Effect of Adeno-Associated Virus Serotype and Genomic Structure on Liver Transduction and Biodistribution in Mice of Both Genders

A comprehensive atlas of AAV tropism in the mouse

Gene therapy with adeno-associated virus (AAV) vectors requires knowledge of their tropism within the body. Here we analyze the tropism of 10 naturally occurring AAV serotypes (AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAVrh8, AAVrh10, and AAVrh74) following systemic delivery into male and female mice. A transgene-expressing ZsGreen and Cre recombinase was used to identify transduction in a cell-dependent manner based on fluorescence. Cre-driven activation of tdTomato fluorescence offered superior sensitivity for transduced cells. All serotypes except AAV3B and AAV4 had high liver tropism. Fluorescence activation revealed transduction of unexpected tissues, including adrenals, testes, and ovaries. Rare transduced cells within tissues were also readily visualized. Biodistribution of AAV genomes correlated with fluorescence, except in immune tissues. AAV4 was found to have a pan-endothelial tropism while also targeting pancreatic beta cells. This public resource enables selection of the best AAV serotypes for basic science and preclinical applications in mice.

Nanomedicine for Maternal and Fetal Health

Conception, pregnancy, and childbirth are complex processes that affect both mother and fetus. Thus, it is perhaps not surprising that in the United States alone, roughly 11% of women struggle with infertility and 16% of pregnancies involve some sort of complication. This presents a clear need to develop safe and effective treatment options, though the development of therapeutics for use in women's health and particularly in pregnancy is relatively limited. Physiological and biological changes during the menstrual cycle and pregnancy impact biodistribution, pharmacokinetics, and efficacy, further complicating the process of administration and delivery of therapeutics. In addition to the complex pharmacodynamics, there is also the challenge of overcoming physiological barriers that impact various routes of local and systemic administration, including the blood-follicle barrier and the placenta. Nanomedicine presents a unique opportunity to target and sustain drug delivery to the reproductive tract and other relevant organs in the mother and fetus, as well as improve the safety profile and minimize side effects. Nanomedicine-based approaches have the potential to improve the management and treatment of infertility, obstetric complications, and fetal conditions.

Quantification of full and empty particles of adeno-associated virus vectors via a novel dual fluorescence-linked immunosorbent assay

The adeno-associated virus (AAV) vector is one of the most advanced platforms for gene therapy because of its low immunogenicity and non-pathogenicity. The concentrations of both AAV vector empty particles, which do not contain DNA and do not show any efficacy, and AAV vector full particles (FPs), which contain DNA, are important quality attributes. In this study, a dual fluorescence-linked immunosorbent assay (dFLISA), which uses two fluorescent dyes to quantify capsid and genome titers in a single analysis, was established. In dFLISA, capture of AAV particles, detection of capsid proteins, and release and detection of the viral genome are performed in the same well. We demonstrated that the capsid and genomic titers determined by dFLISA were comparable with those of analytical ultracentrifugation. The FP ratios determined by dFLISA were in good agreement with the expected values. In addition, we showed that dFLISA can quantify the genomic and capsid titers of crude samples. dFLISA can be easily modified for measuring other AAV vector serotypes and AAV vectors with different genome lengths. These features make dFLISA a valuable tool for the future development of AAV-based gene therapies.

A Comprehensive Atlas of AAV Tropism in the Mouse

Gene therapy with Adeno-Associated Viral (AAV) vectors requires knowledge of their tropism within the body. Here we analyze the tropism of ten naturally occurring AAV serotypes (AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAVrh8, AAVrh10 and AAVrh74) following systemic delivery into male and female mice. A transgene expressing ZsGreen and Cre recombinase was used to identify transduction in a cell-dependent manner based on fluorescence. Cre-driven activation of tdTomato fluorescence offered superior sensitivity for transduced cells. All serotypes except AAV3B and AAV4 had high liver tropism. Fluorescence activation revealed transduction of unexpected tissues, including adrenals, testes and ovaries. Rare transduced cells within tissues were also readily visualized. Biodistribution of AAV genomes correlated with fluorescence, except in immune tissues. AAV4 was found to have a pan-endothelial tropism while also targeting pancreatic beta cells. This public resource enables selection of the best AAV serotypes for basic science and preclinical applications in mice.

Targeting cytokine and chemokine signaling pathways for cancer therapy

Cytokines are critical in regulating immune responses and cellular behavior, playing dual roles in both normal physiology and the pathology of diseases such as cancer. These molecules, including interleukins, interferons, tumor necrosis factors, chemokines, and growth factors like TGF-β, VEGF, and EGF, can promote or inhibit tumor growth, influence the tumor microenvironment, and impact the efficacy of cancer treatments. Recent advances in targeting these pathways have shown promising therapeutic potential, offering new strategies to modulate the immune system, inhibit tumor progression, and overcome resistance to conventional therapies. In this review, we summarized the current understanding and therapeutic implications of targeting cytokine and chemokine signaling pathways in cancer. By exploring the roles of these molecules in tumor biology and the immune response, we highlighted the development of novel therapeutic agents aimed at modulating these pathways to combat cancer. The review elaborated on the dual nature of cytokines as both promoters and suppressors of tumorigenesis, depending on the context, and discussed the challenges and opportunities this presents for therapeutic intervention. We also examined the latest advancements in targeted therapies, including monoclonal antibodies, bispecific antibodies, receptor inhibitors, fusion proteins, engineered cytokine variants, and their impact on tumor growth, metastasis, and the tumor microenvironment. Additionally, we evaluated the potential of combining these targeted therapies with other treatment modalities to overcome resistance and improve patient outcomes. Besides, we also focused on the ongoing research and clinical trials that are pivotal in advancing our understanding and application of cytokine- and chemokine-targeted therapies for cancer patients.

Recent advances in various adeno-associated viruses (AAVs) as gene therapy agents in hepatocellular carcinoma

Primary liver cancer, which is scientifically referred to as hepatocellular carcinoma (HCC), is a significant concern in the field of global health. It has been demonstrated that conventional chemotherapy, chemo-hormonal therapy, and conformal radiotherapy are ineffective against HCC. New therapeutic approaches are thus urgently required. Identifying single or multiple mutations in genes associated with invasion, metastasis, apoptosis, and growth regulation has resulted in a more comprehensive comprehension of the molecular genetic underpinnings of malignant transformation, tumor advancement, and host interaction. This enhanced comprehension has notably propelled the development of novel therapeutic agents. Therefore, gene therapy (GT) holds great promise for addressing the urgent need for innovative treatments in HCC. However, the complexity of HCC demands precise and effective therapeutic approaches. The adeno-associated virus (AAV) distinctive life cycle and ability to persistently infect dividing and nondividing cells have rendered it an alluring vector. Another appealing characteristic of the wild-type virus is its evident absence of pathogenicity. As a result, AAV, a vector that lacks an envelope and can be modified to transport DNA to specific cells, has garnered considerable interest in the scientific community, particularly in experimental therapeutic strategies that are still in the clinical stage. AAV vectors emerge as promising tools for HCC therapy due to their non-immunogenic nature, efficient cell entry, and prolonged gene expression. While AAV-mediated GT demonstrates promise across diverse diseases, the current absence of ongoing clinical trials targeting HCC underscores untapped potential in this context. Furthermore, gene transfer through hepatic AAV vectors is frequently facilitated by GT research, which has been propelled by several congenital anomalies affecting the liver. Notwithstanding the enthusiasm associated with this notion, recent discoveries that expose the integration of the AAV vector genome at double-strand breaks give rise to apprehensions regarding their enduring safety and effectiveness. This review explores the potential of AAV vectors as versatile tools for targeted GT in HCC. In summation, we encapsulate the multifaceted exploration of AAV vectors in HCC GT, underlining their transformative potential within the landscape of oncology and human health.

