Standardization of the CFU-GM assay using hematopoietic growth factors

The colony-forming unit-granulocyte-macrophage (CFU-GM) assay is used commonly to assess adequacy of progenitor number in bone marrow transplantation. The assay is poorly standardized, resulting in variability of results between and within laboratories. We assessed three variables that contribute to the lack of standardization. The colony-stimulating activity of human placental-conditioned medium (HPCM) was compared with combinations of recombinant hematopoietic growth factors (HGF) in 5 normal bone marrow donors. A protocol for batch testing of fetal calf serum (FCS) is described. In addition, a rigid training program has been introduced to minimize interstaff and intrastaff variability in the counting of colonies. We show that a five-factor combination of interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), and stem cell factor (SCF) produces a mean increase of 85% in colony number. Some combinations of three HGF produce similar growth to HPCM, and all four HGF combinations are equivalent or superior to HPCM. Batch testing of FCS shows variability between batches. We show significant interstaff and intrastaff variability between a new and experienced staff member that improves following a period of training. In summary, the use of recombinant HGF in association with a rigorous program of batch testing of FCS and staff training results in a CFU-GM assay that can be standardized between laboratories.

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.

Growth factors and their impact on transfusion medicine

Hematopoietic growth factors, glycoproteins that stimulate self-renewal, differentiation, and proliferation of responsive hematopoietic cells, promise to revolutionize transfusion medicine. Recombinant DNA technology has made several of these cytokines available at pharmacologic doses, and new candidate agents for clinical application appear regularly. Growth factors prescribed for patients have already reduced the requirement for red blood cell and granulocyte transfusions in selected clinical circumstances. A lineage-specific thrombopoietin will likely limit the need for platelet transfusions. Hematopoietic cytokine injections have also been used to increase the number of red blood cells, granulocytes and circulating primitive progenitor cells in blood donors. Cytokine-stimulated peripheral blood progenitor cell infusions have complemented and, in some instances, replaced bone marrow for adjunctive cancer chemotherapy and for bone marrow transplantation. Finally, synergistic combinations of cytokines can effect ex vivo expansion of lymphocytes and of progenitor cells to provide novel blood components. Hematopoietic growth factors are still expensive and their long-term effects remain to be determined. However, as the biologic activities of cytokines and the physiology of hematopoietic progenitor cells become better understood, the clinical application of novel cellular components may redefine the concept of blood transfusion.

Hematopoietic cell proliferation and differentiation

The use of colony-stimulating factors to stimulate hematopoietic cell proliferation and differentiation in vivo is under still increasing investigation, particularly in the field of stem cell transplantation. This review discusses recently published results and tries to extrapolate lines of future development from the achievements reached to date.

Cyclophosphamide dose escalation in combination with vincristine and actinomycin-D (VAC) in gross residual sarcoma. A pilot study without hematopoietic growth factor support evaluating toxicity and response

PURPOSE

The Intergroup Rhabdomyosarcoma Study (IRS) initiated an escalating-dose cyclophosphamide (Cyc) pilot without hematopoietic growth factor (HGF) support in combination with vincristine (Vcr) and actinomycin-D (Amd), known as VAC, to establish a Cyc dose with myelotoxicity comparable to an ifosfamide (Ifos), Vcr, and Amd combination regimen (VAI). A Cyc dose equivalent to Ifos was to be determined when comparable myelotoxicity was achieved.

PATIENTS AND METHODS

Patients with either rhabdomyosarcoma or undifferentiated soft-tissue sarcoma and gross residual (clinical group III) disease were eligible for the VAC pilot. Feasibility and toxicity were evaluated in the VAC pilot at each Cyc level before escalating the dose. Starting at CYC 1.2 g/m2 dose escalation was planned at increments of 20-25% in cohorts of 8-10 patients until myelotoxicity at a severe or worse grade was seen in > 90% of the patients.

RESULTS

One hundred nineteen eligible patients were evaluated for toxicity and response at four Cyc levels: 1.2, 1.5, 1.8, and 2.2 g/m2. Eight of 87 (9%) evaluable at 2.2 g/m2 had a toxic death. Six of these were attributable to myelotoxicity. Patients age 1-3 years were most vulnerable. The overall complete response (CR) rate of 68% was poorly predicted by the weeks 8 and 20 CR rates of 20 and 40%, respectively. During the first year and overall, myelotoxicity at 2.2 g/m2'1 with VAC was comparable to Ifos 1.8 g/m2'5. Cyc was relatively more myelotoxic than Ifos in the second year of the VAC pilot. Based on actual amount of drug given, a standardized Ifos dose of 9.0 g/m2 was equivalent to 2.1 g/m2 of Cyc, giving an Ifos/Cyc ratio of 4.3.

