261. Directed Evolution of an Antibody-Evading Cardiac Tropic AAV Vector

Gene delivery vectors based on natural serotypes of adeno-associated viruses (AAV) have demonstrated promise in both preclinical models and human clinical trials for several disease targets, including advanced heart failure. However, delivery challenges, including low to no transduction with natural AAV serotypes in the presence of neutralizing antibodies and lack of specific and/or efficient distribution to many potential target tissues, remain obstacles to AAV gene therapy reaching its full potential. Directed evolution has proven to be a powerful approach to generate AAV vectors with novel capabilities, and previous work has shown that AAV can evolve to significantly overcome neutralization by anti-AAV antibodies, both in vitro and in vivo. AAV vectors with enhanced evasion in the presence of anti-AAV antibodies were evaluated for specificity to various tissues. A shuffled AAV variant (Sh100-7) composed of AAV1, 6, and 8 with additional point mutations was found to efficiently and preferentially transduce cardiac tissue. Variant Sh100-7 is capable of enhanced transduction of and specificity for the murine heart in both naive and human IVIG (intravenous immunoglobulin) passively immunized mice following intravenous administration. In naive mice, administration of variant Sh100-7 leads to significantly higher gene expression in the heart (over 7-fold higher compared to AAV2). Sh100-7 preferentially transduces the heart compared to all other tissues (including skeletal muscle), and the heart:liver gene expression ratio for Sh100-7 of 60:1 is over 33-fold higher than AAV2 and 6-fold higher than a previously published myocardium-tropic vector. In a human IVIG-passively immunized mouse model, Sh100-7-mediated gene expression in the heart is only decreased 4-fold, while AAV2-mediated gene expression in the heart is decreased 123-fold. In the presence of antibodies, the heart:liver gene expression ratio for Sh100-7 (14:1) remains over 23-fold higher than AAV2. In vivo tropism of Sh100-7 in a large animal model is currently under evaluation. The ability to specifically transduce cardiac cells through intravenous delivery could enable simpler administration of gene therapy products for heart disease and the use of lower doses (which could reduce vector immune responses). Furthermore, the increased resistance to circulating anti-AAV antibodies may enable the use of Sh100-7 in the future treatment of patients with high antibody titers that are currently ineligible for AAV gene therapy.