Investigation of the safety and feasibility of AAV1/SERCA2a gene transfer in patients with chronic heart failure supported with a left ventricular assist device - the SERCA-LVAD TRIAL

The SERCA-LVAD trial was a phase 2a trial assessing the safety and feasibility of delivering an adeno-associated vector 1 carrying the cardiac isoform of the sarcoplasmic reticulum calcium ATPase (AAV1/SERCA2a) to adult chronic heart failure patients implanted with a left ventricular assist device. The SERCA-LVAD trial was one of a program of AAV1/SERCA2a cardiac gene therapy trials including CUPID1, CUPID 2 and AGENT trials. Enroled subjects were randomised to receive a single intracoronary infusion of 1 × 10¹³ DNase-resistant AAV1/SERCA2a particles or a placebo solution in a double-blinded design, stratified by presence of neutralising antibodies to AAV. Elective endomyocardial biopsy was performed at 6 months unless the subject had undergone cardiac transplantation, with myocardial samples assessed for the presence of exogenous viral DNA from the treatment vector. Safety assessments including ELISPOT were serially performed. Although designed as a 24 subject trial, recruitment was stopped after five subjects had been randomised and received infusion due to the neutral result from the CUPID 2 trial. Here we describe the results from the 5 patients at 3 years follow up, which confirmed that viral DNA was delivered to the failing human heart in 2 patients receiving gene therapy with vector detectable at follow up endomyocardial biopsy or cardiac transplantation. Absolute levels of detectable transgene DNA were low, and no functional benefit was observed. There were no safety concerns in this small cohort. This trial identified some of the challenges of performing gene therapy trials in this LVAD patient cohort which may help guide future trial design.

Calcium upregulation by percutaneous administration of gene therapy in patients with cardiac disease (CUPID 2): a randomised, multinational, double-blind, placebo-controlled, phase 2b trial

BACKGROUND

Sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) activity is deficient in the failing heart. Correction of this abnormality by gene transfer might improve cardiac function. We aimed to investigate the clinical benefits and safety of gene therapy through infusion of adeno-associated virus 1 (AAV1)/SERCA2a in patients with heart failure and reduced ejection fraction.

METHODS

We did this randomised, multinational, double-blind, placebo-controlled, phase 2b trial at 67 clinical centres and hospitals in the USA, Europe, and Israel. High-risk ambulatory patients with New York Heart Association class II-IV symptoms of heart failure and a left ventricular ejection fraction of 0·35 or less due to an ischaemic or non-ischaemic cause were randomly assigned (1:1), via an interactive voice and web-response system, to receive a single intracoronary infusion of 1 × 10(13) DNase-resistant particles of AAV1/SERCA2a or placebo. Randomisation was stratified by country and by 6 min walk test distance. All patients, physicians, and outcome assessors were masked to treatment assignment. The primary efficacy endpoint was time to recurrent events, defined as hospital admission because of heart failure or ambulatory treatment for worsening heart failure. Primary efficacy endpoint analyses and safety analyses were done by modified intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01643330.

FINDINGS

Between July 9, 2012, and Feb 5, 2014, we randomly assigned 250 patients to receive either AAV1/SERCA2a (n=123) or placebo (n=127); 243 (97%) patients comprised the modified intention-to-treat population. Patients were followed up for at least 12 months; median follow-up was 17·5 months (range 1·8-29·4 months). AAV1/SERCA2a did not improve time to recurrent events compared with placebo (104 vs 128 events; hazard ratio 0·93, 95% CI 0·53-1·65; p=0·81). No safety signals were noted. 20 (16%) patients died in the placebo group and 25 (21%) patients died in the AAV1/SERCA2a group; 18 and 22 deaths, respectively, were adjudicated as being due to cardiovascular causes.

INTERPRETATION

CUPID 2 is the largest gene transfer study done in patients with heart failure so far. Despite promising results from previous studies, AAV1/SERCA2a at the dose tested did not improve the clinical course of patients with heart failure and reduced ejection fraction. Although we did not find evidence of improved outcomes at the dose of AAV1/SERCA2a studied, our findings should stimulate further research into the use of gene therapy to treat patients with heart failure and help inform the design of future gene therapy trials.

FUNDING

Celladon Corporation.

Small Molecular Allosteric Activator of the Sarco/Endoplasmic Reticulum Ca2+-ATPase (SERCA) Attenuates Diabetes and Metabolic Disorders

Dysregulation of endoplasmic reticulum (ER) Ca(2+) homeostasis triggers ER stress leading to the development of insulin resistance in obesity and diabetes. Impaired function of the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) has emerged as a major contributor to ER stress. We pharmacologically activated SERCA2b in a genetic model of insulin resistance and type 2 diabetes (ob/ob mice) with a novel allosteric activator, CDN1163, which markedly lowered fasting blood glucose, improved glucose tolerance, and ameliorated hepatosteatosis but did not alter glucose levels or body weight in lean controls. Importantly, CDN1163-treated ob/ob mice maintained euglycemia comparable with that of lean mice for >6 weeks after cessation of CDN1163 administration. CDN1163-treated ob/ob mice showed a significant reduction in adipose tissue weight with no change in lean mass, assessed by magnetic resonance imaging. They also showed an increase in energy expenditure using indirect calorimetry, which was accompanied by increased expression of uncoupling protein 1 (UCP1) and UCP3 in brown adipose tissue. CDN1163 treatment significantly reduced the hepatic expression of genes involved in gluconeogenesis and lipogenesis, attenuated ER stress response and ER stress-induced apoptosis, and improved mitochondrial biogenesis, possibly through SERCA2-mediated activation of AMP-activated protein kinase pathway. The findings suggest that SERCA2b activation may hold promise as an effective therapy for type-2 diabetes and metabolic dysfunction.

Discovery of enzyme modulators via high-throughput time-resolved FRET in living cells

We have used a "two-color" SERCA (sarco/endoplasmic reticulum calcium ATPase) biosensor and a unique high-throughput fluorescence lifetime plate reader (FLT-PR) to develop a high-precision live-cell assay designed to screen for small molecules that perturb SERCA structure. A SERCA construct, in which red fluorescent protein (RFP) was fused to the N terminus and green fluorescent protein (GFP) to an interior loop, was stably expressed in an HEK cell line that grows in monolayer or suspension. Fluorescence resonance energy transfer (FRET) from GFP to RFP was measured in the FLT-PR, which increases precision 30-fold over intensity-based plate readers without sacrificing throughput. FRET was highly sensitive to known SERCA modulators. We screened a small chemical library and identified 10 compounds that significantly affected two-color SERCA FLT. Three of these compounds reproducibly lowered FRET and inhibited SERCA in a dose-dependent manner. This assay is ready for large-scale HTS campaigns and is adaptable to many other targets.

Design of a phase 2b trial of intracoronary administration of AAV1/SERCA2a in patients with advanced heart failure: the CUPID 2 trial (calcium up-regulation by percutaneous administration of gene therapy in cardiac disease phase 2b)

OBJECTIVES

Impaired cardiac isoform of sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA2a) activity is a key abnormality in heart failure patients with reduced ejection fraction. The CUPID 2 (Calcium Up-Regulation by Percutaneous Administration of Gene Therapy in Cardiac Disease Phase 2b) trial is designed to evaluate whether increasing SERCA2a activity via gene therapy improves clinical outcome in these patients.

BACKGROUND

Intracoronary delivery of recombinant adeno-associated virus serotype 1 (AAV1)/SERCA2a improves intracellular Ca(2+) handling by increasing SERCA2a protein levels and, as a consequence, restores systolic and diastolic function. In a previous phase 2a trial, this therapy improved symptoms, functional status, biomarkers, and left ventricular function, and reduced cardiovascular events in advanced heart failure patients.

METHODS

CUPID 2 is a phase 2b, double-blind, placebo-controlled, multinational, multicenter, randomized event-driven study in up to 250 patients with moderate-to-severe heart failure with reduced ejection fraction and New York Heart Association functional class II to IV symptoms despite optimal therapy. Enrolled patients will be at high risk for recurrent heart-failure hospitalizations by virtue of having elevated N-terminal pro-B-type natriuretic peptide/BNP (>1,200 pg/ml, or >1,600 pg/ml if atrial fibrillation is present) and/or recent heart failure hospitalization. The primary endpoint of time-to-recurrent event (heart failure-related hospitalizations in the presence of terminal events [all-cause death, heart transplant, left ventricular assist device implantation or ambulatory worsening heart failure]) will be assessed using the joint frailty model. This ongoing trial is expected to complete recruitment in 2014, with the required number of 186 recurrent events estimated to occur by mid 2015.

RESULTS

Available data indicate that calcium up-regulation by AAV1/SERCA2a gene therapy is safe and of potential benefit in advanced heart failure patients.

