What Is Type 1 Diabetes?

What This Article Covers

Type 1 diabetes (T1D) is a lifelong autoimmune condition in which the body's own immune system destroys the insulin-producing beta cells of the pancreas, leaving the body unable to regulate blood sugar without external insulin. This article explains what causes T1D, how it's diagnosed, what standard-of-care management looks like today, and where stem cell and cell-based research — including islet transplantation and stem-cell-derived islet replacement — currently stands. As of 2026, no cell therapy is broadly FDA-approved as a T1D treatment or cure; insulin remains the essential, life-sustaining therapy for everyone with this diagnosis.

What Is Type 1 Diabetes?

Type 1 diabetes occurs when the immune system mistakenly attacks and destroys the beta cells inside clusters of pancreatic tissue called the islets of Langerhans. Beta cells are the body's only source of insulin, the hormone that allows cells to take up glucose from the blood for energy. Once enough beta cells are destroyed, the body can no longer produce sufficient insulin, and blood glucose rises to dangerous levels. According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), an estimated 1.7 million U.S. adults were living with type 1 diabetes as of 2021, along with roughly 304,000 children and teens under age 20. T1D is distinct from type 2 diabetes, which primarily involves insulin resistance rather than autoimmune beta-cell destruction, though both result in high blood sugar.

Causes

T1D is classified as an autoimmune disease: for reasons not fully understood, the immune system generates antibodies that target and kill beta cells. Research points to a combination of genetic susceptibility and environmental triggers — such as certain viral infections — that may set off this immune attack in people who are predisposed to it. It is not caused by diet, sugar intake, or lifestyle, and it cannot currently be prevented. The disease can be diagnosed at any age, though it's most commonly identified in children, teens, and young adults.

Symptoms and Diagnosis

Because insulin production drops off relatively quickly once the autoimmune attack accelerates, T1D symptoms often appear suddenly, over days to a few weeks. Common symptoms include:

• Frequent urination (polyuria) and excessive thirst (polydipsia)
• Unexplained weight loss despite increased hunger
• Fatigue and blurred vision
• Slow-healing sores or frequent infections
• In more advanced or undiagnosed cases, nausea, vomiting, abdominal pain, rapid breathing, and confusion — signs of diabetic ketoacidosis (DKA), a life-threatening buildup of blood acids (ketones) that occurs when the body, lacking insulin, begins breaking down fat for fuel. DKA is a medical emergency and, per the American Diabetes Association (ADA), can be the first sign that someone has type 1 diabetes.

Diagnosis relies on blood glucose testing (fasting plasma glucose, random glucose, or A1C), followed by autoantibody testing to confirm an autoimmune process and distinguish T1D from other forms of diabetes. C-peptide testing, which measures the body's own residual insulin production, and genetic testing may be used when the diagnosis is unclear.

Standard Care Today

There is currently no cure for type 1 diabetes. Management centers on replacing the insulin the body can no longer make and closely monitoring blood glucose to avoid both high (hyperglycemia) and dangerously low (hypoglycemia) levels. The ADA's 2026 Standards of Care in Diabetes reflect an ongoing shift toward earlier, broader use of diabetes technology:

• Insulin therapy remains foundational, delivered via multiple daily injections, insulin pens, or continuous subcutaneous insulin pumps, guided by updated dosing algorithms in the 2026 Standards.
• Continuous glucose monitors (CGMs) are now recommended "at diabetes onset and anytime thereafter" for anyone who could benefit — a broadened recommendation compared with prior guidance.
• Automated insulin delivery ("artificial pancreas") systems, which pair a CGM with an insulin pump to adjust dosing automatically, are increasingly accessible; the 2026 Standards removed certain prerequisite requirements that previously limited who could start pump or automated-delivery therapy.
• The 2026 Standards also expanded guidance on screening people at risk for T1D (such as relatives of people already diagnosed) using autoantibody testing, enabling earlier detection before symptoms like DKA appear.

With consistent insulin therapy and monitoring, people with T1D can manage blood glucose effectively, though it remains a demanding, round-the-clock condition with risks of both short-term emergencies (severe hypoglycemia, DKA) and long-term complications (cardiovascular, kidney, nerve, and eye disease) if blood sugar runs high over time.

Where Stem Cell and Cell Therapy Research Stands

Because T1D is fundamentally a disease of missing beta cells, replacing those cells has long been a research goal — and this is genuinely one of the more encouraging areas of regenerative medicine right now, with real caveats attached.

Islet transplantation, using islet cells recovered from deceased organ donors, has been studied for over two decades and can, in some patients, restore insulin production. However, donor tissue is scarce, and recipients require lifelong immunosuppression, limiting this approach to a small subset of patients with especially difficult-to-control disease.

Stem-cell-derived islet replacement is the newer, more scalable frontier. The most advanced program is Vertex Pharmaceuticals' zimislecel (VX-880), which uses insulin-producing islet cells derived from stem cells (rather than scarce donor tissue) infused into the patient. In Phase 1/2 data presented at the ADA's 2025 Scientific Sessions and published in the New England Journal of Medicine, 10 of 12 participants followed for at least a year no longer required injected insulin, with a 92% average reduction in daily insulin dose across all participants and elimination of severe hypoglycemic episodes from day 90 onward. The FDA has granted zimislecel Regenerative Medicine Advanced Therapy (RMAT) and Fast Track designations, and it has PRIME designation in Europe and an Innovation Passport in the UK — signals that regulators see meaningful promise, not markers of approval. A pivotal Phase 3 trial is underway, with global regulatory submissions anticipated in 2026. Importantly, zimislecel still requires chronic immunosuppressive drugs to prevent immune rejection of the transplanted cells, which carries its own risks and currently limits candidacy to people with the most severe, hard-to-manage T1D. A related Vertex program pairing stem-cell-derived islets with an implantable device (VX-264) did not meet its efficacy goals in Phase 1/2 testing and was discontinued in 2025, underscoring that not every approach in this field succeeds.

Separate research lines are exploring ways to avoid the immunosuppression problem altogether, including gene-edited "hypoimmune" stem-cell-derived islets and encapsulation devices designed to shield transplanted cells from immune attack, as well as autoimmune-focused approaches (such as immune-modulating or cell-based therapies aimed at halting the underlying autoimmune attack rather than only replacing cells). These remain earlier-stage and investigational.

As of this writing, no stem-cell-derived or cell-based islet therapy is FDA-approved for type 1 diabetes; all such approaches remain investigational and available only through clinical trials or, in rare cases, expanded access programs — not as a general-purpose treatment or cure.

Bottom Line

Type 1 diabetes is a serious, lifelong autoimmune disease in which the immune system destroys the pancreas's insulin-producing cells, and insulin therapy — alongside modern tools like CGMs and automated insulin delivery — remains the essential, non-negotiable standard of care. Cell-based research, particularly stem-cell-derived islet replacement programs like Vertex's zimislecel, has produced genuinely exciting early results, including sustained insulin independence in most treated patients in early trials. But this remains investigational, requires immunosuppression, and is not an approved treatment available to the general T1D population today. Anyone with type 1 diabetes should continue standard insulin-based care under their endocrinologist's guidance and treat any cell-therapy option as a research opportunity to discuss with their care team — not a currently available substitute for insulin.