No description available.

No description available.

Cyclical thrombocytopenia (CT) is a rare hematological disease characterized by periodic oscillations in the platelet count. Although first reported in 1936, the pathogenesis and an effective therapy remain to be identified. Since besides fluctuations in platelet levels the patients hematological profile have been consistently normal, a destabilization of a peripheral control mechanism might play an important role in the genesis of this disorder. In this thesis, we investigate through computer simulations the mechanisms underlying the platelet oscillations observed in CT. First, we collected the data published in the last 40 years and quantified the significance of the platelet fluctuations using Lomb-Scargle periodograms. Our analysis reveals that the incidence of the statistically significant periodic data is equally distributed in men and women. The mathematical model proposed in this thesis captures the essential features of hematopoiesis and successfully duplicates the characteristics of CT. With the same parameter changes, the model is able to fit the platelet counts and to qualitatively reproduce the TPO oscillations (when data is available). Our results indicate that a variation in the megakaryocyte maturity, a slower relative growth rate of megakaryocytes, as well as an increased random destruction of platelets are the critical elements generating the platelet oscillations in CT. / La thrombocytopénie cyclique (TC) est une rare maladie hématologique caracteriséepar des oscillations périodiques dans les plaquettes sanguines. Bien qu'elle fût évoquéepour la première fois en 1936, la maladie et une thérapie efficace restent à trouver.Puisque malgré les fluctuations au niveau des plaquettes, les profiles hématologiquesdes patients restent toujour normaux, une destabilisation du méchanisme de contrôlepériphérique peut jouer un rôle important dans la formation de ce maladie. Dans cettethèse, nous recherchons à travers des simulations informatiques les mechanismes sousjacentaux oscillations des plaquettes observées dans TC. En premier lieu, nous avonscollecté les données publiées ces 40 dernière années et quantifié l'importance des fluctuationsdes plaquettes en utilisant les périodograms Lomb-Scargle. Notre analysestatistique révèle que les données périodiques sont équitablement distribuée chez leshommes et les femmes. Le modèle mathématique proposé dans cette thèse prenden compte les caractéristiques essentielles de la production des cellules sanguineset reproduit avec succès les charactéristiques de TC. Avec les même changementde parametèrs, le modèle reproduit bien le comportement des plaquettes sanguineset donne qualitativement les même oscillations que TPO (quand les données sontdisponibles). Nos résultats indiquent que les éléments critiques générant les oscillationsdes plaquettes dans TC sont une variation dans la maturité du mégakaryocytes,un taux de croissance relativement lent des mégakaryo cytes , ainsi que une augmentationaléatoire de destruction des plaquettes.

The overall aim of my thesis is to gain insight into the cellular and molecular basis of the hierarchical organization of the human blood system, and how these normal development processes are subverted into leukemogenesis. To date, the major cellular classes that comprise human blood remain ill defined as rigorous clonal analysis required to define the self-renewal and lineage potential of single cells has not yet been performed. Here, identification CD49f as a novel marker of human HSC led to the ability to transplant single human HSC in NOD-scid IL2Rgc-/- mice. Loss of CD49f and Thy1 uniquely demarcated multi-potent progenitors (MPP) from HSC. The classical model of hematopoiesis posits the segregation of lymphoid and myeloid lineages as the earliest fate decision during lineage restriction from HSC. The validity of this model in the mouse has been questioned; however, little is known about the lineage potential of human progenitors. By clonally mapping the developmental potential of seven progenitor classes from neonatal cord blood and adult bone marrow, human multi-lymphoid progenitors (MLP) were identified as a distinct population of Thy1-/loCD45RA+ cells in the CD34+CD38- stem cell compartment that can give rise to all lymphoid cell types, as well as monocytes, macrophages and dendritic cells. This indicates that these myeloid lineages arise in early lymphoid lineage specification. Thus, as in the mouse, human hematopoiesis does not follow a rigid model of myeloid-lymphoid segregation. While non-genetic mechanisms govern cell-fate commitment and lineage specification, hematopoietic malignancies are often initiated by aberrant gene rearrangements that can subvert normal cellular processes. Full transformation requires the accumulation of multiple genetic lesions. Most tumours exhibit dramatic genetic heterogeneity downstream of the initiating oncogenic event and are composed of pockets of genetically distinct clonal subpopulations. However little is known of how diversity evolves or the impact diversity has on functional properties. Here, using xenografting and DNA copy number alteration (CNA) profiling of human BCR-ABL1 lymphoblastic leukaemia, it was demonstrated that genetic diversity occurs in functionally defined leukaemia-initiating cells (L-IC) and that many diagnostic patient samples contain multiple genetically distinct L-IC subclones. Reconstructing the subclonal genetic ancestry of several samples by CNA profiling demonstrated a branching multi-clonal evolution model of leukaemogenesis, rather than linear succession. For some patient samples, the predominant diagnostic clone repopulated xenografts, while in others it was outcompeted by minor subclones. Reconstitution with the predominant diagnosis clone was associated with more aggressive growth properties in xenografts, deletion of CDKN2A/B, and a trend to poor patient outcome. Our findings link clonal diversity with L-IC function and underscore the importance of developing therapies that eradicate all intratumoural subclones.

