Secondary infections rejuvenate the intestinal CD103 + tissue-resident memory T cell pool.

Resident T lymphocytes (T RM ) protect tissues during pathogen reexposure. Although T RM phenotype and restricted migratory pattern are established, we have a limited understanding of their response kinetics, stability, and turnover during reinfections. Such characterizations have been restricted by the absence of in vivo fate-mapping systems. We generated two mouse models, one to stably mark CD103 + T cells (a marker of T RM cells) and the other to specifically deplete CD103 - T cells. Using these models, we observed that intestinal CD103 + T cells became activated during viral or bacterial reinfection, remained organ-confined, and retained their original phenotype but failed to reexpand. Instead, the population was largely rejuvenated by CD103 + T cells formed de novo during reinfections. This pattern remained unchanged upon deletion of antigen-specific circulating T cells, indicating that the lack of expansion was not due to competition with circulating subsets. Thus, although intestinal CD103 + resident T cells survived long term without antigen, they lacked the ability of classical memory T cells to reexpand. This indicated that CD103 + T cell populations could not autonomously maintain themselves. Instead, their numbers were sustained during reinfection via de novo formation from CD103 - precursors. Moreover, in contrast to CD103 - cells, which require antigen plus inflammation for their activation, CD103 + T RM became fully activated follwing exposure to inflammation alone. Together, our data indicate that primary CD103 + resident memory T cells lack secondary expansion potential and require CD103 - precursors for their long-term maintenance.