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T de Witte

Publications and source records attributed to T de Witte.

At least 91 records · Page 5Linked to original sources
PubMed1995

Cytotoxic potency of CD22-ricin A depends on intracellular routing rather than on the number of internalized molecules.

Cytotoxicity of immunotoxins (ITs) varies considerably depending on factors like the capability of the target antigen to internalize IT molecules, intracellular processing and routing of the IT. We studied factors that may influence cytotoxicity of CD22-ricin A IT to several B cell lines. The antigen density varied from 5.9 x 10(3) to 6.0 x 10(4) molecules/cell. The ID50, determined by protein synthesis inhibition, varied from 2.1 x 10(-12) to 3.8 x 10(-11) M IT in absence and from 2.8 x 10(-14) M to 5.2 x 10(-12) M IT in presence of the cytotoxicity enhancer NH4Cl (6 mM). In absence as well as in presence of NH4Cl no correlation could be found between antigen density and ID50. No relation was observed either with the rate of cytotoxicity. Even in cell lines with a low antigen density, such as KM3, protein synthesis was quickly inhibited. In order to investigate whether the cytotoxicity was dependent on the number of internalized molecules the kinetics of internalization and exocytosis of degraded 125I-labelled CD22 molecules were studied. After 24 h the number of internalized CD22 molecules was highest in Ramos (154,500), followed by Daudi (110,300) and KM3 (69,900). However, despite the higher internalization rate of Daudi the rate of cytotoxicity of 10(-8) M IT was comparable with KM3. NH4Cl did not influence the number of internalized molecules but postponed degradation of CD22. In conclusion, CD22-ricin A is a very potent and fast acting IT even for elimination of target cells that express low numbers of antigen. These results may have implication for treatment of different B cell malignancies with CD22-ricin A.

Ammonium Chloride↗
PubMed1995

Intensive chemotherapy for poor prognosis myelodysplasia (MDS) and secondary acute myeloid leukemia (sAML) following MDS of more than 6 months duration. A pilot study by the Leukemia Cooperative Group of the European Organisation for Research and Treatment in Cancer (EORTC-LCG).

We conducted a prospective, multicenter pilot study of remission induction therapy in patients with poor prognosis MDS and AML evolving from a preceding phase of MDS. Fifty evaluable patients from 15 institutions were treated with one or two remission-induction courses consisting of i.v. idarubicin 12 mg/m2/day on days 1, 2, and 3 combined with a continuous i.v. infusion of cytarabine of 200 mg/m2/day on days 1 to 7. Of the 27 complete remitters (54%), 23 received a consolidation course which was identical to the remission-induction course except for the idarubicin 12 mg/m2 which was given on day 1 only. Fifteen patients received maintenance therapy consisting of six courses of cytarabine 10 mg/m2, s.c. twice daily, for 14 days. Two complete remitters were allografted and five patients received an ABMT. The median survival of all 50 treated patients was 14 months. The median duration of disease-free survival was 11 months with two patients in CR more than 2 years after entering CR. Twenty-four of the 27 remitters have relapsed. Four patients died during remission-induction therapy, but no patient died as a result of persisting hypoplasia. No fatal complications occurred during the consolidation and maintenance courses. Age and stage of disease had no significant impact on CR rate nor on remission duration. The CR rate was significantly (P = 0.03) higher in patients with only normal metaphases compared to patients with cytogenetic abnormalities. The DFS at 2 years was 33 vs 8%, respectively, for patients without or with cytogenetic abnormalities (P = 0.02). This study shows that patients below the age of 60 years with poor risk features are candidates for treatment with combination chemotherapy. A complete remission rate of more than 50% may be expected. Maintaining remission after remission-induction chemotherapy is a difficult issue. Patients not eligible for allogeneic BMT may be treated with intensive post-remission chemotherapy or autologous BMT.

Adolescent↗
PubMed1995

Erythrocyte repopulation after major ABO incompatible transplantation with lymphocyte-depleted bone marrow.