CONCLUSION

Myelotoxicity using 2.2 g Cyc/m2 in a single intravenous infusion was dose limiting in this VAC pilot without HGF. In the first year and overall, myelotoxicity is comparable to that with VAI using Ifos at 9.0 g/m2. An ongoing IRS-IV randomized trial of VAC and VAI should provide a comparison of the efficacy of Ifos and Cyc in children and adolescents with embryonal or alveolar rhabdomyosarcoma and undifferentiated soft-tissue sarcomas.

Myelodysplastic syndrome

Myelodysplastic syndrome continues to present a formidable clinical challenge. Despite considerable effort, no therapy apart from allogeneic bone marrow transplantation has been shown to prolong survival. Lack of effective therapy for myelodysplastic syndrome is of further concern given recent reports on the high incidence of myelodysplastic syndrome in patients undergoing intensive chemotherapy and radiation therapy for other malignancies. However, significant strides have been made in the past year toward understanding the molecular pathogenesis of some forms of myelodysplastic syndrome, as well as developing new approaches for therapy of myelodysplastic syndrome. This review highlights recent advances in the molecular genetics of myelodysplastic syndrome, including clonality analysis and identification of genes that are causally implicated in the pathogenesis of myelodysplastic syndrome; results from recent clinical trials for therapy of myelodysplastic syndrome using growth factors, chemotherapy or both; and recent literature on therapy-related myelodysplastic syndrome in intensively treated patients.

Hematopoietic stem cell compartment: acute and late effects of radiation therapy and chemotherapy

The bone marrow is an important dose-limiting cell renewal tissue for chemotherapy, wide-field irradiation, and autologous bone marrow transplantation. Over the past 5-10 years a great deal has been discovered about the hematopoietic stem cell compartment. Although the toxicity associated with prolonged myelosuppression continues to limit the wider use of chemotherapy and irradiation, ways are being discovered to circumvent this toxicity such as with the increasing use of cytokines. This review describes what is known of how chemotherapy and irradiation damage stem cells and the microenvironment, how cytokines protect hematopoietic cells from radiation damage and speed marrow recovery after chemotherapy or marrow transplantation, and how various types of blood marrow cells contribute to engraftment and long-term hematopoiesis after high doses of cytotoxic agents and/or total body irradiation.

An effective strategy for decontamination, ex vivo expansion, and storage of human fetal liver hematopoietic stem cells

The transplantation of human fetal tissue has the potential to cure a variety of life-threatening diseases. The strategy for procurement, quality control, and functional assessment of human fetal liver HSC may prove useful for the transplantation of other fetal tissues. In addition to technical limitations, there are ethical and legal issues which need to be resolved before widespread use of fetal tissue. Further development of regulatory standards for the acquisition and distribution of fetal tissues will foster the application of this novel technology.

Differentiation of human mast cells from bone-marrow and cord-blood progenitor cells by factors produced by a mouse stromal cell line

Human bone-marrow or cord-blood progenitors (i.e., CD34+ cells) are easily purified by immunological methods and can be cultured on normal human-bone-marrow stromal cells for limited periods of time. Under these culture conditions, the number of progenitors declines in a few weeks and these cells disappear completely in less than 8 weeks. This fact suggests that this culture system is deprived of growth factor(s) able to support the self-renewal of stem cells. We have developed the culture of immunomagnetically purified human-bone-marrow- or cord-blood-derived CD34+ cells on a supportive mouse lipoblastic stromal cell line, MS-5. The long-term survival of clonogenic cells was analyzed in these cultures and compared with the results obtained by culture on human-bone-marrow stromal cells. The results demonstrated that only coculture of CD34+ cells on MS-5 layers allows the survival of clonogenic progenitors for at least 12 weeks. Cytospin smears were regularly performed and cell morphology was examined after classical staining methods (i.e., M.G.G. and toluidine blue staining). Histologic analysis demonstrated the growth of mast-cell-like metachromatic cells after the second week of incubation on MS-5 layer. The highest percentage of these cells was observed after 8 weeks, and averaged about 30 percent for cord-blood cells and 70 percent for bone-marrow cells. To further confirm the nature of the metachromatic cells obtained under this culture condition, immunohistochemical staining of tryptase was performed on the same samples. The results demonstrated similar percentages of tryptase+ cells and of metachromatic elements. Measurement of cellular histamine demonstrated that culture of CD34+ cells on MS-5 monolayers induced the formation and increase of this mediator. To determine whether the contact between MS-5 layers and CD34+ cells was an absolute requirement for the development of mast cells, CD34+ cells were cultured in the presence of MS-5 conditioned medium. This condition allowed the development of similar percentage of mast cells when compared with the coculture experiments, indicating that a soluble factor was involved in mast cell differentiation. Whatever the soluble factor(s) responsible for this mast cell growth activity, our culture system allows us to obtain significant amounts of highly enriched normal human mast cell populations useful for further studies on the reactivity of this cell subset.

