The current roadblocks to hematopoietic stem cell (HSC) therapies include the rarity of matched donors for bone marrow transplant, engraftment failures, common shortages of donated blood, and the inability to expand HSCs ex vivo in large numbers. These major obstacles would cease to exist if an extensive, bankable, inexhaustible, and patient-matched supply of blood were available. The recent validation of hemogenic endothelium (blood vessel cells lining the vessel wall give rise to blood stem cells) has introduced new possibilities in hematopoietic stem cell therapy. As the phenomenon of hemogenic endothelium only occurs during embryonic development, we aim to understand the requirements for the process and to re-engineer mature human endothelium (blood vessels) into once again producing blood stem cells (HSCs). The approach of re-engineering tissue specific de-differentiation will accelerate the pace of discovery and translation to human disease. Engineering endothelium into large-scale hematopoietic factories can provide substantial numbers of pure hematopoietic stem cells for clinical use. Higher numbers of cells, and the ability to grow cells from matched donors (or the patients themselves) will increase engraftment and decrease rejection of bone marrow transplantation. In addition, the ability to program mature lineage restricted cells into more primitive versions of the same cell lineage will capitalize on cell renewal properties while minimizing malignancy risk.
Bone marrow transplantation saves the lives of millions with leukemia and other diseases including genetic or immunologic blood disorders. California has over 15 centers serving the population for bone marrow transplantation. While bone marrow transplantation can be seen as a standard to which all stem cell therapies should aspire, there still remains the difficulty of finding matched donors, complications such as graft versus host disease, and the recurrence of malignancy. While cord blood has provided another donor source of stem cells and improved engraftment, it still requires pooling from multiple donors for sufficient cell numbers to be transplanted, which may increase transplant risk. By understanding how to reprogram blood vessels (such as those in the umbilical cord) for production of blood stem cells (as it once did during human development), it could eventually be possible to bank umbilical cord vessels to provide a patient matched reproducible supply of pure blood stem cells for the entire life of the patient. Higher numbers of cells, and the ability to grow cells from matched donors (or the patients themselves) will increase engraftment and decrease rejection of bone marrow transplantation. In addition, the proposed work will introduce a new approach to engineering human cells. The ability to turn back the clock to near mature cell specific stages without going all the way back to early embryonic stem cell stages will reduce the risk of malignancy.
The overall objective of this proposal is to engineer mature human endothelial cells for in vitro production of hematopoietic stem cells (HSC) that could be used for clinical transplantation. The applicant proposes to test two different methods to achieve this goal. The scientific rationale for the first approach is based on the recent findings that hemogenic endothelium differentiates to HSC during embryonic development. By studying this differentiation process at a molecular level the applicant hopes to identify and test candidate factors that might be used to reprogram mature endothelial cells to hemogenic endothelial cells. For the second approach, the applicant will modify current methods used to generate induced pluripotent stem cells (iPSCs) to achieve tissue-specific partial de-differentiation of mature endothelial cells to a hemogenic state. In addition, hemogenic endothelial cells produced by the proposed methods will be immortalized to generate a continual source of hematopoiesis. It is hypothesized that a strategy involving co-opting tissue specific factors to de-differentiate mature cells into a natural primitive state will have a safety advantage over the alternative approach of differentiating HSCs from pluripotent stem cells.
- The lack of sufficient amounts of mature donor-matched hematopoietic stem cells is a major roadblock for treatment of multiple diseases. Therefore, if successful, the proposed research may have a major impact in the clinic.
- If the approach of partial dedifferentiation to a desired precursor cell type is successful, it may establish a precedent that can be applied to other cell types.
- The scientific rationale for the proposed research is logical and compelling. The project is highly innovative in its intent to partially reprogram mature endothelial cells to their embryonic hemogenic state.
- Reviewers had some concerns about feasibility of the project because of the potential difficulty in obtaining the key human tissue samples needed, a lack of compelling preliminary data that the gene expression data would yield interpretable results, and the ambitiousness of proposing to look at multiple tissues from two different species.
- The proposed immortalization of the hemogenic endothelial cells for the continuous production of HSC may face potential regulatory challenges for its clinical application.
Principal Investigator (PI)
- The PI is a physician scientist trained in medicine, developmental biology and stem cell biology with an outstanding background to pursue research in hematopoiesis.
- The PI has already authored many publications in high impact journals.
- The PI has secured grants from other funding agencies.
- The proposed mentors are world-renowned experts in highly relevant fields of stem cell research and hematopoiesis. Each has a strong mentoring track record and will provide complementary expertise to the PI.
- The applicant institution provides an outstanding, intellectually stimulating environment for physician-scientist career development, offering core services, adequate start up and lab space as well as protected time for research.
- The applicant institution has an excellent track record in development of physician scientists, and a strong commitment to researchers and clinicians in the area of stem cell research.
- The proposal was considered to be highly responsive and unlikely to get funding from traditional funding agency due to exploratory nature of the research.