Targeting Impaired Type I Interferon-IL-27 Signaling Rescues T Regulatory Cell Suppressive Function in Relapsing-Remitting Multiple Sclerosis.

T Regulatory T cells (Tregs) from patients with relapsing-remitting multiple sclerosis (RRMS) exhibit impaired suppressive function, yet the underlying molecular mechanisms remain elusive. Single-cell RNA sequencing (scRNAseq) of ex vivo-sorted Tregs from RRMS patients and matched healthy controls (HCs) revealed down-regulation of type I IFN (IFN) and IL-27 signaling pathways in RRMS Tregs. These Tregs showed reduced expression of IFN-stimulated genes (ISGs) (ISG15, MX1, IFITM1, IFI44L, OAS1), as well as key mediators of Treg suppressive function (LGALS3, CD81, FCRL3, CD7, CSTB), all suggesting a key role of decreased IFN signaling in RRMS Treg dysfunction. To therapeutically target IFN signaling pathways and improve Treg suppressive functions, we used cGAMP-loaded microparticles (MPs) to activate the stimulator of IFN genes (STING) in experimental autoimmune encephalomyelitis (EAE). cGAMP-MP treatment ameliorated EAE via induction of Tregs expressing IL-27R, IL-10, TGF-b, and Granzyme B. This effect was abolished in Treg-specific IL-27R (TregΔIl27ra) knockout mice, confirming that IL-27 signaling is essential for Treg suppression. In vitro IL-27 stimulation of RRMS-derived Tregs restored expression of IFN pathway genes (IRF1, IFNGR, IFI16) and Treg suppressive genes (ICOS, IKZF3, IL7R, TIGIT). Thus, we propose that IL-27 pre-stimulation may restore their suppressive function and migration (via CCR6, CCR7, S100A11 and S1PR4) to the central nervous system (CNS) in future clinical trials.