Phase 2 clinical trial of a recombinant adeno-associated viral vector expressing α1-antitrypsin: interim results

AAV-Mediated Gene Therapy for Research and Therapeutic Purposes

Adeno-associated virus (AAV) is a small, nonenveloped virus that was adapted 30 years ago for use as a gene transfer vehicle. It is capable of transducing a wide range of species and tissues in vivo with no evidence of toxicity, and it generates relatively mild innate and adaptive immune responses. We review the basic biology of AAV, the history of progress in AAV vector technology, and some of the clinical and research applications where AAV has shown success.

Cell-Mediated Immunity to AAV Vectors, Evolving Concepts and Potential Solutions

Adeno-associated virus (AAV) vectors are one of the most efficient in vivo gene delivery platforms. Over the past decade, clinical trials of AAV vector-mediated gene transfer led to some of the most exciting results in the field of gene therapy and, recently, to the market approval of an AAV-based drug in Europe. With clinical development, however, it became obvious that the host immune system represents an important obstacle to successful gene transfer with AAV vectors. In this review article, we will discuss the issue of cytotoxic T cell responses directed against the AAV capsid encountered on human studies. While over the past several years the field has acquired a tremendous amount of information on the interactions of AAV vectors with the immune system, a lot of questions are still unanswered. Novel concepts are emerging, such as the relationship between the total capsid dose and the T cell-mediated clearance of transduced cells, the potential role of innate immunity in vector immunogenicity highlighted in preclinical studies, and the cross talk between regulatory and effector T cells in the determination of the outcome of gene transfer. There is still a lot to learn about immune responses in AAV gene transfer, for example, it is not well understood what are the determinants of the kinetics of activation of T cells in response to vector administration, why not all subjects develop detrimental T cell responses following gene transfer, and whether the intervention strategies currently in use to block T cell-mediated clearance of transduced cells will be safe and effective for all gene therapy indications. Results from novel preclinical models and clinical studies will help to address these points and to reach the important goal of developing safe and effective gene therapy protocols to treat human diseases.

Alpha-1 antitrypsin deficiency: new developments in augmentation and other therapies

Alpha 1 antitrypsin deficiency (AATD) is a rare cause of chronic obstructive pulmonary disease. The lung disease is thought to be caused primarily by a lack of effective protection against the harmful effects of neutrophil elastase due to the low AAT levels in the lung. Patients may also develop liver disease due to polymerisation of AAT within hepatocytes. Consequently there has been much research over the years into AAT augmentation therapy in patients with lung disease, initially intravenously, and more recently in inhaled forms. This review article will discuss the role of augmentation therapy in AATD and the current status of recombinant AAT. The potential for other therapeutic strategies, such as blocking polymer formation, enhancing autophagy, gene therapy and stem cell-based treatment, will also be discussed more briefly.

Cellular unfolded protein response against viruses used in gene therapy

Viruses are excellent vehicles for gene therapy due to their natural ability to infect and deliver the cargo to specific tissues with high efficiency. Although such vectors are usually "gutted" and are replication defective, they are subjected to clearance by the host cells by immune recognition and destruction. Unfolded protein response (UPR) is a naturally evolved cyto-protective signaling pathway which is triggered due to endoplasmic reticulum (ER) stress caused by accumulation of unfolded/misfolded proteins in its lumen. The UPR signaling consists of three signaling pathways, namely PKR-like ER kinase, activating transcription factor 6, and inositol-requiring protein-1. Once activated, UPR triggers the production of ER molecular chaperones and stress response proteins to help reduce the protein load within the ER. This occurs by degradation of the misfolded proteins and ensues in the arrest of protein translation machinery. If the burden of protein load in ER is beyond its processing capacity, UPR can activate pro-apoptotic pathways or autophagy leading to cell death. Viruses are naturally evolved in hijacking the host cellular translation machinery to generate a large amount of proteins. This phenomenon disrupts ER homeostasis and leads to ER stress. Alternatively, in the case of gutted vectors used in gene therapy, the excess load of recombinant vectors administered and encountered by the cell can trigger UPR. Thus, in the context of gene therapy, UPR becomes a major roadblock that can potentially trigger inflammatory responses against the vectors and reduce the efficiency of gene transfer.

Comparative next-generation sequencing of adeno-associated virus inverted terminal repeats

The inverted terminal repeats (ITRs) of adeno-associated virus (AAV) are notoriously difficult to sequence owing to their high GC-content (70%) and palindromic sequences that result in the formation of a very stable, 125 bp long, T-shaped hairpin structure. Here we evaluate the performance of two widely used next-generation sequencing platforms, 454 GS FLX (Roche) and MiSeq Benchtop Sequencer (Illumina), in analyzing ITRs in comparatively sequencing linear amplification-meditated PCR (LAM-PCR) amplicons derived from AAV-concatemeric structures. While our data indicate that both platforms can sequence complete ITRs, efficiencies (MiSeq: 0.11% of sequence reads; 454: 0.02% of reads), frequencies (MiSeq: 171 full ITRs, 454: 3 full ITRs), and rates of deviation from the derived ITR consensus sequence (MiSeq: 0.8%–1.3%; 454: 0.5%) did differ. These results suggest that next-generation sequencing platforms can be used to specifically detect ITR mutations and sequence complete ITRs.

Sustained normalization of neurological disease after intracranial gene therapy in a feline model

Progressive debilitating neurological defects characterize feline G(M1) gangliosidosis, a lysosomal storage disease caused by deficiency of lysosomal β-galactosidase. No effective therapy exists for affected children, who often die before age 5 years. An adeno-associated viral vector carrying the therapeutic gene was injected bilaterally into two brain targets (thalamus and deep cerebellar nuclei) of a feline model of G(M1) gangliosidosis. Gene therapy normalized β-galactosidase activity and storage throughout the brain and spinal cord. The mean survival of 12 treated G(M1) animals was >38 months, compared to 8 months for untreated animals. Seven of the eight treated animals remaining alive demonstrated normalization of disease, with abrogation of many symptoms including gait deficits and postural imbalance. Sustained correction of the G(M1) gangliosidosis disease phenotype after limited intracranial targeting by gene therapy in a large animal model suggests that this approach may be useful for treating the human version of this lysosomal storage disorder.

