TRMs empower non-invasive immune monitoring with skin-ready microneedles

The study combines skin-resident memory T cell (TRM) recall with hydrogel-coated microneedle patches to non-invasively sample antigen-specific T cells from skin and blood. In mice, TRM priming and recall at the skin enabled sampling of thousands of live antigen-specific lymphocytes, surpassing conventional peripheral blood assessments. In a human case of allergic contact dermatitis, TRM reactivation followed by microneedle application captured diverse immune cells and cytokines from the interstitial fluid, with sampling efficiency comparable to or better than suction blisters and better suitability for longitudinal monitoring. The approach is antigen-agnostic and could enable broad, repeated immune monitoring across vaccination, infection, and autoimmune contexts, though larger cohorts and antigen-defined readouts are needed for broader clinical translation.