By Hendra Lukman 
Stanford Medicine researchers have achieved a groundbreaking breakthrough in the fight against Type 1 diabetes, demonstrating in animal models that a combined transplant of blood-forming stem cells and pancreatic islet cells from an immunologically mismatched donor can completely prevent or fully reverse the disease. This innovative approach cultivates a unique "hybrid immune system" within the recipient, effectively halting the autoimmune assault on insulin-producing cells without inducing dangerous side effects. The findings, published in the Journal of Clinical Investigation, offer significant hope for a transformative treatment for Type 1 diabetes and other autoimmune conditions.
A Novel Approach to Immune Tolerance
Type 1 diabetes is a chronic autoimmune disorder characterized by the immune system’s misguided attack and destruction of the insulin-producing beta cells within the pancreatic islets. This process leads to a deficiency in insulin, a hormone essential for regulating blood sugar levels, necessitating lifelong management through insulin injections and careful monitoring. Current treatments focus on managing the symptoms rather than addressing the root cause of the immune system’s malfunction.
The Stanford team, led by Dr. Seung K. Kim, a professor of developmental biology, gerontology, endocrinology, and metabolism, has built upon years of research into stem cell transplantation and immune tolerance. Their latest study successfully navigated the complex challenge of Type 1 diabetes, which involves not only replacing the destroyed islet cells but also re-educating the recipient’s immune system to prevent further destruction.
"The possibility of translating these findings into humans is very exciting," stated Dr. Kim, who also directs the Stanford Diabetes Research Center and the Northern California Breakthrough T1D Center of Excellence. "The key steps in our study — which result in animals with a hybrid immune system containing cells from both the donor and the recipient — are already being used in the clinic for other conditions. We believe this approach will be transformative for people with Type 1 diabetes or other autoimmune diseases, as well as for those who need solid organ transplants."
Building on Prior Successes: From Induced to Autoimmune Diabetes
This new research significantly advances findings from a 2022 study by Dr. Kim and his collaborators. In that earlier work, researchers induced diabetes in mice using toxins to eliminate insulin-producing cells. They then employed a pre-transplant regimen involving immune-targeting antibodies and low-dose radiation, followed by a transplant of blood stem cells and islet cells from an unrelated donor. This protocol successfully restored blood sugar control in the mice.
The latest study presented a more formidable challenge: preventing or curing diabetes driven by the body’s own immune system, mirroring human Type 1 diabetes. In this scenario, transplanted islets face a dual threat: they are recognized as foreign tissue by the recipient’s immune system, and their destruction is actively pursued by an immune system already programmed to target islet cells.
"Just like in human Type 1 diabetes, the diabetes that occurs in these mice results from an immune system that spontaneously attacks the insulin-producing beta cells in pancreatic islets," explained Dr. Kim. "We need to not only replace the islets that have been lost but also reset the recipient’s immune system to prevent ongoing islet cell destruction. Creating a hybrid immune system accomplishes both goals."
A Simple Tweak for Potent Protection
A critical hurdle in treating autoimmune diseases with stem cell transplantation is the inherent difficulty in preparing the recipient’s immune system for the transplant without exacerbating the underlying autoimmune condition. The Stanford team discovered a relatively straightforward solution to this problem.
Graduate and medical student Preksha Bhagchandani, the lead author of the research, along with Dr. Stephan Ramos, a postdoctoral fellow and co-author, incorporated a medication commonly used for autoimmune diseases into the pre-transplant regimen developed in 2022. This adjusted protocol proved remarkably effective.
In the study, 19 out of 19 mice treated with this modified protocol and subsequently receiving a combined blood stem cell and islet cell transplant did not develop Type 1 diabetes. Furthermore, in a separate cohort of mice that already had long-standing Type 1 diabetes, nine out of nine were fully cured following the same combined transplant procedure. Crucially, none of the animals developed graft-versus-host disease (GVHD), a serious complication where the donor’s immune cells attack the recipient’s healthy tissues. Following the transplants, the mice no longer required immune suppressive drugs or insulin for the entire six-month study period.
The researchers highlighted that the antibodies, drugs, and low-dose radiation employed in their mouse model are already standard components of clinical practice for blood stem cell transplantation. This familiarity with existing protocols makes the transition of this strategy towards human trials for Type 1 diabetes a realistic and promising next step.
A Foundation in Kidney Tolerance Research
The scientific underpinnings of this groundbreaking work are deeply rooted in extensive research on inducing immune tolerance for solid organ transplants. Dr. Kim and his colleagues drew inspiration from the pioneering work of the late Dr. Samuel Strober, a professor of immunology and rheumatology, and his collaborators, including study co-author Dr. Judith Shizuru, a professor of medicine.
