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.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/31884 |
| Date | 11 January 2012 |
| Creators | Notta, Faiyaz |
| Contributors | Dick, John E. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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