DECIPHERING THE BIOLOGICAL CHARACTERISTICS OF HUMAN HAEMOGENIC ENDOTHELIUM

The continuous production of all mature blood cells in an adult organism is sustained by a population of blood stem cells that resides in the bone marrow. Those are the cells which ensure reconstitution of the blood system upon bone marrow transplantation in the treatment of blood malignancies. Unfortunately, shortages of bone marrow donors or lack of compatible donors result in patients remaining for too long on transplant waiting lists. An alternative source of blood stem cells usable for transplantation in the clinic relies on the in vitro differentiation of pluripotent stem cells. However, this therapeutical aim will only be achieved with a full understanding of the differentiation processes and the thorough characterization of clinically useful cell populations. To date, this remains one of the principal limitations and most difficult challenge of the regenerative medicine field.
During embryonic life, all blood cells including adult blood stem cells are generated from precursor cells termed haemogenic endothelium. However, despite the fundamental importance of the haemogenic endothelium in establishing the blood system, we still know very little about this cell population. In this project, we propose to explore the molecular and cellular characteristics of this progenitor population derived from the in vitro differentiation of human pluripotent stem cells. First, we will investigate the level of heterogeneity of the haemogenic endothelium population generated during the course of in vitro differentiation. Next, we will explore whether the cell fate specification of the haemogenic endothelium can be modulated by culture conditions. Finally, we will dissect at the molecular level the progressive changes involved in the transition from endothelium to blood cells.
The successful completion of this project will lead to a better characterisation of haemogenic endothelium generated upon the differentiation of pluripotent stem cells. Findings from this project will advance our understanding of early human haematopoiesis and inform the design and optimization of differentiation protocols for the generation of haematopoietic cell populations usable in the clinic for regenerative medicine purposes.

Haematopoietic stem cells (HSCs) provide a continuous supply of blood cells throughout life and have been used for decades in the clinic to treat haematopoietic malignancies and diseases. However shortage of compatible bone marrow donors remains a major limitation for the wider application of this treatment. Alternative sources of HSCs usable in the clinic could be derived from the in vitro differentiation of pluripotent stem cells. However, this therapeutical aim can only be achieved with a full understanding of the differentiation processes and the thorough characterization of clinically useful cell populations. To date, this remains one of the principal limitations and most difficult challenge of the regenerative medicine field.
All blood cells, including HSCs, are derived from mesoderm precursors which differentiate into a transient and specialized population of endothelial cells termed haemogenic endothelium (HE). Through an endothelial to haematopoietic transition, HE cells give rise to blood progenitors. This transition has been documented in most species studied to date and was shown to occur during both extra-embryonic and intra-embryonic haematopoiesis. As such, the HE plays a central role in the establishment of the haematopoietic system. However, despite its fundamental importance, we know very little about this cell population. Due to the limited access to in vivo-derived tissues, the in vitro differentiation of human pluripotent stem cells offers a powerful model system for the in-depth study of the HE. Here, we propose to investigate at the molecular and cellular level the plasticity, heterogeneity and potential of human HE cells generated upon the differentiation of pluripotent stem cells.
Findings from this project will advance our understanding of early human haematopoiesis and inform the design and optimization of protocols for the generation of haematopoietic cell populations usable in the clinic for regenerative medicine purposes.

The long term outcome of this programme of research will result in the generation of better protocols to differentiate haemogenic endothelium toward haematopoietic progenitors which might be used in the clinic for regenerative purposes, resulting in improved "health and wealth" benefits. The data obtained as a result of support by MRC will be disseminated through publication in peer reviewed international academic journals, during conference presentations in the UK and abroad, and online making them available to the broader scientific community. Datasets will be deposited in publicly accessible databases upon publication. Communication of our research to a wider audience will be achieved through public events organized by the University of Manchester. Every opportunity will be taken to engage the general public, politicians and journalists with our research.