Enhanced hematopoietic activity of a human granulocyte/macrophage colony-stimulating factor-interleukin 3 fusion protein

Gene transfer using a novel fusion protein, GAL4/invasin

The delivery of DNA to target cells using simple, defined, nonviral systems has become an area of intense interest in gene therapy. We describe here the development and characterization of one such novel system. A recombinant, bifunctional, fusion protein was expressed and purified from Escherichia coli. This protein consists of the DNA-binding domain of the yeast transcription factor GAL4 fused to the cell binding, internalization domain of the Yersinia pseudotuberculosis inv gene product, invasin. This protein, GAL4/Inv, together with poly-L-lysine, formed complexes with a chloramphenicol acetyltransferase (CAT) reporter plasmid that contains eight repeats of the GAL4 consensus recognition sequence. These complexes were shown to transfect target cells in an invasin receptor-dependent manner, resulting in transient CAT expression. A simple, targeted DNA delivery vehicle, as we describe here, represents a viable approach to nonviral gene delivery.

Frequency of Fetal Cells in Sorted Subpopulations of Nucleated Erythroid and CD34+ Hematopoietic Progenitor Cells From Maternal Peripheral Blood

Fetal cells that circulate in maternal peripheral blood (PB) during pregnancy offer a potential source of nucleated fetal material for noninvasive prenatal diagnosis. Fluorescence-activated cell sorting was used to target two populations of fetal cells: nucleated erythroid cells (NECs; CD71/glycophorin-A+ CD45lo-int CD34−) and hematopoietic progenitor cells (CD34+ cells; CD34++ CD71/glycophorin-A− CD45int). Fetal cells were detected by fluorescence in situ hybridization (FISH) using directly conjugated chromosome X and Y probes in 65% (13 of 20) of the maternal PBs (fetal karyotype 46,XY). The frequency of fetal cells isolated from the NEC and CD34+ fractions was, respectively, 0 to 14 and 0 to 7 cells per 2 × 107 previously frozen maternal cells (≈20 mL of blood). In nonfrozen samples, the yield and recovery of fetal cells was moderately improved. Culturing the CD34+ sorted fractions in serum-free media with cytokines improved the quality of the FISH preparations and resulted in a slight expansion in detectable fetal cells. The frequency of fetal cells isolated from cultured CD34+ fractions was 0 to 35 and 0 to 93 cells per 2 × 107 previously frozen and nonfrozen maternal PB cells, respectively. These results document the isolation, characterization, and enumeration of fetal cells from the maternal periphery that appear to be present in most, but not all, samples analyzed.

Construction of a recombinant human GM-CSF/MCAF fusion protein and study on itsin vitro andin vivo antitumor effects

A novel cytokine fusion protein was constructed by fusing granulocyte macrophage colony stimulating factor (GM-CSF) with monocyte chemotactic activating factor (MCAF), which acts as a factor directing effector cells (monocytes) to a target site. The recombinant human GM-CSF/MCAF fusion protein could sustain the growth of GMCSF-dependent cell line TF1 and was chemotactic for monocytes. Thein vitro antitumor effect showed that rhGM-CSF/MCAF could activate monocytes to inhibit the growth of several human tumor cell lines, including a promyelocyte leukemia cell line HL-60, a lung adenocarcinoma cell line A549, a hepatoma cell line SMMC-7721 and a melanoma cell line Bowes. Furthermore, the cytotoxicity of monocytes activated by rhGM-CSF/MCAF against HL-60 and A549 was greater than that activated by GM-CSF or MCAF alone, even greater than that activated by a combination of GM-CSF and MCAF, suggesting that the fusion protein has synergistic or enhanced effects. Thein vivo antitumor effect indicated that rhGM-CSF/MCAF had marked antitumor effect against A549 tumor in nude mice and even completely suppressed tumor formation. rhGM-CSF/MCAF was significantly more effective in inhibiting tumor growth than rhGM-CSF. Histological analysis showed that tumor site injected with rhGM-CSF/MCAF was infiltrated by a large number of monocytes while a sparse infiltration of monocytes was observed at the tumor site injected with rhGM-CSF or normal saline, suggesting that the antitumor effect of rhGM-CSF/MCAF was mediated by the recruitment of a large number of monocytes to the tumor site.

Recombinant cytokines and hematopoietic growth factors in allogeneic and autologous bone marrow transplantation

Use of recombinant hematopoietic growth factors in the course of bone marrow transplantation has revolutionized this modality by significantly improving the safety of the procedure. It is anticipated that use of cytokines in combination and the introduction of newer agents will further reduce costs and improve antitumor responses as well.