AAV-mediated hepatic LPL expression ameliorates severe hypertriglyceridemia and acute pancreatitis in Gpihbp1 deficient mice and rats

GPIHBP1 plays an important role in the hydrolysis of triglyceride (TG) lipoproteins by lipoprotein lipases (LPLs). However, Gpihbp1 knockout mice did not develop hypertriglyceridemia (HTG) during the suckling period but developed severe HTG after weaning on a chow diet. It has been postulated that LPL expression in the liver of suckling mice may be involved. To determine whether hepatic LPL expression could correct severe HTG in Gpihbp1 deficiency, liver-targeted LPL expression was achieved via intravenous administration of the adeno-associated virus (AAV)-human LPL gene, and the effects of AAV-LPL on HTG and HTG-related acute pancreatitis (HTG-AP) were observed. Suckling Gpihbp1-/- mice with high hepatic LPL expression did not develop HTG, whereas Gpihbp1-/- rat pups without hepatic LPL expression developed severe HTG. AAV-mediated liver-targeted LPL expression dose-dependently decreased plasma TG levels in Gpihbp1-/- mice and rats, increased post-heparin plasma LPL mass and activity, decreased mortality in Gpihbp1-/- rat pups, and reduced the susceptibility and severity of both Gpihbp1-/- animals to HTG-AP. However, the muscle expression of AAV-LPL had no significant effect on HTG. Targeted expression of LPL in the liver showed no obvious adverse reactions. Thus, liver-targeted LPL expression may be a new therapeutic approach for HTG-AP caused by GPIHBP1 deficiency.

Liver directed adeno-associated viral vectors to treat metabolic disease

The liver is the metabolic center of the body and an ideal target for gene therapy of inherited metabolic disorders (IMDs). Adeno-associated viral (AAV) vectors can deliver transgenes to the liver with high efficiency and specificity and a favorable safety profile. Recombinant AAV vectors contain only the transgene cassette, and their payload is converted to non-integrating circular double-stranded DNA episomes, which can provide stable expression from months to years. Insights from cellular studies and preclinical animal models have provided valuable information about AAV capsid serotypes with a high liver tropism. These vectors have been applied successfully in the clinic, particularly in trials for hemophilia, resulting in the first approved liver-directed gene therapy. Lessons from ongoing clinical trials have identified key factors affecting efficacy and safety that were not readily apparent in animal models. Circumventing pre-existing neutralizing antibodies to the AAV capsid, and mitigating adaptive immune responses to transduced cells are critical to achieving therapeutic benefit. Combining the high efficiency of AAV delivery with genome editing is a promising path to achieve more precise control of gene expression. The primary safety concern for liver gene therapy with AAV continues to be the small risk of tumorigenesis from rare vector integrations. Hepatotoxicity is a key consideration in the safety of neuromuscular gene therapies which are applied at substantially higher doses. The current knowledge base and toolkit for AAV is well developed, and poised to correct some of the most severe IMDs with liver-directed gene therapy.

Production and Purification of Adeno-Associated Viral Vectors for the Development of Immune-Competent Mouse Models of Persistent Hepatitis B Virus Replication

Mice infected with a recombinant adeno-associated virus carrying a replication-competent hepatitis B virus genome (rAAV-HBV) via the intravenous route establish a persistent HBV replication in hepatocytes and develop immune tolerance. They serve as models to evaluate antiviral immunity and to assess potential therapeutic approaches for chronic HBV infection. Combining selected HBV variants and different mouse genotypes allows for addressing a broad spectrum of research questions. This chapter describes the basic principles of the rAAV-HBV mouse model, rAAV-HBV production and purification methods, and finally, the in vivo application.

Recombinant adeno-associated virus 8 vector in gene therapy: Opportunities and challenges

In recent years, significant breakthroughs have been made in the field of gene therapy. Adeno-associated virus (AAV) is one of the most promising gene therapy vectors and a powerful tool for delivering the gene of interest. Among the AAV vectors, AAV serotype 8 (AAV8) has attracted much attention for its efficient and stable gene transfection into specific tissues. Currently, recombinant AAV8 has been widely used in gene therapy research on a variety of diseases, including genetic diseases, cancers, autoimmune diseases, and viral diseases. This paper reviewed the applications and challenges of using AAV8 as a vector for gene therapy, with the aim of providing a valuable resource for those pursuing the application of viral vectors in gene therapy.

Single Systemic Administration of a Gene Therapy Leading to Disease Treatment in Metachromatic Leukodystrophy Arsa Knock-Out Mice

Metachromatic leukodystrophy (MLD) is a rare, inherited, demyelinating lysosomal storage disorder caused by mutations in the arylsulfatase-A gene (ARSA). In patients, levels of functional ARSA enzyme are diminished and lead to deleterious accumulation of sulfatides. Herein, we demonstrate that intravenous administration of HSC15/ARSA restored the endogenous murine biodistribution of the corresponding enzyme, and overexpression of ARSA corrected disease biomarkers and ameliorated motor deficits in Arsa KO mice of either sex. In treated Arsa KO mice, when compared with intravenously administered AAV9/ARSA, significant increases in brain ARSA activity, transcript levels, and vector genomes were observed with HSC15/ARSA Durability of transgene expression was established in neonate and adult mice out to 12 and 52 weeks, respectively. Levels and correlation between changes in biomarkers and ARSA activity required to achieve functional motor benefit was also defined. Finally, we demonstrated blood-nerve, blood-spinal and blood-brain barrier crossing as well as the presence of circulating ARSA enzyme activity in the serum of healthy nonhuman primates of either sex. Together, these findings support the use of intravenous delivery of HSC15/ARSA-mediated gene therapy for the treatment of MLD.SIGNIFICANCE STATEMENT Herein, we describe the method of gene therapy adeno-associated virus (AAV) capsid and route of administration selection leading to an efficacious gene therapy in a mouse model of metachromatic leukodystrophy. We demonstrate the therapeutic outcome of a new naturally derived clade F AAV capsid (AAVHSC15) in a disease model and the importance of triangulating multiple end points to increase the translation into higher species via ARSA enzyme activity and biodistribution profile (with a focus on the CNS) with that of a key clinically relevant biomarker.

RNF130 Regulates LDLR Availability and Plasma LDL Cholesterol Levels

BACKGROUND

Removal of circulating plasma low-density lipoprotein cholesterol (LDL-C) by the liver relies on efficient endocytosis and intracellular vesicle trafficking. Increasing the availability of hepatic LDL receptors (LDLRs) remains a major clinical target for reducing LDL-C levels. Here, we describe a novel role for RNF130 (ring finger containing protein 130) in regulating plasma membrane availability of LDLR.

METHODS

We performed a combination of gain-of-function and loss-of-function experiments to determine the effect of RNF130 on LDL-C and LDLR recycling. We overexpressed RNF130 and a nonfunctional mutant RNF130 in vivo and measured plasma LDL-C and hepatic LDLR protein levels. We performed in vitro ubiquitination assays and immunohistochemical staining to measure levels and cellular distribution of LDLR. We supplement these experiments with 3 separate in vivo models of RNF130 loss-of-function where we disrupted Rnf130 using either ASO (antisense oligonucleotides), germline deletion, or AAV CRISPR (adeno-associated virus clustered regularly interspaced short palindromic repeats) and measured hepatic LDLR and plasma LDL-C.

RESULTS

We demonstrate that RNF130 is an E3 ubiquitin ligase that ubiquitinates LDLR resulting in redistribution of the receptor away from the plasma membrane. Overexpression of RNF130 decreases hepatic LDLR and increases plasma LDL-C levels. Further, in vitro ubiquitination assays demonstrate RNF130-dependent regulation of LDLR abundance at the plasma membrane. Finally, in vivo disruption of Rnf130 using ASO, germline deletion, or AAV CRISPR results in increased hepatic LDLR abundance and availability and decreased plasma LDL-C levels.

CONCLUSIONS

Our studies identify RNF130 as a novel posttranslational regulator of LDL-C levels via modulation of LDLR availability, thus providing important insight into the complex regulation of hepatic LDLR protein levels.

Various AAV Serotypes and Their Applications in Gene Therapy: An Overview

Despite scientific discoveries in the field of gene and cell therapy, some diseases still have no effective treatment. Advances in genetic engineering methods have enabled the development of effective gene therapy methods for various diseases based on adeno-associated viruses (AAVs). Today, many AAV-based gene therapy medications are being investigated in preclinical and clinical trials, and new ones are appearing on the market. In this article, we present a review of AAV discovery, properties, different serotypes, and tropism, and a following detailed explanation of their uses in gene therapy for disease of different organs and systems.