CONCLUSIONS

The CUPID 2 trial is designed to study the effects of this therapy on clinical outcome in these patients. (Calcium Up-Regulation by Percutaneous Administration of Gene Therapy in Cardiac Disease Phase 2b [CUPID-2b]; NCT01643330).

Stem cell factor gene transfer promotes cardiac repair after myocardial infarction via in situ recruitment and expansion of c-kit+ cells

RATIONALE

There is growing evidence that the myocardium responds to injury by recruiting c-kit(+) cardiac progenitor cells to the damage tissue. Even though the ability of exogenously introducing c-kit(+) cells to injured myocardium has been established, the capability of recruiting these cells through modulation of local signaling pathways by gene transfer has not been tested.

OBJECTIVE

To determine whether stem cell factor gene transfer mediates cardiac regeneration in a rat myocardial infarction model, through survival and recruitment of c-kit(+) progenitors and cell-cycle activation in cardiomyocytes, and explore the mechanisms involved.

METHODS AND RESULTS

Infarct size, cardiac function, cardiac progenitor cells recruitment, fibrosis, and cardiomyocyte cell-cycle activation were measured at different time points in controls (n=10) and upon stem cell factor gene transfer (n=13) after myocardial infarction. We found a regenerative response because of stem cell factor overexpression characterized by an enhancement in cardiac hemodynamic function: an improvement in survival; a reduction in fibrosis, infarct size and apoptosis; an increase in cardiac c-kit(+) progenitor cells recruitment to the injured area; an increase in cardiomyocyte cell-cycle activation; and Wnt/β-catenin pathway induction.

CONCLUSIONS

Stem cell factor gene transfer induces c-kit(+) stem/progenitor cell expansion in situ and cardiomyocyte proliferation, which may represent a new therapeutic strategy to reverse adverse remodeling after myocardial infarction.

High-throughput FRET assay yields allosteric SERCA activators

Using fluorescence resonance energy transfer (FRET), we performed a high-throughput screen (HTS) in a reconstituted membrane system, seeking compounds that reverse inhibition of sarcoplasmic reticulum Ca-ATPase (SERCA) by its cardiac regulator, phospholamban (PLB). Such compounds have long been sought to correct aberrant Ca(2+) regulation in heart failure. Donor-SERCA was reconstituted in phospholipid membranes with or without acceptor-PLB, and FRET was measured in a steady-state fluorescence microplate reader. A 20 000-compound library was tested in duplicate. Compounds that decreased FRET by more than three standard deviations were considered hits. From 43 hits (0.2%), 31 (72%) were found to be false-positives upon more thorough FRET testing. The remaining 12 hits were tested in assays of Ca-ATPase activity, and six of these activated SERCA significantly, by as much as 60%, and several also enhanced cardiomyocyte contractility. These compounds directly activated SERCA from heart and other tissues. These results validate our FRET approach and set the stage for medicinal chemistry and preclinical testing. We were concerned about the high rate of false-positives, resulting from the low precision of steady-state fluorescence. Preliminary studies with a novel fluorescence lifetime plate reader show 20-fold higher precision. This instrument can dramatically increase the quality of future HTS.

Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID): a phase 2 trial of intracoronary gene therapy of sarcoplasmic reticulum Ca2+-ATPase in patients with advanced heart failure

BACKGROUND

Adeno-associated virus type 1/sarcoplasmic reticulum Ca(2+)-ATPase was assessed in a randomized, double-blind, placebo-controlled, phase 2 study in patients with advanced heart failure.

METHODS AND RESULTS

Thirty-nine patients received intracoronary adeno-associated virus type 1/sarcoplasmic reticulum Ca(2+)-ATPase or placebo. Seven efficacy parameters were assessed in 4 domains: symptoms (New York Heart Association class, Minnesota Living With Heart Failure Questionnaire), functional status (6-minute walk test, peak maximum oxygen consumption), biomarker (N-terminal prohormone brain natriuretic peptide), and left ventricular function/remodeling (left ventricular ejection fraction, left ventricular end-systolic volume), plus clinical outcomes. The primary end point success criteria were prospectively defined as achieving efficacy at 6 months in the group-level (concordant improvement in 7 efficacy parameters and no clinically significant worsening in any parameter), individual-level (total score for predefined clinically meaningful changes in 7 efficacy parameters), or outcome end points (cardiovascular hospitalizations and time to terminal events). Efficacy in 1 analysis had to be associated with at least a positive trend in the other 2 analyses. This combination of requirements resulted in a probability of success by chance alone of 2.7%. The high-dose group versus placebo met the prespecified criteria for success at the group-level, individual-level, and outcome analyses (cardiovascular hospitalizations) at 6 months (confirmed at 12 months) and demonstrated improvement or stabilization in New York Heart Association class, Minnesota Living With Heart Failure Questionnaire, 6-minute walk test, peak maximum oxygen consumption, N-terminal prohormone brain natriuretic peptide levels, and left ventricular end-systolic volume. Significant increases in time to clinical events and decreased frequency of cardiovascular events were observed at 12 months (hazard ratio=0.12; P=0.003), and mean duration of cardiovascular hospitalizations over 12 months was substantially decreased (0.4 versus 4.5 days; P=0.05) on high-dose treatment versus placebo. There were no untoward safety findings.

CONCLUSIONS

The Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID) study demonstrated safety and suggested benefit of adeno-associated virus type 1/sarcoplasmic reticulum Ca(2+)-ATPase in advanced heart failure, supporting larger confirmatory trials.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov. Unique identifier: NCT00454818.

SERCA2a Gene Transfer Therapy for Heart Failure

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Measurement of human and murine stem cell factor (c-kit ligand)

Stem cell factor (SCF) is an early-acting, hematopoietic growth factor that binds to the receptor encoded by the proto-oncogene c-kit. It is a potent growth factor for primitive bone marrow cells as well as thymocytes. This unit describes three protocols for detecting human and murine SCF. In the first, human or rodent SCF is measured by its ability to stimulate proliferation of the human megakaryoblastic leukemia cell line, UT-7. Because rat and mouse SCF bind well to human c-kit, human and rodent SCF can both be measured using the first basic protocol. In an Alternate Protocol, rodent SCF is assayed by its ability to stimulate proliferation of the clonal murine mast cell line, MC/9. Human SCF is not very active on rodent cells and thus cannot be measured using this protocol. Both of the cell proliferation assays lack specificity because they are capable of detecting other cytokines in addition to SCF. The third protocol is a radioreceptor assay using the human erythroleukemia cell line, OCIM1; it specifically measures murine or human SCF and not other cytokines. Support protocols describe maintenance of UT-7 and MC/9 cells and preparation of plasma membranes from OCIM1 cells.

Antigen-Specific Cytolysis by Neutrophils and NK Cells Expressing Chimeric Immune Receptors Bearing ζ or γ Signaling Domains

TCR- and IgG-binding Fc receptors (FcγR) mediate a variety of critical biologic activities including cytolysis via the structurally related ζ- and γ-chains. In previous studies, we have described chimeric immune receptors (CIR) in which the ligand-binding domain of a heterologous receptor or Ab is fused directly to the cytoplasmic domain of the TCR ζ-chain. Such ζ-CIRs efficiently trigger cytotoxic function of both T and NK cells in a target-specific manner. In this report, we compared the ability of both ζ- and γ-CIRs to activate the cytolytic function of two distinct classes of FcγR-bearing effectors, NK cells and neutrophils. Mature neutrophils expressing ζ- and γ-CIR were generated in vivo from murine hemopoietic stem cells following transplantation of syngeneic mice with retrovirally transduced bone marrow or in vitro from transduced human CD34+ progenitors following differentiation. Both ζ- and γ-based CIRs were capable of activating target-specific cytolysis by both NK cells and neutrophils, although the ζ-CIR was consistently more efficient. The experimental approach described is a powerful one with which to study the role of nonlymphoid effector cells in the host immune system and permits the rational design of immunotherapeutic strategies that rely on harnessing multiple immune cell functions via CIR-modified hemopoietic stem cells or progenitors.

