Small-molecule inhibitors targeting the DNA-binding domain of STAT3 suppress tumor growth, metastasis and STAT3 target gene expression in vivo

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in malignant tumors and has important roles in multiple aspects of cancer aggressiveness. Thus targeting STAT3 promises to be an attractive strategy for treatment of advanced metastatic tumors. Although many STAT3 inhibitors targeting the SH2 domain have been reported, few have moved into clinical trials. Targeting the DNA-binding domain (DBD) of STAT3, however, has been avoided due to its 'undruggable' nature and potentially limited selectivity. In a previous study, we reported an improved in silico approach targeting the DBD of STAT3 that resulted in a small-molecule STAT3 inhibitor (inS3-54). Further studies, however, showed that inS3-54 has off-target effect although it is selective to STAT3 over STAT1. In this study, we describe an extensive structure and activity-guided hit optimization and mechanistic characterization effort, which led to identification of an improved lead compound (inS3-54A18) with increased specificity and pharmacological properties. InS3-54A18 not only binds directly to the DBD and inhibits the DNA-binding activity of STAT3 both in vitro and in situ but also effectively inhibits the constitutive and interleukin-6-stimulated expression of STAT3 downstream target genes. InS3-54A18 is completely soluble in an oral formulation and effectively inhibits lung xenograft tumor growth and metastasis with little adverse effect on animals. Thus inS3-54A18 may serve as a potential candidate for further development as anticancer therapeutics targeting the DBD of human STAT3 and DBD of transcription factors may not be 'undruggable' as previously thought.

Experimental basis of cord blood transplantation

Efforts are needed to enhance the efficacy of cord blood (CB) transplantation. Laboratory information set the stage for the first and subsequent CB transplants, and will be instrumental in continuing to advance the field. This paper offers a brief understanding of the current state of hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC) biology, a look back at laboratory studies leading to the first CB transplants, and a discussion of the possible means to enhance CB transplantation. Results show that physical recovery of greater numbers of HPCs is possible after CB is collected by perfusing the placenta, but how realistic this procedure is for collection of CB to be banked is open to question. We also show that the chemokine stromal cell-derived factor-1/CXCL12 can enhance the ex vivo expansion of CB HPCs beyond that of the combination of SCF, Flt3-ligand and TPO. Advances in cytokine and stromal cell biology, and in intracellular signals mediating the effects of cytokines/stromal cells should be considered in the context of future efforts to enhance functional activities of donor CB HSCs and HPCs and the microenvironmental niche of the recipient, which is required for acceptance and nurturing these HSCs/HPCs.

SDF-1α/CXCL12 enhances retroviral-mediated gene transfer into immature subsets of human and murine hematopoietic progenitor cells

Genetic modification of hematopoietic stem and progenitor cells has the potential to treat diseases affecting blood cells. Oncoretroviral vectors have been used for gene therapy; however, clinical success has been limited in part by low gene transfer efficiencies. We found that the presence of stromal-derived factor 1 (SDF-1alpha)/CXCL12 during retroviral transduction significantly enhanced, in a dose-dependent fashion, gene transfer into immature subsets of high proliferative human and murine hematopoietic progenitor cells. Murine mononuclear bone marrow cells and purified c-Kit(+)Lin(-) bone marrow cells were prestimulated and transduced with the bicistronic retroviral vector MIEG3 on Retronectin-coated surfaces in the presence and absence of SDF-1. SDF-1 enhanced gene transduction of murine bone marrow and c-Kit(+)Lin(-) cells by 35 and 29%, respectively. Moreover, SDF-1 enhanced transduction of progenitors in these populations by 121 and 107%, respectively. SDF-1 also enhanced transduction of human immature subsets of high proliferative progenitors present in either nonadherent mononuclear or CD34(+) umbilical cord blood cells. Transduction of hematopoietic progenitors was further increased by preloading Retronectin-coated plates with retrovirus using low-speed centrifugation followed by increasing cell-virus interactions through brief centrifugation during the transduction procedure. These results may be of clinical relevance.

Chemokine regulation of hematopoiesis and the involvement of pertussis toxin-sensitive G alpha i proteins

Chemokines have been implicated in regulation of various aspects of hematopoiesis, including negative regulation of the proliferation of immature subsets of myeloid progenitor cells (MPCs), chemotaxis of MPCs, and survival enhancement of MPCs after delayed growth factor addition. Since chemokine receptors are seven-transmembrane-spanning G-protein-linked receptors and the chemotactic effect in vitro of the CXC chemokine SDF-1 is pertussis toxin (PT)-sensitive, implying the involvement of G alpha i proteins as mediators of SDF-1-induced chemotaxis, we evaluated the effects of PT on other chemokine actions influencing MPCs. While the in vitro survival-enhancing effects of SDF-1 on GM-CSF and steel factor-dependent mouse bone marrow granulocyte macrophage progenitors (CFU-GM) were pertussis toxin-sensitive, the suppressive effects of the CC chemokine MIP-1 alpha and the CXC chemokine IL-8 on colony formation by GM-CSF and steel factor-sensitive CFU-GM were insensitive to pertussis toxin. These results suggest that not all chemokine-mediated effects on MPCs are necessarily mediated through pertussis toxin-sensitive G alpha i proteins.

The exodus subfamily of CC chemokines inhibits the proliferation of chronic myelogenous leukemia progenitors

Chemokines are a family of related proteins that regulate leukocyte infiltration into inflamed tissue and play important roles in disease processes. Among the biologic activities of chemokines is inhibition of proliferation of normal hematopoietic progenitors. However, chemokines that inhibit normal progenitors rarely inhibit proliferation of hematopoietic progenitors from patients with chronic myelogenous leukemia (CML). We and others recently cloned a subfamily of CC chemokines that share similar amino-terminal peptide sequences and a remarkable ability to chemoattract T cells. These chemokines, Exodus-1/LARC/MIP-3alpha, Exodus-2/SLC/6Ckine/TCA4, and Exodus-3/CKbeta11/MIP-3beta, were found to inhibit proliferation of normal human marrow progenitors. The study described here found that these chemokines also inhibited the proliferation of progenitors in every sample of marrow from patients with CML that was tested. This demonstration of consistent inhibition of CML progenitor proliferation makes the 3 Exodus chemokines unique among chemokines. (Blood. 2000;95:1506-1508)

Altered responsiveness to chemokines due to targeted disruption of SHIP

SHIP has been implicated in negative signaling in a number of hematopoietic cell types and is postulated to downregulate phosphatidylinositol-3-kinase- (PI-3K-) initiated events in diverse receptor signaling pathways. Because PI-3K is implicated in chemokine signaling, we investigated whether SHIP plays any role in cellular responses to chemokines. We found that a number of immature and mature hematopoietic cells from SHIP-deficient mice manifested enhanced directional migration (chemotaxis) in response to the chemokines stromal cell-derived factor-1 (SDF-1) and B-lymphocyte chemoattractant (BLC). SHIP(-/-) cells were also more active in calcium influx and actin polymerization in response to SDF-1. However, colony formation by SHIP-deficient hematopoietic progenitor cell (HPCs) was not inhibited by 13 myelosuppressive chemokines that normally inhibit proliferation of HPCs. These altered biologic activities of chemokines on SHIP-deficient cells are not caused by simple modulation of chemokine receptor expression in SHIP-deficient mice, implicating SHIP in the modulation of chemokine-induced signaling and downstream effects.

