Phenotypic and genotypic characterisation of juvenile myelomonocytic leukaemia

Abstract

Paediatric myelodysplastic syndromes and Juvenile Myelomonocytic Leukaemia (JMML) are very rare haematological diseases of childhood, with an estimated incidence of 1 case per million. Due to their rarity there is relatively little known about their natural history and disease biology. As a result, there are often significant challenges in establishing a diagnosis and there are very few treatment options available for these children. The only curative treatment is bone marrow transplantation but even this is associated with a high risk of disease relapse, particularly in JMML where relapse rates are approaching 35%. In the work described here, I first set up a national observational study to prospectively collect serial patient samples in order to phenotypically and molecularly characterise these patients at diagnosis and to establish the basis for a prospective natural history study. The clinical and molecular characterisation of these diseases allowed me to devise new diagnostic and management algorithms for paediatric MDS and JMML. In order to understand more about the biology of this group of disorders I decided to focus on JMML as this was the largest distinct group of patients enrolled in the study. My specific aim has been to identify and characterise the disease-propagating population in JMML (the JMML 'leukaemic stem cells, LSC); which is a crucial step in understanding the disease evolution and dynamics of relapse. Prior to this work, there was almost nothing known about the haematopoietic hierarchy in JMML and the impact of JMML-associated mutations on haematopoiesis. With this study I analysed the JMML haematopoietic stem cell and progenitor cell (HSPC) compartments gaining new insights into the architecture of the JMML HSPC and their lineage potential. Using a single cell genotyping approach I was able to map the JMML mutations onto the haematopoietic hierarchy identifying for the first time the cellular compartment in which the JMML-associated mutations originate. The stem cell capacity of candidate JMML LSC was assessed with in vitro and in vivo stem cell assays establishing the identification of the disease propagating population(s). Molecular techniques, including RNA sequencing, then allowed me to molecularly characterise the JMML LSC and identify putative disease-specific targets and biomarkers that might be utilised in the future for disease burden monitoring and more effective treatments.</p