These earlier investigations demonstrated that a bone marrow transplant from a partially immunologically matched human donor could establish a hybrid immune system in the recipient. This hybrid system allowed for the long-term acceptance of a kidney transplant from the same donor, often eliminating the need for ongoing immunosuppressive drugs. In some patients, kidney function remained stable for decades without rejection.
Blood stem cell transplants are a well-established treatment for various blood and immune system cancers, such as leukemia and lymphoma. However, these procedures typically involve high-dose chemotherapy and radiation to eradicate the patient’s original immune system, often leading to severe side effects. Dr. Shizuru and her team have been instrumental in developing a less intense and safer preparation method for individuals with non-cancerous conditions like Type 1 diabetes. This gentler approach aims to reduce bone marrow activity just enough to allow donor blood stem cells to engraft and flourish.
"Based on many years of basic research by us and others, we know that blood stem cell transplants could also be beneficial for a wide range of autoimmune diseases," commented Dr. Shizuru. "The challenge has been to devise a more benign pre-treatment process, diminishing risk to the point that patients suffering from an autoimmune deficiency that may not be immediately life-threatening would feel comfortable undergoing the treatment."
The hybrid immune system fostered by the combined transplant appears to achieve this delicate balance. "Now we know that the donated blood stem cells re-educate the recipient animal’s immune system to not only accept the donated islets, but also not attack its healthy tissues, including islets," Dr. Kim explained. "In turn, the donated blood stem cells and the immune system they produce learn to not attack the recipient’s tissues, and graft-versus-host disease can be avoided."
Future Hurdles and Broader Implications
Despite the highly encouraging results in mice, significant challenges remain before this innovative strategy can be widely applied to treat Type 1 diabetes in humans. A primary obstacle is the current reliance on islets obtained from deceased donors. Furthermore, the blood stem cells and islet cells must originate from the same individual. The quantity of islet cells typically recovered from a single donor may also not always be sufficient to reverse established Type 1 diabetes.
The Stanford team is actively exploring solutions to these limitations. Promising avenues include the laboratory production of vast quantities of islet cells from pluripotent human stem cells and the development of techniques to enhance the survival and functionality of transplanted donor islets post-transplantation.
Beyond Type 1 diabetes, Dr. Kim, Dr. Shizuru, and their collaborators envision this gentle pre-conditioning strategy opening doors to stem cell transplants for a spectrum of other autoimmune diseases, including rheumatoid arthritis and lupus. It could also offer a less arduous treatment option for non-cancerous blood disorders like sickle cell anemia, for which current stem cell transplant methods are still quite harsh. Moreover, the approach holds potential for facilitating transplants involving mismatched solid organs, a long-sought goal in transplant medicine.
"The ability to reset the immune system safely to permit durable organ replacement could rapidly lead to great medical advances," Dr. Kim concluded.
The research was supported by grants from the National Institutes of Health, Breakthrough T1D Northern California Center of Excellence, Stanford Bio-X, the Reid Family, the H.L. Snyder Foundation and Elser Trust, the VPUE Research Fellowship at Stanford, and the Stanford Diabetes Research Center.
About Type 1 Diabetes:
Type 1 diabetes is an autoimmune condition that typically develops in childhood or adolescence. It accounts for approximately 5-10% of all diabetes cases. The exact cause is unknown, but genetic predisposition and environmental factors are believed to play a role. In 2022, an estimated 1.4 million Americans lived with Type 1 diabetes, including over 200,000 children and adolescents. The global prevalence of Type 1 diabetes is projected to rise, underscoring the urgent need for effective treatments and potential cures. Management strategies currently focus on intensive blood glucose monitoring, insulin therapy, diet, and exercise to prevent complications such as cardiovascular disease, kidney damage, nerve damage, and vision loss.
The Significance of Immune Tolerance:
Achieving immune tolerance, the state where the body’s immune system accepts foreign tissue without rejection, is a central goal in transplantation and autoimmune disease research. Traditionally, this has been managed through broad immunosuppressive drugs, which carry significant risks of infection and other side effects. The development of methods to induce specific immune tolerance, such as the hybrid immune system approach demonstrated by the Stanford team, represents a paradigm shift, offering the potential for long-term acceptance of transplanted cells or organs with minimal or no need for immunosuppression. This breakthrough directly addresses the limitations of current treatments for Type 1 diabetes and holds immense promise for a wide array of other immune-mediated conditions.
