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M Flasshove

Publications and source records attributed to M Flasshove.

32 records · Page 2Linked to original sources
PubMed1996

Density enrichment and characterization of hematopoietic progenitors and stem cells from umbilical cord blood.

Umbilical cord blood (UCB) is being used for hematopoietic rescue after myeloablative therapy in a rapidly growing number of patients. Recent developments of cord blood banking, ex vivo progenitor expansion and gene therapy techniques have raised the issue of efficient progenitor and stem cell enrichment procedures using UCB. We have used discontinuous density gradient techniques to analyze progenitor distribution in the mononuclear cell fraction of cord blood. This resulted in establishment of a highly reproducible, rapid, cost-effective single-step density separation method that generates a light density fraction, which when compared to conventional mononuclear cells has a high number of clonogenic progenitors, can be extensively expanded in vitro for up to 21 days and has the ability to sustain long-term hematopoiesis when inoculated on a preformed stromal layer. It can also serve as an efficient target for retrovirally mediated gene transfer, utilizing a vector expressing a mutated dihydrofolate reductase gene that confers methotrexate resistance.

Cell Culture Techniques↗
PubMed1996

Constitutive overexpression of the cytidine deaminase gene confers resistance to cytosine arabinoside in vitro.

In search of potential therapeutic targets for enhancing the cellular detoxification of cytosine-arabinoside (ara-C), we transfected the human CDD cDNA gene into murine fibroblast cells and examined the effect of increased CDD expression on the cellular resistance to ara-C. Several cell lines were established which consistently demonstrated a 2.5-3.0-fold increase in cellular CDD activity and exhibited an up to 3.0-3.5-fold increase in the IC50 value of ara-C with regard to inhibition of cell proliferation or DNA synthesis, respectively. In the absence of ara-C, these cells maintained unaltered morphology and growth characteristics as compared with parental cells and mock-transfected controls. In addition, we examined the CDD and dCK activity in hematopoietic cells and found CD34+ hematopoietic progenitor cells to reveal a low ratio of CDD/dCK activity. Together, these data suggest that constitutive overexpression of the CDD gene correlates with increased ara-C resistance and thus may prove useful in considering attempts to attenuate ara-C-induced toxicity on hematopoietic progenitor cells.

Adult↗
PubMed1995

Ex vivo expansion and selection of human CD34+ peripheral blood progenitor cells after introduction of a mutated dihydrofolate reductase cDNA via retroviral gene transfer.

Retroviral gene transfer into human myeloid precursor cells allows introduction of marker genes as well as genes conferring resistance to chemotherapeutic drugs. We transduced a human mutant dihydrofolate reductase (DHFR) cDNA into CD34 antigen-positive peripheral blood cells from patients with breast or ovarian cancer obtained after treatment with chemotherapy and granulocyte colony-stimulating factor (G-CSF). This mutant DHFR has been shown to confer resistance to methotrexate (MTX) in murine bone marrow. We established a transduction protocol that permitted ex vivo expansion and selection of transduced early progenitor cells. The number of progenitor cells from transduced CD34-positive cells increased 50-fold after cytokine prestimulation with interleukin-1 (IL-1), c-kit ligand (KL; stem cell factor), and IL-3 and 2 weeks in liquid culture. Transduced colony-forming unit-granulocyte-macrophage (CFU-GM), assayed directly after the transduction procedure, were protected completely against 2 x 10(-8) mol/L MTX, a concentration that significantly reduced the CFU-GM detected in the control population. Gene transfer of the mutant DHFR led to a twofold selective advantage for a pre-CFU population after exposure to MTX in liquid culture (P < .001). Polybrene, in contrast with protamine, significantly inhibited the expansion of progenitors. The presence of proviral DNA was monitored by polymerase chain reaction (PCR) and was detected in greater than 80% of CFU-GM and ex vivo expanded pre-CFU. We have demonstrated that human hematopoietic precursor cells can be expanded extensively after retroviral gene transfer. The same population of early progenitors can be selected ex vivo with low-dose MTX. As long-term expression of transduced genes in human hematopoietic cells remains a problem in vivo, these results may have implications for future clinical trials, especially for the introduction of nonselectable genes.

Antigens, CD↗
PubMed1995

Increased resistance to methotrexate in human hematopoietic cells after gene transfer of the Ser31 DHFR mutant.