Hematopoiesis describes the formation and development of blood cells. All blood cells originate from a pluripotent hematopoietic stem cell (HSC) which has the capacity for long and short term self-renewal as well as differentiation into myeloid or lymphoid lineages. The balance between HSC differentiation and proliferation is tightly controlled by both extrinsic and intrinsic factors. During leukemogenesis, this regulation is disrupted as transformation events lead to changes in proliferation, differentiation, and survival. Two distinct experimental strategies were utilized to examine the role of the hematopoietic adaptor protein GADS (GRB2-related adaptor downstream of SHC) in both leukemogenesis and in normal hematopoiesis. Philadelphia chromosome positive (Ph+) leukemias, including chronic myeloid leukemia (CML) and B cell acute lymphoblastic leukemia (B-ALL), are mediated by the oncogenic BCR-ABL fusion protein. Animal modeling experiments utilizing retroviral transduction and subsequent bone marrow transplantation have demonstrated that BCR-ABL generates both myeloid and lymphoid disease in mice when whole bone marrow is used as donor material. Strikingly, we observe that the lymphoid disease is absent in experiments completed with Gads-deficient bone marrow expressing BCR-ABL. Gads-deficient mice were generated previously and display a decrease in mature T cells, indicating that GADS is critical to T cell differentiation. Through immunophenotyping analysis we observed that Gads-deficient mice have increased numbers of lymphoid progenitors and HSCs. The increased number of HSCs in Gads-deficient mice did not induce enhanced HSC function as Gads-deficient bone marrow cells have impaired repopulation potential. Our data suggests that the T cell defect previously observed in Gads-deficient mice may be due to an early block in differentiation and functional defect in the HSC. Taken together, our studies demonstrate that GADS is a critical mediator in the hematopoietic system for both normal and leukemic differentiation and proliferation.

