Continuous intravenous infusion of human mesenchymal stromal cell-derived small extracellular vesicles in spinal cord injured rat modulates extracellular matrix and has greater therapeutic efficacy than multiple single injections

Intravenous (IV) administration of human bone marrow mesenchymal stromal/stem cell-derived small extracellular vesicles (hMSC-sEVs) improves motor recovery in spinal cord-injured rats. We previously observed that daily IV injections over three days were theapeuticaly effective, whereas a single injection with an equivalent total dose was not, indicating that a temporally dispersed regimen is crucial for efficacy. DiR-labeled hMSC-sEVs accumulated in M2 macrophages at the injury site, with excess vesicles cleared via the kidneys within 24 h. To determine whether prolonged continuous delivery can enhance therapeutic outcomes, we compared motor recovery in SCI rats receiving hMSC-sEVs via daily IV injections versus continuous infusion of the same quantity of hMSC-sEVs over 3 or 6 days via osmotic pumps. Continuous intra-jugular IV infusion using an osmotic pump over three days accelerated the onset of motor recovery compared to daily injections. Extending the infusion to six days further enhanced recovery despite the same total dose. Molecular analyses revealed that hMSC-sEVs are enriched in microRNAs targeting fibrosis pathways relative to control serum sEVs. In vitro uptake of hMSC-sEVs by M2 macrophages significantly suppressed the expression of genes associated with extracellular matrix production. Furthermore, MSC-sEV-treated animals showed reductions in fibronectin and collagen 1 and 5 proteins at the lesion site, compared to PBS treated rats. These findings suggest that prolonged continuous infusion of hMSC-sEVs results in greater motor function recovery than daily injections of the same amount, potentially by modulating macrophage-mediated extracellular matrix deposition.