TIGIT and psoriatic arthritis: This CD4− cluster largely expressed Foxp3, Helios, and TIGIT (Fig. 4I) as well as CD25, CD39, CTLA-4, CD71, HLA-DR, and low CD127 (Fig. 4H), thus mirroring CD8+ Treg-like cells which have been described in inflamed joints of rheumatoid arthritis (RA), psoriatic arthritis (PsA), and spondylarthritis [41, 42].