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T M Dexter

Publications and source records attributed to T M Dexter.

At least 109 records · Page 6Linked to original sources
PubMed1992

Macrophage-inflammatory protein protects multipotent hematopoietic cells from the cytotoxic effects of hydroxyurea in vivo.

Macrophage inflammatory protein-1 alpha (MIP-1 alpha) has been assessed for its potential in vivo to protect hematopoietic progenitor cells from the cytotoxic effects of a cycle-specific drug--in this case hydroxyurea (HU). Two doses of HU, 7 hours apart, were administered to mice to induce spleen colony-forming unit (CFU-S) cycling and then to kill them during DNA-synthesis. MIP-1 alpha, in a variety of dose and time combinations, was injected before the second dose of HU in an attempt to prevent recruitment or maintain CFU-S quiescence, and thus protect them from the second dose of HU. Without MIP-1 alpha, recovery of the CFU-S population was complete in 7 days. In a dose-dependent manner, MIP-1 alpha either reduced the initial kill and accelerated recovery, or completely protected the CFU-S population. We conclude that MIP-1 alpha does protect multipotent progenitor cells in vivo and that these observations provide a base from which to build practical clinical applications.

Animals↗
PubMed1992

The mouse M-lysozyme gene domain: identification of myeloid and differentiation specific DNasel hypersensitive sites and of a 3'-cis acting regulatory element.

The mouse M-lysozyme gene is exclusively expressed in myeloid cells of the blood system being progressively turned on upon cell differentiation. In this study the mechanism controlling this tissue- and differentiation stage-specific gene expression was analyzed at the level of chromatin structure. A complex pattern consisting of constitutive and differentiation dependent DNasel hypersensitive sites (HSs) was found in a set of various myeloid cell lines, representing different stages of maturity. The chromatin of a lymphoid cell line, which does not express the lysozyme gene, is completely insensitive to DNasel digestion. Chromatin analysis of two multipotent hematopoietic stem cell lines which can be differentiated in vitro to mature myeloid cells confirmed that these identified DNasel HSs are specific for distinct differentiation stages, rather than being a characteristic feature of the cell lines. Additionally, the stem cell studies revealed that the hypersensitivity of the chromatin domain is already established at the multipotent stage. DNA fragments spanning a cell type- and differentiation stage-specific cluster of HSs in the 3' region of the gene showed enhancer activity in all cell types tested. In the light of this lack of specificity, we suggest that cell type-specific modification of the chromatin structure in this region may play a role in determining the binding of a widespread transcription factor, and hence contribute to the time specificity of lysozyme M gene expression.

Animals↗
PubMed1992

Haemopoietic cell kinetics in humans treated with rGM-CSF.

We have investigated the kinetics of myeloid cell proliferation in the marrow of patients with small-cell lung cancer and treated with 10 daily subcutaneous injections of granulocyte/macrophage colony-stimulating factor (GM-CSF). Bone marrow, obtained before and during treatment with the growth factor, was labelled in vitro with tritiated thymidine (3H-TdR). A 3rd bone-marrow sample was obtained 1 hr following an intravenous injection of 3H-TdR. Subsequent daily blood samples were also collected, and 3H-TdR labelling was assessed on these and the marrow preparations by autoradiography. GM-CSF treatment increased the peripheral granulocytic cells nearly 5-fold, but this included significant eosinophilia, so that the neutrophilic granulocytes increased only 3.3-fold. These cells were released from the marrow over a normal time scale, but their peripheral half-life was about 6 times longer than normal and they were probably functionally defective. Furthermore, significant numbers of immature cells were released from the marrow. Neutrophil production stimulated by GM-CSF was thus overestimated by measurement of the apparent peripheral granulocytosis. Increased labelling indices and grain counts in the proliferating granulocytic cells of the marrow indicate shortened cell-cycle times, and the excess granulocyte production appears to be the result of extra amplification divisions in the proliferative compartments.

Carcinoma, Small Cell↗
PubMed1992

Erythropoietin and myeloid colony stimulating factors.