Retroviral gene transfer into hematopoietic cells has many experimental as well as clinical applications. Although transduction efficiency of retroviral vectors is higher than with conventional methods, selection of successfully transduced cells may become mandatory for efficient in vivo transfer. We have been evaluating a retroviral construct that meets the criteria for a clinically acceptable selection system. The Ser31 dihydrofolate reductase (DHFR) mutant confers resistance to methotrexate (MTX) due to decreased binding of the drug. while its enzymatic activity remains adequate for normal folate metabolism. Transduction of this vector into murine hematopoietic cells has been recently described and increase in MTX resistance could be observed. We investigated transduction of CD34-antigen positive subpopulations of hematopoietic progenitor cells and CD34-positive/CD38-negative subpopulations enriched for stem cells. We focused on two sources of primary hematopoietic cells, umbilical cord blood (UCB) and peripheral blood (PB) harvested from patients after mobilization with chemotherapy and/or cytokines. Both contain a large number of lineage restricted and pluripotent progenitor cells and can be expanded extensively ex vivo. Potential clinical applications of gene therapy in such cell populations include correction of inborn enzymatic diseases and support of high-dose chemotherapy by transplanting ex vivo transduced progenitor cells rendered more resistant to cytotoxic drugs. The feasibility and efficiency of retroviral transduction into UCB and PB has been reported recently.

Antigens, CD34↗
PubMed1994

Serum cytokine levels in cancer patients treated with different schedules of ultra-low-dose interleukin-2.

Interleukin-2 (IL-2) induces secondary cytokines in vivo that may mediate antitumor effects as well as toxicity. The course and quantity of this in vivo reaction may depend on scheduling of IL-2 due to changes in responsiveness of the respective producer cells. This was evaluated in a phase-Ib study with ultra-low-dose IL-2 at 0.9 and 4.5 MIU/m2 administered once daily subcutaneously either once weekly (4 doses, stratum I), three times a week every other day (9 doses, stratum II), or five times a week every other week (10 doses, stratum III). Twenty-eight patients with advanced cancer were randomly assigned to the six treatment groups. Serum levels of IL-2, secondary cytokines, and soluble receptors were significantly increased after a single dose of 0.9 MIU/m2 s.c. demonstrating systemic efficacy. Baseline levels and native responsiveness were recovered after a 1-week treatment-free interval in stratum I patients with the exception of sCD8 that was still increased although readily inducible at that time. Stratum II patients exhibited a prolonged and possibly continuous elevation of all serum parameters studied. Values did not increase beyond the 2nd week of therapy and even decreased with respect to sCD8 and neopterin. A sequential mode of administration (stratum III) may obviate some of these adaptive mechanisms as evidenced from a progressive increase of neopterin and sCD8 levels after the second treatment cycle, although induction of sTNFRI was saturable under these conditions. Thus, scheduling of IL-2 profoundly affects in vivo responses as evidenced from cytokine and soluble receptor serum levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Structural analysis of the deoxycytidine kinase gene in patients with acute myeloid leukemia and resistance to cytosine arabinoside.

Deficiency of deoxycytidine kinase (dCK) activity represents one possible cause of resistance to cytosine arabinoside (ara-C). Mutations of the dCK gene have recently been shown to be responsible for dCK deficiency and increased resistance in vitro. In order to define the relevance of this mechanism in vivo, we analyzed the dCK gene in 16 adult patients with relapsed/refractory acute myeloid leukemia (AML) and clinical resistance to standard-dose and/or high-dose ara-C. Southern blot analysis using genomic DNA from peripheral blood or bone marrow samples containing > or = 70% leukemic blasts and agarose gel electrophoresis of cDNA obtained by RT-PCR did not reveal gross rearrangements of the dCK gene. Sequencing of the dCK coding region showed point mutations in seven patients. Besides two silent mutations (or RFLPs) in codon 42 and 86, base pair mutations resulting in amino acid replacements were found in five patients affecting codon 20, 93, 98, 99, and 154, respectively. dCK cDNA clones from three patients with > or = 50% of sequenced clones revealing the specific base pair alteration were bacterially expressed in E. coli and analyzed for dCK activity. Normal enzyme activity was found in two patients (codon 20 and 98), and a complete loss of activity in one patient (codon 99). We conclude that structural alteration of the coding region of the dCK gene represents one possible mechanism for ara-C resistance in vivo, but, considering the frequency of this event, other mechanisms may play a more important role for clinical resistance to ara-C in patients with AML.

Adult↗
PubMed1993

Immunomodulatory effects of ultra-low-dose interleukin-2 in cancer patients: a phase-IB study.

