Project Summary/Abstract Rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA) are chronic autoimmune diseases of the joint punctuated by periodic arthritis flares. Clinicians have long recognized that each affected person develops an individual pattern of affected joints, and that this pattern remains stable over time through disease remission and flares. We recently identified the presence of synovial resident memory T cells (TRM) in arthritic joints and showed that they mediate arthritis flares. Correspondingly, depleting these cells ameliorates disease recurrence, indicating that TRM can be targeted as a novel approach in arthritis therapy. The long-term objective of the proposal is to define the mediators of TRM development and maintenance in the synovium and determine if these pathways can be therapeutically targeted to treat arthritis. The specific aims of this proposal utilize 2 complementary approaches in mice and human studies to identify the mediators of synovial TRM development. Aim 1 utilizes a mouse model of inflammatory arthritis developed by the PI to define the lineage and differentiation process of synovial TRM. Aim 2 utilizes a human synovial organoid system to interrogate the impact of the synovial microenvironment, namely synovial stromal cells, on TRM formation and survival. We expect that these studies will identify critical mediators of TRM development, which may represent novel therapeutic targets for inflammatory arthritis. The candidate is an M.D./Ph.D. pediatric rheumatologist at Boston Children’s Hospital. This proposal builds upon her foundational knowledge of immunology to extend her skillset into antibody-coupled single cell sequencing, bioinformatics, organoid models of human synovium, and CRISPR gene targeting. The proposal includes a comprehensive mentoring and didactic plan that will allow her to successfully learn new skills and gain expertise in each of these important areas. The primary mentor, Dr. Peter Nigrovic, is a rheumatologist and expert in the pathophysiology of inflammatory arthritis. The candidate has assembled a K08 advisory committee consisting of Dr. Michael Brenner, Dr. Rachael Clark, and Dr. Soumya Raychaudhuri, who each have specific expertise in various aspects of this proposal such as analysis of single-cell sequencing data, 3D models of human synovium, and expertise in TRM biology in human disease. The candidate is committed to a career in translational research with the goal of becoming an independent lab-based investigator focusing on local mechanisms to autoimmune disorders. The proposed studies, training plan, and exceptional environment at Boston Children’s Hospital, Brigham and Women’s Hospital and Harvard Medical School will enable her to successfully transition to an independent PI and leader in this field.