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Michael Hallek

Publications and source records attributed to Michael Hallek.

At least 19 recordsLinked to original sources
PubMed2026

Proteolytic activation of executioner caspase-3 and -7 regulates different physiological processes in mice.

Caspase-3 (CASP3) and caspase-7 (CASP7) are the two major executioner caspases that are proteolytically activated by upstream initiator caspases. They possess almost indistinguishable activity, which has led to the overall view that these caspases have functionally redundant roles. Here, we generate knock-in mice expressing cleavage-resistant CASP3(D175A) or CASP7(D198A). Our results show that proteolytic activation of CASP3 and CASP7 is decisive for their activity in vivo and controls redundant processes during embryonic development as combined expression of both CASP3(D175A) and CASP7(D198A) causes embryonic lethality. In adult mice, however, activation of CASP3 and CASP7 controls different processes in different tissues, without the involvement of apoptosis. While CASP7 activation is required for male fertility by controlling spermatogenesis, CASP3 activation appears crucial for lymphoid tissue development by regulating interferon signalling. Our findings shed light on emerging roles of caspases in non-apoptotic processes and provide impetus for reconsidering their involvement in physiological and pathological conditions.

Animals↗
PubMed2026

MRD-2 in the GHSG HD21 trial assessed by a validated circulating tumor DNA sequencing assay.

Beyond cure, major goals in patients with Hodgkin lymphoma (HL) are tailoring treatment to a patient's individual risk for relapse to reduce acute and late toxicities, identifying candidates for early incorporation of novel agents, and making treatment affordable on a global level. Minimal residual disease (MRD) assessment by circulating tumor DNA (ctDNA) sequencing emerged as a promising strategy to achieve these goals; however, previous studies differed in sampling time points, assay validation, and definitions for MRD negativity. Here, we applied LymphoVista, a validated ctDNA sequencing assay for genotyping and MRD monitoring in lymphoma, to samples obtained from the German Hodgkin Study Group (GHSG) HD21 trial after 2 cycles of treatment (MRD-2) using a case-cohort design. Patients with positive MRD-2 result were at higher risk for relapse, progression, or death compared with MRD-2-negative patients (4-year progression-free survival [PFS], 36.7% vs 82.2%; hazard ratio, 5.3; 95% confidence interval, 2.0-13.8; P = .0008). After inverse probability weighting accounting for the number of events in the full reference set, patients with positive and negative MRD-2 results had 4-year PFS rates of 72.2% vs 95.3%. Combining MRD-2 with positron emission tomography after 2 cycles of BrECADD/eBEACOPP (PET-2) can identify patients at very low and patients at very high risk of relapse, progression, or death. In summary, these results suggest that MRD-2 assessment by LymphoVista allows for early outcome prognostication in patients with HL and could be used as a tool to improve treatment guidance on its own or in conjunction with PET-2.

Humans↗
PubMed2005

Gene transfer preferentially selects MHC class I positive tumour cells and enhances tumour immunogenicity.

The modulated expression of MHC class I on tumour tissue is well documented. Although the effect of MHC class I expression on the tumorigenicity and immunogenicity of MHC class I negative tumour cell lines has been rigorously studied, less is known about the validity of gene transfer and selection in cell lines with a mixed MHC class I phenotype. To address this issue we identified a C26 cell subline that consists of distinct populations of MHC class I (H-2D/K) positive and negative cells. Transient transfection experiments using liposome-based transfer showed a lower transgene expression in MHC class I negative cells. In addition, MHC class I negative cells were more sensitive to antibiotic selection. This led to the generation of fully MHC class I positive cell lines. In contrast to C26 cells, all transfectants were rejected in vivo and induced protection against the parental tumour cells in rechallenge experiments. Tumour cell specificity of the immune response was demonstrated in in vitro cytokine secretion and cytotoxicity assays. Transfectants expressing CD40 ligand and hygromycin phosphotransferase were not more immunogenic than cells expressing hygromycin resistance alone. We suggest that the MHC class I positive phenotype of the C26 transfectants had a bearing on their immunogenicity, because selected MHC class I positive cells were more immunogenic than parental C26 cells and could induce specific anti-tumour immune responses. These data demonstrate that the generation of tumour cell transfectants can lead to the selection of subpopulations that show an altered phenotype compared to the parental cell line and display altered immunogenicity independent of selection marker genes or other immune modulatory genes. Our results show the importance of monitoring gene transfer in the whole tumour cell population, especially for the evaluation of in vivo therapies targeted to heterogeneous tumour cell populations.

