Autoreactive T Cell Function in Vitiligo

T cells are effector cells of autoimmunity that migrate to find their targets, produce cytokines that recruit and activate other immune cells, and destroy their target cells in affected tissue. Vitiligo is an autoimmune disease of the skin in which cytotoxic CD8+ T cells target pigment-making melanocytes, which results in disfiguring white spots that are particularly devastating for those with darker skin and thus leads to health disparities for the most vulnerable of our population. Vitiligo is an ideal disease in which to investigate mechanisms of organ- specific autoimmunity because disease phenotype can be directly correlated to molecular pathways. That is, affected skin can be observed and sampled, target cells and antigens are known, and translational research tools are available. Vitiligo shares genetic risk alleles and other mechanisms with autoimmune diseases like type 1 diabetes and multiple sclerosis that are more difficult to study in human patients. Through vitiligo we can develop a comprehensive understanding of organ-specific autoimmunity as it progresses within human tissue. In vitiligo and models of other human autoimmune diseases, autoreactive T cell responses are commonly char- acterized as homogenous, with an “all or nothing” result. This is partly due to the fact that mouse models of autoimmunity are frequently based on a single high-affinity CD8+ cytotoxic clone transferred and activated arti- ficially. However, we found that T cells infiltrating vitiligo skin lesions are polyclonal and heterogeneous, with different antigenic specificities and activation states. Cytotoxic CD8+ T cells organize into clustered units within the epidermis that appear to attack melanocytes, while CD4+ and Treg cells are at the periphery of these clus- ters. Together, these data indicate that T cell interactions in vitiligo are more complex than previously under- stood. Our central hypothesis is that polyclonal CD8+, CD4+, and Treg cell communications coordinate mela- nocyte destruction and determine vitiligo clinical phenotypes. This project will determine how autoreactive T cell clonal diversity and localization define the clinical disease phenotype, how T cell subtypes interact with each other to coordinate autoimmunity, and how T cells orches- trate melanocyte destruction within the skin. First, we will determine the in vivo location, spatial relationships, and functional characteristics of T cell clones in different clinical phenotypes of vitiligo, such as early incipient vs. late established lesions, active vs. stable disease, and single vs. multiple locations. Next, we will character- ize the function and reactivity of T cells isolated directly from the skin of these lesions. We will use primary T cell and skin organ culture, T cell functional assays, T cell receptor affinity assays, the sequential fluorescence in situ hybridization (seqFISH+) Core, and advanced computational methods. This project is translational in approach because it will create new mechanistic understanding of how T cells mediate the initiation, progres- sion, and maintenance of autoimmunity during vitiligo. Together these aims will define molecular mechanisms utilized by autoreactive T cells and identify key functional pathways, supporting new therapeutic interventions.