Antigen-specific cytolysis by neutrophils and NK cells expressing chimeric immune receptors bearing zeta or gamma signaling domains

TCR- and IgG-binding Fc receptors (Fc gamma R) mediate a variety of critical biologic activities including cytolysis via the structurally related zeta- and gamma-chains. In previous studies, we have described chimeric immune receptors (CIR) in which the ligand-binding domain of a heterologous receptor or Ab is fused directly to the cytoplasmic domain of the TCR zeta-chain. Such zeta-CIRs efficiently trigger cytotoxic function of both T and NK cells in a target-specific manner. In this report, we compared the ability of both zeta- and gamma-CIRs to activate the cytolytic function of two distinct classes of Fc gamma R-bearing effectors, NK cells and neutrophils. Mature neutrophils expressing zeta- and gamma-CIR were generated in vivo from murine hemopoietic stem cells following transplantation of syngeneic mice with retrovirally transduced bone marrow or in vitro from transduced human CD34+ progenitors following differentiation. Both zeta- and gamma-based CIRs were capable of activating target-specific cytolysis by both NK cells and neutrophils, although the zeta-CIR was consistently more efficient. The experimental approach described is a powerful one with which to study the role of nonlymphoid effector cells in the host immune system and permits the rational design of immunotherapeutic strategies that rely on harnessing multiple immune cell functions via CIR-modified hemopoietic stem cells or progenitors.

Functional transplant of megabase human immunoglobulin loci recapitulates human antibody response in mice

We constructed two megabase-sized YACs containing large contiguous fragments of the human heavy and kappa (kappa) light chain immunoglobulin (Ig) loci in nearly germline configuration, including approximately 66 VH and 32 V kappa genes. We introduced these YACs into Ig-inactivated mice and observed human antibody production which closely resembled that seen in humans in all respects, including gene rearrangement, assembly, and repertoire. Diverse Ig gene usage together with somatic hypermutation enables the mice to generate high affinity fully human antibodies to multiple antigens, including human proteins. Our results underscore the importance of the large Ig fragments with multiple V genes for restoration of a normal humoral immune response. These mice are likely to be a valuable tool for the generation of therapeutic antibodies.

Systemic T cell-independent tumor immunity after transplantation of universal receptor-modified bone marrow into SCID mice

Gene modification of hematopoietic stem cells (HSC) with antigen-specific, chimeric, or "universal" immune receptors (URs) is a novel but untested form of targeted immunotherapy. A human immunodeficiency virus (HIV) envelope-specific UR consisting of the extracellular domain of human CD4 linked to the zeta chain of the T cell receptor (CD4 zeta) was introduced ex vivo into murine HSC by retroviral transduction. After transplantation into immunodeficient SCID mice, sustained high level expression of CD4 zeta was observed in circulating myeloid and natural killer cells. CD4 zeta-transplanted mice were protected from challenge with a lethal dose of a disseminated human leukemia expressing HIV envelope. These results demonstrate the ability of chimeric receptors bearing zeta-signaling domains to activate non-T cell effector populations in vivo and thereby mediate systemic immunity.

Human thymocyte responsiveness to stem cell factor: synergy with interleukin-2 for the generation of NK/LAK cytotoxicity

Human recombinant stem cell factor (SCF) increases the viability and cell size of a subset of thymocytes in vitro, but does not independently induce phenotypic changes on thymocytes indicative of T cell differentiation. The SCF-responsive thymocytes have characteristics of large granular cells, that do not express T, B or NK cell-related antigens, and are primarily found in immature thymocyte subsets. These large granular thymocytes do not display cytotoxic activity. However, SCF acts synergistically with IL-2 in the generation of cytotoxic effector cells from thymocyte precursors. Synergy in cytotoxicity is observed to both NK-sensitive and NK-resistant targets. Studies of the SCF receptors on thymocytes show that receptors are expressed on mature 'bright' CD3+ cells, immature 'dim' CD3+ cells as well as CD3- cells. IL-2 increases the frequency of SCF receptor-positive cells in cultured thymocytes, which may explain its synergy with SCF in the generation of NK/LAK cytotoxicity. These data show that SCF enhances the functional development of thymic NK/LAK cells in vitro.

Long-term treatment of canine cyclic hematopoiesis with recombinant canine stem cell factor

Grey collie dogs have cyclic fluctuations in their blood cell counts caused by a regulatory defect of hematopoietic stem cells. To examine the role of stem cell factor (SCF) or its receptor in this disorder, we investigated the stimulatory effects of recombinant canine SCF (rc-SCF) on in vitro marrow cultures, cloned and sequenced the grey collie SCF gene, and treated three grey collies with rc-SCF, either alone or in combination with recombinant canine granulocyte colony-stimulating factor (rcG-CSF). Colony-forming unit granulocyte-macrophage formation from grey collie or normal dog marrow showed similar dose-response curves for rc-SCF. Cloning and sequencing the SCF gene for two grey collies showed no evidence of mutations in the coding region of the SCF gene. Treatment with rc-SCF (10 to 100 micrograms/kg/d) did not induce neutrophilia except at the highest dose (100 micrograms/kg/d), but daily rc-SCF abrogated the neutropenic periods in doses of 20 micrograms/kg/d or greater. Combination of rc-G-CSF (0.5 to 1.0 microgram/kg/d) with rc-SCF treatment (20 to 50 micrograms/kg/d) suggested a synergistic effect, ie, the neutrophil levels on combined therapy were higher than the sum of the levels when these two cytokines were given separately. Long-term treatment of these dogs with rc-SCF in doses of 10 to 30 micrograms/kg/d was generally well tolerated, suggesting that SCF may be useful as a therapy for some chronic hypoproliferative disorders of hematopoiesis.

Cell surface expression of c-kit receptors by childhood acute myeloid leukemia blasts is not of prognostic value: a report from the Childrens Cancer Group

The prognostic significance of c-kit receptor expression on leukemic blast cells was determined in 122 children with acute myeloid leukemia (AML) entered onto Childrens Cancer Group protocol 213. Clinical and laboratory characteristics as well as outcome were analyzed according to the percentage of blast cells expressing c-kit receptors and the relative number of c-kit receptors per cell as determined by indirect immunofluorescence. c-kit receptor expression was strongly associated with the expression of the CD34 antigen. However, contrary to findings in adult patients with AML, c-kit receptor expression by childhood AML blast cells was not predictive of a poor response to therapy.

Splenic primitive hematopoietic stem cell (PHSC) activity is enhanced by steel factor because of PHSC proliferation

To test whether primitive hematopoietic stem cells (PHSCs) are stimulated by Steel (SI) factor (c-kit ligand) in vivo, donor mice were studied after three or seven daily injections of SI factor. PHSC activity was measured as long-term erythroid and lymphoid competitive repopulating ability. Cells to be tested (usually marrow or spleen cells from treated donors) were mixed with untreated competitor marrow that produces erythrocytes and lymphocytes that are genetically distinguishable from the donors by differences in hemoglobin (Hb) and glucosephosphate isomerase (GPI) markers. These cell mixtures were injected into lethally irradiated hosts, and after 111 to 293 days, functional abilities of donor PHSC populations were assessed and expressed as percentages of donor-type Hb and GPI in the host's circulating erythrocytes and lymphocytes, respectively. A striking increase in splenic PHSC activity occurred after seven daily injections of SI factor, with a much smaller increase after three daily injections. Both three and seven daily injections of SI factor slightly reduced marrow PHSC activity. Rapid cycling greatly increases PHSC vulnerability to 5-fluorouracil (5FU). To test whether SI factor stimulates PHSCs into rapid cycling, donor mice were given a dose of 5FU in addition to SI factor. The increase in splenic PHSCs after 7 days of treatment with SI factor occurred to a similar degree whether donors were or were not treated with 5FU on day 8. However, a dose of 5FU on day 4 of the SI factor treatments almost totally prevented the increase in splenic PHSC activity. Apparently this increased activity requires PHSC cycling throughout the period of SI factor treatment.

[Effects of recombinant stem cell factor on the proliferation in vitro of LT12 acute promyelocytic leukemic cell line]

Stem cell factor is a recently identified earliest-acting hematopoietic growth factor and a ligand for the c-kit proto-oncogen. Based on our recent observations that recombinant rat interleukin-3 (IL3), human interleukin-6 (IL6) and murine granulocyte-macrophage colony stimulating factor (GM-CSF) possessed different degrees of suppressive activities on the proliferation of LT 12 cell line derived from BNML rat leukemic model, SCF was evaluated alone and in combination with either IL3, IL6 or GM-CSF for effects on leukemopoiesis in vitro. The results indicated that SCF alone had suppressive effect on DNA synthesis and colony forming unit-leukemic blast (CFU-L) in LT12 cells. 100ng/ml of SCF caused substantial reduction in colony number and 3H-TdR uptake although this suppression was of lower magnitude than those induced by IL3, IL6 or GM-CSF. Enhanced suppression on the proliferation of LT12 cells was observed when SCF was used in combination with one of these three factors. Among these combinations, SCF+GM-CSF or SCF+IL6 resulted in more suppression on LT12 cells than SCF+IL3 did. Combination of SCF with two or three factors produced even more suppression. No apparent effect on the size of leukemic colony was seen. Furthermore, in growth kinetics study of LT12 cells in the presence of SCF production of LT12 cells declined. Thus, SCF appears to have divergent hematopoietic activities on BNML rat model: effective stimulation of granulopoiesis and weak suppression of leukemopoiesis.

