Extracellular Vesicle-Encapsulated Adeno-Associated Viruses for Therapeutic Gene Delivery to the Heart

BACKGROUND

Adeno-associated virus (AAV) has emerged as one of the best tools for cardiac gene delivery due to its cardiotropism, long-term expression, and safety. However, a significant challenge to its successful clinical use is preexisting neutralizing antibodies (NAbs), which bind to free AAVs, prevent efficient gene transduction, and reduce or negate therapeutic effects. Here we describe extracellular vesicle-encapsulated AAVs (EV-AAVs), secreted naturally by AAV-producing cells, as a superior cardiac gene delivery vector that delivers more genes and offers higher NAb resistance.

METHODS

We developed a 2-step density-gradient ultracentrifugation method to isolate highly purified EV-AAVs. We compared the gene delivery and therapeutic efficacy of EV-AAVs with an equal titer of free AAVs in the presence of NAbs, both in vitro and in vivo. In addition, we investigated the mechanism of EV-AAV uptake in human left ventricular and human induced pluripotent stem cell-derived cardiomyocytes in vitro and mouse models in vivo using a combination of biochemical techniques, flow cytometry, and immunofluorescence imaging.

RESULTS

Using cardiotropic AAV serotypes 6 and 9 and several reporter constructs, we demonstrated that EV-AAVs deliver significantly higher quantities of genes than AAVs in the presence of NAbs, both to human left ventricular and human induced pluripotent stem cell-derived cardiomyocytes in vitro and to mouse hearts in vivo. Intramyocardial delivery of EV-AAV9-sarcoplasmic reticulum calcium ATPase 2a to infarcted hearts in preimmunized mice significantly improved ejection fraction and fractional shortening compared with AAV9-sarcoplasmic reticulum calcium ATPase 2a delivery. These data validated NAb evasion by and therapeutic efficacy of EV-AAV9 vectors. Trafficking studies using human induced pluripotent stem cell-derived cells in vitro and mouse hearts in vivo showed significantly higher expression of EV-AAV6/9-delivered genes in cardiomyocytes compared with noncardiomyocytes, even with comparable cellular uptake. Using cellular subfraction analyses and pH-sensitive dyes, we discovered that EV-AAVs were internalized into acidic endosomal compartments of cardiomyocytes for releasing and acidifying AAVs for their nuclear uptake.

CONCLUSIONS

Together, using 5 different in vitro and in vivo model systems, we demonstrate significantly higher potency and therapeutic efficacy of EV-AAV vectors compared with free AAVs in the presence of NAbs. These results establish the potential of EV-AAV vectors as a gene delivery tool to treat heart failure.

Gene editing reverses arrhythmia susceptibility in humanized PLN-R14del mice: modelling a European cardiomyopathy with global impact

AIMS

A mutation in the phospholamban (PLN) gene, leading to deletion of Arg14 (R14del), has been associated with malignant arrhythmias and ventricular dilation. Identifying pre-symptomatic carriers with vulnerable myocardium is crucial because arrhythmia can result in sudden cardiac death, especially in young adults with PLN-R14del mutation. This study aimed at assessing the efficiency and efficacy of in vivo genome editing, using CRISPR/Cas9 and a cardiotropic adeno-associated virus-9 (AAV9), in improving cardiac function in young adult mice expressing the human PLN-R14del.

METHODS AND RESULTS

Humanized mice were generated expressing human wild-type (hPLN-WT) or mutant (hPLN-R14del) PLN in the heterozygous state, mimicking human carriers. Cardiac magnetic resonance imaging at 12 weeks of age showed bi-ventricular dilation and increased stroke volume in mutant vs. WT mice, with no deficit in ejection fraction or cardiac output. Challenge of ex vivo hearts with isoproterenol and rapid pacing unmasked higher propensity for sustained ventricular tachycardia (VT) in hPLN-R14del relative to hPLN-WT. Specifically, the VT threshold was significantly reduced (20.3 ± 1.2 Hz in hPLN-R14del vs. 25.7 ± 1.3 Hz in WT, P < 0.01) reflecting higher arrhythmia burden. To inactivate the R14del allele, mice were tail-vein-injected with AAV9.CRISPR/Cas9/gRNA or AAV9 empty capsid (controls). CRISPR-Cas9 efficiency was evaluated by droplet digital polymerase chain reaction and NGS-based amplicon sequencing. In vivo gene editing significantly reduced end-diastolic and stroke volumes in hPLN-R14del CRISPR-treated mice compared to controls. Susceptibility to VT was also reduced, as the VT threshold was significantly increased relative to controls (30.9 ± 2.3 Hz vs. 21.3 ± 1.5 Hz; P < 0.01).