Dominant myelopoietic effector functions mediated by chemokine receptor CCR1

Macrophage inflammatory protein (MIP)-1alpha, a CC chemokine, enhances proliferation of mature subsets of myeloid progenitor cells (MPCs), suppresses proliferation of immature MPCs, and mobilizes mature and immature MPCs to the blood. MIP-1alpha binds at least three chemokine receptors. To determine if CCR1 was dominantly mediating the above activities of MIP-1alpha, CCR1-deficient (-/-) mice, produced by targeted gene disruption, were used. MIP-1alpha enhanced colony formation of marrow granulocyte/macrophage colony-forming units (CFU-GM), responsive to stimulation by granulocyte/macrophage colony-stimulating factor (GM-CSF), and CFU-M, responsive to stimulation by M-CSF, from littermate control CCR1(+/+) but not CCR1(-/-) mice. Moreover, MIP-1alpha did not mobilize MPCs to the blood or synergize with G-CSF in this effect in CCR1(-/-) mice. However, CCR1(-/-) mice were increased in sensitivity to MPC mobilizing effects of G-CSF. Multi-growth factor-stimulated MPCs in CCR1(-/-) and CCR1(+/+) marrow were equally sensitive to inhibition by MIP-1alpha. These results implicate CCR1 as a dominant receptor for MIP-1alpha enhancement of proliferation of lineage-committed MPCs and for mobilization of MPCs to the blood. CCR1 is not a dominant receptor for MIP-1alpha suppression of MPC proliferation, but it does negatively impact G-CSF-induced MPC mobilization.

Effects of CC, CXC, C, and CX3C chemokines on proliferation of myeloid progenitor cells, and insights into SDF-1-induced chemotaxis of progenitors

Chemokines have been implicated in the regulation of stem/progenitor cell proliferation and movement. The purpose of the present study was to assess a number of new chemokines for suppressive activity and to delve further into SDF-1-mediated chemotaxis of progenitor cells. This report extends the list of chemokines that have suppressive activity against immature subsets of myeloid progenitors stimulated to proliferate by multiple growth factors to include: MCP-4/CK beta-10, MIP-4/CK beta-7, I-309, TECK, GCP-2, MIG and lymphotactin. The suppressive activity of a number of other chemokines was confirmed. Additionally, pretreatment of the active chemokines with an acetylnitrile solution enhanced specific activity of a number of these chemokines. The new chemokines found to be lacking suppressive activity include: MCP-2, MCP-3, eotaxin-1, MCIF/HCC-1/CK beta-1, TARC, MDC, MPIF-2/eotaxin-2/CK beta-6, SDF-1 and fractalkine/neurotactin. Overall, 19 chemokines, crossing the CC, CXC, and C subgroups, have now been found to be myelosuppressive, and 14 chemokines crossing the CC, CXC and CX3C subgroups have been found to lack myelosuppressive activity under the culture conditions of our assays. Because of the redundancy in chemokine/chemokine receptor interactions, it is not yet clear through which chemokine receptors many of these chemokines signal to elicit suppressive activities. It was also found that SDF-1-induced chemotaxis of progenitors can occur in the presence of fibronectin (FN) and extracellular matrix components and that FN effects involve activation of beta 1-, and possibly alpha 4-, integrins.

Enhanced myeloid progenitor cell cycling and apoptosis in mice lacking the chemokine receptor, CCR2

Chemokines regulate hematopoiesis in part by influencing the proliferative status of myeloid progenitor cells (MPC). Human MCP-1/murine JE, a myelosuppressive chemokine, specifically binds C-C chemokine receptor 2 (CCR2). Transgenic mice containing a targeted disruption in CCR2 that prevents expression of CCR2 mRNA and protein and have MPC that are insensitive to inhibition by MCP-1 and JE in vitro were assessed for potential abnormalities in growth of bone marrow (BM) and spleen MPC. MPC in both unseparated and c-kit+lin- populations of BM from CCR2-deficient (-/-) mice were in a greatly increased proliferation state compared with CCR2 littermate control (+/+) mice, an effect not apparent with progenitors from spleens of CCR2 (-/-) mice. Increased cycling status of CCR2 (-/-) BM MPC did not result in increased numbers of nucleated cells or MPC in BM or spleens of CCR2 (-/-) mice. Possible reasons for this apparent discrepancy were highlighted by flow cytometric analysis of c-kit+lin- BM cells and colony formation by MPC subjected to delayed addition of growth factors. The c-kit+lin- population of BM cells from CCR2 (-/-) mice had a significantly higher percentage of apoptotic cells than those from CCR2 (+/+) BM. However, elevated apoptosis was not associated with decreased numbers of c-kit+lin- cells. The increased percentage of apoptotic c-kit+lin- cells was due to elevated apoptosis within the c-kitdimlin-, but not the c-kitbrightlin-, subpopulations of cells. Consistent with enhanced apoptosis of phenotypically defined cells, MPC from CCR2 (-/-) BM and purified c-kit+lin- cells demonstrated decreased cell survival in vitro upon delayed addition of growth factors. The data suggest that signals received by CCR2 limit proliferation of progenitor cells in the BM, but also enhance survival of these cells.

p21(cip-1/waf-1) deficiency causes deformed nuclear architecture, centriole overduplication, polyploidy, and relaxed microtubule damage checkpoints in human hematopoietic cells

A recent hypothesis suggests that tumor-specific killing by radiation and chemotherapy agents is due to defects or loss of cell cycle checkpoints. An important component of some checkpoints is p53-dependent induction of p21(cip-1/waf-1). Both p53 and p21 have been shown to be required for microtubule damage checkpoints in mitosis and in G1 phase of the cell cycle and they thus help to maintain genetic stability. We present here evidence that p21(cip-1/waf-1) deficiency relaxes the G1 phase microtubule checkpoint that is activated by microtubule damage induced with nocodazole. Reduced p21(cip-1/waf-1) expression also results in gross nuclear abnormalities and centriole overduplication. p53 has already been implicated in centrosome regulation. Our findings further suggest that the p53/p21 axis is involved in a checkpoint pathway that links the centriole/centrosome cycle and microtubule organization to the DNA replication cycle and thus helps to maintain genomic integrity. The inability to efficiently upregulate p21(cip-1/waf-1) in p21(cip-1/waf-1) antisense-expressing cells in response to microtubule damage could uncouple the centrosome cycle from the DNA cycle and lead to nuclear abnormalicies and polyploidy. A centrosome duplication checkpoint could be a new target for novel chemotherapy strategies.