Characterization of cultured mast cells derived from Ws/Ws mast cell-deficient rats with a small deletion at tyrosine kinase domain of c-kit

The Ws mutant allele of rats represents a 12-base deletion at the tyrosine kinase domain of the c-kit gene. Although homozygous Ws/Ws rats were deficient in both connective tissue-type mast cells (CTMC) and mucosal-type mast cells (MMC), mast cells did develop when bone marrow cells of Ws/Ws rats were cultured in the presence of concanavalin A-stimulated spleen cell conditioned medium (ConA-SCM). Although the proliferative response of rat cultured mast cells (RCMC) derived from Ws/Ws rats to ConA-SCM was comparable to that of RCMC derived from control normal (+/+) rats, the proliferative response of Ws/Ws RCMC to rat recombinant stem cell factor (rrSCF; a ligand for the c-kit receptor tyrosine kinase) was much lower than that of +/+ RCMC. However, a slight c-kit kinase activity was detectable in Ws/Ws RCMC, and the proliferation of Ws/Ws RCMC was accelerated when rrSCF was added to ConA-SCM. Because CTMC contain rat mast cell protease-I (RMCP-I) and MMC contain RMCP-II, the phenotype of +/+ and Ws/Ws RCMC in various culture conditions was evaluated by immunohistochemistry of RMCPs. Both +/+ and Ws/Ws RCMC showed the MMC-like phenotype (RMCP-I-/II+) when they were cultured with ConA-SCM alone. Most +/+ RCMC and about half of Ws/Ws RCMC acquired a novel protease (RMCP-I+/II+) phenotype when they were cultured with rrSCF alone. However, because the number of Ws/Ws RCMC dropped to one-tenth in the medium containing rrSCF alone, the absolute number of Ws/Ws RCMC with the RMCP-I+/II+ phenotype did not increase significantly. The effect of rrSCF in inducing the novel phenotype was suppressed when ConA-SCM was added to rrSCF. In contrast, +/+ and Ws/Ws RCMC cocultured with +/+ fibroblasts showed the RMCP-I+/II+ phenotype even in the presence of ConA-SCM. Moreover, a fibroblast cell line derived from SI/SI mouse embryos that did not produce SCF did not support the survival of both +/+ and Ws/Ws RCMC but did induce the RMCP-I+/II+ phenotype in about half of +/+ and Ws/Ws RCMC when their survival was supported by the addition of ConA-SCM. The normal signal transduction through the c-kit receptor did not appear to be prerequisite for the acquisition of the RMCP-I+/II+ phenotype.

In vitro effects of stem-cell factor or interleukin-3 on myelosuppression associated with AIDS

OBJECTIVE

To determine whether the early-acting hematopoietic growth factors stem-cell factor (SCF) or interleukin-3 (IL-3), are able to overcome the bone-marrow suppressive effects of cytokines or drugs involved in the hematologic abnormalities that accompany HIV-1 infection.

DESIGN

In vitro colony formation assays of normal human bone-marrow cells exposed to the myelosuppressive drugs, zidovudine, interferon-alpha (IFN-alpha) and ganciclovir, or the myelosuppressive cytokines, tumor necrosis factor-alpha (TNF-alpha) or transforming growth factor-beta (TGF-beta), implicated in HIV dysmyelopoiesis.

RESULTS

SCF (10 ng/ml) enhanced the numbers of erythroid (BFU-E) colonies in the presence of zidovudine or ganciclovir (P < 0.05) and myeloid [colony-forming unit granulocyte macrophage (CFU-GM)] colonies in the presence of ganciclovir or IFN-alpha (P < 0.05) relative to controls. IL-3 (10 ng/ml) also improved erythroid colony numbers in the presence of zidovudine (P < 0.05) and CFU-GM in the presence of IFN-alpha (P < 0.05). Neither factor consistently altered the inhibition of TGF-beta or TNF-alpha. The 50% inhibitory concentration (IC50) of the myelosuppressive agents was altered in only one setting, using IL-3 in the presence of zidovudine.

CONCLUSIONS

These data suggest that SCF or IL-3 may have a therapeutic application in overcoming hematopoietic abnormalities associated with drugs commonly used in the care of AIDS patients. However, they may have less capacity to overcome the bone-marrow inhibitory effects of the endogenous cytokines TNF-alpha and TGF-beta.

The in vivo effects of steel factor on natural killer lineage cells in murine spleen and bone marrow

Steel factor (S1F), also known as stem cell factor, is a potent growth stimulator of hemopoietic progenitor cells. In the context of transplantation of hemopoietic cells to irradiated allogeneic hosts, natural killer (NK) cells exert restrictive control on hemopoietic cell proliferation, and are regularly found in elevated concentration in areas of intense hemopoiesis. The present study was designed to examine the effects with time of S1F in vivo on the numbers of NK cells, identified by the presence of the NK 1.1 surface molecule, in the spleen and bone marrow. Throughout the first 3 days of S1F exposure, NK cell numbers, in spite of rapid (1 day) and significant increases in the other hemopoietic cell lineages, did not change in either the spleen or the bone marrow. However, NK cells were increased 2-fold in both organs by 7 days of S1F exposure. At this time, immature granuloid and erythroid cells and the large lymphoid cells in the spleen had more than doubled their respective control numbers and in the bone marrow, immature granuloid cells increased by 47% of control levels. The presence of a late, but not early, influence of S1F on NK cells of the spleen and bone marrow suggests an indirect effect of S1F on this lineage, occurring only when S1F-stimulated hemopoiesis becomes sufficiently intense, providing, thus, an abundance of NK cell targets.

In vivo administration of stem cell factor to mice increases the absolute number of pluripotent hematopoietic stem cells

We have examined the effects of administration of stem cell-factor (SCF) on the number and distribution of pluripotent hematopoietic stem cells (PHSC) in normal mice. Using the competitive repopulation assay we found that in vivo administration of SCF increases the absolute number of PHSC per mouse threefold. The increased numbers of PHSC are found in the peripheral blood and spleen of the SCF-treated animals. The spleen and peripheral blood stem cells completely repopulated the erythroid, myeloid, and lymphoid lineages of irradiated or W/Wv hosts, similar to bone marrow PHSC. PHSC from the peripheral blood of SCF-treated mice have a lineage marker-negative, c-kit-positive phenotype that is indistinguishable from that of bone marrow PHSC. The increase in the absolute number of spleen PHSC is associated with efficient gene transfer to these cells without prior treatment with 5-fluorouracil. This is a US government work. There are no restrictions on its use.

Stem cell factor influences the proliferation and erythroid differentiation of the MB-02 human erythroleukemia cell line by binding to a high-affinity c-kit receptor

Stem cell factor (SCF) acts in synergy with other growth factors such as erythropoietin (Epo), granulocyte-macrophage colony-stimulating factor (GM-CSF), or interleukin-3 (IL-3), to stimulate the growth of primitive hematopoietic cells. Because of the prominent role of CSF in the maintenance of normal erythropoiesis in vivo, we examined the effects of SCF on the Epo-inducible human erythroleukemia cell line MB-02, and characterized the c-kit receptor in these cells. MB-02 cells cultured in serum-containing media do not survive in the absence of exogenous growth factors, but the addition of SCF, Epo, or IL-3 as a single factor enhanced MB-02 survival. Furthermore, in the presence of Epo, SCF (5 to 25 ng/mL) enhanced MB-02 proliferation in a dose-dependent manner, and increased the relative and absolute number of benzidine-positive cells generated. SCF also enhanced cell proliferation in the presence of either IL-3 or low concentrations of GM-CSF. A neutralizing anti-c-kit receptor monoclonal antibody (SR-1) blocked binding of 125I-SCF to MB-02 cells by 98%, and the effect of SCF on MB-02 growth, c-kit receptor-binding parameters were quantitated by equilibrium-binding experiments with 125I-SCF. MB-02 cells display a single class of high-affinity (50 pmol/L) c-kit receptors, with approximately 8,000 receptors per cell. The molecular weight of the c-kit receptor was determined by affinity cross-linking 125I-SCF to MB-02 cells. 125I-SCF-c-kit receptor complexes of approximately 155,000 and approximately 310,000 daltons were found, likely representing the monomeric and dimeric forms of the c-kit receptor. The binding affinity and molecular weight of the c-kit receptor on MB-02 cells are similar to those of normal human marrow cells. These results suggest that SCF synergizes with Epo to influence not only the proliferation but the erythroid differentiation of MB-02 cells. Thus, the MB-02 cell line may be a useful model in which to investigate the molecular mechanisms of SCF action.