Intravenous adeno-associated virus serotype 8 encoding urocortin-2 provides sustained augmentation of left ventricular function in mice

Urocortin-2 (UCn2) peptide infusion increases cardiac function in patients with heart failure, but chronic peptide infusion is cumbersome, costly, and provides only short-term benefits. Gene transfer would circumvent these shortcomings. Here we ask whether a single intravenous injection of adeno-associated virus type 8 encoding murine urocortin-2 (AAV8.UCn2) could provide long-term elevation in plasma UCn2 levels and increased left ventricular (LV) function. Normal mice received AAV8.UCn2 (5×10¹¹ genome copies, intravenous). Plasma UCn2 increased 15-fold 6 weeks and >11-fold 7 months after delivery. AAV8 DNA and UCn2 mRNA expression was persistent in LV and liver up to 7 months after a single intravenous injection of AAV8.UCn2. Physiological studies conducted both in situ and ex vivo showed increases in LV +dP/dt and in LV -dP/dt, findings that endured unchanged for 7 months. SERCA2a mRNA and protein expression was increased in LV samples and Ca²⁺ transient studies showed an increased rate of Ca²⁺ decline in cardiac myocytes from mice that had received UCn2 gene transfer. We conclude that a single intravenous injection of AAV8.UCn2 increases plasma UCn2 and increases LV systolic and diastolic function for at least 7 months. The simplicity of intravenous injection of a long-term expression vector encoding a gene with paracrine activity to increase cardiac function is a potentially attractive strategy in clinical settings. Future studies will determine the usefulness of this approach in the treatment of heart failure.

Attenuation of monocrotaline-induced pulmonary hypertension by luminal adeno-associated virus serotype 9 gene transfer of prostacyclin synthase

Idiopathic pulmonary arterial hypertension (iPAH) is associated with high morbidity and mortality. We evaluated whether luminal delivery of the human prostacyclin synthase (hPGIS) cDNA with adeno-associated virus (AAV) vectors could attenuate PAH. AAV serotype 5 (AAV5) and AAV9 vectors containing the hPGIS cDNA under the control of a cytomegalovirus-enhanced chicken β-actin (CB) promoter or vehicle (saline) were instilled into lungs of rats. Two days later, rats were injected with monocrotaline (MCT, 60 mg/kg) or saline. Biochemical, hemodynamic, and morphologic assessments were performed when the rats developed symptoms (3-4 weeks) or at 6 weeks. Luminal (airway) administration of AAV5 and AAV9CBhPGIS vectors (MCT-AAV5 and MCT-AAV9 rats) significantly increased plasma levels of 6-keto-PGF1(α) as compared with MCT-controls, and closely resembled levels measured in rats not treated with MCT (saline-saline). Right ventricular (RV)/left ventricular (LV)+septum (S) ratios and RV systolic pressure (RVSP) were greater in MCT-control rats than in saline-saline rats, whereas the ratios and RVSP in MCT-AAV5CBhPGIS and MCT-AAV9CBhPGIS rats were similar to saline-saline rats. Thickening of the muscular media of small pulmonary arteries of MCT-control rats was detected in histological sections, whereas the thickness of the muscular media in MCT-AAV5CBhPGIS and MCT-AAV9CBhPGIS rats was similar to saline-saline controls. In experiments with different promoters, a trend toward increased levels of PGF1(α) expression was detected in lung homogenates, but not plasma, of MCT-treated rats transduced with an AAV9-hPGIS vector containing a CB promoter. This correlated with significant reductions in the RV/LV+S ratio and RVSP in MCT-AAV9CBhPGIS rats that resembled levels in saline-saline rats. No changes in levels of PGF1(α), RV/LV+S, or RVSP were detected in rats transduced with AAV9-hPGIS vectors containing a modified CB promoter (CB7) or a distal epithelial cell-specific promoter (CC10). Thus, AAV9CBhPGIS vectors prevented development of MCT-induced PAH and associated pulmonary vascular remodeling.

The potential of adeno-associated viral vectors for gene delivery to muscle tissue

INTRODUCTION

Muscle-directed gene therapy is rapidly gaining attention primarily because muscle is an easily accessible target tissue and is also associated with various severe genetic disorders. Localized and systemic delivery of recombinant adeno-associated virus (rAAV) vectors of several serotypes results in very efficient transduction of skeletal and cardiac muscles, which has been achieved in both small and large animals, as well as in humans. Muscle is the target tissue in gene therapy for many muscular dystrophy diseases, and may also be exploited as a biofactory to produce secretory factors for systemic disorders. Current limitations of using rAAVs for muscle gene transfer include vector size restriction, potential safety concerns such as off-target toxicity and the immunological barrier composing of pre-existing neutralizing antibodies and CD8(+) T-cell response against AAV capsid in humans.

AREAS COVERED

In this article, we will discuss basic AAV vector biology and its application in muscle-directed gene delivery, as well as potential strategies to overcome the aforementioned limitations of rAAV for further clinical application.

EXPERT OPINION

Delivering therapeutic genes to large muscle mass in humans is arguably the most urgent unmet demand in treating diseases affecting muscle tissues throughout the whole body. Muscle-directed, rAAV-mediated gene transfer for expressing antibodies is a promising strategy to combat deadly infectious diseases. Developing strategies to circumvent the immune response following rAAV administration in humans will facilitate clinical application.

Immune responses to intramuscular administration of alipogene tiparvovec (AAV1-LPL(S447X)) in a phase II clinical trial of lipoprotein lipase deficiency gene therapy

Cellular immune responses to adeno-associated viral (AAV) vectors used for gene therapy have been linked to attenuated transgene expression and loss of efficacy. The impact of such cellular immune responses on the clinical efficacy of alipogene tiparvovec (Glybera; AAV1-LPL(S447X); uniQure), a gene therapy consisting of intramuscular administration of a recombinant AAV1 mediating muscle-directed expression of lipoprotein lipase (LPL), was investigated. Five subjects with LPL deficiency (LPLD) were administered intramuscularly with a dose of 1 × 10(12) gc/kg alipogene tiparvovec. All subjects were treated with immune suppression starting shortly before administration of alipogene tiparvovec and maintained until 12 weeks after administration. Systemic antibody and T cell responses against AAV1 and LPL(S447X), as well as local cellular immune responses in the injected muscle, were investigated in five LPLD subjects. Long-term transgene expression was demonstrated despite a transient systemic cellular response and a stable humoral immune response against the AAV1 capsid protein. Cellular infiltrates were found in four of the five subjects but were not associated with adverse clinical events or elevation of inflammation markers. Consistent herewith, CD8+ T cells in the infiltrates lacked cytotoxic potential. Furthermore, FoxP3+/CD4+ T cells were found in the infiltrates, suggesting that multiple mechanisms contribute to local tolerance. Systemic and local immune responses induced by intramuscular injection of alipogene tiparvovec did not appear to have an impact on safety and did not prevent LPL transgene expression. These findings support the use of alipogene tiparvovec in individuals with LPLD and indicate that muscle-directed AAV-based gene therapy remains a promising approach for the treatment of human diseases.