High-dose interleukin-(IL-2) has been broadly studied in tumor therapy, yet it may be inhibitory to T-cell-dependent immunity. Therefore immune and tumour responses mediated by low-dose IL-2 were studied systematically with respect to the feedback organisation of immune responses. IL-2 was administered once daily at three dose levels: 0.18, 0.9, 4.5 MIU/m2 according to three different schedules requiring subcutaneous (s.c.) injection once weekly (four doses, stratum I), thrice weekly every other day (nine doses, stratum II), or five times weekly every other week (ten doses, stratum III). A total of 46 patients with advanced cancer were randomly assigned to one of the nine treatment groups. Systemic effects were induced at doses as low as 0.18 MIU/m2 IL-2 s.c. as demonstrated from measurable IL-2 serum levels, induction of circulating IL-6, a transient lymphopenia, and stimulation of delayed-type hypersensitivity (DTH) responses of the skin. Analysis of the different IL-2 schedules demonstrated (a) prolonged effects of once-weekly injections on DTH responses, lymphocyte and eosinophil counts, and (b) maximum increase of eosinophil counts and preferential expansion of activated NK cells with repeated injections every 48 h or 72 h (stratum II), while sequential treatment according to stratum III was found to be more potent in increasing the number of activated T cells. A tumour response was observed in 1/15 patients with renal cell carcinoma who experienced more than 50% tumour regression for 8 months; 12 patients had stable disease for 4 months (median). These data demonstrate prolonged immunological effects of ultra-low doses of s.c. IL-2 despite its short half-life. Furthermore, scheduling of IL-2 was found to affect immune responsiveness specifically as demonstrated by the differential effects on natural killer and T cell populations.

Adult↗
PubMed1992

Morphometric investigation of human myocardium in arterial hypertension and valvular aortic stenosis.

UNLABELLED: Both arterial hypertension and aortic stenosis lead to pressure overload of the left ventricle. As intramyocardial vasculature is confronted with pressure overload in hypertension but not in aortic stenosis, structural differences are to be expected in both forms of left ventricular hypertrophy. With the aid of morphometry, we investigated human myocardium from autopsied hearts from six patients with arterial hypertension and 10 controls, as well as myectomy specimens from cardiac surgery from 14 patients with aortic stenosis. Mean left ventricular myocytic diameter was significantly (P less than 0.05) increased compared with controls (12.4 +/- 1.5 microns) during hypertension (+27%) as well as aortic stenosis (+65%) (P less than 0.05). This was combined with a greater volume density of perimyocytic fibrosis (controls = 0.8 +/- 0.4 V upsilon %) during hypertension (+250%) and aortic stenosis (+587%) (P less than 0.05). Walls of intramyocardial arterioles (external diameter 20-40 and 40-80 microns) were thickened to 32% and 44% (P less than 0.05) during hypertension, but not during aortic stenosis. Compared with controls, perivascular fibrosis of these arterioles was increased by +215% and 61% (P less than 0.05), respectively, during hypertension, but not during aortic stenosis. CONCLUSIONS: Myocytic hypertrophy and increased perimyocytic fibrosis accompany intraventricular pressure overload (hypertension and aortic stenosis) in human hearts. Myocardial structure as a result of arterial hypertension, but not aortic stenosis, is also characterized by intramyocardial arteriole wall-thickening and increased perivascular fibrosis. Thus, distinct structural reaction patterns are noted in the cardiac hypertrophy associated with hypertension and aortic stenosis.

Aged↗
PubMed1990

Recombinant human granulocyte-macrophage colony-stimulating factor and low-dose cytosine-arabinoside in the treatment of patients with myelodysplastic syndromes. A phase II study.

As part of a multicenter trial 12 patients with myelodysplastic syndromes (MDS) were treated with 14-day-cycles of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF; 250 micrograms/m2 day s.c.). In addition, all patients received 20 mg/m2/day s.c. cytosine-arabinoside (Ara-C) 12 h after GM-CSF except for patients suffering from refractory anemia (RA) according to FAB classification. Courses were repeated after 4 weeks. In 11 evaluable patients, results according to FAB-classified MDS were as follows: RA, 1/2 response (R), 1/2 stable disease (SD); RAEB, 2/3 R, 1/3 SD; RAEB-T, 1/6 CR, 1/6 PR, 2/6 R, 2/6 progression; CMML, 1/2 SD. In 2 patients with RAEB-T, overt acute myeloid leukemia was observed 2 and 10 weeks after initiation of treatment. With few exceptions, treatment resulted in a prompt increase in granulocytes and eosinophiles. This was associated with improvement of infectious complications. Increases in red cells and platelets occurred variably and was apparently associated with responses of the underlying disease. Dose limiting side effects consisted of fever, severe fatigue and dolent local reactions at the site of GM-CSF injection. In addition, nausea and diarrhoea occurred frequently. Less often, respiratory and cardiovascular side effects were encountered. In summary, GM-CSF +/- Ara-C in MDS results in objective remission with manageable toxicity. Conceivably, this regimen will serve as a base for future treatment strategies against MDS.

