As a prerequisite for clinical application, we determined the long-term 
therapeutic effectiveness and safety of adeno-associated virus (AAV)-S100A1 gene 
therapy in a preclinical large animal model of heart failure. S100A1, a positive 
inotropic regulator of myocardial contractility, becomes depleted in failing 
cardiomyocytes in humans and animals, and myocardial-targeted S100A1 gene 
transfer rescues cardiac contractile function by restoring sarcoplasmic 
reticulum calcium (Ca(2+)) handling in acutely and chronically failing hearts in 
small animal models. We induced heart failure in domestic pigs by balloon 
occlusion of the left circumflex coronary artery, resulting in myocardial 
infarction. After 2 weeks, when the pigs displayed significant left ventricular 
contractile dysfunction, we administered, by retrograde coronary venous 
delivery, AAV serotype 9 (AAV9)-S100A1 to the left ventricular, non-infarcted 
myocardium. AAV9-luciferase and saline treatment served as control. At 14 weeks, 
both control groups showed significantly decreased myocardial S100A1 protein 
expression along with progressive deterioration of cardiac performance and left 
ventricular remodeling. AAV9-S100A1 treatment prevented and reversed these 
functional and structural changes by restoring cardiac S100A1 protein levels. 
S100A1 treatment normalized cardiomyocyte Ca(2+) cycling, sarcoplasmic reticulum 
calcium handling, and energy homeostasis. Transgene expression was restricted to 
cardiac tissue, and extracardiac organ function was uncompromised. This 
translational study shows the preclinical feasibility of long-term therapeutic 
effectiveness of and a favorable safety profile for cardiac AAV9-S100A1 gene 
therapy in a preclinical model of heart failure. Our results present a strong 
rationale for a clinical trial of S100A1 gene therapy for human heart failure 
that could potentially complement current strategies to treat end-stage heart 
failure.