Development of Fit Epidermal Resident Memory T Cells Requires Antigen Encounter in the Skin.

CD8+ tissue resident memory T cells (TRM) develop from effectors that are recruited into peripheral tissues by infection or inflammation where they persist and provide defense against subsequent challenges. Long-term persistence of epidermal TRM requires autocrine TGFβ that is transactivated by integrins expressed on keratinocytes. In response to inflammation, the availability of TGFβ transactivation is limited. Antigen-experienced TRM that encountered antigen in the epidermis during their development are more fit and outcompete bystander TRM for TGFβ transactivation resulting in their enrichment in the epidermis. Transcriptomic analysis of endogenous epidermal TRM revealed that antigen-experienced TRM were enriched for TRM signature genes while bystander TRM retained the transcriptome of an earlier developmental state. Following antigen recall, antigen-experienced TRM displayed accelerated proliferation kinetics compared with bystanders that was determined by the TCR signal-strength during their differentiation the skin. Finally, antigen experienced TRM expressed TGFβRIII, which increases avidity of the TGFβRI/II receptor complex. Selective ablation of Tgfbr3 from antigen experienced TRM reduced their capacity to persist when TGFβ activation was limited thus rendering them phenotypically like bystander TRM. In sum, antigen-driven TCR signaling in the epidermis during TRM differentiation represents a required final step in ontogeny resulting in a lowered requirement on TGFβ transactivation for persistence and increased proliferation during recall responses that together result in the enhanced fitness of antigen-experience epidermal TRM. Cohorts of wildtype C57BL/6 mice were infected on the left flank with VV by skin scarification. DNFB was applied to the right flank 5 days post infection to recruit into the skin circulating CD8 effectors expanded by infection. Mice were then rested for 50+ days to allow for the formation of TRM. Cells were pooled from 10 mice, enriched by percoll gradient centrifugation and purified by double FACSorting based on expression of CD90 and CD8. On August 15, 2025, the Series was reorganized in order to include tissue-specific samples.