Gene Therapy In Pompe Disease Research Articles

Lentiviral gene therapy with IGF2-tagged GAA normalizes the skeletal muscle proteome in murine Pompe disease

Pompe disease is a lysosomal storage disorder caused by deficiency of acid alpha-glucosidase (GAA), resulting in glycogen accumulation with profound pathology in skeletal muscle. We recently developed an optimized form of lentiviral gene therapy for Pompe disease in which a codon-optimized version of the GAA transgene (LV-GAAco) was fused to an insulin-like growth factor 2 (IGF2) peptide (LV-IGF2.GAAco), to promote cellular uptake via the cation-independent mannose-6-phosphate/IGF2 receptor. Lentiviral gene therapy with LV-IGF2.GAAco showed superior efficacy in heart, skeletal muscle, and brain of Gaa−/− mice compared to gene therapy with untagged LV-GAAco. Here, we used quantitative mass spectrometry using TMT labeling to analyze the muscle proteome and the response to gene therapy in Gaa−/− mice. We found that muscle of Gaa−/− mice displayed altered levels of proteins including those with functions in the CLEAR signaling pathway, autophagy, cytoplasmic glycogen metabolism, calcium homeostasis, redox signaling, mitochondrial function, fatty acid transport, muscle contraction, cytoskeletal organization, phagosome maturation, and inflammation. Gene therapy with LV-GAAco resulted in partial correction of the muscle proteome, while gene therapy with LV-IGF2.GAAco resulted in a near-complete restoration to wild type levels without inducing extra proteomic changes, supporting clinical development of lentiviral gene therapy for Pompe disease. SignificanceLysosomal glycogen accumulation is the primary cause of Pompe disease, and leads to a cascade of pathological events in cardiac and skeletal muscle and in the central nervous system. In this study, we identified the proteomic changes that are caused by Pompe disease in skeletal muscle of a mouse model. We showed that lentiviral gene therapy with LV-IGF2.GAAco nearly completely corrects disease-associated proteomic changes. This study supports the future clinical development of lentiviral gene therapy with LV-IGF2.GAAco as a new treatment option for Pompe disease.

Gene therapy for glycogen storage diseases.

Glycogen storage disorders (GSDs) are inherited disorders of metabolism resulting from the deficiency of individual enzymes involved in the synthesis, transport, and degradation of glycogen. This literature review summarizes the development of gene therapy for the GSDs. The abnormal accumulation of glycogen and deficiency of glucose production in GSDs lead to unique symptoms based upon the enzyme step and tissues involved, such as liver and kidney involvement associated with severe hypoglycemia during fasting and the risk of long-term complications including hepatic adenoma/carcinoma and end stage kidney disease in GSD Ia from glucose-6-phosphatase deficiency, and cardiac/skeletal/smooth muscle involvement associated with myopathy +/- cardiomyopathy and the risk for cardiorespiratory failure in Pompe disease. These symptoms are present to a variable degree in animal models for the GSDs, which have been utilized to evaluate new therapies including gene therapy and genome editing. Gene therapy for Pompe disease and GSD Ia has progressed to Phase I and Phase III clinical trials, respectively, and are evaluating the safety and bioactivity of adeno-associated virus vectors. Clinical research to understand the natural history and progression of the GSDs provides invaluable outcome measures that serve as endpoints to evaluate benefits in clinical trials. While promising, gene therapy and genome editing face challenges with regard to clinical implementation, including immune responses and toxicities that have been revealed during clinical trials of gene therapy that are underway. Gene therapy for the glycogen storage diseases is under development, addressing an unmet need for specific, stable therapy for these conditions.

What’s new and what’s next for gene therapy in Pompe disease?

Introduction Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-⍺-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome. Areas covered Gene therapy offers several advantages including prolonged and consistent GAA expression and correction of skeletal muscle as well as the critical CNS pathology. We provide a systematic review of the preclinical and clinical outcomes of adeno-associated viral mediated gene therapy and alternative gene therapy strategies, highlighting what has been successful. Expert opinion Although the preclinical and clinical studies so far have been promising, barriers exist that need to be addressed in gene therapy for Pompe disease. New strategies including novel capsids for better targeting, optimized DNA vectors, and adjuctive therapies will allow for a lower dose, and ameliorate the immune response.