The production of blood cells in the body is controlled by at least 20 polypeptide growth factors. Most of these factors have been cloned and many expressed in bacterial and eukaryotic systems to give biologically active proteins. Currently, these recombinant human proteins are undergoing intensive evaluation for their use in treating primary haemopoietic diseases, or stimulating normal haemopoiesis following drug-, radiation- or virus-induced trauma of the bone marrow. Erythropoietin (EPO) and the myeloid colony stimulating factors (IL-3, G-CSF, GM-CSF and M-CSF) were among the first to be cloned and expressed.

Animals↗
PubMed1992

Colony-stimulating factors in the clinic.

Recombinant purified human haemopoietic growth factors are available for clinical trials and some have been licensed for therapeutic use. Some haemopoietic lineages (erythroid, neutrophilic, monocyte-macrophagic) can be selectively stimulated in order to ameliorate the cytopenias that follow cytotoxic treatment, or that characterize some haematological syndromes, and to stimulate mature cell function. Advances in the knowledge of receptor-ligand interactions and of transduction mechanisms, plus the production of synthetic or mutant molecules that may mimic, potentiate or antagonize the effects of the natural growth factors, should make novel therapeutic approaches possible.

Animals↗
PubMed1992

Biological and structural properties of MIP-1 alpha expressed in yeast.

The murine macrophage inflammatory proteins-1 alpha (MIP-1 alpha) and MIP-1 beta are distinct but closely related cytokines. Partially purified mixtures of the two proteins affect neutrophil function and cause local inflammation and fever. The particular properties of MIP-1 alpha have not been well studied, although it has been identified as being identical to an inhibitor of haemopoietic stem cell growth. We have expressed MIP-1 alpha in yeast cells and purified it to sequence homogeneity. Structural analysis of this biologically active material by circular dichroism and fluorescence spectroscopy confirms that MIP-1 alpha has a very similar secondary and tertiary structure to platelet factor 4 and interleukin 8 with which it shares limited sequence homology. The in-vitro stem cell inhibitory properties have been confirmed using a range of murine progenitor cells including purified bone marrow progenitor cells (FACS-1), the FDCP-mix A4 cell line, and spleen colony forming unit (CFU-S) populations. Plateau levels of inhibition of stem cell growth were achieved using concentrations of 0.15 micrograms/ml MIP-1 alpha. We have also demonstrated that MIP-1 alpha is active in vivo: 5 micrograms of MIP-1 alpha per mouse given as a bolus injection, protects stem cells from subsequent in-vitro killing by tritiated thymidine. MIP-1 alpha was also shown to enhance the proliferation of more committed progenitor granulocyte macrophage-colony forming cells (GM-CFC) in response to granulocyte macrophage-colony stimulating factor (GM-CSF).

Animals↗
PubMed1992

Cell adhesion in the stromal regulation of haemopoiesis.

Haemopoiesis occurs in close physical contact with elements of the bone marrow stroma. This review examines some adhesion molecules which are expressed in haemopoietic environments. These molecules may act to maintain cell contact between haemopoietic progenitors and the cellular and extracellular matrix elements of the marrow stroma. A review is undertaken of several families of adhesion molecules and their ligands, including integrins, CD44, LEC-CAMs, CAMs and variant glycosylation patterns expressed by haemopoietic cells. Both CD44 and integrin receptors have been implicated in mediating important cellular interactions within the haemopoietic system and the significance of these and other molecules in haemopoiesis is discussed.

Amino Acid Sequence↗
PubMed1992

The capacity of peripheral blood stem cells mobilised with chemotherapy plus G-CSF to repopulate irradiated marrow stroma in vitro is similar to that of bone marrow.

