Circulating CD4+ memory T cells give rise to a CD69+ resident memory T cell population in non-inflamed human skin

The blood of human adults contains a pool of circulating CD4+ memory T cells and normal human skin contains a CD4+CD69+ memory T cell population that produce IL17 in response to Candida albicans. Here we studied the generation of CD4+CD69+ memory T cells in human skin from a pool of circulating CD4+ memory T cells. Using adoptive transfer of human PBMC into a skin-humanized mouse model we discovered the generation of CD4+CD69+ resident memory T cells in human skin in absence of infection or inflammation. These CD4+CD69+ resident memory T cells were activated and displayed heightened effector function in response to Candida albicans. These studies demonstrate that a CD4+CD69+ T cell population can be established in human skin from a pool of circulating CD4+ memory T cells in absence of infection/inflammation. The described process might be a novel way to spread antigen-specific immunity at large barrier sites even in absence of infection or inflammation.