Determining the Pathogenic Roles of Granzyme K+ CD8 T Cells Unexpectedly Expanded in Rheumatoid Arthritis Synovium and Other Diseased Tissues - Project Summary/Abstract This proposal is a five-year research plan with an overarching goal of determining the dominant effector functions of granzyme K-expressing CD8 T cells in synovial tissue in rheumatoid arthritis. Inflamed synovial tissue from patients with rheumatoid arthritis contains a large number of CD8 T cells, in some cases representing up to 30% of live cells. We have found that these cells do not express high levels of genes and proteins typically expressed by cytotoxic T lymphocytes, such as GZMB (granzyme B), PRF1 (perforin), and GNLY (granulysin). Instead, these CD8 cells express large amounts of granzyme K, a protease with a cleavage specificity very different from granzyme B. Similar granzyme K-expressing cells have also been detected in tissues in several other autoimmune diseases as well as in many different cancers. Given the abundance of this cell type at the sites of disease in so many different human conditions, determining the effect of granzyme K-expressing CD8 T cells on surrounding cells is vital for understanding their role in disease pathogenesis and for determining how best to target these cells with new treatments. The specific aims proposed here will investigate the effector mechanisms of granzyme K-expressing CD8 T cells using a strategic combination of in vivo, in vitro, and in situ approaches. Aim 1 uses an antigen-induced mouse model of inflammatory arthritis to determine whether granzyme K-expressing cells in inflamed joints are antigen-specific and -activated or whether they are antigen-independent bystander cells, i.e., recruited and activated by the general inflammatory milieu of the synovium. Aim 2 systemically dissects the relative potency of known effector functions of granzyme K-expressing CD8 T cells on the recruitment, activation, and differentiation of myeloid cells, one of the most pro-inflammatory cell types in rheumatoid arthritis synovium and other inflamed tissues. Aim 3 uses multiplex imaging and spatial transcriptomics to identify and compare molecular footprints of granzyme K+ CD8 T cell-associated effector functions in human rheumatoid arthritis synovial tissue samples. This study integrates mouse models, mechanistic cellular immunology studies, and cutting-edge spatial technologies to a newly identified CD8 T cell subset that is highly enriched in rheumatoid arthritis synovium and many other human diseases. This work builds on a long-standing collaboration of the PI, a rheumatologist and translational cellular human and mouse immunologist, and co-I Dr. Fan Zhang, a computational biologist with expertise in synovial tissue -omics analysis and spatial transcriptomic methods development. The findings of this study will inform the design of new therapeutics for rheumatoid arthritis and other autoimmune diseases.
