Although tissue-resident memory T cells (T cells) are critical in fighting infection, their fate after local pathogen re-encounter is unknown. Here we found that skin T cells engaged virus-infected cells, proliferated in situ in response to local antigen encounter and did not migrate out of the epidermis, where they exclusively reside. As a consequence, secondary T cells formed from pre-existing T cells, as well as from precursors recruited from the circulation. Newly recruited antigen-specific or bystander T cells were generated in the skin without displacement of the pre-existing T cell pool. Thus, pre-existing skin T cell populations are not displaced after subsequent infections, which enables multiple T cell specificities to be stably maintained within the tissue.

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