In the past two decades, regulatory T (Treg) cells have emerged as a dedicated immune population crucial for the negative regulation of immune responses. Nonetheless, the precise effector mechanisms underlying Treg cell-mediated suppression in a specific tissue microenvironment under a particular immunological condition remains incompletely understood. To date, accumulating evidence has suggested that similar to the conventional T (Tconv) cells they regulate, Treg cells come in “different flavors” both phenotypically and functionally. In addition to the heterogeneity of the Treg cells that control different types of T cell immune responses, the presence of distinct Treg cell populations in many nonlymphoid tissues have also started to be appreciated. In this proposal, though establishing a novel mouse model that could allow us to deplete a desired Treg cell subset in a temporally controlled manner, we will determine the cellular role of a specific Klrg1-expressing Treg cell population in maintaining peripheral tissue homeostasis under both physiologic and pathologic conditions. Moreover, by employing a cutting-edge single-cell transcriptomic approach, we will gain further molecular and cellular insights into the impact of Klrg1+ Treg cell depletion on the immune system in a particular tissue microenvironment in an unbiased manner. Collectively, our proposed studies will not only provide a comprehensive assessment of the Klrg1+ Treg cell subset in Treg cell-mediated immune regulation but will also facilitate a better understanding of the potential effector mechanisms by which Klrg1+ Treg cells maintain peripheral tissue homeostasis. Accomplishing the aims proposed in this application will undoubtedly extend our fundamental knowledge of a distinct Treg cell subset in immune regulation and provide further insights into the development of new therapeutic means targeting Treg cells to treat a wide range of human immune disorders.