Highlight
The Phase 1 study of allogeneic regulatory T-cell (Treg) therapy in Amyotrophic Lateral Sclerosis (ALS) yielded several critical findings for the field of neuroimmunology:
- Zero dose-limiting toxicities: The use of off-the-shelf, non-HLA-matched umbilical cord blood Tregs was well-tolerated without the need for lymphodepletion or immunosuppression.
- Significant functional stabilization: In participants with complete data, the rate of functional decline (ALSFRS-R) slowed from -1.66 points/month pre-treatment to -0.41 points/month during the treatment phase.
- Scalable therapeutic model: Unlike previous autologous Treg trials, this allogeneic approach offers a viable path for large-scale clinical application.
Background: The Neuroinflammatory Cascade in ALS
Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the progressive loss of motor neurons in the brain and spinal cord. While the primary pathology involves protein misfolding and excitotoxicity, evidence increasingly suggests that neuroinflammation plays a pivotal role in accelerating disease progression. In the early stages of ALS, regulatory T cells (Tregs) provide a neuroprotective environment by suppressing pro-inflammatory microglia. However, as the disease advances, Tregs often become dysfunctional or diminished in number, allowing for unchecked neurotoxic inflammation.
Previous clinical efforts have focused on autologous Treg therapy—extracting a patient’s own cells, expanding them ex vivo, and re-infusing them. While promising, autologous therapy is limited by high costs, manufacturing complexity, and the fact that a patient’s own cells may already be functionally compromised by the disease state. The study by Shneider et al., recently published in NEJM Evidence, explores a paradigm shift: using “off-the-shelf,” allogeneic Tregs derived from healthy umbilical cord blood.
Study Design: The TREG-ALS Trial
This Phase 1, open-label study was designed to evaluate the safety and preliminary efficacy of a cryopreserved, allogeneic Treg product (TREG). The study enrolled six participants with a median age of 48.5 years and a baseline Revised ALS Functional Rating Scale (ALSFRS-R) score of 31.5. A unique aspect of this trial was the absence of lymphodepletion or concomitant interleukin-2 (IL-2) administration, which are often required in cell therapies to ensure cell survival but can introduce significant toxicity.
Intervention Protocol
Participants received a fixed dose of 100 million cells per infusion. The regimen consisted of four weekly infusions (induction phase) followed by six monthly infusions (maintenance phase). The primary endpoints were focused on safety, specifically dose-limiting toxicities (DLTs) such as severe infusion reactions, cytokine release syndrome (CRS), or regimen-related death. Secondary exploratory endpoints included changes in the ALSFRS-R slope and the monitoring of serum/plasma neurofilament light (NfL) and various inflammatory cytokines.
Key Findings: Safety and Functional Outcomes
The primary outcome of the study was successfully met: no dose-limiting toxicities were observed across the cohort. Despite the allogeneic nature of the cells and the lack of HLA matching, there were no cases of grade 3 or 4 cytokine release syndrome or significant infusion reactions. This confirms that allogeneic Tregs are immunologically privileged enough to be administered safely in an ambulatory setting without aggressive pre-conditioning.
Impact on Disease Progression
The preliminary efficacy data were particularly striking. In the four participants who completed sufficient follow-up, the mean ALSFRS-R slope of decline showed a significant improvement:
- Pre-treatment: -1.66 ± 1.03 points per month
- During treatment: -0.41 ± 0.45 points per month
- Post-treatment: -0.60 ± 0.59 points per month
This represents a substantial slowing of functional loss during the period of active Treg administration. While the small sample size necessitates caution, the stabilization of the ALSFRS-R score is a signal rarely seen in early-phase ALS trials.
Biomarker Insights: NfL and Cytokine Dynamics
To understand the biological impact of the therapy, researchers tracked neurofilament light (NfL), a sensitive biomarker of axonal injury. While NfL levels remained relatively stable in most participants, the study noted heterogeneous responses in inflammatory markers. Specifically, macrophage inflammatory protein-1 delta (MIP-1δ), cutaneous T cell-attracting chemokine (CTACK), and growth-regulated oncogene alpha (GROα) showed varying correlations with clinical scores.
The relationship between these markers and the ALSFRS-R score suggests that Treg therapy may modulate the peripheral immune environment in a way that reflects central nervous system health. However, the variability between patients highlights the need for larger studies to identify which “immune endotypes” of ALS respond most robustly to T-cell-based interventions.
Expert Commentary and Clinical Implications
The transition from autologous to allogeneic Treg therapy is a landmark shift for ALS research. By using umbilical cord-derived cells, clinicians can ensure the use of “young,” highly suppressive cells that have not been exposed to the chronic inflammatory environment of an aging or diseased patient. Furthermore, the “off-the-shelf” nature of this product addresses the scalability issues that have plagued cellular medicine.
Mechanistic Plausibility
The biological rationale for Treg therapy in ALS is robust. Tregs are known to promote the transition of microglia from a pro-inflammatory M1-like state to a neuroprotective M2-like state. In the context of this study, the sustained clinical benefit seen during the monthly maintenance phase suggests that regular “top-offs” of healthy Tregs may be necessary to maintain this anti-inflammatory balance in the spinal cord and motor cortex.
Study Limitations
As a Phase 1 study, the primary limitation is the small sample size (n=6). Additionally, the lack of a placebo control group makes it difficult to definitively attribute the slowed decline to the therapy alone, although the intra-patient comparison of pre-treatment vs. treatment slopes provides a strong internal control. Future Phase 2 trials will require a double-blind, randomized design to confirm these preliminary efficacy signals.
Conclusion
The TREG-ALS trial provides compelling evidence that allogeneic, “off-the-shelf” regulatory T cells are safe and potentially transformative for patients with ALS. By demonstrating that high-dose Treg infusions can be administered without lymphodepletion and still correlate with a marked slowing of functional decline, this study paves the way for a new class of immunotherapy in neurodegeneration. If validated in larger cohorts, this approach could offer a scalable, accessible treatment for a disease that currently has very few effective therapeutic options.
Funding and ClinicalTrials.gov
This research was supported by grants from the ALS Association and various private foundations. ClinicalTrials.gov Identifier: NCT04055623.
References
Shneider NA, Nesta AV, Rifai OM, et al. Clinical Safety and Preliminary Efficacy of Regulatory T Cells for ALS. NEJM Evid. 2025;4(5):EVIDoa2400249. doi:10.1056/EVIDoa2400249.
