Serum Levels Of GM-CSF Research Articles

Lenalidomide (LMID) Significantly Enhances Circulating Serum Levels of IL-2 and IL-15 Levels, NK Expansion and Activation and NK and LAK Cytotoxicity in Children with Refractory/Recurrent Solid Tumors: A Children's Oncology Group Phase I Consortium Report

LMID is approved by the FDA for adults with specific subsets of MDS and relapsed multiple myeloma and also has anti-tumor activity in adults with relapsed/refractory NHL (Wiernik, et al, JCO, 2008). Although the exact mechanism of LMID anti-tumor activity is unknown, it appears to be related to its immunomodulatory and anti-angiogenic properities. Bartlett et al (BJC, 2004) demonstrated in adults with advanced cancer that following LMID treatment there were an increased number of NK cells and enhanced NK function presumably through the increased production of immunocytokines secondary to T-cell activation (Bartlett et al, personal communication). IL-2 and IL-15 are critically important immunocytokines in NK cell development and functional activation (Caliguiri, et al, Blood 2006). We evaluated the immunomodulatory effects of LMID in a phase 1 trial of oral LMID administered daily × 21 days, every 28 days at 7 doses ranging from (15–70 mg/m2) in children with advanced cancer. Serum levels of GM-CSF, IL-2, IL-8 and IL-15 were measured by ELISA. NK (CD3−/56+) and Treg (CD4+/25+) levels in addition to intracellular granzyme B and the NK activation marker, LAMP-1 (CD107-A) were measured by flow cytometry. NK (K562) and LAK (Daudi) cytotoxicity were measured by europium assay at a 20:1 (E:T ratio). 26 children, median age 16 (5–21), 11M/15F: 1 rhabdomyosarcoma, 6 osteosarcoma, 10 other sarcoma, 2 hepatoblastoma, 7 other were enrolled in this study. Results are expressed as mean ± SD (pre and post LMID). Statistical analyses were performed with INSTAT (Graph Pad, San Diego, CA). The following significant changes in immunomodulatory function across all dose levels are shown in the table below.PretreatmentDay 21P valueGMCSF (pg/ml)17.02 ± 10.76122.5 ± 117.63<0.05IL-2 (pg/ml)30.72± 31.10138.09 ± 41.07<0.05IL-15 (pg/ml)21.35 ± 14.60381.50 ± 126.90<0.05NK cytotoxicity (%)26.24 ± 10.6155.16 ± 18.55<0.05LAK cytotoxicity (%)15.49 ± 7.0332.97 ± 13.75<0.05Intracellular granzyme B (%)1.82± 2.4519.44 ± 11.82<0.05LAMP-1 (%)2.01 ± 1.6619.64 ± 9.38<0.05NK cell/CD3−/56+ (%)9.28 ± 7.0729.92 ± 17.16<0.05Treg (CD4+/25+) (%)25.68± 18.0412.08 ± 11.27<0.05NK cell number (mm3)187.63 ± 162.01769.48 ± 526.54<0.05Bartlett et al has suggested that there may be a difference in immunomodulatory response by LMID dose. There was a significant trend in the correlation between dose and immunomodulation. These results suggest that LMID has profound immunomodulatory and immune activating effects in children with advanced solid tumors. In particular, the significant increase in serum IL-2 and IL-15 cytokine levels and the increase in NK and LAK cytotoxicity in children with advanced cancer suggest an activation of TH1 and NK immune subsets by LMID. Further studies are required to determine the benefit of LMID immunomodulatory effects in children with specific malignancies.

Autologous Tumor Combined with a GM-CSF-Secreting Cell Line Vaccine (GVAX®) Following Autologous Stem Cell Transplant (ASCT) in Multiple Myeloma.

