Ökosystem statt Nutzwald
Wichtiger Teilerfolg in der Gentherapie : Interview mit Dr. Marion Gabriele Ott und Dr. Manuel Grez
Marion Gabriele Ott
- Die Septische Granulomatose (CGD) ist eine seltene Erkrankung, die auf einem genetischen Defekt bestimmter weißer Blutzellen beruht, die darauf spezialisiert sind, in den Körper eingedrungene Pilze und Bakterien aufzuspüren und zu vernichten. Frankfurter Ärzten und Wissenschaftlern um Prof. Dr. Dieter Hoelzer vom Klinikum der Johann Wolfgang Goethe-Universität und Dr. Manuel Grez vom Chemotherapeutischen Forschungsinstitut Georg-Speyer-Haus gelang es, eine intakte Kopie des defekten Gens in Blutstammzellen von zwei erwachsenen CGD-Patienten einzuschleusen und so die Funktion der Fresszellen teilweise wieder herzustellen. Eine vollständige Heilung gelang jedoch nicht – ein Patient verstarb zwei Jahre nach der zunächst erfolgreichen Behandlung an seiner Grunderkrankung. Im Gespräch mit Dr. Anne Hardy berichten Dr. Marion Gabriele Ott (Arbeitsgruppe Hoelzer) und Dr. Manuel Grez (Georg-Speyer-Haus) über die Höhen und Tiefen ihrer gentherapeutischen Forschung.
Vaccination Directed against the Human Endogenous Retrovirus-K Envelope Protein Inhibits Tumor Growth in a Murine Model System
Sarah M. Büchner
Winfried S. Wels
Barbara S. Schnierle
- Human endogenous retrovirus (HERV) genomes are chromosomally integrated in all cells of an individual. They are normally transcriptionally silenced and transmitted only vertically. Enhanced expression of HERV-K accompanied by the emergence of anti-HERV-K-directed immune responses has been observed in tumor patients and HIV-infected individuals. As HERV-K is usually not expressed and immunological tolerance development is unlikely, it is an appropriate target for the development of immunotherapies. We generated a recombinant vaccinia virus (MVA-HKenv) expressing the HERV-K envelope glycoprotein (ENV), based on the modified vaccinia virus Ankara (MVA), and established an animal model to test its vaccination efficacy. Murine renal carcinoma cells (Renca) were genetically altered to express E. coli beta-galactosidase (RLZ cells) or the HERV-K ENV gene (RLZ-HKenv cells). Intravenous injection of RLZ-HKenv cells into syngenic BALB/c mice led to the formation of pulmonary metastases, which were detectable by X-gal staining. A single vaccination of tumor-bearing mice with MVA-HKenv drastically reduced the number of pulmonary RLZ-HKenv tumor nodules compared to vaccination with wild-type MVA. Prophylactic vaccination of mice with MVA-HKenv precluded the formation of RLZ-HKenv tumor nodules, whereas wild-type MVA-vaccinated animals succumbed to metastasis. Protection from tumor formation correlated with enhanced HERV-K ENV-specific killing activity of splenocytes. These data demonstrate for the first time that HERV-K ENV is a useful target for vaccine development and might offer new treatment opportunities for diverse types of cancer.
The viral vector vaccine VSV-GP boosts immune response upon repeated applications
Lisa Mareike Egerer
Dorothee von Laer
- Poster presentation AIDS Vaccine 2012 Boston, MA, USA. 9-12 September 2012
Background: Vesicular stomatitis virus (VSV) is a potent candidate vaccine vector for various viral diseases (e.g. HIV, HCV, RSV). The biggest limitation of VSV, however, is its neurotoxicity, which limits application in humans. The second drawback is that VSV induces neutralizing antibodies rapidly and is thus ineffective as a vaccine vector upon repeated applications. Our group has recently shown that VSV pseudotyped with the glycoprotein (GP) of the lymphocytic choriomeningitis virus (LCMV), VSV-GP, is not neurotoxic. The aim of this project was to evaluate the potential of VSV-GP as a vaccine vector.
Methods: For this purpose, we used Ovalbumin (OVA) as a model antigen and analyzed immunogenicity of GP-pseudotyped and wildtype VSV containing OVA (VSV-GP-OVA and VSV-OVA) in vitro and in vivo in mouse models.
