CD4 and rheumatoid arthritis: Studies tracking TCRs across tissues or longitudinally in RA patients have identified shared T cell clones in different joints27,28, clonal expansion of specific cell subsets29, persistence of expanded clones over time30, and overrepresented gene rearrangements that may suggest shared antigenic targets28,31,32; however, reactivity of expanded TCRs from RA synovial CD4 + T cells to citrullinated peptides has been difficult to demonstrate33.