We identified a cluster of CD4+FOXP3+ Tregs (characterized by high CD4, FOXP3, PDCD1, CTLA4, TIGIT, and IL2RA expression, Figure 2—figure supplement 2A, B) that showed increased frequency in RA patients compared to OA (Figure 2—figure supplement 2C). Here, CTLA4 is linked to rheumatoid arthritis.