PECAM1 and Alzheimer disease: In both WT and AD mice, the engraftment of hUCB-MSCs in the brain parenchyma was not detectable, however the localization of MSCs was detected in the vessels of the brain (3 of 3 WT mice, and 3 of 3 AD mice) as confirmed by staining the vessels with CD31, a blood vessel marker, and the cells with the anti-mitochondria antibody (Fig 6A and 6B).