Activated donor immune cells may prevent severe complication after allogeneic stem cell transplantation
· Medical Xpressby Nadine Berger, Johannes Gutenberg University Mainz
edited by Lisa Lock, reviewed by Andrew Zinin
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Researchers have successfully conducted the first clinical trial using activated regulatory T cells (ATregs, Actileucel)—derived from white blood cells of healthy blood donors. This novel cell therapy aims to prevent graft-versus-host disease (GvHD) following an allogeneic stem cell transplant. The Phase I/II study has yielded extremely encouraging results: ATregs can be produced within 24 hours and injected immediately afterward; administration is safe and well-tolerated by patients—a significant step toward a widely available cell therapy. The research is published in Transplantation and Cellular Therapy.
A complication that reduces the chances of recovery
Allogeneic stem cell transplantation, in which a patient with blood cancer receives stem cells from a healthy donor, is the only chance of a cure for many patients. However, acute graft-versus-host disease (aGvHD) poses a high risk associated with the procedure. Immune cells derived from the graft attack the patient's own protein structures, often with severe consequences for the skin, liver and intestines.
Natural regulatory T cells, which act as the immune system's "brakes," can prevent this fatal reaction. However, their widespread clinical use has so far been hindered by the fact that they had to be laboriously isolated from the transplant of a genetically compatible donor and cultured in the laboratory for weeks—a process that is not feasible for most patients.
Activation instead of proliferation: The ATreg principle
The ATreg process developed by ActiTrexx in Mainz takes a different approach. Regulatory T cells (Tregs) are harvested from the blood of healthy, unrelated blood donors and stimulated with a patented activator for 16 hours—without the otherwise standard, complex and weeks-long process of cell proliferation in the laboratory.
"Early on in the development of the cell therapy, we were able to demonstrate that this activation significantly enhances the natural tolerance-promoting effect of Tregs. As a result, significantly fewer cells are needed to prevent dangerous graft rejection," explains Dr. Andrea Tüttenberg, co-founder, CEO and medical director of ActiTrexx GmbH, as well as a researcher at the Department of Dermatology at University Medical Center Mainz.
"Since the cells do not have to come from the original transplant donor themselves, but rather from a genetically incompatible third-party donor, ATreg can be produced as needed from a standard blood donation by a healthy, voluntary donor and administered within 24 hours of production—a decisive advantage for the universal applicability of ATreg."
Results of the first clinical trial in humans
In the multicenter study "ATreg-001" (EU CT Number 2024-516599-14-00), 10 patients at sites in Mainz, Dresden, Münster and Dortmund received the cell therapy about 10 days after their stem cell transplant, in addition to standard treatment. Using a dose-escalation design, three consecutive dose levels were tested. The primary objective of the study was to evaluate the safety and feasibility of this novel procedure.
The results are encouraging and exceed expectations for an initial safety study: The administration of ATreg itself did not result in any serious side effects during or after the infusion. This was not assured for a preparation derived from genetically mismatched blood donors. All treated patients showed successful engraftment of their stem cell transplant. Furthermore, during the 100-day observation period following transplantation, no patient developed severe grade 3–4 graft-versus-host disease. No transplant-related mortality was observed either.
"These initial clinical data impressively demonstrate the feasibility and favorable safety profile of ATreg, without the logistically very complex process of cell expansion from genetically compatible donors," says Dr. Helmut Jonuleit, co-founder and chief scientific officer (CSO) of ActiTrexx GmbH, inventor of the underlying technology and director of research at the Department of Dermatology at University Medical Center Mainz. "As a result, GvHD could become significantly less dangerous in the future, and the search for suitable stem cell donors will also be simplified, since an exact genetic match with the patient becomes less important."
Outlook
This first phase I study, involving only a small number of patients, shows promising results for a completely new generation of cell therapies. Rapid production without long-term expansion addresses one of the biggest bottlenecks in previous Treg therapies. ActiTrexx views the results as a positive signal for further clinical testing of ATreg as a novel cell therapy to prevent GvHD and considers this an important milestone on the path to a more widely available treatment. To demonstrate potential superiority over standard prophylaxis, the next step will be a randomized, controlled follow-up study with a larger and more uniformly treated patient group.
More information
Andrea Tuettenberg et al, Gp120-Activated Allogeneic Regulatory T cells for Prevention of Graft-versus-Host-Disease: A First-in-Human Trial, Transplantation and Cellular Therapy (2026). DOI: 10.1016/j.jtct.2026.08.054
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Allergy and immunologyOncology Provided by Johannes Gutenberg University Mainz Who's behind this story?
Lisa Lock
BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021. Full profile →
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