Intra-arterial transplantation of low-dose stem cells provides functional recovery without adverse effects after stroke.

Cell transplantation therapy for cerebral infarction has emerged as a promising treatment to reduce brain damage and enhance functional recovery. We previously reported that intra-arterial delivery of bone marrow mesenchymal stem cells (MSCs) enables superselective cell administration to the infarct area and results in significant functional recovery after ischemic stroke in a rat model. However, to reduce the risk of embolism caused by the transplanted cells, an optimal cell number should be determined. At 24 h after middle cerebral artery occlusion and reperfusion, we administered human MSCs (low dose: 1 × 10(4) cells; high dose: 1 × 10(6) cells) and then assessed functional recovery, inflammatory responses, cell distribution, and mortality. Rats treated with high- or low-dose MSCs showed behavioral recovery. At day 8 post-stroke, microglial activation was suppressed significantly, and interleukin (IL)-1β and IL-12p70 were reduced in both groups. Although high-dose MSCs were more widely distributed in the cortex and striatum of rats, the degree of intravascular cell aggregation and mortality was significantly higher in the high-dose group. In conclusion, selective intra-arterial transplantation of low-dose MSCs has anti-inflammatory effects and reduces the adverse effects of embolic complication, resulting in sufficient functional recovery of the affected brain.