Ten out of twelve patients with type 1 diabetes no longer needed insulin injections a year after an experimental cell transplant. The lab-grown cells survived in the body and began producing the hormone on their own, helping to maintain blood sugar levels.

It would seem a solution has been found. But there is a serious problem: to prevent the immune system from destroying the transplanted cells, patients had to take immunosuppressive drugs. Such treatment carries the risk of dangerous complications.

The study results were published in June 2025 in the medical journal New England Journal of Medicine. And in 2026, new scientific data emerged on another approach that could help overcome the main obstacle — immune rejection of cells.

How transplanted cells began producing insulin

In type 1 diabetes, the immune system mistakenly attacks the insulin-producing cells of the pancreas. Without this hormone, the body cannot use glucose normally, so a person must regularly administer insulin through injections or a special pump.

Modern devices help control blood sugar levels and automatically deliver the needed doses of the hormone. But they do not restore the body's lost ability to produce insulin on its own.

Scientists decided to take a different path — not to improve injections, but to replace the destroyed cells.

For this, Vertex Pharmaceuticals developed an experimental therapy called zimislecel, previously known as VX-880.

From stem cells in the laboratory, they grow special cells similar to those found in the pancreas. They can respond to changes in glucose levels and release insulin when needed.

The most unusual aspect is the transplant site. Doctors inject the cells into a blood vessel leading to the liver. There they can engraft, receive nutrients from surrounding vessels, and do their work.

The patient's pancreas is not restored. Instead, the transplanted cells located in the liver begin producing insulin.

What happened a year after the transplant

The study included people with long-standing type 1 diabetes who regularly experienced dangerous episodes of sudden blood sugar drops. Some could not feel the approach of such a state in time.

Even modern treatments for these patients do not always provide sufficient protection against severe complications, including loss of consciousness and seizures.

The published analysis included 14 people who were followed for at least a year. Two received a reduced dose of cells, the other 12 — the full dose.

Before the transplant, all participants had virtually no signs of producing their own insulin. After the procedure, researchers detected C-peptide in each of them — a substance produced together with insulin that helps assess the function of transplanted cells.

This meant that the new cells had engrafted and begun functioning.

But the main result was something else: 365 days after the transplant, 10 of the 12 patients who received the full cell dose managed without insulin injections.

This was not simply about giving up injections.

All 12 patients had glycated hemoglobin levels — an indicator reflecting average blood sugar concentration over several months — below 7%. More than 70% of the time, glucose levels stayed within the target range.

From the third month after transplant until the end of the first year, no severe episodes of dangerous low blood sugar were recorded.

Thus, the transplanted cells not only produced insulin but also significantly improved diabetes control.

Why this does not yet mean a cure for diabetes

There is a serious downside to such promising results.

In type 1 diabetes, the immune system destroys the body's own insulin-producing cells. Transplanted cells may also become its target, as the body sees them as foreign.

Therefore, all study participants were prescribed immunosuppressive drugs. Such therapy helps protect the new cells but at the same time weakens the body's defense against infections.

In the study, three participants experienced severe neutropenia — a dangerous drop in certain white blood cells that fight infections.

During longer follow-up, two participants died. The first — about 20 months after the transplant from severe fungal meningitis that developed after sinus surgery complicated by a skull base injury. The patient had also been receiving high doses of steroids and immunosuppressive drugs. Researchers linked the infection to immunosuppressive therapy.

The second participant died about 30 months later due to progression of a pre-existing condition with severe memory and other brain function impairments.

Neither of these deaths was attributed by researchers to the transplanted cells themselves. However, they show how serious the overall treatment risks can be, especially with the need for long-term immunosuppression.

Moreover, the study was small, without a separate control group, and the published results were interim. It is not yet known how long the transplanted cells will be able to maintain their function.

Can new cells be protected without suppressing immunity?

This is exactly the challenge researchers are now trying to solve.

One option is to place the cells in special protective implants. Such devices should allow oxygen and nutrients to pass, release insulin, and simultaneously prevent immune attacks.

But implementing the idea proved difficult. In March 2025, Vertex announced the termination of further clinical development of the experimental VX-264 system: the protective implant did not provide the necessary efficacy.

Another path is to modify the cells themselves through genetic engineering so that the immune system has a harder time recognizing them as foreign.

Here, encouraging results have appeared.

In July 2026, researchers reported in the New England Journal of Medicine on 14 months of follow-up of a patient with type 1 diabetes who had received genetically modified insulin-producing cells.

Unlike the zimislecel study, this involved donor pancreatic cells specially modified by genetic engineering.

They were transplanted into the forearm muscle. Notably, the patient did not receive immunosuppressive drugs.

After 14 months, the cells continued to produce insulin and respond to glucose changes. Researchers found no signs of significant immune attack on the transplant.

This is important confirmation that genetically modified cells can function for extended periods in the human body without systemic immunosuppression.

However, there is a fundamental difference from the "10 out of 12" result.

In the new experiment, only one person participated. They received a relatively small number of cells, insufficient to fully supply the body with insulin. Therefore, the patient continued with insulin therapy.

Thus, scientists have demonstrated two different achievements: in one case, transplanted cells allowed patients to stop insulin injections but required immune suppression. In the other, the cells were able to work without such protection, but did not yet provide the body with enough hormone.

Now researchers must try to combine both results.

When will diabetes treatment without constant injections become available?

Transplantation of insulin-producing cells is no longer a purely experimental idea.

In June 2023, the U.S. Food and Drug Administration (FDA) approved Lantidra, a cellular therapy made from donor pancreatic cells of deceased individuals.

However, its use is limited to certain adults with type 1 diabetes who continue to have recurrent severe low blood sugar episodes despite intensive treatment. In addition, the transplant requires immunosuppression, and the supply of donor cells is limited.

Zimislecel potentially solves one of these problems: the needed cells are grown from stem cells in the laboratory, so production should not depend on a constant supply of donor organs.

But as of October 2026, this therapy remains experimental. In an August report, Vertex stated the continuation of clinical trials and patient enrollment, without naming a confirmed date for the therapy's registration.

The main result has been achieved: laboratory-grown cells can take over insulin production in people with type 1 diabetes. The next challenge is to make them work long enough without requiring permanent immune suppression.

This will largely determine whether cell therapy can one day become available not only to a small group of patients with severe complications, but also to a much larger number of people with type 1 diabetes.

For now, the experimental results do not justify abandoning prescribed insulin therapy. Stopping insulin administration on your own in type 1 diabetes can be life-threatening.

Sources: New England Journal of Medicine — zimislecel study (2025); New England Journal of Medicine — 14-month follow-up of genetically modified cells (2026); Vertex Pharmaceuticals; FDA.