Lab-Grown Insulin Cells for Type 1 Diabetes: Inside the Zimislecel Trial

Imagine living with type 1 diabetes for decades.

You check your sugar all day. You count every carb. And still, a few times a year, your blood sugar crashes so hard you can't help yourself. Someone else has to. Over time your body stops warning you it's coming.

Now imagine getting one infusion, and a year later you aren't taking insulin at all.

That is what happened to 10 of 12 people in a small trial of a lab-grown cell therapy called zimislecel. The results were published in the New England Journal of Medicine in 2025 (Reichman et al., 2025). It is one of the most important stem cell results in years.

It is also not something you can get. Not from us, not from any clinic. And it comes with a price most headlines skip. Let's go through all of it.

What Is Zimislecel?

Zimislecel (formerly called VX-880) is an experimental cell therapy from Vertex Pharmaceuticals. It is made of fully differentiated islet cells. Those are the cells in the pancreas that make insulin and sense blood sugar. In type 1 diabetes, the immune system destroys them.

Here's the key idea. Instead of taking islets from a deceased organ donor, Vertex grows them in a lab, starting from stem cells, until they become working islet cells. Then they are infused into the portal vein, which carries blood to the liver. The cells settle in the liver and start making insulin when blood sugar rises.

The patient also takes immunosuppressive drugs. Without them, the body would attack the new cells the same way it attacked the original ones.

What Did the Zimislecel Trial Actually Show?

The trial is called FORWARD (NCT04786262). The published results cover the early phase 1–2 part.

Who was in it

Adults with type 1 diabetes who had impaired awareness of low blood sugar and a history of severe hypoglycemic events. In other words, people for whom insulin alone was becoming dangerous. Every one of them had undetectable C-peptide at the start, meaning their bodies were making essentially no insulin of their own.

How it was done

Two people got a half dose. Twelve got a full dose of about 0.8 billion cells as a single infusion. All of them took a steroid-free immunosuppressive regimen. Each had at least 12 months of follow-up.

What they found

• Engraftment: all 14 patients started producing their own C-peptide after the infusion, a sign the cells had taken hold and were making insulin.
• Severe lows: all 12 full-dose patients were free of severe hypoglycemic events from day 90 to day 365.
• Blood sugar control: all 12 got their HbA1c (a roughly three-month average of blood sugar) under 7% and spent more than 70% of the time in the target range of 70 to 180 mg/dL.
• Insulin: 10 of the 12 (83%) were not using any injected insulin at day 365. Vertex reported a mean 92% drop in daily insulin dose across all 12 (Vertex, June 2025).

Those are strong numbers for a disease where "cure" has been the punchline of a cruel joke for a hundred years. The researchers themselves were careful, though. Their conclusion was that the results "support the hypothesis" that zimislecel can restore islet function, "warranting further clinical investigation." That's scientist for: promising, not proven.

What Are the Risks and Trade-Offs?

This is the part people skim. Don't.

Immunosuppression for as long as the cells are there

Vertex states plainly that zimislecel "requires chronic immunosuppressive therapy to protect the islet cells from immune rejection." These drugs lower your defenses against infections and carry their own long-term risks. You trade insulin shots for anti-rejection pills. For someone having severe lows they can't feel, that may be a good trade. For most people with well-controlled type 1 diabetes, it may not be.

Serious adverse events and two deaths

The most common serious adverse event was neutropenia, a drop in infection-fighting white blood cells, in 3 patients. Two patients died. One died of cryptococcal meningitis, a fungal brain infection. The other died of severe dementia with agitation, from progression of a neurocognitive problem that was already there before the study. Vertex reported both deaths as unrelated to zimislecel, and said the safety profile was "generally consistent with the immunosuppressive regimen used in the study, the infusion procedure, and complications from long-standing diabetes."

Read that last sentence again. Even when the cells themselves aren't the problem, the whole package can be.

Is Zimislecel FDA-Approved or Available Yet?

No. Vertex itself says zimislecel "is investigational and has not been approved by health authorities globally."

