Contributions
Abstract: EP751
Type: E-Poster Presentation
Session title: Hematopoiesis, stem cells and microenvironment
Background
In adults, most hematopoietic stem and progenitor cells (HSPCs) reside within the bone marrow (BM), giving rise to all mature blood cells. Yet at any given time, a small proportion of HSPCs circulates in peripheral blood (PB), and under severe stress and disease, also the spleen can significantly contribute to blood production. However, the cellular, molecular and functional composition of circulating and extramedullary HSPC pools remains unexplored.
Aims
Here I will discuss the single cell characterisation of the adult human HSPC pool found in the two main extramedullary haematopoietic tissues, spleen and PB, comparing and contrasting it to BM.
Methods
Using matched and unmatched samples from deceased and living donors, we profiled more than 115,000 single CD34+ HSPCs by scRNA-seq and/or CITE-Seq and 3,900 single phenotypic haematopoietic stem cells / multipotent progenitors (HSC/MPPs) in functional assays.
Results
We find largely distinct HSPC compositions in extramedullary tissues and BM. The topography of the hematopoietic hierarchy in BM supports continuous HSPC proliferation and blood production. In contrast, modelling active differentiation using scRNA-seq data and flow cytometry analysis detect few to no proliferating progenitor cells in extramedullary tissues. Together with a balance of early to late progenitors heavily shifted to early progenitors in spleen and PB, this indicates a cellular configuration in extramedullary tissues positioned for lineage-primed demand-adapted haematopoiesis. Importantly, the vast majority of HSC/MPPs in spleen and non-mobilised PB are molecularly distinct from those found in BM, differing in adhesion molecules and lineage priming properties. Finally, single cell functional assays demonstrate that steady-state non-mobilised PB is dominated by quiescent HSC-like cells functionally restricted to erythrocyte and megakaryocyte production. The functional bias of PB HSC/MPPs towards a largely erythro-megakaryocyte skewed lineage output becomes imbalanced with age and in haematological conditions.
Conclusion
In summary, the cellular and functional composition of HSPC circulating in PB is uniquely different from that of BM. We show that alterations in this composition faithfully report impairments of haematopoiesis. Our study thus identifies extramedullary cellular reservoirs for demand-adapted haematopoiesis and provides a framework of clinical relevance.
Keyword(s): Extramedullary hematopoiesis, Hematopoietic stem and progenitor cells
Abstract: EP751
Type: E-Poster Presentation
Session title: Hematopoiesis, stem cells and microenvironment
Background
In adults, most hematopoietic stem and progenitor cells (HSPCs) reside within the bone marrow (BM), giving rise to all mature blood cells. Yet at any given time, a small proportion of HSPCs circulates in peripheral blood (PB), and under severe stress and disease, also the spleen can significantly contribute to blood production. However, the cellular, molecular and functional composition of circulating and extramedullary HSPC pools remains unexplored.
Aims
Here I will discuss the single cell characterisation of the adult human HSPC pool found in the two main extramedullary haematopoietic tissues, spleen and PB, comparing and contrasting it to BM.
Methods
Using matched and unmatched samples from deceased and living donors, we profiled more than 115,000 single CD34+ HSPCs by scRNA-seq and/or CITE-Seq and 3,900 single phenotypic haematopoietic stem cells / multipotent progenitors (HSC/MPPs) in functional assays.
Results
We find largely distinct HSPC compositions in extramedullary tissues and BM. The topography of the hematopoietic hierarchy in BM supports continuous HSPC proliferation and blood production. In contrast, modelling active differentiation using scRNA-seq data and flow cytometry analysis detect few to no proliferating progenitor cells in extramedullary tissues. Together with a balance of early to late progenitors heavily shifted to early progenitors in spleen and PB, this indicates a cellular configuration in extramedullary tissues positioned for lineage-primed demand-adapted haematopoiesis. Importantly, the vast majority of HSC/MPPs in spleen and non-mobilised PB are molecularly distinct from those found in BM, differing in adhesion molecules and lineage priming properties. Finally, single cell functional assays demonstrate that steady-state non-mobilised PB is dominated by quiescent HSC-like cells functionally restricted to erythrocyte and megakaryocyte production. The functional bias of PB HSC/MPPs towards a largely erythro-megakaryocyte skewed lineage output becomes imbalanced with age and in haematological conditions.
Conclusion
In summary, the cellular and functional composition of HSPC circulating in PB is uniquely different from that of BM. We show that alterations in this composition faithfully report impairments of haematopoiesis. Our study thus identifies extramedullary cellular reservoirs for demand-adapted haematopoiesis and provides a framework of clinical relevance.
Keyword(s): Extramedullary hematopoiesis, Hematopoietic stem and progenitor cells