Forty-four out of 258 allogeneic BMT were performed across the major ABO barrier. Donor erythrocyte repopulation could be evaluated in 30 cases. Fifty-eight patients transplanted with an ABO compatible or minor incompatible graft served as the control group. All patients received a marrow graft depleted of lymphocytes by counterflow centrifugation. Less than 10(8) residual erythrocytes were present in the graft. Cyclosporin A was used as immunoprophylaxis after transplantation. Erythrocyte repopulation was measured using a fluorescent microsphere method. An adapted transfusion policy was applied. Eight out of 30 patients (27%) with major ABO incompatibility had no detectable donor erythrocytes 2 months after BMT. Up to 3 months after BMT donor erythrocyte repopulation was significantly delayed in the ABO incompatible group (P < or = 0.03). Significantly more erythrocyte transfusions were required in the ABO incompatible group (P < 0.001). Six patients with blood group O (20%) developed pure red cell aplasia which resolved in five without therapeutic intervention. In these six patients anti-A antibody titers were persistently high the first 3 months after BMT. This was in contrast with 22 patients with timely recovery of erythropoiesis in whom anti-A and anti-B antibody titers showed a steady decrease after BMT. The incidence of immunohematological complications in these patients who received a lymphocyte depleted major ABO incompatible graft is similar (20%) to the incidence reported in the literature. Serious morbidity related to major ABO incompatibility did not occur.

ABO Blood-Group System↗
PubMed1994

Effect of isotype on internalization and cytotoxicity of CD19-ricin A immunotoxins.

We analyzed the effect of isotype variation on effectiveness of B-cell CD19 immunotoxins (IT) by using class switch variants (CLB-B4-IgG1 and CLB-B4-IgG2a) conjugated to ricin A. Notably, IgG1-IT appeared to be approximately 100-fold more potent than IgG2a-IT toward B-cell lines Daudi and KM3. Binding and internalization studies with 125I-labeled monoclonal antibodies (mAbs) revealed a higher cellular uptake of IgG1 compared to IgG2a, despite similar binding affinities. Following removal of the Fc part, both mAbs internalized at the same rate as IgG2a, indicating that the Fc part of IgG1 is involved in enhanced cellular uptake. The involvement of Fc gamma RII (CD32) in this process was demonstrated by a decreased cytotoxicity of IgG1-IT (and not IgG2a-IT) in the presence of Fc gamma RII-blocking mAbs AT10 or IV.3. To identify the isoform responsible for this phenomenon, internalization of IgG1 and IgG2a in 11 B-cell lines and malignant B-cells of 8 patients was compared with expression of Fc gamma RII subclasses. In addition to four cell lines (Daudi, KM3, Nalm6, and Raji), the malignant B-cells of two patients showed enhanced uptake of IgG1 relative to IgG2a. Only the Fc gamma RIIa transcript was found in all B-cells. Furthermore, enhanced uptake of IgG1 correlated with rosetting of erythrocytes sensitized with anti-glycophorin A mAb of IgG1 isotype rather than with Fc gamma RIIa membrane expression levels. These data support the idea that functional Fc gamma RIIa is involved in the enhanced IgG1 uptake observed in a subset of B-cells. Our study, therefore, points to an important role for the Fc region of IT in the delivery of cytotoxic effects.

Antibodies, Monoclonal↗
PubMed1994

Quantitation of follicular non-Hodgkin's lymphoma cells carrying t(14;18) in a patient before and after allogeneic bone marrow transplantation.

BACKGROUND: A competitive PCR method was developed, enabling accurate quantitation of residual lymphoma cells carrying the t(14;18) in blood and bone marrow samples of follicular non-Hodgkin's lymphoma (NHL) patients during treatment. PATIENTS AND METHODS: A patient with residual lymphoma cells received an allogeneic bone marrow transplantation (BMT). Since BMT, the patient has been in continuing clinical complete remission. RESULTS: Using the competitive PCR and two-step PCR method, we were able to demonstrate a gradual decline in the number of lymphoma cells within consecutive patient blood and bone marrow samples after BMT. CONCLUSIONS: The competitive PCR is a suitable method for the detection of minimal residual disease. Further research might reveal the clinical relevance of data obtained by this method.

Adult↗
PubMed1994

Primitive multilineage progenitor cells predominate in peripheral blood early after mobilization with high-dose cyclophosphamide and GM-CSF or G-CSF.