Plasmapheresis eliminates the negative impact of AAV antibodies on microdystrophin gene expression following vascular delivery

Duchenne muscular dystrophy is a monogenic disease potentially treatable by gene replacement. Use of recombinant adeno-associated virus (AAV) will ultimately require a vascular approach to broadly transduce muscle cells. We tested the impact of preexisting AAV antibodies on microdystrophin expression following vascular delivery to nonhuman primates. Rhesus macaques were treated by isolated limb perfusion using a fluoroscopically guided catheter. In addition to serostatus stratification, the animals were placed into one of the three immune suppression groups: no immune suppression, prednisone, and triple immune suppression (prednisone, tacrolimus, and mycophenolate mofetil). The animals were analyzed for transgene expression at 3 or 6 months. Microdystrophin expression was visualized in AAV, rhesus serotype 74 sero-negative animals (mean: 48.0 ± 20.8%) that was attenuated in sero-positive animals (19.6 ± 18.7%). Immunosuppression did not affect transgene expression. Importantly, removal of AAV binding antibodies by plasmapheresis in AAV sero-positive animals resulted in high-level transduction (60.8 ± 18.0%), which is comparable with that of AAV sero-negative animals (53.7 ± 7.6%), whereas non-pheresed sero-positive animals demonstrated significantly lower transduction levels (10.1 ± 6.0%). These data support the hypothesis that removal of AAV binding antibodies by plasmapheresis permits successful and sustained gene transfer in the presence of preexisting immunity (natural infection) to AAV.

Passive immunization against HIV/AIDS by antibody gene transfer

Despite tremendous efforts over the course of many years, the quest for an effective HIV vaccine by the classical method of active immunization remains largely elusive. However, two recent studies in mice and macaques have now demonstrated a new strategy designated as Vectored ImmunoProphylaxis (VIP), which involves passive immunization by viral vector-mediated delivery of genes encoding broadly neutralizing antibodies (bnAbs) for in vivo expression. Robust protection against virus infection was observed in preclinical settings when animals were given VIP to express monoclonal neutralizing antibodies. This unorthodox approach raises new promise for combating the ongoing global HIV pandemic. In this article, we survey the status of antibody gene transfer, review the revolutionary progress on isolation of extremely bnAbs, detail VIP experiments against HIV and its related virus conduced in humanized mice and macaque monkeys, and discuss the pros and cons of VIP and its opportunities and challenges towards clinical applications to control HIV/AIDS endemics.

Role of the vector genome and underlying factor IX mutation in immune responses to AAV gene therapy for hemophilia B

Background

Self-complementary adeno-associated virus (scAAV) vectors have become a desirable vector for therapeutic gene transfer due to their ability to produce greater levels of transgene than single-stranded AAV (ssAAV). However, recent reports have suggested that scAAV vectors are more immunogenic than ssAAV. In this study, we investigated the effects of a self-complementary genome during gene therapy with a therapeutic protein, human factor IX (hF.IX).

Methods

Hemophilia B mice were injected intramuscularly with ss or scAAV1 vectors expressing hF.IX. The outcome of gene transfer was assessed, including transgene expression as well as antibody and CD8⁺ T cell responses to hF.IX.

Results

Self-complementary AAV1 vectors induced similar antibody responses (which eliminated systemic hF.IX expression) but stronger CD8⁺ T cell responses to hF.IX relative to ssAAV1 in mice with F9 gene deletion. As a result, hF.IX-expressing muscle fibers were effectively eliminated in scAAV-treated mice. In contrast, mice with F9 nonsense mutation (late stop codon) lacked antibody or T cell responses, thus showing long-term expression regardless of the vector genome.

Conclusions

The nature of the AAV genome can impact the CD8⁺ T cell response to the therapeutic transgene product. In mice with endogenous hF.IX expression, however, this enhanced immunogenicity did not break tolerance to hF.IX, suggesting that the underlying mutation is a more important risk factor for transgene-specific immunity than the molecular form of the AAV genome.

α-1-Antitrypsin deficiency: clinical variability, assessment, and treatment

The recognition of α-1-antitrypsin deficiency, its function, and its role in predisposition to the development of severe emphysema was a watershed in our understanding of the pathophysiology of the condition. This led to the concept and development of intravenous replacement therapy used worldwide to protect against lung damage induced by neutrophil elastase. Nevertheless, much remained unknown about the deficiency and its impact, although in recent years the genetic and clinical variations in manifestation have provided new insights into assessing impact, efficacy of therapy, and development of new therapeutic strategies, including gene therapy, and outcome measures, such as biomarkers and computed tomography. The current article reviews this progress over the preceding 50 years.

Reprogramming adipose tissue-derived mesenchymal stem cells into pluripotent stem cells by a mutant adeno-associated viral vector

Induced pluripotent stem (iPS) cells have great potential for personalized regenerative medicine. Although several different methods for generating iPS cells have been reported, improvement of safety and efficiency is imperative. In this study, we tested the feasibility of using a triple tyrosine mutant AAV2 (Y444+500+730F) vector, designated AAV2.3m, to generate iPS cells. We developed a polycistronic rAAV2.3m vector expressing three reprogramming factors, Klf4, Oct4, and Sox2, and then used this vector to infect mouse adipose-derived mesenchymal stem cells (AT-MSCs) to induce the generation of iPS cells. We demonstrated that (1) the triple tyrosine mutant AAV2 vector is able to reprogram mouse adult adipose tissue-derived stem cells into the pluripotent state. Those rAAV2.3m-derived iPS (rAAV2.3m-iPS) cells express endogenous pluripotency-associated genes including Oct4, Sox2, and SSEA-1, and form teratomas containing multiple tissues in vivo; (2) c-myc, an oncogene, is dispensable in rAAV2.3m-mediated cellular reprogramming; and (3) transgene expression is undetectable after reprogramming, whereas vector DNA is detectable, indicating that transgenes are silenced. These results indicated the rAAV vector may have some advantages in generating iPS cells.