Animals↗
PubMed2005

Transduction of CLL cells by CD40 ligand enhances an antigen-specific immune recognition by autologous T cells.

Several features of chronic lymphocytic leukemia (CLL) suggest that immune-based strategies may have therapeutic potential. A promising approach is provided by the transduction of CLL cells with CD40 ligand (CD40L) by viral vectors to enhance their immunogenicity. We compared the antigen-presenting capacity of CD40L-transduced CLL cells with mock-transduced or CD40L-stimulated CLL cells (CD40-CLL). A significantly higher number of T cells could be expanded using CD40L-transduced CLL cells as antigen-presenting cells (APCs) compared with the control group (P = .008). Using 5 different CLL-associated tumor antigens, including fibromodulin, MDM2 (murine double minute 2), survivin, p53, and KW-13, we show in interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assays after 35 days of in vitro culture that the number of antigen-specific autologous T cells was also significantly higher when CD40L-transduced CLL cells were used as APCs (P < .001). Thus, CD40L-transduced CLL cells are able to induce an antigen-specific T-cell response and might be superior to CD40-CLL cells for immune-based therapeutic strategies in CLL.

Aged↗
PubMed2005

Reduced frequencies and suppressive function of CD4+CD25hi regulatory T cells in patients with chronic lymphocytic leukemia after therapy with fludarabine.

Globally suppressed T-cell function has been described in many patients with cancer to be a major hurdle for the development of clinically efficient cancer immunotherapy. Inhibition of antitumor immune responses has been mainly linked to inhibitory factors present in cancer patients. More recently, increased frequencies of CD4+CD25hi regulatory T cells (Treg cells) have been described as an additional mechanism reducing immunity. We assessed 73 patients with B-cell chronic lymphocytic leukemia (CLL) and 42 healthy controls and demonstrated significantly increased frequencies of cytotoxic T lymphocyte-associated protein 4 (CTLA4+)-, Forkhead box P3 (FOXP3+)-, glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR+)-, CD62L+-, transforming growth factor beta1 (TGF-beta1+)-, interleukin 10 (IL-10+)-Treg cells in patients with CLL, with highest frequencies in untreated or progressing patients presenting with extended disease. Most surprisingly, in the majority of patients with CLL treated with fludarabine-containing therapy regimens the inhibitory function of Treg cells was decreased or even abrogated. In addition, frequencies of Treg cells were significantly decreased after therapy with fludarabine. In light of similar findings for cyclophosphamide the combination of fludarabine and cyclophosphamide might be further exploited in strategies reducing immunosuppression prior to cancer immunotherapy.

Adult↗
PubMed2005

Adeno-associated virus serotypes 1 to 5 mediated tumor cell directed gene transfer and improvement of transduction efficiency.

