Recirculating regulatory T cells mediate thymic regeneration through amphiregulin following damage.

Thymic injury associated with disease or cancer treatment reduces T cell production and makes patients more vulnerable to infections and cancers. Here, we examined the role of regulatory T (Treg) cells on thymic regeneration. Treg cell frequencies increased in the thymus in various acute injury models. Depletion of Treg cells impaired thymic regeneration, impacting both the thymocyte compartment and the stromal cell compartment; adoptive transfer of Treg cells enhanced regeneration. Expansion of circulating Treg cells, as opposed to that of tissue resident or recent thymic emigrants, explained this increase, as seen using parabiotic and adoptive transfer models. Single-cell analyses of recirculating Treg cells revealed expression of various regenerative factors, including the cytokine amphiregulin. Deletion of amphiregulin in these Treg cells impaired regeneration in the injured thymus. We identified an analogous population of CD39(+)ICOS(+) Treg cells in the human thymus. Our findings point to potential therapeutic avenues to address aging- and treatment-induced immunosuppression.