ResearchPod Summary
Gene therapy using adeno-associated viruses (AAVs) is a promising strategy for treating heart failure. However, pre-existing neutralizing antibodies (NAbs) in patients often bind to AAV vectors, significantly reducing their therapeutic efficacy. This study investigates the potential of extracellular vesicle-encapsulated AAVs (EV-AAVs) to overcome this immunological barrier, characterize their delivery mechanism, and evaluate their functional impact in pre-immunized models of myocardial infarction.
The researchers developed a two-step iodixanol density-gradient ultracentrifugation method to purify highly concentrated EV-AAVs from HEK293T cell cultures, ensuring minimal contamination from free AAV capsids. They performed comprehensive biochemical characterization—including transmission electron microscopy, RNA sequencing, and protein profiling—to validate that the isolated particles were genuine AAV-carrying extracellular vesicles. To test efficacy, they conducted in vitro experiments using human cardiomyocytes and in vivo experiments in pre-immunized mouse models, comparing the performance of EV-AAVs against free AAVs in the presence of NAbs.
EV-AAVs demonstrated significantly higher resistance to NAb-mediated neutralization compared to free AAVs, retaining high transduction efficiency even in the presence of high antibody titers. In a mouse model of myocardial infarction, intramyocardial delivery of EV-AAV9-SERCA2a successfully improved cardiac function, ejection fraction, and fractional shortening in pre-immunized mice, whereas standard AAV9-SERCA2a showed significantly reduced efficacy. Furthermore, mechanistic studies revealed that EV-AAVs are internalized into acidic endosomal and lysosomal compartments, where the vesicular membrane facilitates the release of AAVs, supporting their subsequent nuclear translocation. The study also noted that EV-AAVs exhibit cardiotropic expression, with higher transgene expression in cardiomyocytes compared to non-myocytes.
The clinical utility of AAV-based gene therapy is currently constrained by high NAb prevalence, which excludes many patients and prevents redosing. This research demonstrates that encapsulating AAVs within extracellular vesicles provides a robust protective shield against these antibodies. By revealing the intracellular trafficking pathway of EV-AAVs, the study provides a foundational rationale for developing next-generation vectors that can extend gene therapy access to NAb-positive patients and allow for repeat therapeutic administration.
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