Lee Ann Lawson

Pompe disease gene therapy

Pompe disease is an autosomal recessive metabolic myopathy caused by the deficiency of the lysosomal enzyme acid alpha-glucosidase and results in cellular lysosomal and cytoplasmic glycogen accumulation. A wide spectrum of disease exists from hypotonia and severe cardiac hypertrophy in the first few months of life due to severe mutations to a milder form with the onset of symptoms in adulthood. In either condition, the involvement of several systems leads to progressive weakness and disability. In early-onset severe cases, the natural history is characteristically cardiorespiratory failure and death in the first year of life. Since the advent of enzyme replacement therapy (ERT), the clinical outcomes have improved. However, it has become apparent that a new natural history is being defined in which some patients have substantial improvement following ERT, while others develop chronic disability reminiscent of the late-onset disease. In order to improve on the current clinical outcomes in Pompe patients with diminished clinical response to ERT, we sought to address the cause and potential for the treatment of disease manifestations which are not amenable to ERT. In this review, we will focus on the preclinical studies that are relevant to the development of a gene therapy strategy for Pompe disease, and have led to the first clinical trial of recombinant adeno-associated virus-mediated gene-based therapy for Pompe disease. We will cover the preliminary laboratory studies and rationale for a clinical trial, which is based on the treatment of the high rate of respiratory failure in the early-onset patients receiving ERT.

The respiratory neuromuscular system in Pompe disease.

Pompe disease is due to mutations in the gene encoding the lysosomal enzyme acid α-glucosidase (GAA). Absence of functional GAA typically results in cardiorespiratory failure in the first year; reduced GAA activity is associated with progressive respiratory failure later in life. While skeletal muscle pathology contributes to respiratory insufficiency in Pompe disease, emerging evidence indicates that respiratory neuron dysfunction is also a significant part of dysfunction in motor units. Animal models show profound glycogen accumulation in spinal and medullary respiratory neurons and altered neural activity. Tissues from Pompe patients show central nervous system glycogen accumulation and motoneuron pathology. A neural mechanism raises considerations about the current clinical approach of enzyme replacement since the recombinant protein does not cross the blood-brain-barrier. Indeed, clinical data suggest that enzyme replacement therapy delays symptom progression, but many patients eventually require ventilatory assistance, especially during sleep. We propose that treatments which restore GAA activity to respiratory muscles, neurons and networks will be required to fully correct ventilatory insufficiency in Pompe disease.

B-Cell Depletion and Immunomodulation before Initiation of Enzyme Replacement Therapy Blocks the Immune Response to Acid Alpha-Glucosidase in Infantile-Onset Pompe Disease

OBJECTIVE To evaluate whether B-cell depletion before enzyme replacement therapy (ERT) initiation can block acid alpha-glucosidase (GAA) antibody responses and improve clinical outcomes. STUDY DESIGN Six subjects with Pompe disease (including 4 cross-reacting immunologic material-negative infants) aged 2-8 months received rituximab and sirolimus or mycophenolate before ERT. Four subjects continued to receive sirolimus, rituximab every 12 weeks, and intravenous immunoglobulin monthly for the duration of ERT. Sirolimus trough levels, IgG, CD3, CD4, CD8, CD19, CD20, N-terminal pro-brain natriuretic peptide, creatine kinase, creatine kinase-MB, C-reactive protein, platelets, alkaline phosphatase, gamma-glutamyl transferase, aspartate aminotransferase, and alanine aminotransferase were measured regularly. RESULTS Immunomodulation achieved B-cell depletion without adverse effects. After 17-36 months of rituximab, sirolimus and ERT, all subjects lacked antibodies against GAA, 4 continued to gain motor milestones, yet 2 progressed to require invasive ventilation. The absence of infusion-associated reactions allowed the use of accelerated infusion rates. CONCLUSION B-cell depletion and T-cell immunomodulation in infants naïve to ERT was accomplished safely and eliminated immune responses against GAA, thereby optimizing clinical outcome; however, this approach did not necessarily influence sustained independent ventilation. Importantly, study outcomes support the initiation of immunomodulation before starting ERT, because the study regimen allowed for prompt initiation of treatment.

B-cell depletion is protective against anti-AAV capsid immune response: a human subject case study

Gene therapy strategies for congenital myopathies may require repeat administration of adeno-associated viral (AAV) vectors due to aspects of the clinical application, such as: (i) administration of doses below therapeutic efficacy in patients enrolled in early phase clinical trials; (ii) progressive reduction of the therapeutic gene expression over time as a result of increasing muscle mass in patients treated at a young age; and (iii) a possibly faster depletion of pathogenic myofibers in this patient population. Immune response triggered by the first vector administration, and to subsequent doses, represents a major obstacle for successful gene transfer in young patients. Anti-capsid and anti-transgene product related humoral and cell-mediated responses have been previously observed in all preclinical models and human subjects who received gene therapy or enzyme replacement therapy (ERT) for congenital myopathies. Immune responses may result in reduced efficacy of the gene transfer over time and/or may preclude for the possibility of re-administration of the same vector. In this study, we evaluated the immune response of a Pompe patient dosed with an AAV1-GAA vector after receiving Rituximab and Sirolimus to modulate reactions against ERT. A key finding of this single subject case report is the observation that B-cell ablation with rituximab prior to AAV vector exposure results in non-responsiveness to both capsid and transgene, therefore allowing the possibility of repeat administration in the future. This observation is significant for future gene therapy studies and establishes a clinically relevant approach to blocking immune responses to AAV vectors.

