Le facteur de transcription Ikaros est un régulateur essentiel de la lymphopoïèse. Ikaros est nécessaire à la différenciation des lymphocytes B et joue aussi un rôle important dans la suppression des LAL-T. Contrairement aux souris mutantes nulles pour Ikaros, les souris mutantes hypomorphes IkL/L développent des lymphocytes B matures après la naissance. Avec l’âge, toutes les souris IkL/L développent des leucémies T Notch dépendantes avec des mutations similaires à celles trouvées chez les patients atteints de LAL-T. La souris IkL/L est donc un excellent modèle pour étudier l’activation des cellules B matures et la pathogenèsedes LAL-T. Nous avons montré que la délétion spécifique du promoteur et de l’exon 1 de Notch1 dans les cellules T conduit à l’activation de promoteurs cryptiques dans la région 3’ du gène, qui génèrent des transcrits codant pour des protéines Notch1 constitutivement actives qui accélèrent la leucémogenèse dans la souris IkL/L. De plus, nous mettrons en évidence l’existence de cellules initiatrices de leucémie dans les tumeurs IkL/L puisque nous avons trouvé que des cellules ayant la capacité de s’auto-renouveler représentent 1 sur 500. Enfin, nous avons montré que les cellules B IkL/L ont une activation excessive d’ERK et dep38 après la stimulation du BCR, ce qui résulte en une hyper-prolifération et une production d’autoanticorps liés au lupus systémique érythémateux. Nos résultats suggèrent qu’Ikaros est un régulateur négatif de l’activation des lymphocytes B. / The Ikaros transcription factor is a critical regulator of lymphopoeisis. Ikaros is needed for the differentiation of B cell and plays an important role in tumor suppression in T cells. Contrary to the other Ikaros targeted mutant mice, the IkL/L mouse develops mature B cells after birth. With age, it develops Notch dependent tumors with similar mutations as thosefound in human T cell acute lymphoblastic leukemia (T-ALL). Thus, the IkL/L mouse is an excellent model to study mature B cell activation and T-ALL tumor development. Here, we have shown that the deletion of the promoter and exon1 of the Notch1 gene in IkL/L T cells activates a cryptic promoter in the 3’ region which leads to the production of truncated, constitutively activated Notch1 proteins that accelerate tumorigenesis in the IkL/L mice. Moreover, we give evidence for the existence of LICs in the IkL/L tumors as we have found a specific subpopulation of cells with a frequency of 1 in 500 which show self-renewal capacity. In addition, we demonstrated that some tumor cells have the ability to efflux the Hoechst dye and that this side population is enriched in quiescent cells. Finally, we elucidate that IkL/L B cells display an enhanced activation of ERK and p38 after BCR stimulation that results in hyper-proliferation and the production of autoantibodies relatedto systemic lupus erythematosus (SLE). Our results suggest that Ikaros is a negative regulator of B cell activation.

Introduction: In acute myeloid leukemia (AML), leukemia initiating cells exist within the CD34+/CD38- cell compartment. They are assumed to be more resistant to chemotherapy, enriched in minimal residual disease cell populations, and responsible for relapse. Purpose: We evaluated clinical and biological associations and the prognostic impact of a high diagnostic CD34+/CD38- cell burden in AML patients receiving an allogeneic stem cell transplantation (HSCT) in complete remission. Here, the therapeutic approach is mainly based on immunological graft-versus-leukemia effects. Methods: Percentage of bone marrow CD34+/CD38- cell burden in 169 AML patients at diagnosis was measured using flow cytometry. The optimal cutoff of 6% was applied and used to evaluate the impact of a high CD34+/CD38- cell burden on outcome. Results: The CD34+/CD38- cell burden and was highly variable (median 0.5%, range 0-89% of all mononuclear cells). A high CD34+/CD38- cell burden at diagnosis associated with worse genetic risk and secondary AML. Patients with a high CD34+/CD38- cell burden had shorter relapse-free and overall survival, which may be mediated by residual leukemia initiating cells in the CD34+/CD38- cell population, escaping the graft-versus-leukemia effect after allogeneic HSCT. Conclusion: Evaluating the CD34+/CD38- cell burden at diagnosis may help to identify patients at high risk of relapse after allogeneic HSCT. Further studies to understand leukemia initiating cell biology and develop targeting therapies to improve outcomes of AML patients are needed.:Bibliographische Beschreibung / Bibliographic description 1 Einleitung / Introduction 2 Epidemiology and AML diagnosis 2 Therapeutic options in AML 3 Genetic risk classification for therapeutic decisions in AML 6 Immunophenotyping in AML 10 Leukemia Initiating Cells 11 Objectives of the here presented study 13 Publikation / Publication 14 Anlage / Supplemental Material 23 Zusammenfassung / Summary 48 Weiterführende Arbeiten / Future developments GPR56 as new LIC marker 52 Referenzen / References 55 Referenz der Publikation / Reference of the publication 60 Erklärung über die eigenständige Abfassung der Arbeit 61 Curriculum Vitae 62 Komplette Publikationsliste 65 Danksagung 74