In vitro production of megakaryocytes from PIXY321 versus GM-CSF-mobilized peripheral blood progenitor cells

The generation of megakaryocytes (MK) from cultured peripheral blood progenitor cells (PBSC), harvested via apheresis, from 18 female breast cancer patients treated with either PIXY321 or GM-CSF was compared. Nonadherent mononuclear cells (MNC) were cultured in liquid suspension with 50 U/ml thrombopoietin (TPO) and 2.5% autologous heparinized plasma for 12 days. Flow cytometric analysis was used to measure the percentage of CD34+ on day 1 and CD41+ cells on day 12. The frequency of CD34+ cells was greater in GM-CSF-mobilized samples than in PIXY321-mobilized samples, and MK/MNC yields correlated directly with the number of CD34+ cells seeded, PIXY321-mobilized samples produced more MKs per CD34+ cell than GM-CSF-mobilized samples. Overall, there was no significant difference in the MK/MNC yield between PIXY321- and GM-CSF-mobilized samples. Cyclophosphamide (CY) increased the frequency of CD34+ cells and the corresponding MK/MNC yield for both cytokines, but had no effect on the MK/CD34+ yield. Compared to GM-CSF, PIXY321 mobilization resulted in increased CD34+ cell commitment to the MK lineage.

Bioactive murine and human interleukin-12 fusion proteins which retain antitumor activity in vivo

Interleukin-12 (IL-12) is unique amongst cytokines in being a disulfide-linked heterodimer of two separately encoded subunits (p35 and p40). We expressed single chain IL-12 proteins from retroviral constructs in which the two IL-12 subunits were linked by a 6-15 amino acid polypeptide linker, with deletion of the 22 amino acid leader sequence of the trailing subunit. The murine fusion protein IL-12.p40.L.delta p35 containing a (Gly4Ser)3 linker was stably expressed, bioactive in vitro, and had an apparent specific activity comparable to that of native and recombinant IL-12. Western blotting confirmed that murine IL-12.p40.L.delta p35 retained the linking polypeptide sequences. The analogous human IL-12.p40.L.delta p35 fusion protein containing a Gly6Ser linker was bioactive with an apparent specific activity comparable to recombinant human IL-12. In a preexisting CMS-5 tumor model, CMS-5 cells secreting either native or fusion protein forms of IL-12 prolonged survival and led to complete tumor regression.

Phase I/II study of PIXY321 in combination with cyclophosphamide and carboplatin in the treatment of ovarian cancer

OBJECTIVE

Our purpose was to evaluate the safety and biologic effects of PIXY321 after chemotherapy in patients with ovarian carcinoma.

STUDY DESIGN

A multicenter, nonrandomized, phase I/II study of subcutaneously administered PIXY321 after the second cycle of chemotherapy in cohorts of three or more patients at 50, 125, 250, 500, 750, or 100 micrograms/m2 per day.

RESULTS

Cyclophosphamide (600 mg/m2) and carboplatin (400 mg/m2) were administered every 28 days to 34 patients. At doses > or = 500 mg/m2 per day, the median nadir platelet and median nadir absolute neutrophil counts in cycle 2 (with PIXY321) compared with cycle 1 (control) were both higher in 13 of 26 (50%) patients. Twenty-one patients were withdrawn from the study. A total of 17 of 21 (81%) were removed for myelosuppression (n = 15) or PIXY321 toxicity (n = 2). A total of 28 of 34 (82%) patients had injection site reactions. Thirty-seven nonhematologic grade 3 events occurred.

CONCLUSIONS

At these doses and schedules PIXY321 can be safely administered. Aggressive dosing of cyclophosphamide and carboplatin could not be maintained for six cycles in the majority (62%) of patients.

