Myeloid cell kinetics in mice treated with recombinant interleukin-3, granulocyte colony-stimulating factor (CSF), or granulocyte-macrophage CSF in vivo.

Myeloid cell kinetics in mice treated with pure hematopoietic growth factors have been investigated using tritiated thymidine labeling and autoradiography. Mice were injected subcutaneously with 125 micrograms/kg granulocyte colony-stimulating factor (G-CSF) (in some cases 5 micrograms/kg), or 10 micrograms/kg of granulocyte-macrophage CSF (GM-CSF), or interleukin-3 (IL-3) every 12 hours for 84 hours. 3HTdR labeling was performed in vivo after 3 days of treatment. G-CSF increased the peripheral neutrophil count 14-fold and increased the proportion and proliferation rate of neutrophilic cells in the marrow, suppressing erythropoiesis at the same time. Newly produced mature cells were released into the circulation within 24 hours of labeling, compared with a normal appearance time of about 96 hours. By contrast, GM-CSF and IL-3 had little effect on either marrow cell kinetics or on the rate of release of mature cells, although GM-CSF did stimulate a 50% increase in peripheral neutrophils. Monocyte production was also increased about eightfold by G-CSF and 1.5-fold by GM-CSF, but their peak release was only slightly accelerated. While the peripheral half-lives of the neutrophilic granulocytes were normal, those of the monocytes were dramatically reduced, perhaps due to sequestration in the tissues for functional purposes. The stimulated monocyte production in the case of G-CSF required an additional five cell cycles, a level that might have repercussions on the progenitor compartments.     

Increased respiratory burst activity of neutrophils in patients with aplastic anemia: effects of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor.

The superoxide (O2-)-releasing capacity in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) and the priming effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) and granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on FMLP-induced O2-release were investigated in neutrophils from 13 patients with aplastic anemia (AA). The O2(-)-releasing capacity of AA neutrophils (0.85 +/- 0.36 nmol/5 min/1 x 10(5) cells, n = 13) was significantly (p < 0.01) increased as compared with that of normal neutrophils (0.24 +/- 0.12 nmol/5 min/1 x 10(5) cells, n = 17). There was no close relationship between the O2(-)-releasing capacity and the peripheral blood neutrophil count or the plasma concentration of C-reactive protein. The plasma concentrations of G-CSF and GM-CSF were not elevated to the detectable levels (< 0.1 ng/ml and < 0.2 ng/ml, respectively) in all patients tested. FMLP-induced O2(-)-release was further enhanced by pretreatment of cells with rhG-CSF or rhGM-CSF for 10 min at 37 degrees C, except that no significant priming by rhG-CSF was observed in five patients. The priming effect of rhGM-CSF was consistently greater than that of rhG-CSF in all patients. The i.v. administration of rhGM-CSF (6 micrograms/kg body weight/day) to one patient resulted in an increase in neutrophil O2(-)-release stimulated by FMLP. These findings indicate that neutrophils from AA patients are already primed in vivo for enhanced release of O2- and that these neutrophil functions are further potentiated by rhG-CSF or rhGM-CSF.     

Comparative analysis of the in vivo radioprotective effects of recombinant granulocyte colony-stimulating factor (G-CSF), recombinant granulocyte-macrophage CSF, and their combination.

The purpose of the present study was to evaluate and compare the in vivo radioprotective effects of pre-total body irradiation (TBI) conditioning with recombinant granulocyte colony-stimulating factor (rG-CSF) and recombinant granulocyte-macrophage CSF (rGM-CSF) in a large series of lethally and supralethally irradiated mice. Also analyzed were the radioprotective effects of simultaneous as well as sequential combinations of rG-CSF and rGM-CSF. Our findings in 1,180 mice provide direct evidence that in vivo administration of rG-CSF or rGM-CSF before TBI protects a significant fraction of mice from the lethal effects of LD100/30 TBI. At equivalent doses, rG-CSF displayed a more potent radioprotective activity than rGM-CSF. Not only was rG-CSF radioprotective at much smaller doses than rGM-CSF, the survival rate after lethal TBI was also significantly higher in mice receiving optimally radioprotective doses of rG-CSF as compared with mice receiving optimally radioprotective doses of rGM-CSF. Pretreatment of mice with rGM-CSF markedly attenuated the radioprotective affects of rG-CSF in lethally as well as supralethally irradiated mice. Pretreatment with rG-CSF followed by rGM-CSF was slightly more effective than rG-CSF alone in supralethally irradiated mice but not in lethally irradiated mice. Notably, marked differences among different strains of mice were noted regarding the optimally radioprotective doses of rG-CSF or rGM-CSF as well as probability of survival and median survival time after lethal or supralethal TBI. This report confirms and extends previous studies concerning the potential of cytokines in prevention or therapy of lethal radiation injury.     