Background: Preclinical models have demonstrated enhanced cancer vaccine efficacy when administered early following ASCT and accompanied by vaccine-primed lymphocyte infusion.Methods: Patients with untreated myeloma were enrolled and underwent a bone marrow harvest to obtain tumor cells for vaccine processing. Patients eligible for ASCT following induction chemotherapy received a pre-transplant vaccination followed by leukapheresis to collect “primed” lymphocytes that were reinfused with the stem cell graft. Eight post-transplant vaccinations were administered at 3-week intervals starting 6 weeks posttransplant. The vaccine formulation consisted of irradiated autologous tumor cells admixed with GM-CSF-secreting K562 cells (CG9962) at a ratio of 5:2, respectively. Three dose levels were assigned (1, 4, and 10 x107 tumor cells/vaccination) based on tumor cell yield from the bone marrow harvest.Results: 22 patients underwent tumor harvest, 18 completed induction chemotherapy, and 16 proceeded to vaccination (1 at 1 x 107,4 at 4x107, and 13 at 10x107) and ASCT. At baseline, the median b2 microglobulin was 4 (2–14) and 35% had an IgA subtype. No grade 3/4 vaccine-related toxicities were observed. Median time to neutrophil engraftment (>500) and platelet engraftment (>50K) was 10 days. Local vaccine injection site reactions were observed in all patients. Delayed-type hypersensitivity (DTH) reactions to injections of irradiated autologous tumor cells were induced in only 1/15 patients after 4 post-transplant vaccines, but 4/10 were positive at one year post transplant. Induction of autologous tumor-reactive antibodies as well as antibodies reactive against CG9962 cells was observed. In vitro studies have demonstrated the induction and adoptive transfer of tumor-specific cellular immune responses that can be followed throughout the post-transplant period. Reproducible serum GM-CSF levels were achieved with repeated vaccinations suggesting no increased clearance of CG9962 cells due to induction of an allogeneic immune response. Of the 16 patients that have completed the ASCT, there were 6 complete and 5 partial remissions, for an overall response rate of 69%. Three patients with rising paraprotein levels early post-transplant have demonstrated paraprotein declines following initiation of post-transplant vaccines, suggesting a possible vaccine-mediated effect.Conclusions: These data demonstrate the feasibility of this vaccine approach and show the therapeutic potential of K562 GVAX® vaccination in the ASCT setting in multiple myeloma.

Enhancement of repopulation and hematopoiesis of bone marrow cells in irradiated mice by oral administration of PG101, a water-soluble extract from Lentinus lepideus.

PG101 is a water-soluble extract from Lentinus lepideus. It is a potential biological response modifier that activates selective cytokines in vitro, mainly by controlling cellular transcription factor NF-kappaB. Effects of PG101 were tested on bone marrow cells in irradiated mice. Mice were irradiated with a dose of 6 Gy and were given PG101 by gavages daily for 24 days. In PG101-treated mice, the number of colony-forming cells, including colony-forming units (CFU)-granulocytes/macrophages (GM) and erythroid burst-forming units (BFU-E), were increased to almost the levels seen in nonirradiated control as early as 8 days after irradiation. Two-color flow cytometric analysis using antibodies to ER-MP12 and ER-MP20 suggested that in the bone marrow cell population, PG101 increased the number of granulocytes (ER-MP12(-)20(med)) and myeloid progenitors (ER-MP12(+)20(+)). Analysis of surface c-Kit and Gr-1 proteins in bone marrow cells indicated that PG101 might induce differentiation of progenitor cells to granulocytes and/or proliferation of the committed cells. Lastly, oral administration of PG101 highly increased serum levels of GM-CSF, IL-6, and IL-1beta. Interestingly, the level of TNF-alpha was elevated by irradiation in control mice, but was maintained at the background level in PG101-treated mice, suggesting that PG101 might effectively suppress TNF-alpha-related pathologic conditions. Our results strongly suggest the great potential of PG101 as an immune enhancer during radiotherapy and/or chemotherapy.

In Vivo Effects of IL-4, IL-10, and Amifostine on Cytokine Production in Patients with Acute Myelogenous Leukemia

Both IL-4 and IL-10 have been shown in vitro to inhibit leukemia cell secretion of IL-1β, GM-CSF, and TNFα, and increase leukemia cell release of IL-1ra. In this study, we have investigated the in vivo effects of IL-4, IL-10, and amifostine on cytokine production in patients with acute myelogenous leukemia (AML). Serum IL-1ra, IL-1β, TNFα, GM-CSF, and SCF levels were measured in AML patients who received IL-4, IL-10, or amifostine. No significant changes in the serum levels of IL-1ra, IL-1β, TNFα, GM-CSF, and SCF were found in AML patients who received amifostine. Both IL-4 and IL-10 were found to increase serum IL-1ra. This data is in accord with the in vitro studies. However, EL-4 increased serum GM-CSF levels and IL-10 increased serum IL-1β and TNFα levels. These in vivo effects of the two cytokines differ from their in vitro effects. Despite the similar effects of IL-4 and IL-10 on cytokine production by AML cells in vitro, different effects were observed in AML patients in vivo. EL-4 increased serum SCF levels, whereas IL-10 decreased serum SCF levels. IL-4 increased serum GM-CSF levels, whereas IL-10 had no effect on them. Although IL-10 increased serum IL-1β and TNFα levels, EL-4 had no effect on them. These findings indicate that the in vitro effects of IL-4 and IL-10 do not necessarily reflect their in vivo effects, and that the complex effects of the two cytokines on serum cytokine levels make it difficult to predict their therapeutic potential.

