Mast cell development in health and systemic mastocytosis

Abstract

Hematopoietic progenitors in the bone marrow differentiate into several immune cells, including mast cells. Mast cell progenitors leave the bone marrow, circulate through the blood, and home to the periphery where they mature. This thesis aims to gain more insights into the development of mast cells in health and in the mast cell disease systemic mastocytosis (SM). This disease is characterized by infiltrates of neoplastic mast cells in different tissues and the presence of the D816V mutation in the KIT gene. In this thesis we study mast cells and their progenitors in peripheral blood and bone marrow by using multi-color fluorescenceactivated cell sorting that enables characterization and isolation of cells of interest. Sorted cells were analyzed using culture experiments, cytochemical stainings techniques, and genetic mutation profiling.

In study I we analyzed peripheral blood samples from SM patients for the presence of mast cells, which are absent in blood of healthy subjects. In this study we demonstrated the presence of circulating mature mast cells in the peripheral blood of patients with advanced forms of SM. In study II we assessed the role of SCF and KIT signaling in mast cell development and differentiation. Treatment with the tyrosine kinase inhibitor imatinib, which prevents KIT signaling, did not reduce the percentage of mast cell progenitors in vivo. Using in vitro culture experiments, we further showed that mast cell progenitors from peripheral blood survive, differentiate, and partially mature without SCF and KIT signaling. In study III we aimed to investigate the KIT D816V distribution throughout the hematopoietic landscape. We developed an assay that allows the detection of the KIT D816V mutation in single cells sorted from the bone marrow of SM patient. We detected the KIT D816V mutation throughout the hematopoietic landscape, from stem cells to the mast cells lineage. However flow cytometry analysis showed that the frequencies of different hematopoietic stem and progenitors were comparable in SM patients and controls. In addition, we demonstrated that mast cells originate from FcεRI+ bone marrow progenitors, and we described aberrant CD45RA expression on mast cells from SM patients. In study IV we further investigated the cell-forming potential of FcεRI+ common myeloid progenitors (CMPs) in the bone marrow, identified in study III. We found distinct subpopulations within the FcεRI+ CMPs using antibodies against CD203c and integrin β7. Culture experiments showed that CD203c+ FcεRI+ CMPs differentiate into mast cells and basophils, whereas CD203c− FcεRI+ CMPs form mast cells, basophils, and erythroid cells. Granulocyte-monocyte progenitors, which form neutrophils, did not generate mast cells and basophils, clearly separating the development of different granulocytes.

Taken together, this thesis provides clinical and biological insights into mast cell development in health and systemic mastocytosis.