Comparisons of infant and adult mice reveal age effects for liver depot gene therapy in Pompe disease

Comparisons of infant and adult mice reveal age effects for liver depot gene therapy in Pompe disease

Advancements in AAV-mediated Gene Therapy for Pompe Disease.

Pompe disease (glycogen storage disease type II) is caused by mutations in acid α-glucosidase (GAA) resulting in lysosomal pathology and impairment of the muscular and cardio-pulmonary systems. Enzyme replacement therapy (ERT), the only approved therapy for Pompe disease, improves muscle function by reducing glycogen accumulation but this approach entails several limitations including a short drug half-life and an antibody response that results in reduced efficacy. To address these limitations, new treatments such as gene therapy are under development to increase the intrinsic ability of the affected cells to produce GAA. Key components to gene therapy strategies include the choice of vector, promoter, and the route of administration. The efficacy of gene therapy depends on the ability of the vector to drive gene expression in the target tissue and also on the recipient’s immune tolerance to the transgene protein. In this review, we discuss the preclinical and clinical studies that are paving the way for the development of a gene therapy strategy for patients with early and late onset Pompe disease as well as some of the challenges for advancing gene therapy.

Comparisons of Infant and Adult Mice Reveal Age Effects for Liver Depot Gene Therapy in Pompe Disease

Pompe disease is caused by the deficiency of lysosomal acid α-glucosidase (GAA). It is expected that gene therapy to replace GAA with adeno-associated virus (AAV) vectors will be less effective early in life because of the rapid loss of vector genomes. AAV2/8-LSPhGAA (3 × 1010 vector genomes [vg]/mouse) was administered to infant (2-week-old) or adult (2-month-old) GAA knockout mice. AAV vector transduction in adult mice significantly corrected GAA deficiency in the heart (p < 0.0001), diaphragm (p < 0.01), and quadriceps (p < 0.001) for >50 weeks. However, in infant mice, the same treatment only partially corrected GAA deficiency in the heart (p < 0.05), diaphragm (p < 0.05), and quadriceps (p < 0.05). The clearance of glycogen was much more efficient in adult mice compared with infant mice. Improved wire hang test latency was observed for treated adults (p < 0.05), but not for infant mice. Abnormal ventilation was corrected in both infant and adult mice. Vector-treated female mice demonstrated functional improvement, despite a lower degree of biochemical correction compared with male mice. The relative vector dose for infants was approximately 3-fold higher than adults, when normalized to body weight at the time of vector administration. Given these data, the dose requirement to achieve similar efficacy will be higher for the treatment of young patients.

Gene Therapy for Pompe Disease: The Time is now.

Pompe disease (PD) is caused by the deficiency of the lysosomal enzyme acid α-glucosidase (GAA), resulting in systemic pathological glycogen accumulation. PD can present with cardiac, skeletal muscle, and central nervous system manifestations, as a continuum of phenotypes among two main forms: classical infantile-onset PD (IOPD) and late-onset PD (LOPD). IOPD is caused by severe GAA deficiency and presents at birth with cardiac hypertrophy, muscle hypotonia, and severe respiratory impairment, leading to premature death, if not treated. LOPD is characterized by levels of residual GAA activity up to ∼20% of normal and presents both in children and adults with a varied severity of muscle weakness and motor and respiratory deficit. Enzyme replacement therapy (ERT), based on repeated intravenous (i.v.) infusions of recombinant human GAA (rhGAA), represents the only available treatment for PD. Upon more than 10 years from its launch, it is becoming evident that ERT can extend the life span of IOPD and stabilize disease progression in LOPD; however, it does not represent a cure for PD. The limited uptake of the enzyme in key affected tissues and the high immunogenicity of rhGAA are some of the hurdles that limit ERT efficacy. GAA gene transfer with adeno-associated virus (AAV) vectors has been shown to reduce glycogen storage and improve the PD phenotype in preclinical studies following different approaches. Here, we present an overview of the different gene therapy approaches for PD, focusing on in vivo gene transfer with AAV vectors and discussing the potential opportunities and challenges in developing safe and effective gene therapies for the disease. Based on emerging safety and efficacy data from clinical trials for other protein deficiencies, in vivo gene therapy with AAV vectors appears to have the potential to provide a therapeutically relevant, stable source of GAA enzyme, which could be highly beneficial in PD.

Liver depot gene therapy for Pompe disease.

