Editorial: Role of Tissue-Localized Regulatory T Cells in Health and Disease

Bevin Smith¹Diane Mathis Mathis²Ali A. Zarrin^1*

• ¹TRexBio Inc, San Francisco, United States
• ²Department of Immunology, Harvard Medical School, Boston, United States

The identity and stability of Tregs hinge on Foxp3, which is maintained by a network of epigenetic and transcriptional regulators. In this collection, Christensen et al. and Subramanyam et al. reveal how distinct coregulators safeguard this lineage. Loss of Sin3a, a chromatin modifying cofactor of Hdac1/2, destabilizes Foxp3 and reduces Tregs, leading to impaired immune regulation. Deletion of the transcription factor CREB in Tregs reduces Foxp3 expression and polarizes to a Th2-like phenotype displaying co-expression of ST2, IL-10, and IL-13. The functionality of these Tregs is retained and the enhanced production of IL-10 mediates a protective eXect within a T cell transfer colitis model. Together, these studies underscore the diverse ways coregulators aXect Foxp3 stability and function and highlight the need to better understand how such pathways shape tissue-localized Tregs in humans.Genetic background shapes Treg composition and function. Santamaria et al. identify a genomic region that may promote GITR high PD-1+ autoreactive Tregs in the NOD mouse model of type-1 diabetes. In contrast, Liu et al. sought to establish a causal relationship between genetic variants on disease outcome. Subsetting Tregs into specific fractions using combinations of surface markers, they find genetically predicted associations between the CD39+CD8+ regulatory cells in the co-occurrence of autoimmune disorders and certain lymphomas. Together, these studies illustrate how germline variation can shape Treg compartments, highlighting the need to integrate developmental and genetic perspectives in understanding Treg biology.The migration and retention of tissue Tregs depends on their repertoire of adhesion molecules along with chemokine receptors. Cheru et al., show that while tissue-localized Tregs share a core identity across organs, they are profoundly shaped by local microenvironmental cues, giving rise to heterogenous phenotypes and functions. Cell-cell interactions and cell-independent influences within the tissue microenvironment contribute to the transcriptional profiles of Tregs. Xiang et al. extend this view by highlighting how reciprocal interplay between these tissue-specific elements on both Tregs and eXector T cells, the conflicting Yin and Yang, are critical in maintaining the immunological steady state, and how imbalances may be key drivers of disease. Together, these studies emphasize that tissue residency is not simply about localization, but about continuous dialogue with the surrounding niche. Collectively, the articles in this research topic illustrate that tissue-localized Tregs are far more than static suppressors of immunity: they are dynamic, context-dependent players that integrate transcriptional, genetic, and environmental cues to shape outcomes across health and disease. From epigenetic mechanisms that safeguard Foxp3 stability, to genetic influences that bias Treg diXerentiation, to microenvironmental signals that diversify their tissue functions, each contribution underscores the flexibility of this lineage. The diseasefocused studies further reveal the dual nature of Tregs: protective in some contexts, pathogenic in others; whether in infection, cancer, or fibrotic repair. Looking ahead, the field faces the challenge of translating these mechanistic insights into therapeutic strategies that can enhance or restrain Tregs in a tissue-and disease-specific manner. As the boundary between tolerance, immunity and regeneration continues to blur, understanding the principles that govern tissue Treg biology will be essential for designing the next generation of eXective immunotherapies.