Human embryonic stem cells hold promise for treating a variety of diseases because of their capacity to differentiate into any cell type in the body and replace damaged tissues. A major limitation of using embryonic stem cells for transplantation is that they express major histocompatibility antigens that have the potential to be recognized by the patient’s immune system as foreign and be rejected. At present, few studies have addressed if and how the immune system detects and rejects tissues derived from embryonic stem cells. It is necessary to understand the immunological responses that occur to foreign human embryonic stem cell-derived tissues to be able to monitor these parameters in future studies seeking to achieve immune tolerance to these grafts. A critical step before implementing stem cell therapies for treatment of human diseases is to establish their immunogenicity in relevant preclinical models. Study of the human immune system responses to the cells derived from embryonic stem cells has been limited by the lack of an appropriate preclinical animal model. For this reason, we developed a novel mouse model that shows long-term reconstitution with a complete range of human blood cells. Furthermore, these mice develop strong immune responses providing a powerful model system to study human immune function to embryonic stem cell derived transplanted tissues. We propose to study the immune response in humanized mice that receive human embryonic stem cell-derived pancreatic cell transplants. We have chosen to focus this research work on pancreatic lineage cells with the ultimate goal of developing novel therapeutic strategies for treatment of Type 1 diabetes. Type 1 diabetes is an autoimmune disease that strikes both children and adults. Diabetes is widely prevalent in the United States with over 23.6 million children and adults affected by this devastating disease (7.8% of the population). Approximately, 1.6 million new cases of diabetes are diagnosed each year and it is the seventh leading cause of death in the United States. Persons with type 1 diabetes are dependent upon giving themselves insulin injections daily to control their blood sugar levels. Unfortunately, insulin is not a cure for diabetes, nor does it prevent its severe complications, which include kidney failure, blindness, heart disease, stroke, and amputation. The knowledge gained through this research work would be an extremely important achievement toward improving not only islet transplantation for the treatment of diabetes, but can be applied to transplantation of other stem cell-derived tissues. Ultimately, in addition to developing new tools for improved imaging of human stem cell-derived transplants and the identification of immunological assays for clinical management of patients, this work will help to understand the mechanisms of tolerance and approaches for tolerance induction.
Statement of Benefit to California:
Development of methods for regenerative medicine using tissues derived from human embryonic stem cells will result in therapies that have the potential to improve the health and quality of life for millions of Californians and human populations world wide. Type I diabetes is the 7th leading cause of death in the United States and affects over 23.6 million children and adults representing 7.8% of the U.S. population. The cost for treatment of diabetes is estimated at $174 billion annually including $116 billion for direct medical costs and $58 billion for indirect costs related to disability, work loss and premature mortality. The research that we propose in this application will lead to an improved understanding of how the human immune system responds to islet cell transplants derived from human embryonic stem cells. This information is critical to enable the development of therapies to induce tolerance and prevent the rejection of islet cell transplants. Furthermore, through this research we will develop a battery of immune monitoring assays that can be used in the diagnostic setting to monitor graft acceptance or rejection and improve the clinical management of the patient and transplant outcome. This research will also benefit Californians by disseminating the scientific findings and tools developed in this work to researchers throughout California. If funded, this research work will create 2 new jobs that create tax revenue for the State of California
This is a project to study the immune reaction to transplantation of human embryonic stem cell-derived pancreatic lineage cells (PLCs), the cells damaged in Type 1 diabetes. The principal investigator (PI) proposes to use a humanized bone marrow, fetal liver and thymus (BLT) mouse model to determine how the adaptive immune system responds to HLA-incompatible transplants of hESC-derived PLCs, and to develop biomarkers or immune-monitoring assays that will distinguish rejection from tolerance. In Aim 1, the PI will characterize the ability of hESC-derived PLCs to engraft in the human BLT mouse model and in immunodeficient control mice, and establish the kinetics of engraftment and rejection. In Aim 2, the PI will analyze the immune response to hESC-derived PLCs in the BLT mouse model. Sub-aims include correlating T-cell phenotypes and alloreactivity with transplant outcome, and characterizing the humoral response to transplanted PLCs. Finally, the PI will define immunologic memory to the graft in pre-sensitized mice. The goals are to achieve a better understanding of the mechanistic basis of alloreactivity and to develop novel strategies for tolerance induction, aiming primarily at future control of Type I diabetes. Reviewers commented that the combination of hESC-derived PLCs and the humanized mouse model was novel and creative. They agreed that the project would have translational impact if successful. In general, reviewers described this as a solid grant application with a carefully-developed experimental plan and logical aims. However, they were split about the project’s feasibility. Some reviewers commented that the preliminary data is supportive of the model and proves that the research team can perform the experiments proposed. Other reviewers were concerned that the PI might not be able to produce PLC cells in sufficient numbers to conduct the experiments, and that expression of the reporter genes in PLCs might not be long-term enough to allow the study of the cells in vivo. There was also concern that the cells might not engraft and that they would not survive long enough to allow the PI to conduct the trafficking experiments. Reviewers were also split about the validity of the hu-BLT mouse as a surrogate model for assessing human immune responses to hESC-derived cells. One reviewer was convinced that studying graft rejection in a relevant humanized animal model is likely to contribute insights not achievable in man and that the evidence in the application suggested that the hu-BLT mouse model is appropriate for testing alloreactivity. Another reviewer commented that although the hu-BLT model is one of the most promising surrogate models, the immune response in this mouse has not been validated as truly human in nature and the proposal lacked experiments to better define these mechanisms in the mouse model. This reviewer suggested that the PI needed to define which populations in the hu-BLT system are responsible for antigen presentation, and whether these mechanisms are similar to those present in the human. Finally, reviewers were not very enthusiastic about the experimental design. They judged that a more focused approach to characterizing the immune response against PLCs was needed, and that Aim 2 in particular applies a battery of immunological tests rather than taking a hypothesis-driven approach. The emphasis on direct versus indirect antigen presentation was described as contrived and lacking in vivo correlation. In addition, one reviewer argued that the approach of preventing PLC rejection using immunosuppressive drugs will tell us little that is of interest or new. This reviewer argued that there are many innovative approaches to tolerance induction, both locally within the graft or systemically, that would be far more informative on this question and would provide more mechanistic information. The PI is an accomplished leader in the field of immune monitoring and HLA typing. The track records of the PI and co-investigator demonstrate expertise in immunologic characterization of transplanted tissues and embryonic stem cells, respectively, and each has made outstanding contributions to the field. Although the PI has assembled a large team of co-investigators and consultants from various disciplines to assist in achieving the goals, most will commit 2 to 5% effort, which raised some concern regarding their true commitment to the project. In particular, there was concern that the person generating the BLT mice will only dedicate 5% effort to the project. Overall, while reviewers appreciated the creative idea of using the human BLT mouse model to study the immune response to hESC-derived transplanted cells, their enthusiasm was dampened by feasibility concerns, perceived weaknesses in the experimental approach, and the absence of a hypothesis-driven plan.