Intranasal antibody gene transfer in mice and ferrets elicits broad protection against pandemic influenza

The emergence of a new influenza pandemic remains a threat that could result in a substantial loss of life and economic disruption worldwide. Advances in human antibody isolation have led to the discovery of monoclonal antibodies (mAbs) that have broad neutralizing activity against various influenza strains, although their direct use for prophylaxis is impractical. To overcome this limitation, our approach is to deliver antibody via adeno-associated virus (AAV) vectors to the site of initial infection, which, for respiratory viruses such as influenza, is the nasopharyngeal mucosa. AAV vectors based on serotype 9 were engineered to express a modified version of the previously isolated broadly neutralizing mAb to influenza A, FI6. We demonstrate that intranasal delivery of AAV9.FI6 into mice afforded complete protection and log reductions in viral load to 100 LD₅₀ (median lethal dose) of three clinical isolates of H5N1 and two clinical isolates of H1N1, all of which have been associated with historic human pandemics (including H1N1 1918). Similarly, complete protection was achieved in ferrets challenged with lethal doses of H5N1 and H1N1. This approach serves as a platform for the prevention of natural or deliberate respiratory diseases for which a protective antibody is available.

Safety profile of recombinant adeno-associated viral vectors: focus on alipogene tiparvovec (Glybera®)

There has been great interest over the past two decades in developing gene therapies (GTs) to treat a variety of diseases; however, translating research findings into clinical treatments have proved to be a challenge. A major milestone in the development of GT has been achieved with the approval of alipogene tiparvovec (Glybera(®)) in Europe for the treatment of familial lipoprotein lipase deficiency. At this important stage with the evolution of GT into the clinic, this review will examine the safety aspects GT with adeno-associated virus (AAV) vectors. The topics that will be covered include acute reactions, immunological reactions to the AAV capsid and expressed transgene, viral biodistribution and shedding, DNA integration and carcinogenicity. These safety aspects of GT will be discussed with a focus on alipogene tiparvovec, in addition to other AAV vector GT products currently in clinical development.

Human Treg responses allow sustained recombinant adeno-associated virus-mediated transgene expression

Recombinant adeno-associated virus (rAAV) vectors have shown promise for the treatment of several diseases; however, immune-mediated elimination of transduced cells has been suggested to limit and account for a loss of efficacy. To determine whether rAAV vector expression can persist long term, we administered rAAV vectors expressing normal, M-type α-1 antitrypsin (M-AAT) to AAT-deficient subjects at various doses by multiple i.m. injections. M-specific AAT expression was observed in all subjects in a dose-dependent manner and was sustained for more than 1 year in the absence of immune suppression. Muscle biopsies at 1 year had sustained AAT expression and a reduction of inflammatory cells compared with 3 month biopsies. Deep sequencing of the TCR Vβ region from muscle biopsies demonstrated a limited number of T cell clones that emerged at 3 months after vector administration and persisted for 1 year. In situ immunophenotyping revealed a substantial Treg population in muscle biopsy samples containing AAT-expressing myofibers. Approximately 10% of all T cells in muscle were natural Tregs, which were activated in response to AAV capsid. These results suggest that i.m. delivery of rAAV type 1-AAT (rAAV1-AAT) induces a T regulatory response that allows ongoing transgene expression and indicates that immunomodulatory treatments may not be necessary for rAAV-mediated gene therapy.

Neutrophil elastase-mediated lung disease

Elastases of both the neutrophil and macrophage have been implicated in lung disease initiation and progression. Although it is unlikely that these proteases evolved for the purpose of injuring lung tissue, the elastin-rich connective tissue framework of the lungs appears to be particularly susceptible to the action of elastolytic proteases. Assuming that neutrophil elastase most likely plays a role in the migration of neutrophils toward a site of inflammation and degradation of proteins from invading organisms or other products of the inflammatory response, it is the role of inhibitors of this protease to protect normal tissues from its effects. In alpha-1 antitrypsin deficiency we find an experiment of nature that disrupts this protease-anti-protease balance, resulting in an increased risk of destructive lung disease.

Humoral Immune Response to AAV

Adeno-associated virus (AAV) is a member of the family Parvoviridae that has been widely used as a vector for gene therapy because of its safety profile, its ability to transduce both dividing and non-dividing cells, and its low immunogenicity. AAV has been detected in many different tissues of several animal species but has not been associated with any disease. As a result of natural infections, antibodies to AAV can be found in many animals including humans. It has been shown that pre-existing AAV antibodies can modulate the safety and efficacy of AAV vector-mediated gene therapy by blocking vector transduction or by redirecting distribution of AAV vectors to tissues other than the target organ. This review will summarize antibody responses against natural AAV infections, as well as AAV gene therapy vectors and their impact in the clinical development of AAV vectors for gene therapy. We will also review and discuss the various methods used for AAV antibody detection and strategies to overcome neutralizing antibodies in AAV-mediated gene therapy.

A reliable and feasible qPCR strategy for titrating AAV vectors

BACKGROUND

Previous studies have revealed that traditional real-time quantitative PCR (qPCR) underestimates adeno-associated virus (AAV) titer. Because the inverted terminal repeat (ITR) exists in all AAV vectors, the only remaining element from the wild genome could form special configurations to interfere with qPCR titration. To solve this problem, a modified and universal qPCR method was tested and established.

MATERIAL AND METHODS

In this work, there was a great variation in titration of ssAAV2-EGFP (Enhanced Green Fluorescence Protein) and scAAV2-EGFP genome by traditional qPCR. For ssAAV2-EGFP, the highest titer was found by using the targeting EGFP primers and the lowest titer was measured by those targeting bovine growth hormone polyA element (pBGH) primers.

RESULTS

Experimental data were reverse for ssAAV2-EGFP and scAAV2-EGFP. Here we report an improved and universal SmaI qPCR method, based on cleaving all ITRs in AAV2 genome by SmaI with several advantages: (1) impact of all ITRs in ssAAV2 and scAAV2 was dismissed; (2) titers increased remarkably, up to 7-fold, especially for scAAV2; (3) the variation of titers was reduced when different primers were applied. A similar phenomenon was also observed in other ssAAV2 and scAAV2 products when the range of titration was at 3×107 to 7×109 V.G/µl in this study.

CONCLUSIONS

This modified qPCR strategy can increase rAAV' titer and reduce titration variance, possibly become a universal method for titrating AAV vectors.

CpG-depleted adeno-associated virus vectors evade immune detection

Due to their efficient transduction potential, adeno-associated virus (AAV) vectors are leading candidates for gene therapy in skeletal muscle diseases. However, immune responses toward the vector or transgene product have been observed in preclinical and clinical studies. TLR9 has been implicated in promoting AAV-directed immune responses, but vectors have not been developed to circumvent this barrier. To assess the requirement of TLR9 in promoting immunity toward AAV-associated antigens following skeletal muscle gene transfer in mice, we compared immunological responses in WT and Tlr9-deficient mice that received an AAV vector with an immunogenic capsid, AAVrh32.33. In Tlr9-deficient mice, IFN-γ T cell responses toward capsid and transgene antigen were suppressed, resulting in minimal cellular infiltrate and stable transgene expression in target muscles. These findings suggest that AAV-directed immune responses may be circumvented by depleting the ligand for TLR9 (CpG sequences) from the vector genome. Indeed, we found that CpG-depleted AAVrh32.33 vectors could establish persistent transgene expression, evade immunity, and minimize infiltration of effector cells. Thus, CpG-depleted AAV vectors could improve outcome of clinical trials of gene therapy for skeletal muscle disease.

