UNDERSTANDING MOLECULAR MECHANISMS UNDERLYING DEVELOPMENT OF HIGHLY REGENERATIVE HUMAN HAEMATOPOIETIC STEM CELLS

Blood stem cells, also called haematopoietic stem cells (HSCs), give rise to the adult blood system. Since HSCs can self-renew, these sustain production of various blood cell types throughout the entire life of an animal. How these important cells emerge during embryo development is one of the most intriguing questions of stem cell and developmental biology. HSCs are important components of the bone marrow and umbilical cord blood, which are broadly used for clinical transplantation into patients who have blood disorders or cancers and require restoration of their blood system. More than 50,000 HSC transplantations are performed yearly worldwide, but demand for HSCs outstrips supply. Despite extensive efforts, the search for methods to produce high quality HSCs from alternative cell sources, in the laboratory conditions has met with limited success. It remains a puzzle, why in spite of great hopes, pluripotent stem cells (hPSCs) that can generate blood cells in the Petri dish, fail to generate true HSCs. The most likely reason for this is that our understanding of how these cells first emerge during embryo development, particularly in humans, remains insufficient. We aim here to address this gap in fundamental knowledge by interrogating functions of genes expressed during human HSC embryonic development.

This project is based on our achievements in the field of embryonic development of adult HSCs, both in mouse and human. We previously found that HSCs first emerge in the region inside the embryo, which encompasses the dorsal aorta, called now the AGM region, and identified these HSCs by surface markers. Furthermore, we have found that these first HSCs emerging in the human AGM region possess an enormous regenerative potential, much higher than umbilical cord blood HSCs, which are currently used for transplantation in clinics. This vast regenerative potential makes the properties of the first HSCs emerging in the human AGM region highly attractive not only for fundamental stem cell biology but also for clinical applications.

Using cell purification, molecular biology and bioinformatics methods, we have revealed those genes that are expressed in the first HSCs but not in the similar cell population derived from hPSCs in culture. Some of these genes must be responsible for the development of the highly regenerative HSCs in the embryo and our main goal here is to identify them and understand - what exactly they do in the HSCs during development? To address this question, we will engineer hPSCs in which these normally silent genes will be expressed. This will allow us to determine the effects of these genes on important HSC characteristics, such as self-renewal potential and generation of immune cells. Ultimately, we will test whether any combination of these genes will result in the generation of clinically relevant, highly potent transplantable HSCs. To this end, we will transplant the cells into so-called xenograft NSG mice, in which human blood cells can be maintained. Additionally, we will test, whether these genes can enhance the regenerative power of HSCs within umbilical cord blood transplants.

This study will provide deep insights into fundamental molecular mechanisms of normal and, potentially, inborne pathological processes underlying human blood development. This will also help us to gain a better control of HSC manipulations in laboratory conditions and in the long-term help with development of new cell-based therapies to meet clinical demands.

Over 50,000 HSC transplantations in clinics are performed annually worldwide, but demand outstrips supply. Despite widespread efforts, the search for methods enabling the generation of bona fide HSCs in vitro has met with limited success, primarily due to poor understanding of molecular mechanisms underlying HSC development in the embryo, particularly in humans.
We have shown that the first HSCs emerging in the human embryo possess enormous regenerative potential, significantly exceeding that of HSCs from adult sources, making their properties highly attractive for clinical applications. It is therefore important to elucidate the genetic mechanisms underpinning emergence of these HSCs. This is the main focus of our research project.
Our recent analysis identified the genes that are expressed in these HSCs, but are silent in their counterparts derived from human pluripotent stem cells (hPSCs). Some of these genes must be responsible for the development of highly regenerative HSCs in the embryo. We have also identified hPSC-specific genes, which might be negative regulators of HSC development.
Based on our unique expertise in functional analysis of human embryo HSC development, we will interrogate gene functions using efficient in vitro and in vivo screening systems with the focus on transcription factors (TFs) that are key cell fate regulators. To delineate key molecular mechanisms underlying HSC development, we will explore a spectrum of biological effects elicited by TFs and ultimately determine their capacity to transform hPSCs-derived progenitors into transplantable HSCs.
This study will provide deep mechanistic insight into normal and potentially congenital pathological processes underlying human blood development and inform strategies to gain better control of ex vivo HSC manipulations. Ultimately, this is critical to drive forward new cell-based therapies to meet clinical demand for HSCs and help move medical treatment towards personalized medicine