Basic Biology IV
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.
Statement of Benefit to California:
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 goal of this proposal is to engineer mature endothelium, the inner cellular layer of blood vessels, for in vitro production of hematopoietic (blood-forming) stem cells (HSCs). Such hemogenic properties are normally found only in certain blood vessels early in embryonic development. The rationale for the proposed study is based on the hypothesis that the molecular programs responsible for HSC formation from embryonic endothelium can be reactivated in mature endothelium. To test this hypothesis, the applicant has proposed two aims. In the first, a global gene expression analysis will be used to identify factors differentially expressed in early versus mature endothelial cells; these factors will then be assessed for their ability to reprogram mature endothelial cells into cells capable of HSC production. Next, in Aim 2, a human disease model will be explored to identify new factors regulating the hemogenic program. Significance and Innovation - The proposal addresses a roadblock in the field of HSC transplantation, as current approaches for ex vivo production of multipotent HSC from human pluripotent stem cells have not yet been successful. - The project takes a novel approach toward derivation of HSCs from alternate cell sources, but its technical execution lacks innovation and sophistication. - If successful, the proposed research could have significant impact on advancing the development of HSC-based therapeutics. Feasibility and Experimental Design - Preliminary data are sparse and not compelling, and much of the Preliminary Data section consists of a description of planned experiments rather than actual preliminary data. - Concerns were raised about a number of aspects of the experimental design. - The global gene expression analysis will miss post-transcriptional modifications that might be important in the regulation of the hemogenic program. - The rationale for choosing the human diseased tissue in Aim 2 as a model of hemogenic endothelium was considered unconvincing, and reviewers questioned basic assumptions underlying this aim. - Reviewers questioned the feasibility of obtaining sufficient samples and amounts of embryonic hemogenic endothelium. Principal Investigator (PI) and Research Team - The PI is well qualified, having made significant contribution to the hemogenic endothelium hypothesis. - Collaborators have been recruited to provide expertise in computational data analysis and stem cell biology. The research environment is outstanding. Responsiveness to the RFA - The proposed research is responsive to the RFA, as it utilizes human cells and is designed to interrogate hematopoietic stem cell development.