Production of interleukin 1beta by human hematopoietic progenitor cells

The production of interleukin 1beta (IL-1beta) by human hematopoietic stem/progenitor cells was studied to explore the concept that these cells are not merely responders to stimuli from their microenvironment, but can themselves produce a powerful biomodulator. Cells with a CD34+ CD45RA(lo) CD71(lo) phenotype were purified from human umbilical cord blood and cultured one per well in serum-free medium with a mixture of cytokines. Cells that had divided over 2-5 d to form doublets were identified and the daughter cells were studied individually. 91% (460/506) of daughter cells had clonogenic potential. Analysis of these individual daughter cells by reverse transcription-polymerase chain reaction showed that 29% of them (14/48) were positive for IL-1beta mRNA. One of the cells that was strongly positive for IL-1beta mRNA had a sibling that generated 366,000 cells of multiple lineages after 14 d. IL-1beta converting enzyme mRNA, which is necessary to produce IL-1beta, was also detected by reverse transcription-polymerase chain reaction at the single-cell level. Moreover, enzyme immunoassay for mature secreted IL-1beta in culture supernatants demonstrated the production of IL-1beta protein by these cells. This was confirmed by fluorescent immunostaining of the cells for human IL-1beta which showed a significant portion of positive cells. Taken together, the results demonstrate the capacity of early hematopoietic cells to synthesize IL-1beta. The capacity of human hematopoietic stem/progenitor cells to produce IL-1beta may be involved in regulation of their proliferation and differentiation under certain circumstances and dysregulation of this process may be modified in leukemogenesis.

The thrombocytopenia of cancer. Prospects for effective cytokine therapy

The previous 10 years have witnessed the development of increasing needs for platelet transfusion in support of aggressive therapies of malignancy. Despite gains in our understanding of platelet preparation, storage, and transfusion, alternative therapies are clearly desirable. During the late 1980s at least six distinct cytokines that display effects on megakaryocyte growth and differentiation-IL-3, KL, GM-CSF, IL-6, IL-11, and LIF- and a synthetic growth factor, PIXY 321, were cloned and characterized. Although none of these cytokines fulfill all of the physiologic roles of thrombopoietin, in its absence several have undergone extensive preclinical and preliminary clinical testing. Of these, IL-11 and PIXY 321 hold promise for clinical amelioration of thrombocytopenia in cancer patients. With the recent cloning of thrombopoietin and its promise in preclinical trials, the role of each of these recombinant proteins in clinical medicine is undergoing careful evaluation. As with erythropoietin and G-CSF before it, given its normal role in the regulation of platelet production, Tpo would appear to provide the greatest physiologic stimulus to platelet production in states of natural and iatrogenic marrow failure. Careful clinical trials of the agent are needed to determine whether the hormone will fulfill this promise. The following decade will most certainly see the resolution of many of the complications of thrombocytopenia and its transfusional support.

The hematoregulatory peptide, SK&F 107647, in combination with antifungal therapy in murine Candida albicans infections

SK&F 107647, a novel synthetic low molecular weight peptide, has been shown to be a potent hematoregulatory agent. We have previously demonstrated that SK&F 107647 administration can prolong survival in both immunosuppressed and normal mice challenged with the opportunistic fungal pathogen Candida albicans. Additionally, we have determined the effect of prophylactic SK&F 107647 treatment combined with conventional antifungal therapy on the survival of mice challenged with a lethal dose of C. albicans. Prophylactic treatment with SK&F 107647 or therapeutic treatment with the antifungals fluconazole or amphotericin B significantly increased the survival rates of immunosuppressed mice challenged with a lethal dose of C. albicans. However, the combination of SK&F 107647 treatment followed by antifungal therapy resulted in statistically significant increases in survival over that observed with either therapy alone. These results indicated that the hematoregulatory factor(s) elicited by SK&F 107647 enhance the survival of mice treated with conventional therapies in a model of experimental systemic candidiasis. Key words: SK&F 107647, Candida albicans, hematoregulatory, fluconazole, amphotericin B.

Regulation of murine B cell growth and differentiation by CD30 ligand

A ligand for CD30 has been recently cloned, and has been shown to have sequence homology with the tumor necrosis factor family of cytokines. CD30 ligand (CD30L) was found to be induced on helper T cell clones, and its receptor was expressed on freshly isolated and activated murine B cells. Recombinant murine CD30L was found to share many functional properties with CD40 ligand (CD40L) in the regulation of murine B cell growth and differentiation in vitro. CD30L stimulated B cell proliferation, antigen-specific antibody production, and polyclonal immunoglobulin secretion in a cytokine-dependent manner. In particular, the stimulation of B cell proliferation by CD30L required interleukin (IL)-4 and IL-5, induction of anti-sheep red blood cell antibody-secreting B cells by CD30L required IL-2 and IL-5, and optimal induction of polyclonal immunoglobulin secretion required IL-4 and IL-5. Under these conditions, the polyclonal secretion of IgG1, IgA, IgG3 and IgE was induced. The induction of immunoglobulin secretion by CD30L was independent of CD40L, as B cells from CD40L deficient-mice responded normally to CD30L treatment. We conclude that CD30L is a potent mediator of B cell growth and differentiation in vitro and may play a role in cognate T cell-B cell interactions.

