The clinical potential of pluripotent stem cells for use in regenerative medicine will be realized only when the process by which tissues are generated from these cells is significantly more efficient and controlled than is currently the case. Fundamental questions remain about the mechanisms by which pluripotent stem cells differentiate into mature tissue. The overall goal of this research proposal is to discover if the cell types produced during differentiation of PSC produce the microenvironment needed for specialized tissue stem cells to develop.
To approach this question we will use the hematopoietic (“blood-forming”) system as our model, as it is the best characterized tissue in terms of differentiation pathways and offers a range of unique technical tools with which to rigorously study questions of differentiation. Adult hematopoietic stem cells survive and grow in the bone marrow only if they are physically close to specialized cell types, the so-called hematopoietic stem cell “niche”. We hypothesize that hematopoietic stem cells are not produced from pluripotent cells because the cells that form the niche and provide the necessary signals are not present during this early stage of differentiation.
Our research proposal has three specific aims. The first aim is to determine if a single cell type derived from pluripotent cells can generate both blood cells and the cells of the hematopoietic niche. The second aim is to identify the types of niche cells produced from pluripotent cells and define how each of them affect the growth of adult stem cells. In the third aim, the cell types that are found in aim 2 to best support adult hematopoiesis, will then be tested for their ability to promote the production of hematopoietic stem cells from pluripotent stem cells.
The findings from these studies will have broad applicability to the production of other types of tissues from pluripotent stem cells, all of which have stem cells that require interaction with a specialized niche. In addition to the biological questions explored in this proposal, our focus on the blood system has direct clinical relevance to the field of bone marrow and cord blood transplantation. The development of a human hematopoietic niche from pluripotent stem cells could potentially be used to expand hematopoietic stem cells from adult tissues like cord blood. Most importantly, the ability to control differentiation from pluripotent stem cells into the blood lineage could provide an unlimited source of matched cells for transplantation for patients with leukemia and other diseases of the bone marrow and the immune system who currently lack suitable donors.
The unique combination of pluripotentiality and unlimited capacity for proliferation has raised the hope that pluripotent stem cells 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, much is still to be learned about the mechanisms by which pluripotent stem cells differentiate into mature tissue. The clinical potential of pluripotent stem cells for regenerative medicine will be realized only when the process by which tissues are generated from these cells is significantly more efficient and better controlled than is currently the case.
The research proposed in this application has broad potential benefits for Californians both through the biological questions it will answer and the relevance of these studies for clinical translation. Our goal is to understand the way the microenvironment influences tissue production from pluripotent stem cells, a critical issue for the field of stem cell biology. Specifically we will explore the question- Do the cell types produced during differentiation of pluripotent stem cells produce an adequate microenvironment for the differentiation of tissue or are some cells inhibitory to tissue production? 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 great relevance for the clinical production of other types of tissues from pluripotent stem cells, such as islets, neural cells and cardiac muscle.
In addition to the broad biological questions explored in this proposal, our focus on the blood system has direct clinical relevance to the field of bone marrow and cord blood transplantation. One goal in the proposal is to generate a cellular platform from pluripotent stem cells that will create an environment in which adult blood stem cells can grow and be expanded. Cell numbers collected from cord blood at birth are often insufficient for transplantation in adult patients and older children. The development of a human cell culture system that could expand the number of cord blood stem cells would provide new opportunities for transplantation for patients with leukemia and other diseases of the bone marrow and the immune system who currently lack suitable donors. 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.
The proposal aims to investigate the role of the microenvironment in the production of tissue-specific stem cells derived from human pluripotent stem cells (hPSCs). Despite continued efforts in the field, the production of true hematopoietic stem cells (HSC) from pluripotent stem cells has been a roadblock for investigators. The goal of this proposal is to define the mesodermal pathways through which the critical elements of the HSC niche are derived from hPSC and investigate how various cell types, produced during differentiation, negatively and positively regulate hematopoietic fate and production of definitive HSC. Three aims are proposed. The first aim is to determine if a single cell type derived from pluripotent cells can generate both blood cells and the cells of the hematopoietic niche. The second aim is to identify the types of niche cells produced from pluripotent cells and define how each of them affect the growth of adult stem cells. The third aim will test the cell types, which are found to best support adult hematopoiesis, for their ability to promote the production of hematopoietic stem cells from pluripotent stem cells.
Significance and Innovation:
- Overall, reviewers considered the proposal to be addressing an important problem in the field and, if successful, the project would have a major impact on both our fundamental understanding of human hematopoiesis and on the future therapeutic uses of hESCs.
- The approach was noted to be high risk but the importance of the goal makes it worth pursuing.
- Innovation was found in the use of a novel population of mesodermal progenitors previously identified by the investigative team, the focus on the cellular niche, and the possible creation of a new paradigm, if the applicant’s hypothesis is correct, to increase efficiency of tissue-specific stem cell generation from hPSCs.
- One reviewer considered the rationale weak because the specific role of mesoderm-derived support cells is unclear, and many other cell types present during differentiation could be equally beneficial.
Feasibility and Experimental Design:
- The first aim, focused on illuminating clonal relationships among cells derived from hPSCs, is likely to generate very important and impactful observations regarding the stepwise cellular processes involving differentiation.
- It is uncertain whether the applicant can regenerate the niche in vitro, but the proposed experiments provide some logical steps towards this goal.
- The proposal included extensive, high quality, preliminary data that are relevant to the proposed study.
- Aim 2 was thought to be the most experimentally intriguing goal, but reviewers expressed some concerns about its feasibility because of uncertainty about niche properties and potential differences between the niche for adult cells and the niche needed for initial differentiation from hESC.
- Reviewers found the relationship among the aims unclear and not fully explained, and this was considered a weakness.
Principal Investigator (PI) and Research Team:
- The team, infrastructure, expertise, and background knowledge in the area of hematopoiesis are strong elements of the proposal.
- The resources available at the applicant institution are adequate to carry out the proposed research.
Responsiveness to RFA:
- The proposal was considered responsive to the RFA as it addresses a basic biological mechanism and focuses on human source material and an important problem in regenerative medicine.