Isolation and characterization of LMC, a novel lymphocyte and monocyte chemoattractant human CC chemokine, with myelosuppressive activity

By searching the Expressed Sequence Tag (EST) data base, we identified a partial cDNA sequence encoding a novel human CC chemokine. The entire cDNA sequence was determined and revealed a CC chemokine whose mature protein consisted of 100 amino acids with predicted molecular weight of 11 kd. The chemokine preferantially chemoattracted lymphocytes and monocytes but not neutrophils. It was, therefore, named LMC (Lymphocyte and Monocyte Chemoattractant). LMC exhibited potent myelosuppressive activity, which was comparable to that of MIP-1alpha. We identified several bacterial artificial clones (BAC) containing the LMC gene along with two human CC chemokine subfamily members; leukotactin-1 (Lkn-1) and CKbeta8-1/CKbeta8. This data suggests that the LMC gene is located at human chromosome 17q which encompasses a human CC chemokine gene cluster.

Multiple inhibitory cytokines induce deregulated progenitor growth and apoptosis in hematopoietic cells from Fac-/- mice

We used a murine model containing a disruption of the murine homologue (Fac) of Fanconi Anemia group C (FAC) to evaluate the role of Fac in the pathogenesis of bone marrow (BM) failure. Methylcellulose cultures of BM cells from Fac-/- and Fac+/+ mice were established to examine the growth of multipotent and lineage-restricted progenitors containing inhibitory cytokines, including interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-1alpha (MIP-1alpha). Clonogenic growth of Fac-/- progenitors was reduced by 50% at 50- to 100-fold lower concentrations of all inhibitory cytokines evaluated. We hypothesized that the aberrant responsiveness to inhibitory cytokines in clonogenic cells may be a result of deregulated apoptosis. To test this hypothesis, we performed the TUNEL assay on purified populations of primary BM cells enriched for hematopoietic progenitors or differentiated myeloid cells. After stimulation with TNF-alpha, accentuated apoptosis was observed in both populations of Fac-/- cells. In addition, deregulated apoptosis was also noted in the most immature phenotypic population of hematopoietic cells after stimulation with MIP-1alpha. Together these data suggest a role of Fac in affecting the signaling of multiple cytokine pathways and support cytokine-mediated apoptosis as a major mechanism responsible for BM failure observed in FA patients.

The contribution of animal models to the development of treatments for hematologic recovery following myeloablative therapy: a review

This review describes the role that animal models have played in the development of clinical procedures for growth factor and hematopoietic cell therapies following high-dose cancer chemotherapy, radiotherapy or both. Data are discussed describing animal models that add to the understanding of human hematopoiesis, including myeloid and lymphoid lineage localization and in vivo maturation. Finally, current animal models of cytokine and cell therapies are presented in the context of their contributions to early clinical trials and future therapies. These studies underscore the past and current contributions animal investigations have made to improving clinical therapies.

Regulation of myelopoiesis by murine fibroblastic and adipogenic cell lines

The regulation of hematopoiesis has been suggested to take place in close association with various cell types found in the bone marrow (BM) microenvironment. In the present study the role of fibroblasts, adipocytes and cell surface heparan sulfate in regulating hematopoiesis in an in vitro mouse system was examined. Mouse BM cells were allowed to adhere to a mouse embryo fibroblast cell line (C3H 10T1/2) or a clonally derived adipogenically determined derivative (Clone D) of the 10T1/2 cell line. Nonadherent cells were removed, cultures were overlaid with semisolid media supplemented with growth factors and colony formation by granulocyte-macrophage (CFU-GM), erythroid (BFU-E) and multipotential (CFU-GEMM) progenitor cells was quantitated. Adherence and co-culture of BM cells with the fibroblast cell line resulted in increased numbers of total CFU-GM and CFU-GEMM colonies. In contrast, adherence and co-culture of BM cells with the adipocytic cell line resulted in an increase only in CFU-GEMM colonies. Morphological analysis revealed a preferential adherence/growth of granulocyte and macrophage progenitors at the expense of bipotent granulocyte-macrophage progenitors to the fibroblastic cell line and an increase in the adherence/growth of granulocyte progenitors to the adipogenic cell line. Progenitor cell adherence was abolished when the fibroblastic or adipocytic cell lines were pretreated with heparitinase. These results demonstrate enhanced proliferation/differentiation of hematopoietic progenitor cells when there is direct contact between hematopoietic progenitors and cell types characteristic of those found in the microenvironment and that heparan sulfate and different types of stromal cells appear to play different roles in this interaction.

In vivo effects of recombinant interleukin-11 on myelopoiesis in mice

Purified recombinant human interleukin-11 (rhuIL-11) was assessed for its in vivo effects on the proliferation and differentiation of hematopoietic progenitors as well as its capacity to accelerate the recovery of a drug-suppressed hematopoietic system. Dosage and time sequence studies demonstrated that administration of IL-11 to normal mice resulted in increases in absolute numbers of femoral marrow and splenic myeloid (granulocyte-macrophage colony-forming unit [CFU-GM], burst-forming unit-erythroid [BFU-E], CFU-granulocyte, erythroid, macrophage, megakaryocyte) progenitor cells and in stimulation of these progenitors to a higher cell cycling rate. This was associated with increased numbers of circulating neutrophils. Administration of IL-11 to mice pretreated with cyclophosphamide decreased the time required to regain normal levels of neutrophil and platelet counts in peripheral blood. In addition, IL-11 accelerated reconstitution to normal range of myeloid progenitors from bone marrow and spleen of myelosuppressed mice. These data suggest that IL-11 may play an important role in the regulation of hematopoiesis, and the application of this novel cytokine may have clinical therapeutic benefits.

Human multipotential progenitor cells (CFU-GEMM) have extensive replating capacity for secondary CFU-GEMM: an effect enhanced by cord blood plasma

The replating capability of human umbilical cord blood (CB) multipotential (CFU-GEMM) progenitors was assessed in vitro as an estimate of self-renewal using erythropoietin (Epo), steel factor (SLF), and either fetal bovine serum (FBS) or CB plasma. This study found a much higher replating efficiency for CB CFU-GEMM than previously reported, in terms of the percentage of colonies that could be replated, the number of secondary colonies per replated primary colony, and the size of secondary colonies. Moreover, the majority of secondary colonies were CFU-GEMM-derived. Although the percentages of bone marrow CFU-GEMM that replate was similar to that for CB CFU-GEMM and the sizes of secondary bone marrow and CB CFU-GEMM were also similar, replated CB CFU-GEMM gave rise to far greater numbers of secondary colonies. No tertiary colonies were observed when secondary CFU-GEMM were replated. Detection of extensive secondary replating potential was enhanced by the addition of CB plasma to the cultures. This activity was not found in either adult blood (PB) plasma, umbilical cord vein endothelial cell-conditioned medium (ECCM), FBS plus ECCM, or FBS plus the combination of interleukin-1 (IL-1), IL-3, IL-6, IL-11, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor. Whether the CB plasma-enhancing activity for CFU-GEMM replating capacity is attributable to a novel factor or factors, or represents effects of other known cytokines, alone or in combination, remains to be determined. Of particular relevance, these studies suggest that human CFU-GEMM have some degree of stemness and perhaps should be classified as a subset of stem cells.