CONCLUSIONS

This study is the first to show that disruption of hPLN-R14del allele by AAV9-CRISPR/Cas9 improves cardiac function and reduces VT susceptibility in humanized PLN-R14del mice, offering preclinical evidence for translatable approaches to therapeutically suppress the arrhythmogenic phenotype in human patients with PLN-R14del disease.

Arrhythmia Mechanism and Dynamics in a Humanized Mouse Model of Inherited Cardiomyopathy Caused by Phospholamban R14del Mutation

BACKGROUND

Arginine (Arg) 14 deletion (R14del) in the calcium regulatory protein phospholamban (hPLN^R14del) has been identified as a disease-causing mutation in patients with an inherited cardiomyopathy. Mechanisms underlying the early arrhythmogenic phenotype that predisposes carriers of this mutation to sudden death with no apparent structural remodeling remain unclear.

METHODS

To address this, we performed high spatiotemporal resolution optical mapping of intact hearts from adult knock-in mice harboring the human PLN^WT (wildtype [WT], n=12) or the heterozygous human PLN^R14del mutation (R14del, n=12) before and after ex vivo challenge with isoproterenol and rapid pacing.

RESULTS

Adverse electrophysiological remodeling was evident in the absence of significant structural or hemodynamic changes. R14del hearts exhibited increased arrhythmia susceptibility compared with wildtype. Underlying this susceptibility was preferential right ventricular action potential prolongation that was unresponsive to β-adrenergic stimulation. A steep repolarization gradient at the left ventricular/right ventricular interface provided the substrate for interventricular activation delays and ultimately local conduction block during rapid pacing. This was followed by the initiation of macroreentrant circuits supporting the onset of ventricular tachycardia. Once sustained, these circuits evolved into high-frequency rotors, which in their majority were pinned to the right ventricle. These rotors exhibited unique spatiotemporal dynamics that promoted their increased stability in R14del compared with wildtype hearts.

CONCLUSIONS

Our findings highlight the crucial role of primary electric remodeling caused by the hPLN^R14del mutation. These inherently arrhythmogenic features form the substrate for adrenergic-mediated VT at early stages of PLN^R14del induced cardiomyopathy.

Abstract 170: Exosomal AAV-mediated SERCA2a Gene Transfer Improves Cardiac Function in a Mouse Model of Heart Failure

Adeno-associated viruses (AAVs) are promising therapeutic tools for gene delivery to the heart. However, pre-existing antibodies (NAbs) to many cardiotropic AAV serotypes naturally present in humans pose a critical challenge for the translation of gene therapies to clinical applications. Here, we describe the use of exosomal AAVs (eAAV) as a robust heart gene delivery system that improves transduction efficiency while protecting from pre-existing immunity to the viral capsid. To obtain eAAV specimens from conditioned medium from AAV-producing HEK-293T cells, we have developed a state-of-the-art multi-step ultracentrifugation strategy. We demonstrated through electron microscopy-based visualization, size distribution measurements and distribution of AAV genomes in post-centrifugation iodixanol gradients, that our purification process enables isolation of eAAVs with high purity and minimal contamination with standard AAVs. Efficiency of heart targeting was then evaluated for eAAV9 or eAAV6 and standard AAV9 or AAV6 in human cardiomyocytes (hCMs) in vitro and in passive immunity nude mouse model in vivo . Regardless of the presence or absence of NAbs, we demonstrated that eAAVs are more efficient in transduction of cells in the same titer ranges as standard AAVs. To test the therapeutic efficacy, eAAV9-SERCA2a or AAV9-SERCA2a were injected intramyocardially in post-myocardial infarction (MI) mice preinjected with NAbs. Remarkably, eAAV9-SERCA2a outperformed standard AAVs 6 weeks post-MI, significantly improving cardiac function in the presence of NAbs (%EF 55.14 ± 3.50 vs. 27.31 ± 1.63, respectively). Additionally, we demonstrated in vivo that eAAV9-mediated gene delivery is more specific to CMs than to other cell types present in the heart, which suggests that eAAVs preserve cardiotropic properties of AAV9 serotype. With examination of colocalization of eAAVs and markers specific for endosomes (Rab5 and Rab7) in hCMs in vitro , our preliminary data indicated that eAAV infectious entry potentially involves trafficking via endocytic compartments. In conclusion, these results underline the therapeutic potential of eAAVs to evade NAbs, and to facilitate the clinical translation of AAV-based gene therapies to a larger human population.

