Objective
Our objective is to cure type 1 diabetes by combining genetically engineered stem cell-derived insulin-producing beta cells and regulatory T cells into a therapy that both replaces lost insulin-producing beta cells and protects the new beta cells from immune destruction without using immunosuppressive drugs. This will be accomplished without restrictions in beta cell availability, as lab-grown stem cell-derived beta cells are unlimited, or the need for long-term immune suppression, as the customized regulatory T cells specifically recognize and locally protect the stem cell-derived beta cells and reeducate the recipient’s immune system to not attack the stem cell-derived beta cells. Our strategy has the potential to be a major leap forward for all type 1 diabetes patients.
Background Rationale
Type 1 diabetes (T1D) is devastating autoimmune disease caused by the destruction of the beta cells of the pancreas by the patient’s own immune system. Beta cells secrete insulin, a hormone required to control blood sugar levels. Without beta cells, T1D patients depend on insulin injections multiple times a day. If not enough insulin is injected, patients risk hyperglycemia, leading to heart disease, nerve damage, vision loss, kidney damage, and even coma. If too much insulin is injected, patients risk hypoglycemia, which can lead to seizures, coma, and even death. Constant blood sugar monitoring and insulin administration is no match for the precision with which beta cells naturally control blood sugar levels, greatly affecting the quality of life of T1D patients. Ideally, one would replace the lost beta cells with new ones. Transplanting islets, the endocrine part of the pancreas that contains beta cells, from deceased donors into T1D patients confers exogenous insulin independence for years. Yet, its widespread implementation faces two major challenges. One is a shortage of cadaveric islets, especially given that islets pooled from three to four donors are needed for one patient. To address this challenge, we have developed methods to convert human stem cells, which can be grown in the lab in virtually infinite quantities, into functional insulin-producing beta cells. Second, simply replacing the lost beta cells does not address what caused the disease in the first place, their immune destruction. Of note, cadaveric and stem cell-derived beta cells are not genetically matched to the patient, being threatened by autoimmune and alloimmune rejection. Currently, islet transplant patients receive immunosuppressive drugs that broadly inhibit the immune system. While these drugs can protect the islet transplant for years, they are toxic to the liver, kidneys, and nervous system, and leave the patients susceptible to infections and cancer. Children can additionally suffer stunted growth and cognitive impairment. What if we could specifically protect transplanted beta cells from immune attack while leaving the rest of the immune system intact? There is an immune cell type dedicated to inhibiting specific immune responses, preventing autoimmunity – the regulatory T cell (Treg). Tregs can protect tissues from immune attack. Yet, to do so they must be stimulated by their target molecule, known as antigen. Such antigen-specific Tregs are very rare in the blood, only few in a million, and antigens in beta cells and no other cell in the body remain unknown. We reasoned that, instead of searching for a naturally occurring target molecule on beta cells, we could engineer our own unique inert cell surface molecule into stem cells. Beta cells derived from these modified stem cells would also have this unique bait on their cell surface. To create Tregs specific to these engineered stem cell-derived beta cells, we would isolate total Tregs from blood and genetically engineer an artificial receptor on their surface, a chimeric antigen receptor or CAR, specific to the unique bait on the beta cells, allowing the engineered Tregs to specifically recognize and protect engineered beta cells. With this combination engineered cell therapy, we make both the lock and the key for localized immune protection of off-the-shelf beta cells, aiming to treat T1D patients without the hurdles of islet shortage or immunosuppressive drug toxicity.