Tumor-related leukocytosis is linked with poor prognosis in patients with lung carcinoma.

Tumor-related leukocytosis is a paraneoplastic syndrome that is encountered occasionally in the clinical course of patients with lung carcinoma. Recently, autonomous production of hematopoietic cytokines (granulocyte-colony stimulating factor [G-CSF], granulocyte-macrophage-colony stimulating factor [GM-CSF], and interleukin-6 [IL-6]) were identified in some of these patients. However, the incidence and clinical characterization of this phenomenon have not been clarified. During a 7-year period, 227 patients with carcinoma of the lung were investigated, and 33 patients were diagnosed with tumor-related leukocytosis. Except for one patient with small cell lung carcinoma, the other 32 patients had nonsmall cell lung carcinoma, and the highest incidence is recognized in large cell carcinoma. These 33 patients were examined for serum G-CSF, GM-CSF, and IL-6 levels using enzyme immunoassays and enzyme-linked immunosorbent assays. Tumor specimens were stained for antihuman cytokine (G-CSF, GM-CSF, and IL-6) monoclonal antibodies. Sixteen patients showed high serum G-CSF levels, 4 patients showed high serum GM-CSF levels, and 18 patients showed high serum IL-6 levels. Twelve specimens stained positively against anti-G-CSF antibody. Two specimens stained positively against anti-GM-CSF antibody, and three specimens were stained positively against anti-IL-6 antibody, including one double positive specimen for both G-CSF and IL-6. All specimens that were positive for monoclonal antibodies were from patients with nonsmall cell lung carcinoma. These patients had a poor outcome compared with the other patients. Tumor-related leukocytosis and cytokine production frequently occur in the clinical course of lung carcinoma, and this phenomenon is related mainly to nonsmall cell lung carcinoma. Its occurrence appears to be an ominous prognostic sign in patients with lung carcinoma.

Immunogenetic Therapy of Human Melanoma Utilizing Autologous Tumor Cells Transduced to Secrete Granulocyte-Macrophage Colony-Stimulating Factor

We performed a clinical study of five patients with melanoma to evaluate the immunobiological effects of retrovirally transduced autologous tumor cells given as a vaccine to prime draining lymph nodes. Patients were inoculated with both wild-type (WT) and GM-CSF gene-transduced tumor cells in different extremities. Approximately 7 days later, vaccine-primed lymph nodes (VPLNs) were removed. There was an increased infiltration of dendritic cells (DCs) in the GM-CSF-secreting vaccine sites compared with the WT vaccine sites. This resulted in a greater number of cells harvested from the GM-CSF-VPLNs compared with the WT-VPLNs at a time when serum levels of GM-CSF were not detectable. Four of five patients proceeded to have the adoptive transfer of GM-CSF-VPLN cells secondarily activated and expanded ex vivo with anti-CD3 MAb and IL-2. One patient had a durable complete remission of metastatic tumor. Utilizing cytokine (IFN-gamma, GM-CSF, IL-10) release assays, GM-CSF-VPLN T cells manifested diverse responses when exposed to tumor antigen in vitro. In two of two patients, GM-CSF-VPLN T cell responses were different from those of matched WT-VPLN cells. This study documents measurable immunobiologic differences of GM-CSF-transduced tumor cells given as a vaccine compared with WT tumor cells. The complete tumor remission in one patient provides a rationale to pursue this approach further.

