['Loss of the endothelium and its replacement by a thick thrombus are structural features of human abdominal aortic aneurysms (AAAs). In AAAs, the relationship between aortic diameter expansion, the presence of thrombus, and the lack of endothelial cells (ECs) remains unexplored. We hypothesized that reendothelialization by cell therapy would modulate aortic wall destruction and ultimately stabilize AAAs. We evaluated the impact of local seeding of rat aortic ECs or peripheral blood-derived outgrowth ECs on AAA evolution.', 'Rat aortic ECs (n=30) or serum-free medium (controls; n=29) were seeded endovascularly immediately (day 0) or 14 days after surgery in the rat xenograft model. Rat aortic EC seeding prevented AAA formation and stabilized formed AAAs at 28 days (diameter increase at day 0+28, 51±6% versus 83±6%; day 14+28, -1±4% versus 22±6% in rat aortic ECs and controls, respectively; P<0.01). This stabilizing effect was associated with the reestablishment of the endothelial lining, the suspension of proteolysis, and the reconstitution of new aortic wall rich in smooth muscle cells and extracellular matrix. Transplanted rat aortic ECs did not participate directly in aortic wall repair but exerted their healing properties through paracrine mechanisms involving the upregulation of endothelium-derived stabilizing factors and the recruitment of resident vascular cells. In rats, the transplantation of outgrowth ECs (n=7) significantly reduced by 30% the progression of AAAs and restored the abluminal endothelium at 28 days compared with controls (n=9).'] Does reestablishment of the endothelial lining by endothelial cell therapy stabilize experimental abdominal aortic aneurysms?