Effects in vivo of recombinant human inhibin on myelopoiesis in mice

Inhibin, a protein dimer, has been implicated in negative regulation of human erythropoiesis in vitro. In this study, purified recombinant human (rhu) inhibin was assessed for its effect in vivo on the proliferation of hematopoietic progenitor cells in C3H/HeJ mice. Administration of single doses of inhibin i.v. to mice resulted 24 hrs later in significant decreases in cell cycling status of marrow and splenic granulocyte-macrophage (CFU-GM), erythroid (BFU-E) and multipotential (CFU-GEMM) progenitors. While no apparent effect was observed on marrow cellularity or on absolute numbers of marrow CFU-GM and BFU-E, inhibin significantly reduced absolute numbers of marrow CFU-GEMM, spleen nucleated cellularity and also absolute numbers of CFU-GM, BFU-E and CFU-GEMM in the spleen. The results demonstrate in vivo myelosuppressive effects for inhibin and demonstrate that effects in vivo are not restricted to erythropoiesis.

Increased osteoclast development after estrogen loss: mediation by interleukin-6

Osteoclasts, the cells that resorb bone, develop from hematopoietic precursors of the bone marrow under the control of factors produced in their microenvironment. The cytokine interleukin-6 can promote hematopoiesis and osteoclastogenesis. Interleukin-6 production by bone and marrow stromal cells is suppressed by 17 beta-estradiol in vitro. In mice, estrogen loss (ovariectomy) increased the number of colony-forming units for granulocytes and macrophages, enhanced osteoclast development in ex vivo cultures of marrow, and increased the number of osteoclasts in trabecular bone. These changes were prevented by 17 beta-estradiol or an antibody to interleukin-6. Thus, estrogen loss results in an interleukin-6-mediated stimulation of osteoclastogenesis, which suggests a mechanism for the increased bone resorption in postmenopausal osteoporosis.

Growth characteristics and expansion of human umbilical cord blood and estimation of its potential for transplantation in adults

We estimated whether single collections of cord blood contained sufficient cells for hematopoietic engraftment of adults by evaluating numbers of cord blood and adult bone marrow myeloid progenitor cells (MPCs) as detected in vitro with steel factor (SLF) and hematopoietic colony-stimulating factors (CSFs). SLF plus granulocyte-macrophage (GM)-CSF detected 8- to 11-fold more cord blood GM progenitors [colony-forming units (CFU)-GM] than cells stimulated with GM-CSF or 5637 conditioned medium (CM), growth factors previously used to estimate cord blood CFU-GM numbers. SLF plus erythropoietin (Epo) plus interleukin 3 (IL-3) enhanced detection of cord blood multipotential (CFU-GEMM) progenitors 15-fold compared to stimulation with Epo plus IL-3. Under the same conditions, bone marrow CFU-GM and CFU-GEMM were only enhanced in detection 2- to 4- and 6- to 8-fold. Increased detection of cord blood CFU-GEMM correlated directly with decreased detection of cord blood erythroid burst-forming units (BFU-E). In contrast, adult bone marrow CFU-GEMM and BFU-E numbers were both enhanced by SLF plus Epo plus IL-3. This suggests that most cord blood BFU-E may actually be CFU-GEMM. Cord blood collections (n = 17) contained numbers of MPCs (especially CFU-GM) similar to the number found in nine autologous bone marrow collections. To assess additional sources of MPCs, the peripheral blood of 1-day-old infants was assessed. However, average concentrations of MPCs circulating in these infants were only 30-46% that in their cord blood. Expansion of cord blood MPCs was also evaluated. Incubation of cord blood cells for 7 days with SLF resulted in 7.9-, 2.2-, and 2.7-fold increases in numbers of CFU-GM, BFU-E, and CFU-GEMM compared to starting numbers; addition of a CSF with SLF resulted in even greater expansion of MPCs. The results suggest that cord blood contains a larger number of early profile MPCs than previously recognized and that there are probably sufficient numbers of cells in a single cord blood collection to engraft an adult. Although the expansion data must be considered with caution, as human marrow repopulating cells cannot be assessed directly, in vitro expansion of cord blood stem and progenitor cells may be feasible for clinical transplantation.

Clinical and biological aspects of human umbilical cord blood as a source of transplantable hematopoietic stem and progenitor cells

Presented is a short review of the current status fo the clinical and biological aspects of using human umbilical cord blood as a source of transplantable hematopoietic stem and progenitor cells.

Effects in vivo of purified recombinant human activin and erythropoietin in mice

Activin has been shown to act in vitro as an erythroid specific enhancing activity for erythropoietin (epo)-stimulated erythroid (BFU-E) and multipotential (CFU-GEMM) progenitor cells. To evaluate effects in vivo, purified recombinant activin-A and epo were administered s.c. to hypertransfused polycythemic mice for analysis of iron (59Fe) uptake, and to previously untreated mice for effects on reticulocyte release and proliferation of bone marrow (BM) and spleen (Spl) hematopoietic progenitors (CFU-GEMM, BFU-E, CFU-GM) and BM stem (CFU-S) cells. Activin alone had no effect in polycythemic BDF1 mice, but synergised with epo to significantly enhance 59Fe-incorporation into erythrocytes. In untreated C3H/HeJ mice, a single dose of activin enhanced reticulocyte release in 24 h to the level seen with epo. Activin plus epo did not further enhance reticulocyte release. Reticulocyte release was still apparent at day 4 in mice given epo twice a day for 3 days, but not in mice given activin twice a day for 3 days. Activin or epo each significantly enhanced the percent cells in S-phase of BM and Spl CFU-GEMM, BFU-E and CFU-GM in C3H/HeJ, W/Wv and Sl/Sld mice and BM CFU-S in BDF1 mice. The combination of epo plus activin did not further enhance proliferation. These results demonstrate activin's erythropoietic enhancing activities in vivo, and also activin and epo induction of enhanced proliferation of non-erythroid, as well as erythroid progenitors.

The kit receptor and its ligand, steel factor, as regulators of hemopoiesis

Mouse strains carrying mutations at the Dominant White Spotting (W) locus or the Steel (Sl) locus are anemic and display defects in pigmentation and gametogenesis. In W mutants the anemia is due to a deficiency of hemopoietic stem cells and, in Sl mutants, to a deficiency of supporting stromal cells in the bone marrow. The W locus encodes the c-kit proto-oncogene product, a cell surface receptor with protein-tyrosine kinase activity, and the Sl locus encodes its ligand, a hemopoietic cytokine known variously as Steel factor (SLF), mast cell growth factor, stem cell factor, and Kit ligand. SLF can synergize with a number of other cytokines to stimulate growth of hemopoietic progenitors in vitro and stimulates blood cell production in vivo in animals. Here we review the biological activities of SLF, with particular emphasis on its effects on hemopoietic stem and progenitor cells. We also discuss present knowledge of the molecules involved in SLF-triggered signal transduction, and speculate on potential therapeutic applications for SLF in human disease.