Multi-compartmental oral delivery systems for nucleic acid therapy in the gastrointestinal tract

Gene and RNA interference therapies have significant potential for alleviating countless diseases, including many associated with the gastro-intestinal (GI) tract. Unfortunately, oral delivery of genes and small interfering RNA (siRNA) is very challenging due to the extracellular and intracellular barriers. In this review, we discuss the utilization of multi-compartmental delivery systems for oral administration of nucleic acid therapies. Some of the illustrative examples of multi-compartmental systems include solid nanoparticles-in-microsphere, solid nanoparticles-in-emulsion, and liquid nanoparticles-in-emulsion. Using type B gelatin nanoparticles encapsulated in poly(ε-caprolactone) microspheres, we have prepared nanoparticles-in-microsphere oral system (NiMOS) for gene and siRNA delivery for the treatment of inflammatory bowel disease (IBD). The results of these studies show that the multi-compartmental formulations can overcome many of the barriers for effective oral gene and siRNA delivery.

Suppression of lymph node and lung metastases of endometrial cancer by muscle-mediated expression of soluble vascular endothelial growth factor receptor-3

Lymph node metastasis is the most important prognostic factor of endometrial cancer. However, effective therapy has not been established against lymph node metastasis. In this study, we explored the efficacy of gene therapy targeting lymph node metastasis of endometrial cancer by suppressing the action of vascular endothelial growth factor (VEGF)-C through soluble VEGF receptor-3 (sVEGFR-3) expression. For this purpose, we first conducted a model experiment by introducing sVEGFR-3 cDNA into an endometrial cancer cell line HEC1A and established HEC1A/sVEGFR-3 cell line with high sVEGFR-3 expression. The conditioned medium of HEC1A/sVEGFR-3 cells inhibited lymphatic endothelial cell growth in vitro, and sVEGFR-3 expression in HEC1A cells suppressed in vivo lymph node and lung metastases without inhibiting the growth of a subcutaneously inoculated tumor. To validate the therapeutic efficacy, adeno-associated virus vectors encoding sVEGFR-3 were injected into the skeletal muscle of mice with lymph node metastasis. Lymph node and lung metastases of HEC1A cells were completely suppressed by the muscle-mediated expression of sVEGFR-3 using adeno-associated virus vectors. These results suggest the possibility of gene therapy against lymph node and lung metastases of endometrial cancer by using muscle-mediated expression of sVEGFR-3.

Environment acidity triggers release of recombinant adeno-associated virus serotype 2 from a tunable matrix

Successful design of a pH responsive polyelectrolyte-based virus delivery matrix with extracellular release triggered by tumor acidosis has been achieved. Recombinant adeno-associated virus serotype 2 (AAV2) is loaded in the polyelectrolyte-based matrix (AAV2-matrix), which is formed by a biodegradable copolymer of poly(polyethylene glycol-1-(3-aminopropyl)imidazole-dl-aspartic acid) with tuned pH response based on inclusion of polyethyleneimine (PEI(800)). Physico-chemical properties of AAV2-matrix are optimized to minimize cellular interactions until a tumor acidosis-like environment protonates the matrix, reverses ζ-potential and causes particles to swell, releasing the AAV2 virus. The pH-dependent release is highly controllable and potentially useful to optimize site specific viral delivery.

Optical inhibition of motor nerve and muscle activity in vivo

INTRODUCTION

There is no therapeutic approach that provides precise and rapidly reversible inhibition of motor nerve and muscle activity for treatment of spastic hypertonia.

METHODS

We used optogenetics to demonstrate precise and rapidly reversible light-mediated inhibition of motor nerve and muscle activity in vivo in transgenic Thy1::eNpHR2.0 mice.

RESULTS

We found optical inhibition of motor nerve and muscle activity to be effective at all muscle force amplitudes and determined that muscle activity can be modulated by changing light pulse duration and light power density.

CONCLUSIONS

This demonstration of optical inhibition of motor nerves is an important advancement toward novel optogenetics-based therapies for spastic hypertonia.

Transgenic models of Alzheimer's disease: better utilization of existing models through viral transgenesis

Animal models have been used for decades in the Alzheimer's disease (AD) research field and have been crucial for the advancement of our understanding of the disease. Most models are based on familial AD mutations of genes involved in the amyloidogenic process, such as the amyloid precursor protein (APP) and presenilin 1 (PS1). Some models also incorporate mutations in tau (MAPT) known to cause frontotemporal dementia, a neurodegenerative disease that shares some elements of neuropathology with AD. While these models are complex, they fail to display pathology that perfectly recapitulates that of the human disease. Unfortunately, this level of pre-existing complexity creates a barrier to the further modification and improvement of these models. However, as the efficacy and safety of viral vectors improves, their use as an alternative to germline genetic modification is becoming a widely used research tool. In this review we discuss how this approach can be used to better utilize common mouse models in AD research. This article is part of a Special Issue entitled: Animal Models of Disease.

Immune responses to AAV vectors: overcoming barriers to successful gene therapy

Gene therapy products for the treatment of genetic diseases are currently in clinical trials, and one of these, an adeno-associated viral (AAV) product, has recently been licensed. AAV vectors have achieved positive results in a number of clinical and preclinical settings, including hematologic disorders such as the hemophilias, Gaucher disease, hemochromatosis, and the porphyrias. Because AAV vectors are administered directly to the patient, the likelihood of a host immune response is high, as shown by human studies. Preexisting and/or recall responses to the wild-type virus from which the vector is engineered, or to the transgene product itself, can interfere with therapeutic efficacy if not identified and managed optimally. Small-scale clinical studies have enabled investigators to dissect the immune responses to the AAV vector capsid and to the transgene product, and to develop strategies to manage these responses to achieve long-term expression of the therapeutic gene. However, a comprehensive understanding of the determinants of immunogenicity of AAV vectors, and of potential associated toxicities, is still lacking. Careful immunosurveillance conducted as part of ongoing clinical studies will provide the basis for understanding the intricacies of the immune response in AAV-mediated gene transfer, facilitating safe and effective therapies for genetic diseases.

