Potentiation of granulocyte colony-stimulating factor-induced mobilization of circulating progenitor cells by seven-day pretreatment with interleukin-3

Granulocyte colony-stimulating factor (G-CSF) as a single agent is increasingly used for the mobilization of peripheral blood progenitor cells (PBPCs) for stem cell tranplantation. In patients with perturbed hematopoiesis the mobilizing capacity of G-CSF alone may be inadequate. We have shown in rhesus monkeys that interleukin-3 (IL-3) pretreatment markedly potentiated the increase in PBPC numbers by subsequent administration of granulocyte/macrophage-CSF (GM-CSF). Here we studied the effect of IL-3 pretreatment on G-CSF-induced mobilization of PBPCs in 6 patients with Hodgkin's disease (n = 5) or non-Hodgkin's lymphoma (n = 1) who had low progenitor cell numbers because of previous chemotherapy. Patients were treated in cycle 1 with G-CSF at a dose of 5 μg/kg/d for 5 days and, after a treatment-free interval, received cycle 2 consisting of 5 μg/kg/d of IL-3 for 7 days followed by G-CSF again at a dose of 5 μg/kg/d for 5 days. G-CSF alone increased the the mean number of circulating colony-forming units-GM (CFU-GM) by 21-fold, the number of burst-forming units-erythroid (BFU-E) by 9-fold, and the number of CFU-mix by 24-fold over pretreatment values. Treatment with 5 μg/kg/d of IL-3 for 7 days did not mobilize by itself but significantly potentiated G-CSF-induced mobilization of all progenitor cell types leading to a 56-, 15-, and 46-fold increase over baseline of CFU-GM, BFU-E, and CFU-mix numbers, respectively. In 2 patients in whom leukapheresis was performed after G-CSF alone the target number of 2 x 10⁶/kg CD34⁺ cells was not reached. However, leukapheresis after the IL-3/G-CSF combination obtained ≥2 x 10⁶/kg CD34⁺ cells in 3 of 6 patients, including both patients who had inadequate collection after G-CSF alone. In one patient adequate function of mobilized progenitors could be shown by the demonstration of rapid trilineage engraftment after infusion of progenitors after myeloablative chemotherapy. Seven-day pretreatment with IL-3 may be a useful mean to augment mobilization of circulating progenitors by G-CSF. The combination of IL-3 and G-CSF seems to allow the procurement of sufficient numbers of PBPCs in some patients who cannot be mobilized adequately by G- CSF alone.