The change in phenotype, number and proliferative capacity of peripheral blood hematopoietic progenitors (PBHP) was studied in six patients with multiple myeloma during hematopoietic recovery after mobilization with high-dose cyclophosphamide and GM-CSF or G-CSF. In all six patients the first CD34+ cells appearing in the peripheral blood (PB) after cytoreductive treatment were predominantly CD34+/33- (> 70%). At later stages when leukapheresis procedures were started, the CD34+/33+ cells predominated in five of six patients. In leukapheresis harvests of peripheral blood, and in bone marrow addition of SCF and IL-6 to the culturing medium enhanced the plating efficiency. In peripheral blood an increase from 12 to 22% for CD34+/33+ and from 6 to 14% for CD34+/33- was observed. In normal bone marrow we observed an increase from 15 to 23% for CD34+/33+ and from 7 to 17% for CD34+/33-. Highly proliferative progenitors (>500 cells) in the CD34+/33- fraction appeared to be dependent on the addition of 'stem cell recruiting factors' (SCF and IL-6); in bone marrow the percentage of wells with >500 cells increased from 0.9 to 12.6% after SCF+IL-6 and in PBHP from 2 to 9%. We conclude that the first progenitors appearing in the peripheral blood after priming with high-dose cyclophosphamide and GM- or G-CSF have a more primitive immunophenotype, CD34+/33-.

Adult↗
PubMed1994

Treatment of patients with acute promyelocytic leukemia. The EORTC-LCG experience. EORTC Leukemia Cooperative Group.

Acute promyelocytic leukemia (M3) is, as one of the FAB subtypes of AML, included in the EORTC/GIMEMA AML-8A and 8B randomized trials. In these trials 1519 patients were included, 477 of them in non-Italian EORTC-LCG centers and 1042 in GIMEMA centers. A total of 80 patients were classified as M3 including 18 patients with M3-variant. Thirty-nine were male and 41 female. Ages ranged from 15 to 59 years; 25 (31.3%) of them were younger than 30, 34 (42.5%) between 30 and 45, and 21 (26.3%) older than 45 years of age. 56.3% of the patients had leukocytes less than 5 x 10(9)/l at the time of diagnosis vs. 24.9% of the patients belonging to the other FAB subtypes. Remission induction consisted of a standard protocol with 3 days daunorubicin and 7 days of cytosine arabinoside. Forty-three patients (53.8%) achieved a complete remission compared to 64.6% of the remaining AML patients. After salvage treatment this percentage increased to 70%, which is the same as for the other AML subtypes. Thirteen (16.3%) patients died during remission induction, mainly due to hemorrhagic complications. This percentage is significantly higher than the death rate (9.1%) in the other FAB subtypes of AML. All patients received one course of consolidation treatment. Post consolidation treatment could be either standard maintenance, intensive consolidation courses, autologous or allogeneic transplantation, according to the guidelines of the treatment protocols. At present, relapses almost all in the bone marrow, are seen in only 34.9% of the M3 patients, compared to 48.4% in the remaining AML patients. Disease-free survival for patients less than 45 years of age with the M2 and M3 subtypes was approximately 50% at 3 years compared to 30-40% for the other FAB subtypes. Despite the higher death rate during induction, the long-term survival results were better for M3 patients in comparison with the remaining AML patients. The projected survival at 3 years was 50% for M3 patients vs. 38% for remaining patients.

Adolescent↗
PubMed1994

Toxicity of idarubicin and doxorubicin towards normal and leukemic human bone marrow progenitors in relation to their proliferative state.