Phenotypic characterization of stem cell factor-dependent human foetal liver-derived mast cells

Human foetal liver cells are an enriched source of mast cell progenitors that complete their differentiation and mature in response to stem cell factor, the ligand for Kit, in liquid culture. These mast cells are Kit+, metachromatic with toluidine blue+, tryptase+, histamine+ and show ultrastructure features of mast cells. Using a panel of monoclonal antibodies (mAb) against different cell-surface antigens (33 mAb were used), the cell-surface phenotype of human stem cell factor-dependent foetal liver-derived mast cells was examined by flow cytometry. Consistent with previous reports on tissue-derived mast cells, those derived from foetal liver in vitro expressed HLA class I, CD9, CD29, CD33, CD43, CD45 and Kit. Unlike mast cells dispersed from tissue, a high expression of CD13 was found. Also, these in vitro-derived mast cells express little, if any, high-affinity IgE receptor. However, small amounts of mRNA for the alpha-chain in foetal liver-derived mast cells compared to KU812 cells (a human basophil-like cell line) could be detected by Northern blotting. Full expression of Fc epsilon RI may require additional growth factor(s).

Recombinant human stem cell factor mediates chemotaxis of small-cell lung cancer cell lines aberrantly expressing the c-kit protooncogene

Accumulating evidence suggests that c-kit and its ligand, stem cell factor (SCF), play an important role in the regulation of at least three lineages of stem cell growth and possibly in leukemogenesis, while only limited data are available that suggest possible involvement of c-kit/SCF in the development of human solid tumors such as lung cancer. We have recently reported that c-kit is aberrantly expressed almost exclusively in small-cell lung cancer (SCLC) among various types of solid tumors. The present study revealed that c-kit protein ectopically expressed in SCLC is indistinguishable from that in leukemia cell lines with megakaryocytic characteristics with respect to amount, molecular size, and autophosphorylation status in response to recombinant human SCF. Furthermore, significant chemotactic response as well as moderate in vitro cell growth was induced in SCLC cell lines by the addition of recombinant human SCF, suggesting that c-kit/SCF may play an important biological role in the development of SCLC. Our extensive search for activating mutations naturally occurring in the c-kit gene revealed an amino acid substitution in the transmembrane domain of an SCLC cell line, although the functional consequences of this variant allele are yet to be determined.

Soluble stem cell factor in human serum

Stem cell factor (SCF) is a recently described factor active in the early stages of hematopoiesis. It can exist in membrane-bound form and in proteolytically released soluble form. The levels and nature of SCF in human serum are described. As determined by an enzyme-linked immunosorbent assay performed for 257 samples, SCF level in serum averaged 3.3 +/- 1.1 ng/mL. The serum SCF was partially purified by immunoaffinity chromatography and analyzed by glycosidase treatments in conjunction with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The results show that the SCF has N-linked and O-linked carbohydrate and corresponds to the soluble form, at or about 165 amino acids in length. The findings suggest functional importance for soluble SCF in humans.

Regulation of mouse peritoneal mast cell secretory function by stem cell factor, IL-3 or IL-4

We examined whether three cytokines that promote mouse mast cell development, the c-kit ligand stem cell factor (SCF), IL-3, or IL-4, also can directly stimulate or modulate mouse peritoneal mast cell (PMC) mediator release. Challenge of purified PMC with rat rSCF164 at 20 to 100 ng/ml for 30 min induced a modest release of serotonin (5-HT), whereas IL-3 or IL-4 did not directly stimulate 5-HT release. Experiments in which PMC were exposed to each cytokine for 15 min, and then to DNP-HSA Ag or anti-IgE antibody for a further 15 min, showed that SCF, but not IL-3 or IL-4, had an additive effect on the 5-HT release induced by either of the IgE cross-linking agents. In longer term experiments, SCF (0.16 to 500 ng/ml), IL-3 (2.5 to 100 ng/ml), or IL-4 (0.06 to 2.5 ng/ml) was added to peritoneal cell cultures for 48 h, during which the cells were passively sensitized with IgE anti-DNP antibody. Incubation of either unfractionated or highly purified PMC preparations with each of the three cytokines resulted in a concentration-related increase in 5-HT release upon subsequent challenge of the cells with DNP-HSA Ag. However, after pretreatment of peritoneal cells for 48 h with each cytokine, only IL-4 (10 ng/ml) enhanced release of 5-HT induced by calcium ionophore A23187 (0.25 microM); IL-3 (100 ng/ml) had no effect, whereas SCF (100 ng/ml) significantly inhibited ionophore-induced release. Although IL-3 or SCF up-regulate responsiveness to IgE-dependent stimuli, we detected no effect of these cytokines on the binding of [125I]IgE to PMC. This suggests that the enhancing effects of SCF or IL-3 on IgE-dependent 5-HT release did not simply reflect changes in the amount of IgE bound to the cells. In conclusion, we found that SCF, IL-3, or IL-4 each exerted a different spectrum of stimulatory, costimulatory, or regulatory effects on the secretory function of mouse PMC.

Development of human mast cells from umbilical cord blood cells by recombinant human and murine c-kit ligand

Both human and mouse c-kit ligand induced differentiation of human mast cells in a long-term culture of the mononuclear cells of umbilical cord blood. Growth factor activity for human mast cells present in conditioned medium of BALB/3T3 fibroblasts was due to mouse c-kit ligand. Recombinant c-kit ligand induced differentiation and proliferation of mast cell progenitors in early stages of culture. However, apparent selective growth of mast cells by c-kit ligand in cord blood cell cultures is mainly due to the effect of the cytokine to selectively maintain survival of immature mast cells. Electron microscopic analysis indicated that human mast cells developed by c-kit ligand were similar to human mast cells in the lung and gut mucosa, while those developed in coculture of cord blood cells with Swiss albino/3T3 fibroblasts were similar to skin mast cells. This conclusion was supported by the fact that the majority of mast cells developed by c-kit ligand contained only tryptase in their granules, whereas those developed in the cocultures contained both tryptase and chymase. It was also found that mast cells developed by c-kit ligand were immature even after culture for 14 weeks. Nevertheless, these cells express Fc epsilon RI, and could be sensitized with human IgE for anti-IgE-induced release of histamine, prostaglandin D2, and leukotriene C4.

Regulation of mouse peritoneal mast cell secretory function by stem cell factor, IL-3 or IL-4

We examined whether three cytokines that promote mouse mast cell development, the c-kit ligand stem cell factor (SCF), IL-3, or IL-4, also can directly stimulate or modulate mouse peritoneal mast cell (PMC) mediator release. Challenge of purified PMC with rat rSCF164 at 20 to 100 ng/ml for 30 min induced a modest release of serotonin (5-HT), whereas IL-3 or IL-4 did not directly stimulate 5-HT release. Experiments in which PMC were exposed to each cytokine for 15 min, and then to DNP-HSA Ag or anti-IgE antibody for a further 15 min, showed that SCF, but not IL-3 or IL-4, had an additive effect on the 5-HT release induced by either of the IgE cross-linking agents. In longer term experiments, SCF (0.16 to 500 ng/ml), IL-3 (2.5 to 100 ng/ml), or IL-4 (0.06 to 2.5 ng/ml) was added to peritoneal cell cultures for 48 h, during which the cells were passively sensitized with IgE anti-DNP antibody. Incubation of either unfractionated or highly purified PMC preparations with each of the three cytokines resulted in a concentration-related increase in 5-HT release upon subsequent challenge of the cells with DNP-HSA Ag. However, after pretreatment of peritoneal cells for 48 h with each cytokine, only IL-4 (10 ng/ml) enhanced release of 5-HT induced by calcium ionophore A23187 (0.25 microM); IL-3 (100 ng/ml) had no effect, whereas SCF (100 ng/ml) significantly inhibited ionophore-induced release. Although IL-3 or SCF up-regulate responsiveness to IgE-dependent stimuli, we detected no effect of these cytokines on the binding of [125I]IgE to PMC. This suggests that the enhancing effects of SCF or IL-3 on IgE-dependent 5-HT release did not simply reflect changes in the amount of IgE bound to the cells. In conclusion, we found that SCF, IL-3, or IL-4 each exerted a different spectrum of stimulatory, costimulatory, or regulatory effects on the secretory function of mouse PMC.

