Peripheral regulatory CD8+CD28−KLRG1+ T cells as markers of disease and treatment response in rheumatoid arthritis

Objective CD3 + CD8 + CD28 − cells are increased in the periphery and tissues of rheumatoid arthritis (RA) patients. The aim of this study was to characterise CD3 + CD8 + CD28 − cells for the presence of cell surface receptors that regulate immune activation and function and to track their presence in a disease model of RA. Cell surface receptors expressed by CD3 + CD8 + CD28 − cells were then related to serological and clinical disease parameters to establish whether these cells are prognostic of a clinical response to conventional DMARDs. Method Using healthy donor peripheral blood mononuclear (PBMC) cell surface expression of > 50 candidate markers were tested using flow cytometry and compared against CD28 expression. The prevalence of cells expressing the most suitable candidate was investigated in the collagen induced arthritis (CIA) and the antigen-induced arthritis (AIA) models. Fifty RA patients were recruited from University Hospital of Wales (UHW) rheumatology outpatient clinic. Clinical and serological markers of inflammation were noted, and PBMC were analysed using flow cytometry +/− in vitro stimulation. Results CD3 + CD8 + CD28 − T cells express CD244, CD57, CX3CR1 and KLRG1. The strongest inverse correlate of CD28 expression was KLRG1. CD3 + CD8 + CD28 − KLRG1 + cells were elevated in experimental models of RA. Notably, Il-10-deficiency was linked with exacerbated arthritis and an increase in the number of CD3 + CD8 + CD28 − KLRG1 + cells, suggesting a regulatory role for Il-10 in their development or survival. In RA patients, CD3 + CD8 + CD28 − KLRG1 + cells correlate with ACPA, RF and ESR, and produce more IL-10 than controls. Finally, these cells are higher in early arthritis patients that do not respond to treatment with synthetic DMARDs at six months. Conclusion KLRG1 is a marker for regulatory CD3 + CD8 + CD28 − cells. The presence of CD3 + CD8 + CD28-KLRG1 + cells increases with certain measures of disease, and is indicative of poor treatment response to DMARDs in early arthritis. Key Messages KLRG1 is a marker of CD28 negativity on CD8 T cells CD3 + CD8 + CD28 − KLRG1 + cells are increased in CIA mice and correlate with disease severity. CD3 + CD8 + CD28 − KLRG1 + cells positively correlate with ESR / ACPA and RF in patients. CD3 + CD8 + CD28 − KLRG1 + cells are increased in Il-10-deficient mice with inflammatory arthritis. CD3 + CD8 + CD28 − KLRG1 + cells produce more Il-10 than CD3 + CD8 + CD28 + KLRG1 − cells in RA patients. CD3 + CD8 + CD28 − KLRG1 + cells are higher in patients who do not respond to treatment with synthetic DMARDs after six months.