 2. Clonogenic assays allowing the numeration of Colony Forming Unit after ex vivo culture of EPC including: - CFU-EC, which are EPC of myeloid subtype also called early EPC will be determined according to the previously described method of Hill et al. The non-adherent fraction of mononuclear cells will be plated on fibronectin coated dishes in Endocult medium. the number of endothelial colonies will be counted after a 48h culture - High Proliferative Potential CFU, which are true angioblasts will be determined by Ingrams method 21. Mononuclear cells are plated on fibronectin-coated plates in EGM-2MV culture medium and late EPC colonies are enumerated after 10-15 days of culture. - three-dimension methyl cellulose assay in which the only added growth factor is VEGF. The CFU-EC are numbered after 14 days as usually performed for haematopoietic stem cells. Effect of hypoxia on the equilibrium between endothelial damage and repair According to Ingram, the normal vascular endothelium contains high proliferating potency EPC 22 suggesting that late EPC may also originate from the vessel wall. In addition, local hypoxia might also mobilize EPC 23. 