BACKGROUND: Gene therapy is an attractive new approach for the treatment of cancer. Therefore, the development of efficient vector systems is of crucial importance in this field. Different adeno-associated virus (AAV) serotypes have been characterized so far, which show considerable differences in tissue tropism. Consequently, we aimed to characterize the most efficient serotype for this application. METHODS: To exclude all influences other than those provided by the capsid, all serotypes contained the same transgene cassette flanked by the AAV2 inverted terminal repeats. We systematically compared these vectors for efficiency in human cancer cell directed gene transfer. In order to identify limiting steps, the influence of second-strand synthesis and proteasomal degradation of AAV in a poorly transducible cell line were examined. RESULTS: AAV2 was the most efficient serotype in all solid tumor cells and primary melanoma cells with transduction rates up to 98 +/- 0.3%. Transduction above 70% could be reached with serotypes 1 (in cervical and prostate carcinoma) and 3 (in cervical, breast, prostate and colon carcinoma) using 1000 genomic particles per cell. In the colon carcinoma cell line HT-29 proteasomal degradation limited AAV1-AAV4-mediated gene transfer. Moreover, inefficient second-strand synthesis prevents AAV2-mediated transgene expression in this cell line. CONCLUSIONS: Recent advances in AAV-vector technology suggest that AAV-based vectors can be used for cancer gene therapy. Our comparative analysis revealed that, although AAV2 is the most promising candidate for such an application, serotypes 1 and 3 are valid alternatives. Furthermore, the use of self-complementary AAV vectors and proteasome inhibitors significantly improves cancer cell transduction.

Cell Line, Tumor↗
PubMed2005

Efficient gene transfer of CD40 ligand into ovarian carcinoma cells with a recombinant adeno-associated virus vector.

Recombinant adeno-associated virus type 2 (rAAV) has many properties of an ideal vector for gene therapy: broad spectrum of susceptible cells, efficient gene transfer, persistent transgene expression in vivo, and no indiction of vector-related toxicity. Ovarian carcinoma cell lines, however, were previously reported to be quite resistant to rAAV transduction. Using an optimized adenovirus-free packaging system, highly purified rAAV vectors coding for the enhanced green fluorescent protein (AAV/EGFP) and for mCD40 ligand (AAV/CD40L) were generated. Their transduction efficiency in ovarian carcinoma cell lines was assessed with and without irradiation prior to infection. As measured by flow cytometry, transgene expression in up to 92% of cells was achieved with AAV/EGFP. gamma-irradiation (20 Gy) significantly increased the transduction rates up to 3.5-fold in cell lines with low susceptibility to AAV infection. The aquired capability of AAV/CD40L transduced tumor cells to activate dendritic cells was demonstrated in a second step. Dendritic cells were generated from human peripheral blood monocytes and maturized by stimulation with IL-4 and GM-CSF. Co-cultivation of mCD40L transgenic tumor cells with these dendritic cells resulted in strong ELISA-determined expression of IL-12 as an indicator of dendritic cell activation. We conclude that transduction of tumor cells with rAAV encoding mCD40L is a promising strategy for tumor immunotherapy which may be further developed to a vaccination approach with transgenic ovarian carcinoma cells generated by ex vivo transduction.

Animals↗
PubMed2005

Chronic lymphocytic leukemia: novel prognostic factors and their relevance for risk-adapted therapeutic strategies.

BACKGROUND AND OBJECTIVES: Many years ago it was established that prompt treatment of early stage chronic lymphocytic leukemia (CLL), the stage at which almost two-thirds of CLL patients present, has no benefit over a management of watching and waiting, then treating progression. However, this fact was based on series treated ineffectually with chlorambucil, which were not stratified according to prognostic markers. DESIGN AND METHODS: The prognosis and clinical course of CLL are heterogeneous. While some patients may have a normal life expectancy without requiring treatment, others die of drug-resistant disease as early as within two years of presentation. However, unlike the situation in non-Hodgkin's lymphoma, there is no standard Prognostic Index that can be used to group patients with CLL according to likely outcome or to guide treatment. RESULTS: A number of clinical and biological factors of prognostic relevance, which may add to the classical assessment provided by the staging systems, have been identified. These include clinical characteristics, such as age, gender and performance status, and laboratory parameters reflecting the tumor burden or disease activity, such as lymphocyte count, lactate dehydrogenase (LDH) increase, bone marrow infiltration pattern or lymphocyte doubling time. Recently more informative prognostic parameters have been identified: serum markers such as soluble CD23, b2-microglobulin or thymidine kinase and genetic markers of tumor cells, such as genomic aberrations, gene abnormalities (p53, ATM), the mutation status of the variable segments of the immunoglobulin heavy chain genes (IGVH) or surrogate markers for these factors, such as CD38 and ZAP-70. INTERPRETATION AND CONCLUSIONS: From the clinician's perspective the importance of this new knowledge is how it affects treatment. It is now possible to produce molecular remissions even in advanced disease using combinations of purine analogs and monoclonal antibodies. Moreover, potentially curative therapeutic modalities such as autologous and allogeneic stem cell transplantation are becoming safer. Clinical trials of effective treatment stratified by more reliable prognostic markers are surely now warranted.