Results: We showed that both vectors infected murine bone marrow-derived dendritic cells (bmDCs) in vitro. These bmDCs were able to activate OVA specific CD8+ and CD4+ T cells. Immunization experiments in mice revealed that both VSV-OVA and VSV-GP-OVA induced functional OVA-specific cytotoxic T cells (CTLs) after a single immunization. In addition, with both viruses, mice generated antibodies against OVA. However, boosting with the same virus was only possible for the GP-pseudotyped virus but not for wild type VSV. The efficacy of repeated immunization with VSV-OVA was most likely limited by high levels of neutralizing antibodies, which we detected after the first immunization. In contrast, no neutralizing antibodies against VSV-GP were induced even after boosting.
Conclusion: Taken together, we showed that the non-neurotoxic VSV-GP is able to induce specific T cell and B cell responses against the model antigen OVA to the same level as the wild type VSV vector. However, in contrast to wild type VSV, VSV-GP-OVA boosted the immune response upon repeated applications. Thus, VSV-GP is a promising novel vaccine vector.
The T-Cell Oncogene Tal2 Is a Target of PU.1 and Upregulated during Osteoclastogenesis
- Transcription factors play a crucial role in regulating differentiation processes during human life and are important in disease. The basic helix-loop-helix transcription factors Tal1 and Lyl1 play a major role in the regulation of gene expression in the hematopoietic system and are involved in human leukemia. Tal2, which belongs to the same family of transcription factors as Tal1 and Lyl1, is also involved in human leukaemia. However, little is known regarding the expression and regulation of Tal2 in hematopoietic cells. Here we show that Tal2 is expressed in hematopoietic cells of the myeloid lineage. Interestingly, we found that usage of the Tal2 promoter is different in human and mouse cells. Two promoters, hP1 and hP2 drive Tal2 expression in human erythroleukemia K562 cells, however in mouse RAW cells only the mP1 promoter is used. Furthermore, we found that Tal2 expression is upregulated during oesteoclastogenesis. We show that Tal2 is a direct target gene of the myeloid transcription factor PU.1, which is a key transcription factor for osteoclast gene expression. Strikingly, PU.1 binding to the P1 promoter is conserved between mouse and human, but PU.1 binding to P2 was only detected in human K562 cells. Additionally, we provide evidence that Tal2 influences the expression of the osteoclastic differentiation gene TRACP. These findings provide novel insight into the expression control of Tal2 in hematopoietic cells and reveal a function of Tal2 as a regulator of gene expression during osteoclast differentiation.
Target-specific glioma therapy in an immunocompetent mouse model : meeting abstract
- Objective: Establishment of an immunocompetent mouse model representing the typical progressive stages observed in malignant human gliomas for the in vivo evaluation of novel target-specific regimens. Methods: Isolated clones from tumours that arose spontaneously in GFAP-v-src transgenic mice were used to develop a transplantable brain tumour model in syngeneic B6C3F1 mice. STAT3 protein was knocked down by infection of tumour cells with replication-defective lentivirus encoding STAT3-siRNA. Apoptosis is designed to be induced by soluble recombinant TRAIL + chemical Bcl-2/Bcl-xL inhibitors. Results: Striatal implantation of 105 mouse tumour cells resulted in the robust development of microscopically (2 – 3 mm) infiltrating malignant gliomas. Immunohistochemically, the gliomas displayed the astroglial marker GFAP and the oncogenic form of STAT3 (Tyr-705-phosphorylated) which is found in many malignancies including gliomas. Phosphorylated STAT3 was particularly prominent in the nucleus but was also found at the plasma membrane of peripherally infiltrating glioma cells. To evaluate the role of STAT3 in tumour progression, we stably expressed siRNA against STAT3 in several murine glioma cell lines. The effect of STAT3 depletion on proliferation, invasion and survival will be first assessed in vitro and subsequently after transplantation in vivo. Upstream and downstream components of the STAT3 signalling pathway as well as possible non-specific side effects of STAT3-siRNA expression after lentiviral infection will be examined, too. Conclusions: Its high rate of engraftment, its similarity to the malignant glioma of origin, and its rapid locally invasive growth should make this murine model useful in testing novel therapies for malignant gliomas.
