Graphical abstract. AA patients with higher number of Treg B cells before IST are more likely to respond to therapy. Following response to IST, responder patients have a higher number of Treg B cells compared with nonresponders. Treg B cells are enriched with cell-cycle–related proteins and are more likely to enter the cell cycle compared with Treg A subpopulations. In vitro expanded Tregs are also phenotypically closer to Treg B than Treg A. T_conv, conventional CD4⁺ T cells.