Intra-vital fluorescence microscopy for intra-myocardial graft detection following cell transplantation

Introduction: The aim of our study was the development of a potentially clinically applicable approach, which allows for intra-myocardial detection of the transplanted cells without the need for collection of tissue samples. Intra-myocardial transplantation of myocytes and bone marrow derived cells is currently under clinical evaluation as a therapy of heart failure. A major limitation of all clinical studies for myocardial restoration through cell transfer is the inability to track the fate of the transplanted cells. Methods: Fetal canine cardiomyocytes were labelled with the non-toxic fluorescent membrane dye Vybrant (R) CM-DiI and injected into the free wall of the left ventricle of six adult mongrel dogs. For subsequent tracking of the cellular graft, the dogs were re-operated and an intra-vital microscope was mounted above the exposed heart within the thorax. Results: Two months following cell transplantation, the fluorescent graft was visible by intra-vital microscopy using a 10x magnification. Histological studies served as microscopic control and confirmed the presence of DiI-labelled cells at the site of injection. Connexin 43 immunoreactivity was visible at junctional complexes between donor and recipient cells, suggesting morphologic coupling as a result of gap junction formation. Conclusions: Our results demonstrate that in vivo detection of transplanted cells in the heart is feasible. Further technical adjustments will facilitate thoracoscopic and therefore less invasive application of this method.