Discovery of a novel lineage of regulatory T (Treg) cells, which are CD4+FoxA1+, as major regulators of responsiveness to IFN-β therapy in patients with relapsing-remitting multiple sclerosis (RRMS), is important for further optimization of this first in class disease-modifying therapy (DMT). The gene discussed is FOXA1; the disease is relapsing-remitting multiple sclerosis.