Survival of the fittest: positive selection of CD4+ T cells expressing a membrane-bound fusion inhibitor following HIV-1 infection
Stephen E. Braun
Fay Eng Wong
Jörn E. Schmitz
Laurent M. Humeau
John J. Rossi
Dorothee von Laer
R. PauL Johnson
- Although a variety of genetic strategies have been developed to inhibit HIV replication, few direct comparisons of the efficacy of these inhibitors have been carried out. Moreover, most studies have not examined whether genetic inhibitors are able to induce a survival advantage that results in an expansion of genetically-modified cells following HIV infection. We evaluated the efficacy of three leading genetic strategies to inhibit HIV replication: 1) an HIV-1 tat/rev-specific small hairpin (sh) RNA; 2) an RNA antisense gene specific for the HIV-1 envelope; and 3) a viral entry inhibitor, maC46. In stably transduced cell lines selected such that >95% of cells expressed the genetic inhibitor, the RNA antisense envelope and viral entry inhibitor maC46 provided the strongest inhibition of HIV-1 replication. However, when mixed populations of transduced and untransduced cells were challenged with HIV-1, the maC46 fusion inhibitor resulted in highly efficient positive selection of transduced cells, an effect that was evident even in mixed populations containing as few as 1% maC46-expressing cells. The selective advantage of the maC46 fusion inhibitor was also observed in HIV-1-infected cultures of primary T lymphocytes as well as in HIV-1-infected humanized mice. These results demonstrate robust inhibition of HIV replication with the fusion inhibitor maC46 and the antisense Env inhibitor, and importantly, a survival advantage of cells expressing the maC46 fusion inhibitor both in vitro and in vivo. Evaluation of the ability of genetic inhibitors of HIV-1 replication to confer a survival advantage on genetically-modified cells provides unique information not provided by standard techniques that may be important in the in vivo efficacy of these genes.
Role of p53 serine 46 in p53 target gene regulation
Simon J. van Heeringen
Hendrik G. Stunnenberg
- The tumor suppressor p53 plays a crucial role in cellular growth control inducing a plethora of different response pathways. The molecular mechanisms that discriminate between the distinct p53-responses have remained largely elusive. Here, we have analyzed the p53-regulated pathways induced by Actinomycin D and Etoposide treatment resulting in more growth arrested versus apoptotic cells respectively. We found that the genome-wide p53 DNA-binding patterns are almost identical upon both treatments notwithstanding transcriptional differences that we observed in global transcriptome analysis. To assess the role of post-translational modifications in target gene choice and activation we investigated the genome-wide level of phosphorylation of Serine 46 of p53 bound to DNA (p53-pS46) and of Serine 15 (p53-pS15). Interestingly, the extent of S46 phosphorylation of p53 bound to DNA is considerably higher in cells directed towards apoptosis while the degree of phosphorylation at S15 remains highly similar. Moreover, our data suggest that following different chemotherapeutical treatments, the amount of chromatin-associated p53 phosphorylated at S46 but not at pS15 is higher on certain apoptosis related target genes. Our data provide evidence that cell fate decisions are not made primarily on the level of general p53 DNA-binding and that post-translationally modified p53 can have distinct DNA-binding characteristics.
Retargeted natural killer cells for adoptive cancer immunotherapy
- NK cells are part of the innate immune system, and are important players in the body’s first defence line against virus-infected and malignantly transformed cells. While T cells recognize neoplastic cells in an MHC-restricted fashion, NK cells do not require prior sensitization and education about the target. In leukemia and lymphoma patients undergoing allogeneic hematopoietic stem cell transplantation not only T cells but also NK cells have been found to mediate potent graft-versus-tumor effects. Hence, autologous or donor-derived NK cells hold great promise for cancer immunotherapy. Since the generation of highly purified NK cell products for clinical applications is labor-intensive and time consuming, established human NK cell lines such as NK-92 are also being considered for clinical protocols. NK-92 cells display phenotypic and functional characteristics similar to activated primary NK cells. While NK-92 cells are highly cytotoxic towards malignant cells of hematologic origin, they do not affect healthy human tissues. NK-92 cells can be expanded under GMP-compliant conditions, and can therefore be provided in sufficient numbers with defined phenotypic characteristics for clinical applications. Safety of NK-92 cells for adoptive immunotherapy was already shown in two phase I/II clinical trials. In contrast to malignant cells of hematologic origin, most