Mast cell growth factor (c-kit ligand) supports the growth of human multipotential progenitor cells with a high replating potential

The replating capability of human multipotential (colony-forming unit-granulocyte-erythrocyte-macrophage-megakaryocyte [CFU-GEMM]) and erythroid (burst-forming unit-erythroid [BFU-E]) progenitors was assessed in vitro as a potential measure of self-renewal using purified, recombinant (r) human (hu) or murine (mu) mast cell growth factor (MGF), a ligand for the c-kit proto-oncogene receptor. Primary cultures of human umbilical cord blood or adult human bone marrow cells were initiated in methylcellulose with erythropoietin (Epo) alone or in combination with rhu interleukin-3 (IL-3) or MGF. Individual day 14 to 18 CFU-GEMM or BFU-E colonies were removed from primary cultures and reseeded into secondary methylcellulose cultures containing a combination of Epo, MGF, and rhu granulocyte-macrophage colony-stimulating factor (GM-CSF). The data showed a high replating efficiency of cord blood and bone marrow CFU-GEMM in response to Epo + MGF in terms of the percentage of colonies that could be replated and the number of secondary colonies formed per replated primary colony. The average number of hematopoietic colonies and clusters apparent from replated cultures of cord blood or bone marrow CFU-GEMM stimulated by Epo + MGF was greater than with Epo + rhuIL-3 or Epo alone. Replated cord blood CFU-GEMM gave rise to CFU-GEMM, BFU-E, and GM colony-forming units (CFU-GM) in secondary cultures. Replated bone marrow CFU-GEMM gave rise mainly to CFU-GM in secondary cultures. A more limited capacity for replating of cord blood and bone marrow BFU-E was observed. These studies show that CFU-GEMM responding to MGF have an enhanced replating potential, which may be promoted by MGF. These studies also support the concept that MGF acts on more primitive progenitors than IL-3.

Influence of T-lymphocytes and lactoferrin on the survival-promoting effects of IL-1 and IL-6 on human bone marrow granulocyte-macrophage and erythroid progenitor cells

Purified recombinant human (rhu) interleukin (IL)-1 alpha, rhuIL-6, iron saturated lactoferrin (LF), and T-lymphocytes were assessed for their effects on the survival of granulocyte-macrophage (granulocyte-macrophage colony-forming units, CFU-GM) and erythroid (erythroid burst-forming units, BFU-E) progenitor cells from human low-density (LD) and nonadherent LD T-lymphocyte-depleted (NALT-) bone marrow (BM) cells. Colony-stimulating factor (CSF) deprivation studies showed that 10 ng/ml IL-1 alpha could promote the survival of CFU-GM and BFU-E from NALT- BM cells. Concentrations of 1 ng/ml IL-1 alpha and 1-100 ng/ml IL-6 alone could not promote progenitor cell survival from NALT- BM cells; however, concentrations of 1 ng/ml each of IL-1 alpha and IL-6 could synergize to promote the survival of CFU-GM but not of BFU-E. The combination of these low concentrations of IL-1 alpha and IL-6 could, however, support the survival of BFU-E in the presence of purified T-lymphocytes. LF could decrease the survival of CFU-GM and BFU-E from LD but not from NALT- BM cells, apparently due to the inhibition of IL-1 release from monocytes in this cell population. The suppressive effect of LF on the survival of those progenitor cells was abolished by concentrations of 10 ng/ml IL-1 alpha or 1 ng/ml each of IL-1 alpha and IL-6. These results demonstrate that the survival of human marrow CFU-GM and BFU-E can be influenced by IL-1, IL-6, LF, and T-lymphocytes.

CD45 cell surface antigens are linked to stimulation of early human myeloid progenitor cells by interleukin 3 (IL-3), granulocyte/macrophage colony-stimulating factor (GM-CSF), a GM-CSF/IL-3 fusion protein, and mast cell growth factor (a c-kit ligand)

CD45 antigens are protein tyrosine phosphatases. A possible link was evaluated between expression of CD45 antigens on human myeloid progenitor cells (MPC) (colony-forming unit-granulocyte/macrophage [CFU-GM], burst-forming unit-erythroid [BFU-E], and colony-forming unit-granulocyte/erythroid/macrophage/megakaryocyte [CFU-GEMM]) and regulation of MPC by colony-stimulating factors (CSF) (interleukin 3 [IL-3], GM-CSF, G-CSF, M-CSF, and erythropoietin [Epo]), a GM-CSF/IL-3 fusion protein, and mast cell growth factor (MGF; a c-kit ligand). Treatment of cells with antisense oligodeoxynucleotides (oligos) to exons 1 and 2, but not 4, 5, or 6, of the CD45 gene, or with monoclonal anti-CD45, significantly decreased CFU-GM colony formation stimulated with GM-CSF, IL-3, fusion protein, and GM-CSF + MGF, but not with G-CSF or M-CSF. It also decreased GM-CSF, IL-3, fusion protein, and MGF-enhanced Epo-dependent BFU-E and CFU-GEMM colony formation, but had little or no effect on BFU-E or CFU-GEMM colony formation stimulated by Epo alone. Similar results were obtained with unseparated or purified (greater than or equal to one of two cells being a MPC) bone marrow cells. Sorted populations of CD343+ HLA-DR+ marrow cells composed of 90% MPC were used to demonstrate capping of CD45 after crosslinking protocols. Also, a decreased percent of CD45+ cells and CD45 antigen density was noted after treatment of column-separated CD34+ cells with antisense oligos to exon 1 of the CD45 gene. These results demonstrate that CD45 cell surface antigens are linked to stimulation of early human MPC by IL-3, GM-CSF, a GM-CSF/IL-3 fusion protein, and MGF.

Effect of murine mast cell growth factor (c-kit proto-oncogene ligand) on colony formation by human marrow hematopoietic progenitor cells

Purified natural (n) and recombinant (r) murine (mu) mast cell growth factor (MGF, a c-kit ligand) were evaluated alone and in combination with r human (hu) erythropoietin (Epo), rhu granulocyte-macrophage colony-stimulating factor (rhuGM-CSF), rhuG-CSF, and/or rhuM-CSF for effects in vitro on colony formation by multipotential (colony-forming unit-granulocyte, erythroid, monocyte, megakaryocyte [CFU-GEMM]), erythroid (burst-forming unit erythroid [BFU-E]) and granulocyte-macrophage (CFU-GM) progenitor cells from normal human bone marrow. MGF was a potent enhancing cytokine for Epo-dependent CFU-GEMM and BFU-E colony formation, stimulating more colonies and of a larger size than either rhu interleukin-3 (rhuIL-3) or rhuGM-CSF. MGF, especially at lower concentrations, also acted with rhuIL-3 or rhuGM-CSF to enhance Epo-dependent CFU-GEMM and BFU-E colony formation. MGF had little stimulating activity for CFU-GM colonies by itself, but in combination with suboptimal to optimal amounts of rhuGM-CSF enhanced the numbers and the size of CFU-GM colonies in an additive to greater than additive manner. While we did not detect an effect of MGF on CFU-G colony numbers stimulated by maximal concentrations of rhuG-CSF, MGF did enhance the size of CFU-G-derived colonies. MGF did not enhance the activity of rhuM-CSF. In a comparative assay, maximal concentrations of rmu and rhuMGF were equally effective in the enhancement of human bone marrow colony formation, but rhuMGF, in contrast to rmuMGF, did not at the concentrations tested enhance colony formation by mouse bone marrow cells. MGF effects on BFU-E, CFU-GM, and CFU-GEMM may be direct acting ones as MGF-enhanced colony formation by these cells in highly enriched progenitor cell populations of CD34 HLA-DR+ and CD34 HLA-DR+CD33- sorted cells in which greater than or equal to 1 of 2 cells was a BFU-E plus CFU-GM plus CFU-GEMM. MGF appears to be an early acting cytokine that preferentially stimulates the growth of immature hematopoietic progenitor cells.