Progress, and prospects in the therapeutic armamentarium of persons with congenital hemophilia. Defining the place for liver-directed gene therapy

In persons with congenital severe hemophilia A (HA) living in high-income countries, twice weekly intravenous infusions of extended half-life (EHL) factor VIII (FVIII) products, or weekly/biweekly/monthly subcutaneous injections of emicizumab are the gold standard home treatments to grant days without hurdles and limitations. Once weekly/twice monthly infusions of EHL Factor IX (FIX) products achieve the same target in severe hemophilia B (HB). Gene therapy, which is likely to be licensed for clinical use within 1-2 years, embodies a shift beyond these standards. At an individual patient level, a single functional gene transfer leads to a > 10-yr almost full correction of the hemostatic defect in HB and to a sustained (3-6-yrs) expression of FVIII sufficient to discontinue exogenous clotting factor administrations. At the doses employed, the limited liver toxicity of systemically infused recombinant adeno-associated virus (rAAV) vectors is documented by long-term (12-15 yrs) follow-ups, and pre-existing high-titer neutralizing antibodies to the AAV5 vector are no longer an exclusion criterion for effective transgene expression with this vector. A safe durable treatment that converts a challenging illness to a phenotypically curable disease, allows persons to feel virtually free from the fears and the obligations of hemophilia for years/decades. Along with patient organizations and health care professionals, communicating to government authorities and reimbursement agencies the liberating potential of this substantial innovation, and disseminating across the Centers updated information on benefits and risks of this strategy, will align expectations of different stakeholders and establish the notion of a potentially lifelong cure of hemophilia.

Preclinical evaluation of FLT190, a liver-directed AAV gene therapy for Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by loss of alpha-galactosidase A (α-Gal A) activity and is characterized by progressive accumulation of glycosphingolipids in multiple cells and tissues. FLT190, an investigational gene therapy, is currently being evaluated in a Phase 1/2 clinical trial in patients with Fabry disease (NCT04040049). FLT190 consists of a potent, synthetic capsid (AAVS3) containing an expression cassette with a codon-optimized human GLA cDNA under the control of a liver-specific promoter FRE1 (AAV2/S3-FRE1-GLAco). For mouse studies FLT190 genome was pseudotyped with AAV8 for efficient transduction. Preclinical studies in a murine model of Fabry disease (Gla-deficient mice), and non-human primates (NHPs) showed dose-dependent increases in plasma α-Gal A with steady-state observed 2 weeks following a single intravenous dose. In Fabry mice, AAV8-FLT190 treatment resulted in clearance of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3) in plasma, urine, kidney, and heart; electron microscopy analyses confirmed reductions in storage inclusion bodies in kidney and heart. In NHPs, α-Gal A expression was consistent with the levels of hGLA mRNA in liver, and no FLT190-related toxicities or adverse events were observed. Taken together, these studies demonstrate preclinical proof-of-concept of liver-directed gene therapy with FLT190 for the treatment of Fabry disease.

Sex-Gender-Based Differences in Metabolic Diseases

Sexual dimorphism creates different biological and cellular activities and selective regulation mechanisms in males and females, thus generating differential responses in health and disease. In this scenario, the sex itself is a source of physiologic metabolic disparities that depend on constitutive genetic and epigenetic features that characterize in a specific manner one sex or the other. This has as a direct consequence a huge impact on the metabolic routes that drive the phenotype of an individual. The impact of sex is being clearly recognized also in disease, whereas male and females are more prone to the development of some disorders, or have selective responses to drugs and therapeutic treatments. Actually, very less is known regarding the probable differences guided by sex in the context of inherited metabolic disorders, owing to the scarce consideration of sex in such restricted field, accompanied by an intrinsic bias connected with the rarity of such diseases. Metabolomics technologies have been ultimately developed and adopted for being excellent tools for the investigation of metabolic mechanisms, for marker discovery or monitoring, and for supporting diagnostic procedures of metabolic disorders. Hence, metabolomic approaches can excellently embrace the discovery of sex differences, especially when associated to the outcome or the management of certain inborn errors of the metabolism.

Sex-split analysis of pathology and motor-behavioral outcomes in a mouse model of CLN8-Batten disease reveals an increased disease burden and trajectory in female Cln8mnd mice

BACKGROUND

CLN8-Batten disease (CLN8 disease) is a rare neurodegenerative disorder characterized phenotypically by progressive deterioration of motor and cognitive abilities, visual symptoms, epileptic seizures, and premature death. Mutations in CLN8 results in characteristic Batten disease symptoms and brain-wide pathology including accumulation of lysosomal storage material, gliosis, and neurodegeneration. Recent investigations of other subforms of Batten disease (CLN1, CLN3, CLN6) have emphasized the influence of biological sex on disease and treatment outcomes; however, little is known about sex differences in the CLN8 subtype. To determine the impact of sex on CLN8 disease burden and progression, we utilized a Cln8^mnd mouse model to measure the impact and progression of histopathological and behavioral outcomes between sexes.

RESULTS

Several notable sex differences were observed in the presentation of brain pathology, including Cln8^mnd female mice consistently presenting with greater GFAP⁺ astrocytosis and CD68⁺ microgliosis in the somatosensory cortex, ventral posteromedial/ventral posterolateral nuclei of the thalamus, striatum, and hippocampus when compared to Cln8^mnd male mice. Furthermore, sex differences in motor-behavioral assessments revealed Cln8^mnd female mice experience poorer motor performance and earlier death than their male counterparts. Cln8^mnd mice treated with an AAV9-mediated gene therapy were also examined to assess sex differences on therapeutics outcomes, which revealed no appreciable differences between the sexes when responding to the therapy.

CONCLUSIONS

Taken together, our results provide further evidence of biologic sex as a modifier of Batten disease progression and outcome, thus warranting consideration when conducting investigations and monitoring therapeutic impact.

Adeno-associated virus-based malaria booster vaccine following attenuated replication-competent vaccinia virus LC16m8Δ priming

We previously demonstrated that boosting with adeno-associated virus (AAV) type 1 (AAV1) can induce highly effective and long-lasting protective immune responses against malaria parasites when combined with replication-deficient adenovirus priming in a rodent model. In the present study, we compared the efficacy of two different AAV serotypes, AAV1 and AAV5, as malaria booster vaccines following priming with the attenuated replication-competent vaccinia virus strain LC16m8Δ (m8Δ), which harbors the fusion gene encoding both the pre-erythrocytic stage protein, Plasmodium falciparum circumsporozoite (PfCSP) and the sexual stage protein (Pfs25) in a two-dose heterologous prime-boost immunization regimen. Both regimens, m8Δ/AAV1 and m8Δ/AAV5, induced robust anti-PfCSP and anti-Pfs25 antibodies. To evaluate the protective efficacy, the mice were challenged with sporozoites twice after immunization. At the first sporozoite challenge, m8Δ/AAV5 achieved 100% sterile protection whereas m8Δ/AAV1 achieved 70% protection. However, at the second challenge, 100% of the surviving mice from the first challenge were protected in the m8Δ/AAV1 group whereas only 55.6% of those in the m8Δ/AAV5 group were protected. Regarding the transmission-blocking efficacy, we found that both immunization regimens induced high levels of transmission-reducing activity (>99%) and transmission-blocking activity (>95%). Our data indicate that the AAV5-based multistage malaria vaccine is as effective as the AAV1-based vaccine when administered following an m8Δ-based vaccine. These results suggest that AAV5 could be a viable alternate vaccine vector as a malaria booster vaccine.

AAV-mediated BMP7 gene therapy counteracts insulin resistance and obesity

Type 2 diabetes, insulin resistance, and obesity are strongly associated and are a major health problem worldwide. Obesity largely results from a sustained imbalance between energy intake and expenditure. Therapeutic approaches targeting metabolic rate may counteract body weight gain and insulin resistance. Bone morphogenic protein 7 (BMP7) has proven to enhance energy expenditure by inducing non-shivering thermogenesis in short-term studies in mice treated with the recombinant protein or adenoviral vectors encoding BMP7. To achieve long-term BMP7 effects, the use of adeno-associated viral (AAV) vectors would provide sustained production of the protein after a single administration. Here, we demonstrated that treatment of high-fat-diet-fed mice and ob/ob mice with liver-directed AAV-BMP7 vectors enabled a long-lasting increase in circulating levels of this factor. This rise in BMP7 concentration induced browning of white adipose tissue (WAT) and activation of brown adipose tissue, which enhanced energy expenditure, and reversed WAT hypertrophy, hepatic steatosis, and WAT and liver inflammation, ultimately resulting in normalization of body weight and insulin resistance. This study highlights the potential of AAV-BMP7-mediated gene therapy for the treatment of insulin resistance, type 2 diabetes, and obesity.