Increased progenitor cell proliferation in the peripheral blood of patients with bronchial asthma: The role of nitric oxide

Background: Asthma exacerbation is associated with increased numbers of circulating CD34 + progenitor cells, which may migrate to airways and develop into mature cells under the effects of cytokines and hematopoietic factors. Nitric oxide (NO) generation is enhanced in asthma and is known to suppress human hematopoiesis. Objectives: We studied circulating progenitor cells in the blood of patients with varying severity of asthma and examined the contribution of NO to their proliferation into eosinophil-forming colonies ex vivo. Methods: With use of multiparameter flow cytometric analyses, the cell numbers and intracellular inducible NO synthase (iNOS) immunoreactivity of circulating CD34 + cells in peripheral blood was measured. The serum level of GM-CSF or IL-5 was also determined. The colonies grown from progenitor cells were cultured in methylcellulose either in the presence or absence of growth factors, including GM-CSF, stem cell factor, and IL-3. Results: A significantly greater number of circulating CD34 + cells increased together with higher intracellular iNOS immunoreactivity in moderate asthmatics compared with mild intermittent asthmatics and healthy subjects. There was no significant difference in iNOS immunoreactivities or CD34 + progenitor cell numbers between healthy subjects and those with mild intermittent asthma. Serum levels of GM-CSF or IL-5 were significantly higher in all asthmatics compared with healthy subjects and correlated with circulating CD34 + cells. A greater number of colonies was grown either in the presence or absence of growth factors with a higher percentage of cells of eosinophil lineage in asthmatics than in health subjects. N G -nitro-L-arginine methyl ester potentiated and sodium nitroprusside inhibited the colony growth in both asthmatic and healthy subjects without a significant change in the percentage of eosinophil lineage. Conclusions: The production of NO from progenitor cells or other circulating cells may act in an autocrine or paracrine fashion to regulate progenitor cell growth and colony formation. However, this is not sufficient to control the increased proliferation of progenitor cells observed in asthma. (J Allergy Clin Immunol 1999;104:803-10.)

Receptor Clearance Obscures the Magnitude of Granulocyte-Macrophage Colony-Stimulating Factor Responses in Mice to Endotoxin or Local Infections

AbstractMarrow cells from mice lacking high-affinity receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF; βc−/− mice) were shown to bind and internalize much less GM-CSF than cells from normal (βc+/+) mice. βc−/− mice were used to determine the effect of negligible receptor-mediated clearance on detectible GM-CSF responses to the intravenous injection of endotoxin or the intraperitoneal injection of casein plus microorganisms. Unlike the minor serum GM-CSF responses to endotoxin seen in βc+/+ mice, serum GM-CSF levels rose 30-fold to 9 ng/mL in βc−/− mice even though loss of GM-CSF in the urine was greater than in βc+/+ mice. Organs from βc−/− and βc+/+ mice had a similar capacity to produce GM-CSF in vitro, as did peritoneal cells from both types of mice when challenged in vitro by casein. However, when casein was injected intraperitoneally, βc−/− mice developed higher and more sustained levels of GM-CSF than did βc+/+ mice. The data indicated that receptor-dependent removal of GM-CSF masks the magnitude of GM-CSF responses to endotoxin and local infections. Because of this phenomenon, serum GM-CSF concentrations can be a misleading index of the occurrence or nonoccurrence of GM-CSF responses to infections.

Receptor Clearance Obscures the Magnitude of Granulocyte-Macrophage Colony-Stimulating Factor Responses in Mice to Endotoxin or Local Infections

Marrow cells from mice lacking high-affinity receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF; βc−/− mice) were shown to bind and internalize much less GM-CSF than cells from normal (βc+/+) mice. βc−/− mice were used to determine the effect of negligible receptor-mediated clearance on detectible GM-CSF responses to the intravenous injection of endotoxin or the intraperitoneal injection of casein plus microorganisms. Unlike the minor serum GM-CSF responses to endotoxin seen in βc+/+ mice, serum GM-CSF levels rose 30-fold to 9 ng/mL in βc−/− mice even though loss of GM-CSF in the urine was greater than in βc+/+ mice. Organs from βc−/− and βc+/+ mice had a similar capacity to produce GM-CSF in vitro, as did peritoneal cells from both types of mice when challenged in vitro by casein. However, when casein was injected intraperitoneally, βc−/− mice developed higher and more sustained levels of GM-CSF than did βc+/+ mice. The data indicated that receptor-dependent removal of GM-CSF masks the magnitude of GM-CSF responses to endotoxin and local infections. Because of this phenomenon, serum GM-CSF concentrations can be a misleading index of the occurrence or nonoccurrence of GM-CSF responses to infections.

