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.
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.
The overall goal of this proposal is to engineer antigen-specific T regulatory cells (Tregs) to alleviate both autoimmune responses and the rejection of transplanted insulin-producing cells in a mouse model of Type 1 Diabetes. Tregs are specialized cells of the immune system that serve to suppress immune responses and maintain tolerance to self-antigens. Type 1 Diabetes is an autoimmune disease in which pancreatic beta cells are not recognized as self and are thus destroyed by the immune system. The applicant proposes to utilize the immunosuppressive capacity of Tregs to both counter this autoimmunity and promote tolerance to grafts of replacement insulin-producing cells. There are three Specific Aims: (1) to isolate and expand Tregs from human Type 1 Diabetes patients and engineer these cells to express islet-specific antigens; (2) to assess the functionality of these cells in vitro and in vivo in a mouse model of diabetes; and (3) to generate insulin producing cells from human embryonic stem cells (hESCs) and test the ability of engineered Tregs to block rejection of these cells following transplant.
Reviewers described this proposal as highly innovative, and were confident that the state-of-the-art technology will generate novel research tools. Reviewers agreed that the proposal could have a major impact and significantly advance the clinical applicability of stem cell therapies, particularly as the in vivo model system closely mimics the human system. However, they did caution that translation to the clinic could present significant regulatory and economic challenges, given the multi-faceted nature of the proposed therapeutic.
The reviewers found the scientific rationale for this proposal to be strong. The approach is logical and soundly based on prior work by the Principal Investigator’s (PI’s) research group and others using animal models of diabetes. The research plan is well-organized and carefully designed, and includes appropriate controls and targeted outcomes. The project is quite ambitious but reviewers were reassured of its merit by clearly delineated timelines and milestones. They also praised the substantial supporting preliminary data, which gave them confidence in the feasibility of the project. Reviewers did express concern about the in vivo phenotypic stability of engineered Tregs, and they would have appreciated a discussion of the potential plasticity of these cells following transplant. In fact, reviewers noted that pitfalls and alternative approaches were not well-described throughout the application. However, overall the work was considered very compelling.
Reviewers noted that the PI has an outstanding track record in the fields of autoimmunity and tolerance. They appreciated that the Co-Investigator contributes considerable expertise in stem cell biology and beta cell differentiation from hESCs. Reviewers described the assembled research team as highly qualified to carry out the proposed research.
Overall, reviewers were strongly supportive of this innovative proposal from an exceptional group of investigators. They found the scientific rationale to be quite strong and agreed that the project would have a major impact if successful.
- Bruce Blazar
- Maria Grazia Roncarolo