Confocal microscopic studies revealed that immunoreactivity of CD31 per unit volume in the border area between the ischemic core and the penumbra in the administration of 5 × 105 OGD-PBMCs was more prominent than that found in the sham-operated group, and administration of normoxic PBMCs and 1 × 105 OGD-PBMCs at 28 days after cerebral ischemia (i.e., at 21 days after administration) (all P < 0.001). The gene discussed is PECAM1; the disease is brain ischemia.