After treatment of patients with intermediate or high grade non-Hodgkin lymphoma with chemotherapy plus G-CSF the numbers of haemopoietic progenitor cells in the circulation increased to a mean of 226-fold for mixed CFC (Mix-CFC), 278-fold for GM-CFC and 29-fold for erythroid burst forming unit (BFU-E). The mean increase was modest (7-12-fold) for patients treated with chemotherapy alone. Peripheral blood mononuclear cells harvested at the time of the peak in the numbers of progenitors, or 2-4 days before the peak, seeded onto irradiated marrow stroma in vitro, repopulated the stroma and generated active haemopoiesis at least as effectively as bone marrow cells on a cell per cell basis. This is in contrast to the poor repopulating capacity of pretreatment blood. The results indicate that not only the progenitor cells, but also the repopulating stem cells migrated into the blood after chemotherapy plus G-CSF in sufficient numbers to allow harvesting and successful grafting without the possible complication of late haemopoietic failure.

Adult↗
PubMed1992

Recombinant human interleukin 4 (IL-4) given as daily subcutaneous injections--a phase I dose toxicity trial.

Recombinant Interleukin 4 was administered by subcutaneous injection at daily doses of 0.5, 1.0 or 5.0 micrograms kg-1 to nine patients as part of a Phase I Dose Toxicity Study. Dose limiting toxicity was reached at 5 micrograms kg-1 day-1. Symptoms of toxicity included fatigue, 'flu like symptoms and elevated liver enzymes. Modest but significant elevations of neutrophil and platelet counts occurred. No clear evidence of antitumour effects emerged although pain in metastatic lymph nodes and a small fall in myeloma paraprotein levels during dosing were observed. In vitro and murine in vivo studies indicate that patients with lymphoproliferative disease should be selected for Phase II trials.

Bone Marrow↗
PubMed1992

Human cord blood: a source of transplantable stem cells?

In a preliminary study we have shown that optimally collected human umbilical cord (HUC) blood cells grow significantly better in long term cultures (LTC) than normal adult marrow cells (NBM) p = 0.0007. The LTC findings are supported by the observation in clonogenic assay that a similar number of GM-CFC colonies can be grown from HUC blood and NBM mononuclear cells (MNC). Also there is a trend towards a higher proportion of primitive erythroid (BFU-E) and primitive megakaryocyte colonies (MK-CFC containing greater than 20 cells) in HUC blood compared with NBM. We suggest that further work on the feasibility of a HLA typed, cryopreserved HUC blood bank as a source of unrelated haemopoietic 'stem' cells for clinical transplantation is indicated.

Blood Cell Count↗
PubMed1991

Interferon-gamma stimulates the survival and influences the development of bipotential granulocyte-macrophage colony-forming cells.

The effects of interferon-gamma (IFN-gamma) on a highly enriched population of granulocyte-macrophage colony-forming cells (GM-CFC) were assessed. When added with myeloid growth factors (interleukin-3 [IL-3], granulocyte-macrophage colony-stimulating factor [GM-CSF], or macrophage-CSF [M-CSF]), IFN-gamma inhibited the formation of colonies in soft agar assays. Furthermore IFN-gamma stimulated an increase in the number of macrophages present in colonies formed in the presence of IL-3. IFN-gamma also inhibited M-CSF-, GM-CSF-, or IL-3-stimulated [3H]-thymidine incorporation in highly enriched GM-CFC. However, when added in the absence of hematopoietic growth factors, IFN-gamma promoted the survival of GM-CFC and had a modest stimulatory effect on DNA synthesis. The direct interaction of the IFN with GM-CFC was confirmed by showing its ability to rapidly activate the sodium/hydrogen antiport in GM-CFC, as do the mitogens GM-CSF, M-CSF, and IL-3. However, the effect of IFN-gamma on intracellular pH and DNA synthesis was transient and pretreatment with IFN markedly inhibited the ability of GM-CSF, M-CSF, and IL-3 to activate the sodium/hydrogen antiport. IFN-gamma has a dual effect on GM-CFC, decreasing the rate of cell death but also limiting the proliferative response to CSFs.

Animals↗
PubMed1991

The effects on hematopoiesis of recombinant stem cell factor (ligand for c-kit) administered in vivo to mice either alone or in combination with granulocyte colony-stimulating factor.