Expression of GM-CSF receptor and “in vitro” effects of GM-CSF on human fibroblasts

In the present study the effects of Granulocyte-Macrophage Colony Stimulating Factor (GMCSF) on fibroblast growth and activity have been studied. In this regard the AA have evaluated in primary cultures of human gengival normal fibroblasts (PG1 cells): a)-the expression of GM-CSF receptor (GM-CSFR) (alfa unit) on the cell surface; b)the in vitro effects of different doses of GM-CSF on the GM-CSFR expression and on the proliferation and activity of fibroblasts. PG1 cells have been stimulated in vitro with different concentrations of GM-CSF (10, 50, 80 ,100 and 150 ng/ml) using promonocytic cell line U937 as positive control for GM-CSFR expression. GM-CSFR was investigated by flow cytometry, with mouse monoclonal antibody (mAb) against the alfa chain of the human GM-CSFR and fluorescein-conjugated goat antimouse immunoglobulin G (IgG). At high GM-CSF concentration (80 ng/ml) the AA observed: 1)-A marked increase of GM-CSFR expression evaluated as fluorescence intensity (about three fold in respect to the controls); 2)-Maximal increase of PG1 cells proliferation. Moreover immunofluorescence on fibroblasts obtained from culture plates showed increased actin stress fibers and fibronectin production with low stimulation by GM-CSF, while higher concentration of this cytokine determined increased proliferation of cells, but a decreased formation of actine fibers and vinculin plaques. These results demonstrate: 1)-The presence of GM-CSFR on the surface of fibroblasts; 2)-The proliferation and the synthesis activity of these cells (in vitro) are modulated by different concentration of GM-CSF. We hypothesize that GM-CSF until 80 ng/ml can upregulate the expression of the receptor. Therefore, on the basis of previous findings of high serum levels of GM-CSF in course of scleroderma, a disease characterized by fibroblast hyperactivity, a possible role of this cytokine in the pathogenic process of this disease can be hypotesized.

The biological consequences of excess GM-CSF levels in transgenic mice also lacking high-affinity receptors for GM-CSF.

GM-CSF transgenic mice were crossed with mice with homozygous inactivation of the gene encoding the common beta chain (beta c) of the GM-CSF receptor to produce mice with constitutively elevated GM-CSF levels but no high-affinity GM-CSF receptors. GM-CSF transgenic beta c -/- mice had exceptionally elevated serum GM-CSF levels but failed to develop the abnormal peritoneal cell population, eye destruction or tissue lesions characteristic of GM-CSF transgenic beta c +/+ mice. The alveolar proteinosis of beta c -/- mice was not altered in GM-CSF transgenic beta c -/- mice. Levels of GM-CSF mRNA in transgenic GM-CSF beta c -/- were elevated but lower than in transgenic beta +/+ mice and the higher serum GM-CSF levels were traced in part to the longer serum half-life of GM-CSF in beta c -/- than in beta c +/+ mice although urinary loss of GM-CSF was higher in beta c -/- than in +/+ mice. The data indicate that the transgenic phenotype was due to stimulation by GM-CSF and not an insertional effect, that low-affinity receptors are not capable of initiating tissue pathology even in the presence of excess GM-CSF levels and that autocrine production of GM-CSF by GM-CSF-responsive cells also fails to induce changes in these cells. The results support current dogma that the action of polypeptide regulators is mediated exclusively by activation of high-affinity membrane receptors.

Serum levels of GM-CSF are elevated in patients with thrombocytopenia: Abboud MR, Laver J, Xu F, Weksler B, et al. Br J Haematol 92:486–488, 1996

Serum levels of GM-CSF are elevated in patients with thrombocytopenia: Abboud MR, Laver J, Xu F, Weksler B, et al. Br J Haematol 92:486–488, 1996

Serum levels of GM-CSF are elevated in patients with thrombocytopenia.

Serum levels of GM-CSF, IL-3 and IL-6 were measured in patients with immune thrombocytopenia (ITP), non-immune thrombocytopenia (NIT), autoimmune haemolytic anaemia (AIHA) and neutropenia. 8/10 children with ITP had elevated serum levels of GM-CSF (mean 18.4 pg/ml) while thrombocytopenic, but only two had detectable levels (mean 4.5 pg/ml) after normalization of the platelet count. In patients with NIT a significant inverse correlation between platelet count and serum levels of GM-CSF was observed. IL-3 and IL-6 levels were not significantly elevated in thrombocytopenic patients and only two of the nine patients with either AIHA or neutropenia had detectable levels of GM-CSF. Thus, GM-CSF may play a role in the response of severe thrombocytopenia.