Stem cell factor in combination with granulocyte colony-stimulating factor (CSF) or granulocyte-macrophage CSF synergistically increases granulopoiesis in vivo.

Recombinant rat stem cell factor (rrSCF) and recombinant human granulocyte colony-stimulating factor (G-CSF) coinjected for 1 week in rats cause a synergistic increase in mature marrow neutrophils accompanied by a striking decrease in erythroid and lymphoid marrow elements. The spleens of the same rats show increased granulopoiesis as well as increased erythropoiesis as compared with the spleens of rats treated with either growth factor alone. Splenic extramedullary erythropoiesis may act to compensate for the decrease in marrow erythropoiesis. The coinjection of rrSCF and G-CSF causes an increase in marrow mast cells at the end of 1 week, but the increase is much less than in rrSCF-alone-treated rats. The combination of rrSCF and G-CSF increases the rate of release of marrow neutrophils into the circulation and causes a dramatic synergistic peripheral neutrophilia, beginning especially after 4 days of treatment. Colony-forming assays of all experimental groups showed a synergistic increase in colony-forming unit granulocyte-macrophage (CFU-GM) in the marrow, but not in peripheral blood, after coincubation with SCF plus granulocyte-macrophage CSF (GM-CSF) as opposed to GM-CSF alone, showing anatomic compartmentalization between a more primitive marrow CFU-GM subset and a more mature peripheral blood CFU-GM subset. In vivo daily administration of SCF plus GM-CSF results in a synergistic increase in marrow neutrophils, but not the striking synergistic increase in circulating neutrophils that is observed with SCF plus G-CSF.     

Comparison of interferon-gamma, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor for priming leukocyte-mediated hyphal damage of opportunistic fungal pathogens

Proinflammatory cytokines have been proposed as adjunctive therapeutic agents to enhance the host immune response during infections caused by opportunistic fungi. The study compared the differential in vitro priming effects of interferon-gamma (IFN-gamma), granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) on hyphal damage of opportunistic fungi mediated by isolated neutrophils (polymorphonuclear leukocytes, PMNL) and buffy coat cells (polymorphonuclear leukocytes/peripheral blood mononuclear cells, PMNL/PBMC) from healthy donors. IFN-gamma (1000 U/mL) effectively primed both PMNL and PMNL/PBMC for enhanced hyphal damage of Aspergillus fumigatus, Fusarium solani, and Candida albicans. G-CSF (100 ng/mL) increased hyphal damage mediated by both PMNL and PMNL/PBMC against F. solani, and GM-CSF (100 ng/mL) augmented the antifungal activity of PMNL/PBMC against hyphal forms of both F. solani and C. albicans. IFN-gamma may be superior to G-CSF or GM-CSF for enhancing the microbicidal activity of PMNL and PMNL/PBMC against opportunistic fungi.     

Role of granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor in the development of an acute neutrophil inflammatory response in mice

The intraperitoneal injection into mice of casein preparations containing bacteria induced a rapid accumulation of neutrophils within 3 hours due to selective release of mature cells from the bone marrow. Significant increases in the concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) occurred in the peritoneal cavity during the process, but the intraperitoneal injection of neither CSF induced a significant accumulation of neutrophils and the coinjection of G-CSF and casein failed to enhance the neutrophil response. The lack of involvement of either CSF in the neutrophil migration was confirmed by the development of typical neutrophil exudates when casein was injected into mice with inactivation of the genes encoding GM-CSF, G-CSF, or the beta-common chain of the GM-CSF receptor. However, preinjection of G-CSF increased the number of marrow neutrophils available for migration and did result in increased numbers of neutrophils in the peritoneal cavity after casein injection. Typical eosinophil inflammatory responses to the injection of casein or thioglycollate occurred in GM-CSF -/ -mice but not in beta c -/- mice, suggesting that interleukin-5 was necessary for this response.     