Effects of recombinant canine stem cell factor, a c-kit ligand, and recombinant granulocyte colony-stimulating factor on hematopoietic recovery after otherwise lethal total body irradiation

The effects of recombinant canine stem cell factor (rcSCF) on hematopoiesis were studied in normal dogs and in dogs given otherwise lethal total body irradiation (TBI) without marrow transplant. Results were compared with previous and concurrent data with recombinant granulocyte colony-stimulating factor (rG-CSF). Four normal dogs received 200 micrograms rcSCF per kilogram body weight daily either by continuous intravenous infusion for 28 days (n = 2) or by subcutaneous (SC) injection in two divided doses for 20 days (n = 2). All dogs showed at least a twofold increase in peripheral blood neutrophil counts starting approximately 7 days after the initiation of treatment. Hematocrit level and monocyte, lymphocyte, eosinophil, reticulocyte, and platelet counts were not elevated. Marrow sections after rcSCF treatment showed panhyperplasia. The only toxicity was facial edema during the first few days of rcSCF administration, presumably caused by mast cell stimulation. Ten dogs were given 400 cGy TBI at 10 cGy/min from two opposing 60Co sources. They were given no marrow infusion and received 200 micrograms/kg/d rcSCF SC in two divided doses for 21 days starting within 2 hours of TBI. Five of the 10 dogs showed complete and sustained hematopoietic recovery and survived as compared with 1 of 28 control dogs not receiving growth factor (P < .005). RcSCF treatment allowed for hematopoietic recovery in two of seven dogs administered 500 cGy of TBI but in none of five dogs given 600 cGy of TBI. Results with rcSCF are similar to those obtained with rG-CSF. The rate of neutrophil recovery in rcSCF-treated dogs after 400 cGy TBI was not different from that of rG-CSF-treated dogs (P = .65), but the rate of platelet recovery was faster (P = .06) in the rcSCF-treated animals. Combined treatment with rcSCF and rcG-CSF after 500 cGy TBI did not result in strongly improved survival as compared with results obtained with either factor alone.

Reversible expansion of primate mast cell populations in vivo by stem cell factor

Mast cell development in mice is critically regulated by stem cell factor (SCF), the term used here to designate a product of fibroblasts and other cell types that is a ligand for the tyrosine kinase receptor protein encoded by the proto-oncogene c-kit. However, the factors which regulate the size of mast cell populations in primates are poorly understood. Here we report that the subcutaneous administration of recombinant human SCF (rhSCF) to baboons (Papio cynocephalus) or cynomolgus monkeys (Macaca fascicularis) produced a striking expansion of mast cell populations in many anatomical sites, with numbers of mast cells in some organs of rhSCF-treated monkeys exceeding the corresponding values in control monkeys by more than 100-fold. Animals treated with rhSCF did not exhibit clinical evidence of mast cell activation, and discontinuation of treatment with rhSCF resulted in a rapid decline of mast cell numbers nearly to baseline levels. These findings are the first to demonstrate that a specific cytokine can regulate mast cell development in primates in vivo. They also provide the first evidence, in any mammalian species, to indicate that the cytokine-dependent expansion of tissue mast cell populations can be reversed when administration of the cytokine is discontinued.

Rat stem cell factor and IL-6 preferentially support the proliferation of c-kit-positive murine hemopoietic cells rather than their differentiation

We have investigated the effect of stem cell factor (SCF) alone and in combination with interleukin-3 (IL-3) or interleukin-6 (IL-6) on the proliferation and maintenance of primitive hemopoietic progenitor cells. Results from liquid preculture of either unfractionated bone marrow cells or lineage (Lin)-c-kit+ cells indicates that the combination of SCF + IL-3 results in the greatest expansion of total nucleated cell numbers; however, the combination of SCF + IL-6 results in the greatest expansion of colony-forming cells in culture (CFU-C) and in spleen (CFU-S). Morphologic examination confirmed the increase in immature cells after culture with SCF + IL-6 and, therefore, this combination is deemed superior for the expansion of primitive cells in liquid culture. Reconstitution assays using congenic mice (Ly5) revealed that cultured cells in the presence of SCF + IL-6 contained stem cells that were capable of reconstituting the hemopoiesis in lethally irradiated mice. Although it remains unclear whether SCF + IL-6 directly supports the self-renewal of stem cells, SCF + IL-6 is a powerful tool for manipulating primitive hemopoietic cells in vitro.

Recombinant human stem cell factor stimulates differentiation of mast cells from dispersed human fetal liver cells

We have previously shown the development in vitro of tryptase+ human mast cells from fetal liver cells cocultured with murine 3T3 fibroblasts. In this study, recombinant human stem cell factor (rhuSCF), the ligand for the c-kit proto-oncogene product called Kit, stimulated the growth and differentiation primarily of mast cells from dispersed fetal liver cells, whereas recombinant human interleukin-3 (rhuIL-3) stimulated the differentiation of basophils along with other cell types. Cultures of fetal liver cells were initiated and maintained in the presence of rhuSCF or rhuIL-3 for up to 6 weeks. Metachromatic cells in cytospins were identified as mast cells primarily on the basis of tryptase expression, and as MCT or MCTC by immunohistochemistry using monoclonal antibodies against tryptase and chymase, whereas basophils were metachromatic, polymorphonuclear, and lacked these proteases. Levels of tryptase and histamine were measured by radioimmunoassay, tryptase and chymase activities by peptide hydrolysis, and cell surface Kit by flow cytometry with the monoclonal antibody YB5.B8. The predominant presence of mast cells occurred only in the cultures supplemented with rhuSCF. The percentage and total number of mast cells increased over time with increasing concentrations of rhuSCF and reached a plateau at 55 ng/mL. At this concentration of rhuSCF, mast cells first appeared by day 7; by day 42, 106% of the starting number of cells were present and 85% of these were tryptase+, 31% being weakly chymase+. These mast cells appeared immature by ultrastructural criteria; most cells were mononuclear, but some had nuclei with deeply divided lobes. DNA synthesis in tryptase+ mast cells at days 21 and 28 of culture with rhuSCF was demonstrated by incorporation of bromodeoxyuridine. Calculated levels of histamine (1.2 pg/mast cell) and tryptase (0.9 pg/mast cell) were similar to those determined previously in coculture experiments with murine 3T3 fibroblasts. Chymase activity was undetectable in most cell extracts. On day 0, 4% to 20% of fetal liver cells expressed cell surface Kit. In the presence of rhuSCF, the percentages and total numbers of Kit+ cells and the apparent concentration of Kit per cell increased along with the number of tryptase+ cells. In the presence of rhuIL-3, toluidine blue+, tryptase- cells first and maximally appeared at day 14 (11% +/- 2.5%). The percentage of these toluidine blue+ cells then declined to about 6% by days 21 and 35, while the total number of positive cells declined over 10-fold. Kit+ cells in the presence of rhuIL-3 declined from 9% on day 3 to 2% on day 35.(ABSTRACT TRUNCATED AT 400 WORDS)

The production of steel factor mRNA in Diamond-Blackfan anaemia long-term cultures and interactions of steel factor with erythropoietin and interleukin-3

Diamond-Blackfan anaemia (DBA) is a congenital macrocytic anaemia. To investigate whether DBA is due to hyporesponsiveness to or hypoproduction of Steel factor (SF), we compared the in vitro responsiveness of the BFU-E contained in the Ficoll-Hypaque non-adherent cell fraction of six DBA marrows with that of four normal marrows and one transient erythroblastopenia of childhood (TEC) marrow. In addition, we studied the effect of soluble SF on long-term marrow cultures (LTMC) and analysed the stromal cells from these cultures for SF mRNA transcripts. All the patients showed an erythropoietin dose-related increase of small BFU-E. The number and size of BFU-E was increased with the addition to the epo of IL-3 or SF; IL-3+SF was not synergistic. The addition of soluble SF to LTMC of DBA patients was associated with a small but consistent increase in non-adherent cell production and an increase in the number of progenitors. Messenger RNA from immortalized stromal cell lines of three patients and from primary bone marrow stromal cells of one patient showed the presence of expected SF transcripts by PCR analysis. These results demonstrate that this group of DBA patients responds to SF and produces SF mRNA normally, indicating that SF itself is not involved in DBA pathophysiology. The effects observed suggest that, despite the lack of evidence for a causative role, SF may prove to be effective treatment for such patients.

Isolation of rat bone marrow mast lineage cells using Thy 1.1 and rat stem cell factor

Recent reports have shown that various marrow-derived cell populations respond vigorously to recombinant rat stem cell factor (rrSCF164), one form of the kit-ligand. In the present study, we isolated cell populations from rat bone marrow using the Thy 1.1 antigen (an antigen that in the rat is differentially expressed on primitive hemopoietic progenitor cells) and fluorescently conjugated rrSCF164 (rrSCF164-PE). We show that rrSCF164 only stimulates cells that are enriched in the brightest Thy 1.1 populations (Thy 1.1bright). Numerous cell lines were generated by serial passage in rrSCF164 containing medium, and the prototypic cell lines have been designated SRT002 and SRT003. Each cell line retains the Thy 1.1bright phenotype and does not respond to interleukins (IL) 1-8, IL-10, granulocyte (G) colony-stimulating factor (CSF), granulocyte macrophage (GM) CSF, M-CSF, or crude preparations of mitogen-stimulated T-cell supernatants. The Thy 1.1bright population of rat marrow was subdivided into a subset that binds rrSCF164-PE (Thy 1.1bright, rrSCF164+). The majority of these cells possess certain characteristics in common with marrow-derived mast cells and the Thy 1.1bright, rrSCF164 responsive cell lines, having similar granule morphology, being metachromatic, and reacting positively with alcian blue. Moreover, rats treated with rrSCF164 displayed significant increases in Thy 1.1bright, rrSCF164+ cells in the bone marrow. These studies show that the combination of Thy 1.1 and rrSCF164 makes possible the isolation of a unique subset of rat bone marrow cells that differentially express the Thy 1.1 antigen and the cell surface receptor c-kit, the majority of which are morphologically similar to marrow-derived mast cells.

