OVERALL – PROJECT SUMMARY Organ-specific autoimmunity requires a series of precise cellular interactions to coordinate target cell destruc- tion within complex tissues. 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. 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 ob- served and sampled, target cells and antigens are known, and translational research tools are available. Viti- ligo shares genetic risk alleles and other mechanisms with autoimmune diseases like type 1 diabetes and mul- tiple sclerosis, which are more difficult to study in human patients. Through vitiligo we can develop a compre- hensive understanding of organ-specific autoimmunity as it progresses within human tissue. Our objective is to determine the mechanisms by which autoreactive T cells navigate the skin, communicate with neighboring cells, engage and destroy melanocytes, and create long-term memory of autoimmunity di- rectly within vitiligo lesions. We generated an extensive set of high-resolution, translational multiomics data from vitiligo patient skin and assembled it into an integrated communication network among multiple cell types that coordinate disease progression. This provides clues into vitiligo pathogenesis that must now be validated, dissected, and reassembled to reveal fundamental concepts of autoimmunity. Thus, we hypothesize that auto- reactive T cell function is carefully coordinated by cellular signals within the microenvironment of the epidermis. To test this hypothesis, we will leverage existing data, a multidisciplinary team of leading investigators, cutting edge tools designed for discovery, and an innovative strategy to discover how skin cells coordinate autoim- munity during vitiligo. Project 1 will investigate Autoreactive T cell Function in Vitiligo to determine how autore- active T cell clonal diversity and localization define the clinical disease phenotype and coordinate melanocyte destruction. Project 2 will focus on Cell-Cell Communications and Tissue Memory in Vitiligo to dissect the mechanisms by which ligand-receptor interactions coordinate T cell localization, function, and inflammatory memory. These projects will be supported by the High-Resolution Spatial Transcriptomics Research Core us- ing seq-FISH+ to translate our vitiligo multiomics data into a complete spatial understanding of cellular position and communication within vitiligo lesions. The Administrative Core will promote communication, ensure scien- tific achievement, and monitor fiscal management to support focus on research goals and implementation. We expect to create an integrated understanding of coordinated cellular communications and interactions that drive vi...