Adeno-associated-virus-mediated gene delivery to ovaries restores fertility in congenital infertile mice

Oocytes and granulosa cells closely interact with each other during follicular development, and a lack of appropriate signaling between them results in infertility. Attempts to manipulate oocyte microenvironment have been impeded by the impermeability of the blood-follicle barrier (BFB). To establish a strategy for manipulating oogenesis, we use adeno-associated viruses (AAVs), which have a unique ability of transcytosis. Microinjecting of AAVs into the ovarian stroma penetrates the BFB and achieves long-term gene expression. Introduction of an AAV carrying the mouse Kitl gene restores oogenesis in congenitally infertile KitlSl-t/KitlSl-t mutant mouse ovaries, which lack Kitl expression but contain only primordial follicles. Healthy offspring without AAV integration are born by natural mating. Therefore, AAV-mediated gene delivery not only provides a means for studying oocyte-granulosa interactions through the manipulation of the oocyte microenvironment but could also be a powerful method to treat female infertility resulting from somatic cell defects.

Genetic Modification of the AAV5 Capsid with Lysine Residues Results in a Lung-tropic, Liver-detargeted Gene Transfer Vector

Intravenous (IV) administration of naturally occurring adeno-associated virus (AAV) vectors are liver tropic, with a significant proportion of the total vector dose mediating gene expression in liver hepatocytes. AAV capsids that are directed towards other organs such as lung may be useful for therapy of non-liver-based diseases. Based on the knowledge that the lung capillary endothelium is the first capillary bed encountered by an intravenously administered AAV vector, and that the lung endothelium glycocalyx is enriched in negatively charged sialic acid, we hypothesized that adding positively changed lysine residues to the AAV capsid would enhance AAV biodistribution to the lung following intravenous administration. Using site directed mutagenesis, two lysine residues were inserted into variable loop VIII of the AAV serotype 5 capsid vector (AAV5-PK2). Organ distribution of AAV5-PK2 was compared to AAV5, AAVrh.10, AAV2, and AAV2-7m8 4 wk after intravenous administration (1011 gc) to C57Bl/6 male mice. As predicted, following intravenous administration, AAAV5-PK2 had the highest biodistribution in the lung (p<0.02 compared to AAV5, AAVrh.10, AAV2 and AAV2-7m8). Further, biodistribution to liver of AAV5-PK2 was 2-logs decreased compared to AAV5 (p<10-4) with a ratio of AAV5-PK2 lung to liver of 62-fold compared to AAV5 of 0.2-fold (p<0.0003). The AAV5-PK2 capsid represents a lung-tropic AAV vector that is also significantly detargeted from the liver, a property that may be useful in lung directed gene therapies.

In Vivo Mouse Models for Hepatitis B Virus Infection and Their Application

Despite the availability of effective vaccination, hepatitis B virus (HBV) infection continues to be a major challenge worldwide. Research efforts are ongoing to find an effective cure for the estimated 250 million people chronically infected by HBV in recent years. The exceptionally limited host spectrum of HBV has limited the research progress. Thus, different HBV mouse models have been developed and used for studies on infection, immune responses, pathogenesis, and antiviral therapies. However, these mouse models have great limitations as no spread of HBV infection occurs in the mouse liver and no or only very mild hepatitis is present. Thus, the suitability of these mouse models for a given issue and the interpretation of the results need to be critically assessed. This review summarizes the currently available mouse models for HBV research, including hydrodynamic injection, viral vector-mediated transfection, recombinant covalently closed circular DNA (rc-cccDNA), transgenic, and liver humanized mouse models. We systematically discuss the characteristics of each model, with the main focus on hydrodynamic injection mouse model. The usefulness and limitations of each mouse model are discussed based on the published studies. This review summarizes the facts for considerations of the use and suitability of mouse model in future HBV studies.

Use of an adeno-associated virus serotype Anc80 to provide durable cure of phenylketonuria in a mouse model

Phenylketonuria (PKU) is the most common inborn error of metabolism of the liver, and results from mutations of both alleles of the phenylalanine hydroxylase gene (PAH). As such, it is a suitable target for gene therapy via gene delivery with a recombinant adeno-associated virus (AAV) vector. Here we use the synthetic AAV vector Anc80 via systemic administration to deliver a functional copy of a codon-optimized human PAH gene, with or without an intron spacer, to the Pah^enu2 mouse model of PKU. Dose-dependent transduction of the liver and expression of PAH mRNA were present with both vectors, resulting in significant and durable reduction of circulating phenylalanine, reaching near control levels in males. Coat color of treated Pah^enu2 mice reflected an increase in pigmentation from brown to the black color of control animals, further indicating functional restoration of phenylalanine metabolism and its byproduct melanin. There were no adverse effects associated with administration of AAV up to 5 × 10¹² VG/kg, the highest dose tested. Only minor and/or transient variations in some liver enzymes were observed in some of the AAV-dosed animals which were not associated with pathology findings in the liver. Finally, there was no impact on cell turnover or apoptosis as evaluated by Ki-67 and TUNEL staining, further supporting the safety of this approach. This study demonstrates the therapeutic potential of AAV Anc80 to safely and durably cure PKU in a mouse model, supporting development for clinical consideration.

Next Step in Gene Delivery: Modern Approaches and Further Perspectives of AAV Tropism Modification

Today, adeno-associated virus (AAV) is an extremely popular choice for gene therapy delivery. The safety profile and simplicity of the genome organization are the decisive advantages which allow us to claim that AAV is currently among the most promising vectors. Several drugs based on AAV have been approved in the USA and Europe, but AAV serotypes’ unspecific tissue tropism is still a serious limitation. In recent decades, several techniques have been developed to overcome this barrier, such as the rational design, directed evolution and chemical conjugation of targeting molecules with a capsid. Today, all of the abovementioned approaches confer the possibility to produce AAV capsids with tailored tropism, but recent data indicate that a better understanding of AAV biology and the growth of structural data may theoretically constitute a rational approach to most effectively produce highly selective and targeted AAV capsids. However, while we are still far from this goal, other approaches are still in play, despite their drawbacks and limitations.

Reduced spontaneous itch in mouse models of cholestasis

Pruritus is one of the most distressing symptoms in cholestatic patients. Plasma autotaxin (ATX) activity correlates with the severity of pruritus in cholestatic patients, but the pathophysiology is unclear. To study pruritus in mice, we measured scratch activity in cholestatic Atp8b1 mutant mice, a model for Progressive Familial Intrahepatic Cholestasis type 1, and wild type mice (WT) with alpha-naphthylisothiocyanate (ANIT)-induced cholestasis. To induce cholestasis, Atp8b1 mutant mice received a diet containing 0.1% cholic acid (CA) and WT mice were treated with ANIT. In these mice ATX was also overexpressed by transduction with AAV-ATX. Scratch activity was measured using an unbiased, electronic assay. Marked cholestasis was accomplished in both Atp8b1 mutant mice on a CA-supplemented diet and in ANIT-treatment in WT mice, but scratch activity was decreased rather than increased while plasma ATX activity was increased. Plasma ATX activity was further increased up to fivefold with AAV-ATX, but this did not induce scratch activity. In contrast to several reports two cholestatic mouse models did not display increased scratch activity as a measure of itch perception. Increasing plasma ATX activity by overexpression also did not lead to increased scratch activity in mice. This questions whether mice are suitable to study cholestatic itch.

Efficacy of AAV8-hUGT1A1 with Rapamycin in neonatal, suckling, and juvenile rats to model treatment in pediatric CNs patients

A clinical trial using adeno-associated virus serotype 8 (AAV8)-human uridine diphosphate glucuronosyltransferase 1A1 (hUGT1A1) to treat inherited severe unconjugated hyperbilirubinemia (Crigler-Najjar syndrome) is ongoing, but preclinical data suggest that long-term efficacy in children is impaired due to loss of transgene expression upon hepatocyte proliferation in a growing liver. This study aims to determine at what age long-term efficacy can be obtained in the relevant animal model and whether immune modulation allows re-treatment using the same AAV vector. Neonatal, suckling, and juvenile Ugt1a1-deficient rats received a clinically relevant dose of AAV8-hUGT1A1, and serum bilirubin levels and anti-AAV8 neutralizing antibodies (NAbs) in serum were monitored. The possibility of preventing the immune response toward the vector was investigated using a rapamycin-based regimen with daily intraperitoneal (i.p.) injections starting 2 days before and ending 21 days after vector administration. In rats treated at postnatal day 1 (P1) or P14, the correction was (partially) lost after 12 weeks, whereas the correction was stable in rats injected at P28. Combining initial vector administration with the immune-suppressive regimen prevented induction of NAbs in female rats, allowing at least partially effective re-administration. Induction of NAbs upon re-injection could not be prevented, suggesting that this strategy will be ineffective in patients with low levels of preexisting anti-AAV NAbs.

