One of the most exciting prospects arising from the description of stem cells is the possibility of generating tissues or cells that can be used to regenerate or replace damaged or non-functional cells. In this way, it may be possible to reverse debilitating diseases such as Parkinson's Disease or diabetes. Tremendous progress has been made towards understanding how stem cells can be turned into the appropriate cell populations to treat different diseases. However, before a stem cell derived tissue can be transplanted, the same donor histocompatability tissue matching problems have to be overcome as for a transplant patient. Usually, transplant recipient patients require extended immunosuppression to prevent rejection mechanisms turning on. An alternative approach is to instruct or tolerize the recipients immune system of the immunologic "color" of the stem cells, what histocompatibility match the stem cell displays. By turning off the immune response to these tissue antigens in advance, subsequent transplant of stem cell derived cells or tissues will not be rejected. This approach has shown success in normal transplant models typically using bone marrow cells as the tolerizing cell. We propose to replicate this effort using stem cell based products. The best immunologic instructor is a population of cells called dendritic cells. We aim to develop stem cell based dendritic cells manipulated to tolerize the immune response of a recipient. With this reagent, we will have a tool to allow successful engraftment of stem cell based regenerative therapies in any individual. We have already established robust protocols to generate dendritic cells from stem cells. We will now compare the different mechanisms for generating tolerizing versions of these dendritic cells. After establishing the most robust approach in tissue culture, we will assess the function of these tolerizing dendritic cells in an animal model, using bone marrow transplant as our readout. Our final aim is to replicate the tissue culture differentiation to dendritic cell and manipulation to a tolerizing population using human stem cells. The problem of stem cell transplant rejection is a fundamental issue to the successful development of regenerative reagents based on stem cells. The success of tolerizing protocols in conventional transplant surgery now clearly indicates that tolerance is a possible resolution to tissue rejection reactions. The protocols developed in this application will define a way to do this.
Statement of Benefit to California:
The number of degenerative diseases and injuries that may respond to therapeutic intervention using regenerative stem cell based reagents has increased enormously in recent years. This is thanks in no small part to the leadership role the State of California has played in supporting and advancing stem cell research. Despite these efforts, there are not many widespread examples of stem cell based regenerative therapies. There are many reasons why so few treatment using stem cells currently exist, not least of them is the significant issue of transplant tolerance and immunologic rejection of stem cell based therapies. Our proposed research seeks to define a protocol to overcome the immunologic rejection of stem cell based reagents. In so doing, we aim to provide a broadly applicable approach to prepare a patient for stem cell based therapeutics. The generation of this protocol is an important step for the application of any stem cell based therapeutic. The development of this protocol will have broad impact on all the stem cell based reagents developed with California and elsewhere and will address a technical bottleneck that is limiting the application of novel reagents that could greatly improve the quality of life and productivity for residents of California. Additionally, development of this protocol would clearly establish California as a key leader in advancing clinical application for stem cell biology. This would have a significant impact of the interests and business related to regenerative medicine and their future growth.
The overall goal of this proposal is the development of tolerance-inducing transplant protocols utilizing dendritic cells (DCs) derived from human embryonic stem cells (hESCs). DCs function mainly as antigen-presenting cells, activating T cells, and so, with appropriate manipulation, these cells could be harnessed to promote tolerance to subsequent tissue grafts. The applicant proposes three Specific Aims: (1) to determine the best approach to deriving tolerigenic DCs from mouse ESCs (mESCs); (2) to assess the tolerigenic properties of these mESC-derived DCs in a mouse model; and (3) to adapt the DC derivation protocol to hESCs. Reviewers did not find this proposal to be particularly innovative. They noted that the hypothesis that DCs can be used to induce tolerance is not novel, nor are the specific approaches proposed to generate tolerigenic DCs. Reviewers agreed that this project could have an impact if successful as the approach could be used to facilitate acceptance of a range of tissue grafts. Reviewers cited a number of weaknesses in the research plan. They noted that while the scientific rationale for pursuing tolerigenic DCs is appropriate, the research plan is lacking key elements. For example, the applicant does not propose to test DC response to inflammatory signals, their phenotypic stability in vivo, or expression of chemokine and homing receptors necessary for migration to the appropriate locations to induce tolerance. Reviewers noted that the experimental design also lacks critical details, including host preparation prior to DC immunization and conditioning regimens for subsequent transplants. A major reviewer concern was that the applicant does not thoroughly address the specificity of tolerigenic DCs. These DCs may be generally immunosuppressive rather than allospecific and nonspecific tolerizing effects may not be beneficial. Reviewers praised the Principal Investigator (PI) and assembled research team. They described the PI as an experienced investigator with an outstanding record of publication and many high-profile publications. They also appreciated the contributions of the highly qualified Co-Investigator in the fields of hESC biology and DC differentiation. Reviewers noted that the proposal brings together three excellent research groups at the applicant institution, creating a team well-qualified to carry out the proposed research. Overall, while reviewers agreed that this proposal has a sound scientific rationale and is supported by an excellent research team, the proposal was not novel and flaws in the research plan led reviewers to conclude that the proposal was unlikely to succeed.