Human Mesenchymal Stromal Cell-Derived Extracellular Vesicles Modify Microglial Response and Improve Clinical Outcomes in Experimental Spinal Cord Injury

No current clinical intervention can alter the course of acute spinal cord injury (SCI), or appreciably improve neurological outcome. Mesenchymal stromal cells (MSCs) have been shown to modulate the injury sequelae of SCI largely via paracrine effects, although the mechanisms remain incompletely understood. One potential modality is through secretion of extracellular vesicles (EVs). In this study, we investigate whether systemic administration of EVs isolated from human MSCs (MSCEv) has the potential to be efficacious as an alternative to cell-based therapy for SCI. Additionally, we investigate whether EVs isolated from human MSCs stimulated with pro-inflammatory cytokines have enhanced anti-inflammatory effects when administered after SCI. Immunohistochemistry supported the quantitative analysis, demonstrating a diminished inflammatory response with apparent astrocyte and microglia disorganization in cord tissue up to 10 mm caudal to the injury site. Locomotor recovery scores showed significant improvement among animals treated with MSCEv. Significant increases in mechanical sensitivity threshold were observed in animals treated with EVs from either naive MSC (MSCEv(wt)) or stimulated MSC (MSCEv(+)), with a statistically significant increase in threshold for MSCEv(+)-treated animals when compared to those that received MSCEv(wt). In conclusion, these data show that treatment of acute SCI with extracellular vesicles derived from human MSCs attenuates neuroinflammation and improves functional recovery.