Predominantly CD8+ (Supplementary Fig. S7B), clusters 4 and 10 (cluster 10: 0.5% ± 0.24 of SF T cells, 0.0% in HC/JIA PB, Fig. 4G) show a phenotype of PD-1highTIGIThigh (Fig. 4G) suggesting a possible exhausted CD4− T-cell phenotype in SF [38, 39]. Here, CD8A is linked to juvenile idiopathic arthritis.