Influence of murine mast cell growth factor (c-kit ligand) on colony formation by mouse marrow hematopoietic progenitor cells

Purified natural and recombinant murine mast cell growth factor (MGF, a c-kit ligand) were evaluated alone and in combination with other cytokines for effects in vitro on colony formation by multipotential (CFU-GEMM), erythroid (BFU-E) and granulocyte-macrophage (CFU-GM) progenitor cells from BDF1 mouse bone marrow. Both preparations stimulated Epo-dependent CFU-GEMM and enhanced Epo-dependent BFU-E colony numbers and size. MGF had some stimulating activity for CFU-GM. When used in combination with plateau concentrations of pokeweed mitogen mouse spleen cell conditioned medium or granulocyte-macrophage colony stimulating factor (CSF), MGF enhanced in greater than additive fashion colony formation by CFU-GM. MGF also enhanced the size of colonies formed, an enhancement greatest for colonies containing granulocytes and macrophages. MGF did not enhance Macrophage-CSF stimulated colony numbers or size. MGF seems to be an early acting cytokine with preferential effects on the growth of more immature hematopoietic progenitor cells.

Human umbilical cord blood: a clinically useful source of transplantable hematopoietic stem/progenitor cells

This is a review and discussion of studies leading to the first use of human umbilical cord blood, material usually discarded, for the provision of stem/progenitor cells for clinical hematopoietic reconstitution. This prospect arose as a result of extensive studies of the harvesting and cryopreservation of cord blood and of its numerical content of progenitor cells demonstrable in vitro. A male patient with Fanconi anemia (FA) was conditioned with a modified regimen of cyclophosphamide and irradiation that accommodates the abnormally high sensitivity to these agents that is characteristic of FA. Cryopreserved cord blood had been retrieved at birth from a female sibling known from prenatal testing to be unaffected by FA and to be human leukocyte antigen (HLA)-compatible with the prospective sibling recipient. After conditioning and therapeutic infusion of thawed cord blood, successful hematopoietic reconstitution was indicated by the general health of the patient, who had previously required supportive transfusions, by satisfactory hematological criteria and by counts of hematopoietic progenitor cells of various types in the bone marrow. Complete engraftment of the myeloid system with donor cells was evident from cytogenetics, ABO typing, study of DNA polymorphisms, and normal cellular resistance to cytotoxic agents that reveal the fragility of FA cells; the blood contained a residuum of host lymphocytes exhibiting chromosomal damage, but the trend has been towards eliminating these damaged cells. This implies that cord blood from a single individual should provide sufficient reconstituting cells for effective hematopoietic repopulation of an autologous or an HLA-compatible allogeneic recipient.

Effect in vivo of multiple injections of purified murine and recombinant human macrophage colony-stimulating factor to mice

Hematopoietic efficacy in vivo of multiple injections of purified murine L-cell and recombinant human macrophage colony-stimulating factors (M-CSF; specific activity, greater than 2 x 10(7) units/mg) was assessed in mice. Injections i.v. of sterile saline or 20,000 units of M-CSF were administered once (at 0 h), twice (at 0 and 12 h), or three times (at 0, 12, and 24 h) to C57BL/6 x DBA/2 F1 mice. Numbers and cycling rates of marrow and spleen granulocyte-macrophage, erythroid, and multipotential progenitor cells were assessed 32-36 h after the first injection. Marrow, spleen, and peripheral blood cellularity was assessed at intervals of up to 105 h. Progenitor cell cycling rates were significantly increased after one and two injections of M-CSF but were reduced to a slow or noncycling state after three injections. For marrow cells, the third injection resulted in a significant suppression of hematopoietic progenitor cell cycling compared to the control group. No significant changes were noted for number of progenitors per femur or spleen, for marrow, spleen, or peripheral blood cellularity, or for differential cell counts in these organs after any of the M-CSF treatment schedules. Suppression of progenitor cell proliferation noted after three injections of M-CSF may at least partially explain why repeated injections of 20,000 units of M-CSF fails to increase bone marrow, spleen, or blood cellularity even though one injection of M-CSF increases cycling rates of the hematopoietic progenitors.

Influence of IL-1 alpha and -1 beta on the survival of human bone marrow cells responding to hematopoietic colony-stimulating factors

Purified recombinant human (rhu) IL-1 alpha and IL-1 beta were evaluated for their effects on the proliferation and survival of granulocyte-macrophage (CFU-GM) and erythroid (BFU-E) progenitor cells from normal human bone marrow (BM). Using nonadherent low density T lymphocyte depleted (NALT-) BM cells cultured in the presence or absence of IL-1, CSF-deprivation studies demonstrated that IL-1 alpha or IL-1 beta by itself did not enhance the proliferation of CFU-GM or BFU-E. They did, however, promote the survival of progenitors responding to the delayed addition of media conditioned by the 5637 cell line (5637 conditioned medium), rhu GM-CSF and erythropoietin. The survival promoting effects of IL-1 alpha on CFU-GM and BFU-E were neutralized by anti-IL-1 alpha mAb added to the cultures. The survival promoting effect of IL-1 alpha did not appear to be mediated by CSF, because neither CSF nor erythroid burst promoting activity were detectable in cultures in which NALT- cells were incubated with rhuIL-1 alpha. In addition, suboptimal concentrations of rhu macrophage CSF (CSF-1), G-CSF, GM-CSF, and IL-3, which were just below the levels that would stimulate colony formation, did not enhance progenitor cell survival. Survival of CFU-GM and BFU-E in low density (LD) bone marrow cells did not decrease as drastically as that in NALT- BM cells, and exogenously added IL-1 did not enhance progenitor cell survival of CFU-GM and BFU-E in LD BM cells. However, addition of anti-IL-1 beta decreased survival of CFU-GM and BFU-E in LD BM cells. These results implicate IL-1 in the prolonged survival of human CFU-GM and BFU-E.