Here's where it stands as of October 2026, from Vertex's own updates:

• January 2026: Vertex said it had finished enrolling the phase 1/2/3 study but "temporarily postponed completion of dosing" while it ran an internal manufacturing analysis (Vertex, January 11, 2026).
• Spring 2026: in its first-quarter results, Vertex said the analysis was complete and dosing had resumed (Vertex Q1 2026 results).
• August 2026: the study "continues to enroll and dose patients," and Vertex said it expects to give updated timelines "later this year." It also announced that the FDA cleared a trial for VX-017, a version designed to work for patients of any blood type (Vertex Q2 2026 results, August 3, 2026).
• The registry: as last updated September 1, 2026, the trial record lists an estimated primary completion date of December 31, 2027. That is a trial date, not an approval date.

Back in 2025, Vertex talked about filing for approval in 2026. Its 2026 updates have not repeated that target. So the honest answer to "when can I get it?" is: nobody outside Vertex and the regulators knows yet.

If someone offers you "stem cell islets" outside a registered clinical trial, that is not this product.

Has Any Islet Cell Therapy Been Approved?

Yes, one, and it isn't made from stem cells. In June 2023 the FDA approved Lantidra, an islet cell therapy made from deceased donor pancreases, for adults with type 1 diabetes who can't reach their blood sugar targets because of repeated severe lows (FDA, June 28, 2023).

In its two studies, 21 of 30 participants did not need insulin for a year or more. Five never had a single day without insulin. And the FDA noted that most participants had at least one serious adverse reaction tied to the infusion procedure or to the immunosuppressive drugs.

The problem with donor islets is supply. There are only so many donor pancreases. Growing islets in a lab is an attempt to solve that problem. That's why zimislecel matters.

Is This the Same as Stem Cell Therapy for Diabetes at a Clinic?

No. And this is where a lot of people get confused, sometimes on purpose.

"Stem cell therapy" is a loose phrase. Zimislecel is not a stem cell injection. It is a finished, manufactured islet cell product that does one job: make insulin. It goes through the FDA's full drug approval process, the same way any new biologic does.

Mesenchymal stem cells, or MSCs, are a different kind of cell. They don't turn into islet cells and they don't make insulin. Researchers study them mostly for how they signal to other cells and how they may affect inflammation. Some trials are looking at MSCs in diabetes, but nobody has shown that MSCs can replace insulin in type 1 diabetes.

So when you see a headline about lab-grown islets, don't let anyone stretch it into a claim about a different product. That includes us.

Where The Stem Cell Club Fits

We offer umbilical cord Wharton's Jelly MSC options sourced from an FDA-registered U.S. lab. FDA registration covers the lab's facility and manufacturing standards. It is not FDA approval of the product, and our offerings are not FDA-approved to diagnose, treat, cure, or prevent any disease, including diabetes.

We do not offer zimislecel. Nobody outside a clinical trial does. Our cells are not islet cells, they do not make insulin, and they are not a substitute for insulin or for anything your endocrinologist prescribes. If you have type 1 diabetes, please don't stop or change your insulin based on anything you read online, including this.

If you want to follow zimislecel, the place to look is the trial record and Vertex's own updates, and the person to talk to is your endocrinologist. They can tell you whether you'd even fit the trial's criteria.

If you're curious about how MSCs differ from other cell types, our breakdown of Japan's first iPS cell therapy approvals walks through that. Our look at what the 2026 knee arthritis trials actually show is a good example of how mixed MSC evidence can be. And our guide to stem cell therapy and FDA approval explains what "approved" really means.

Questions to Ask Anyone Selling Stem Cells for Diabetes

• What exact cells are these? Islet cells, MSCs, something else? From where?
• Do they make insulin? If they say yes and it isn't a registered trial, ask for the published study on that exact product.
• What is the FDA status? If they say "FDA-approved for diabetes," that's not true for any stem cell product today.
• Are you asking me to change my insulin? That decision belongs to you and your diabetes doctor, nobody else.
• What are the side effects you actually see? Read our page on stem cell therapy side effects before any appointment.

Frequently Asked Questions