The immune system is vital to protect the body against foreign invaders, such as viruses and bacteria. However, the protection brought about by the immune system can also prevent acceptance of transplanted tissues or organs. The rejection of transplanted tissues or organs by the host can typically be prevented by use of drugs called immunosuppressants. Immunosuppressants can dampen the immune response to foreign tissues and organs and allow for the tissue or organ to engraft to the host and carry out its function; without immunosuppression the transplant will not engraft. On this basis, it is also expected that stem cell-based transplants will also require immunosuppression for engraftment. Although use of immunosuppression can allow a transplant to engraft, it also weakens the immune defense against disease-causing foreign invaders. Thus, development of other mechanisms to prevent rejection of stem cell-based therapeutics is warranted.
Importantly, the lack of an immune response in a pregnant mother against the embryo or fetus that carries proteins foreign to her body suggests that the embryo or fetus has an innate means to suppress the immune system. If this ability to avoid immune rejection is innate to the embryo, then it may also be innate to the cells that make up the embryo. Indeed, research suggests that embryonic stem cells do not induce an immune response and can actually dampen an active immune response. Based on these observations, our laboratory and others examined the immune response to human embryonic stem cells differentiated in a manner compliant to FDA guidelines into a cell type with the potential to treat neurological diseases and traumas. The immune response to these differentiated cells was similar to undifferentiated human embryonic stem cells. This finding suggests that certain cells derived from embryonic stem cells might possess properties that can be innately tolerated by the immune system.
Although the differentiated cells were shown to be privileged from immune attack in isolated tests of immune reactions, there is no evidence that the cells will be tolerated by the immune system in animal models of trauma that have intact and ongoing immune reactions. Our proposed research project will therefore determine the ability of differentiated cells to interact or interfere with the immune system. This is possible because we have developed tools to differentiate reciprocal transplant and host responses. We also propose to examine if this effect is also present in another differentiated cell type derived from the same or a different line of human embryonic stem cells. The information gathered from this research will be important for determination of what interactions occur in both the transplant and the host during the initial period after transplantation and will help determine the immunosuppression needs for human embryonic cell transplants in this neural trauma.
Statement of Benefit to California:
This program will position California for international competitiveness in this emerging area of biotechnology, as our studies are critical to the clinical development of the two hESC-derivates used in our studies, one of which is within 12 months of being used in human clinical trials, and the second is within 12 months of being presented to the FDA for an IND. Thus, California will benefit from supporting the discovery of what will become the first and second human embryonic stem cell-based clinical trials in the world. This will result in California being a focus of the stem cell industry, including large pharmaceutical companies that will eventually participate in the latter stage stem cell clinical trials. Clinically relevant scientific advances lead to the development of biotechnology companies, creating jobs and taxation. Funding for this proposal will directly create new jobs. In these challenging economic times, we feel that any award should be spent in a manner which enhances the local and state economy, in essence returning direct value to the citizens of California. To this end, we have purposely selected suppliers of equipment and services that are located in the state of California. In addition, due to the booming medical device and biotechnology industries in California, we feel that all new hires can be obtained from within the state of California.
The overall goal of this proposal is to investigate the ability of cells differentiated from human embryonic stem cells (hESCs) to dampen the immune response following transplantation into an animal model of neural trauma. In previous work, the applicant has found that these cells alter the host microenvironment and modulate neuroinflammation. In this proposal, the applicant proposes to elucidate the mechanisms by which these hESC-derived cells affect host inflammation and immune responses. There are three Specific Aims: (1) to assess the ability of hESC-derived cells transplanted into an animal model of neural trauma to up- or down-regulate an array of selected genes involved in inflammation and immune responses; (2) to extend this assessment to another hESC-derived cell type, as well as cells derived from distinct hESC lines; and (3) to further extend this assessment to hESC-derived cells that have been genetically modified to express an anti-inflammatory cytokine.
Reviewers did not find this proposal to be particularly innovative or creative. They noted that while the use of transplanted cells to modulate the immune response in the context of neural trauma may be novel, it has been described in the context of other neurological disorders such as multiple sclerosis. Reviewers were also not convinced that the proposal would have a major impact on the field. While the proposed experiments will likely generate a wealth of data, it is not clear how these data will be subsequently used to improve the survival and function of transplanted cells.
The reviewers found the research plan to be generally logical and achievable but questioned the scientific rationale for key aspects. For example, justification for the selection of genes of interest is not presented and the advantages of using this subset, rather than a microarray, are not clear. Reviewers also questioned the time points for analysis following neural trauma. They noted that many groups have shown that the levels of several inflammatory molecules are upregulated acutely after injury and then rapidly decline back to baseline. Thus the choice of time points beginning 2 weeks after injury may cause many of the critical and massive early changes to be missed. Further, interpretation of results could be problematic as the changes in histology and behavior at later time points may be due to drastic effects in the early period following transplant that are preserved at later time points rather than immunomodulation per se. Reviewers also raised some concerns about the experimental design. They noted that xenotransplantation of human cells into an animal model presents a major problem, as data obtained may not accurately represent the allogeneic transplants expected in human clinical studies. Regarding the experiments proposed in Aim 3, it was not clear to reviewers why the specific cytokine was chosen for overexpression. They also noted that an important control for these experiments would be to ensure that the transplanted, genetically modified cells survive and express the cytokine for prolonged periods.
Reviewers commented that the Principal Investigator (PI) on this project is an expert in his field and a leader in translational studies of ES-derived cells for treatment of neural trauma. However, the application lists the PI as both the stem cell and the immunology expert for this proposal. Reviewers did not consider the PI to be an expert in immunology, and although consultation with immunological experts is mentioned, the level of consultation is not clear. The project would benefit greatly from the inclusion of a dedicated Co-Investigator with such expertise.
Overall, reviewers raised a number of concerns that substantially reduced their enthusiasm for this proposal. They questioned the scientific rationale for certain aspects of the research plan and were not convinced that the data generated from the proposed experiments would have a major impact on the field. Further, the lack of a dedicated Co-Investigator with immunology expertise, as required by the RFA, was considered a major weakness of the proposal.