In Vivo Optical Bioluminescence Imaging of Collagen-supported Cardiac Cell Grafts

Background: Histology-based survival assessment of cell grafts does not allow for in vivo follow-up. In this study we introduce two new experimental models for longitudinal in vivo survival studies of cardiac cell grafts using optical bioluminescence imaging. Methods: H9c2 cardiomyoblasts expressing both firefly luciferase (fluc) and green fluorescent protein (GFP) reporter genes were implanted into Lewis rats. In Model 1, H9c2-fluc-IRES-GFP cells (0.5 × 10⁶) were implanted into a cryoinjured abdominal wall muscle. Cells were injected using either liquid collagen (Matrigel [MG]) or phosphate-buffered saline (PBS) suspension. Cell survival was evaluated in vivo using bioluminescence imaging on days 1, 5 and 10 post-operatively. In model 2, rats underwent ligation of the left anterior descending (LAD) artery. The donor hearts were harvested, and the infarcted region was restored ex situ using 1 × 10⁶ H9c2-fluc-IRES-GFP cells seeded in collagen matrix (Gelfoam [GF]) or suspended in PBS (n = 8/group). Hearts were then transplanted into the abdomen of syngeneic recipients. Optical bioluminescence imaging was performed on Days 1, 5, 8 and 14 post-operatively. After 4 weeks, immunohistologic studies were performed. Results: For model 1, at day 5, bioluminescence signals were markedly higher for the H9c2/MG group (449 ± 129 photons/second × 10³) compared with the H9c2/PBS group (137 ± 82 photons/second × 10³) (p < 0.05). For model 2, bioluminescence signals were significantly (p < 0.04) higher in the H9c2/GF group compared with plain cell injection on days 5 (534 ± 115 vs 219 ± 34) and 8 (274 ± 34 vs 180 ± 23). Data were in accordance with GFP immunohistology. Conclusions: Optical bioluminescence is a powerful method for assessment of cardiac cell graft survival in vivo. Collagen matrices support early survival of cardiomyoblasts after transplantation into injured musculature.