AM5, a protein-associated polysaccharide, stimulates hematopoiesis and modulates the expression of endogenous hematopoietic growth factors in murine long-term bone marrow cultures

We have investigated the mechanism behind the hematopoietic stimulation mediated by AM5, a protein-associated polysaccharide that stimulates in vivo the murine hematopoietic system. A dose-dependent increase in hematopoietic progenitors was observed in long-term bone marrow cultures (LTBMCs) treated in vitro with AM5. The stimulatory effect was more marked in colony-forming units-granulocyte-macrophage (CFU-GM) than in CFU-spleen (CFU-S) progenitors and also more significant in the supernatant than in the adherent layer. This stimulatory effect was reversible, and continuous stimulation with high doses of AM5 was conductive to a progressive exhaustion of the culture. The analysis of the CFU-GM stimulating activity present in the supernatant of AM5-treated cultures revealed a dose-dependent induction of granulocyte-macrophage colony-stimulating activity (GM-CSA), in contrast with control cultures in which no CSA was detected. Northern blots of LTBMC-adherent layers obtained after in vitro treatment with AM5 revealed a significant mRNA expression for interleukin 1 alpha (IL-1 alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage CSF (M-CSF) and granulocyte CSF (G-CSF), in contrast with adherent layers from untreated cultures which only expressed, in detectable levels, M-CSF and stem cell factor (SCF). The SCF expression was down-modulated in AM5-treated cultures. Our results strongly suggest that the hematopoietic stimulation induced by AM5 is mediated by the modulated expression of endogenous hematopoietic growth factors.

Combined antileukemic activity of pIXY 321 and Ara-C against human acute myeloid leukemia cells

Prolonged administration of conventional (100 mg/m2/day) or low dose Ara-C (20 mg/m2/day) has been associated with significant clinical antileukemic effects in AML and myelodysplastic syndromes. These doses and schedules of Ara-C yield plasma Ara-C concentrations in the range of 10 to 100 nM. Utilizing concentrations and a schedule of Ara-C treatment, representative of Ara-C exposures in these clinical situations, we performed in vitro studies to examine the effects of co-treatment with pIXY 321 on Ara-C induced apoptosis and Ara-C-mediated colony growth inhibition of human myeloid leukemia HL-60 cells. Significantly greater internucleosomal DNA fragmentation, higher percentage of morphologically recognizable apoptotic cells and increased colony growth inhibition were observed following treatment with 100 versus 10 nM Ara-C for 5 days. Simultaneous exposure to 10 ng/ml pIXY 321 resulted in significantly increased colony growth inhibition as well as DNA fragmentation and apoptosis due to 10 nM but not 100 nM Ara-C. These concentrations of Ara-C inhibited c-myc and did not induce c-jun mRNA expression. These effects of Ara-C on c-myc and c-jun expressions were not influenced by co-treatment with pIXY 321. Neither treatment with pIXY 321 or Ara-C alone, nor co-treatment with pIXY 321 and Ara-C, significantly altered the intracellular p26BCL-2 levels in HL-60 cells. These results indicate that co-treatment with pIXY 321 significantly increases low dose Ara-C-induced apoptosis and thereby its antileukemic activity.

CD45 isoform expression on human haemopoietic cells at different stages of development

Alternate splicing and glycosylation produce multiple CD45 isoforms which are selectively expressed on the surface of cells of the haemopoietic system. The expression of CD45RA, CD45RB and CD45RO on CD34+ and CD34- haemopoietic cells from umbilical cord blood, bone marrow and fetal liver were studied by flow cytometry. CD34+ subpopulations defined by CD45 isoform expression were sorted from bone marrow and tested in long-term culture assays. By combining results of functional studies with phenotypic data and previously published information, the following pattern of CD45 isoform expression on early haemopoietic cells was established. The most primitive CD34+ cells are CD45RO+ CD45RB+ and express low or undetectable levels of CD45RA. Upon erythroid differentiation, CD34+ cells remain CD45RO+ CD45RB+, whereas commitment into the myeloid and lymphoid lineages coincides with down-regulation of CD45RO and up-regulation of CD45RA. As a result, the majority of CD34+ cells can be divided into two mutually exclusive populations of cells which express either CD45RO or CD45RA. This notion was confirmed in this study by three-colour immunofluorescence. The alternative expression of various CD45 isoforms on functionally distinct haemopoietic cells suggests an important role for these molecules in the proliferation and differentiation of haemopoietic cells.

