Multiomic profiling of leukemic stem cells in myeloid leukemia: implications for immunotherapy

Abstract

Despite the extensive array of therapies available for treating hematological malignancies, a major challenge in hemato-oncology lies in therapy resistance, which primarily is caused by residual resistant leukemic stem cells (LSC). In order to eliminate leukemic cells, it is crucial to understand the molecular mechanisms enabling their survival and to identify specific targetable markers for LSC to spare healthy cells. While tyrosine kinase inhibitors (TKI) provide a favorable prognosis for patients with chronic myeloid leukemia (CML), a fraction of patients suffers from disease progression or relapse upon treatment discontinuation. Acute myeloid leukemia (AML) on the other hand is a complex disease and despite development of novel therapies, survival prognosis remains poor. A common denominator for these diseases is the therapy-resistant LSC that propagate and cause a relapse. Hence, the main goal of this thesis was to identify novel targets on residual LSC by dissecting the heterogeneity among hematopoietic stem and progenitor cells (HSPC) in healthy and diseased conditions. In Paper I we provide a comprehensive molecular map of early human HSPC differentiation. Detailed analyzes of immature cell compartments identified novel HSC markers, including CD273/PD-L2. Functional validation showed that CD273hi cells have a quiescent profile and delayed in vitro differentiation, compared to CD273low cells. Furthermore, we revealed changes in the distribution of the most immature cells and lineage differentiation propensities upon ageing. Paper II focused on detailed multiomic profiling of the CD34+ cells in bone marrow samples of CML patients. The most important finding of this study was the detection of two novel LSC markers, von Willebrand factor (VWF) and TIM3. Paper III aimed at understanding the effects of short-term hydroxyurea (HU) treatment on HSPC in CML patients. The results implicate HU-induced increased the frequency of erythroid progenitors and accumulation of cell subsets with S/G2/M phase-related gene profile. With Paper IV, we aimed to investigate the impact of HLA-B genotypes on outcome during histamine dihydrochloride (HDC) and interleukin 2 (IL-2) immunotherapy. The HLA-B*44 allele, which is a weak ligand to the inhibitory NK cell receptor, KIR3DL1, was found to be associated with poor survival. Our results suggest that a strong ligand-receptor interaction induces enhanced NK cell function, which may result in better leukemia control and prolonged survival. In summary, the results from this thesis could serve as basis for a development of targeted treatment for TKI-resistant LSC in CML and relapse-preventive approaches in AML.