GM-CSF is a multilineage CSF because it stimulates the proliferation and differentiation of HPCs into neu-

trophil, eosinophil, and monocyte colonies. GM-CSF functions in conjunction with other cytokines, ery-thropoietin and IL-3, to promote the proliferation and differentiation of erythroid and megakaryocytic progenitors, respectively. Administration of GM-CSF not only increases the number of monocytes but also increases the function of monocytes and macrophages including oxidative metabolism, cytotoxicity, and Fc-dependent phagocytosis. GM-CSF enhances dendritic cell maturation, proliferation, and migration.24 The ability of GM-CSF to mobilize PBSC was first reported by Socinski et al.25 in 13 patients with sarcoma. After 4-7 days of GM-CSF at doses of 4-64 ^g/kg per day by continuous infusion, they found an 18-fold increase in peripheral blood CFU-GM and an eightfold increase in erythroid burst-colony forming units (BFU-E). Haas et al.26 observed an 8.5-fold increase in the number of circulating CFU-GM using a continuous infusion of GM-CSF at 250 ^g/m2 per day. A total of six aphereses were performed and the median number of MNC and CFU-GM collected was 36 X 109 and 209 X 104, respectively.

The efficacy of GM-CSF for stem cell mobilization has been compared with G-CSF in both normal donors and in cancer patients. Peters et al.27 suggested that GM-CSF is less efficacious than G-CSF in mobilization and found that the total numbers of CD 34+, CD 33+, and CD7+ cells collected per kg were higher in G-CSF mobilization than with GM-CSF. Weisdorf et al.28 found no significant advantage for either drug as mobilizing agents for PBSC used for autologous transplant in lymphoma patients. Lane et al.29 evaluated the PBSC mobilization efficacy of G-CSF at 10 ^g/kg per day (n = 8), GM-CSF 10 ^g/kg per day (n = 5), or GM plus G-CSF each at 5 ^g/kg per day (n = 5) in normal donors. The median CD34+ cell yield with the combination regimen and with G-CSF was significantly higher than with GM-CSF alone. It is widely accepted that as a single agent, G-CSF mobilizes more CD34+ cells than does GM-CSF.

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