Abstract 104: AAV-Exosomes: A Novel Platform for Myocardial Gene Delivery for Cardioprotection

Introduction: Adeno-associated viruses (AAVs) are viral vectors of choice for delivering genes for long-term expression due to their safety in clinics. However, pre-existing immunity to AAVs from naturally present neutralizing antibodies (NAbs, present in between 60% and 90% of population) poses a significant challenge for AAV-mediated gene delivery. NAbs prevent AAVs from infecting target cells, greatly reducing transduction efficiency and, therefore, the clinical efficacy. Thus, it is essential to develop novel AAV-based vectors that circumvent the effect of NAbs.

Objectives: We aimed to investigate the ability of exosome-encapsulated AAVs (AAVExo) to evade NAbs and serve as a highly efficient gene transfer tool for cardiovascular therapeutics.

Methods and Results: We developed a multi-step purification strategy using iodixanol density gradient to isolate AAVExo with minimal contamination from free AAVs (AAV1, 6 or 9). Biochemical assays, flow cytometry, IVIS Spectrum in vivo optical imaging and echocardiography were used to detect AAV-mediated gene delivery and evaluate cardiac function. AAV6Exo-mCherry and AAV9Exo-FLuc were resistant to NAbs and significantly improved expression of mCherry and firefly luciferase (FLuc) both in mouse and human (iPSC-derived) cardiomyocytes in vitro , and in murine hearts in vivo (in nude mice preinjected with NAbs), compared to free AAVs. To test the therapeutic efficacy of AAVExo-mediated gene delivery in the presence of NAbs, we injected AAV9-SERCA2a or AAV9Exo-SERCA2a into post-MI hearts of nude mice preinjected with IVIg (human intravenous immunoglobulin) preparation. Hearts treated with AAV9Exo-SERCA2a had significantly improved cardiac function compared to those treated with free AAV9-SERCA2a (%EF 62.6 ± 9.8 vs. 28.4 ± 5.3, respectively; 2 weeks after surgery).

Conclusion: Delivery of AAVs protected by carrier exosomes is a promising approach to circumvent the issue of NAbs in AAV-based gene therapy, which can be used in the entire population of patients and may result in higher gene delivery efficacy.

Abstract 373: An Animal Model of Left Atrial Thrombus

Left atrial thrombus (LAT) is a common funding of some cardiovascular diseases such as congestive heart failure (CHF), atrial fibrillation and myocardial injury. There is no proper animal model of LAT to date. The present study reports a model of congestive heart failure in rats that is characterized by LAT.

Methods: LAT were induced by aortic banding 2 months plus 30 minutes ischemia and reperfusion 1 m followed with aortic de-banding 1 m in rats. Cardiac function and blood flow velocity were assessed by echocardiography. Masson’s stainings were conducted for histology.

Results: congestive heart failure (CHF) in rats with LAT showed significant dilatation in left atrium (CHF = 56 ± 18 mm, N = 7, Control = 25 ± 6 mm, N = 10), significant decrease in left appendage blood flow velocity (CHF = 4.20 ± 0.09, Control = 0.21 ± 0.05 m/s) and mitral valve blood velocity (CHF = 0.76 ± 0.09 m/s, Control = 1.01 ± 0.04 m/s). Histology data showed that mature LAT had a complete membrane; the thrombus was characterized by significant fibrosis in middle and out layers. The outer layer of thrombus had microvessels and the cells were nucleated. The central part of the thrombus had very little fibrosis and showed necrosis. Small thrombus (0.05 - 0.1 mm) had a base from which the blood clot grew. Atrial neo-intimal fibrosis plays an important role in the formation of the base of microembolization. However, in some cases, micro-thrombi (<0.01 mm) showed no fibrotic base.

Conclusion: left atrial thrombus results from blood flow congestion. However, it is still not clear whether the thrombus is due to vascular proliferation from the atrial wall or through adhesion of coagulation fibers to the atrial wall.

Figure. A. echocardiographic imaging. B. left atrial area . C. mitral valve blood velocity. D. echocardiography of left atrial blood velocity. E. left atrial blood flow velocity. F. regular imaging of LAT. G. cross sectional imaging. H. small LAT. I. endometrial fibrosis. J. micro thrombus. K. coagulation fiber.