Low incidence of hepatocellular carcinoma in mice and cats treated with systemic adeno-associated viral vectors

Adeno-associated viral (AAV) vectors have emerged as the preferred platform for in vivo gene transfer because of their combined efficacy and safety. However, insertional mutagenesis with the subsequent development of hepatocellular carcinomas (HCCs) has been recurrently noted in newborn mice treated with high doses of AAV, and more recently, the association of wild-type AAV integrations in a subset of human HCCs has been documented. Here, we address, in a comprehensive, prospective study, the long-term risk of tumorigenicity in young adult mice following delivery of single-stranded AAVs targeting liver. HCC incidence in mice treated with therapeutic and reporter AAVs was low, in contrast to what has been previously documented in mice treated as newborns with higher doses of AAV. Specifically, HCCs developed in 6 out 76 of AAV-treated mice, and a pathogenic integration of AAV was found in only one tumor. Also, no evidence of liver tumorigenesis was found in juvenile AAV-treated mucopolysaccharidosis type VI (MPS VI) cats followed as long as 8 years after vector administration. Together, our results support the low risk of tumorigenesis associated with AAV-mediated gene transfer targeting juvenile/young adult livers, although constant monitoring of subjects enrolled in AAV clinical trial is advisable.

Gene Therapy for Inherited Bleeding Disorders

Decades of preclinical and clinical studies developing gene therapy for hemophilia are poised to bear fruit with current promising pivotal studies likely to lead to regulatory approval. However, this recent success should not obscure the multiple challenges that were overcome to reach this destination. Gene therapy for hemophilia A and B benefited from advancements in the general gene therapy field, such as the development of adeno-associated viral vectors, as well as disease-specific breakthroughs, like the identification of B-domain deleted factor VIII and hyperactive factor IX Padua. The gene therapy field has also benefited from hemophilia B clinical studies, which revealed for the first time critical safety concerns related to immune responses to the vector capsid not anticipated in preclinical models. Preclinical studies have also investigated gene transfer approaches for other rare inherited bleeding disorders, including factor VII deficiency, von Willebrand disease, and Glanzmann thrombasthenia. Here we review the successful gene therapy journey for hemophilia and pose some unanswered questions. We then discuss the current state of gene therapy for these other rare inherited bleeding disorders and how the lessons of hemophilia gene therapy may guide clinical development.

Long-Term Liver Expression of an Apolipoprotein A-I Mimetic Peptide Attenuates Interferon-Alpha-Induced Inflammation and Promotes Antiviral Activity

Apolipoprotein A-I mimetic peptides are amphipathic alpha-helix peptides that display similar functions to apolipoprotein A-I. Preclinical and clinical studies have demonstrated the safety and efficacy of apolipoprotein A-I mimetic peptides in multiple indications associated with inflammatory processes. In this study, we evaluated the effect of the long-term expression of L37pA in the liver by an adeno-associated virus (AAV-L37pA) on the expression of an adeno-associated virus encoding interferon-alpha (AAV-IFNα). Long-term IFNα expression in the liver leads to lethal hematological toxicity one month after AAV administration. Concomitant administration of AAV-L37pA prevented the lethal toxicity since the IFNα expression was reduced one month after AAV administration. To identify the mechanism of action of L37pA, a genomic and proteomic analysis was performed 15 days after AAV administration when a similar level of IFNα and interferon-stimulated genes were observed in mice treated with AAV-IFNα alone and in mice treated with AAV-IFNα and AAV-L37pA. The coexpression of the apolipoprotein A-I mimetic peptide L37pA with IFNα modulated the gene expression program of IFNα, inducing a significant reduction in inflammatory pathways affecting pathogen-associated molecular patterns receptor, dendritic cells, NK cells and Th1 immune response. The proteomic analysis confirmed the impact of the L37pA activity on several inflammatory pathways and indicated an activation of LXR/RXR and PPPARα/γ nuclear receptors. Thus, long-term expression of L37pA induces an anti-inflammatory effect in the liver that allows silencing of IFNα expression mediated by an adeno-associated virus.

Insulin Fused to Apolipoprotein A-I Reduces Body Weight and Steatosis in DB/DB Mice

Background: Targeting long-lasting insulins to the liver may improve metabolic alterations that are not corrected with current insulin replacement therapies. However, insulin is only able to promote lipogenesis but not to block gluconeogenesis in the insulin-resistant liver, exacerbating liver steatosis associated with diabetes.

Methods: In order to overcome this limitation, we fused a single-chain insulin to apolipoprotein A-I, and we evaluated the pharmacokinetics and pharmacodynamics of this novel fusion protein in wild type mice and in db/db mice using both recombinant proteins and recombinant adenoassociated virus (AAV).

Results: Here, we report that the fusion protein between single-chain insulin and apolipoprotein A-I prolonged the insulin half-life in circulation, and accumulated in the liver. We analyzed the long-term effect of these insulin fused to apolipoprotein A-I or insulin fused to albumin using AAVs in the db/db mouse model of diabetes, obesity, and liver steatosis. While AAV encoding insulin fused to albumin exacerbated liver steatosis in several mice, AAV encoding insulin fused to apolipoprotein A-I reduced liver steatosis. These results were confirmed upon daily subcutaneous administration of the recombinant insulin-apolipoprotein A-I fusion protein for six weeks. The reduced liver steatosis was associated with reduced body weight in mice treated with insulin fused to apolipoprotein A-I. Recombinant apolipoprotein A-I alone significantly reduces body weight and liver weight, indicating that the apolipoprotein A-I moiety is the main driver of these effects.

Conclusion: The fusion protein of insulin and apolipoprotein A-I could be a promising insulin derivative for the treatment of diabetic patients with associated fatty liver disease.

Sex Differences Revealed in a Mouse CFA Inflammation Model with Macrophage Targeted Nanotheranostics

Monocyte derived macrophages (MDMs) infiltrate sites of infection or injury and upregulate cyclooxygenase-2 (COX-2), an enzyme that stimulates prostaglandin-E2 (PgE2). Nanotheranostics combine therapeutic and diagnostic agents into a single nanosystem. In previous studies, we demonstrated that a nanotheranostic strategy, based on theranostic nanoemulsions (NE) loaded with a COX-2 inhibitor (celecoxib, CXB) and equipped with near-infrared fluorescent (NIRF) reporters, can specifically target circulating monocytes and MDMs. The anti-inflammatory and anti-nociceptive effects of such cell-specific COX-2 inhibition lasted several days following Complete Freund's Adjuvant (CFA) or nerve injury in male mice. The overall goal of this study was to investigate the extended (up to 40 days) impact of MDM-targeted COX-2 inhibition and any sex-based differences in treatment response; both of which remain unknown. Our study also evaluates the feasibility and efficacy of a preclinical nanotheranostic strategy for mechanistic investigation of the impact of such sex differences on clinical outcomes.

Methods: CFA was administered into the right hind paws of male and female mice. All mice received a single intravenous dose of NIRF labeled CXB loaded NE twelve hours prior to CFA injection. In vivo whole body NIRF imaging and mechanical hypersensitivity assays were performed sequentially and ex vivo NIRF imaging and immunohistopathology of foot pad tissues were performed at the end point of 40 days.

Results: Targeted COX-2 inhibition of MDMs in male and female mice successfully improved mechanical hypersensitivity after CFA injury. However, we observed distinct sex-specific differences in the intensity or longevity of the nociceptive responses. In males, a single dose of CXB-NE administered via tail vein injection produced significant improved mechanical hypersensitivity for 32 days as compared to the drug free NE (DF-NE) (untreated) control group. In females, CXB-NE produced similar, though less prominent and shorter-lived effects, lasting up to 11 days. NIRF imaging confirmed that CXB-NE can be detected up to day 40 in the CFA injected foot pad tissues of both sexes. There were distinct signal distribution trends between males and females, suggesting differences in macrophage infiltration dynamics between the sexes. This may also relate to differences in macrophage turnover rate between the sexes, a possibility that requires further investigation in this model.

