Atherosclerosis destabilizes regulatory T cells (Tregs) resulting in multiple families of exTregs

How regulatory T cells (Tregs) lose lineage identity during chronic inflammation remains poorly understood. Here, using inducible Foxp3 lineage tracing together with single-cell transcriptomic, proteomic and T cell receptor (TCR) profiling in atherosclerosis-prone mice, we identify Treg destabilization as a staged and branching differentiation process rather than an abrupt loss of lineage identity. Conventional Tregs (cTregs) first transition through an effector Treg (eTreg) intermediate characterized by attenuation of the CD25–STAT5 axis while retaining core Treg features, before diversifying into eight transcriptionally distinct exTreg states, including Tfh-like, cytotoxic, Th1-like inflammatory, Th1-like cytotoxic and proliferative populations. Trajectory inference, TCR clonotype analysis and experimental Treg-to-exTreg conversion independently converged on this developmental framework, revealing that clonally related exTregs acquire distinct effector programs. Mechanistically, we identify Treg-intrinsic IL-6R signaling as an important driver of this process. IL-6 accelerated exTreg generation in vitro, whereas Treg-specific deletion of Il6ra reduced inflammatory exTreg differentiation and attenuated atherosclerosis in vivo. Together, these findings establish a framework for Treg destabilization during atherosclerosis and provide a conceptual basis for preserving Treg lineage stability in chronic inflammatory disease.