Single-cell perspectives on mast cells in health and systemic mastocytosis

Mast cells play a critical role in the human immune system and in adults originate from the bone marrow through hematopoiesis. Mast cells are known to contribute to allergic diseases, and deregulation of mast cell development leads to mast cell disorders such as mastocytosis. This thesis focused on investigating mast cell development in health and mastocytosis using the single-cell sequencing platform.

In Study I, we characterized circulating mast cell progenitors using single-cell transcriptomics. We revealed the presence of previously unidentified high-affinity IgE receptor positive mast cell progenitors, and characterized the transcriptomic changes that occur as multipotent progenitors differentiate towards mast cells. We additionally identified regulators that affect mast cell progenitor differentiation and survival.

In Study II we employed single-cell chromatin accessibility sequencing to identify several transcriptomic factors that regulate mast cell differentiation, notably GATA1. Combining timepoint single-cell transcriptomic sequencing with perturbation of GATA1 using CRISPR-Cas9 revealed that loss of GATA1 deregulates erythropoiesis while driving progenitors to form mature and functional mast cells. In contrast, overexpression of GATA1 accelerates erythropoiesis with little to no effect on mast cell development.

In the second half of the thesis, we focused on investigating molecular causes of systemic mastocytosis. In Study III, a combination of proteomics and single-cell transcriptomics uncovered CCL23 as a potential biomarker of systemic mastocytosis. In Study IV we genotyped KIT D816V, a mutation associated with systemic mastocytosis, on the single-cell level in tandem with transcriptomics. We additionally reveal that KIT D816V mutant progenitors overwhelmingly form erythroid precursors that do not form mature red blood cells.

In conclusion, this thesis improves our understanding of mast cell development in healthy and aberrant conditions such as systemic mastocytosis. Our findings will further inform the treatment of allergic diseases and mast cell neoplasie.

List of scientific papers

I. Chenyan Wu*, Daryl Boey*, Oscar Bril, Jennine Grootens, MS Vijayabaskar, Chiara Sorini, Maria Ekoff, Nicola K Wilson, Johanna S Ungerstedt, Gunnar Nilsson, Joakim S Dahlin. Single-cell transcriptomics reveals the identity and regulators of human mast cell progenitors. Blood Advances. 2022. 6 (15): 4439-4449. https://doi.org/10.1182/bloodadvances.2022006969

II. Jiezhen Mo*, Daryl Boey*, Fredrik Wermeling, Gunnar Nilsson, Joakim S Dahlin. GATA1 acts as a bifurcating switch between the mast cell and erythroid lineage. [Manuscript]

III. Stina Söderlund, Daryl Boey, Wouter van Midden, Matilda Kjellander, Kajsa Ax, Hong Qian, Joakim S Dahlin, Johanna Ungerstedt. Proteomic and transcriptomic screening demonstrates increased mast cell-derived CCL23 in systemic mastocytosis. J Allergy Clin Immunol. 2023 Feb 21;S0091-6749(23)00214-2. https://doi.org/10.1016/j.jaci.2023.01.033

IV. Daryl Boey*, Chenyan Wu*, Sofia Papavasileiou*, Jiezhen Mo, Johanna S. Ungerstedt, Gunnar Nilsson, Joakim S Dahlin. Single-cell transcriptional analyses uncovers the hematopoietic landscape in systemic mastocytosis. [Manuscript]

* Equal contribution