Type 1 diabetes (T1D) is caused by the destruction of insulin producing b-cells in the pancreatic islets by an overactive self immune system. Due to lack of ways of preventing T1D, insulin administration is currently most common method of treatment, but susceptible to developing serious, long-term complications. Islet transplantation provides an excellent alternative and can improve glycemic control and reduce the risk of further complications associated with diabetes. Transplantation of pancreas or isolated islets across immune barriers has been conducted with some efficacy but is limited by inadequate organ availability and the need for long-term non-specific immunosuppression. The ability to transplant a renewable supply of islets or β-cells would have a dramatic impact on the disease. Human embryonic stem cells (hESC) represent one of the most promising alternative sources of β-cells, given their pluripotent and self-renewing properties. However, we hypothesized that the immunocompetent recipients will recognize the product as foreign (and autoimmune-self) due to MHC-mismatch (allogeneic) between donor and recipient, leading to transplant rejection. Thus, in order to make stem cell-derived islet cell therapy both commercially and clinically viable, β-cell protective therapies need to be developed to combat the strong allogeneic immune response, as well as the recurrent autoimmune attack which caused the disease in the first place.
In previous studies, we have shown that a small population of CD4+ regulatory T cells (Tregs) plays a critical role in controlling self-reactivity thus maintaining immune tolerance. Adoptive immunotherapy with Tregs into diabetes prone non-obese diabetic (NOD) mice can restore immune tolerance leading to a long-term cure of T1D and have shown a lot of promise for the treatment of autoimmune diseases in the preclinical studies. A key parameter has been the enhanced activity of antigen specificity in directing the tissue-protective functions of Tregs. Thus, in this proposal, we proposed to exploit antigen-specific Treg to selectively regulate ongoing immune responses while avoiding the need for pan-immunosuppression. In the past year, we have made significant, albeit slow progress in this effort. We have taken significant steps to develop an approach to expand alloantigen-specific Tregs (those that recognize and suppress immune responses against foreign tissues) from patients with T1D. We have cloned and expressed self-antigen-specific T cell receptor genes in expanded Tregs to determine their ability to suppress stem cell-derived islet transplants. We have established a humanized mouse model to test the hypothesis that engineered antigen-specific Tregs will potently suppress rejection of stem cells. We set up a mouse model of islet transplantation by implanting human islets (from cadavers) in mice lacking a functional immune system. These islets were functional and produced insulin to control normal glucose levels in mice. However, when these mice were complemented with human immune system, the islet grafts were rejected by the allogeneic immune response. This provides an excellent mimic to the human islet transplant where a similar allogeneic immune response leads to the graft rejection. This will provide a setting for testing the engineered Tregs. More over, we have shown that self-antigen and alloreactive Tregs can be generated and transferred in to this humanized mouse setting. Unfortunately, we were unable to test the stem cell-derived islets in this setting as yet due to unexpected challenges in our efforts to produce these cells due to technical problems. However, significant progress has been made to rectify these problems and we are confident that we will succeed in using stem cell-derived islets in the coming year.
Reporting Period:
Year 2
Type 1 diabetes (T1D) is caused by the destruction of insulin producing b-cells in the pancreatic islets by an overactive self immune system. Due to lack of ways of preventing T1D, insulin administration is currently most common method of treatment, but susceptible to developing serious, long-term complications. Islet transplantation provides an excellent alternative and can improve glycemic control and reduce the risk of further complications associated with diabetes. Transplantation of pancreas or isolated islets across immune barriers has been conducted with some efficacy but is limited by inadequate organ availability and the need for long-term non-specific immunosuppression. The ability to transplant a renewable supply of islets or β-cells would have a dramatic impact on the disease. Human embryonic stem cells (hESC) represent one of the most promising alternative sources of β-cells, given their pluripotent and self-renewing properties. However, we hypothesized that the immunocompetent recipients will recognize the product as foreign (and autoimmune-self) due to MHC-mismatch (allogeneic) between donor and recipient, leading to transplant rejection. Thus, in order to make stem cell-derived islet cell therapy both commercially and clinically viable, β-cell protective therapies need to be developed to combat the strong allogeneic immune response, as well as the recurrent autoimmune attack which caused the disease in the first place.
In previous studies, we have shown that a small population of CD4+ regulatory T cells (Tregs) plays a critical role in controlling self-reactivity thus maintaining immune tolerance. Adoptive immunotherapy with Tregs into diabetes prone non-obese diabetic (NOD) mice can restore immune tolerance leading to a long-term cure of T1D and have shown a lot of promise for the treatment of autoimmune diseases in the preclinical studies. A key parameter has been the enhanced activity of antigen specificity in directing the tissue-protective functions of Tregs. Thus, in this proposal, we proposed to exploit antigen-specific Treg to selectively regulate ongoing immune responses while avoiding the need for pan-immunosuppression. In the past year, we have made significant, albeit slow progress in this effort. We have taken significant steps to develop an approach to expand alloantigen-specific Tregs (those that recognize and suppress immune responses against foreign tissues). We have developed a process for isolating and expanding alloantigen-specific Tregs to determine their ability to suppress stem cell-derived islet transplants. We have established a humanized mouse model to test the hypothesis that alloantigen-specific Tregs will potently suppress rejection of stem cells. We set up a mouse model of islet transplantation by implanting human islets (from cadavers) in mice lacking a functional immune system. These islets were functional and produced insulin to control normal glucose levels in mice. However, when these mice were complemented with human immune system, the islet grafts were rejected by the allogeneic immune response. This provides an excellent mimic to the human islet transplant where a similar allogeneic immune response leads to the graft rejection. This will provide a setting for testing the allospecific Tregs.