Biomarkers↗
PubMed2004

Fibromodulin as a novel tumor-associated antigen (TAA) in chronic lymphocytic leukemia (CLL), which allows expansion of specific CD8+ autologous T lymphocytes.

Fibromodulin (FMOD) was shown to be highly overexpressed in chronic lymphocytic leukemia (CLL) cells compared with normal B lymphocytes by gene expression profiling. Therefore FMOD might serve as potential tumor-associated antigen (TAA) in CLL, enabling expansion of FMOD-specific T cells. In CLL samples derived from 16 different patients, high expression of FMOD by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was detectable in contrast to normal B lymphocytes. We used unpulsed native CLL cells and CD40 ligand (CD40L)-stimulated CLL cells as antigen-presenting cells (APCs) to expand autologous T cells from 13 patients. The number of T cells during 4 weeks of in vitro culture increased 2- to 3.5-fold and the number of T cells recognizing FMOD peptides bound to HLA-A2 dimers increased 10-fold. The expanded T cells also were able to secrete interferon-gamma (IFN-gamma) upon recognition of the antigen demonstrated by IFN-gamma ELISPOT assays. T cells not only recognized HLA-A2-binding FMOD peptides presented by transporter-associated with antigen-processing (TAP)-deficient T2 cells, but also FMOD overexpressing autologous CLL cells in an HLA-A2-restricted manner. In summary, FMOD was shown for the first time to be naturally processed and presented as TAA in primary CLL cells, enabling the expansion of autologous tumor-specific T cells.

Adult↗
PubMed2004

Rituximab and alemtuzumab induce a nonclassic, caspase-independent apoptotic pathway in B-lymphoid cell lines and in chronic lymphocytic leukemia cells.

The monoclonal antibodies (MoAbs) alemtuzumab (anti-CD52) and rituximab (anti-CD20) produce objective clinical responses in patients with chronic lymphocytic leukemia (CLL). However, their mechanisms of action are not fully understood. Therefore, we investigated the mechanisms of lymphoma and CLL cell killing by two anti-CD20 antibodies (rituximab, B1) and by alemtuzumab. All antibodies induced complement-independent cell death in B-lymphoid cell lines Raji, Ramos, and Mec-1. The efficiency of cell killing was increased by the addition of human complement in Raji but not Ramos cells. Both alemtuzumab and rituximab also killed freshly isolated CLL cells, with a much stronger response for alemtuzumab (from eight of eight patients) compared to rituximab (from two of six patients). Cell morphology and Western blot analyses revealed that the antibody-induced cell death lacked some typical features of apoptosis such as chromatin condensation or poly-ADP-ribose polymerase (PARP) cleavage. Taken together, the results suggest that the tumor killing activity of these MoAbs is not only mediated by complement-mediated cytotoxicity (CDC) or antibody-dependent cytotoxicity (ADCC), but also by a nonclassic, caspase-independent apoptotic pathway.

Alemtuzumab↗
PubMed2004

Requirement of Src kinases Lyn, Hck and Fgr for BCR-ABL1-induced B-lymphoblastic leukemia but not chronic myeloid leukemia.