A circularly permuted recombinant interleukin 4 toxin with increased activity

Fusion of ligands such as growth factors to other proteins often dramatically reduces the affinity of the ligand for its receptor. With recombinant DNA techniques, the attachment point between the two proteins has until now been restricted to either the amino or the carboxyl terminus of the ligand. However, binding may be greatly compromised if both ends are close to the site at which the ligand binds to its receptor. To construct a single-chain growth factor fusion protein with the connection at a new site on the growth factor, we constructed a DNA fragment encoding circularly permuted interleukin 4 (IL4), termed IL4(38-37). This was accomplished by placing a start codon before position 38, connecting codons 1 and 129 with a sequence encoding a peptide linker, and placing a stop codon after codon 37 of IL4. IL4(38-37) was fused via its new carboxyl terminus, Lys37, to a truncated form of Pseudomonas exotoxin. The purified circularly permuted IL4-toxin bound to the IL4 receptor with 10-fold higher affinity than an IL4-toxin in which the toxin was fused to the carboxyl terminus of IL4. Circular permuteins of growth factors can improve the effectiveness of recombinant fusion proteins, because the junction can be moved to a site on the growth factor which allows it to bind with higher affinity.

PIXY321 (GM-CSF/IL-3 fusion protein): biology and early clinical development

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) are functionally related hematopoietins with overlapping but distinct hematopoietic effects. GM-CSF supports more myeloid progenitor cells, whereas IL-3 promotes more erythroid, megakaryocytic and multipotential progenitor cells. Their complementary in vivo biological effects and cross competition for receptor binding prompted the development of PIXY321, a synthetic hybrid protein of GM-CSF and IL-3. PIXY321 binds to cell lines expressing specific receptors for either ligand, and it exhibits enhanced biological activity in human hematopoietic progenitor cell assays. In preclinical studies, PIXY321 has been shown to accelerate both neutrophil and platelet recovery in rhesus monkeys subjected to sublethal irradiation. Based on these preclinical observations, clinical trials have been initiated examining the therapeutic potential of this agent in ameliorating treatment- or disease-related hematopoietic suppression. The early results indicate that PIXY321 can stimulate multilineage hematopoiesis in vivo and enhance neutrophil and platelet recovery following chemotherapy and bone marrow transplantation (BMT). These results suggest that PIXY321 elicits the biological effects of both its component cytokines and represents a novel means of delivering two independent but interactive cytokines in combination.

Homodimeric murine interleukin-3 agonists indicate that ligand dimerization is important for high-affinity receptor complex formation

Homodimeric murine interleukin 3 (mIL-3) agonists were generated by intermolecular cystine-bonding. Steady-state binding assays and association kinetics performed at 4 degrees C using these agonists revealed specific binding to both the high- and low-affinity receptor. DSS-mediated crosslinking studies performed at 4 degrees C with agonist concentrations compatible with high-affinity receptor complex formation allowed to detect protein complexes of the alpha chain, the beta chain(s) and the high-affinity receptor complex migrating with apparent molecular weights of 90 kDa, 140 kDa, and above 180 kDa, respectively. In contrast, monomeric mIL-3 was crosslinked to the alpha chain receptor only unless high concentrations were used. Binding studies performed at 4 degrees C revealed a positive cooperative interaction of monomeric mIL-3 with the low-affinity receptor. Proliferation studies and association kinetics performed at 37 degrees C showed that under physiological conditions these agonists were at least 2- to 3-fold more potent than monomeric mIL-3. We therefore propose that dimerization of mIL-3 may be involved in high-affinity receptor complex formation.

c-kit ligand augments granulocyte-macrophage colony growth from patients with 5q- syndrome

In vitro studies may serve as a guide to clinical strategies with cytokines. In this study, marrows from 26 patients with myelodysplastic syndrome (MDS) were assayed for myeloid progenitor cells in agar gel. Colony stimulating activity was provided by the recombinant human colony stimulating factors granulocyte-macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), interleukin 3 (IL-3), fusion protein (FP), c-kit ligand (KL) or GM-CSF combined with other cytokines (KL, IL-3). Decreased colony forming units granulocyte-macrophage (CFU-GM) were detected in most cases (69%) compared with normal controls. Neither FP nor the combination of GM-CSF + IL-3 produced more colonies than GM-CSF alone. The number of CFU-GM did not correlate with French American British (FAB) class. All marrows (7) from patients with 5q- showed augmentation of GM-CSF induced colonies with the addition of KL. In contrast, KL augmentation was noted in only 42% of other MDS marrows (p = 0.01). This in vitro result suggests that 5q- may predict a group of MDS patients with a likelihood to respond to the combination of GM-CSF + KL.

