hLifeOct 22, 2026

Former Regulatory T Cells: From Misunderstood Artifact to Potential Treatment Target

Longevity & Aging Weekly Brief ↗PubMed ↗DOI ↗

Updated Oct 23, 2026

Abstract

Three interdependent factors—environmental stress, epigenetic erasure, and metabolic rewiring—cooperatively drive the conversion of stable regulatory T cells to pathogenic ex-regulatory T cells.

Regulatory T cells (Tregs) can transition to ex-regulatory T cells (ex-Tregs), which may contribute to autoimmunity and aging.
The Treg-specific demethylated region (TSDR) helps differentiate committed Tregs from temporary FOXP3 expressers.
Environmental factors such as interleukin-1β and interleukin-6 are associated with Treg instability.
Dysfunction in the TET2 gene may lead to hypermethylation of TSDR, impacting Treg stability.
Metabolic changes driven by mechanistic target of rapamycin (mTOR) may influence the conversion to ex-Tregs.
Key uncertainties remain about ex-Treg heterogeneity and the potential for reversing epigenetic changes in humans.

Simplified

Regulatory T cell (Treg) instability has evolved from a debated artifact into a central concept in immunology, though the mechanisms driving the transition from a stable suppressor to a pathogenic ex-regulatory T cell (ex-Treg) remain unclear. This review synthesizes findings from fate-mapping, epigenetic, and metabolic studies in mouse models and human systems, tracing the ex-Treg concept through three phases: controversy, epigenetic reconciliation, and current views. The Treg-specific demethylated region (TSDR) distinguishes truly committed Tregs from transient forkhead box P3 (FOXP3) expressers. Three interdependent factors-environmental stress (interleukin-1β [IL-1β], interleukin-6 [IL-6]), epigenetic erasure (ten-eleven translocation 2 [TET2] dysfunction leading to TSDR hypermethylation), and metabolic rewiring (mechanistic target of rapamycin [mTOR]-driven glycolysis)-cooperatively drive ex-Treg conversion. The "self vs non-self" hypothesis frames instability as an evolved checkpoint balancing tolerance with host defense. Ex-Tregs contribute to autoimmunity and aging but also offer therapeutic opportunities in cancer. Key uncertainties persist regarding ex-Treg heterogeneity, epigenetic reversibility, and translation to humans. Future directions should focus on biomarker discovery and engineering epigenetically stable Tregs for therapy. Collectively, these advances position Treg instability as a pivotal regulator of immune homeostasis and highlight the promise of therapeutically targeting this pathway to advance treatments for autoimmunity, aging, and cancer.

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Former Regulatory T Cells: From Misunderstood Artifact to Potential Treatment Target

Abstract

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