Diversity and Clonality of T Cell Receptor Repertoire and Antigen Specificities in Small Joints of Early Rheumatoid Arthritis.

Objective: CD4+ T cells are implicated in rheumatoid arthritis (RA) pathology from the strong association between RA and certain HLA class II gene variants. This study was undertaken to examine the synovial T cell receptor (TCR) repertoire, T cell phenotypes, and T cell specificities in small joints of RA patients at time of diagnosis before therapeutic intervention. Methods: Sixteen patients, of whom 11 patients were anti–citrullinated protein antibody (ACPA)–positive and 5 patients were ACPA–, underwent ultrasound‐guided synovial biopsy of a small joint (n = 13) or arthroscopic synovial biopsy of a large joint (n = 3), followed by direct sorting of single T cells for paired sequencing of the αβ TCR together with flow cytometry analysis. TCRs from expanded CD4+ T cell clones of 4 patients carrying an HLA–DRB1*04:01 allele were artificially reexpressed to study antigen specificity. Results: T cell analysis demonstrated CD4+ dominance and the presence of peripheral helper T–like cells in both patient groups. We identified >4,000 unique TCR sequences, as well as 225 clonal expansions. Additionally, T cells with double α‐chains were a recurring feature. We identified a biased gene usage of the Vβ chain segment TRBV20‐1 in CD4+ cells from ACPA+ patients. In vitro stimulation of T cell lines expressing selected TCRs with an extensive panel of citrullinated and viral peptides identified several different virus‐specific TCRs (e.g., human cytomegalovirus and human herpesvirus 2). Still, the majority of clones remained orphans with unknown specificity. Conclusion: Minimally invasive biopsies of the RA synovium allow for single‐cell TCR sequencing and phenotyping. Clonally expanded, viral‐reactive T cells account for part of the diverse CD4+ T cell repertoire. TRBV20‐1 bias in ACPA+ patients suggests recognition of common antigens. [ABSTRACT FROM AUTHOR]