Expression of Thy-1 on human hematopoietic progenitor cells

Expression of Thy-1 on hematopoietic cells from human fetal liver (FL), cord blood (CB), and bone marrow (BM) was studied with a novel anti-Thy-1 antibody, 5E10. Specificity of 5E10 for human Thy-1 was demonstrated by immunoprecipitation of a 25-35-kD molecule, and the sequence of a cDNA that was cloned by immunoselection of COS cells transfected with a cDNA library derived from a 5E10+ cell line. Two- and three-color immunofluorescence staining experiments revealed that the Thy-1 expression is restricted to, an average, 1-4% of FL, CB, and BM cells, and binding to these cell types is essentially restricted to a very small subset of lymphoid cells and approximately 25% of CD34+ cells. Thy-1+ CD34+ cells were further characterized as CD38lo/CD45RO+/CD45RA-/CD71lo/c-kit(lo) and rhodamine 123dull. When CD34+ cells were sorted on the basis of Thy-1 expression, the majority of clonogenic cells were recovered in the CD34+Thy-1- fraction, whereas the majority of cells capable of producing myeloid colonies after 5-8 wk of long-term culture (long-term culture initiating cells) were recovered in the Thy-1+CD34+ fraction. In addition to CD34+ cells, Thy-1 was found to be expressed on a variable, very small number (< 1%) of CD34- mononuclear cells in BM, CB, and peripheral blood that were further characterized as CD3+ CD4+ lymphocytes. The restricted expression of Thy-1 on primitive hematopoietic cells is in agreement with a previous report (Baum et al., 1992. Proc. Natl. Acad. Sci. USA. 89:2804) in which Thy-1 expression was used to enrich for primitive hematopoietic cells from fetal tissue. Compared with those previous studies, we found Thy-1 expression on a larger proportion of CD34+ cells (25% in our study vs. 5% in Baum et al.) and furthermore performed studies on Thy-1 expression on CD34+ cells from CB, FL, and BM in relation to markers that are known to be differentially expressed on hematopoietic cells. Taken together our results indicate that Thy-1-specific antibody 5E10 is an attractive tool for further studies on the biology and purification of human stem cells.

Idiotype/granulocyte-macrophage colony-stimulating factor fusion protein as a vaccine for B-cell lymphoma

To produce a vaccine against cancer, antigens must be found that are preferentially expressed by tumour cells and can induce an immune response against the tumour. The variable regions of the immunoglobulin molecules expressed on malignant B cells (idiotypes) are tumour-specific, but are weak immunogens. To induce an immune response in animals or humans, the idiotypic protein has therefore to be chemically coupled to a strongly immunogenic protein and mixed with an adjuvant. The resulting response can protect animals from subsequent tumour challenge, and cure animals with established tumours in combination with chemotherapy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) augments antigen presentation in a variety of cells. Here we show that by fusing a tumour-derived idiotype to GM-CSF, it can be converted into a strong immunogen capable of inducing idiotype-specific antibodies without other carrier proteins or adjuvants and of protecting recipient animals from challenge with an otherwise lethal dose of tumour cells. This approach may be applicable to the design of vaccines for a variety of other diseases.

Southwestern Internal Medicine Conference: clinical use of hematopoietic growth factors

The hematopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), have been cloned, produced in bacteria and yeast, and approved for clinical use in the treatment of neutropenia. Both factors stimulate the proliferation and maturation of neutrophil progenitors and enhance the effector functions of mature cells by interaction with specific receptors on the cell surface. Serum levels of G-CSF correlate inversely with the neutrophil count, suggesting that G-CSF may be the normal homeostatic regulator of the neutrophil count, while GM-CSF is generally undetectable in the serum and appears under normal physiologic conditions to act locally at inflammatory sites. Phase I and II clinical trials with these factors demonstrated minimal toxicity for G-CSF and mild to moderate dose-dependent toxicity for GM-CSF. Recent clinical trials, including double-blind, randomized studies, support a role for these growth factors in the treatment of chronic neutropenias, such as Kostmann's syndrome, acquired immune deficiency syndrome (AIDS), aplastic anemia, and myelodysplasia, as well as in acute neutropenias, such as cyclic neutropenia, chemotherapy-induced neutropenia, and bone marrow transplantation.