The effect of growth stimulation on the sensitivity of normal and leukemic human bone marrow progenitors to idarubicin and doxorubicin was studied. Clonogenic assays from colony-forming units of the granulocyte-macrophage lineage (CFU-GM) and leukemic clonogenic cells (CFU-L) were applied using human placenta conditioned medium (HPCM) as source of growth factors. Before seeding cells in clonogenic assay they were exposed to the anthracyclines for 2 h without preincubation, or following a 48 h preincubation period in the presence of HPCM. Drug concentrations used ranged from 0.001-0.1 microgram/ml for idarubicin and from 0.1-1.5 microgram/ml for doxorubicin. In addition, a limited number of bone marrow samples were exposed to the cytostatically active metabolite of idarubicin; idarubicinol (Idol; range 0.001-0.1 microgram/ml). Proliferation of CFU-GM and CFU-L during 48 h was measured by iododeoxyuridine (IdUrd) incorporation. Spontaneous proliferation of CFU-GM increased from 38 to 88% after 48 h stimulation by HPCM. The mean number of proliferating CFU-L increased from 40 to 77% when stimulated with HPCM. Doxorubicin inhibited colony formation of CFU-GM and CFU-L to 50% (IC50CFU-GM, IC50CFU-I) at mean concentrations of 0.355 microgram/ml and 0.103 microgram/ml when applied before preincubation with HPCM, and 0.108 microgram/ml and 0.055 microgram/ml when applied after preincubation. Idarubicin appeared the most potent drug in all experiments regardless of the preincubation procedure or sample origin, with average IC50CFU-GM and IC50CFU-L of 0.008 microgram/ml and 0.006 microgram/ml, respectively, when applied before preincubation with HPCM, and 0.006 microgram/ml and 0.005 microgram/ml when applied after preincubation with HPCM. Idarubicinol showed intermediate potency with average IC50CFU-GM of 0.022 microgram/ml and 0.023 microgram/ml when applied before and after preincubation with HPCM, respectively. In order to assess the effect of growth stimulation on drug sensitivity, samples were evaluated pair-wise (sensitivity of the same sample before vs. after preincubation with HPCM) and were submitted to the Wilcoxon test for matched pairs. Statistically significant enhancement of cytotoxicity was demonstrated for Doxorubicin vs. CFU-GM (p < or = 0.021) and a strong trend versus CFU-L (p = 0.06). The data further demonstrate that proliferation-dependency of doxorubicin toxicity is more pronounced for CFU-GM than for CFU-L. These data also show that idarubicin and idarubicinol toxicity is proliferation-independent. Idarubicin is relatively more potent than doxorubicin in suppressing the growth potential of low or nonproliferating progenitors.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗
PubMed1994

Antisense BCR-ABL oligonucleotides induce apoptosis in the Philadelphia chromosome-positive cell line BV173.

BCR-ABL antisense oligonucleotides can specifically reduce colony formation of early hematopoietic progenitor cells from chronic myeloid leukemia (CML) patients. Little is known about the mechanism of this inhibition. We studied the inhibition of the bcr-abl oncogene using fluorescein-labeled phosphorothioate oligonucleotides in the Philadelphia chromosome-positive cell line BV173. Oligonucleotide stability, uptake, bcr-abl mRNA degradation, inhibition of cell proliferation, and cell death were studied. The oligonucleotide uptake was directly dependent on the extracellular concentration and was constant over the first 18 h of incubation. After that the uptake rate decreased. We detected a decrease in bcr-abl mRNA after 3 days of treatment with antisense oligonucleotides, but much less in controls. The controls used in the experiments were the sense oligonucleotide, equimolar amounts of sense and antisense, and an untreated control. Antisense oligonucleotides completely inhibited cell growth of BV173 cells and did not inhibit growth of HL-60 cells, whereas control oligonucleotides had no such effect on either cell line. An oligonucleotide specific for the other CML breakpoint was also effective in reducing cell growth of BV173. By the use of a DNA double staining technique to discriminate between necrotic and apoptotic cells, we detected a large number of apoptotic cells in antisense treated BV173 cultures after 5 days of treatment as compared to controls. We conclude that antisense BCR-ABL oligonucleotides reduce bcr-abl mRNA expression in BV173 cells mainly in a sequence-specific manner and induce apoptosis.

Apoptosis↗
PubMed1994

A randomized phase II study of low-dose cytosine arabinoside (LD-AraC) plus granulocyte-macrophage colony-stimulating factor (rhGM-CSF) in myelodysplastic syndromes (MDS) with a high risk of developing leukemia. EORTC Leukemia Cooperative Group.