Conclusions: For the first time, this study provides unique insight into MDM dynamics and the early as well as longer-term targeted effects and efficacy of a clinically translatable nanotheranostic agent on MDM mediated inflammation. Our data supports the potential of nanotheranostics as presented in elucidating the kinetics, dynamics and sex-based differences in the adaptive or innate immune responses to inflammatory triggers. Taken together, our study findings lead us closer to true personalized, sex-specific pain nanomedicine for a wide range of inflammatory diseases.

Gene therapy for progressive familial intrahepatic cholestasis type 3 in a clinically relevant mouse model

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare monogenic disease caused by mutations in the ABCB4 gene, resulting in a reduction in biliary phosphatidylcholine. Reduced biliary phosphatidylcholine cannot counteract the detergent effects of bile salts, leading to cholestasis, cholangitis, cirrhosis and ultimately liver failure. Here, we report results from treating two- or five-week-old Abcb4-/- mice with an AAV vector expressing human ABCB4, resulting in significant decreases of PFIC3 disease biomarkers. All male mice achieved a sustained therapeutic effect up through 12 weeks, but the effect was achieved in only 50% of females. However, two-week-old females receiving a second inoculation three weeks later maintained the therapeutic effect. Upon sacrifice, markers of PFIC3 disease such as, hepatosplenomegaly, biliary phosphatidylcholine and liver histology were significantly improved. Thus, AAV-mediated gene therapy successfully prevented PFIC3 symptoms in a clinically relevant mouse model, representing a step forward in improving potential therapy options for PFIC3 patients.

Advances of adeno-associated virus applied in gene therapy to hemophilia from bench work to the clinical use

Hemophilia A and B are diseases caused by a single gene deficiency and are thus suitable for gene therapy. In recent clinical research, adeno-associated virus (AAV) was employed by several teams in the treatment of hemophilia A and B, and the outcomes were encouraging. In this review, we summarized the most recent research on the mechanism and application of AAV in the treatment of hemophilia, trying to analyze the advantages of AAV gene therapy and the main challenges in its clinical use. We also summarized the clinical trials involving hemophilia, especially those employing AAV gene therapy to treat hemophilia A and B, some of which have already been completed and some that are still ongoing. From the reports of the completed clinical trials, we tried to determine the correlations among AAV dose, AAV serotype, immune response, and gene expression time. Finally, taking into account the most recent studies investigating AAV capsid modification, transgene optimization, and AAV chaperones, we summarized the direction of basic research and clinical applications of AAV in the future.

Treatment of Experimental Autoimmune Encephalomyelitis by Sustained Delivery of Low-Dose IFN-α

Multiple sclerosis (MS) is a chronic autoimmune disease with no curative treatment. The immune regulatory properties of type I IFNs have led to the approval of IFN-β for the treatment of relapsing-remitting MS. However, there is still an unmet need to improve the tolerability and efficacy of this therapy. In this work, we evaluated the sustained delivery of IFN-α1, either alone or fused to apolipoprotein A-1 by means of an adeno-associated viral (AAV) system in the mouse model of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis. These in vivo experiments demonstrated the prophylactic and therapeutic efficacy of the AAV-IFN-α or AAV-IFN-α fused to apolipoprotein A-1 vectors in experimental autoimmune encephalomyelitis, even at low doses devoid of hematological or neurologic toxicity. The sustained delivery of such low-dose IFN-α resulted in immunomodulatory effects, consisting of proinflammatory monocyte and T regulatory cell expansion. Moreover, encephalitogenic T lymphocytes from IFN-α-treated mice re-exposed to the myelin oligodendrocyte glycoprotein peptide in vitro showed a reduced proliferative response and cytokine (IL-17A and IFN-γ) production, in addition to upregulation of immunosuppressive molecules, such as IL-10, IDO, or PD-1. In conclusion, the results of the present work support the potential of sustained delivery of low-dose IFN-α for the treatment of MS and likely other T cell-dependent chronic autoimmune disorders.

AAV-Mediated Gene Delivery to the Liver: Overview of Current Technologies and Methods

Adeno-associated virus (AAV) vectors to treat liver-specific genetic diseases are the focus of several ongoing clinical trials. The ability to give a peripheral injection of virus that will successfully target the liver is one of many attractive features of this technology. Although initial studies of AAV liver gene transfer revealed some limitations, extensive animal modeling and further clinical development have helped solve some of these issues, resulting in several successful clinical trials that have reached curative levels of clotting factor expression in hemophilia. Looking beyond gene replacement, recent technologies offer the possibility for AAV liver gene transfer to directly repair deficient genes and potentially treat autoimmune disease.

Preclinical Development of an AAV8-hUGT1A1 Vector for the Treatment of Crigler-Najjar Syndrome

Adeno-associated viruses (AAVs) are among the most efficient vectors for liver gene therapy. Results obtained in the first hemophilia clinical trials demonstrated the long-term efficacy of this approach in humans, showing efficient targeting of hepatocytes with both self-complementary (sc) and single-stranded (ss) AAV vectors. However, to support clinical development of AAV-based gene therapies, efficient and scalable production processes are needed. In an effort to translate to the clinic an approach of AAV-mediated liver gene transfer to treat Crigler-Najjar (CN) syndrome, we developed an (ss)AAV8 vector carrying the human UDP-glucuronosyltransferase family 1-member A1 (hUGT1A1) transgene under the control of a liver-specific promoter. We compared our construct with similar (sc)AAV8 vectors expressing hUGT1A1, showing comparable potency in vitro and in vivo. Conversely, (ss)AAV8-hUGT1A1 vectors showed superior yields and product homogeneity compared with their (sc) counterpart. We then focused our efforts in the scale-up of a manufacturing process of the clinical product (ss)AAV8-hUGT1A1 based on the triple transfection of HEK293 cells grown in suspension. Large-scale production of this vector had characteristics identical to those of small-scale vectors produced in adherent cells. Preclinical studies in animal models of the disease and a good laboratory practice (GLP) toxicology-biodistribution study were also conducted using large-scale preparations of vectors. These studies demonstrated long-term safety and efficacy of gene transfer with (ss)AAV8-hUGT1A1 in relevant animal models of the disease, thus supporting the clinical translation of this gene therapy approach for the treatment of CN syndrome.

ZFN-Mediated In Vivo Genome Editing Corrects Murine Hurler Syndrome

Mucopolysaccharidosis type I (MPS I) is a severe disease due to deficiency of the lysosomal hydrolase α-L-iduronidase (IDUA) and the subsequent accumulation of the glycosaminoglycans (GAG), leading to progressive, systemic disease and a shortened lifespan. Current treatment options consist of hematopoietic stem cell transplantation, which carries significant mortality and morbidity risk, and enzyme replacement therapy, which requires lifelong infusions of replacement enzyme; neither provides adequate therapy, even in combination. A novel in vivo genome-editing approach is described in the murine model of Hurler syndrome. A corrective copy of the IDUA gene is inserted at the albumin locus in hepatocytes, leading to sustained enzyme expression, secretion from the liver into circulation, and subsequent uptake systemically at levels sufficient for correction of metabolic disease (GAG substrate accumulation) and prevention of neurobehavioral deficits in MPS I mice. This study serves as a proof-of-concept for this platform-based approach that should be broadly applicable to the treatment of a wide array of monogenic diseases.

AAV8-mediated overexpression of mPCSK9 in liver differs between male and female mice

BACKGROUND AND AIMS

The recombinant adeno-associated viral vector serotype 8 expressing the gain-of-function mutation of mouse proprotein convertase subtilisin/kexin type 9 (AAV8- PCSK9) is a new model for the induction of hypercholesterolemia. AAV8 preferentially infects hepatocytes and the incorporated liver-specific promoter should ensure expression of PCSK9 in the liver. Since tissue distribution of AAVs can differ between male and female mice, we investigated the differences in PCSK9 expression and hypercholesterolemia development between male and female mice using the AAV8-PCSK9 model.

METHODS

Male and female C57BL/6 mice were injected with either a low-dose or high-dose of AAV8-PCSK9 and fed a high-fat diet. Plasma lipid levels were evaluated as a measure of the induction of hypercholesterolemia.

