Diabetes milestone: In major breakthrough, stem cell infusion restores insulin production in type 1 patients

In a first-of-its-kind clinical trial, scientists from the University of Toronto have shown that a single infusion of zimislecel — an allogeneic stem cell-derived islet therapy — can restore natural insulin production in people with type 1 diabetes. Within a year of treatment, participants no longer experienced severe hypoglycemia, a major breakthrough for those living with this chronic disease.

More than 8 million people globally suffer from type 1 diabetes, a condition where the immune system destroys insulin-producing beta cells. Without these cells, blood glucose control becomes a constant battle, and patients must rely on insulin therapy to prevent serious complications.

Though technologies like continuous glucose monitors and automated insulin pumps have improved disease management, most patients still struggle to meet glycemic targets — especially those with impaired hypoglycemia awareness, who can’t sense when their blood sugar drops dangerously low.

While pancreatic islet or whole-organ transplants can restore glucose regulation, these methods depend on donor availability and often require multiple grafts to achieve even partial insulin independence. A scalable, consistent solution has long remained elusive.

In the study, published in The New England Journal of Medicine, researchers tested zimislecel in a Phase I/II trial involving 14 adults across North America and Europe. Participants were between 18 and 65 years old, had impaired hypoglycemia awareness, and had experienced at least two severe hypoglycemic events in the previous year. Each received a single portal-vein infusion of zimislecel and continued using continuous glucose monitoring.

Among the 12 who received the full dose, all were free from severe hypoglycemia, maintained HbA1c levels below 7%, and stayed within the recommended glucose range more than 70% of the time in the first year. Ten stopped insulin altogether, while the other two significantly reduced their doses.

The most common serious side effect was neutropenia, occurring in three participants. Two deaths were reported — one due to cryptococcal meningitis following off-protocol steroid use, and another linked to worsening of a pre-existing neurocognitive condition.

Researchers concluded that zimislecel restored islet function and sharply improved glycemic control, offering a scalable alternative to insulin therapy and donor transplants. However, the open-label trial was limited by its small cohort and non-prespecified outcomes. A larger, more rigorous trial is now underway to confirm these results.