Tissue-intrinsic γδ T cells critically regulate Tissue-Resident Memory CD8 T cells

Because Tissue-Resident Memory T (TRM) cells contribute critically to body-surface immunoprotection and/or immunopathology in multiple settings, their regulation is biologically and clinically important. Interestingly, TRM commonly develop in epithelia part-shaped by innate-like lymphocytes that become tissue-intrinsic during development. Here we show that polyclonal TRM cells induced by allergic contact dermatitis (ACD) interact with signature intraepidermal {gamma}{delta} T cells, facilitating a feedback-loop wherein TRM-derived IFN{gamma} upregulates PD-L1 on {gamma}{delta} cells that can thereupon regulate PD1+ TRM. Thus, TRM induced by ACD in mice lacking either local {gamma}{delta} cells, or lacking a single gene (IFN{gamma}R) expressed by local {gamma}{delta} cells, displayed enhanced proliferative and effector potentials. Those phenotypes were associated with strikingly limited motility, reduced TRM quality. and an impaired capacity to restrain melanoma. Thus, inter-individual and tissue-specific variation in how tissue-intrinsic lymphocytes integrate with TRM may sit upstream of variation in responses to cancer, allergens and other challenges, and may likewise underpin inflammatory pathologies repeatedly observed in {gamma}{delta}-deficient animals.