Global cardiac-specific transgene expression using cardiopulmonary bypass with cardiac isolation

Background. The available techniques for intravascular gene delivery to the heart are inefficient and not organ-specific. Yet, effective treatment of heart failure will likely require transgene expression by the majority of cardiac myocytes. To address this problem, we developed a novel cannulation technique that achieves efficient isolation of the heart in situ using separate cardiopulmonary bypass (CPB) circuits for the heart and body in dogs. Methods. The arterial inflow and venous effluent from the two circuits were physically isolated. The efficiency of separation was 98% to 99% in three preliminary experiments using Evans Blue dye-labeled albumin. In 6 dogs, the cardiac circuit was perfused with oxygenated crystalloid cardioplegia at 37°C containing 4 × 1011 particles of an adenovirus encoding LacZ (AdCMVLacZ) with a perfusion pressure of 170 to 200 mm Hg for 15 minutes allowing virus to recirculate through the heart 15 times. Cross-clamp time was 26 ± 2 minutes and CPB time was 90 ± 3 minutes. Results. Five animals survived and were euthanized at 7 days. β-Galactosidase activities measured using a chemiluminescent assay were three orders of magnitude higher in all areas of the heart than in the liver. Histological analyses revealed heterogeneous X-Gal staining of myocytes in all areas of the myocardium. Conclusions. Despite using a constitutive promoter, this technique yields relatively cardiac-specific transgene expression and is potentially translatable to clinical applications. Future studies will allow for further optimization of the conditions necessary for vector-mediated gene delivery to the heart.