Effect of Adipose-derived Stem Cell Exosomes in Alleviating Experimental Autoimmune Encephalomyelitis by Reducing the Th17-related Immune Response in the Central Nervous System.

BACKGROUND: Multiple Sclerosis (MS) is an immune-mediated neuroinflammatory disease of the central nervous system. Its progression is driven by persistent inflammation and demyelination, which are largely exacerbated by an imbalance between pathogenic Th17 lymphocytes and immunosuppressive regulatory T cells (Tregs). Exosomes derived from Adipose-Derived Stem Cells (ADSC-EXOs) have emerged as promising therapeutic agents because of their robust immunomodulatory properties and ability to cross the Blood-Brain Barrier (BBB). However, their capacity to modulate Th17/Treg dynamics within the CNS and to exert sustained immunoregulatory effects has not been fully elucidated. This study investigated the efficacy of ADSC-EXOs in ameliorating Experimental Autoimmune Encephalomyelitis (EAE), and examined the underlying mechanisms governing their influence on the Th17/Treg balance. METHODS: EAE was induced in C57BL/6 mice through immunization using the MOG₃₅-₅₅ peptide antigen, followed by four intravenous administrations of ADSC-EXOs at 3-day intervals. Exosome identity and purity were confirmed using nanoparticle tracking analysis, transmission electron microscopy, and western blotting for exosomal markers. Clinical scores and body weights were monitored for 42 days. CNS histopathology, microglial activation, and the distribution of Th17 (IL-17A⁺/CD4⁺) and Treg (Foxp3⁺/CD4⁺) cells were evaluated using immunostaining, flow cytometry, and qRT-PCR. RESULTS: ADSC-EXO-treated mice exhibited significantly reduced clinical scores compared to untreated EAE mice (CS: 2.3 vs. 3.0 at day 42), along with decreased demyelination and suppressed microglial activation. Immunofluorescence revealed a marked reduction in Th17 cells in both the brain (82.0 vs. 14.7 cells/mm²) and spinal cord (68.0 vs. 36.1 cells/mm²) ADSC-EXO-treated mice compared to untreated EAE controls. This was accompanied by a reciprocal increase in Treg cells in the treated cohort (brain: 42.6 vs. 14.6 cells/mm²; spinal cord: 40.0 vs. 14.3 cells/mm²). The upregulation of anti-inflammatory markers (Foxp3, CTLA-4, and TGF-β) further confirmed restoration of the Th17/Treg balance. DISCUSSION: ADSC-EXOs ameliorated EAE pathology by selectively modulating CNS immune responses. Rather than broadly suppressing inflammation, ADSC-EXO treatment reshaped the immune microenvironment by restoring the dynamic balance between pathogenic Th17 cells and regulatory T cells. Notably, ADSC-EXOs suppressed microglial activation without overt effects on astrocytes, suggesting a targeted immunomodulatory mechanism within the inflamed CNS. Furthermore, the persistence of immune cell rebalancing beyond the period of exosome retention suggests a prolonged immunoregulatory effect. This may reflect a stable immunoregulatory state maintaining Treg function independently of continued exosome presence, although the precise mechanisms remain unclear. CONCLUSION: ADSC-EXOs exert therapeutic effects in EAE by attenuating Th17 differentiation, suppressing inflammatory cytokine expression, and promoting Treg-mediated immunoregulation. These findings position ADSC-EXOs as a promising cell-free therapeutic strategy for MS and other autoimmune neuroinflammatory disorders.