Description of Project
Type 1 diabetes (T1D) is a chronic condition that affects more than 1 million Americans. Most are diagnosed at a very early age. Their bodies cannot control blood sugar levels, because their immune system recognizes and destroys the beta cells in the islets of the pancreas. Beta cells are responsible for producing insulin, a hormone required to control blood sugar. High blood sugar levels can lead to nerve pain, amputations, blindness, and even death. T1D patients depend on constant blood sugar monitoring and insulin injections. One promising treatment for T1D is pancreatic islet transplantation, that is transplanting islets from a deceased donor into a T1D patient to restore insulin production. This can free patients from daily insulin injections for years. However, this therapy in its current form has serious limitations. First, there is a severe shortage of high-quality islets, exacerbated by the fact that it takes islets from up to four deceased donors combined to transplant into a single T1D patient to achieve independence from insulin injections. Second, donor islets are targeted for destruction by the patient’s immune system due to the patient’s autoimmune reaction against beta cells and alloimmune rejection against genetically mismatched tissues. Recipients thus require strong immunosuppressive drugs that indiscriminately inhibit the immune system, increasing susceptibility to infections and cancer and damaging multiple organs. These toxic side effects are especially nefarious for children and adolescents, which can also suffer growth and cognitive impairments. Moreover, the T1D patient’s immune system can still eventually destroy the transplanted islets. To address the shortage of donor beta cells, we have developed a way to grow large numbers of insulin-producing beta cells from human stem cells in the lab. This creates a potentially unlimited supply of cells for transplant. Yet, a major hurdle remains: how to protect these cells from the patient’s immune system without toxic immunosuppressive drugs? Regulatory T cells, or Tregs, are the cells of the immune system that help prevent harmful immune reactions, such as those involved in autoimmunity and in transplant rejection. Tregs are most effective when they recognize specific targets, called antigen-specific Tregs, but they’re extremely rare, including the ones that recognize insulin-producing beta cells. To solve this, we developed a new strategy: we engineered both the lab-grown stem cell-derived beta cells (sBCs) to contain a unique marker on their surface and the patient’s own Tregs to recognize that shared marker. In our first version, we created sBCs with a molecule called truncated epidermal growth factor receptor (EGFRt) on their surface and designed Tregs with a receptor called a chimeric antigen receptor, or CAR, to detect EGFR. This combinatorial engineering successfully protected the sBCs from immune attack in animal models, proving our concept. However, EGFR is found in many parts of the human body, not exclusively on engineered sBCs, making this pair not compatible with clinical testing. Hence, we developed a new marker called truncated anterior gradient protein 2 (AGR2t), a harmless, lab-designed surface protein that is not on the surface of other tissues and does not trigger unwanted immune responses. We also built custom Tregs with a CAR specific to AGR2t. Next, we will test how well AGR2t-tagged sBCs are protected by AGR2t CAR Tregs from different types of killer immune cells in the test tube and in cutting edge advanced mouse models that mimic the human immune system and T1D. This research holds enormous potential to pave the way for a powerful new treatment that restores natural insulin production and keeps the immune system in check in a precise manner, offering real hope to the millions of people living with T1D.
Anticipated Outcome
We anticipate that our work will result in the creation of a new effective and safe treatment for type 1 diabetes (T1D) that replenishes the insulin-producing beta cells lost in people with T1D with transplanted beta cells and protects the new beta cells from destruction by the T1D patient’s immune system without using immunosuppressive drugs. We genetically engineered regulatory T cells (Tregs), immune cells dedicated to quelling unwanted immune attacks and inflammation, to bind to and become stimulated by a unique bait protein. In parallel, we genetically engineered stem cells to present that unique bait protein on their surface. Beta cells (and any other cells) derived from these engineered stem cells also have the unique bait on their surface. Our engineered Tregs will protect our engineered beta cells from immune attack in the Petri dish and in the most advanced mouse models of human T1D available. After this project is completed, the next step will be to prepare for human trials. We will use off-the-shelf human stem cells and human Tregs isolated from patients’ blood. Both the bait protein on the engineered beta cells and the receptor for the bait protein on the engineered Tregs are novel molecules we developed and tested and are compatible with use in humans. Importantly, the off-the-shelf insulin-producing beta cells and the autologous protective Tregs can be made in large quantities using medical-grade methods, frozen for storage, and shipped to different locations without losing their effectiveness after thawing. This means the treatment could be manufactured in one place and delivered to patients with T1D somewhere else, bringing us closer to a potential cure for T1D accessible to everyone.
Relevance to T1D
Type 1 diabetes (T1D) is a devastating disease that happens when the body’s immune system mistakenly recognizes and destroys beta cells. These cells in the pancreas make insulin, a hormone needed to control blood sugar. About 1 in 10 people with diabetes have T1D. In the United States alone, T1D costs the healthcare system and economy more than $40 billion every year. While people with T1D can manage their condition with daily insulin injections, a healthy diet, and careful blood sugar monitoring, there is still no cure. The only treatment that comes close involves transplanting insulin-producing beta cells from a deceased donor pancreas, along with powerful medications to stop the immune system from rejecting the transplanted cells. This can help some people live without needing insulin shots for years. However, this option is limited by a severe shortage of pancreas donors (currently, it is necessary to pool pancreases from three or four donors to harvest enough beta cells to transplant into one recipient) and the toxic side effects of the immunosuppressive drugs, which are especially damaging in children and adolescents (these include growth and cognitive impairments in addition to damage to many organs). New and better treatments to prevent or reverse T1D are urgently needed. The new treatment we are proposing to develop is particularly relevant to T1D because it addresses both the pancreas donor shortage and the immunosuppressive drug toxicity, holding the potential to provide a cure that would benefit all T1D patients irrespective of age, genetics, or disease stage.