Translational potential of GMP-grade human umbilical cord-derived mesenchymal stem cells (UC-MSCs) in traumatic spinal cord injury: a preclinical study in rat

Background Traumatic spinal cord injury (SCI) often results in irreversible motor, sensory, and autonomic dysfunction, with limited effective treatment options currently available. Human umbilical cord-derived mesenchymal stem cells (UC-MSCs) represent a promising therapeutic approach due to their immunomodulatory, neuroprotective, and regenerative properties. However, the lack of comprehensive efficacy data using GMP-grade cells, uncertainty regarding optimal dosing, and incomplete understanding of their mechanisms have hindered clinical translation. Methods A T10-level SCI model was established in 50 Sprague‒Dawley rats using Allen’s weight-drop method. The animals were randomly divided into five groups: Sham, Model, Solvent, Low-dose (1 × 10⁷ cells/kg), and High-dose (3 × 10⁷ cells/kg). GMP-grade human UC-MSCs were administered intravenously on post-injury days 3 and 7. A comprehensive evaluation was performed using BBB scoring for locomotor function, MRI for lesion volume assessment, histopathological examination (H&E and Nissl staining), ELISA for serum cytokine quantification, immunofluorescence for GFAP and GAP-43 expression, single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs), in vivo UC-MSCs tracking, and sRNA sequencing of human UC-MSC-derived exosomes. Results The high-dose UC-MSC treatment demonstrated significant therapeutic effects, including: improved hindlimb motor function (BBB scores from days 7 to 21), reduced spinal cord lesion volume, attenuated pathological damage (decreased cavity formation, preserved neuronal morphology, increased neuron density), and suppressed acute inflammation (reduced TNF-α and IL-6 levels). Additionally, high-dose treatment decreased astrocyte activation (reduced GFAP expression), enhanced neuronal plasticity (increased GAP-43), modulated immune cell populations (increased naïve CD4⁺/CD8⁺ T cells, decreased memory B cells), and downregulated SCI-activated genes (including Kras and Nfkb1). In vivo tracking revealed initial pulmonary accumulation of UC-MSCs followed by clearance within 3 days. sRNA sequencing of human UC-MSC-derived exosomes identified several human-derived miRNAs (hsa-miR-21-5p, hsa-let-7a-5p, hsa-miR-10b-5p, hsa-miR-451a, and hsa-miR-10a-5p) potentially involved in the repair process. Conclusions GMP-grade human UC-MSCs exert therapeutic effects in SCI through multiple mechanisms, including anti-inflammatory actions, inhibition of glial scarring, neuroprotection, and immune modulation. The high-dose regimen (3 × 10⁷ cells/kg) demonstrated superior efficacy across functional, structural, and molecular endpoints. This study provides critical preclinical evidence supporting the clinical application of UC-MSCs for SCI treatment and elucidates their underlying therapeutic mechanisms.