Expression of the Kit and KitA receptor isoforms in human acute myelogenous leukemia

Genetic and biologic evidence suggests that the Kit receptor tyrosine kinase is important in early events in hematopoietic stem cell differentiation. Two naturally occurring isoforms of the Kit receptor, termed Kit and KitA, were originally described in mouse cells and, subsequently, in human cells. These isoforms differ by the presence (KitA) or absence (Kit) of four amino acids (Gly-Asn-Asn-Lys) that lie immediately outside the transmembrane domain. RNase protection was used to measure the levels of Kit and KitA mRNA in normal bone marrow and the blast cells from individuals with acute myelogenous leukemia (AML). Although both isoforms were present in all the AML samples tested, there was considerable heterogeneity in the relative levels of the two transcripts, with Kit to KitA RNA ratios varying from as low as 1.3 to as high as 12. In contrast, the ratio of Kit to KitA transcripts in normal bone marrow was tightly clustered between 4.4 and 5.5. Because alterations in the relative levels of expression of Kit and KitA may affect the ability of a cell to respond to the Kit ligand, Steel factor, we examined the Kit/KitA RNA ratio in AML patients that differed with respect to a number of diagnostic, prognostic, and biologic parameters. The relative levels of Kit to KitA RNA was independent of French-American-British subtype, response to therapy, and primary and secondary plating efficiencies in vitro. Thus, these data suggest that the relative levels of the two isoforms of the Kit receptor in AML are not associated with any obvious biologic or clinical parameters and, therefore, may reflect naturally occurring changes in splicing mechanisms as stem cells differentiate.

Polymerase chain reaction detection of a novel human KIT (mast/stem cell growth factor receptor) gene polymorphism by single-strand conformation polymorphism analysis or by SmaI or BstNI cleavage

We describe a common single-base polymorphism of the KIT gene that alters both SmaI and BstNI restriction sites, but is most easily detected as a single-strand conformation polymorphism (SSCP) using the polymerase chain reaction (PCR).

Hematopoietic growth factors in pediatrics

The human recombinant hematopoietic growth factors have attracted widespread interest because of their potential efficacy in a number of clinical settings. Recombinant human erythropoietin is now an established therapy to treat and prevent the anemia associated with chronic renal failure in children and adults. This agent also shows extraordinary promise to stimulate erythrocyte production and reduce transfusion requirements in premature infants. Granulocyte and granulocyte-macrophage colony-stimulating factors stimulate the production and function of myeloid cells and have provided major clinical benefit to children with congenital disorders of neutrophil production. The myeloid growth factors also show great promise in reducing the duration and severity of neutropenias associated with cytotoxic cancer treatment and in improving granulocyte production in patients with human immunodeficiency virus infections.

Ex vivo differentiation therapy as a method of leukemic cell purging in murine bone marrow expansion cultures

We investigated the use of differentiation therapy as a method of purging bone marrow (BM) of leukemic cells in ex vivo murine BM expansion cultures (delta-cultures). In clonal cultures and in suspension cultures a combination of the differentiation-inducing agents granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-6, and all-trans-retinoic acid (ATRA) was found to be most effective in inducing the differentiation of the murine myelomonocytic leukemic cell line WEHI 3B D+ LacZ clone 2.8 (clone 2.8). Furthermore, we investigated the activity of a mutant form of IL-6, mutein, and found it to have a greater specific activity in cell proliferation assays and in a clone 2.8 differentiation assay than the native form of IL-6. Coculture of clone 2.8 and BM in IL-1 and kit-ligand-stimulated delta-cultures showed that the added stimuli, G-CSF, mutein, and ATRA, decreased the expansion of leukemic cells. Mice transplanted with G-CSF, mutein, and ATRA-purged BM had an increased survival time relative to nonpurged controls. The addition of G-CSF, mutein, and ATRA to delta-cultures did not result in any impairment of hematopoietic stem cells when measured 5 wk after transplantation.

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.

[Function,molecular structure and gene expression of macrophage colony-stimulating factor]

Human urinary macrophage colony-stimulating factor (hM-CSF) is a glycoprotein with a molecular weight of 85 kDa which consists of two homologous subunits with a molecular weight of 43 kDa. It stimulates monocyte production through the stimulation of progenitor cells to differentiate to mature monocytes as well as neutrophil production through the stimulation of mature monocytes to produce granulocyte-macrophage and granulocyte CSF. It also enhances platelet production through the production of megakaryocyte potentiator (Meg-POT). Recently, proteoglycan type M-CSF has been found by our group. This type of M-CSF has a molecular weight of greater than 200 kDa and consists of a 43 kDa subunit and a 150-200 kDa subunit, the latter of which contains chondroitin sulfate glycosaminoglycan. This proteoglycan type M-CSF binds to extra-cellular matrix at the part of glycosaminoglycan. In addition to hematopoiesis-stimulating activity, M-CSF has a promoting activity on monocyte tumor-killing, osteoclast production and differentiation of cytotrophoblasts to syncytiotrophoblasts which secrete gonadotropin. M-CSF receptor (M-CSF-R) was found as a product of proto-oncogene, c-fms which consists of 972 amino acids. Mutations at Tyr 969 and Ser 301 of M-CSF-R has been found in patients with myelodysplastic syndrome and monocytic leukemia.

