-GM. Circulating CFU-GEMM and day 14 CFU-GM were increased on day 7 of therapy whereas circulating BFU-E were reduced in the majority of patients. After i.v. bolus injection of IL-3 an acute effect on the peripheral blood count with neutrophilia and, after an initial nadir, monocytosis was observed. IL-6 serum-levels increased in 5 out of 14 patients after IL-3 administration with concomitant side effects in 2 patients in whom IL-6 levels increased above 75 pg/ml. In the majority of the patients a stimulation of peripheral leukocytes and platelets was observed during the 15 day treatment course. In conclusion rhIL-3 induces a multilineage response in vivo by stimulating proliferation of hemopoietic progenitor cells with a resulting elevation in peripheral blood counts.