Pre-existing anti-adeno-associated virus antibodies as a challenge in AAV gene therapy

Adeno-associated virus (AAV)-based vectors are promising tools for gene therapeutic applications, in part because AAVs are nonpathogenic viruses, and vectors derived from them can drive long-term transgene expression without integration of the vector DNA into the host genome. AAVs are not strongly immunogenic, but they can, nonetheless, give rise to both a cellular and humoral immune response. As a result, a significant fraction of potential patients for AAV-based gene therapy harbors pre-existing antibodies against AAV. Because even very low levels of antibodies can prevent successful transduction, antecedent anti-AAV antibodies pose a serious obstacle to the universal application of AAV gene therapy. In this review, we discuss the current knowledge of the role of anti-AAV antibodies in AAV-based gene therapy with a particular emphasis on approaches to overcome the hurdle that they pose.

Optimization of the capsid of recombinant adeno-associated virus 2 (AAV2) vectors: the final threshold?

The ubiquitin-proteasome pathway plays a critical role in the intracellular trafficking of AAV2 vectors, and phosphorylation of certain surface-exposed amino acid residues on the capsid provides the primary signal for ubiquitination. Removal of several critical tyrosine (Y) and serine (S) residues on the AAV2 capsid has been shown to significantly increase transduction efficiency compared with the wild-type (WT) vectors. In the present study, site-directed mutagenesis of each of the 17 surface-exposed threonine (T) residues was conducted, and the transduction efficiency of four of these mutants, T455V, T491V, T550V, and T659V, was observed to increase up to 4-fold in human HEK293 cells in vitro. The most critical Y, S, and T mutations were subsequently combined, and the quadruple-mutant (Y444+500+730F+T491V) AAV2 vector was identified as the most efficient. This vector increased the transduction efficiency ∼24-fold over the WT AAV2 vector, and ∼2-3-fold over the previously described triple-mutant (Y444+500+730F) vector in a murine hepatocyte cell line, H2.35, in vitro. Similar results were obtained in murine hepatocytes in vivo following tail vein injection of the Y444+500+730F+T491V scAAV2 vector, and whole-body bioluminescence imaging of C57BL/6 mice. The increase in the transduction efficiency of the Y-T quadruple-mutant over that of the Y triple-mutant correlated with an improved nuclear translocation of the vectors, which exceeded 90%. These observations suggest that further optimization of the AAV2 capsid by targeting amino acid residues involved in phosphorylation may not be possible. This study has thus led to the generation of a novel Y444+500+730F+T491V quadruple-mutant AAV2 vector with potential for use in liver-directed human gene therapy.

Hydrogels for lentiviral gene delivery

INTRODUCTION

Gene delivery from hydrogel biomaterials provides a fundamental tool for a variety of clinical applications including regenerative medicine, gene therapy for inherited disorders and drug delivery. The high water content and mild gelation conditions of hydrogels support their use for gene delivery by preserving activity of lentiviral vectors and acting to shield vectors from any host immune response.

AREAS COVERED

Strategies to control lentiviral entrapment within and retention/release from hydrogels are reviewed. The authors discuss the ability of hydrogel design parameters to control the transgene expression profile and the capacity of hydrogels to protect vectors from (and even modulate) the host immune response.

EXPERT OPINION

Delivery of genetic vectors from scaffolds provides a unique opportunity to capitalize on the potential synergy between the biomaterial design for cell processes and gene delivery. Hydrogel properties can be tuned to directly control the events that determine the tissue response to controlled gene delivery, which include the extent of cell infiltration, preservation of vector activity and vector retention. While some design parameters have been identified, numerous opportunities for investigation are available in order to develop a complete model relating the biomaterial properties and host response to gene delivery.

Engineered AAV vector minimizes in vivo targeting of transduced hepatocytes by capsid-specific CD8+ T cells

Recent clinical trials have shown that evasion of CD8(+) T-cell responses against viral capsid is critical for successful liver-directed gene therapy with adeno-associated viral (AAV) vectors for hemophilia. Preclinical models to test whether use of alternate serotypes or capsid variants could avoid this deleterious response have been lacking. Here, the ability of CD8(+) T cells ("cap-CD8," specific for a capsid epitope presented by human B*0702 or murine H2-L(d) molecules) to target AAV-infected hepatocytes was investigated. In a murine model based on adoptive transfer of ex vivo expanded cap-CD8, AAV2-transduced livers showed CD8(+) T-cell infiltrates, transaminitis, significant reduction in factor IX transgene expression, and loss of transduced hepatocytes. AAV8 gene transfer resulted in prolonged susceptibility to cap-CD8, consistent with recent clinical findings. In contrast, using an AAV2(Y-F) mutant capsid, which is known to be less degraded by proteasomes, preserved transgene expression and largely avoided hepatotoxicity. In vitro assays confirmed reduced major histocompatibility complex class I presentation of this capsid and killing of human or murine hepatocytes compared with AAV2. In conclusion, AAV capsids can be engineered to substantially reduce the risk of destruction by cytotoxic T lymphocytes, whereas use of alternative serotypes per se does not circumvent this obstacle.

Development, validation and use of ELISA for antibodies to human alpha-1 antitrypsin

Evaluation of human antibody responses to alpha-1 antitrypsin (AAT) in clinical trials and clinical practice has been limited by the lack of a validated assay. Here we describe the development and validation of an ELISA method for quantification of human and nonhuman primate antibody responses to human AAT. A reference anti-human AAT serum standard was generated using sera from a cynomolgus macaque injected with a recombinant adeno-associated virus vector expressing human AAT. The ELISA was validated for use with human serum dilutions as low as 1:10 and was able to distinguish between specific responses in cynomolgus serum and non-specific increases in apparent antibody titer in serum from subjects in a clinical trial of an AAT gene therapy vector.

Minicircle DNA vectors achieve sustained expression reflected by active chromatin and transcriptional level

Current efforts in nonviral gene therapy are plagued by a pervasive difficulty in sustaining therapeutic levels of delivered transgenes. Minicircles (plasmid derivatives with the same expression cassette but lacking a bacterial backbone) show sustained expression and hold promise for therapeutic use where persistent transgene expression is required. To characterize the widely-observed silencing process affecting expression of foreign DNA in mammals, we used a system in which mouse liver presented with either plasmid or minicircle consistently silences plasmid but not minicircle expression. We found that preferential silencing of plasmid DNA occurs at a nuclear stage that precedes transport of mRNA to the cytoplasm, evident from a consistent >25-fold minicircle/plasmid transcript difference observed in both nuclear and total RNA. Among possible mechanisms of nuclear silencing, our data favor chromatin-linked transcriptional blockage rather than targeted degradation, aberrant processing, or compromised mRNA transport. In particular, we observe dramatic enrichment of H3K27 trimethylation on plasmid sequences. Also, it appears that Pol II can engage the modified plasmid chromatin, potentially in a manner that is not productive in the synthesis of high levels of new transcript. We outline a scenario in which sustained differences at the chromatin level cooperate to determine the activity of foreign DNA.

