Phase-dependent efficacy of intravenous amniotic mesenchymal stem cells in a rat spinal cord injury model

• Intravenous amniotic MSC administration on day 1 post-injury yields the greatest functional recovery, followed by day 7, while day 3 provides minimal benefit. • Day-1 treatment reduces neutrophil infiltration during its peak, and day-7 treatment reduces macrophage infiltration during its peak, but day-3 treatment fails to attenuate either. • Day-3 administration paradoxically increases systemic inflammation and activates complement and coagulation pathways, correlating with worse outcomes. • Therapeutic efficacy of MSC is phase-dependent, supporting a strategy that matches treatment timing to the dominant inflammatory cell population.