Regulation of immunomodulatory functions by granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor in vivo

 The present study was designed to investigate in vivo immunomodulatory properties of hematopoietic growth factors. The influence on the activation of cytokine synthesis and on the expression of surface antigens associated with cellular activation of G-CSF or GM-CSF was investigated in cancer patients receiving these factors. One single dose of growth factor was administered to patients with bladder cancer (G-CSF group) or small cell lung cancer (GM-CSF group) before chemotherapy. After cytoreductive chemotherapy patients received supportive therapy with G-CSF or GM-CSF. Peripheral blood mononuclear cells and plasma samples were obtained for flow cytometry, Northern blot analysis, and assessment of cytokine protein levels after single-dose as well as after continous cytokine administration. Our results demonstrate differences in the induction of biological activities by GM-CSF and G-CSF in vivo which correlate well with in vitro findings. Among mature hematopoietic cells the effect of G-CSF is restricted to the granulocyte lineage. With GM-CSF moderate but unequivocal modulation of monocyte function was observed. On peripheral blood monocytes expression of MHC class-II molecules and CD44 was markedly stimulated. After one single dose of GM-CSF, plasma levels of sCD25 and IL-1RA were significantly induced (p<0.0001, p=0.032, respectively) and a trend to increased IL-8 levels was observed. The changes in plasma proteins were not correlated with shifts of mRNA expression for IL-8 and IL-1RA. T-cell activation was not observed with either cytokine. These results suggest that immunomodulatory features are differentially regulated by G-CSF and GM-CSF. The clinical relevance of a selective use of both hematopoietic growth factors in various disease settings remains to be determined. Received: 20 March 1996 / Accepted: 19 July 1996     

Differential effects of granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor in children with severe congenital neutropenia.

Severe congenital neutropenia (SCN) is a disorder of myelopoiesis characterized by severe neutropenia secondary to a maturational arrest at the level of promyelocytes. We treated five patients with SCN with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) for 42 days and subsequently, between 1 and 3 months later, with rhG-CSF for 142 days. The objective was to evaluate the safety and ability of these factors to elicit a neutrophil response. rhGM-CSF was administered at a dose of 3 to 30 micrograms/kg/d (30 to 60 minutes, intravenously). In all patients, a specific, dose-dependent increase in the absolute granulocyte counts was observed. However, in four patients this increase was due to an increase in eosinophils, and in only one patient it was due to an increase in the absolute neutrophil counts (ANC). Subsequently, all patients received rhG-CSF at a dose of 3 to 15 micrograms/kg/d subcutaneously. In contrast to rhGM-CSF treatment, all five patients responded to rhG-CSF during the first 6 weeks of treatment with an increase in the ANC to above 1,000/microL. The level of ANC could be maintained during maintenance treatment. In one patient, the increase in ANC was associated with an improvement of a severe pneumonitis caused by Peptostreptococcus and resistant to antibiotic treatment. No severe bacterial infections occurred in any of the patients during CSF treatment. All patients tolerated rhGM-CSF and rhG-CSF treatment without severe side effects. These results demonstrate the beneficial effect of rhG-CSF in SCN patients.     

Human arterial smooth muscle cells synthesize granulocyte colony-stimulating factor in response to interleukin-1 alpha and tumor necrosis factor-alpha.