The ligand for c-kit, stem cell factor, stimulates the circulation of cells that engraft lethally irradiated baboons

Recombinant human stem cell factor (SCF), the ligand for c-kit, has been shown to stimulate increased numbers of hematopoietic progenitor cells of multiple types to circulate in the blood of baboons, but it was not known if the cells stimulated to circulate by SCF contained cells capable of engrafting and rescuing lethally irradiated baboons. Peripheral blood mononuclear cells (PBMNC) were collected by leukapheresis from four untreated control baboons and from three baboons on the 10th or 11th day of treatment with SCF (200 micrograms/kg/d). All animals were transplanted with 1.00 to 1.04 x 10(8)/kg of cryopreserved autologous PBMNC after treatment with a single dose of 1,020 cGy total body irradiation (TBI). Three animals were transplanted with PBMNC that had been collected during SCF treatment, 24 to 38 days after the last dose of SCF. Rapid trilineage engraftment was documented by bone marrow biopsy in all three. The mean time to a total white blood cell count (WBC) > or = 500/microL, WBC > or = 1,000/microL, and an absolute neutrophil count (ANC) > or = 500/microL was 15 +/- 3 (mean +/- SD), 19 +/- 1, and 19 +/- 2 days, respectively. Two animals remain alive with stable engraftment more than 180 and 245 days posttransplant. The third died of sepsis 32 days posttransplant with a hypercellular marrow showing trilineage engraftment. The surviving animals were transfusion independent by 10 and 59 days posttransplant. Four control animals were transplanted with PBMNC collected in the absence of SCF stimulation. One was treated for 11 days with SCF (200 micrograms/kg/d) after PBMNC were collected. This animal was transplanted 25 days after the last dose of SCF. None of the four control animals engrafted and they died 13, 16, 28, and 38 days posttransplant with marrow aplasia. Treatment with SCF stimulates the circulation of cells that engraft and rescue lethally irradiated baboons. The characteristics of the transplantable cells present in the circulation are now amenable to direct study.

Effects of stem cell factor on osteoclast-like cell formation in long-term human marrow cultures

Stem cell factor (SCF) is a newly described hematopoietic growth factor that stimulates the growth of primitive hematopoietic progenitors and mast cells. Since the osteoclast precursor is hematopoietic in origin, we tested SCF for its capacity to stimulate the formation of osteoclast-like multinucleated cells (MNC) in long-term human marrow cultures. These MNC express an osteoclast phenotype and form resorption lacunae on calcified matrices. Addition of SCF alone (0.1 pg/ml to 100 ng/ml) to long-term marrow cultures did not increase MNC formation. However, treatment of these cultures sequentially with SCF for 1 week followed by 1,25-(OH)2D3 for the second and third weeks of culture significantly enhanced MNC formation. [3H]Thymidine incorporation studies showed that SCF increased the proliferation of MNC precursors. These data suggested that SCF was acting on early MNC precursors. We then tested the capacity of SCF to stimulate the formation of colonies of committed precursors for osteoclast-like MNC. SCF (20 pg/ml to 20 ng/ml) enhanced osteoclast precursor formation in unfractionated bone marrow mononuclear cells but was unable to increase osteoclast precursor formation when a highly purified population of hematopoietic precursors was used as the target cells for SCF. These data suggest that SCF works in concert with other factors produced by nonhematopoietic marrow cells to increase the precursor pool for osteoclasts and that other factors, such as 1,25-(OH)2D3, complete the differentiation process to the mature osteoclast.

Induction of differentiation of human mast cells from bone marrow and peripheral blood mononuclear cells by recombinant human stem cell factor/kit-ligand in long-term culture

In the murine system, a number of cytokines (including interleukin-3 [IL-3], IL-4, and stem cell factor [SCF]) promote the growth of mast cells (MCs). However, so far little is known about factors controlling differentiation of human MCs. Recent data suggest that human MCs express receptors (R) for SCF. The aim of the present study was to investigate whether recombinant human (rh) SCF induces differentiation of human MCs from their precursor cells. For this purpose, bone marrow (BM; normal donors, n = 6) and peripheral blood (PB; normal donors, n = 11) mononuclear cells (MNC) were cultured in the presence of rhSCF, rhIL-3, rhIL-4, rhIL-9, recombinant human macrophage colony-stimulating factor (rhM-CSF), or control medium in long-term (8 weeks) suspension cultures. After 4 weeks, up to 5% of the MNC (BM and PB) cultured in the presence of rhSCF, but not in the presence of other cytokines, were found to exhibit the characteristics of MCs. These MCs expressed the YB5.B8-reactive domain of the SCF R as well as IgE R, as determined by combined toluidine blue/immunofluorescence staining. Myeloid antigens, likewise expressed on human basophils (ie, CD11b, CDw65, and Bsp-1), could not be detected on these cells. Furthermore, rhSCF, but not rhIL-3, rhIL-4, rhIL-9, or rhM-CSF, induced dose- and time-dependent increases in the formation of cellular tryptase (an MC-specific enzyme) (rhSCF [100 ng/mL], 1,308 +/- 679 ng/mL v control medium, 18 +/- 6 ng/mL tryptase on day 35 of PB cell cultures), as well as an increase in cellular histamine. After 6 to 8 weeks, when other mature hematopoietic cells decreased, MCs still could be detected in culture, with up to 40% of all cells being MCs. To test whether rhSCF also activates tissue MCs, we performed histamine release experiments (dispersed tissue; lung, n = 3; uterus, n = 3). SCF was found to enhance (by up to 3.4-fold) the capacity of the MCs to release histamine upon cross-linkage of IgE R with anti-IgE. Together, these observations suggest that rhSCF induces in vitro differentiation of human MCs from their BM and PB precursor cells in long-term culture and upregulates MC releasability.

Radioprotection of mice by recombinant rat stem cell factor

Treatment with recombinant rat stem cell factor (rSCF) protects mice from the lethal effects of irradiation. Mice treated with a single dose of rSCF prior to irradiation of up to 1150 rads [given as a split dose (1 rad = 0.01 Gy)] resulted in > 80% long-term survival, whereas a single injection given after the last dose of irradiation was not radioprotective. The combination of pre- and posttreatment (-20 h, -2 h, and +4 h) with rSCF resulted in 100% survival of otherwise lethally irradiated mice. Using this optimum schedule of rSCF administration, a radioprotective factor of 1.3-1.35 was achieved. The major cause of death in the control animals was massive bacteremia consisting of enteric organisms. The rSCF-treated animals had a much lower frequency of septicemia, due primarily to a rapid hematopoietic recovery of bone marrow function not evident in control animals.

Interaction of human bone marrow fibroblasts with megakaryocytes: role of the c-kit ligand

Human kit ligand (KL), also known as stem cell factor (SCF), steel factor, or mast cell growth factor, is a recently identified hematopoietic growth factor whose receptor is the product of the c-kit proto-oncogene. Alternative splicing of the pre-mRNA of KL/SCF results in secreted and membrane-bound forms of the protein. We and others have recently shown that the c-kit gene product is expressed on human megakaryocytes and that soluble KL/SCF in combination with granulocyte-macrophage colony-stimulating factor, interleukin-3 (IL-3), or IL-6 increased megakaryocyte progenitor colony formation (CFU-MEG) and stimulated mature megakaryocytes. Here we show that adhesion of human megakaryocytes to bone marrow stromal fibroblasts, which express the membrane-bound form of KL/SCF (mKL/SCF), is mediated in part by the interaction between mKL/SCF and the c-kit protein. This interaction also results in marrow fibroblast-stimulated proliferation but not an increase in ploidy of megakaryocytes; when the two cell types were separated by a transoluble membrane, proliferation did not occur. Adhesion and proliferation of human megakaryocytes to an immortalized murine stromal cell line SI/SI lacking the KL/SCF gene was impaired, whereas transfection of SI/SI cells with human mKL/SCF significantly increased both adhesion and proliferation. Marrow stromal fibroblast mKL/SCF may serve both as an adhesion structure and as a growth-potentiating factor for megakaryocytes in the bone marrow.