Stem cell factor (SCF) is the ligand for the receptor encoded by the c-kit proto-oncogene. Mutations of either c-kit or the SCF gene are responsible for the defects of W and SI mutant mice, which both suffer a macrocytic anemia, the former associated with defective stem cells and the latter with a defective hematopoietic microenvironment. PEGylated recombinant rat SCF was administered to normal or splenectomized mice for up to 21 days. SCF was found to be a modest stimulator of peripheral blood neutrophil numbers in both groups of animals. The peak in neutrophil numbers was higher and occurred earlier in splenectomized mice. Bone marrow and spleen cellularity changed little during treatment but the content of interleukin-3-responsive progenitor cells and spleen colony-forming cells (CFU-S) reached very high levels, particularly in the spleen. Using recombinant human granulocyte colony-stimulating factor (rhG-CSF), we have shown that SCF induces a greater than additive increase in both blood neutrophils and blood-borne CFU-S. This synergy was seen throughout the dose range and may indicate a clinical role for SCF either alone or in augmenting the activity of G-CSF upon blood neutrophils and transplantable stem cells.

Animals↗
PubMed1991

Myeloid cell kinetics in mice treated with recombinant interleukin-3, granulocyte colony-stimulating factor (CSF), or granulocyte-macrophage CSF in vivo.

Myeloid cell kinetics in mice treated with pure hematopoietic growth factors have been investigated using tritiated thymidine labeling and autoradiography. Mice were injected subcutaneously with 125 micrograms/kg granulocyte colony-stimulating factor (G-CSF) (in some cases 5 micrograms/kg), or 10 micrograms/kg of granulocyte-macrophage CSF (GM-CSF), or interleukin-3 (IL-3) every 12 hours for 84 hours. 3HTdR labeling was performed in vivo after 3 days of treatment. G-CSF increased the peripheral neutrophil count 14-fold and increased the proportion and proliferation rate of neutrophilic cells in the marrow, suppressing erythropoiesis at the same time. Newly produced mature cells were released into the circulation within 24 hours of labeling, compared with a normal appearance time of about 96 hours. By contrast, GM-CSF and IL-3 had little effect on either marrow cell kinetics or on the rate of release of mature cells, although GM-CSF did stimulate a 50% increase in peripheral neutrophils. Monocyte production was also increased about eightfold by G-CSF and 1.5-fold by GM-CSF, but their peak release was only slightly accelerated. While the peripheral half-lives of the neutrophilic granulocytes were normal, those of the monocytes were dramatically reduced, perhaps due to sequestration in the tissues for functional purposes. The stimulated monocyte production in the case of G-CSF required an additional five cell cycles, a level that might have repercussions on the progenitor compartments.

Animals↗
PubMed1991

Expression of the GM-CSF gene after retroviral transfer in hematopoietic stem cell lines induces synchronous granulocyte-macrophage differentiation.

Multipotent murine stem cell lines (FDC-Pmix) depend on IL-3 for self-renewal and proliferation and can be induced to differentiate into multiple hematopoietic lineages. Single FDC-Pmix cells infected with retroviral vectors expressing GM-CSF are induced to differentiate into granulocytes and macrophages. This results in a complete loss of clonogenic cells if IL-3 is not exogenously supplied; however, multipotent variants can be selected that do not terminally differentiate if cells are kept in the presence of IL-3. Unidirectional and synchronous granulocyte and macrophage differentiation accompanied with loss of self-renewal capacity is induced when IL-3 is removed. Our data indicate that activation of the GM-CSF receptor induces differentiation of stem cells by an instructive mechanism that can be blocked by the activated IL-3 receptor. A model of how receptors can induce proliferation and cell-specific differentiation by two separate pathways is discussed.

Animals↗
PubMed1991

Growth factors in development, transformation, and tumorigenesis.