Gene therapy for Pompe disease has advanced to early phase clinical trials, based upon proof-of-concept data indicating that gene therapy could surpass the benefits of the current standard of care, enzyme replacement therapy (ERT). ERT requires frequent infusions of large quantities of recombinant human acid α-glucosidase (GAA), whereas gene therapy involves a single infusion of a vector that stably transduces tissues to continuously produce GAA. Liver-specific expression of GAA with an adeno-associated virus (AAV) vector established stable GAA secretion from the liver accompanied by receptor-mediated uptake of GAA, which corrected the deficiency of GAA and cleared the majority of accumulated glycogen in the heart and skeletal muscle. Liver depot gene therapy was equivalent to ERT at a dose of the AAV vector that could be administered in an early phase clinical trial. Furthermore, high-level expression of GAA has decreased glycogen stored in the brain. A unique advantage of liver-specific expression stems from the induction of immune tolerance to GAA following AAV vector administration, thereby suppressing anti-GAA antibodies that otherwise interfere with efficacy. A Phase I clinical trial of AAV vector-mediated liver depot gene therapy has been initiated based upon promising preclinical data (NCT03533673). Overall, gene therapy promises to address limits of currently available ERT, if clinical translation currently underway is successful.

Progress and challenges of gene therapy for Pompe disease

Pompe disease (PD) is a monogenic disorder caused by mutations in the acid alpha-glucosidase gene (Gaa). GAA is a lysosomal enzyme essential for the degradation of glycogen. Deficiency of GAA results in a severe, systemic disorder that, in its most severe form, can be fatal. About a decade ago, the prognosis of PD has changed dramatically with the marketing authorization of an enzyme replacement therapy (ERT) based on recombinant GAA. Despite the breakthrough nature of ERT, long-term follow-up of both infantile and late-onset Pompe disease patients (IOPD and LOPD, respectively), revealed several limitations of the approach. In recent years several investigational therapies for PD have entered preclinical and clinical development, with a few next generation ERTs entering late-stage clinical development. Gene therapy holds the potential to change dramatically the way we treat PD, based on the ability to express the Gaa gene long-term, ideally driving enhanced therapeutic efficacy compared to ERT. Several gene therapy approaches to PD have been tested in preclinical animal models, with a handful of early phase clinical trials started or about to start. The complexity of PD and of the endpoints used to measure efficacy of investigational treatments remains a challenge, however the hope is for a future with more therapeutic options for both IOPD and LOPD patients.

Salmeterol with Liver Depot Gene Therapy Enhances the Skeletal Muscle Response in Murine Pompe Disease.

Gene therapy for Pompe disease with adeno-associated virus (AAV) vectors has advanced into early phase clinical trials; however, the paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up acid α-glucosidase (GAA), has impeded the efficacy of Pompe disease gene therapy. Long-acting selective β2 receptor agonists previously enhanced the CI-MPR expression in muscle. In this study we have evaluated the selective β2 agonist salmeterol in GAA knockout mice in combination with an AAV vector expressing human GAA specifically in the liver. Quadriceps glycogen content was significantly decreased by administration of the AAV vector with salmeterol, in comparison with the AAV vector alone (p < 0.01). Importantly, glycogen content of the quadriceps was reduced to its lowest level by the combination of AAV vector and salmeterol administration. Rotarod testing revealed significant improvement following treatment, in comparison with untreated mice, and salmeterol improved wirehang performance. Salmeterol treatment decreased abnormalities of autophagy in the quadriceps, as shown be lower LC3 and p62. Vector administration reduced the abnormal vacuolization and accumulation of nuclei in skeletal muscle. Thus, salmeterol could be further developed as adjunctive therapy to improve the efficacy of liver depot gene therapy for Pompe disease.

Immunomodulatory, liver depot gene therapy for Pompe disease

Pompe disease is caused by mutations in acid alpha glucosidase (GAA) that causes accumulation of lysosomal glycogen affecting the heart and skeletal muscles, and can be fatal. Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) improves muscle function by reducing glycogen accumulation. Limitations of ERT include a short half-life and the formation of antibodies that result in reduced efficacy. By harnessing the immune tolerance induction properties of the liver, liver-targeted gene delivery (with an adeno-associated virus vector containing a liver specific promoter), suppresses immunity against the GAA introduced by gene therapy. This induces immune tolerance to rhGAA by activating regulatory T cells and simultaneously, corrects GAA deficiency. Potentially, liver-targeted gene therapy can be performed once with lasting effects, by administering a relatively low dose of an adeno-associated virus type 8 vector to replace and induce immune tolerance to GAA.