The action of bryostatin on normal human hematopoietic progenitors is mediated by accessory cell release of growth factors

Since enrichment of human bone-marrow hematopoietic progenitors is becoming more feasible and since purified growth factors are now available, we sought to study the action of growth factors on CD34-positive enriched cultures of human bone-marrow cells. We tested the effect of recombinant human (rh) granulocyte-macrophage colony-stimulating factor (GM-CSF), rh interleukin-3 (IL-3), or a unique biologic response modifier, bryostatin 1, on the growth of purified CD34 cells obtained by limiting dilution in single-cell cultures. We have shown previously that bryostatin 1 stimulates both myeloid and erythroid progenitors of human origin in vitro. In this study both IL-3 and GM-CSF supported colony formation from 500, 100, or single-cell cultures at equivalent plating efficiences, suggesting a direct action of these factors on hematopoietic cell growth. Conversely, bryostatin 1 did not support the growth of CD34 cells in single-cell cultures, and the cloning efficiency increased with increasing the number of cells in the culture. To test whether the indirect action of bryostatin 1 might be mediated through the production of growth factors by accessory cells, studies were performed using antibodies directed against human IL-3 and GM-CSF in culture with bryostatin 1 and normal human bone-marrow cells. Results are consistent with the hypothesis that bryostatin 1 could have a stimulatory effect on the accessory cell populations to produce either IL-3 or GM-CSF. Further support for this notion was obtained by demonstrating that T cells, which are cells known to be able to produce IL-3 and GM-CSF, are stimulated by bryostatin 1 to express messenger RNA (mRNA) for specific growth factors, including GM-CSF. These results provide further support that bryostatin 1 may be a useful clinical agent to stimulate hematopoiesis in vivo.

Hemopoietin-1 activity of interleukin-1 (IL-1) on acute myeloid leukemia colony-forming cells (AML-CFU) in vitro: IL-1 induces production of tumor necrosis factor-alpha which synergizes with IL-3 or granulocyte-macrophage colony-stimulating factor

Interleukin-1 (IL-1) has hemopoietin-1 (H-1) activity, i.e., it synergizes with macrophage-colony stimulating factor (M-CSF), granulocyte-macrophage-CSF (GM-CSF) and interleukin-3 (IL-3) in stimulating in vitro colony formation of hematopoietic progenitor cells. In this study the synergistic activity of IL-1 was investigated on IL-3 and GM-CSF induced growth of acute myeloid leukemia colony forming cells (AML-CFU) in vitro. Among 12 cases of human AML, IL-1 significantly elevated IL-3 stimulated colony numbers in eight instances and enhanced GM-CSF induced colony growth in five cases. As IL-1 is an inducer of cytokine production and since tumor necrosis factor (TNF) elevates IL-3 or GM-CSF induced proliferation of AML-CFU, we examined whether IL-1 enhanced AML-CFU growth via the induction of TNF production. Neutralizing anti-TNF-alpha antibodies significantly decreased IL-1/IL-3 or IL-1/GM-CSF stimulated colony numbers in six of seven cases studied, whereas anti-TNF-beta had no effect, indicating that endogenously produced TNF-alpha costimulated the growth of AML-CFU. Furthermore, AML blast cells stimulated by IL-1 released increased amounts of TNF-alpha (between 25 and 533 pg/ml; median 255 pg/ml) into the culture medium (TNF-alpha specific radioimmunoassay) as compared with noninduced AML cells (less than 1 to 149 pg TNF-alpha/ml; median 31 pg/ml). Thus, the effect of IL-1 on AML-CFU proliferation is not the result of direct activation of AML progenitors, but IL-1 stimulates the release of TNF-alpha by AML cells and endogenous TNF subsequently synergizes with IL-3 or GM-CSF.

A simple and rapid method to determine hematopoietic growth factor activity

A rapid and simple colorimetric microassay method for the determination of hematopoietic growth factor activities was established. The assay was used to detect CSF-1, GM-CSF, and IL-3 activities. The assay was based on the metabolism of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to formazan by metabolically active cells. Results obtained with the colorimetric microassay are comparable with those obtained with the soft agarose assay. Advantages of the colorimetric microassay include the conservation of reagents, the shorter incubation time for the experiment, the shorter assay time, and the ability to evaluate large numbers of samples.