Cytokine technology in basic and applied research on the hematopoietic system

Cytokines are polypeptide molecules important for the regulation and maintenance of immunity and hematopoiesis. Their central role in the control of a number of physiological mechanisms makes them an important area of both basic and applied biomedical research. This review presents an overview of basic and applied biology, and introduces the term cytokine technology to denote the use of cytokines as research tools for understanding the cellular and molecular regulation of hematopoiesis. A number of frontier technologies are reviewed, including fusion toxins, fusion proteins, and animal models of cytokine expression and regulation.

Recombinant human interleukin 3 in clinical oncology

Interleukin 3 (IL-3) is a multipotent hematopoietic growth factor which became available as a recombinant (rh) growth factor for use in the clinic a few years ago. In dose-finding studies, this hematopoietic growth factor has been evaluated without and after standard chemotherapy. Stimulatory effects on leukocytes, neutrophils, eosinophils, monocytes, reticulocytes and platelets were observed in some studies. Chemotherapy postponement due to insufficient bone marrow recovery was less frequent when IL-3 was administered. There are some clinical studies available in which rhIL-3 is combined with rh granulocyte-macrophage colony-stimulating factor (GM-CSF). The results do not clearly suggest superiority of these combinations over rhGM-CSF alone, but this may be partly due to the time scheduling of the growth factors. Administration s.c. is not inferior to i.v. Side effects mainly consist of flu-like symptoms and headache. The role of rhIL-3 after high-dose chemotherapy and autologous bone marrow reinfusion is still questionable. The addition of rhIL-3 to rhGM-CSF both administered after chemotherapy may allow a very high yield of peripheral stem cells suitable for bone marrow reconstitution after high-dose chemotherapy. rhIL-3 can stimulate leukemia tumor cell proliferation in vitro as well as proliferation of solid tumor cell lines. It is not yet clear in which way rhIL-3 combined with chemotherapy will effect tumor response and patient survival. It is too early to define the exact place of rhIL-3 in oncology. Additional studies with rhIL-3 alone and in combination with other growth factors are needed.

Therapeutic use of granulocyte-macrophage colony-stimulating factor (GM-CSF). A review of recent experience

Recombinant cytokines are now available for clinical use. Several colony-stimulating factors (CFS) have been identified which induce activation, proliferation and maturation of myeloid lineage cells. Recent therapeutic trials with granulocyte-macrophage colony-stimulating factors (GM-CSF) in association with chemotherapy, bone marrow transplantation and leukemia treatment are reviewed. GM-CSF as primary treatment for myelodysplasia and other types of bone marrow failure is also of interest. Colony-stimulating factor therapy in AIDS may be useful in order to reduce myelodepression caused by antiviral treatment and chemotherapy for associated malignancies like Kaposi's sarcoma. However, the effect of neutrophil count increase on infection is far from clear, and the real benefit of GM-CSF in cancer therapy has yet to be demonstrated.

Long-term erythropoiesis from constant numbers of CD34+ cells in serum-free cultures initiated with highly purified progenitor cells from human bone marrow

To directly study the biological properties of purified hematopoietic colony-forming cell precursors, cells with a CD34+ CD45RAlo CD71lo phenotype were purified from human bone marrow using density separation and fluorescence-activated cell sorting, and were cultured in serum-free culture medium supplemented with various cytokines. In the presence of interleukin 3 (IL-3), IL-6, erythropoietin, and mast cell growth factor (a c-kit ligand), cell numbers increased approximately 10(6)-fold over a period of 4 wk, and the percentage of cells that expressed transferrin receptors (CD71) increased from less than 0.1% at day 0 to greater than 99% at day 14. Interestingly, the absolute number of CD34+ CD71lo cells did not change during culture. When CD34+ CD71lo cells were sorted from expanded cultures and recultured, extensive cell production was repeated, again without significant changes in the absolute number of cells with the CD34+ CD71lo phenotype that were used to initiate the (sub)cultures. These results document that primitive hematopoietic cells can generate progeny without an apparent decrease in the size of a precursor cell pool.