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

ABSTRACT Pompe disease is an inherited disorder due to a mutation in the gene that encodes acid &agr;‐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 2–15 years, 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 180 days. 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. HighlightsChildren with Pompe disease and ventilatory insufficiency received AAV1‐CMG‐GAA.Exercise alone did not change respiratory muscle function in any subjects.In less‐affected children, dynamic respiratory function improved after gene therapy.

Altered activation of the tibialis anterior in individuals with Pompe disease: Implications for motor unit dysfunction

Pompe disease is a progressive disease that affects skeletal muscles and leads to loss of ambulation. We investigated the activation of the tibialis anterior (TA) in late‐onset Pompe disease (LOPD) individuals during maximal voluntary contraction (MVC) and evoked involuntary responses.

Diaphragm Pacing as a Rehabilitative Tool for Patients With Pompe Disease Who Are Ventilator-Dependent: Case Series.

Background and Purpose Pompe disease is an inherited disorder notable for severe, progressive ventilatory compromise. Although ventilatory failure has been attributed to myofiber dysfunction secondary to diaphragmatic glycogen accumulation, neural involvement of the phrenic motor system is also a prominent feature. Direct diaphragm pacing supplements respiratory function in other disorders of the phrenic motor system. Accordingly, it is hypothesized that augmented neuromuscular activity via diaphragm pacing would promote weaning from mechanical ventilation in patients with Pompe disease who are unresponsive to conventional, muscle-directed treatments. Case Description Three patients with Pompe disease developed diaphragm paresis that resulted in chronic mechanical ventilation dependence. After preoperative inspiratory muscle strengthening exercises failed to improve function, fine-wire pacing electrodes were laparoscopically implanted into the diaphragm. Diaphragm conditioning was initiated the first postoperative week and consisted of gradual increases in stimulation parameters, lengthening of stimulation sessions, and ventilator weaning. Ventilation and intramuscular electromyographic activity were recorded periodically during conditioning to quantify diaphragm neuromuscular function. Outcomes During paced breathing without mechanical ventilation, tidal volumes increased, and 2 patients were weaned from daytime ventilator dependence within the first 3 months of pacing, which has been sustained over the long-term. A third patient reduced reliance on daytime ventilation, but weaning was delayed by malacia of the large airways. In all patients, pacing appeared to facilitate spontaneous phrenic motor unit activity during independent breathing without ventilator or pacer support. Discussion The findings are consistent with the view that diaphragm pacing has potential rehabilitative value to reduce reliance on mechanical ventilation in people with Pompe disease, but further study is needed. Diaphragm pacing represents a paradigm shift in the management of respiratory insufficiency for Pompe disease that warrants further controlled examination.

Respiratory motor function in individuals with centronuclear myopathies.

Introduction: Individuals with X‐linked myotubular myopathy (XLMTM) and other centronuclear myopathies (CNMs) frequently have profound respiratory insufficiency that requires support early in life. Still, few quantitative data exist to characterize respiratory motor function in CNM. Methods: We evaluated the reliance upon mechanical ventilation (MV), ventilatory kinematics, unassisted tidal volumes, and maximal respiratory pressures in 14 individuals with CNMs, including 10 boys with XLMTM. Results: Thirteen participants required full‐time, invasive MV. Maximal inspiratory pressures were higher in subjects who breathed unsupported at least 1 hour/day as compared with 24‐hour MV users [33.7 (11.9–42.3) vs. 8.4 (6.0–10.9) cm H2O, P < 0.05]. Years of MV dependence correlated significantly with MEP (r = −0.715, P < 0.01). Conclusions: Respiratory function in CNMs may be related to deconditioning from prolonged MV and/or differences in residual respiratory muscle strength. Results from this study may assist in evaluating severe respiratory insufficiency in neuromuscular clinical care and research. Muscle Nerve 53: 214–221, 2016

Development of a novel observer reported outcome tool as the primary efficacy outcome measure for a rare disease randomized controlled trial

We developed an Observer-Reported Outcome (ObsRO) survey instrument to be applied in a multicenter, placebo-controlled, crossover randomized controlled trial of dichloroacetate in children with pyruvate dehydrogenase complex deficiency. The instrument quantifies a subjects at-home level of functionality, as reported by a parent/caregiver, who were instrumental in providing the clinical descriptors and domains that formed the instruments content. Feasibility testing of the ObsRO tool showed it to be easy to use and comprehensive in capturing the major clinical functional limitations of affected children and requires less than 5min for a parent/caregiver to complete daily.