Long-term neurologic and cardiac correction by intrathecal gene therapy in Pompe disease

Pompe disease is a lysosomal storage disorder caused by acid-α-glucosidase (GAA) deficiency, leading to glycogen storage. The disease manifests as a fatal cardiomyopathy in infantile form. Enzyme replacement therapy (ERT) has recently prolonged the lifespan of these patients, revealing a new natural history. The neurologic phenotype and the persistence of selective muscular weakness in some patients could be attributed to the central nervous system (CNS) storage uncorrected by ERT. GAA-KO 6neo/6neo mice were treated with a single intrathecal administration of adeno-associated recombinant vector (AAV) mediated gene transfer of human GAA at 1 month and their neurologic, neuromuscular, and cardiac function was assessed for 1 year. We demonstrate a significant functional neurologic correction in treated animals from 4 months onward, a neuromuscular improvement from 9 months onward, and a correction of the hypertrophic cardiomyopathy at 12 months. The regions most affected by the disease i.e. the brainstem, spinal cord, and the left cardiac ventricular wall all show enzymatic, biochemical and histological correction. Muscle glycogen storage is not affected by the treatment, thus suggesting that the restoration of muscle functionality is directly related to the CNS correction. This unprecedented global and long-term CNS and cardiac cure offer new perspectives for the management of patients.

Low-Dose Liver-Targeted Gene Therapy for Pompe Disease Enhances Therapeutic Efficacy of ERT via Immune Tolerance Induction

Pompe disease results from acid α-glucosidase (GAA) deficiency, and enzyme replacement therapy (ERT) with recombinant human (rh) GAA has clinical benefits, although its limitations include the short half-life of GAA and the formation of antibody responses. The present study compared the efficacy of ERT against gene transfer with an adeno-associated viral (AAV) vector containing a liver-specific promoter. GAA knockout (KO) mice were administered either a weekly injection of rhGAA (20 mg/kg) or a single injection of AAV2/8-LSPhGAA (8 × 1011 vector genomes [vg]/kg). Both treatments significantly reduced glycogen content of the heart and diaphragm. Although ERT triggered anti-GAA antibody formation, there was no detectable antibody response following AAV vector administration. The efficacy of three lower dosages of AAV2/8-LSPhGAA was evaluated in GAA-KO mice, either alone or in combination with ERT. The minimum effective dose (MED) identified was 8 × 1010 vg/kg to reduce glycogen content in the heart and diaphragm of GAA-KO mice. A 3-fold higher dose was required to suppress antibody responses to ERT. Efficacy from liver gene therapy was slightly greater in male mice than in female mice. Vector dose correlated inversely with anti-GAA antibody formation, whereas higher vector doses suppressed previously formed anti-GAA antibodies as late as 25 weeks after the start of ERT and achieved biochemical correction of glycogen accumulation. In conclusion, we identified the MED for effective AAV2/8-LSPhGAA-mediated tolerogenic gene therapy in Pompe disease mice.

Inspiratory muscle conditioning exercise and diaphragm gene therapy in Pompe disease: Clinical evidence of respiratory plasticity

Pompe disease is an inherited disorder due to a mutation in the gene that encodes acid α-glucosidase (GAA). Children with infantile-onset Pompe disease develop progressive hypotonic weakness and cardiopulmonary insufficiency that may eventually require mechanical ventilation (MV). Our team conducted a first in human trial of diaphragmatic gene therapy (AAV1-CMV-GAA) to treat respiratory neural dysfunction in infantile-onset Pompe. Subjects (aged 2–15years, full-time MV: n=5, partial/no MV: n=4) underwent a period of preoperative inspiratory muscle conditioning exercise. The change in respiratory function after exercise alone was compared to the change in function after intramuscular delivery of AAV1-CMV-GAA to the diaphragm with continued exercise. Since AAV-mediated gene therapy can reach phrenic motoneurons via retrograde transduction, we hypothesized that AAV1-CMV-GAA would improve dynamic respiratory motor function to a greater degree than exercise alone. Dependent measures were maximal inspiratory pressure (MIP), respiratory responses to inspiratory threshold loads (load compensation: LC), and physical evidence of diaphragm activity (descent on MRI, EMG activity). Exercise alone did not change function. After AAV1-CMV-GAA, MIP was unchanged. Flow and volume LC responses increased after dosing (p<0.05 to p<0.005), but only in the subjects with partial/no MV use. Changes in LC tended to occur on or after 180days. At Day 180, the four subjects with MRI evidence of diaphragm descent had greater maximal voluntary ventilation (p<0.05) and tended to be younger, stronger, and use fewer hours of daily MV. In conclusion, combined AAV1-CMV-GAA and exercise training conferred benefits to dynamic motor function of the diaphragm. Children with a higher baseline neuromuscular function may have greater potential for functional gains.