Influence of IL-1 alpha and -1 beta on the survival of human bone marrow cells responding to hematopoietic colony-stimulating factors

Purified recombinant human (rhu) IL-1 alpha and IL-1 beta were evaluated for their effects on the proliferation and survival of granulocyte-macrophage (CFU-GM) and erythroid (BFU-E) progenitor cells from normal human bone marrow (BM). Using nonadherent low density T lymphocyte depleted (NALT-) BM cells cultured in the presence or absence of IL-1, CSF-deprivation studies demonstrated that IL-1 alpha or IL-1 beta by itself did not enhance the proliferation of CFU-GM or BFU-E. They did, however, promote the survival of progenitors responding to the delayed addition of media conditioned by the 5637 cell line (5637 conditioned medium), rhu GM-CSF and erythropoietin. The survival promoting effects of IL-1 alpha on CFU-GM and BFU-E were neutralized by anti-IL-1 alpha mAb added to the cultures. The survival promoting effect of IL-1 alpha did not appear to be mediated by CSF, because neither CSF nor erythroid burst promoting activity were detectable in cultures in which NALT- cells were incubated with rhuIL-1 alpha. In addition, suboptimal concentrations of rhu macrophage CSF (CSF-1), G-CSF, GM-CSF, and IL-3, which were just below the levels that would stimulate colony formation, did not enhance progenitor cell survival. Survival of CFU-GM and BFU-E in low density (LD) bone marrow cells did not decrease as drastically as that in NALT- BM cells, and exogenously added IL-1 did not enhance progenitor cell survival of CFU-GM and BFU-E in LD BM cells. However, addition of anti-IL-1 beta decreased survival of CFU-GM and BFU-E in LD BM cells. These results implicate IL-1 in the prolonged survival of human CFU-GM and BFU-E.

Human umbilical cord blood as a potential source of transplantable hematopoietic stem/progenitor cells

The purpose of this study was to evaluate human umbilical cord blood as an alternative to bone marrow in the provision of transplantable stem/progenitor cells for hematopoietic reconstitution. Although no direct quantitative assay for human hematopoietic repopulating cells is at present available, the granulocyte-macrophage progenitor cell (CFU-GM) assay has been used with success as a valid indicator of engrafting capability. We examined greater than 100 collections of human umbilical cord blood for their content of nucleated cells and granulocyte-macrophage, erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells, in many cases both before and after cryopreservation. First it was determined that granulocyte-macrophage, erythroid, and multipotential progenitor cells remained functionally viable in cord blood untreated except for addition of anticoagulant for at least 3 days at 4 degrees C or 25 degrees C (room temperature), though not at 37 degrees C, implying that these cells could be satisfactorily studied and used or cryopreserved for therapy after transport of cord blood by overnight air freight carriage from a remote obstetrical service. Granulocyte-macrophage progenitor cells from cord blood so received responded normally to stimulation by purified recombinant preparations of granulocyte-macrophage, granulocyte, and macrophage colony-stimulating factors and interleukin 3. The salient finding, based on analysis of 101 cord blood collections, is that the numbers of progenitor cells present in the low-density (less than 1.077 gm/ml) fraction after Ficoll/Hypaque separation typically fell within the range that has been reported for successful engraftment by bone marrow cells. Another observation of practical importance is that procedures to remove erythrocytes or granulocytes prior to freezing, and washing of thawed cells before plating, entailed large losses of progenitor cells, the yield of unwashed progenitor cells from unfractionated cord blood being many times greater. The provisional inference is that human umbilical cord blood from a single individual is typically a sufficient source of cells for autologous (syngeneic) and for major histocompatibility complex-matched allogeneic hematopoietic reconstitution.

Suppressive effects in vivo of purified recombinant human H-subunit (acidic) ferritin on murine myelopoiesis

Purified recombinant human heavy-chain (acidic) ferritin (rHF) was assessed in vivo in mice for effects on the proliferation (percentage of cells in S-phase) and absolute numbers of granulocyte-macrophage (CFU-GM), erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells in the femur and spleen and on the nucleated cells in the marrow, spleen, and blood. rHF significantly decreased cycling rates and absolute numbers of marrow and splenic hematopoietic progenitors and marrow and blood nucleated cellularity. These effects were apparent in BDF1, C3H/Hej and DBA/2 mice and were dose dependent, time related, and reversible. Suppressive effects were noted within three hours for progenitor cell cycling, within 24 hours for progenitor cell numbers, and within 48 hours for circulating neutrophils. Additionally, hematopoietic progenitor cells in DBA/2 mice infected with the polycythemia-inducing strain of the Friend virus complex (FVC-P) were insensitive to the in vivo administration of rHF. These studies demonstrate activity of rHF in vivo on myelopoiesis of normal but not FVC-P-infected mice. Since rHF suppresses hematopoietic progenitor cell proliferation from normal donors in vitro and from normal mice in vitro and in vivo but does not suppress progenitor cells from patients with leukemia in vitro or from mice with FVC-P-infection in vitro or in vivo, rHF may be useful as a candidate adjunct molecule for the protection of normal hematopoietic progenitor cells during chemotherapy.

Recombinant human granulocyte-colony stimulating factor and recombinant human macrophage-colony stimulating factor synergize in vivo to enhance proliferation of granulocyte-macrophage, erythroid, and multipotential progenitor cells in mice

Combinations of low dosages of purified recombinant human (rh) macrophage-colony stimulating factor (M-CSF; also termed CSF-1) and rh granulocyte-colony stimulating factor (G-CSF) were compared alone and in combination for their influence on the cycling rates and numbers of bone marrow and splenic granulocyte-macrophage, erythroid, and multipotential progenitor cells in vivo in mice pretreated with iron-saturated human lactoferrin (LF). LF was used to enhance detection of the stimulating effects of exogenously added CSFs. Concentrations of each CSF that were not active in vivo when given alone were active when given together, with the other CSF. The concentrations of rhM-CSF and rhG-CSF needed to increase progenitor cell cycling in the marrow and spleen were reduced by factors of 40-200 when these CSFs were administered in combination with low dosages of the other CSF. At the concentrations of rhM-CSF and rhG-CSF tested, synergism was not noted on absolute numbers of progenitor cells or total nucleated cell counts per organ or circulating in the blood. These findings may have potential relevance when considered in a clinical setting where the CSFs might be used in combination with other biotherapy and/or chemotherapy.

Synergistic interaction of hematopoietic colony stimulating and growth factors in the regulation of myelopoiesis

Synergistic interactions in the regulation of myelopoiesis have been noted in vitro and in vivo and are discussed. Moreover, data is presented to highlight such synergistic interactions in vitro and in vivo. It is shown that purified recombinant human B-cell stimulating factor-1/interleukin-4 (rh BSF-1/IL-4) synergizes with rh Granulocyte (G)-Colony Stimulating Factor (CSF), but not with rh Granulocyte-Macrophage (GM)-CSF, rh IL-3, or rh Macrophage CSF (CSF-1) to enhance colony formation in vitro by normal human bone marrow cells. This synergism is restricted to granulocyte progenitors. Also, it is shown that rh G-CSF or rh CSF-1 enhance the proliferation of granulocyte-macrophage progenitor cells (CFU-GM) in vivo in mice pretreated with human lactoferrin, and when added together these preparations of CSF act synergistically. It is apparent that a true understanding of how myeloid blood cell production is regulated requires insight into how molecules collaborate with or antagonise one another.

