 The cytokine SDF-1 is released in response to hypoxia, is crucial for progenitor cell homing and recruitment of cells for neovascularisation. Invasion capacity is closely related to the cytokine SDF-1 and the SDF-1 receptor CXCR4 Ceradini et al. 2004. The in vivo neovascularisation capacity of progenitor cells is closely correlated to their functional capacity as SDF-1 induced invasion or colony-forming capacity Heeschen et al. 2004; Britten et al. 2003; Assmus et al. 2007. 