Japan Trial Shows Islet Transplants Cut Dangerous Lows in T1D

Japan Trial Demonstrates Islet Transplantation Safely Restores Blood Sugar Control in Type 1 Diabetes

A study from Japan offers encouraging new evidence that islet transplantation — a procedure that implants insulin-producing cells from a donor pancreas — can dramatically improve blood sugar control and eliminate dangerous low blood sugar episodes in people living with type 1 diabetes (T1D).

Conducted by researchers at Kyoto University's Graduate School of Medicine and published in Transplantation Direct (2025), this multicenter clinical trial is one of the first rigorous prospective studies to evaluate islet transplantation outcomes specifically in an Asian population — a group historically underrepresented in global diabetes transplant research.

What the Researchers Did

Eight adults with type 1 diabetes received allogeneic islet transplants — meaning donor islet cells were infused into the portal vein of the liver, where they take up residence and begin producing insulin. Participants received between one and three infusions depending on their response. To prevent rejection, patients were placed on a carefully monitored regimen of immunosuppressive medications, including antithymocyte globulin, calcineurin inhibitors, and mycophenolate mofetil.

Key Results

The results were striking. Six of the eight recipients (75%) met the primary success benchmark: an HbA1c below 7.4% at one year, combined with zero severe hypoglycemic events from one month through twelve months post-transplant.

Even more impressive was the improvement in average blood sugar control over time. Median HbA1c dropped from a starting point of 7.3% down to 6.3% by day 375 and further to 6.1% by day 730 — levels approaching what many endocrinologists consider near-normal glycemic control. In US blood sugar terms, this represents a shift from an estimated average glucose of roughly 163 mg/dL at baseline to approximately 131 mg/dL at one year and 128 mg/dL at two years.

Participants also reported improved hypoglycemia awareness — the ability to sense and respond to dropping blood sugar levels, a critical safety issue for many long-term T1D patients. Glucose variability, another key marker of diabetes control, improved significantly as well.

Importantly, no serious surgical complications — such as internal bleeding or dangerous blood clots in the portal vein — were reported.

Why This Matters for US Patients

For American patients with brittle or hard-to-control type 1 diabetes, islet transplantation represents a potentially life-changing option that remains underutilized. The American Diabetes Association (ADA) acknowledges islet transplantation as a therapeutic option for select T1D patients with severe hypoglycemia unawareness, yet access in the US remains limited to specialized centers.

This Japanese trial is valuable for several reasons. First, it confirms that the strong outcomes seen in North American and European trials — particularly the landmark Edmonton Protocol studies — extend to Asian populations, supporting the procedure's broad applicability. Second, it demonstrates that a streamlined immunosuppression protocol can be both effective and safe. Third, the elimination of severe hypoglycemic events is especially meaningful: in the US, severe hypoglycemia sends tens of thousands of T1D patients to emergency rooms each year.

If you or a loved one struggles with hypoglycemia unawareness or unstable blood sugars despite best efforts with insulin therapy, this research underscores that islet transplantation deserves a serious conversation with your endocrinologist or diabetes care team.

Study Citation

Anazawa, Marubashi, Kodama. Efficacy and Safety of Allogeneic Islet Transplantation Demonstrated by a Multicenter Clinical Trial in Japan. Transplantation Direct, 2025. PMID: 39936131. DOI: 10.1097/TXD.0000000000001765