Specificity, frequency, and phenotype of citrullinated-specific T cells vary with disease activity in rheumatoid arthritis.

In rheumatoid arthritis (RA), CD4+ T cells specific for citrullinated antigens (cit-antigens) are key drivers of disease, but knowledge about epitopes and phenotypes remains limited. We characterized the frequency and phenotype of cit-specific CD4+ T cells in peripheral blood using HLA class II tetramers combined with computational analysis of phenotypic clusters to simultaneously detect peptides derived from 5 cit-antigens (aggrecan, vimentin, fibrinogen, cartilage intermediate layer protein, and α-enolase) previously implicated in RA pathogenesis. In a cross-sectional cohort, cit-aggrecan-, cit-vimentin-, and cit-fibrinogen-specific T cells were more frequent in participants with RA than healthy volunteers, associated with active disease, and had Th1-like and stem-like lineages in RA. In a longitudinal cohort investigating response to therapy, the frequency of cit-aggrecan-, cit-vimentin-, and cit-fibrinogen-specific CD4+ T cells was significantly higher at baseline and further elevated in responders. Furthermore, the frequency of cit-specific Th1-like cells in responders decreased over time. In contrast, the frequency of Th1-like cells in non-responders increased over time. Collectively, these findings demonstrate that cit-specific CD4+ T cells are expanded in RA and target a broad number of antigens across a breadth of phenotypes. Furthermore, the predominant antigen specificities associate with disease activity and exhibit dynamic changes in phenotype that reflect response to therapy.