Alleviation of lung inflammatory responses by adeno-associated virus 2/9 vector carrying CC10 in OVA-sensitized mice

Asthma is a chronic airway inflammatory disease characterized by eosinophilic infiltration and airway hyperresponsiveness. The over-activated Th2 and lung epithelium cells express many different cytokines, and chemokines mainly contribute to the severity of lung inflammation. Clara cell 10 kD protein (CC10) is highly expressed in airway epithelium cells and exhibits anti-inflammatory and immunomodulatory effects. Adeno-associated virus (AAV) 2/9 vector, composed of AAV2 rep and AAV9 cap genes, can efficiently and specifically target lung epithelium cells. Thus, AAV2/9 vector might carry therapeutic potential gene sequences for the treatment of asthma. This study tested whether AAV2/9 vector carrying CC10 could reduce inflammatory and asthmatic responses in OVA-induced asthmatic mouse model. The results showed that AAV2/9-CC10 vector virus significantly reduced airway hyperresponsiveness, CCL11, interleukin (IL)-4, IL-5, IL-6, IL-13, and eosinophilia in the lungs of sensitized mice. CC10 level in OVA-sensitized mice was rescued with the administration of AAV2/9-CC10 vector virus. Lung tissue remodeling, including collagen deposition and goblet cell hyperplasia, was also alleviated. However, serum levels of OVA-specific IgG1 and IgE as well as Th2 cytokine levels in OVA-stimulated splenocyte culture supernatants were at the comparable levels to the sensitized control group. The results demonstrate that AAV2/9-CC10 vector virus relieved local inflammatory and asthmatic responses in lung. Therefore, we propose that AAV2/9-CC10 vector virus guaranteed sufficient CC10 expression and had an anti-inflammatory effect in asthmatic mice. It might be applied as a novel therapeutic approach for asthma.

Controlled delivery of recombinant adeno-associated virus serotype 2 using pH-sensitive poly(ethylene glycol)-poly-L-histidine hydrogels

Loading of viral vectors in synthetic polymers is a promising strategy for overcoming hurdles associated with viral gene delivery. For enhanced gene expression at a specific site, gene transfer by using hydrogels represents a versatile approach. In this study, adeno-associated virus serotype 2 containing the green fluorescent protein gene (rAAV2-GFP) were loaded into poly(ethylene glycol) (PEG) hydrogels, with and without incorporation of poly-L-hisditine (polyHis). Inclusion of polyHis created pH responsive hydrogels in a physiological range of tissues, containing the damaged vasculature and activated phagocytosis. The fraction of polyHis used controlled the degree of swelling, water uptake and subsequent degradation of the hydrogels and release rate of rAAV2-GFP. The swelling ratio of the PEG-polyHis hydrogels increased inversely with environment pH. As pH declined from 7.4 to 6.0, PEG-polyHis hydrogel swelling ratio and degradation rate increased 875% and 135%, respectively. As a result, release and transduction efficiency of the rAAV2-GFP from PEG-polyHis hydrogel in human HT-1080 fibrosarcoma cells increased significantly compared to a PEG hydrogel. Transduction rate can be controlled by the hydrogels' polyHis concentration and is sensitive to localized decreases in pH consistent with inflammation. This is relevant to optimizing parameters for wound care and regenerative medicine applications.

AAV-based RNAi silencing of NADPH oxidase gp91(phox) attenuates cold-induced cardiovascular dysfunction

Clinical observations and epidemiological surveys indicated that the prevalence of hypertension and heart diseases is increased in cold regions or during winter. Cold exposure increased NADPH oxidase gp91(phox) protein expression in heart, kidneys, and aorta in rats. The aim of this study was to investigate if RNA interference (RNAi) silencing of gp91(phox) would attenuate cold-induced hypertension and cardiovascular and renal damage. The recombinant adeno-associated virus serotype 2 (AAV-2) vector carrying gp91(phox)-shRNA (gp91-shRNA) was constructed for inhibiting gp91(phox) protein expression in cold-exposed rats. Blood pressure (BP) was monitored using a telemetry system. BP was increased in the Control-shRNA and PBS groups within 1 week of exposure to moderate cold (5°C) and reached a plateau after 7 weeks. The cold-induced increase in BP was attenuated significantly by intravenous delivery of gp91-shRNA (1.25×10(10) particles/rat, 0.5 mL). One single dose of gp91-shRNA controlled hypertension for up to 10 weeks. In addition, gp91-shRNA reversed cold-induced vascular dysfunction. gp91-shRNA abolished the cold-induced up-regulation of gp91(phox) protein expression in heart, kidneys, and aorta, confirming effective silencing of gp91(phox). The cold-induced increases in NADPH oxidase activity and superoxide production were eliminated by silencing of gp91(phox), suggesting that the cold-induced up-regulation of NADPH oxidase activity may be attributed to the increased gp91(phox) protein expression. RNAi silencing of gp91(phox) abolished cold-induced cardiac and renal hypertrophy and attenuated aortic, coronary, and renal remodeling. The up-regulation of gp91(phox) may play a critical role in cold-induced cardiovascular dysfunction and organ damage. AAV delivery of gp91-shRNA may be a new and effective therapeutic approach for cold-related cardiovascular disorders.

Recombinant adeno-associated virus: clinical application and development as a gene-therapy vector

Gene therapy is gaining momentum as a method of treating human disease. Initially conceived as a strategy to complement defective genes in monogenic disorders, the scope of gene therapy has expanded to encompass a variety of applications. Likewise, the molecular tools for gene delivery have evolved and diversified to meet these various therapeutic needs. Recombinant adeno-associated virus (rAAV) has made significant strides toward clinical application with an excellent safety profile and successes in several clinical trials. This review covers the basic biology of rAAV as a gene therapy vector as well as its advantages compared with other methods of gene delivery. The status of clinical trials utilizing rAAV is also discussed in detail. In conclusion, methods of engineering the vector to overcome challenges identified from these trials are covered, with emphasis on modification of the viral capsid to increase the tissue/cell-specific targeting and transduction efficiency.