Mammalian tissue development and regeneration take place within a milieu of regulatory growth factors. These affect many parameters of cell development, such that survival, proliferation, differentiation, and certain aspects of cell behavior are all influenced by a balance between stimulatory and inhibitory signals. The precise effect of any given factor is determined by the responding cell type, the concentration of factor, and the presence of other stimuli, such that some growth factors may fulfill a variety of functions under different circumstances. Classically, growth factor stimuli are transmitted into the cell via activation of specific, transmembrane receptors that modify key regulatory proteins in the cytoplasm. These in turn affect the decisions controlling proliferation and differentiation, including changes in gene expression and reactivity to other factors. There are indications that some factors may function both extra- and intracellularly and that this characteristic is correlated with potential oncogenicity. The relatively low transforming ability of extracellular factors alone is probably attributable to the limitations imposed by down-regulation of their cell surface receptors. Aberrant production of secreted growth factors can, however, play decisive roles in tumorigenesis by increasing the proliferation rate and degree of cellular autonomy and extending the area available for tumor expansion.

Animals↗
PubMed1991

Interleukin-3-dependent hematopoietic stem cell lines capable of osteoclast formation in vitro.

Recently we reported that the osteoclast originates from the pluripotent hematopoietic stem cell. However, a detailed analysis of the progenitor and precursor stages of the osteoclast lineage is hard to perform with primary cultures of stem cells. In the present investigation interleukin-3 (IL-3)-dependent multipotent hematopoietic stem cell lines (FDCP-mix), which have many characteristics in common with freshly isolated hematopoietic stem cell lines (FDCP-mix), which have many characteristics in common with freshly isolated hematopoietic stem cells, were assayed for their osteoclast formation capacity. FDCP-mix cell lines A4, C2GM, and 15S were cocultured with periosteum-free 17-day-old fetal metatarsal bones. The effects of culture time, medium composition, and addition of WEHI-3b-conditioned medium (an unpurified IL-3 preparation) on osteoclast formation were studied. 15S cells never differentiated into osteoclasts. Both A4 and C2GM cells were able to generate osteoclasts. Osteoclast formation was visualized by staining for tartrate-resistant acid phosphatase activity and confirmed by 45Ca release assays and electron microscopic studies. Medium supplemented with fetal calf serum clearly supported osteoclast formation from A4 cells better than medium supplemented with cock serum. The difference between fetal calf serum and horse serum is generally less pronounced. C2GM cells formed osteoclasts more readily and, generally, earlier than A4 under all culture conditions. WEHI-3b-conditioned medium addition increased the numbers of osteoclasts and their resorption activity. The coculture of stripped metatarsal bones with FDCP-mix cell lines therefore offers a model system with many possibilities for the study of osteoclastogenesis and its regulation.

Acid Phosphatase↗
PubMed1991

Long-term marrow cultures: in vitro purging of leukaemic cells.

After induction and consolidation chemotherapy, patients with acute myeloid leukaemia (AML) usually achieve clinical remission. However, leukaemic cells, although not readily apparent, persist in most patients since the remissions cannot be sustained without further cytoreductive measures. To eradicate residual disease after induction chemotherapy, various treatment options (particularly allogeneic bone marrow transplantation) have been used. Autologous bone marrow transplantation (ABMT) can also lead to long-term survival, presumably due to the eradication or control of residual disease, but this occurs in only about 50% of cases transplanted. Relapse in the other patients occurs as a consequence of leukaemic cells surviving the conditioning regimen and/or the infusion of leukaemic cells present in the autografted bone marrow. In attempts to decrease the relapse rates after ABMT, chemical or immunological methods for in vitro purging of the harvested bone marrow cells to remove residual leukaemia have been used: the effectiveness of these procedures is unproven. This chapter describes the biology of long-term bone marrow cultures (LTBMC). How the biological differences between normal and leukaemic cells in LTBMC can be exploited to encourage the growth of normal haemopoietic cells at the expense of leukaemic cells, and how these cultured cells can be used in ABMT are discussed. The survival of patients after LTBMC/ABMT and the low relapse rate indicate that this is a useful therapeutic approach in the treatment of patients with leukaemia.

Bone Marrow↗