A c-kit ligand, recombinant human stem cell factor, mediates reversible expansion of multiple CD34+ colony-forming cell types in blood and marrow of baboons

The ligand for the human c-kit, recombinant human stem cell factor (SCF), was administered to baboons at doses of 200, 100, 50, 25, and 10 micrograms/kg/d. SCF induced a dose-dependent expansion of hematopoietic colony-forming cells (CFC) of multiple types in both blood and marrow, including colony-forming unit (CFU) granulocyte-monocyte, burst-forming unit-erythroid, CFU-MIX, and high proliferative potential-CFC. These changes were associated with a dose-dependent leukocytosis, involving all leukocyte lineages, a reticulocytosis, and increases in marrow cellularity. At 200 micrograms/kg/d of SCF, CFC in blood were increased 10-fold to greater than 100-fold. This correlated with an increased frequency of CD34+ cells in blood. The frequency of CFC in blood approached that of marrow in some animals. These changes were reversed within 7 to 14 days of stopping SCF. The results of these studies suggest a role for the c-kit ligand in stimulating the expansion of multiple CFC types in blood and marrow for potential therapeutic purposes.

Support of human hematopoiesis in long-term bone marrow cultures by murine stromal cells selectively expressing the membrane-bound and secreted forms of the human homolog of the steel gene product, stem cell factor

The maintenance and differentiation of hematopoietic stem cells is influenced by cells making up the hematopoietic microenvironment (HM), including bone marrow-derived stromal cells. We and several other investigators have recently demonstrated the molecular basis of abnormal HM observed in the steel mutant mouse and cloned the normal cDNA products of this gene (termed SCF, KL, or MCF). In this report, we focus on the human counterpart of the mouse Steel (Sl) gene. Alternative splicing of the human SCF pre-mRNA transcript results in secreted and membrane-bound forms of the protein. To investigate the role of these two forms of human SCF, we targeted an immortalized stromal cell line derived from fetal murine homozygous (Sl/Sl) SCF-deficient embryos for gene transfer of various human cDNAs encoding SCF. We report that stable stromal cell transfectants can differentially process the two forms of human SCF protein product. We also demonstrate that both soluble SCF and membrane-bound SCF are active in increasing the number of human progenitor cells in the context of stromal cell cultures, although in a qualitatively different manner. Hence, the membrane-bound form of SCF may play an important role in the cell-cell interactions observed between stromal and hematopoietic cells both in vitro and in vivo.

Evidence that stem cell factor is involved in the rebound thrombocytosis that follows 5-fluorouracil treatment

The mechanisms responsible for 5-fluorouracil (5FU)-induced rebound thrombocytosis are not completely understood. SI/SI(d) mice, which do not undergo rebound thrombocytosis in response to 5FU, provide a genetic approach to the study of this phenomenon. Recent reports by several groups that the SI locus encodes a protein known variably as stem cell factor (SCF), mast cell growth factor, or kit ligand, suggests the possibility that the lack of wild-type SCF in SI/SI(d) mice is responsible for their defective response to 5FU-induced thrombocytopenia. It is shown in this report that SCF-treated SI/SI(d) mice are as capable as their wild-type littermates in undergoing rebound thrombocytosis. W/Wv mice, mutated at the locus encoding the SCF receptor, also do not undergo rebound thrombocytosis, but are not responsive to SCF treatment. In normal mice, it is shown by RNA solution hybridization that SCF mRNA expression is increased during the 5FU-induced platelet nadir period. It is also shown by autoradiography that maturing megakaryocytes express SCF receptors, and that in vivo administration of SCF significantly raises the numbers of megakaryocytes, as well as circulating platelet counts. Taken together, these data indicate that SCF may be an important regulator of platelet production under both normal and physiologically disturbed situations.

The human recombinant c-kit receptor ligand, rhSCF, induces mediator release from human cutaneous mast cells and enhances IgE-dependent mediator release from both skin mast cells and peripheral blood basophils

The gene product of the steel locus of the mouse represents a growth factor for murine mast cells and a ligand for the c-kit proto-oncogene receptor, a member of the tyrosine kinase receptor class of oncogenes (for review, see O. N. Witte. 1990. Cell 63:5). We have studied the effect of the human recombinant c-kit receptor ligand stem cell factor (rhSCF) on the release of inflammatory mediators from human skin mast cells and peripheral blood basophils and compared its activity to that of rhIL-3, rhSCF (1 ng/ml to 1 microgram/ml) activated the release of histamine and PGD2 from mast cells isolated from human skin. Analysis by digital video microscopy indicated that purified human skin mast cells (84 +/- 5% pure) responded to rhSCF (0.1 to 1 microgram/ml) challenge with a rapid, sustained rise in intracellular Ca2+ levels that was accompanied by secretion of histamine. A brief preincubation (10 min) of mast cells with rhSCF (0.1 pg/ml to 1 ng/ml) significantly enhanced (100 +/- 35%) the release of histamine induced by anti-IgE (3 micrograms/ml), but was much less effective on IgE-mediated release of PGD2. In contrast, a short term incubation with rhSCF did not potentiate the secretion of histamine activated by substance P (5 microM). A 24-h incubation of mast cells with rhSCF did not affect the release of mediators induced by anti-IgE (3 micrograms/ml), probably due to receptor desensitization, rhSCF (1 ng/ml to 3 micrograms/ml) neither caused release of histamine or leukotriene C4 (LTC4) release from leukocytes of 14 donors, nor induced a rise in intracellular Ca2+ levels in purified (greater than 70%) basophils. Brief preincubation (10 min) of leukocytes with rhSCF (1 ng/ml to 3 micrograms/ml) caused an enhancement (69 +/- 11%) of anti-IgE-induced release of histamine that was significant at concentrations as low as 3 ng/ml (p less than 0.05), whereas it appeared less effective in potentiating IgE-mediated LTC4 release. In contrast, a prolonged incubation (24 h) with rhSCF (0.1 pg/ml to 100 ng/ml) did not enhance the release of histamine or LTC4 induced by anti-IgE (0.1 microgram/ml), whereas rhIL-3 (3 ng/ml) significantly potentiated the release of both mediators.(ABSTRACT TRUNCATED AT 400 WORDS)

The human recombinant c-kit receptor ligand, rhSCF, induces mediator release from human cutaneous mast cells and enhances IgE-dependent mediator release from both skin mast cells and peripheral blood basophils

The gene product of the steel locus of the mouse represents a growth factor for murine mast cells and a ligand for the c-kit proto-oncogene receptor, a member of the tyrosine kinase receptor class of oncogenes (for review, see O. N. Witte. 1990. Cell 63:5). We have studied the effect of the human recombinant c-kit receptor ligand stem cell factor (rhSCF) on the release of inflammatory mediators from human skin mast cells and peripheral blood basophils and compared its activity to that of rhIL-3, rhSCF (1 ng/ml to 1 microgram/ml) activated the release of histamine and PGD2 from mast cells isolated from human skin. Analysis by digital video microscopy indicated that purified human skin mast cells (84 +/- 5% pure) responded to rhSCF (0.1 to 1 microgram/ml) challenge with a rapid, sustained rise in intracellular Ca2+ levels that was accompanied by secretion of histamine. A brief preincubation (10 min) of mast cells with rhSCF (0.1 pg/ml to 1 ng/ml) significantly enhanced (100 +/- 35%) the release of histamine induced by anti-IgE (3 micrograms/ml), but was much less effective on IgE-mediated release of PGD2. In contrast, a short term incubation with rhSCF did not potentiate the secretion of histamine activated by substance P (5 microM). A 24-h incubation of mast cells with rhSCF did not affect the release of mediators induced by anti-IgE (3 micrograms/ml), probably due to receptor desensitization, rhSCF (1 ng/ml to 3 micrograms/ml) neither caused release of histamine or leukotriene C4 (LTC4) release from leukocytes of 14 donors, nor induced a rise in intracellular Ca2+ levels in purified (greater than 70%) basophils. Brief preincubation (10 min) of leukocytes with rhSCF (1 ng/ml to 3 micrograms/ml) caused an enhancement (69 +/- 11%) of anti-IgE-induced release of histamine that was significant at concentrations as low as 3 ng/ml (p less than 0.05), whereas it appeared less effective in potentiating IgE-mediated LTC4 release. In contrast, a prolonged incubation (24 h) with rhSCF (0.1 pg/ml to 100 ng/ml) did not enhance the release of histamine or LTC4 induced by anti-IgE (0.1 microgram/ml), whereas rhIL-3 (3 ng/ml) significantly potentiated the release of both mediators.(ABSTRACT TRUNCATED AT 400 WORDS)