solid tumor cells are not sensitive to unmodified NK-92 cells. Hence, to overcome resistance mechanisms of tumor cells and to broaden the target spectrum of NK-92 cells, gene-modified variants have been generated which express chimeric antigen receptors (CARs) that specifically target tumor surface antigens. The expression of these CARs is sufficient to redirect their cytotoxic activity towards otherwise NK cell-resistant target cells. Extending these earlier approaches, in the framework of this work optimized CAR constructs that target the pancarcinoma antigen epithelial cell adhesion molecule (EpCAM) were derived and functionally characterized. In collaboration with Heike Daldrup-Link’s laboratory (University of California San Francisco, USA) non-invasive imaging modalities to analyze biodistribution and tumor homing properties of retargeted NK-92 cells were evaluated. To enhance the persistence of adoptively transferred NK-92 cells in vivo, means to overcome NK-92 cells’ dependence on exogenous IL-2 for survival and cytolytic activity were investigated. EpCAM is expressed on a variety of tumors of epithelial origin including ovarian, gastric, colorectal, pancreatic, breast, lung and endometrial cancers. In epithelial cells EpCAM is mainly expressed at basolateral membranes, and EpCAM is involved in calcium-independent homotypic cell-cell adhesions. In tumor cells high and de novo EpCAM expression is not only restricted to basolateral membranes but can also be found on apical membranes. Tumor cells retain EpCAM expression throughout tumorigenesis and metastasis formation. Due to its surface expression and immunogenicity EpCAM has been exploited as target for immunotherapy. In earlier work in our group a prototypic, first generation EpCAM-specific CAR construct (31.z) harboring a murine flexible hinge region and murine CD3 ζ as signaling domain was derived and functionally characterized in NK-92 cells. To reduce the immunogenicity for their potential clinical application, this CAR construct was humanized by exchanging the hinge region and the intracellular signaling domain with corresponding sequences of human origin. In T cells incorporation of additional co-stimulatory domains derived from CD28 and 4-1BB significantly enhanced persistence and anti-tumor effects of adoptively transferred cells. Based on these findings a modified, second generation CAR construct encompassing transmembrane and intracellular regions of CD28 in addition to CD3 ζ intracellular signaling domains was derived (31.28.z). Both CAR constructs were stably expressed in NK-92 cells, and furthermore, expression of both CAR variants promoted antigen-specific lysis of antigen-expressing prostate and breast cancer cell lines. In competition experiments the cytotoxic activity of NK-92/31.z and NK-92/31.28.z cells towards antigen-expressing tumor cells was significantly reduced in the presence of parental MOC31 monoclonal antibody, indicating that binding of the EpCAM-specific CAR to its antigen on tumor cells is necessary to trigger antigen-specific cytotoxicity. At high effector to target ratios NK-92/31.28.z cells displayed slightly higher cytotoxic activity towards EpCAM-expressing target cell lines than NK-92/31.z cells, suggesting that incorporation of co-stimulatory domains had beneficial effects on the cytotoxic activity. For clinical applications the development of non-invasive imaging methods is necessary to follow the biodistribution of adoptively transferred cells and guide the identification of responders and non-responders at an early time point. In collaboration with Heike Daldrup-Link’s laboratory the homing properties of EpCAM-specific NK-92 cells to prostate tumor xenografts in rodent models was analyzed (University of California San Francisco, USA). At that time NK-92 cells expressing the second generation EpCAM-specific CAR 31.28.z were not yet available, and thus homing experiments were performed with NK-92 cells expressing the first generation CAR 31.z. For magnetic resonance imaging studies parental and EpCAM-specific NK-92 cells were labeled with clinical applicable ferumoxide particles. Labeled, gene-modified NK-92 cells displayed reduced CAR expression and reduced cytotoxic activity towards EpCAM-expressing DU145 prostate cancer cells in vitro. Nevertheless, MRI revealed specific accumulation of ferumoxide labeled EpCAM-specific NK-92 cells in DU145 tumor xenografts in athymic rats. In tumor sections of treated animals the presence of EpCAM-specific NK-92 cells was verified by Prussian blue and CD57 staining of tumor sections. In another study homing of DiD-labeled EpCAM-specific NK-92 cells to DU145 tumor xenografts was shown by optical imaging. These findings imply that specific targeting of NK-92 cells is retained in vivo, and that non-invasive imaging strategies can be employed to analyze biodistribution of NK-92 cells. Enhanced persistence of adoptively transferred cytotoxic effector cells has a major