Abstract 2882: Directed Evolution of Cardiac Specific Adeno-Associated Vector Variants
Adeno-associated vectors (AAV) have gained popularity in cardiovascular gene transfer because of their distinct characteristics: long-term expression, minimal immune response and strong tropism to cardiac tissue for specific serotypes (such as AAV9). However AAVs have certain limitations: Neutralizing antibodies in 40% of humans for each AAV serotype and non-specificity of the AAV serotypes to various organs. Chimeric viruses composed of capsid proteins of different serotypes, show distinct transduction profiles. To identify hybrid viruses that can selectively transduce cardiomyocytes in vivo, we generated a library of diverse AAV variants, obtained by DNA shuffling, with an enrichment of cardiotropic AAV variants, called biological nanoparticles (BNPs). We selected five BNPs from these experiments: BNP 108, 109, 111, 689, and 693. We then injected these different BNPs using GFP as a marker gene under the control of CMV along with AAV9 into rats (3 in each group and each time point) through their tail vein at a concentration of 1011 vg (viral genomes). We sacrificed the animals at one and four weeks and examined expression in the heart, liver, lung, kidneys, and aorta. We found that at 1 week, BNP 108 and 109 had the best expression in the heart (61±12% of the myocytes with green fluorescence) while BNP 111 and AAV9 had strong cardiac expression at 4 weeks (93±11% and 79±12% of the myocytes with green fluorescence). None of the BNPs showed expression in the liver, lung, kidneys, and aorta, while AAV9 demonstrated widespread expression in all these tissues. Transcoronary injection of BNP111 at a concentration of 1012 vg demonstrated the efficiency of BNP in transducing myocardium of large animals. We also found that all the BNPs are resistant to preexisting neutralizing antibodies against parent serotypes. These results show that directed evolution of AAV variants can yield BNPs that are highly cardiotropic and highly efficient of transducing cardiac tissue without infecting other organs and having resistance to preexisting neutralizing antibodies against parent serotypes. These BNPs may become very useful for clinical applications.