Vascular smooth muscle cells (SMC) are a major cell type comprising the walls of blood vessels. We report the synthesis of granulocyte colony-stimulating factor (G-CSF) by cultured human SMC obtained from the internal mammary artery and thoracic aorta. Interleukin-1 alpha (IL-1 alpha) greatly increased in a dose-dependent manner the amount of this cytokine produced by the SMC, with tumor necrosis factor-alpha (TNF-alpha) being less effective. Newly formed G-CSF could be detected in culture supernatants within 6 hours after IL-1 alpha or TNF-alpha treatment. Northern blot analysis of SMC stimulated with IL-1 alpha and TNF-alpha showed an increase in the amount of mRNA for G-CSF as compared with control cells. Enhanced G-CSF mRNA levels were observed when SMC were treated with cycloheximide in the absence or presence of added cytokine. In vasculitis, the walls of blood vessels become inflamed as evidenced by a leucocytic infiltrate usually dominated by polymorphonuclear neutrophil leukocytes (PMNs). G-CSF is known to stimulate PMNs, and our findings raise the possibility that G-CSF made by SMC contributes to the development of vasculitis lesions.     

In vivo administration of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF, interleukin-1 (IL-1), and IL-4, alone and in combination, after allogeneic murine hematopoietic stem cell transplantation.

BALB/c mice (H-2d) given 10 Gy total body irradiation (TBI) followed by 10(7) bone marrow (BM) and 10(6) spleen cells from C57BL/6 (H-2b) donor mice received recombinant cytokines intraperitoneally (IP) twice daily. The effect on neutrophil recovery rate, graft-v-host disease (GVHD), and survival was assessed. Four reagents were used: granulocyte-colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), interleukin-1 (IL-1) and IL-4, both alone and in combination. The most effective combination for increasing the circulating absolute neutrophil account (ANC) above the control value at day 7 posttransplant was the combination of G-CSF and IL-1 (mean ANC 2.4 +/- 1.6 x 10(9)/L as compared with control value of 0.07 +/- 0.05, P less than .02), followed by G-CSF alone (mean ANC 1.1 +/- 0.2, P less than .0001), the combination of GM-CSF plus IL-1 (mean ANC 0.8 +/- 0.3, P less than .002), and the combination of G-CSF plus GM-CSF (mean ANC 0.8 +/- 0.3, p less than .005). At day 10 posttransplant, the most effective combination in raising the ANC was the combination of G-CSF plus GM-CSF (mean ANC 7.5 +/- 2.3 as compared with control value of 3.5 +/- 1.1, P less than .01), followed by G-CSF alone (mean ANC 6.9 +/- 2.1, P less than .02). At the doses used, neither G-CSF nor GM-CSF had a deleterious effect on the incidence or severity of GVHD; indeed, GM-CSF was associated with improved survival. In contrast, IL-1 at doses greater than or equal to 100 ng twice daily caused marked early mortality, and there was a suggestion that IL-4 at doses of 500 ng twice daily resulted in increased late mortality, possibly owing to exacerbation of GVHD. This model appears to be of value for exploring the use of hematopoietic growth factors before they are used clinically in marrow allograft recipients.     

Neutrophil respiratory burst following liver transplantation: in vitro effects of granulocyte colony-stimulating factor

Early postoperative infections and septic complications are predominant causes of morbidity and mortality in patients following orthotopic liver transplantation (OLTx). Prophylactic granulocyte colony-stimulating factor (G-CSF) administration after OLTx was found to decrease the number of sepsis episodes and sepsis-related mortality. Since polymorphonuclear neutrophils (PMNs) are one of the major determinants of antimicrobial defense, alteration of their functions may influence the development of sepsis in these patients. Therefore, we investigated in vitro whether or not priming with G-CSF affects the neutrophils’ respiratory burst (RB) in immunosuppressed liver-transplanted patients. Venous blood was drawn from liver allograft recipients (n=12) between the 5th and 15th day postoperatively. Patients without clinical signs of infection or rejection were included in this study. Leukocytes were obtained as supernatant following sedimentation and incubated with 1000 IE ml^?1 G-CSF. The RB was measured by the intracellular oxidation of non-fluorescent dihydrorhodamine to the fluorescent rhodamine by flow cytometry. The results were expressed as a percentage of increasing stimulation compared to the control responses, which are made up of the percentage of cells with RB reaction after stimulation with phorbol ester (PMA), bacteria (E. coli), or the combination of a cytokine (TNF-α) and a bacterial peptide (FMLP) in the absence of G-CSF. In vitro priming with G-CSF resulted in significantly increased activity of the RB after PMA (from 71.7% to 85.6%) and TNF-α/FMLP (from 58.4% to 72.7%) stimulation. These data demonstrate that G-CSF in vitro augments the RB of PMNs, thereby suggesting a possible therapeutic role for G-CSF as immunomodulating agent during bacterial and fungal infections following OLTx.     