RESULTS

Injection of mice with low dose AAV8-PCSK9 dramatically elevated both serum PCSK9 and cholesterol levels in male but not female mice. Increasing the dose of AAV8-PCSK9 threefold in female mice rescued the hypercholesterolemia phenotype but did not result in full restoration of AAV8-PCSK9 transduction of livers in female mice compared to the low-dose male mice. Our data demonstrate female mice respond differently to AAV8-PCSK9 injection compared to male mice.

CONCLUSIONS

These differences do not hinder the use of female mice when AAV8-PCSK9 doses are taken into consideration. However, localization to and production of AAV8-PCSK9 in organs besides the liver in mice may introduce confounding factors into studies and should be considered during experimental design.

Somatic Editing of Ldlr With Adeno-Associated Viral-CRISPR Is an Efficient Tool for Atherosclerosis Research

Objective- Atherosclerosis studies in Ldlr knockout mice require breeding to homozygosity and congenic status on C57BL6/J background, a process that is both time and resource intensive. We aimed to develop a new method for generating atherosclerosis through somatic deletion of Ldlr in livers of adult mice. Approach and Results- Overexpression of PCSK9 (proprotein convertase subtilisin/kexin type 9) is currently used to study atherosclerosis, which promotes degradation of LDLR (low-density lipoprotein receptor) in the liver. We sought to determine whether CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated 9) could also be used to generate atherosclerosis through genetic disruption of Ldlr in adult mice. We engineered adeno-associated viral (AAV) vectors expressing Staphylococcus aureus Cas9 and a guide RNA targeting the Ldlr gene (AAV-CRISPR). Both male and female mice received either (1) saline, (2) AAV-CRISPR, or (3) AAV-hPCSK9 (human PCSK9)-D374Y. A fourth group of germline Ldlr-KO mice was included for comparison. Mice were placed on a Western diet and followed for 20 weeks to assess plasma lipids, PCSK9 protein levels, atherosclerosis, and editing efficiency. Disruption of Ldlr with AAV-CRISPR was robust, resulting in severe hypercholesterolemia and atherosclerotic lesions in the aorta. AAV-hPCSK9 also produced hypercholesterolemia and atherosclerosis as expected. Notable sexual dimorphism was observed, wherein AAV-CRISPR was superior for Ldlr removal in male mice, while AAV-hPCSK9 was more effective in female mice. Conclusions- This all-in-one AAV-CRISPR vector targeting Ldlr is an effective and versatile tool to model atherosclerosis with a single injection and provides a useful alternative to the use of germline Ldlr-KO mice.

Homologous recombination mediates stable Fah gene integration and phenotypic correction in tyrosinaemia mouse-model

AIM

To stably correct tyrosinaemia in proliferating livers of fumarylacetoacetate-hydrolase knockout (Fah^-/-) mice by homologous-recombination-mediated targeted addition of the Fah gene.

METHODS

C57BL/6 Fah^∆exon5 mice served as an animal model for human tyrosinaemia type 1 in our study. The vector was created by amplifying human Fah cDNA including the TTR promoter from a lentivirus plasmid as described. The Fah expression cassette was flanked by homologous arms (620 bp and 749 bp long) of the Rosa26 gene locus. Mice were injected with 2.1 × 10⁸ VP of this vector (rAAV8-ROSA26.HAL-TTR.Fah-ROSA26.HAR) via the tail vein. Mice in the control group were injected with 2.1 × 10⁸ VP of a similar vector but missing the homologous arms (rAAV8-TTR.Fah). Primary hepatocytes from Fah^-/- recipient mice, treated with our vectors, were isolated and 1 × 10⁶ hepatocytes were transplanted into secondary Fah^-/- recipient mice by injection into the spleen. Upon either vector application or hepatocyte transplantation NTBC treatment was stopped in recipient mice.

RESULTS

Here, we report successful HR-mediated genome editing by integration of a Fah gene expression cassette into the “safe harbour locus” Rosa26 by recombinant AAV8. Both groups of mice showed long-term survival, weight gain and FAH positive clusters as determined by immunohistochemistry analysis of liver sections in the absence of NTBC treatment. In the group of C57BL/6 Fah^∆exon5 mice, which have been transplanted with hepatocytes from a mouse injected with rAAV8-ROSA26.HAL-TTR.Fah-ROSA26.HAR 156 d before, 6 out of 6 mice showed long-term survival, weight gain and FAH positive clusters without need for NTBC treatment. In contrast only 1 out 5 mice, who received hepatocytes from rAAV8-TTR.Fah treated mice, survived and showed few and smaller FAH positive clusters. These results demonstrate that homologous recombination-mediated Fah gene transfer corrects the phenotype in a mouse model of human tyrosinaemia type 1 (Fah^-/- mice) and is long lasting in a proliferating state of the liver as shown by withdrawal of NTBC treatment and serial transplantation of isolated hepatocytes from primary Fah^-/- recipient mice into secondary Fah^-/- recipient mice. This long term therapeutic efficacy is clearly superior to our control mice treated with episomal rAAV8 gene therapy approach.

CONCLUSION

HR-mediated rAAV8 gene therapy provides targeted transgene integration and phenotypic correction in Fah^-/- mice with superior long-term efficacy compared to episomal rAAV8 therapy in proliferating livers.

Long-Term Sustained Effect of Liver-Targeted Adeno-Associated Virus Gene Therapy for Mitochondrial Neurogastrointestinal Encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in TYMP, the gene encoding the enzyme thymidine phosphorylase (TP). TP dysfunction results in systemic accumulation of the noxious TP substrates thymidine and deoxyuridine. Gene therapy using either a lentiviral vector or adeno-associated vector (AAV) has proven to be a feasible strategy, as both vectors restore biochemical homeostasis in a murine model of the disease. This study shows that the effect of an AAV containing the TYMP coding sequence transcriptionally targeted to the liver persists long term in mice. Although the vector copy number was diluted and AAV-mediated liver TP activity eventually reduced or lost after 21 months at the lowest vector doses, the effect was sustained (with a negligible decrease in TP activity) and fully effective on nucleoside homeostasis for at least 21 months at a dose of 2 × 10¹² vg/kg. Macroscopic visual inspection of the animals' organs at completion of the study showed no adverse effects associated with the treatment. These results further support the feasibility of gene therapy for MNGIE.

Bioengineered AAV Capsids with Combined High Human Liver Transduction In Vivo and Unique Humoral Seroreactivity

Existing recombinant adeno-associated virus (rAAV) serotypes for delivering in vivo gene therapy treatments for human liver diseases have not yielded combined high-level human hepatocyte transduction and favorable humoral neutralization properties in diverse patient groups. Yet, these combined properties are important for therapeutic efficacy. To bioengineer capsids that exhibit both unique seroreactivity profiles and functionally transduce human hepatocytes at therapeutically relevant levels, we performed multiplexed sequential directed evolution screens using diverse capsid libraries in both primary human hepatocytes in vivo and with pooled human sera from thousands of patients. AAV libraries were subjected to five rounds of in vivo selection in xenografted mice with human livers to isolate an enriched human-hepatotropic library that was then used as input for a sequential on-bead screen against pooled human immunoglobulins. Evolved variants were vectorized and validated against existing hepatotropic serotypes. Two of the evolved AAV serotypes, NP40 and NP59, exhibited dramatically improved functional human hepatocyte transduction in vivo in xenografted mice with human livers, along with favorable human seroreactivity profiles, compared with existing serotypes. These novel capsids represent enhanced vector delivery systems for future human liver gene therapy applications.

An Inducible Promoter Responsive to Different Porphyrinogenic Stimuli Improves Gene Therapy Vectors for Acute Intermittent Porphyria

Porphobilinogen deaminase (PBGD) gene therapy represents a promising therapeutic option for acute intermittent porphyria (AIP) patients suffering recurrent acute attacks. A first-in-human Phase I clinical trial confirmed the safety and tolerability of adeno-associated virus (AAV)-AAT-PBGD gene therapy, but higher doses and/or more efficient vectors are needed to achieve therapeutic expression of the transgene. This study assayed the insertion into the promoter of a short enhancer element able to induce transgene expression during exposure to endogenous and exogenous stimuli related to the pathology of the disease. The inclusion in tandem of two elements of the minimal functional sequence of human δ-aminolevulinic acid synthase drug-responsive enhancing sequence (ADRES) positioned upstream of the promoter strongly induced transgene expression in the presence of estrogens, starvation, and certain drugs known to trigger attacks in porphyria patients. The inclusion of two ADRES motives in an AAV vector improved therapeutic efficacy, reducing 10-fold the effective dose in AIP mice. In conclusion, the inclusion of specific enhancer elements in the promoter of gene therapy vectors for AIP was able to overexpress the therapeutic transgene when it is most needed, at the time when porphyrinogenic factors increase the demand for hepatic heme and precipitate acute porphyria attacks.

