eLife assessment
In this study, the authors performed mass cytometry (CyTOF) analysis and T cell receptor (TCR) sequencing to study immune cell composition and expansion of joint-derived Tregs and non-Tregs in Juvenile Idiopathic Arthritis (JIA). They studied different joints affected at the same time and found that the composition and functional characteristics of immune infiltrates are strikingly similar between joints within one patient. The research design of this study is appropriate and the methods used in this study are adequately described in the manuscript. The study may be potentially beneficial for the JIA treatment.