Dexamethasone inhibits tumor necrosis factor-induced granulocyte colony-stimulating factor production in human endothelial cells.

Dexamethasone (10(-5)-10(-7) M) is able to suppress the tumor necrosis factor (TNF)-induced production of granulocyte colony-stimulating factor (G-CSF) in human umbilical vein endothelial cells (HUVEC). Using Western-blot analysis and bioassay for the evaluation of G-CSF protein and activity, a significant decrease in TNF-induced production could be found in cells cultured in the presence of dexamethasone as compared to TNF stimulation in the absence of dexamethasone. No inhibition by dexamethasone was seen in endothelial cells stimulated with interleukin 1 beta (IL-1 beta; 10 U/ml). Addition of IL-1 to cultures stimulated with TNF in the presence of dexamethasone could overcome the inhibitory effects of corticosteroids. Suppression of G-CSF production can, at least in part, explain the functional abnormalities of granulocytes found in patients treated with glucocorticosteroids.     

Effect of exogenous recombinant human granulocyte and granulocyte-macrophage colony-stimulating factor on neutrophil function following allogeneic bone marrow transplantation.

Functional activity of peripheral blood granulocytes was assessed in seven patients and in their normal donors following allogeneic bone marrow transplantation (BMT). Functions studied included superoxide generation (O2-), intracellular killing of Staphylococcus aureus, phagocytosis, and killing of Candida albicans. Neutrophils were tested following preincubation with 300 pM granulocyte-macrophage colony-stimulating factor (GM-CSF), 1.2 nM granulocyte colony-stimulating factor (G-CSF), or buffered solution (diluent) as control. Our data indicate that following BMT, both recipients and their normal donors show GM-CSF- and G-CSF-induced increases in: 1) O2- production in response to fMet-Leu-Phe (fMLP), 2) killing of S. aureus, and 3) phagocytosis of C. albicans. In two patients that showed low candidacidal activity, GM-CSF and G-CSF markedly enhanced the cytotoxic activity of the cells. Our studies indicate that GM-CSF and G-CSF increase "oxygen-dependent" oxidative activities in neutrophils from BMT recipients and their normal donors and enhance the antimicrobial activity of the cells.     

Comparison between granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor in the mobilization of peripheral blood stem cells

Peripheral blood stem cells (PBSC) have become the preferred source of stem cells for autologous transplantation because of the technical advantage and the shorter time to engraftment. Mobilization of CD34+ into the peripheral blood can be achieved by the administration of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), or both, either alone or in combination with chemotherapy. G-CSF and GM-CSF differ somewhat in the number and composition of PBSCs and effector cells mobilized to the peripheral blood. The purpose of this review is to give a recent update on the type and immunologic properties of CD34+ cells and CD34+ cell subsets mobilized by G-CSF or GM-CSF with emphasis on (1) relative efficacy of CD34+ cell mobilization; (2) relative toxicities of G-CSF and GM-CSF as mobilizing agents; (3) mobilization of dendritic cells and their subsets; (4) delineation of the role of adhesion molecules, CXC receptor 4, and stromal cell-derived factor-1 signaling pathway in the release of CD34+ cell to the peripheral blood after treatment with G-CSF or GM-CSF.     

Granulocyte-macrophage colony-stimulating factor (CSF) and multilineage CSF recruit human monocytes to express granulocyte CSF

