Chimeric CNS-targeting-peptide engineered exosomes for experimental autoimmune encephalomyelitis therapy.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) that causes demyelination, neuronal damage and white matter loss, but there is still no known cure. Exosomes are 30-200 nm-sized double-layered membrane vesicles that can easily cross the blood-brain barrier (BBB). Exosomes from umbilical cord mesenchymal stem cells（UMSCs） have been found to treat experimental autoimmune encephalomyelitis (EAE) through the action of anti-inflammatory and immunomodulatory, but its clinical translation has been hampered by their inefficacious accumulation in CNS. Therefore, we developed a TAxI-exos, also known as a TAxI-peptide-chimeric UMSC-exos, for CNS-specific accumulation and curative effect in EAE. We used the EAE model in vivo as well as active T cell and BV-2 cell models in vitro to explore the efficacy and mechanisms. Exosomes from UMSCs with TAxI or DiR labels were given to EAE mice in one dosage (150 g) prior to the peak at day 15. The mice were sacrificed on day 30 so that spinal cords, spleens, and blood could be taken for analysis of demyelination, inflammation, microglia, T-cell subset proportions, and inflammatory cytokine expression. In vitro, PBMCs and splenocytes isolated from healthy C57BL/6 mice were activated and incubated with 0.15 mg/mL of UMSC-exos or TAxI-exos for immune mechanism investigations. Activated BV-2 cells were used to investigate the targeting and controlling polarization ability and mechanism of UMSC-exos and TAxI-exos. As expected, TAxI-exos exhibited significantly greater therapeutic action in EAE mice than UMSC-exos due to their improved targeting-ability. The medication reduced T-cell subset proportions and inflammation, reduced active-microglia proportions and promoted M1 to M2 microglial cell polarization through TNF pathway, upregulated IL-4, IL-10, TGF-β, and IDO-1 expression, and downregulated IL-2, IL-6, IL-17A, IFN-γ, and TNF-α. The CNS-targeting properties of TAxI-exos and their capacity to inhibit degenerative processes in EAE mice have considerable potential therapeutic value for MS and other CNS illnesses.