Cytokine stimulation of multilineage hematopoiesis from immature human cells engrafted in SCID mice

Severe combined immunodeficient (SCID) mice transplanted with human bone marrow were treated with human mast cell growth factor, a fusion of interleukin-3 and granulocyte-macrophage colony-stimulating factor (PIXY321), or both, starting immediately or 1 month later. Immature human cells repopulated the mouse bone marrow with differentiated human cells of multiple myeloid and lymphoid lineages; inclusion of erythropoietin resulted in human red cells in the peripheral blood. The bone marrow of growth factor-treated mice contained both multipotential and committed myeloid and erythroid progenitors, whereas mice not given growth factors had few human cells and only granulocyte-macrophage progenitors. Thus, this system allows the detection of immature human cells, identification of the growth factors that regulate them, and the establishment of animal models of human hematopoietic diseases.

Transforming growth factor-beta: a bidirectional regulator of hematopoietic cell growth

It is now apparent that the transforming growth factor-beta (TGF-beta) family of proteins has potent hematopoietic regulatory properties ranging from effects on the growth and differentiation of primitive stem cells to the differentiated functions of mature cells. Although most reports have described the inhibitory activities of TGF-beta on hematopoiesis, recent evidence supports the concept that TGF-beta can have both inhibitory and stimulatory actions on these systems. These differences depend on the differentiation state of the target cell and the other cytokines interacting with the cell. Furthermore, TGF-beta has direct bidirectional effects on cell surface expression of many cytokine receptors suggesting that it is part of the mechanism of action of TGF-beta. The major biological effect of TGF-beta on hematopoietic cell growth is the reversible inhibition of entry into the cell cycle. Importantly, the effect of in vivo administration of TGF-beta has mimicked the in vitro effects. Ultimately, well designed clinical trials will determine whether the exciting potential of TGF-beta can be used to treat or prevent myelotoxicity and other bone marrow dysfunctions.

Preclinical studies and future directions in the development of new hematologic growth factors

Normal hematopoiesis is controlled by a cascade of interacting hormones collectively referred to as cytokines. These growth factors have been studied both individually and in specific combinations to determine their optimal clinical use. In some cases, the combination of certain cytokines produces a synergistic effect enhancing their efficacy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has demonstrated the ability to stimulate early- and late-phase granulocyte and macrophage progenitor cells, activate mature neutrophils and macrophages, and enhance their peripheral infection fighting performance. Interleukin-3 (IL-3), currently undergoing clinical evaluation, acts early in the development of multiple types of white blood cells and, when used in combination with GM-CSF, also produces a synergistic effect in raising white blood cell and platelet levels. A recombinant protein, PIXY321, has recently been developed that contains both IL-3 and GM-CSF domains. The development of this molecule was supported by the discovery of a dual IL-3-GM-CSF receptor on the surface of hematopoietic progenitor cells. PIXY321 provides a significantly enhanced biologic effect (10-fold greater proliferation) via multiple cross-linking of GM-CSF, IL-3, and dual receptor binding sites. PIXY321 has the same molecular weight as the equivalent molar concentrations of GM-CSF and IL-3 combined and offers the advantage of combination therapy in an easy-to-administer regimen. Another recombinant cytokine, mast cell growth factor (MGF), has shown profound hematopoietic activity in vitro and has the ability to enhance proliferation of hematopoietic stem cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Transplantation of normal and leukemic human bone marrow into immune-deficient mice: development of animal models for human hematopoiesis

The successful engraftment of human hematopoietic cells into immune-deficient mice offers a novel approach to characterize the developmental program of human hematopoiesis. While it is not yet possible to achieve high-level engraftment of all human lineages, several methods have been developed to successfully engraft human lymphoid cells and reconstitute partial immune function. In addition to mature cell types, there is evidence that progenitors and perhaps stem cells can engraft the murine bone marrow. Recent work suggests that provision of exogenous human cytokines significantly increases the level of human cell engraftment and stimulates the development of multiple lineages. Progress has also been made to establish animal models of human hematopoietic diseases such as leukemia, autoimmunity, and infectious diseases.

Hybrid cytokines as hematopoietic growth factors

A large body of in vitro and in vivo data suggests that combinations of cytokines provide the most effective mechanism for stimulating multilineage acceleration of hematopoiesis. Creation of a granulocyte-macrophage colony-stimulating factor (GM-CSF)/interleukin 3 (IL-3) fusion protein has yielded a single therapeutic which has enhanced biological activity in comparison to the individual cytokines from which it is composed. In vivo studies with this fusion protein (PIXY321) suggest that it may provide a means to accelerate both neutrophil and platelet recovery in clinical settings in which hematopoiesis is suppressed. The biology of PIXY321 and the potential for other fusion proteins is discussed.