By Hendra Lukman 
Stanford Medicine scientists have achieved a significant breakthrough in the fight against Type 1 diabetes, demonstrating a novel approach that completely prevented or fully reversed the autoimmune disease in mice. By administering a combination of blood-forming stem cells and pancreatic islet cells from immunologically mismatched donors, researchers successfully engineered a hybrid immune system in the animals, effectively halting the immune system’s destructive attack on insulin-producing cells. This pioneering research, published online on November 18th in the Journal of Clinical Investigation, offers a beacon of hope for millions worldwide afflicted by Type 1 diabetes and potentially other autoimmune conditions.
The core of this transformative strategy lies in the creation of a chimeric immune system. In Type 1 diabetes, the body’s own immune defenses mistakenly identify the insulin-producing islet cells within the pancreas as foreign invaders and launch a relentless assault, leading to their destruction and the subsequent inability of the body to regulate blood sugar. The Stanford team’s innovative method bypasses this autoimmune attack by establishing a new immune equilibrium. Critically, none of the treated mice developed graft-versus-host disease (GvHD), a potentially severe complication where the immune system derived from the donor stem cells attacks the recipient’s healthy tissues. Furthermore, the study reported that the mice’s original immune system ceased its destruction of islet cells, and remarkably, the animals no longer required immune suppressive drugs or insulin for the duration of the six-month study.
"The possibility of translating these findings into humans is very exciting," stated Seung K. Kim, MD, PhD, the KM Mulberry Professor and a distinguished professor across developmental biology, gerontology, endocrinology, and metabolism. He is also the senior author of the study and 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."
A Foundation Built on Prior Research
This latest success builds directly upon a pivotal 2022 study also led by Dr. Kim and his collaborators. In that earlier research, the team induced diabetes in mice using toxins to eliminate their insulin-producing cells. They then employed a carefully orchestrated pre-transplant regimen, involving immune-targeting antibodies and low-dose radiation, followed by the transplantation of blood stem cells and islet cells from an unrelated donor. This combination successfully restored blood sugar control in the experimental animals.
However, the current study presented a more formidable challenge: preventing or curing diabetes driven by autoimmunity, where the immune system spontaneously targets and eradicates the body’s own islet cells. This mirrors the pathophysiology of Type 1 diabetes in humans. In contrast to the induced-diabetes model, where the primary objective was to overcome the recipient’s immune rejection of donor islet cells, the new model introduced a dual threat. The transplanted islets were not only recognized as foreign tissue but were also under siege by an immune system already predisposed to attack islet cells from any source.
"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." The researchers acknowledged that the very biological characteristics that predispose these mice to autoimmune diabetes also complicate the safe preparation of recipients for blood stem cell transplantation.
A Simple Pharmaceutical Tweak for Complete Diabetes Protection
The research team identified a surprisingly straightforward solution to this complex problem. Preksha Bhagchandani, a graduate and medical student and the lead author of the research, along with Stephan Ramos, PhD, a postdoctoral fellow and co-author, incorporated a medication commonly prescribed for autoimmune diseases into the pre-transplant protocol previously established in 2022. This refined regimen, followed by blood stem cell transplantation, led to the development of a hybrid immune system composed of cells from both the donor and the recipient. Crucially, in 19 out of 19 cases, these mice did not develop Type 1 diabetes. In a separate cohort of mice with established, long-standing Type 1 diabetes, a remarkable nine out of nine were cured following the combined blood stem cell and islet cell transplant.
The researchers highlighted that the antibodies, drugs, and low-dose radiation employed in their mouse model are already integral components of standard clinical practice for blood stem cell transplantation. This familiarity significantly strengthens the feasibility of transitioning this strategy towards human clinical trials for individuals with Type 1 diabetes.
Bridging Kidney Tolerance to Hybrid Immunity for Diabetes
This groundbreaking work stands on the shoulders of decades of research, notably the studies led by the late Samuel Strober, MD, PhD, a distinguished professor of immunology and rheumatology, and his colleagues, including study co-author and professor of medicine Judith Shizuru, MD, PhD. Their pioneering investigations demonstrated that bone marrow transplants from partially immunologically matched human donors could successfully establish a hybrid immune system in recipients. This chimeric immune system, in turn, facilitated the long-term acceptance of kidney transplants from the same donor, eliminating the need for ongoing immunosuppressive drugs in some patients and leading to stable kidney function for decades.
Blood stem cell transplants are currently a well-established treatment for various blood and immune system cancers, such as leukemia and lymphoma. However, these procedures typically involve aggressive high-dose chemotherapy and radiation to eradicate the patient’s existing blood and immune system, often resulting in severe side effects. Dr. Shizuru and her team have been instrumental in developing a gentler, less intensive preparatory approach for individuals undergoing blood stem cell transplantation for non-cancerous conditions like Type 1 diabetes. This optimized protocol aims to minimally suppress bone marrow activity, just enough to allow donor blood stem cells to engraft and proliferate.
"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," Dr. Shizuru emphasized. "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 current study provides compelling evidence that this less toxic conditioning regimen, combined with the establishment of a hybrid immune system, is the key to overcoming autoimmune attacks. "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." This dual action of immune tolerance – accepting the donor islets while ceasing attacks on the recipient’s own tissues – is the cornerstone of their success.
Addressing Future Hurdles for Type 1 Diabetes Treatment
Despite the highly encouraging results in the mouse models, significant obstacles must be addressed before this innovative strategy can be widely implemented as a treatment for Type 1 diabetes in humans. A primary challenge is the current reliance on pancreatic islets obtained exclusively from deceased donors. Furthermore, the blood stem cells must originate from the same individual as the islets, creating a logistical hurdle for sourcing matched cell populations. Another critical question is whether the typical number of islet cells recovered from a single donor would consistently be sufficient to reverse established Type 1 diabetes, which is characterized by extensive islet cell loss.
The Stanford research team is actively exploring multifaceted solutions to these limitations. One promising avenue involves the laboratory production of large quantities of functional islet cells derived from pluripotent human stem cells. Simultaneously, researchers are investigating methods to enhance the survival and efficiency of transplanted donor islets after transplantation, potentially increasing the therapeutic yield from each donation.
Beyond Type 1 diabetes, Dr. Kim, Dr. Shizuru, and their colleagues are optimistic that their refined pre-conditioning strategy holds immense potential for treating a broader spectrum of autoimmune diseases. Conditions such as rheumatoid arthritis and lupus, which involve chronic immune system dysregulation, could potentially benefit from this approach. Additionally, the method may offer a gentler alternative for treating non-cancerous blood disorders like sickle cell anemia, for which current blood stem cell transplant procedures remain exceptionally harsh. The research also opens doors for transplants involving mismatched solid organs, a long-standing challenge 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, underscoring the far-reaching implications of their work.
This research was supported by substantial funding from the National Institutes of Health, including grants T32 GM736543, R01 DK107507, R01 DK108817, U01 DK123743, P30 DK116074, and LAUNCH 1TL1DK139565-0. Additional support was provided by the 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. The collaborative efforts and diverse funding streams underscore the significance and broad appeal of this critical research endeavor.
