PRDM1 and myeloid sarcoma: Although we cannot exclude the possibility that other factors may cause fewer circulating TFR cells in MS patients rather than increased splenic TFR cells as observed in mice with a Treg-specific deletion of Blimp1, our study has uncovered Blimp1 as a new regulator that is important for Treg stability during CNS autoimmunity, and has established the in vivo pathological importance of Treg conversion into TH17-like cells.