Therapeutic Window for Intravenous Human Muse Cell Administration in Mouse Spinal Cord Injury

Stage-specific embryonic antigen-3-positive pluripotent-like/macrophage-like multilineage-differentiating stress-enduring (Muse) cells are a distinct subpopulation of mesenchymal stromal cells (MSCs), accounting for 1% to several percent of MSCs. Although stem cell therapy for spinal cord injury (SCI) typically targets the subacute phase to avoid the hostile acute environment, the therapeutic window for Muse cells remains unclear. C57BL/6J mice with severe T9 contusion SCI received a single tail vein injection of human bone marrow-derived (BM) Muse cells, BM-MSCs (both 5 × 10⁴ cells), or vehicle at 2, 8, 14, or 28 days post-injury (DPI) without immunosuppressants. Among the different administration time points, the 2-DPI Muse cell group exhibited significantly higher Basso Mouse Scale scores than the BM-MSC and vehicle groups from 14 days after injection, while no significant differences were observed at the other administration time points. The 2-DPI Muse cell group showed significantly greater homing to the injured spinal cord than the BM-MSC group, with persistent engraftment and neural-lineage marker expression at day 42. Ablation of engrafted Muse cells at day 42 partially reversed locomotor recovery, suggesting that engrafted Muse cells contributed to functional recovery. These findings suggest that intravenous Muse cell therapy exerts timing-dependent therapeutic effects after SCI, with greater efficacy during the early post-injury phase.