A single infusion of a stem cell-based treatment may have cured 10 out of 12 people with the most severe form of type 1 diabetes. One year later, these 10 patients no longer need insulin. The other two patients need much lower doses.

The experimental treatment, called zimislecel and made by Vertex Pharmaceuticals of Boston, involves stem cells that scientists prodded to turn into pancreatic islet cells, which regulate blood glucose levels. The new islet cells were infused and reached the pancreas, where they took up residence.

The study was presented Friday evening at the annual meeting of the American Diabetes Association and published online by The New England Journal of Medicine.

“It’s trailblazing work,” said Dr. Mark Anderson, professor and director of the diabetes center at the University of California in San Francisco. “Being free of insulin is life changing,” added Dr. Anderson, who was not involved in the study.

Vertex, like other drug companies, declined to announce the treatment’s cost before the Food and Drug Administration approves it.

A Vertex spokeswoman said the company had data only on the population it studied so it could not yet say whether the drug would help others with type 1 diabetes.

About two million Americans have type 1 diabetes, which is caused when the immune system destroys islet cells. A subset of islet cells, the beta cells, secrete insulin. Without insulin, glucose cannot enter cells. Patients with type 1 must inject carefully calibrated doses of the hormone to substitute for the insulin their body is missing.

Type 1 is different from the more common type 2 diabetes, which usually occurs later in life.

Controlling insulin levels is a constant, often costly effort. Elevated blood sugar levels can damage the heart, kidneys, eyes and nerves. But if levels fall too low, people can feel shaky, pass out or have seizures.

The patients in the study are among the estimated 30 percent with a complication of type 1 diabetes — hypoglycemic unawareness. Those with the condition have no warning when their glucose levels are falling precipitously. They lack the normal signs like shakiness or sweating that can signal a need for glucose.

Patients with hypoglycemic unawareness can suddenly pass out or have seizures or even die.

It’s a frightening way of life, said Dr. Trevor Reichman, director of the pancreas and islet transplant program at University Health Network, a hospital in Toronto, and first author of the study.

“You worry all day every day where your glucose is and what you eat and when you exercise,” he added.

Patients in the study began to need less insulin within a few months of being infused with new islet cells, and most stopped needing the hormone altogether at about six months, Dr. Reichman said.

He added that patients’ episodes of hypoglycemia went away within the first 90 days of treatment.

If the study continues to show positive results, the company expects to submit an application to the Food and Drug Administration next year.

“For the short term, this looks promising” for severely affected patients like those in the study,” said Dr. Irl B. Hirsch, a diabetes expert at the University of Washington who was not involved in the study.

But patients in the trial had to stay on drugs to prevent the immune system from destroying the new cells. Suppressing the immune system, he said, increases the risk of infections and, over the long term, can increase the risk of cancer.

“The argument is this immunosuppression is not as dangerous as what we typically use for kidneys, hearts and lungs, but we won’t know that definitely for many years,” Dr. Hirsch said.

Patients may have to take the immunosuppressant drugs for the rest of their lives, the Vertex spokeswoman said.

The treatment is the culmination of work that began more than 25 years ago when a Harvard researcher, Doug Melton, vowed to find a cure for type 1 diabetes. His 6-month-old baby boy developed the disease and, then, so did his adolescent daughter. His passion was to find a way to help them and other patients.

He began, he said, with an “unwavering belief that science can solve the most difficult problems.”

It took 20 years of painstaking, repetitive, frustrating work by Dr. Melton and a team of about 15 people to find the right chemical cocktail to turn stem cells into islet cells. He estimated that Harvard and others spent $50 million on the research.

Dr. Peter Butler, a professor of medicine at the University of California, Los Angeles and a consultant to Vertex, said he was awed by the achievement of the Harvard team.

“The fact that it worked at all is just freaking amazing to me,” he said. “I can guarantee there were a thousand negative experiments for every positive one.”

When Dr. Melton finally succeeded, he needed a company to take the discovery into the clinic. He joined Vertex, which took up the challenge.

The first patient to get the experimental therapy, Brian Shelton, got an infusion in 2021. He had been plagued by episodes of plummeting blood sugar that made him lose consciousness. Once he crashed his motorcycle into a wall, and another time he passed out in a yard while working his mail delivery route.

The infusion cured him, but he died shortly afterward from what Vertex described as dementia symptoms that began before his treatment.

Recruitment of the 12 patients in the new report proceeded slowly, Dr. Reichman said, because of the strict entry requirements. Some who qualified backed out when they heard they would have to take immunosuppressive drugs, he added.

One who joined, Amanda Smith, a 36-year-old nurse in London, Ontario, said she jumped at the chance to enter the trial. Six months after the infusion, she no longer needed insulin.

“It’s like a whole new life,” she said.