In a randomized phase II study, patients with myelodysplastic syndromes (MDS) with 10-30% blasts in the bone marrow and hematopoietic failure were treated with low-dose Ara C (2 x 10 mg/m2 subcutaneously (s.c.) days 1-14) and rhGM-CSF (fully glycosylated, Sandoz/Schering-Plough, 2 x 150 micrograms protein/day s.c.) given either following Ara C (days 15-21) or simultaneously (days 8-14) for 1-5 cycles. 108 patients with a median age of 65 years, range 17-80 years and refractory anemia with an excess of blasts (RAEB, n = 54), RAEB with transformation (RAEBt, n = 50) or with chronic myelomonocytic leukemia (CMML, n = 4) were evaluable. Complete remission was achieved in 15 cases (14%), 11 had a partial response (10%), and 16 a minor response (15%). Stable disease was reached in 35 cases (32%). There were 16 cases of toxic death (15%), progression occurred in 15 patients (14%). No differences existed between the two treatment arms with respect to response and duration of response. Prognostic factors for poor response included the presence of cytogenetic abnormalities and a history of previous blood transfusions. Major adverse events during treatment were hemorrhage (55%), infections (54%), and fever associated with GM-CSF administration (40%). The overall response rate ws 39%, median duration was 12.5 months from start of treatment which allowed responding patients to lead good quality life without further therapy. The question whether the combination is indeed superior to LD-Ara C alone is not settled but will be evaluated in an ongoing clinical trial.

Acute Disease↗
PubMed1993

Outcome after allogeneic bone marrow transplant for leukemia in older adults.

OBJECTIVE: To determine whether age over 40 years is associated with adverse outcome after allogeneic bone marrow transplantation for leukemia. DESIGN: A retrospective analysis of outcome after bone marrow transplants for leukemia reported to the International Bone Marrow Transplant Registry (IBMTR) among recipients 30 through 39 years, 40 through 44 years, 45 through 49 years, and 50 years of age and older. SETTING: Transplantations performed in 138 institutions worldwide and reported to the IBMTR. PATIENTS: A total of 2180 recipients of HLA-identical sibling bone marrow transplants for leukemia, divided into four cohorts based on age: 30 through 39 years (n = 1282), 40 through 44 years (n = 527), 45 through 49 years (n = 291), and 50 years and older (n = 80). MAIN OUTCOME MEASURES AND RESULTS: Incidence of leukemia-free survival, graft-vs-host disease, and relapse was comparable among the four age cohorts. Patients with advanced leukemia aged 45 years or older had a slightly higher risk of treatment-related mortality, and the 45- through 49-year-old cohort had a higher risk of interstitial pneumonia. CONCLUSIONS: These data indicate that among leukemia patients over 30 years of age at the time of allogeneic bone marrow transplantation, increasing age into the fifth decade does not adversely affect outcome after transplants from HLA-identical siblings.

Adult↗
PubMed1993

Pentostatin in prolymphocytic leukemia: phase II trial of the European Organization for Research and Treatment of Cancer Leukemia Cooperative Study Group.

BACKGROUND: B-cell prolymphocytic leukemias or T-cell prolymphocytic leukemias are aggressive variants of chronic lymphoid leukemias. The small studies conducted to date have shown median survival durations of approximately 3 years for patients who have B-cell prolymphocytic leukemia and 7.5 months for those who have T-cell prolymphocytic leukemia, compared with about 8 years for patients who have chronic lymphocytic leukemia. In chronic lymphocytic leukemia, chemotherapy consisting of alkylating agents such as cyclophosphamide and chlorambucil combined with prednisone has achieved overall response rates of 50% to 70%, but this regimen has resulted in response rates of less than 25% in prolymphocytic leukemia. Pentostatin (2'-deoxycoformycin; DCF) is a purine analogue that has shown activity in treatment of chronic lymphoid malignancies. PURPOSE: This prospective phase II trial by the Leukemia Cooperative Group of the European Organization for Research and Treatment of Cancer was performed to assess the activity and toxicity of DCF in prolymphocytic leukemia. METHODS: Twenty patients with B-cell or T-cell prolymphocytic leukemia were given DCF at a dosage of 4 mg/m2 intravenously once a week for 3 weeks, then every other week for three doses. Patients who had at least partial response received maintenance therapy once a month for a maximum of 6 months. Fourteen patients had B-cell prolymphocytic leukemia, and six had T-cell prolymphocytic leukemia, as evidenced by morphologic and immunologic criteria; three were previously untreated, eight had been given one or two chemotherapeutic regimens, and nine had been given more than two. RESULTS: One patient died of an unknown cause during the first 6 weeks of treatment, and one died of disseminated toxoplasmosis during the period of maintenance therapy, 5 months after achieving partial remission. Nine (45% response rate) of the 20 patients achieved partial remission, including seven (50%) of 14 with B-cell prolymphocytic leukemia and two (33%) of six with T-cell prolymphocytic leukemia. The median duration of response was 9 months (range, 2-30 months); for patients with B-cell prolymphocytic leukemia, the median remission duration was 12 months. No complete remission was observed. Toxic effects included nausea and vomiting (30%), infections (30%), and transient increase in liver enzymes (35%) and in creatinine (20%) levels. Eight patients experienced thrombocytopenia, the major hematologic toxic effect; four had grade 3 or 4 toxic effects. CONCLUSION: DCF is active in prolymphocytic leukemia, even as salvage therapy in patients who had received multiple prior chemotherapeutic regimens. IMPLICATIONS: Trials using DCF or other purine analogues alone or in combination with standard chemotherapeutic agents in front-line or salvage therapy are warranted to improve the prognosis of patients with prolymphocytic leukemia.