The overall aim of my thesis is to gain insight into the cellular and molecular basis of the hierarchical organization of the human blood system, and how these normal development processes are subverted into leukemogenesis. To date, the major cellular classes that comprise human blood remain ill defined as rigorous clonal analysis required to define the self-renewal and lineage potential of single cells has not yet been performed. Here, identification CD49f as a novel marker of human HSC led to the ability to transplant single human HSC in NOD-scid IL2Rgc-/- mice. Loss of CD49f and Thy1 uniquely demarcated multi-potent progenitors (MPP) from HSC. The classical model of hematopoiesis posits the segregation of lymphoid and myeloid lineages as the earliest fate decision during lineage restriction from HSC. The validity of this model in the mouse has been questioned; however, little is known about the lineage potential of human progenitors. By clonally mapping the developmental potential of seven progenitor classes from neonatal cord blood and adult bone marrow, human multi-lymphoid progenitors (MLP) were identified as a distinct population of Thy1-/loCD45RA+ cells in the CD34+CD38- stem cell compartment that can give rise to all lymphoid cell types, as well as monocytes, macrophages and dendritic cells. This indicates that these myeloid lineages arise in early lymphoid lineage specification. Thus, as in the mouse, human hematopoiesis does not follow a rigid model of myeloid-lymphoid segregation. While non-genetic mechanisms govern cell-fate commitment and lineage specification, hematopoietic malignancies are often initiated by aberrant gene rearrangements that can subvert normal cellular processes. Full transformation requires the accumulation of multiple genetic lesions. Most tumours exhibit dramatic genetic heterogeneity downstream of the initiating oncogenic event and are composed of pockets of genetically distinct clonal subpopulations. However little is known of how diversity evolves or the impact diversity has on functional properties. Here, using xenografting and DNA copy number alteration (CNA) profiling of human BCR-ABL1 lymphoblastic leukaemia, it was demonstrated that genetic diversity occurs in functionally defined leukaemia-initiating cells (L-IC) and that many diagnostic patient samples contain multiple genetically distinct L-IC subclones. Reconstructing the subclonal genetic ancestry of several samples by CNA profiling demonstrated a branching multi-clonal evolution model of leukaemogenesis, rather than linear succession. For some patient samples, the predominant diagnostic clone repopulated xenografts, while in others it was outcompeted by minor subclones. Reconstitution with the predominant diagnosis clone was associated with more aggressive growth properties in xenografts, deletion of CDKN2A/B, and a trend to poor patient outcome. Our findings link clonal diversity with L-IC function and underscore the importance of developing therapies that eradicate all intratumoural subclones.

Hematopoiesis describes the formation and development of blood cells. All blood cells originate from a pluripotent hematopoietic stem cell (HSC) which has the capacity for long and short term self-renewal as well as differentiation into myeloid or lymphoid lineages. The balance between HSC differentiation and proliferation is tightly controlled by both extrinsic and intrinsic factors. During leukemogenesis, this regulation is disrupted as transformation events lead to changes in proliferation, differentiation, and survival. Two distinct experimental strategies were utilized to examine the role of the hematopoietic adaptor protein GADS (GRB2-related adaptor downstream of SHC) in both leukemogenesis and in normal hematopoiesis. Philadelphia chromosome positive (Ph+) leukemias, including chronic myeloid leukemia (CML) and B cell acute lymphoblastic leukemia (B-ALL), are mediated by the oncogenic BCR-ABL fusion protein. Animal modeling experiments utilizing retroviral transduction and subsequent bone marrow transplantation have demonstrated that BCR-ABL generates both myeloid and lymphoid disease in mice when whole bone marrow is used as donor material. Strikingly, we observe that the lymphoid disease is absent in experiments completed with Gads-deficient bone marrow expressing BCR-ABL. Gads-deficient mice were generated previously and display a decrease in mature T cells, indicating that GADS is critical to T cell differentiation. Through immunophenotyping analysis we observed that Gads-deficient mice have increased numbers of lymphoid progenitors and HSCs. The increased number of HSCs in Gads-deficient mice did not induce enhanced HSC function as Gads-deficient bone marrow cells have impaired repopulation potential. Our data suggests that the T cell defect previously observed in Gads-deficient mice may be due to an early block in differentiation and functional defect in the HSC. Taken together, our studies demonstrate that GADS is a critical mediator in the hematopoietic system for both normal and leukemic differentiation and proliferation.

Thesis (M App Sci) -- University of South Australia, 1993

Includes bibliographical references (17 leaves) / vii, 113, [89] leaves, [32] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Generates and exploits activating point mutations in the common ?gb?s subunit (h?gb?sc) of the human GM-CSF, IL-3 and IL-5 receptors. Elucidates the mechanisms by which the isolated mutations confer constitutive activity on h?gb?sc. Identifies the putative all-specific signalling molecules and provides a map of the locations of activating point mutations in h?gb?sc, / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1998

Includes bibliographical references (17 leaves) / vii, 113, [89] leaves, [32] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Generates and exploits activating point mutations in the common ?gb?s subunit (h?gb?sc) of the human GM-CSF, IL-3 and IL-5 receptors. Elucidates the mechanisms by which the isolated mutations confer constitutive activity on h?gb?sc. Identifies the putative all-specific signalling molecules and provides a map of the locations of activating point mutations in h?gb?sc, / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1998