Regulated Expansion of Lympho-hematopoietic Stem and Progenitor Cells from Human Embryonic Stem Cells (hESC)

Regulated Expansion of Lympho-hematopoietic Stem and Progenitor Cells from Human Embryonic Stem Cells (hESC)

Funding Type: 
Comprehensive Grant
Grant Number: 
RC1-00108-B
Award Value: 
$1,653,416
Stem Cell Use: 
Embryonic Stem Cell
Status: 
Closed
Public Abstract: 
The clinical potential of human embryonic stem cells (hESC) for transplantation will be realized only when we can develop methods to control the process of tissue differentiation far more efficiently than is currently the case. From over 40 years of experience with adult stem cells, it is recognized that the growth of transplanted bone marrow is generated from the hematopoietic (“blood-forming”) stem and progenitor cells present in the graft. Mature, differentiated cells that accompany the stem cells disappear rapidly after transplantation as they lack the ability to self renew. It is thus essential when designing clinical approaches that use tissue derived from hESC, to specifically target the production of stem and progenitors that will survive, proliferate and differentiate after transplantation. This proposal addresses three fundamental questions for the entire hESC field 1.Do hESC differentiate through the same pathways that exist in adult tissues, 2.How do the conditions in which hESC are initially derived from blastocysts affect their subsequent potential for generating tissue specific stem and progenitor cells, and 3.How can hESC differentiation be regulated to provide large numbers of tissue specific stem and progenitor cells able to engraft and differentiate long term? Studies of hematopoiesis in mice have provided the conceptual basis for the entire field of stem cell biology. However, fundamental biological and technical differences exist in both hematopoietic and embryonic stem cell biology between the murine and human species. Our group has chosen over the past 15 years to focus on the study of human hematopoietic stem cells and lymphoid (immune system) progenitors, more recently bringing these concepts and tools to study hematopoietic differentiation from hESC. In brief, our aims in this proposal are: 1. To understand the pathways along which the blood and immune system are generated from hESC, 2. To assess if the methods by which hESC are derived affect their capacity for hematopoiesis, and 3. To develop the means to expand hematopoietic stem cells derived from hESC. I believe that there are two broad reasons why these studies are important. First, as a pediatric bone marrow transplant physician, I am keenly aware that profound clinical problems remain for my patients. Matched stem cells from healthy donors are often unavailable and poor recovery of the immune system after transplantation results in an unacceptably high incidence of death and illness from infection. Second, as a stem cell biologist I recognize that the well established tools that can be applied specifically to hematopoietic development from hESC are uniquely able to answer some of the most fundamental questions about how hESC generate tissues and how we can best control the process. With these answers we will be able to tailor our approaches for differentiation to all tissue types and move the intriguing biology of hESC more rapidly and safely to the clinic.
Statement of Benefit to California: 
The unique combination of pluripotentiality and unlimited capacity for proliferation have provoked hope that hESC will one day provide an inexhaustible source of tissue for transplantation and regeneration. Diseases that might be treated from such tissues affect millions of Californians and their families. However, the clinical potential of hESC for regenerative medicine will be realized only when the process of tissue specific differentiation is significantly more efficient and controlled than is currently the case. This research proposal has two broad goals. The first is to explore some of the fundamental biologic questions about how individual human embryonic stem cells (hESC) are recruited into a specific pathway of tissue differentiation. Our approach to these questions will be to use the hematopoietic (“blood-forming”) system as our model, as it is the best characterized tissue in terms of differentiation and offers a range of unique technical tools with which to study these questions rigorously. However, the fundamental concepts formed from these studies will have broad applicability to other types of tissues. By understanding these processes, the development of methods to translate hESC into production of other tissues such as islets, neural cells and cardiac muscle to the clinic will be more successful. The second goal is to develop approaches to efficiently produce elements of the blood and immune system from hESC for use in transplantation of a variety of diseases. Hematopoietic Stem Cell Transplantation (HSCT, aka Bone Marrow Transplantation) is the most mature example of the clinical application of stem cells, representing a life saving procedure for leukemia, lymphoma, and many other types of blood and immune system diseases. Nonetheless, profound clinical problems remain for the HSCT field particularly in the allogeneic setting. These problems include lack of suitable, matched bone marrow donors for many patients and poor recovery of the immune system after transplantation leading to death and illness from infection in an unacceptably large number of patients. The possibility of producing large numbers of compatible hematopoietic stem and progenitor cells suitable for clinical transplantation presents an opportunity to fundamentally change clinical practice in the HSCT field. All scientific findings and technical tools developed in this proposal will be made available to researchers throughout California, under the guidelines from the California Institute of Regenerative Medicine.
Progress Report: 

