A linear ontogeny accounts for the development of naive, memory, and tumor-infiltrating regulatory T cells in mice.

Regulatory T cells (Treg cells) are critical regulators of adaptive immunity and the pathophysiology of antitumoral immunity. Treg cells are both generated during thymic development and induced from peripheral conventional T cells. How these distinct pathways contribute to the homeostasis of circulating Treg cells in health and disease remains unclear. We addressed this question using multiple fate-mapping mouse systems and modeling. Naive and effector/memory (EM) Treg cells exhibit distinct dynamics but are both continuously replenished by de novo generation throughout life. The predominant precursors of circulating EM Treg cells are naive thymic Treg cells and not conventional T cells, a process driven by self rather than foreign antigen recognition. Using the same fate reporters and three tumor models, we demonstrate that infiltrating Treg cells specifically derive from preexisting EM Treg cells. In summary, we define a linear ontogeny of Treg cells from the thymus to EM, driven by self-antigen recognition, that then gives rise to tumor-infiltrating Treg cells.