Kinetics of serum cytokines in adults undergoing peripheral blood progenitor cell transplantation.

We investigated the serum cytokine levels (G-CSF, GM-CSF, IL-1 beta, IL-3 and IL-6) using an ELISA in 14 patients with haematological malignancies undergoing peripheral blood progenitor cell transplantation (PBPCT). Serum G-CSF levels in all patients rose immediately after PBPCT, then gradually decreased as the neutrophil counts began to rise. No detectable serum levels of GM-CSF or IL-1 beta were observed, but serum levels of IL-3 rose transiently immediately following PBPCT. Serum levels of IL-6 rose transiently during a fever in four patients. These observations suggest that G-CSF and IL-3 may contribute to the early haemopoietic reconstitution in PBPCT.

Endogenous serum levels and surface receptor expression of GM-CSF and IL-3 in patients with myelodysplastic syndromes

The majority of patients suffering from myelodysplastic syndromes (MDS) die of complications due to cytopenia. Clinical trials have demonstrated that in an essential number of MDS patients cytopenia can be ameliorated by exogenously supplied growth factors. We investigated endogenous serum levels of GM-CSF and IL-3 in 15 healthy individuals and 34 patients suffering from MDS. No circulating growth factors were detected in the serum of healthy controls, nor was IL-3 measurable in MDS patients. GM-CSF serum levels, however, were elevated in a significant number of patients (26.5%). Levels did not correlate with FAB classification, leukocyte count or chromosomal abnormalities. No significant differences in GM-CSF or IL-3 receptor expression were detected between healthy individuals and MDS patients. One patient with increased endogenous GM-CSF serum level and normal surface receptor expression responded to exogenously applied GM-CSF. In the light of these results, a funetional alteration of growth factor receptors or disturbances of signal transduction pathways must be discussed for MDS.

Subcutaneous granulocyte-macrophage colony-stimulating factor in patients with myelodysplastic syndrome: toxicity, pharmacokinetics, and hematological effects.

The toxicity, pharmacokinetics, and hematologic effects of granulocyte-macrophage colony-stimulating (GM-CSF) were studied in a phase I/II trial of 16 patients with myelodysplastic syndrome (MDS). The GM-CSF was administered subcutaneously (SC) daily so as to achieve prolonged blood levels and to establish an outpatient treatment regimen. Four dose levels were administered for ten days: 0.3 microgram/kg/d (three patients), 1.0 microgram/kg/d (three), 3.0 micrograms/kg/d (four), and 10.0 micrograms/kg/d (six). The most common toxicities were fever and a flu-like syndrome, which were dose-dependent. The maximum-tolerated dose was 10.0 micrograms/kg/d, which induced severe rigors (two patients), fever greater than 40 degrees C (one), severe bronchospasm (one), and WBC 60,000 (one). In one patient, refractory anemia with excess blasts in transformation (RAEB-T) progressed to acute nonlymphocytic leukemia after two doses of GM-CSF, and the patient died of leukemia that did not respond to chemotherapy. After doses of 3.0 and 10.0 micrograms/kg, serum GM-CSF levels peaked at 3.8 to 6.3 hours, and persisted for 14 and 24 hours, respectively. Circulating granulocytes (neutrophils and bands) increased in a dose-dependent manner, as 11 of 13 patients who received greater than or equal to 1.0 microgram/kg/d responded with a two- to 194-fold increase. Although the neutrophils usually returned to pretreatment levels shortly after stopping GM-CSF, two patients continue to exhibit an elevation of neutrophils for 6 months. Dose-related increases in circulating monocytes and eosinophils were also noted. Transient increases in platelet and reticulocyte counts were observed in two and three patients, respectively. Five of the 16 patients later received maintenance GM-CSF at 3 micrograms/kg/d for 2 to 9 weeks. All showed a dramatic increase in neutrophils after 2 weeks. Thereafter, despite continued therapy, the neutrophil count in four patients declined markedly. In conclusion, GM-CSF is well tolerated by the SC route and induces striking, but usually temporary, improvement in the neutropenia of MDS. Larger prospective phase III trials will determine the duration of hematologic responses and the impact on infection, morbidity, and mortality.