49. Minimum Effective Dose of Liver-Targeted Gene Therapy for Pompe Disease Reduced 10-Fold from Prior Estimates

Pompe disease (glycogen storage disease type II; acid maltase deficiency) is a devastating myopathy resulting from acid alpha-glucosidase (GAA) deficiency in striated and smooth muscle. Despite the availability of enzyme replacement therapy (ERT) with recombinant human GAA, many patients have poor outcomes including mortality. ERT has increased survival rates, improved hypotonia, and resolved heart involvement in patients with Pompe disease. However ERT is limited by the short half-life of GAA and the formation of antibody responses that reduced its clinical benefits. The present study compared the efficacy of ERT against an adeno-associated viral (AAV) vector containing a liver-specific promoter, AAV2/8-LSPhGAApA. We hypothesized that liver-specific expression of GAA with AAV2/8-LSPhGAA would suppress the antibody response, continually express GAA, and improve efficacy in comparison with ERT. Preclinical experiments with Pompe disease therapies demonstrated that a very low amount of AAV2/8-LSPhGAApA, 2×1010 vector particles (vp), equivalent to 8×1011 vp/kg body weight, was as effective as long-term ERT. Therefore, we evaluated the biochemical efficacy of 3 lower dosages of AAV2/8-LSPhGAA in GAA knockout (KO) mice, reduced to as low as 2×1010 vp/kg, either alone or in combination with ERT. Biochemical correction in GAA-KO mice was evaluated 8 weeks following vector administration. The minimum effective dose (MED) was at least 10-fold lower than previously estimated, because 8×1010 vp/kg significantly reduced glycogen content in the striated muscle of GAA-KO mice. This MED of AAV2/8-LSPhGAA significantly increased GAA activity in liver (p<0.01), in comparison with untreated GAA-KO mice. Importantly, the MED significantly reduced the glycogen content of heart (p<0.01; Fig. A), and diaphragm (p<0.01; Fig. B), which demonstrated that the glycogen storage in muscle associated with Pompe disease was substantially cross-corrected by GAA secretion from liver accompanied by receptor-mediated uptake in striated muscle. Glycogen clearance, or reduction in comparison with no treatment, was 36% in heart, and 35% in diaphragm. Furthermore, administering ERT by itself had no significant effect on the glycogen content of quadriceps, but ERT following administration of the MED of AAV2/8-LSPhGAA significantly reduced glycogen content of quadriceps (p<0.05; Fig. C) by 38%, indicating that gene therapy with AAV2/8-LSPhGAA made ERT more effective. Vector dose correlated inversely with anti-GAA antibody formation, confirming that immune tolerance to GAA was critical to the efficacy from AAV2/8-LSPhGAApA. In conclusion, the MED for AAV2/8-LSPhGAA has been estimated at least 10-fold lower than previous data suggested, and this dosage would be acceptable as a starting dose for a Phase I clinical trial of gene therapy in Pompe disease.View Large Image | Download PowerPoint Slide