Adult↗
PubMed1993

Proliferation patterns in acute myeloid leukemia: leukemic clonogenic growth and in vivo cell cycle kinetics.

In a prospective study of 33 newly diagnosed patients with acute myeloid leukemia (AML), we analyzed the relationship of proliferation parameters with clinical parameters, response to induction therapy, and survival. The median follow-up was 26 months. The proliferative capacity of the leukemic progenitor cells was studied using colony-forming assays (number of colony-forming units, growth pattern, and spontaneous clonogenic growth capacity). The cell kinetic parameters of the bone marrow blasts were determined by in vivo labeling with iododeoxyuridine and subsequent flow cytometry: labeling index (LI), DNA synthesis time (Ts), potential doubling time. No or only weak relationships were observed between the experimental and clinical parameters such as age, sex, % blasts, white blood cell count, FAB subtype, cytogenetics, and % CD 34+ cells. This suggests that clonogenic growth and cell cycle kinetics of bone marrow blasts are independent cell biologic properties of AML. No association between the proliferation parameters and induction response rate was noticed. Analysis of the overall survival and event-free survival revealed trends to longer survival rates in patients with a below-median LI (< or = 7.6%) and below-median Ts value (< or = 14.3 h). These trends were more pronounced in the group of de novo AML (n = 23), where the prolonged event-free survival in patients with below-median Ts reached statistical significance (p = 0.02). None of the other parameters appeared significantly correlated with survival, although there was a trend to longer survival rates in patients who had no spontaneous clonogenic growth capacity (p = 0.13). In conclusion, proliferation parameters in leukemic cells provide additional information on the cell biologic characteristics of AML, and these parameters may have prognostic value for response and duration of survival in AML.

Adult↗
PubMed1993

Bone marrow transplantation for acute myeloblastic leukaemia: an EBMT Leukaemia Working Party prospective analysis from HLA-typing.

The optimal post-remission therapy for patients with acute myeloblastic leukaemia remains controversial. Allogeneic bone marrow transplantation, autologous bone marrow transplantation, and consolidation chemotherapy are the major options. In order to evaluate their respective value the European Group for Bone Marrow Transplantation conducted a prospective registration study. Patients with newly diagnosed acute myeloblastic leukaemia were registered at the time of HLA-typing and intention to treat in case of presence or absence of an HLA-identical donor was recorded. 27/79 (34%) patients HLA-typed at diagnosis had an identical donor identified. The estimated survivals at 3 years from HLA-typing were 44% and 21% among patients with or without HLA-identical donor, respectively (P = 0.02). 22/26 (85%) patients for whom allogeneic bone marrow transplantation was intended were transplanted but only 15/47 (32%) patients for whom autologous bone marrow transplantation was intended were indeed transplanted (P < 0.001). The survival was 50%, 29% and 17% (P = 0.004) for patients treated with allogeneic bone marrow transplantation, autologous bone marrow transplantation, or chemotherapy, respectively. 40/68 patients HLA-typed in first complete remission had an HLA-identical donor. The estimated 3-year survival among patients typed in first remission with and without HLA-identical donors was 42% and 35% (n.s.), respectively. This technique of early patient registration illustrates the problems of patient selection during the course of the disease and might be used as a complement to randomized trials when comparing bone marrow transplantation and other treatment options.

Adolescent↗