An existing transplant drug has shown promise in slowing the progression of type 1 diabetes in newly diagnosed young people, potentially paving the way for the first therapy that modifies the disease after diagnosis.
Type 1 diabetes is usually diagnosed in childhood or early adulthood. Once it starts, the immune system attacks the pancreas, destroying insulin-producing beta cells. Right now, there aren’t any approved treatments that slow this destructive process once the disease is established.
A new study led by researchers from UZ Leuven, Belgium’s largest university hospital, tested whether a drug called antithymocyte globulin (ATG), an existing immune-suppressing drug, could preserve beta cell function in young people who had just been diagnosed with diabetes.
Ordinarily, ATG is used together with other medicines to prevent and treat the body from rejecting a kidney transplant. It can also be used to treat rejection following transplantation of other organs, such as hearts, gastrointestinal organs, or lungs.
The researchers studied 117 people aged five to 25, who’d been diagnosed with type 1 diabetes within the past three to nine weeks. The participants were from 14 centers across eight European countries and were randomized to be given different doses of ATG (0.1, 0.5, 1.5, or 2.5 mg/kg) or a placebo. ATG was given as a two-day intravenous (IV) infusion. The main goal was to see how well the pancreas could still make insulin after 12 months, measured by C-peptide levels during a special meal test. C-peptide is released into the blood along with insulin by the pancreas.
The 2.5 mg/kg dose worked best, significantly preserving beta cell function compared to placebo. The 0.5 mg/kg dose also worked – although slightly less strong in its effect than the 2.5 mg/kg dose, it was still better than the placebo. The lowest (0.1 mg/kg) and middle (1.5 mg/kg) doses were dropped as the trial went on because they weren’t effective or optimal.
The problem with the 2.5 mg/kg dose was that it produced more side effects. Many participants had serum sickness (82%) and cytokine release syndrome (33%). Serum sickness is an allergic-like immune reaction to proteins found in certain medications and vaccines that are typically derived from horses. ATG is derived from rabbits or horses, which are injected with human T cells. These animals then produce antibodies against these cells, and the animal-derived antibodies are collected and purified for medical use. Cytokine release syndrome (CRS) is a widespread inflammatory response caused by the immune system releasing too many cytokines, immune system messengers, into the bloodstream. At 0.5 mg/kg, these effects were much less frequent (24% and 32%, respectively). Importantly, there were no deaths or treatment-related severe permanent harms.
The findings are promising, showing that ATG, even at a relatively low dose, can slow the loss of insulin-producing cells in young people newly diagnosed with type 1 diabetes. The lower dose also caused fewer side effects, making it a more practical option.
It shows the potential for an old, repurposed, and relatively affordable drug to modify the course of type 1 diabetes after diagnosis, instead of just managing blood sugar levels after the fact. That’s something that has not yet been achieved by existing therapies.
The study was published in The Lancet and presented at the 2025 European Association for the Study of Diabetes (EASD) Annual Meeting, which was held recently in Vienna.