381. Prohypertrophic Agents Enhance the Response to Gene Therapy in Pompe Disease

Pompe disease causes a progressive myopathy resulting from acid α-glucosidase (GAA) deficiency in the heart and skeletal muscle. Enzyme replacement therapy (ERT) with recombinant human (rh) GAA has prolonged the survival of patients. However, complete reversal neuromuscular involvement has not been possible in Pompe disease by treating with ERT. The paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up rhGAA, correlated with a poor response to ERT by muscle in Pompe disease. Clenbuterol, a selective β2 receptor agonist, enhanced the CI-MPR expression in striated muscle, and increased the efficacy of either ERT or gene therapy in murine Pompe disease. The underlying mechanism of clenbuterol's therapeutic action is Igf-1 mediated muscle hypertrophy, which has correlated with increased CI-MPR (also the Igf-2 receptor) expression. In this study we have evaluated 4 new drugs in GAA knockout (KO) mice in combination with an adeno-associated virus (AAV) vector encoding human GAA. The dosage for each drug was selected to induce muscle hypertrophy with an associated increased expression of CI-MPR, analogous to clenbuterol's effects. Three alternative β2 agonists and dehydroepiandrosterone (DHEA) were evaluated in combination with gene therapy in GAA-KO mice. Mice were transgenic for a liver-specific human GAA transgene to induce immune tolerance to introduced GAA. The 3 new β2 agonists were chosen to be long-acting like clenbuterol. Furthermore, DHEA caused muscle hypertrophy similar to the β2 agonists, is available in the US, and was well-tolerated in rodent experiments. Mice were injected with AAV2/9-CBhGAA (1E+11 vector particles) at a dose previously found to be partially effective at clearing glycogen storage from the the heart. Heart GAA activity was significantly increased by either salmeterol (p 0.001), salmeterol (p<0.05), formoterol (p<0.01), or clenbuterol (p<0.01) in combination with the AAV vector, in comparison with untreated mice. Functional testing was performed subsequently, and the wirehang test at 18 weeks following vector administration revealed that the combination of salmeterol and the AAV vector significantly increased latency in comparison with untreated mice (p<0.01), AAV vector alone (p<0.001). Similarly, salmeterol with the vector increased latency significantly more than either DHEA (p<0.001), formoterol (p<0.05), fenoterol (p<0.05), or clenbuterol (p<0.05) with the vector. An important consideration with regard to adjunctive therapy is whether any effects are due to the adjuvant rather than the combined treatment. The most effective individual drugs were evaluated by themselves, and no significant effect upon GAA activity of heart, glycogen content of heart, or wirehang latency was observed, in comparison with untreated mice. Thus, salmeterol should be further developed as adjunctive therapy in combination with either ERT or gene therapy for Pompe disease.

Salmeterol enhances the cardiac response to gene therapy in Pompe disease.

Enzyme replacement therapy (ERT) with recombinant human (rh) acid α-glucosidase (GAA) has prolonged the survival of patients. However, the paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up rhGAA, correlated with a poor response to ERT by muscle in Pompe disease. Clenbuterol, a selective β2 receptor agonist, enhanced the CI-MPR expression in striated muscle through Igf-1 mediated muscle hypertrophy, which correlated with increased CI-MPR (also the Igf-2 receptor) expression. In this study we have evaluated 4 new drugs in GAA knockout (KO) mice in combination with an adeno-associated virus (AAV) vector encoding human GAA, 3 alternative β2 agonists and dehydroepiandrosterone (DHEA). Mice were injected with AAV2/9-CBhGAA (1E+11 vector particles) at a dose that was not effective at clearing glycogen storage from the heart. Heart GAA activity was significantly increased by either salmeterol (p<0.01) or DHEA (p<0.05), in comparison with untreated mice. Furthermore, glycogen content was reduced in the heart by treatment with DHEA (p<0.001), salmeterol (p<0.05), formoterol (p<0.01), or clenbuterol (p<0.01) in combination with the AAV vector, in comparison with untreated GAA-KO mice. Wirehang testing revealed that salmeterol and the AAV vector significantly increased performance, in comparison with the AAV vector alone (p<0.001). Similarly, salmeterol with the vector increased performance significantly more than any of the other drugs. The most effective individual drugs had no significant effect in absence of vector, in comparison with untreated mice. Thus, salmeterol should be further developed as adjunctive therapy in combination with either ERT or gene therapy for Pompe disease.

Using a Simulation to Illustrate Crosscutting Concepts through a Disease Model

Using Pompe disease as a context affords the opportunity for students to consider multiple biological concepts and embraces the Next Generation Science Standards Disciplinary Core Ideas Structure and Function (LS1.A) and Inheritance of Traits (LS3.A) as well as Crosscutting Concepts Structure and Function and Cause and Effect. These crosscutting concepts are very much interrelated as we consider progression of disease from the molecular to the organismal level. The concepts are repeatedly emphasized, providing “explicit instructional support” for students to “develop a cumulative, coherent, and usable understanding of science and engineering.” DNA, proteins, enzymes, genetics, and human disease are taught together through the story of patients with Pompe disease as students engage in a simulated clinical assay and genetic analysis and present their findings in grand rounds. The activity is one of multiple lessons sequenced to scaffold student understanding of clinical and translational science, starting with a first-person perspective of a father who loses his infant son to Pompe and concluding with a role play based on actual events surrounding approval of human clinical trials of gene therapy for Pompe disease.