This year we have begun to test the stem cell-derived islets in this setting. First, we have developed a more efficient and effective protocol for developing pancreatic endoderm from human embryonic stem cells. These cells have been transferred into immunodeficient mice and shown to produce human insulin after some period of time (3 months). In addition, we have developed in vitro modifications of the differentiation process that has enabled the formation of cells that express markers of fully matured insulin producing cells without extensive in vivo maturation whose functionality is currently assessed. Finally, we have been able to mimic this process using a genetically marked ES population (luciferase transduced). This allows for rapid and ongoing analysis of cell survival in transplanted animals to enable rapid and extensive therapeutic interventions.
Finally, we have validated a humanized mouse model that allows an analysis of alloreactive Tregs in this setting. Thus, in the coming year, we fully expect to be able to test the hypotheses posed in the original application, as all the tools are now available. In addition, we will work towards adapting the process to the analysis of iPS cells.
Reporting Period:
Year 3
The goal of this project was to using novel immune techniques to block rejection of human ES cell derived islet precursors in mouse models of diabetes. during the past three years, we identified and developed islet specific regulatory T cells that could be used to suppress immune responses to the stem cell-derived islets. we also established, with some difficulty, a more robust methodology to direct the differentiation of human ES cells into islet precursors for transplantation. the studies were not complete but demonstrated in proof of principle studies that the tools can be generated to address the primary questions posed in this project.
Grant Application Details
Application Title:
Stem cell tolerance through the use of engineered antigen-specific regulatory T cells
Public Abstract:
Type 1 Diabetes (T1D) occurs as a consequence of uncontrolled immune activation, culminating in the destruction of insulin-producing beta-cells. Efforts to prevent or reverse diabetes have been limited by the lack of safe and effective immunotherapies coupled with the inability to restore insulin producing beta-cells. We believe proper immune control to self-tissues to be a fundamental requirement for any effective therapy, whether the goal is prevention of early beta-cell loss, beta-cell regeneration at disease onset, or ultimately beta-cell replacement in cases of established T1D. To impact disease, any effective therapy must first restore a glucose-responsive insulin-producing beta-cell population. Stem cells represent one of the most promising alternative sources of insulin-producing cells. Second, a therapy must combat the persistent autoimmune attack, as well as any attack directed at foreign tissues following transplantation. The goal of this project is to bring together research efforts in these two complementary areas to fill these critical gaps. Previous studies have focused on the use of regulatory T cells (Tregs) as one key means of restoring immune tolerance in T1D. A key parameter has been the importance of antigen specificity in directing the tissue-protective functions of Tregs. In the prevention setting, antigen-specific Tregs were at least 100-fold more effective in controlling diabetes when compared to Tregs with diverse receptors. Importantly, treatment with antigen-specific Tregs is capable of reversing diabetes in the non-obese diabetic (NOD) mouse model of T1D. Likewise, these Tregs have also been shown to be important in preventing tissue rejection in the transplantation setting. Thus, Treg specificity determined by the T cell receptor can be exploited to selectively suppress a particular component of an ongoing immune response. The translation of this knowledge requires a robust means to generate a large number of patient-derived antigen-specific Tregs. The goal of this proposal is to test the hypothesis that the introduction of antigen-specific Tregs will be able to correct the initiating and persistent autoimmunity in T1D, as well as prevent the transplant-mediated destruction of beta-cells following stem cell transplantation. Thus, we propose to develop engineered tissue-directed human regulatory T cells capable of suppressing autoimmune and transplant-related destruction of beta-cells. To generate these cells we will deliver the specific T cell receptors (TCRs) by gene therapy delivery mechanisms to a patient’s own Treg population and test their ability to suppress specific immune responses in immunodeficient mice following beta-cell replacement therapies.
Statement of Benefit to California:
Type 1 diabetes (T1D), previously referred to as Juvenile Diabetes, is a chronic condition that leads to devastating consequences for patients and places a huge financial burden on the California health care system. T1D occurs as a consequence of the systematic immune destruction of the insulin-producing beta cells in the pancreas. Once those cells are destroyed, the production of insulin is dramatically compromised and patients lose the ability to control blood sugar levels. Chronic periods of elevated blood sugar result in numerous secondary complications including heart disease, blindness, kidney failure, and abnormal nervous system function, among others. There is currently no known way to prevent T1D. According to the California Department of Public Health, there were 2.7 million Californians with diabetes in 2007, meaning that 1 out 10 adult Californians has diabetes. Of these, approximately 5-10% of patients have T1D, with the remainder consisting of patients with insulin-resistant type 2 diabetes. Of particular concern, the incidence rate of T1D has been increasing, particularly in children 5 years old and under. T1D is the second most common chronic disease in children, second only to asthma. Consequently T1D, and improved therapeutic approaches for this disease, are issues of great importance to the people of California.
Intensive insulin therapy is the only current treatment for T1D. While effective at reducing blood sugar levels in the short term, insulin therapy does not address the underlying autoimmune attack which leads to T1D. Our studies will explore the potential use of human embryonic stem cells to restore insulin-producing cells. In addition, we are exploring ways to genetically modify (through the use of gene therapy) a population of regulatory cells (Tregs) within the immune system to stop the autoimmune attack that initiates T1D. We expect that these modified Tregs will not only stop the autoimmune process, but will also protect against the immune attack which normally arises against the transplanted tissues and any stem cell-derived tissues. We hope to eventually use these procedures to treat patients with T1D. If successful, our results may allow patients with T1D to discontinue, or greatly reduce the amount of insulin they must currently take to maintain normal blood sugar levels. This approach will directly benefit those with T1D, as well as the general population by reducing the health care burden associated with the care of this chronic disease.