Year 1

It is well recognized from adult stem cell studies that the growth of transplanted bone marrow is generated from the hematopoietic (“blood-forming”) stem and progenitor cells provided by the donor bone marrow. Mature, differentiated cells that accompany the hematopoietic stem cells, disappear rapidly after transplantation as they lack the ability to self-renew. It is thus essential when designing clinical approaches that use tissue derived from human embryonic stem cells (hESC), to specifically target the production of stem and progenitors that will survive, proliferate and differentiate normally after transplantation. We and others have shown that blood cells can be generated from hESC. However, it has become apparent more recently that the types of blood cells that hESC can produce under current conditions are more limited functionally than those found in bone marrow or cord blood. Over the past year of funding, we have studied this problem in the following ways. First, we have identified some of the key genetic differences in the way blood is formed from hESC that may be particularly important in the formation of the lymphoid cells of the immune system. Second, we have identified a very early stage of differentiation at which the pluripotent character of hESC is lost and blood forming potential is gained. We have called this primitive population the “embryonic mesoderm progenitor” (EMP) cells as they have the potential to make many if not all the cells of the mesoderm germ layer. We have developed ways to isolate the EMP cells and have begun to study how genes regulate their production from hESC. Third, we have developed a way to measure the efficiency of the process of blood formation from hESC so that we can find optimal cell lines and conditions for the process. During the next year of funding, we will continue to study the hEMP and other blood progenitors with the ultimate goal of learning how to improve production of the lymphoid immune system from hESC.

Year 2

It is well recognized from adult stem cell studies that the growth of transplanted bone marrow is generated from the hematopoietic (“blood-forming”) stem and progenitor cells provided by the donor bone marrow. Mature, differentiated cells that accompany the hematopoietic stem cells, disappear rapidly after transplantation as they lack the ability to self-renew. It is thus essential when designing clinical approaches that use tissues or cells derived from human embryonic stem cells (hESC), to specifically target the production of stem and progenitors that will survive, proliferate and differentiate normally after transplantation. We and others have shown that blood cells can be generated from hESC. However, it has become apparent more recently that the types of blood cells that hESC can produce under current conditions are more limited functionally than those found in bone marrow or cord blood. Over the past year of funding, we have studied this problem in the following ways. First, we have identified some of the key genetic differences in the way blood is formed from hESC that may be particularly important in the formation of the lymphoid cells of the immune system. Second, we have identified a very early stage of differentiation at which the pluripotent character of hESC is lost and blood forming potential is gained. We have called this primitive population “embryonic mesoderm progenitor” (EMP) cells as they have the potential to make many if not all the cells of the mesoderm germ layer. We have developed ways to isolate the EMP cells and have begun to study how genes regulate their production from hESC. Third, we have developed a way to express genes in hESC and hEMP to try and improve how these cells produce blood. During the next year of funding, we will continue to study the hEMP and other blood progenitors with the ultimate goal of learning how to improve production of the lymphoid immune system from hESC.

Year 3

It is well recognized from adult stem cell studies that the growth of transplanted bone marrow is generated from the hematopoietic (“blood-forming”) stem and progenitor cells provided by the donor bone marrow. Mature, differentiated cells that accompany the hematopoietic stem cells, disappear rapidly after transplantation as they lack the ability to self-renew. It is thus essential when designing clinical approaches that use tissue derived from human embryonic stem cells (hESC), to specifically target the production of stem and progenitors that will survive, proliferate and differentiate normally after transplantation. We and others have shown that blood cells can be generated from hESC. However, it has become apparent more recently that the types of blood cells that hESC can produce under current conditions are more limited functionally than those found in bone marrow or cord blood. Over the past year of funding, we have studied this problem in the following ways. First, we have identified some of the key genetic differences in the way blood is formed from hESC that may be particularly important in the formation of the lymphoid cells of the immune system. Second, we have carefully compared the hematopoietic capacity of six new embryonic stem cell lines developed at UCLA, to identify which are the best for blood formation. This work has been conducted as part of a collaboration with several teams at UCLA. Third, we have developed a way to give a signal to cord blood stem cells that induces them to make large numbers of red blood cells. We are using this same method now to stimulate red blood cell production from hESC. The ultimate goals of these studies is to improve production of hematopoietic cells from hESC for use in transplantation.

Year 4

It is well recognized from adult stem cell studies that the growth of transplanted bone marrow is generated from the hematopoietic (“blood-forming”) stem and progenitor cells provided by the donor bone marrow. Mature, differentiated cells that accompany the hematopoietic stem cells, disappear rapidly after transplantation as they lack the ability to self-renew. It is thus essential when designing clinical approaches that use tissue derived from human embryonic stem cells (hESC), to specifically target the production of stem and progenitors that will survive, proliferate and differentiate normally after transplantation. We and others have shown that blood cells can be generated from hESC. However, it has become apparent more recently that the types of blood cells that hESC can produce under current conditions are more limited functionally than those found in bone marrow or cord blood. During the funding of this proposal we have compared the expression of genes in cells produced by hESC to those found in umbilical cord blood. These studies found that a gene called LNK is expressed in stem cells from hESC but not from cord blood. During completion of this grant over the past 4 months, we have found that inhibiting the expression of LNK increases the production of blood from hESC, suggesting that this pathway is a promising target for future studies aimed at increasing the production of blood-forming stem cells from hESC. Second, as part of a UCLA collaborative study we have studied six new hESC lines generated at UCLA for their ability to produce blood, blood vessels and more recently cardiac muscle. Third, we have developed a way to give a signal to cord blood stem cells that induces them to make large numbers of red blood cells. The ultimate goals of all these studies is to improve production of hematopoietic cells from hESC to provide an inexhaustible source of matched stem cells for transplantation.

© 2013 California Institute for Regenerative Medicine