Human bone marrow stem cell populations have been applied for cardiac regeneration purposes within different clinical settings in the recent past. The migratory capacity of applied stem cell populations towards injured tissue, after undergoing specific peri-interventional harvesting and isolation procedures, represents a key factor limiting therapeutic efficacy. We therefore aimed at analyzing the migratory capacity of human cluster of differentiation (CD) 133 + bone marrow stem cells in vivo after intraoperative harvesting from the sternal bone marrow. Human CD133 + bone marrow stem cells were isolated from the sternal bone marrow of patients undergoing cardiac surgery at our institution. Migratory capacity towards stromal cell-derived factor-1a (SDF-1a) gradients was tested in vitro and in vivo by intravital fluoresecence microscopy, utilizing the cremaster muscle model in severe combined immunodeficient (SCID) mice and analyzing CD133 + cell interaction with the local endothelium. Furthermore, the role of a local inflammatory stimulus for CD133 + cell interaction with the endothelium was studied. In order to describe endothelial response upon chemokine stimulation laser scanning microscopy of histological cremaster muscle samples was performed. SDF-1a alone was capable to induce relevant early CD133 + cell interaction with the endothelium, indicated by the percentage of rolling CD133 + cells (45.9 ± 1.8% in "SDF-1" vs. 17.7 ± 2.7% in "control," p < 0.001) and the significantly reduced rolling velocity after SDF-1a treatment. Furthermore, SDF-1a induced firm endothelial adhesion of CD133 + cells in vivo. Firm endothelial adhesion, however, was significantly enhanced by additional inflammatory stimulation with tumor necrosis factor-a (TNF-a) (27.9 ± 4.3 cells/mm 2 in "SDF-1 + TNF" vs. 2.2 ± 1.1 cells/mm 2 in "control," p < 0.001). CD133 + bone marrow stem cells exhibit sufficient in vivo homing towards SDF-1a gradients in an inflammatory microenvironment after undergoing standardized intraoperative harvesting and isolation from the sternal bone marrow.

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to nonmarrow tissue have not been completely clarified. We describe here the technique of intravital microscopy applied to the mouse cremaster microcirculation for analysis of peripheral bone marrow stem cell migration in vivo. Intravital microscopy of the M. cremaster has been previously introduced in the field of inflammatory research for direct observation of leucocyte interaction with the vascular endothelium. Since sufficient peripheral stem and progenitor cell migration includes similar initial steps of rolling along and firm adhesion at the endothelial lining it is conceivable to apply the M. cremaster model for the observation and quantification of the interaction of intravasculary administered stem cells with the endothelium. As various chemical components can be selectively applied to the target tissue by simple superfusion techniques, it is possible to establish essential microenvironmental preconditions, for initial stem cell recruitment to take place in a living organism outside the bone marrow.