Microparticle-delivered stimulator of interferon genes (STING) agonist suppresses experimental autoimmune encephalomyelitis (EAE) via expansion of FoxP3 +CD4 +Tregs

Abstract

Abstract Background: The cGAS-cyclic GMP-AMP (cGAMP)-stimulator of intracellular STING receptors induces a powerful IFN-I response. Microparticles (MPs), synthesized biodegradable polymer, passively target the APCs, resulting in intracellular delivery of immuno-regulatory treatment with dose sparing and better tolerability. cGAMP MP treatment of EAE induced both IFN-I-dependent and -independent immunosuppressive responses through induction of IL-27 and IL-10. Results: We show that cGAMP MP treatment reduced clinical disease scores of EAE after 3 doses. By flow cytometry, cGAMP MPs decreased absolute number of mononuclear cells in the CNS infiltrates, and the percentages of CD3 −CD45 highCD11 +b Ly6C +monocytes, CD11c +and CD11c +CD11b +DCs, as well as their expression of CD80 and CD86, suggestive of tolerogenic phenotype. Moreover, we detected an increased percentage of FOXP3 +CD4 +Tregs in CNS infiltrates, with increased expression of IL-10, IL-27R, and Granzyme B, and decreased percentage of IL-17A +CD4 +cells in cGAMP MP-treated mice. Furthermore, the supernatants of the in vitroco-cultured cGAMP MP-treated monocytes with CD3 +CD4 +, isolated from EAE spleenocytes, show increased IL-10 and IL-27 levels. Additionally, the in vitroD3 +CD4 +cells show increased FOXP3 +expression with higher CTLA-4, and GITR in cGAMP treated group. Moreover, FOXP3cre+/+ IL-27RA fl/fl mice showed more aggressive disease compared to wild-type mice in attempt to test whether IL-27 induced effect of cGAMP MPs is mediated via Tregs. Conclusion: cGAMP MPs suppress RREAE through induction of tolerogenic APCs and increase secretion of IL-10 and IL-27, which induce Treg expansion indicating its potential use as a tolerogenic therapy in patients with RRMS.