-Specific Tissue-Resident Memory CD4 T Cells Are Abundant in Healthy Human Skin.

The skin is an immunocompetent tissue that harbors several kinds of immune cells and a plethora of commensal microbes constituting the skin microbiome. is a prominent skin pathogen that colonizes a large proportion of the human population. We currently have an incomplete understanding of the correlates of protection against infection, however genetic and experimental evidence has shown that CD4 T cells play a key role in orchestrating a protective anti- immune response. A high -specific memory CD4 T cell response has been reported in the blood of healthy subjects. Since T cells are more abundant in the skin than in blood, we hypothesized that -specific CD4 T cells could be present in the skin of healthy individuals. Indeed, we observed proliferation of tissue-resident memory CD4 T cells and production of IL-17A, IL-22, IFN-γ and TNF-β by cells isolated from abdominal skin explants in response to heat-killed . Remarkably, these cytokines were produced also during an epicutaneous infection of human skin explants. These findings highlight the importance of tissue-resident memory CD4 T cells present at barrier sites such as the skin, a primary entry site for . Further phenotypical and functional characterization of these cells will ultimately aid in the development of novel vaccine strategies against this elusive pathogen.