A groundbreaking clinical trial led by researchers from the University of Toronto has shown that a new stem cell–derived therapy called zimislecel can restore insulin production and prevent dangerous drops in blood sugar in people with type 1 diabetes. Within a year of treatment, participants were able to produce their own insulin again—some even became insulin-free.
Type 1 diabetes affects over 8 million people around the world. It’s a lifelong condition that occurs when the immune system destroys the insulin-producing beta cells in the pancreas. Without these cells, the body can’t regulate blood sugar levels, and patients must inject insulin regularly to avoid serious or even fatal complications.
Even with modern tools like continuous glucose monitors and insulin pumps, most people with type 1 diabetes struggle to keep their blood sugar within the healthy range. One of the most serious risks is severe hypoglycemia—blood sugar dropping too low. Some patients lose the ability to feel the warning signs of hypoglycemia, making it especially dangerous.
Doctors have tried replacing lost beta cells through islet or whole pancreas transplants. These can help restore natural insulin production, but they depend on donor organs, which are limited in supply. Plus, many transplant recipients need several procedures to gain even partial independence from insulin.
That’s why zimislecel is such a breakthrough. Instead of relying on donors, this therapy uses lab-grown islet cells derived from stem cells. The recent study, published in The New England Journal of Medicine, tested whether these lab-grown cells could be safely infused into patients and begin working like the body’s own insulin-producing cells.
The early-stage trial included 14 adults with type 1 diabetes. All had experienced multiple severe hypoglycemic episodes and had impaired awareness of low blood sugar. Each received a one-time infusion of zimislecel into the portal vein—a large blood vessel in the liver. The treatment was carefully monitored across medical centers in North America and Europe.
The results were remarkable. Among the 12 participants who received a full dose of the treatment, all avoided severe hypoglycemia during the first year. They also showed improved blood sugar control, with their average HbA1c (a measure of long-term blood sugar) falling below 7%, the recommended target for diabetes management.
Their blood sugar levels stayed in the healthy range over 70% of the time. Most importantly, 10 of the 12 became insulin-independent—no longer needing injections to manage their condition. The other two required far less insulin than before.
As with any new therapy, safety was closely monitored. The most common serious side effect was neutropenia, a drop in white blood cells, which occurred in three participants.
Sadly, two participants died during the study: one from a brain infection linked to steroid use outside the study protocol, and another from worsening of a pre-existing brain condition. These events were considered unrelated to the zimislecel treatment itself.
The researchers believe this is a major step forward in the search for a reliable, long-term treatment for type 1 diabetes. A single infusion of stem cell–derived islets showed the potential to replace lifelong insulin therapy and reduce dependence on scarce donor organs. Unlike traditional transplants, zimislecel may offer a scalable solution for many more patients.
However, experts caution that this was a small trial without a control group, and more research is needed. The participants were carefully selected, and results may not apply to everyone with type 1 diabetes. A larger, more detailed trial is already underway to confirm these findings and assess long-term outcomes.
Still, for many in the diabetes community, this study brings new hope. A future where people with type 1 diabetes can produce their own insulin again—without constant monitoring, injections, and fear of hypoglycemia—may be closer than ever.
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The research findings can be found in New England Journal of Medicine.
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