Gene Therapy with BMN 270 Results in Therapeutic Levels of FVIII in Mice and Primates and Normalization of Bleeding in Hemophilic Mice

Hemophilia A is an X-linked bleeding disorder caused by mutations in the gene encoding the factor VIII (FVIII) coagulation protein. Bleeding episodes in patients are reduced by prophylactic therapy or treated acutely using recombinant or plasma-derived FVIII. We have made an adeno-associated virus 5 vector containing a B domain-deleted (BDD) FVIII gene (BMN 270) with a liver-specific promoter. BMN 270 injected into hemophilic mice resulted in a dose-dependent expression of BDD FVIII protein and a corresponding correction of bleeding time and blood loss. At the highest dose tested, complete correction was achieved. Similar corrections in bleeding were observed at approximately the same plasma levels of FVIII protein produced either endogenously by BMN 270 or following exogenous administration of recombinant BDD FVIII. No evidence of liver dysfunction or hepatocyte endoplasmic reticulum stress was observed. Comparable doses in primates produced similar levels of circulating FVIII. These preclinical data support evaluation of BMN 270 in hemophilia A patients.

Enhanced liver gene transfer and evasion of preexisting humoral immunity with exosome-enveloped AAV vectors

Results from clinical trials of liver gene transfer for hemophilia demonstrate the potential of the adeno-associated virus (AAV) vector platform. However, to achieve therapeutic transgene expression, in some cases high vector doses are required, which are associated with a higher risk of triggering anti-capsid cytotoxic T-cell responses. Additionally, anti-AAV preexisting immunity can prevent liver transduction even at low neutralizing antibody (NAb) titers. Here, we describe the use of exosome-associated AAV (exo-AAV) vectors as a robust liver gene delivery system that allows the therapeutic vector dose to be decreased while protecting from preexisting humoral immunity to the capsid. The in vivo efficiency of liver targeting of standard AAV8 or AAV5 and exo-AAV8 or exo-AAV5 vectors expressing human coagulation factor IX (hF.IX) was evaluated. A significant enhancement of transduction efficiency was observed, and in hemophilia B mice treated with 4 × 10¹⁰ vector genomes per kilogram of exo-AAV8 vectors, a staggering ∼1 log increase in hF.IX transgene expression was observed, leading to superior correction of clotting time. Enhanced liver expression was also associated with an increase in the frequency of regulatory T cells in lymph nodes. The efficiency of exo- and standard AAV8 vectors in evading preexisting NAbs to the capsid was then evaluated in a passive immunization mouse model and in human sera. Exo-AAV8 gene delivery allowed for efficient transduction even in the presence of moderate NAb titers, thus potentially extending the proportion of subjects eligible for liver gene transfer. Exo-AAV vectors therefore represent a platform to improve the safety and efficacy of liver-directed gene transfer.

Stent-based delivery of adeno-associated viral vectors with sustained vascular transduction and iNOS-mediated inhibition of in-stent restenosis

In-stent restenosis remains an important clinical problem in the era of drug eluting stents. Development of clinical gene therapy protocols for the prevention and treatment of in-stent restenosis is hampered by the lack of adequate local delivery systems. Herein we describe a novel stent-based gene delivery platform capable of providing local arterial gene transfer with adeno-associated viral (AAV) vectors. This system exploits the natural affinity of protein G (PrG) to bind to the Fc region of mammalian IgG, making PrG a universal adaptor for surface immobilization of vector-capturing antibodies (Ab). Our results: 1) demonstrate the feasibility of reversible immobilization of AAV2 vectors using vector tethering by AAV2-specific Ab appended to the stent surface through covalently attached PrG, 2) show sustained release kinetics of PrG/Ab-immobilized AAV2 vector particles into simulated physiological medium in vitro and site-specific transduction of cultured cells, 3) provide evidence of long-term (12 weeks) arterial expression of luciferase with PrG/Ab-tethered AAV2_Luc, and 4) show anti-proliferative activity and anti-restenotic efficacy of stent-immobilized AAV2_iNOS in the rat carotid artery model of stent angioplasty.

Non-clinical Safety and Efficacy of an AAV2/8 Vector Administered Intravenously for Treatment of Mucopolysaccharidosis Type VI

In vivo gene therapy with adeno-associated viral (AAV) vectors is safe and effective in humans. We recently demonstrated that AAV8-mediated liver gene transfer is effective in animal models of mucopolysaccharidosis type VI (MPS VI), a rare lysosomal storage disease that is caused by arylsulfatase B (ARSB) deficiency. In preparing for a first-in-human trial, we performed non-clinical studies to assess the safety of intravenous administrations of AAV2/8.TBG.hARSB produced under good manufacturing practice-like conditions. No toxicity was observed in AAV-treated mice, except for a transient increase in alanine aminotransferase in females and thyroid epithelial hypertrophy. AAV2/8.TBG.hARSB biodistribution and expression confirmed the liver as the main site of both infection and transduction. Shedding and breeding studies suggest that the risk of both horizontal and germline transmission is minimal. An AAV dose-response study in MPS VI mice was performed to define the range of doses to be used in the clinical study. Overall, these data support the non-clinical safety and efficacy of AAV2/8.TBG.hARSB and pave the way for a phase I/II clinical trial based on intravascular infusions of AAV8 in patients with MPS VI.

Successful Repeated Hepatic Gene Delivery in Mice and Non-human Primates Achieved by Sequential Administration of AAV5ch and AAV1

In the gene therapy field, re-administration of adeno-associated virus (AAV) is an important topic because a decrease in therapeutic protein expression might occur over time. However, an efficient re-administration with the same AAV serotype is impossible due to serotype-specific, anti-AAV neutralizing antibodies (NABs) that are produced after initial AAV treatment. To address this issue, we explored the feasibility of using chimeric AAV serotype 5 (AAV5^ch) and AAV1 for repeated liver-targeted gene delivery. To develop a relevant model, we immunized animals with a high dose of AAV5^ch-human secreted embryonic alkaline phosphatase (hSEAP) that generates high levels of anti-AAV5^ch NAB. Secondary liver transduction with the same dose of AAV1-human factor IX (hFIX) in the presence of high levels of anti-AAV5^ch NAB proved to be successful because expression/activity of both reporter transgenes was observed. This is the first time that two different transgenes are shown to be produced by non-human primate (NHP) liver after sequential administration of clinically relevant doses of both AAV5^ch and AAV1. The levels of transgene proteins achieved after delivery with AAV5^ch and AAV1 illustrate the possibility of both serotypes for liver targeting. Furthermore, transgene DNA and RNA biodistribution patterns provided insight into the potential cause of decrease or loss of transgene protein expression over time in NHPs.

Emerging therapies for acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant metabolic disease caused by hepatic deficiency of hydroxymethylbilane synthase (HMBS), the third enzyme of the heme synthesis pathway. The dominant clinical feature is acute neurovisceral attack associated with high production of potentially neurotoxic porphyrin precursors due to increased hepatic heme consumption. Current Standard of Care is based on a down-regulation of hepatic heme synthesis using heme therapy. Recurrent hyper-activation of the hepatic heme synthesis pathway affects about 5% of patients and can be associated with neurological and metabolic manifestations and long-term complications including chronic kidney disease and increased risk of hepatocellular carcinoma. Prophylactic heme infusion is an effective strategy in some of these patients, but it induces tolerance and its frequent application may be associated with thromboembolic disease and hepatic siderosis. Orthotopic liver transplantation is the only curative treatment in patients with recurrent acute attacks. Emerging therapies including replacement enzyme therapy or gene therapies (HMBS-gene transfer and ALAS1-gene expression inhibition) are being developed to improve quality of life, reduce the significant morbidity associated with current therapies and prevent late complications such as hepatocellular cancer or kidney failure in HMBS mutation carriers with long-standing high production of noxious heme precursors. Herein, we provide a critical digest of the recent literature on the topic and a summary of recently developed approaches to AIP treatment and their clinical implications.