Colony-Stimulating Factors↗
PubMedDate not supplied

Subcutaneous low dose arabinosyl-cytosine and oral idarubicin in high risk adult acute myelogenous leukemia.

In order to further explore low dose chemotherapy for high risk acute myelogenous leukemia (AML), low dose Ara-C and oral idarubicin (LAI) were given to 33 patients of 24-84 (median 66) years with AML after myelodysplastic syndrome (MDS) (12 patients), refractory AML (13 patients), and AML with contraindications to intensive chemotherapy (8 patients). Patients received 1 to 4 cycles of Ara-C 10 mg/m2 q 12 h s.c. inject. on days 1-14 and idarubicin 20 mg/m2/d orally days 3, 4, 5. Three Three patients attained complete remission, four patients partial remission and one patient minor response, whereas 11 patients succumbed to early mortality from hemorrhage (two patients) and/or infections (10 patients). Three of 13 patients with heavily pretreated refractory AML went into remission compared to 3/12 with AML after MDS and 1/8 with AML and contraindications against intensive treatment. Median duration of CR is 102 (70-488 +) days. Thirty-two of 33 patients developed grade 4 hematological toxicity requiring platelet transfusions. The non-hematologic toxicity was acceptable. LAI provides a standardized therapeutic option especially for heavily pretreated patients with AML.

Administration, Oral↗
PubMedDate not supplied

Fanconi anemia and beta c deficiency-associated pulmonary alveolar proteinosis as two hereditary diseases of childhood which are potentially curable by stem cell gene therapy but require different therapeutic approaches.

Fanconi anemia (FANC) and pulmonary alveolar proteinosis associated with deficiency of the beta-chain common to the GM-CSF/IL3/IL5 receptors (beta c-PAP) are rare inherited disorders of childhood or adolescence. Hematopoietic stem cell gene therapy aiming at reintroducing the wildtype cDNA as a new concept for the treatment of hereditary diseases may be applicable to FANC and PAP, as both disorders can be successfully treated by allogeneic stem cell transplantation. However, there are important distinctions to be made between the two diseases: FANC seems to be a disorder with functional stem cell deficiency. Thus, introduction of the wildtype cDNA should provide an in vivo growth advantage to genetically corrected stem cells so that corrected cells and their progeny may expand in vivo and slowly repopulate the entire hematopoietic system. In beta c-PAP, the defect has no major impact on proliferation or differentiation of stem cells. Therefore, introduction of the wildtype gene will probably not provide any selective growth advantage and the percentage of corrected cells in the hematopoietic compartment depend on the percentage of stem cells initially transduced as the current technology only allows for transduction of stem cells with low efficiency. The introduction of a second selectable cDNA into the vector might be used to provide selective growth for modified cells and thus overcome a low gene transfer efficiency of stem cells. The correction of rare monogenetic diseases may serve as a model for gene therapy prior to attempts to treat more common and complex polygenetic diseases. The studies outlined here will be helpful envisioning new treatment strategies for other inherited monogenetic diseases such as mucopolysaccharidosis, Gauchers disease or adrenoleukodystrophy.

Animals↗
PubMedDate not supplied

Role of angiogenesis inhibitors in acute myeloid leukemia.

Neovascularization is increasingly recognized as an important factor in the pathogenesis of hematologic malignancies as well as solid tumors. The complex interactions between several cell types and numerous cytokine mediators suggest the involvement of autocrine and paracrine signaling mechanisms. Vascular endothelial growth factor (VEGF) in particular is critical to both stimulation of leukemic growth and proliferation of endothelial cells. Tyrosine kinase receptors specific for certain growth factors represent attractive target molecules for anticancer therapy. SU5416 is a competitive inhibitor of VEGF receptor subtypes VEGFR-1 and VEGFR-2 and stem cell factor receptor c-kit. Preclinical evidence shows that SU5416 effectively inhibits VEGF-induced endothelial cell proliferation and slows growth of subcutaneous solid tumor xenografts. This agent is in late-stage clinical trials in patients with solid tumors, and a Phase 2 study was recently initiated to evaluate its utility in the treatment of acute myeloid leukemia. In this Phase 2 study, investigators are seeking to determine the response rate to the antiangiogenic agent SU5416. Translational research in this study is intended to aid our understanding of the precise mechanisms by which SU5416 affects acute myeloid leukemia cells and the bone marrow microenvironment.

Acute Disease↗