impact on the effectiveness of immunotherapy. Primary cytotoxic effector cells as well as NK-92 cells require IL-2 for their proliferation and to gain full activity of their effector functions. To bypass the need of exogenously supplied cytokines, the expression of chimeric cytokine receptors (CCR) harboring IL-2R β and IL-2R γ chains instead of CD3 ζ as signaling domains might initiate cytokine-like signals upon contact with the respective antigen. These interactions might support growth and survival of NK-92 cells in the absence of exogenous IL-2. As a starting point, a codon-optimized ErbB2-specific CAR consisting of the scFv(FRP5) single chain antibody fragment, a human CD8 α hinge region and human CD3 ζ transmembrane and intracellular domains was used. Transmembrane and intracellular domains of IL-2R β and IL-2R γ chains were amplified from NK-92 cell-derived cDNA, and were used to exchange the CD3 ζ domain in the ErbB2-specific construct. In human primary tumors EpCAM and ErbB2 overexpression are frequently found, and often correlate with poor prognosis. Hence, co-expression of ErbB2-specific CCRs with an EpCAM-specific CAR may provide NK cells with antigen-specific killing via EpCAM recognition and with antigen-dependent growth via binding to ErbB2. However, attempts to activate CCRs in NK-92 cells via co-incubation with antigen-expressing cells or cross-linking of the CCRs with recombinant antigen did not result in cytokine-independent but antigen-dependent growth. Likewise, no triggering of signal transducer and activator of transcription 5 (STAT5) was observed, which is a hallmark of IL-2 mediated signal transduction. The interactions between CCRs and their antigen might not be strong enough to trigger cytokine-like signals supporting the growth of cells in the absence of exogenous cytokines, and furthermore, might not lead to a significant up-regulation of STAT5-mediated signal transduction. An alternative approach to circumvent the need of exogenous cytokines is ectopic expression of homeostatic cytokines IL-2 and IL-15 in lymphocytes. In T cells expression of these cytokines is sufficient to render cells independent from exogenously supplied cytokines. In this work a lentiviral expression vector encoding IL-15 (SIEW-IL15) was generated, and used for transduction of NK-92 cells. This resulted in ectopic expression of IL-15 and cellular proliferation in the absence of exogenously supplied cytokines. Even after prolonged culture without exogenous IL-2, NK-92/IL15 cells retained their cytotoxic activity towards NK-sensitive target cells. Although expression of IL-15 in HC11 and COS-7 cells using the same vector led to secretion of bioactive IL-15 into culture supernatants, neither secreted nor surface-bound IL-15 was detected in NK-92/IL15 cells, implying that IL-15 promotes survival of gene-modified cells in a strictly autocrine fashion. In addition, NK-92 cells that were freshly transduced with SIEW-IL15 could be efficiently enriched by cytokine withdrawal. NK-92/IL15 cells that were co-transduced with an EpCAM-specific CAR retained their ability to grow in the absence of exogenously supplied cytokines and their antigen-specific cytotoxic activity. Based on these results, a bicistronic vector construct was generated allowing the simultaneous expression of a CAR construct and IL-15 as selection marker. EpCAM-specific CAR constructs (31.28.z and 31.TM) were inserted into the bicistronic expression cassette. NK-92 cells were transduced with these bicistronic expression constructs and selected by cytokine withdrawal. After 14 to 21 days of culture in the absence of IL-2 transduced cells grew out from which CAR-expressing NK-92 cells with high and homogenous surface expression were further enriched by FACS sorting. NK-92/31.28.z.IL15 cells displayed high cytotoxic activity towards EpCAM-expressing breast cancer cell lines, while EpCAM-negative melanoma cells were not lysed. The results of this work demonstrate that the expression of first (31.z) and second (31.28.z) generation CARs in NK-92 cells is sufficient to induce antigen-specific cytotoxicity. Furthermore, a specific accumulation of NK-92/31.z cells but not unmodified NK-92 cells was detected in EpCAM-expressing prostate carcinoma xenografts in athymic rats, indicating that specific targeting of these cells is retained in vivo. Ectopic expression of IL-15 renders the cells independent from exogenous cytokines, while they retain their cytotoxic activity even after prolonged culture without IL-2. Furthermore, ectopic expression of IL-15 in NK-92 cells can be used for selective enrichment of gene-modified cells by cytokine withdrawal. Subsequently, bicistronic expression constructs that allow simultaneous expression of a CAR construct and IL-15 as selection marker were generated. Expression of these bicistronic expression vectors in NK-92 cells is feasible, and might facilitate enrichment of gene-modified cells for clinical applications.
