Date: 18 Nov 2009

Serial in vivo imaging of the porcine heart after percutaneous, intramyocardially injected 111In-labeled human mesenchymal stromal cells

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This pilot trial aimed to investigate the utilization of 111In-labeling of mesenchymal stromal cells (MSC) for in vivo tracking after intramyocardial transplantation in a xenotransplantation model with gender mismatched cells. Human male MSC were expanded ex vivo and labeled with 111In-tropolone. Ten female pigs were included. The labeled cells were transplanted intramyocardially using a percutaneous injection system. The 111In activity was determined using gamma camera imaging. Excised hearts were analyzed by fluorescence in situ hybridization (FISH) and microscopy. Gamma camera imaging revealed focal cardiac 111In accumulations up to 6 days after injection (N = 4). No MSC could be identified with FISH, and microscopy identified widespread acute inflammation. Focal 111In accumulation, inflammation but no human MSC were similarly seen in pigs (N = 2) after immunosuppression. A comparable retention of 111In activity was observed after intramyocardial injection of 111In-tropolone (without cells) (N = 2), but without sign of myocardial inflammation. Injection of labeled non-viable cells (N = 1) also led to high focal 111In activity up to 6 days after intramyocardial injection. As a positive control of the FISH method, we identified labeled cells both in culture and immediately after cell injection in one pig. This pilot trial suggests that after intramyocardial injection 111In stays in the myocardium despite possible disappearance of labeled cells. This questions the clinical use of 111In-labeled cells for tracking. The results further suggest that xenografting of human MSC into porcine hearts leads to inflammation contradicting previous studies implying a special immunoprivileged status for MSC.

Stig Lyngbaek and Rasmus S. Ripa contributed equally to this work.