Efficacy and long-term safety of alipogene tiparvovec (AAV1-LPLS447X) gene therapy for lipoprotein lipase deficiency: an open-label trial

We describe the 2-year follow-up of an open-label trial (CT-AMT-011-01) of AAV1-LPL(S447X) gene therapy for lipoprotein lipase (LPL) deficiency (LPLD), an orphan disease associated with chylomicronemia, severe hypertriglyceridemia, metabolic complications and potentially life-threatening pancreatitis. The LPL(S447X) gene variant, in an adeno-associated viral vector of serotype 1 (alipogene tiparvovec), was administered to 14 adult LPLD patients with a prior history of pancreatitis. Primary objectives were to assess the long-term safety of alipogene tiparvovec and achieve a ≥40% reduction in fasting median plasma triglyceride (TG) at 3-12 weeks compared with baseline. Cohorts 1 (n=2) and 2 (n=4) received 3 × 10(11) gc kg(-1), and cohort 3 (n=8) received 1 × 10(12) gc kg(-1). Cohorts 2 and 3 also received immunosuppressants from the time of alipogene tiparvovec administration and continued for 12 weeks. Alipogene tiparvovec was well tolerated, without emerging safety concerns for 2 years. Half of the patients demonstrated a ≥40% reduction in fasting TG between 3 and 12 weeks. TG subsequently returned to baseline, although sustained LPL(S447X) expression and long-term changes in TG-rich lipoprotein characteristics were noted independently of the effect on fasting plasma TG.

Cell and gene therapy for genetic diseases: inherited disorders affecting the lung and those mimicking sudden infant death syndrome

Some of the first human gene therapy trials targeted diseases of the lung and provided important information that will continue to help shape future trials. Here we describe both cell and gene therapies for lung diseases such as cystic fibrosis and alpha-1 antitrypsin disorder as well as fatty acid oxidation disorders that mimic sudden infant death syndrome (SIDS). Human clinical gene therapy trials for cystic fibrosis and alpha-1 antitrypsin have been performed using a variety of vectors including adenovirus, adeno-associated virus, and nonviral vectors. No human clinical gene therapy trials have been performed for disorders of fatty acid oxidation; however, important proof-of-principle studies have been completed for multiple fatty acid oxidation disorders. Important achievements have been made and have yet to come for cell and gene therapies for disorders of the lung and those mimicking SIDS.

Humoral and cellular capsid-specific immune responses to adeno-associated virus type 1 in randomized healthy donors

A major impediment to the use of adeno-associated virus (AAV)-mediated gene delivery to muscle in clinical applications is the pre-existing immune responses against the vector. Pre-existing humoral response to different AAV serotypes is now well documented. In contrast, cellular responses to AAV capsid have not been analyzed in a systematic manner, despite the risk of T cell reactivation upon gene transfer. AAV1 has been widely used in humans to target muscle. In this study, we analyzed PBMCs and sera of healthy donors for the presence of AAV1 capsid-specific T cell responses and AAV1 neutralizing factors. Approximately 30% of donors presented AAV1 capsid-specific T cells, mainly effector memory CD8(+) cells. IFN-γ-producing cells were also observed among effector memory CD4(+) cells for two of these donors. Moreover, to our knowledge, this study shows for the first time on a large cohort that there was no correlation between AAV1-specific T cell and humoral responses. Indeed, most donors presenting specific Ig and neutralizing factors were negative for cellular response (and vice versa). These new data raise the question of prescreening patients not only for the humoral response, but also for the cellular response. Clearly, a better understanding of the natural immunology of AAV serotypes will allow us to improve AAV gene therapy and make it an efficient treatment for genetic disease.

Development and utility of an internal threshold control (ITC) real-time PCR assay for exogenous DNA detection

Sensitive and specific tests for detecting exogenous DNA molecules are useful for infectious disease diagnosis, gene therapy clinical trial safety, and gene doping surveillance. Taqman real-time PCR using specific sequence probes provides an effective approach to accurately and quantitatively detect exogenous DNA. However, one of the major challenges in these analyses is to eliminate false positive signals caused by either non-targeted exogenous or endogenous DNA sequences, or false negative signals caused by impurities that inhibit PCR. Although multiplex Taqman PCR assays have been applied to address these problems by adding extra primer-probe sets targeted to endogenous DNA sequences, the differences between targets can lead to different detection efficiencies. To avoid these complications, a Taqman PCR-based approach that incorporates an internal threshold control (ITC) has been developed. In this single reaction format, the target sequence and ITC template are co-amplified by the same primers, but are detected by different probes each with a unique fluorescent dye. Sample DNA, a prescribed number of ITC template molecules set near the limit of sensitivity, a single pair of primers, target probe and ITC probe are added to one reaction. Fluorescence emission signals are obtained simultaneously to determine the cycle thresholds (Ct) for amplification of the target and ITC sequences. The comparison of the target Ct with the ITC Ct indicates if a sample is a true positive for the target (i.e. Ct less than or equal to the ITC Ct) or negative (i.e. Ct greater than the ITC Ct). The utility of this approach was demonstrated in a nonhuman primate model of rAAV vector mediated gene doping in vivo and in human genomic DNA spiked with plasmid DNA.

Retrograde gene delivery to hypoglossal motoneurons using adeno-associated virus serotype 9

Retrograde viral transport (i.e., muscle to motoneuron) enables targeted gene delivery to specific motor pools. Recombinant adeno-associated virus serotype 9 (AAV9) robustly infects motoneurons, but the retrograde transport capabilities of AAV9 have not been systematically evaluated. Accordingly, we evaluated the retrograde transduction efficiency of AAV9 after direct tongue injection in 129SVE mice as well as a mouse model that displays neuromuscular pathology (Gaa(-/-)). Hypoglossal (XII) motoneurons were histologically evaluated 8 weeks after tongue injection with AAV9 encoding green fluorescent protein (GFP) with expression driven by the chicken β-actin promoter (1 × 10(11) vector genomes). On average, GFP expression was detected in 234 ± 43 XII motoneurons 8 weeks after AAV9-GFP tongue injection. In contrast, tongue injection with a highly efficient retrograde anatomical tracer (cholera toxin β subunit, CT-β) resulted in infection of 818 ± 88 XII motoneurons per mouse. The retrograde transduction efficiency of AAV9 was similar between the 129SVE mice and those with neuromuscular disease (Gaa(-/-)). Routine hematoxylin and eosin staining and cluster of differentiation (CD) immunostaining for T cells (CD3) indicated no persistent inflammation within the tongue or XII nucleus after AAV9 injection. Additional experiments indicated no adverse effects of AAV9 on the pattern of breathing. We conclude that AAV9 can retrogradely infect a significant portion of a given motoneuron pool in normal and dystrophic mice, and that its transduction efficiency is approximately 30% of what can be achieved with CT-β.