Preclinical Development of New Therapy for Glycogen Storage Diseases.

Glycogen storage disease (GSD) consists of more than 10 discrete conditions for which the biochemical and genetic bases have been determined, and new therapies have been under development for several of these conditions. Gene therapy research has generated proof-of-concept for GSD types I (von Gierke disease) and II (Pompe disease). Key features of these gene therapy strategies include the choice of vector and regulatory cassette, and recently adeno-associated virus (AAV) vectors containing tissue-specific promoters have achieved a high degree of efficacy. Efficacy of gene therapy for Pompe disease depend upon the induction of immune tolerance to the therapeutic enzyme. Efficacy of von Gierke disease is transient, waning gradually over the months following vector administration. Small molecule therapies have been evaluated with the goal of improving standard of care therapy or ameliorating the cellular abnormalities associated with specific GSDs. The receptor-mediated uptake of the therapeutic enzyme in Pompe disease was enhanced by administration of β2 agonists. Rapamycin reduced the liver fibrosis observed in GSD III. Further development of gene therapy could provide curative therapy for patients with GSD, if efficacy from preclinical research is observed in future clinical trials and these treatments become clinically available.

368. Simultaneous Delivery of Dual AAV9 Vectors Induces Immune Tolerance and Correction of Pompe Disease Pathology

Enzyme replacement therapy (ERT) for Pompe disease (acid α-glucosidase deficiency; GAA) provokes the development of high titer antibodies against the enzyme and contributes to life threatening infusion associated reactions. AAV-mediated gene therapy stands as a more attractive therapeutic option yet AAV-mediated gene transfer can elicit anti-capsid and anti-transgene responses that modulate its effectiveness. To circumvent deleterious immune responses we sought to develop a dual vector system that targets gene expression to specific tissues simultaneously ameliorating the Pompe disease phenotype and facilitate antigen specific tolerance. Two AAV9 vectors containing a liver-specific promoter (LSP) or a cardiac/neuromuscular-specific promoter (desmin; DES) driving human codon-optimized GAA (coGAA) were combined at a ratio of 1 LSP: 9 DES (1:9) or 9 LSP: 1 DES (9:1) and systemically injected at 5×10e13 vg/kg into 4-6 week old Gaa-/- mice. After 8 weeks, physiologic, immunologic, histologic and biochemical assessments were performed as well as the adoptive transfer of Tregs into naive mice testing for tolerance. GAA activity was significantly increased in AAV treated mice in the heart, diaphragm, liver, quadriceps, sciatic nerve and spinal cord compared to knockouts (p<0.05). The isometric torque generated by the tibialis anterior in all treated groups was significantly greater compared to KO (p<0.05). ECGs revealed the 1:9, but not the 9:1, treated cohort had a normalization of the PR interval similar to age matched wild-type mice (p<0.05). Antibodies against GAA in the 9:1 group were significantly lower than the 1:9 group but titers declined in both groups by weeks 2-6; possibly indicating tolerance. To test for antigen-specific tolerance, Tregs from mice that received AAV9 or vehicle were transferred into naive recipients. One group of mice did not receive Tregs as a control for non-specific suppression. Challenged with ERT at the clinical dose of 20 mg/kg 18 hours, 2 weeks and 4 weeks post-transfer, anti-GAA IgG1 titers were 2.5-fold lower in mice receiving Tregs from AAV-treated donors compared to mice that received Tregs from vehicle donors or no Tregs (p<0.01). Prior to the third injection all mice had a baseline temperature of 36-37°C. Within 5 minutes, and up to 2 hours later, the body temperature of those mice that received Tregs from vehicle treated mice, or no Tregs, dropped to <35°C whereas those mice that received Tregs from AAV treated mice maintained baseline core temperature (p<0.001). This drop in temperature was also accompanied with outward signs of anaphylaxis: piloerection and hyperventilation. Resolving the immunological complications of gene therapy in conjunction with physiologic correction of systemic disease would typically involve the use of immunosuppressives. Here we described a modality involving two combined AAV9 vectors that, in the 1:9 cohort, resulted in the most complete correction of pathology and tolerance induction. These results lay the framework for the use of multiple vectors to address these separate but equally important aspects of gene therapy for Pompe disease.