The Abl kinase inhibitor imatinib mesylate is the preferred treatment for Philadelphia chromosome-positive (Ph(+)) chronic myeloid leukemia (CML) in chronic phase but is much less effective in CML blast crisis or Ph(+) B-cell acute lymphoblastic leukemia (B-ALL). Here, we show that Bcr-Abl activated the Src kinases Lyn, Hck and Fgr in B-lymphoid cells. BCR-ABL1 retrovirus-transduced marrow from mice lacking all three Src kinases efficiently induced CML but not B-ALL in recipients. The kinase inhibitor CGP76030 impaired the proliferation of B-lymphoid cells expressing Bcr-Abl in vitro and prolonged survival of mice with B-ALL but not CML. The combination of CGP76030 and imatinib was superior to imatinib alone in this regard. The biochemical target of CGP76030 in leukemia cells was Src kinases, not Bcr-Abl. These results implicate Src family kinases as therapeutic targets in Ph(+) B-ALL and suggest that simultaneous inhibition of Src and Bcr-Abl kinases may benefit individuals with Ph(+) acute leukemia.

Animals↗
PubMed2004

Targeted gene delivery to vascular tissue in vivo by tropism-modified adeno-associated virus vectors.

BACKGROUND: Gene therapy offers an unprecedented opportunity to treat diverse pathologies. Adeno-associated virus (AAV) is a promising gene delivery vector for cardiovascular disease. However, AAV transduces the liver after systemic administration, reducing its usefulness for therapies targeted at other sites. Because vascular endothelial cells (ECs) are in contact with the bloodstream and are heterogeneous between organs, they represent an ideal target for site-specific delivery of biological agents. METHODS AND RESULTS: We isolated human venous EC-targeting peptides by phage display and genetically incorporated them into AAV capsids after amino acid 587. Peptide-modified AAVs transduced venous (but not arterial) ECs in vitro, whereas hepatocyte transduction was significantly lower than with native AAV. Intravenous infusion of engineered AAVs into mice produced reduced vector accumulation in liver measured 1 hour and 28 days after injection and delayed blood clearance rates compared with native AAV. Peptide-modified AAVs produced enhanced uptake of virions in the vena cava with selective transgene expression. Retargeting was dose dependent, and coinfusion of either heparin or free competing peptides indicated that uptake was principally independent of native AAV tropism and mediated via the peptide. CONCLUSIONS: AAV tropism can be genetically engineered by use of phage display-derived peptides to generate vectors that are selective for the vasculature.

Animals↗
PubMed2004

Development of efficient viral vectors selective for vascular smooth muscle cells.

The vascular smooth muscle cell (SMC) is integral to the pathogenesis of neointimal formation associated with late vein graft failure, in-stent restenosis, and transplant arteriopathy. Viral vectors transduce SMC with low efficiency and hence, there is a need for improvement. We aimed to enhance the efficiency and selectivity of gene delivery to human SMC. Targeting ligands were identified using phage display on primary human saphenous vein SMC with linear and cyclic libraries. Two linear peptides, EYHHYNK (EYH) and GETRAPL (GET), were incorporated into the HI loop of adenovirus (Ad) fibers and the capsid protein of adeno-associated virus-2 (AAV-2). Exposure of human venous SMC to EYH-modified (but not the GET-modified) Ad vector resulted in a significant increase in transgene expression levels at short, clinically relevant exposure times. Similarly, the EYH-modified AAV vector resulted in enhanced gene transfer to human venous SMC but not endothelial cells in a time- and dose-dependent manner. The EYH-modified AAV vector also enhanced (up to 70-fold) gene delivery to primary human arterial SMC. Hence, incorporation of EYH into Ad and AAV capsids resulted in a significant and selective enhancement in transduction of SMC and has implications for improving local gene delivery to the vasculature.

Adenoviridae↗
PubMed2004

Chemotherapy combination treatment regimens with fludarabine in chronic lymphocytic leukemia.