Growth characteristics of marrow hematopoietic progenitor/precursor cells from patients on a phase I clinical trial with purified recombinant human granulocyte-macrophage colony-stimulating factor

Bone marrow cells from patients with leukemia, myelodysplastic syndromes, cancer, and other disorders on a phase I clinical trial with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) were assessed in vitro for numbers of granulocyte-macrophage (CFU-GM), erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells, and for growth patterns (colony-to-cluster ratio) of CFU-GM, cycling rates of CFU-GM, and responsiveness in vitro to colony-stimulating and colony-inhibiting factors. The colony-to-cluster ratio of CFU-GM and the dose-response curves of CFU-GM to stimulation by rhGM-CSF in vitro did not change during the clinical trial. However, the percentage of CFU-GM in DNA synthesis, which is a measure of the proliferative rates of these cells, determined by the high specific activity tritiated thymidine kill technique in vitro, was markedly enhanced in a reversible fashion after administration in vivo of rhGM-CSF. The increased cycling rates of CFU-GM were consistent with the induced increase in neutrophil counts in these patients that has been reported elsewhere. Additionally, marrow CFU-GM from patients given rhGM-CSF in vivo were increased in sensitivity to inhibition in vitro by recombinant human H-subunit (acidic) ferritin in two of eight cases, and were increased in sensitivity to inhibition by lower dosages of recombinant human tumor necrosis factor alpha in all patients evaluated. The sensitivity of CFU-GM to inhibition in vitro by recombinant human interferon gamma and prostaglandin E1 did not change during the clinical trial. These studies demonstrate that the rhGM-CSF is having an effect on CFU-GM in the patients on the phase I clinical trial. This information may be of significance in planning future clinical studies combining rhGM-CSF with chemotherapy and/or other biotherapy.

Preclinical and clinical effects of the hematopoietic colony stimulating factors

Hematopoietic colony stimulating factors are available in purified recombinant form and have used for assessment of hematopoietic activities in mice, monkeys and in phase I clinical trials with humans. This report reviews the preclinical and clinical studies involving these factors.

Modulation of Friend virus infectivity in vivo by administration of purified preparations of human lactoferrin and recombinant murine interleukin-3 to mice

Purified iron-saturated human milk lactoferrin (LF) and purified recombinant murine interleukin-3 (IL-3) were assessed in vivo for their effects on replication of spleen focus forming viruses (SFFV) in spleens of DBA/2 mice injected with the polycythemia-inducing strain of the Friend virus complex. LF and IL-3, inoculated 2 hr prior to the administration of the polycythemia-inducing strain of the Friend virus complex, respectively decreased and increased the replication of SFFV in mice as assessed by the spleen focus forming unit assay in primary and secondary DBA/2 mice. Since virus infectivity is associated with the DNA synthetic phase of the cell cycle and it has been shown elsewhere that LF decreases and IL-3 increases the percent of hematopoietic progenitor cells in S-phase in vivo, the results suggest that the opposing actions of LF and IL-3 on replication of SFFV may reflect the actions of these molecules on cycling of the target cells for SFFV.

The effects of purified recombinant murine interleukin-3 and/or purified natural murine CSF-1 in vivo on the proliferation of murine high- and low-proliferative potential colony-forming cells: demonstration of in vivo synergism

Purified natural murine L cell (macrophage) colony-stimulating factor (nCSF-1) and purified recombinant murine interleukin-3 (rIL-3) were administered to normal or lactoferrin-pretreated mice 20 to 24 hours before sacrifice. rIL-3 and nCSF-1 administered separately increased the percentage of macrophage high-proliferative potential colony-forming cells (HPP-CFC) and low-proliferative potential colony-forming cells (LPP-CFC) in active cell cycle. Endotoxin was not detected in the samples of nCSF-1 or rIL-3 with the Limulus lysate test, and the in vitro and in vivo hematopoietic stimulatory effects of both molecules were abolished or markedly reduced by 30 minutes' treatment at 100 degrees C, which demonstrates that the effects noted in vivo were not due to endotoxin. Combinations of low concentrations of rIL-3 and nCSF-1, which by themselves were inactive, increased the percentage of HPP-CFC and LPP-CFC in active cell cycle in a synergistic fashion. No significant change in the number of HPP-CFC or LPP-CFC per femur or femoral nucleated cellularity was observed. Thus, rIL-3 and nCSF-1 can synergize to effect the proliferation of the same cell populations in vivo.

Protective influence of lactoferrin on mice infected with the polycythemia-inducing strain of Friend virus complex

Purified iron-saturated human lactoferrin (LF) was assessed in vivo for effects on the survival rates of C57BL X DBA/2 f1 (hereafter called BD2F1) (Fv-2sr) mice and titers of spleen focus-forming viruses (SFFV) in BD2F1 and DBA/2 (Fv-2ss) mice inoculated with the polycythemia-inducing strain of the Friend virus complex (FVC-P). LF prolonged the survival rates and decreased the titers of SFFV in mice given FVC-P. Titers of SFFV, assayed 14 days after administration of FVC-P, were measured by the spleen focus-forming unit assay in secondary mouse recipients. Decreases in titers of SFFV were apparent when LF was given in vivo as a single bolus dose of 200 micrograms within 2 h of the Friend virus complex (FVC), or as a total dosage of 200 micrograms given on days 1, 2, 4, 7, 9, and 11 after FVC-P, and to a lesser degree when LF was given as a total dosage of 200 micrograms on days 3, 4, 7, 9, and 11 after FVC-P. No decreases in titers of SFFV were detected when LF was given up to 3 days before or more than 3 days after FVC-P. LF did not appear to be directly inactivating the viruses as it did not inactivate the SFFV or the Friend murine leukemia helper virus in vitro. The results suggest that the protective effect of LF in vivo is probably due to an action on cells responding to the FVC or to an action on cells which influence the cells responding to the FVC or which influence the virus. It has been shown elsewhere that LF decreases the percentage of marrow and spleen hematopoietic progenitor cells that are in DNA synthesis in vivo and this may be the means by which the protective effect of LF is mediated in mice given the FVC.

Synergistic myelopoietic actions in vivo after administration to mice of combinations of purified natural murine colony-stimulating factor 1, recombinant murine interleukin 3, and recombinant murine granulocyte/macrophage colony-stimulating factor

Combinations of low dosages of purified murine hematopoietic colony-stimulating factors (CSFs)--L-cell CSF type 1 (CSF-1), recombinant interleukin 3 (IL-3), and recombinant granulocyte/macrophage CSF (GM-CSF)--were compared with single CSFs for their influence on the cycling rates and numbers of bone marrow granulocyte/macrophage, erythroid, and multipotential progenitor cells in vivo in mice pretreated with human lactoferrin. Lactoferrin was used to enhance detection of the stimulating effects of exogenously administered CSFs. Concentrations of CSFs that were not active in vivo when given alone were active when administered together with other types of CSF. The concentrations of CSF-1, IL-3, and GM-CSF needed to increase progenitor cell cycling rates were reduced by factors of 40-200, 10-50, and 40- greater than 400, respectively; the concentrations needed to increase progenitor cell numbers were reduced by factors of 40-500 (CSF-1), 20-80 (IL-3), and greater than 40- greater than 200 (GM-CSF) when these forms of CSFs were administered in combination with low dosages of one of the other forms of CSFs. The results demonstrate that different CSFs can synergize when administered in vivo to increase the cycling rates and numbers of marrow hematopoietic progenitor cells. These findings may be of relevance physiologically to the regulation of myeloid blood cell production by CSFs.