We assessed the capacity of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) and multilineage (Multi)-CSF to induce release of granulocyte-CSF (G-CSF) by highly purified peripheral blood monocyte (Mo) preparations. Our results reveal that GM-CSF and Multi-CSF, either alone or in a synergistic concert, activate Mo to transcribe G-CSF messenger (m) RNA and release biologically active G- CSF protein into their culture supernatants. G-CSF had no regulatory effect on Mo expression of cytoplasmic G-CSF mRNA levels and G-CSF protein secretion by itself. These differential actions of CSFs provide further insight into self-regulatory mechanisms within the growth factor hierarchy system.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF): receptor biology, signal transduction, and neutrophil activation.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) are two of the growing number of recognized cytokines involved in the regulation of hematopoiesis. The purification of these factors and the subsequent cloning of the cDNAs which encode these proteins have led to their widespread clinical use in the setting of therapy or disease-induced myelosuppression. Although originally purified on the basis of their colony-stimulating properties, GM-CSF and G-CSF may also play important roles in the regulation of effector cell function. The mechanisms underlying progenitor cell proliferation and effector cell stimulation remain poorly understood. However, the characterization of the GM-CSF and G-CSF receptors and recent work in signal transduction are helping to elucidate these mechanisms. This paper will review the biology of the GM-CSF and G-CSF receptors, the mechanisms of post-receptor signal transduction, and the resultant effects on neutrophil function. In addition, the current and potential clinical uses of these factors will be examined in light of their ability to activate and perhaps enhance the function of neutrophils.     

The regulation of neutrophil phospholipase A2 by granulocyte-macrophage colony-stimulating factor and its role in priming superoxide production

Experiments were performed to investigate the relative role of phospholipase A₂(PLA₂) in the activation and cytokine-mediated priming of neutrophil superoxide production. PLA₂ activity was measured with a radiometric assay which discriminates between PLA₂ and the downstream enzyme, 5-lipoxygenase. In cells that had not been primed by prior incubation with granulocyte-macrophage collony stimulating factor (GM-CSF), PLA₂ and NADPH oxidase were differentially stimulated by the chemotactic peptide N-formyl-met-leu-phe (FMLP), calcium ionophore, or phorbol ester. In addition, inhibition of PLA₂ by mepacrine (0–100 μmol/l) did not concomitantly inhibit FMLP-stimulated superoxide production. These findings suggest that the activity of PLA₂ and NADPH oxidase may be uncoupled in the unprimed cell. In cells preincubated with GM-CSF, time- and dose-dependent priming of FMLP-stimulated PLA₂ responses were observed and inhibition of PLA₂ by mepacrine was accompanied by the inhibition of FMLP-stimulated superoxide production down to the level of unprimed cells. The effect of mepacrine was not due to inhibition of FMLP receptor expression. These data suggest that a mepacrine-sensitive PLA₂ may have a role in the GM-CSF mediated priming of superoxide production. Using ionophore-stimulated PLA₂ activity as a model, we showed that Bordatella pertussis toxin did not inhibit GM-CSF mediated priming, demonstrating that a pertussis-sensitive GTP-binding protein does not mediate signal transduction from the GM-CSF receptor to PLA₂. The tyrosine kinase inhibitor, genestein, selectively inhibited GM-CSF primed but not unprimed PLA₂ activity, demonstrating that GM-CSF-mediated priming requires tyrosine kinase activity.     

Recombinant human granulocyte/macrophage colony-stimulating factor enhances monocyte cytotoxicity and secretion of tumor necrosis factor alpha and interferon in cancer patients

The colony-stimulating factors (CSFs) promote the proliferation and differentiation of hematopoietic precursors and more recently have been shown to amplify the functions of mature phagocytes in vitro. In this study recombinant human granulocyte/macrophage colony-stimulating factor (rGM-CSF) was administered to cancer patients to determine whether the cytotoxic and secretory activity of their blood monocytes could be enhanced. Patients with refractory neoplastic disease were treated with rGM-CSF either as a single bolus or as a constant infusion for 14 days at either 100 or 500 micrograms/m2 per day. As has been reported by others, the number of peripheral blood monocytes and granulocytes rose markedly in a dose-response fashion during infusion with rGM-CSF. The functional capacity of monocytes was increased by rGM-CSF, since the cytotoxicity of monocytes against antibody-coated xenogeneic cells was increased during the constant infusion compared to baseline. In addition, monocytes harvested during the constant infusion and stimulated with lipopolysaccharide (LPS) in vitro secreted increased quantities of tumor necrosis factor alpha (TNF-alpha) and interferon (IFN). These data indicate that rGM-CSF can enhance both the number and the function of peripheral blood monocytes in vivo.