Intra-vital fluorescence microscopy for intra-myocardial graft detection following cell transplantation Arjang Ruhparwar, Theo Kofidis, Nicole Ruebesamen, Matthias Karck, Axel Haverich & Ulrich Martin The Department of Thoracic- and Cardiovascular Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany Received 23 September 2004; accepted in revised form 14 January 2005 Key words: cell transplantation, heart failure, imaging, intra-vital microscopy Abstract 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 myo- cardial 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 Ò 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 10· 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 demon- strate 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. Introduction Bio-imaging of transplanted cells in the myocar- dium with respect to survival and integration at the site of injection is of utmost importance for the evaluation of success of cell transplantation. Usually, cell labelling with reporter genes such as b-galactosidase [1] or enhanced green fluorescent protein (eGFP) [2] is used to follow the fate of the transplanted cells. Alternatively, certain fluores- cent dyes such as lipophilic carbocyanine tracers (e.g. CM-DiI) or carboxyfluorescein diacetate succinimidyl ester (CFDA SE) were used to dis- tinguish between donor and recipient cells. In our own group we used the presence of Dystrophin as a parameter for the distinction between recipient and donor cardiomyocytes in a canine model [3]. All labelling approaches mentioned above allow for the discrimination of donor and recipient cells on post-mortem histological sections. Recent progress in cell transplantation and stem cell research led to an increasing number of clinical trials which involve cell-transplantation-based treatment of heart failure [4–6]. The International Journal of Cardiovascular Imaging (2005) 21: 569–574 DOI 10.1007/s10554-005-0654-z Ó Springer 2005