🎗CCR10 Defines a Potent Regulatory T Cell Subset Essential for Kidney Transplant Tolerance through Enhanced Foxp3 Lineage Stability

Introduction: Achieving operational tolerance is the primary goal of kidney transplantation, yet the specific cellular subsets and molecular mechanisms that sustain this state remain poorly defined. While regulatory T cells (Tregs) are essential for immune homeostasis, identifying the critical subpopulations responsible for long-term graft survival is vital for developing targeted therapies. 
Methods: We performed single-cell RNA sequencing to identify differential Treg profiles in tolerant versus non-tolerant kidney transplant recipients. These findings were validated using allogeneic mouse kidney transplantation models of rejection (DBA/2n to C57/B6) and tolerance (DBA/2J to C57/B6). We utilized high-dimensional flow cytometry, a Ccr10^fl/fl Foxp3^EGFP-creERT2 transgenic model for targeted CCR10⁺ Treg depletion, and random X-chromosome inactivation in female mice assessed homing capacity. Graft injury was evaluated by H&E and IHC staining on day 21. The molecular mechanisms governing Foxp3 stability were interrogated via integrated  ATAC-seq, RNA-seq, and CHX pulse-chase assays. 
Results: Analysis revealed that the proportion of CCR10⁺ Tregs was notably increased in the PBMCs of tolerant patients, as well as in the peripheral blood and local kidney grafts of tolerant mice. Functional studies demonstrated that the specific clearance of CCR10⁺ Tregs exacerbated kidney transplant rejection. Interestingly, we found that CCR10⁺ Tregs do not primarily exert their protective effects through enhanced kidney homing, but rather by significantly enhancing their intrinsic immunosuppressive function. Specifically, CCR10 knockout led to a pronounced decline in Foxp3 stability. Furthermore, in an IL-6-rich, highly inflammatory environment, CCR10-/- Tregs exhibited a strong propensity to transdifferentiate into pro-inflammatory Th17 cells. Joint analysis of ATAC-seq and transcriptomics, alongside in vitro assays, demonstrated that this instability was primarily driven by reduced Foxp3 transcription rather than accelerated pro tein degradation.
Conclusion: CCR10⁺ Tregs are increased in both the circulation and local kidney grafts of tolerant individuals, playing a pivotal role in resisting rejection and maintaining immune tolerance. CCR10 preserves the highly immunosuppressive state of Tregs by stabilizing Foxp3 transcription and preventing pro-inflammatory transdifferentiation. Targeting and expanding CCR10⁺ Tregs could be a promising therapeutic strategy for preventing rejection and maintaining long-term allograft tolerance.