Resistenz polyklonaler, reifer T-Zellen gegenüber der Transformation durch retrovirale Transduktion
- Nach den ersten Erfolgen der Gentherapie bei angeborenen Immundefekten wurden einige Fälle von Leukämie nach gammaretroviralem Gentransfer in Blutstammzellen bei Patienten mit „severe combined immunodeficiency“ (SCID-X1) veröffentlicht. Diese entfachten eine Diskussion über das Risiko der Insertionsmutagenese bei der Verwendung gammaretroviraler Vektoren. Durch eine insertionsbedingte Transaktivierung potentieller Onkogene und damit verbundenen malignen Veränderungen können gammaretroviral transduzierte Blutstammzellen Leukämien hervorrufen. Aber nicht nur Blutstammzellen werden als Zielzellen in der Gentherapie genutzt. In der Gruppe von Laer wurde in den letzten Jahren eine neue Gentherapie der HIV-1 Infektion entwickelt. Hierbei werden dem Patienten genetisch geschützte, autologe T-Lymphozyten infundiert. Die Gefahr einer Leukämie durch Insertionsmutagenese sollte im Zuge dieser Studie für reife T-Lymphozyten evaluiert werden. In einer vergleichenden Analyse wurde untersucht, ob der gammaretrovirale Gentransfer in reife T-Lymphozyten die gleiche Genotoxizität birgt wie in hämatopoetische Stammzellen. Hierzu wurden reife T-Lymphozyten und hämatopoetische Progenitoren von C57BL/6(Ly5.1)-Mäusen mit multiplen Kopien gammaretroviraler Vektoren transduziert, die für die potenten T-Zell Onkogene LMO2, TCL1, dTrkA oder das Kontrollgen GFP kodierten. Es wurden sehr hohe Transduktionseffizienzen mit bis zu 70% für reife T-Lymphozyten und bis zu 98% für hämatopoetische Progenitoren erzielt, um möglichst leukämiefördernde Bedingungen zu schaffen. Nach Transplantation in kongene Rag-1 defiziente Empfängertiere (Ly5.2) entwickelten Onkogen-modifizierte Stammzellen nach einer charakteristischen Latenzperiode Leukämien/Lymphome. Am häufigsten wurden unreife, CD8+CD4+ doppelpositive T-Vorläufer Leukämien/Lymphome beobachtet. In einigen Rezipienten führte außerdem eine Überexpression von TCL1 in hämatopoetischen Stammzellen zu der Entwicklung von reifzelligen T-Zell Leukämien/Lymphomen und B-Zell Leukämien/Lymphomen. Die Integrationsanalyse ergab oligo- bis monoklonale Tumore, wobei keine offensichtlich tumorfördernden, die gammaretroviralen Insertionen flankierenden Gene identifiziert werden konnten. Bemerkenswerterweise entwickelte keines der T-Zell transplantierten Empfängertiere ein/e Lymphom/Leukämie, obwohl auch diese Zellen mit den gleichen Vektoren modifiziert wurden und über einen sehr langen Zeitraum persistierten. Um die Kontrollmechanismen dieser Resistenz näher zu untersuchen, wurde eine für den TCR monoklonale, adulte T-Zell Population mit dTrkA transduziert. Nach einer kurzen Latenzperiode entwickelten sich reifzellige T-Zell Leukämien/Lymphome. Anscheinend existiert eine Verbindung zwischen der relativen Transformationsresistenz reifer T-Lymphozyten und dem Konkurrenzverhalten verschiedener T-Zell Klone um stimulatorische MHC-TCR Nischen. Weiterhin wurde in vitro durch gammaretroviralen Transfer von LMO2 ein immortalisierter T-Zell Klon generiert. Dieser zeigte zwar nach einer langen Beobachtungszeit einen CD8-CD4-doppelnegativen Phänotyp, aber auch einen rekombinierten TCR. In vitro überwuchs er eine unmanipulierte Kompetitorpopulation, konnte jedoch nach Transplantation kein/e T-Zell Lymphom/Leukämie induzieren. Die LM-PCR Analyse des Klons lieferte eine sehr interessante Integration zwischen den Genen für die alpha-Ketten des IL-2 und des IL-15 Rezeptors, welche dadurch konstitutiv exprimiert wurden. Dies könnte das erste Beispiel für eine insertionsbedingte Immortalisierung eines adulten T-Zell Klons sein. In der vorliegenden Arbeit konnte zum ersten Mal eindeutig gezeigt werden, dass polyklonale, reife T-Zell Populationen in vivo eine hohe Transformationsresistenz aufweisen. Durch bestimmte Bedingungen können jedoch durchaus maligne Veränderung adulter, reifer T-Lymphozyten induziert werden. Für die Sicherheitsabschätzung gammaretroviraler Gentherapie-Studien mit reifen T-Lymphozyten sind die vorgestellten Ergebnisse von großer Bedeutung und könnten darüber hinaus Aufschluss über die populationsdynamischen Kontrollmechanismen reifer T-Zell Leukämien/Lymphome geben.