Tregs in Focus: How a Nobel-Winning Finding is Shaping Clinical Research

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October 22, 2025

Céline Vandamme, Director, Scientific Business Development

The 2025 Nobel Prize in Physiology or Medicine recognized discoveries that transformed our understanding of how the immune system maintains balance. Mary Brunkow, Frederick Ramsdell, and Shimon Sakaguchi were awarded for uncovering the mechanisms of peripheral immune tolerance, a process that prevents our immune system from unduly attacking the body’s own tissues.¹

Through decades of research, they revealed that immune tolerance is not just established during T-cell development in the thymus but is actively maintained throughout life by a specialized population of FOXP3⁺ regulatory T cells (Tregs). Their research demonstrated that Treg cells act as the immune system’s ‘braking mechanism’, suppressing inappropriate or excessive activation that could harm the body.¹

Their discoveries bridged a gap that had long puzzled immunologists, explaining how the immune system is dynamically self-regulating throughout life to distinguish between harmful invaders and healthy cells. That knowledge paved the way to today’s wave of Treg-focused clinical trials, where researchers are investigating how tipping the immune balance one way or the other can be achieved through precise manipulation of Treg cells.

What is the current focus of Treg clinical trials?

Building on these foundational discoveries, current clinical research is focused on how modulating Treg activity can improve outcomes in patients with cancer and autoimmune diseases.

Oncology

In oncology, Treg clinical trials are exploring ways to reduce the suppressive activity of Tregs within the tumor microenvironment (TME), where these cells often accumulate and inhibit anti-tumor immunity.²

Key approaches under investigation include:

Checkpoint and cytokine modulation, such as combining PD-(L)1 and VEGF inhibitors, which can alter the TME to reduce immune suppression, including Treg activity²

Blocking chemokine receptors, using antibodies that target CCR4 or CCR8 to prevent Tregs from migrating into the TME and deplete them²

Targeted depletion, including next-generation antibody–drug conjugates (ADCs) designed to selectively eliminate Tregs through markers such as CD25³

Early-phase studies show that these strategies can enhance cytotoxic T-cell activity and improve responses to checkpoint inhibitors.^1,² Further research is focused on improving selectivity, ensuring that Tregs in the TME can be modulated without disrupting the peripheral populations needed to maintain overall immune balance.²

Autoimmune diseases

In autoimmune and inflammatory disorders, clinical strategies take the opposite approach by enhancing or stabilizing Tregs to re-establish immune tolerance.

Current research includes:

Cytokine-based stimulation, using low-dose or engineered interleukin-2 (IL-2) therapies that selectively expand Tregs while avoiding activation of effector T cells^4,5

Adoptive or engineered Treg therapies, such as CAR-Tregs and T-cell receptor (TCR)-Tregs, which are being developed to deliver site-specific immune suppression and promote graft tolerance in transplantation^4,5

Early clinical data suggest that these approaches can expand functional Tregs and reduce autoimmune inflammation without broadly suppressing protective immunity. As research progresses, the aim is to improve the scalability, safety, and efficacy of Treg cell therapies to make them more accessible to a broader patient population.⁵

How are Tregs assessed in clinical trials?

Accurate measurement of Tregs is essential for evaluating treatment effects in clinical studies. Assessments are typically performed in both tissue and blood samples, each providing complementary insight into Treg frequency, localization, and function.

Assessment in tissues

Tissue analysis provides spatial information about where Tregs are located and how they interact with other immune cells within the tissue microenvironment. Biomarkers such as FOXP3, CD3, and CD4 are commonly used to identify Tregs in histopathology samples. To capture this in high resolution, researchers can use multiplex imaging platforms such as the Lunaphore COMET™ system to detect dozens of markers at single-cell resolution, enabling high-plex visualization of Tregs and their surrounding context.

Assessment in blood

Blood-based analysis focuses on circulating Tregs, typically defined by CD25 and CD127 expression, with FOXP3 used as a confirmatory marker. Flow cytometry can be used to quantify Treg frequency and phenotype in whole blood or isolated peripheral blood mononuclear cells (PBMCs).

What are the challenges of assessing Tregs in clinical trials?

While these analytical methods are well established, accurately quantifying Tregs in clinical samples can be challenging. Their low frequency and sensitivity to handling, in addition to a reliance on intracellular markers such as FOXP3 mean that even minor differences in sample processing and methodology can impact results.

Sample stability and processing

Tregs are highly sensitive to sample handling, which can make them difficult to assess accurately . During PBMC isolation, there can be up to a fivefold decrease in Treg populations, even when samples are processed within 24 hours of blood draw.

To avoid this, researchers can use CytoChex® blood collection tubes for whole blood collection if Tregs are a key readout, as this approach has been found to better preserve Treg cell frequency and marker expression over time.

Staining resolution

Because FOXP3 is an intracellular marker, accurate detection depends on optimized fixation, permeabilization, and gating. Inconsistent preparation may blur signal distinction and complicate gating.

This can be addressed through optimized staining protocols and refined gating strategies, which can improve the reproducibility and clarity of FOXP3⁺ Treg readouts in whole blood.

Treg heterogeneity

Tregs are not a uniform population. Differences in stability, activation state, and function can complicate data interpretation, particularly when bulk assays average out signals across diverse subsets.

This complexity can be addressed through single-cell transcriptomic and TCR-sequencing approaches, which can identify distinct Treg subpopulations and track how individual clones shift in phenotype or functionality over time. These methods provide a more detailed view of Treg diversity and its relevance to therapeutic response.

Looking ahead

The discoveries recognized by the 2025 Nobel Prize underpin an expanding focus on Tregs in clinical immunology and oncology research. As therapeutic programs increasingly incorporate Treg assessment, advances in sample stabilization, staining workflows, and multi-omic profiling can help deliver more consistent, high-resolution data to help researchers characterize these cells and link their activity to clinical outcomes.

These deeper insights can help pave the way for more precise, effective therapies that could offer new potential to treat cancer and autoimmune diseases.

Contact us to find out how CellCarta’s immunology and biomarker expertise can support Treg assessment and analysis.

References

About the author:

Céline Vandamme is a Scientific Business Director at CellCarta, specializing in the flow cytometry platform. With a PhD in immunology, and a broad expertise gained through her work at various academic and pharmaceutical institutions, Céline has profuse experience in designing flow cytometry assays to support immune monitoring activities in clinical trials.

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