Fludarabine monotherapy is an established treatment for chronic lymphocytic leukemia (CLL), achieving superior remission rates compared with other treatment regimens containing alkylating agents or corticosteroids. However, CLL remains incurable and research continues into finding new treatments for this, the most common leukemia in the Western world. Recent research has focused on the use of fludarabine in combination with other chemotherapeutic agents. Studies published to date indicate that regimens containing fludarabine plus cyclophosphamide, with or without mitoxantrone, achieve overall response (OR) rates of 64-100% and complete response (CR) rates of up to 50%. Administration of cyclophosphamide at a lower dosage (< or =300 mg) appears to reduce the risk of myelosuppression without compromising efficacy. Combinations of fludarabine with prednisone or chlorambucil have been shown to be no more effective than fludarabine monotherapy (OR 27-79% with these combinations), while the combination of fludarabine plus cytarabine proved to be less effective than fludarabine monotherapy. Further studies are needed to evaluate the combinations of fludarabine plus doxorubicin and fludarabine plus epirubicin, as results to date have been inconclusive. More trials are also needed to examine a fludarabine, cytarabine, mitoxantrone and dexamethasone combination that has achieved a promising CR rate of 60% in the one trial reported thus far. Taken together, the results obtained so far with fludarabine plus cyclophosphamide suggest that this combination is more potent than fludarabine monotherapy and is able to increase the CR rate, the OR rate, event-free survival and progression-free survival in patients with CLL.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2004

Progress in the use of adeno-associated viral vectors for gene therapy.

The development of safe and efficient gene transfer vectors is crucial for the success of gene therapy trials. A viral vector system promising to meet these requirements is based on the apathogenic adeno-associated virus (AAV-2), a member of the parvovirus family. The advantages of this vector system is the stability of the viral capsid, the low immunogenicity, the ability to transduce both dividing and non-dividing cells, the potential to integrate site specifically and to achieve long-term gene expression even in vivo, and its broad tropism allowing the efficient transduction of diverse organs including the skin. All this makes AAV-2 attractive and efficient for in vitro gene transfer and local injection in vivo. This review covers the progress made in AAV vector technology including the development of AAV vectors based on other serotypes, summarizes the results obtained by AAV targeting vectors and outlines potential applications in the field of cutaneous gene therapy.

Animals↗
PubMed2003

Transductional and transcriptional targeting of cancer cells using genetically engineered viral vectors.

Gene delivery vectors, including adenovirus (Ad) and adeno-associated virus (AAV), are inefficient and non-selective for cancer due to low levels of viral receptors with high levels on other tissues, including liver. We tested Ads and AAVs with the SIGYPLP-targeting peptide inserted into virus capsids for transduction in a panel of cancer cells. Six of twelve lines (C8161, PC-3, G-CCM, MKN-45, LnCAP and A549) were transduced, independently of native viral tropism. Furthermore the candidate cancer gene therapy promoter FLT-1 was active in three of these six cell lines. This offers the potential for dual targeting of selected cancer cells.

Adenoviridae↗
PubMed2003

Vaccination against B-cell chronic lymphocytic leukemia with trioma cells: preclinical evaluation.

PURPOSE: Trioma cells are lymphoma cells that have been fused to a hybridoma and have thereby been modified to express an immunoglobulin directed against surface receptors of antigen-presenting cells. Trioma cells that potentially include all lymphoma-derived antigens will be targeted to professional antigen-presenting cells in vivo. This allows uptake, processing, and presentation of tumor-derived antigens to T lymphocytes. In a mouse model, vaccination with trioma cells conferred long-lasting, T cell-dependent tumor immunity and was even able to eradicate established lymphomas. Here, we investigated whether this potent approach is effective in the human system. EXPERIMENTAL DESIGN: Malignant cells from 11 patients with B cell chronic-lymphocytic leukemia (B-CLL) were fused to an anti-Fc receptor hybridoma. The resulting trioma cells were extensively characterized with respect to their clonal origin. The induction of autologous tumor-specific T lymphocytes in the presence of trioma and antigen-presenting cells was examined in vitro by determining cytokine secretion in coculture assays. RESULTS: In seven cases, trioma cells could successfully be generated from B-CLL cells. Stimulation of autologous lymphocytes with trioma cells induced a leukemia-specific T-cell response. Immunostimulatory trioma cells were also obtained from two patients with solid B-cell lymphoma. CONCLUSIONS: Trioma-mediated immunization may be a promising adjuvant treatment of human malignancies of the B-cell lineage, particularly of B-CLL, which has still a very poor prognosis. Our in vitro results pave the way for clinical application.

Adult↗