Cardiospecific expression of AAV vectors

Adenoviral vectors have been set for cardiomyocyte gene therapy with considerable transfection rates. However, due to adenoviral immunogenicity, adenoviral transfected cells are frequently subject to specific cellular immune reactions leading to loss of cells and transgene expression. Non‐pathogenic adeno associated vectors lacking immunogenicity have been utilized alternately. Tropism of the most common AAV serotype 2, favoring liver of muscle transfection, has been altered by use of serotypes 1, 6 and 9. We used a model of chronic (4 weeks) regional myocardial transfection of the pig to investigate transfection efficacy of AAV vectors, which were applied to the target region by retroinfusion. Cardiac restriction was ensured by utilization of an MLC‐2v promoter‐CMV‐enhancer construct, fused to a luciferase reporter gene, the activity of which was analyzed. Compared to the wildtype (WT) AAV 2 vector, which barely exceeded background luciferase activity, a vector lacking the heparin binding site of the envelope (AAV2 ΔHep) improved expression only slightly. Substantial increase to 40 000 RLU/mg tissue) was achieved by the addition of VEGF‐A, which enhances vascular permeability. A further 15‐fold increase of luciferase activity was achieved by applying an equal amount of AAV6 virus particles to a pig heart, with a further 5–10 fold increase achieved by utilization of AAV serotype 9. Functionally relevant gene transfer was ensured by applying AAV9 hVEGF/PDGF (0.2/0.4 × 10¹³ virus particles, respectively). 4 weeks after retroinfusion into pig hearts suffering from chronic total LAD‐occlusion (induced by a reduction stent), we found a significant increase of blood flow and regional myocardial function. We conclude that AAV9 is a more efficient AAV vector when compared to WT‐ or ΔHep‐AAV2 or AAV6. Functionally relevant gene expression, as performed by VEGF‐A/PDGF transfection, opens the door for utilization of this vector system for xenotransplant organ priming.