A new stem cell treatment could relieve type 1 diabetes symptoms, according to Penn doctors
Vertex Pharmaceuticals' new therapy, zimislecel, has potential to be a "functional cure," experts say.

A new stem cell treatment could eliminate the need for insulin therapy in people with type 1 diabetes, a disease where the pancreas doesn’t produce insulin, according to a study authored by University of Pennsylvania doctors.
In early clinical trial results, the ability to produce insulin was restored in 10 out of 12 people with type 1 diabetes treated with Vertex Pharmaceuticals’ therapy, zimislecel, according to a study published last month in the New England Journal of Medicine. This means their bodies will be able to regulate blood sugar levels without outside help.
The treatment is made from stem cells, which are cells that haven’t decided what type of cell they want to be. Like recruiters at a career fair chatting up impressionable students, the scientists coax these cells to become pancreatic islet cells, the clusters of cells that regulate blood sugar by producing insulin and other hormones.
These cells are infused into the body and travel to the liver, where they become active.
Zimislecel has the potential to be a “functional cure,” said Marlon Pragnell, vice president of research and science at the American Diabetes Association, who was not involved in the study.
The treatment appears to free patients of the daily symptoms of type 1 diabetes, but it doesn’t address the autoimmune dysfunction that defines the disease. As a result, patients would need lifelong immunosuppressive therapy, which would leave them more vulnerable to getting sick from infections.
“While it’s still early days, if these results can be successfully replicated in larger, more diverse populations, zimislecel could redefine the treatment paradigm for type 1 diabetes,” Pragnell said in an email.
The cost has yet to be announced by the company. Zimislecel is likely still years away from widely reaching patients, if regulators find it is safe and effective.
What is type 1 diabetes?
Type 1 diabetes is an autoimmune disease where the body mistakenly destroys its own insulin-producing cells in the pancreas. Insulin is a hormone that acts much like a key, unlocking the “door” to cells so that sugar can enter. Without it, sugar builds up in the blood.
Over time, high blood sugar can damage the heart, nerves, kidney, and blood vessels.
There is no cure for the disease. People can manage the symptoms by taking insulin injections. However, it can be difficult to maintain the right balance of insulin in the body.
People with the condition can experience severe hypoglycemia, or low blood sugar, if they take more insulin than they need. This may cause seizures, loss of consciousness, comas, and even death.
As many as half of people with type 1 diabetes have at least one severe hypoglycemic event each year.
The clinical trial studied the treatment in 12 people with type 1 diabetes who repeatedly experienced severe hypoglycemia and whose bodies did not produce warning signs of a coming hypoglycemic episode.
The study’s participants were between the ages of 24 and 60. A third were women, and all were white.
How the treatment works
Zimislecel aims to restore the body’s ability to respond in real time to blood sugar fluctuations. When it’s high, insulin comes to the rescue. When it’s low, a complementary hormone, glucagon, rushes out.
Within 90 days of receiving the treatment, none of the 12 study participants experienced severe hypoglycemic events. Ten of them were insulin-independent a year later. The other two only needed small doses of insulin.
Two people died, however, their deaths were deemed unrelated to the treatment, said Michael Rickels, a study author who directs the Pancreatic Islet Cell Transplant Program at Penn. One of the deaths was caused by preexisting health issues involving severe dementia. The other died from meningitis after an elective surgery, in which a medication prohibited by the study protocol was used.
“To take away that burden and allow people to live life the way they would like to can be a really powerful and moving experience,” said Rickels, who has reported serving as a consultant for Vertex Pharmaceuticals.
The catch is that patients require lifelong immunosuppressive therapy to ensure their body doesn’t destroy the new cells like it did the old. Immunosuppression can increase risk of infections and other side effects. It was generally well-tolerated in the study, with most adverse effects being mild or moderate.
Some labs are working on genetically modifying the cell line used so that it would not require immunosuppressants.
“That would be amazing and potentially broaden the therapy to everyone with type 1 diabetes,” said Pragnell, the ADA expert not involved in the study.
The clinical trial is now in a critical phase, in which the treatment will be widely tested in people for long-term safety and efficacy. The company is also initiating a trial for type 1 diabetic patients with a kidney transplant, a population already on immunosuppressants.
If all goes well, Vertex Pharmaceuticals hopes to submit for regulatory approval in 2026.
The only comparable treatment to zimislecel is donislecel, an FDA-approved therapy that involves isolating healthy islets from the pancreases of deceased donors. However, there aren’t enough donor islets to meet demand.
Using stem cells could ensure an unlimited supply.
“The hope is this will provide a more reliable, consistent supply of a sufficient quantity of high-quality islets,” Rickels said.