Gene therapy in canine myotubular myopathy for clinical translation

描述(申请人提供)：肌管蛋白的突变导致X连锁肌管肌病(XLMTM)，这是一种毁灭性的先天性肌肉疾病，导致严重的肌肉无力和呼吸肌衰竭导致的过早死亡。只有支持性的姑息治疗是可用的。我们已经证明，AAV介导的基因替换可以挽救肌管蛋白缺陷小鼠的严重肌肉无力。新的数据显示，使用rAAV-MTM1的单一全身治疗足以长期(至少一年)存活，并基本上完全改善肌管蛋白缺乏的小鼠的症状。然而，对于XLMTM患者的最终治疗，必须使用预测性大动物模型来改进递送系统，评估关键的安全参数，如对载体和转基因的潜在宿主免疫应答，并优化疗效测量。因此，我们开发了一个繁殖群体，在这个群体中，受影响的公狗表现出与人类XLMTM直接相似的表型。在初步研究中，我们证实，在年轻狗的后肢肌肉内注射局部基因替代疗法，改善了肌小管蛋白缺乏的骨骼肌的功能和病理。此外，第一只系统交付rAAV-MTM1的XLMTM犬四肢几乎保持正常力量，正常呼吸功能超过6个月，存活时间比我们群体中任何未经治疗的突变犬多4个月。在小鼠和犬模型上的积极观察促使我们将重点放在系统性rAAV-MTM1基因治疗的发展上。我们假设，适度的肌管蛋白水平将足以维持全身横纹肌的长期功能，包括重要的呼吸肌。我们建议利用犬系统来测试这一假说，并优化媒介选择(目标1)和剂量(目标2)，同时评估潜在的安全问题。为此，我们的具体目标是：目的1.在犬模型中测试系统性MTM1基因替换，使用新型rAAV载体(血清2I8)，该载体可有效地传递到骨骼肌，同时避免肝脏目标2。 确定幼年XLMTM犬全身MTM1基因置换后至少32周内的安全性、有效性和免疫反应参数的剂量-反应关系

DESCRIPTION (provided by applicant): Mutations in myotubularin cause X-linked myotubular myopathy (XLMTM), a devastating congenital muscle disorder causing severe muscle weakness and premature death from respiratory muscle failure. Only supportive, palliative care is available. We have shown that AAV-mediated gene replacement rescued severe muscle weakness in myotubularin-deficient mice. New data show that a single systemic treatment with rAAV-MTM1 sufficed for long-term (at least one year) survival and essentially complete amelioration of symptoms of mice with myotubularin-deficient muscles. However, for eventual therapy of XLMTM patients, it is imperative to employ a predictive large animal model to refine the delivery system, assess critical safety parameters such as the potential host immune response to vector and transgene, and optimize efficacy measurements. We, therefore, developed a breeding colony in which affected male dogs display a phenotype directly analogous to human XLMTM. In preliminary studies we confirmed that local gene replacement therapy, delivered intramuscularly in the hind limb of young dogs, improved both function and pathology in myotubularin-deficient skeletal muscles. Moreover, the first XLMTM dog in which rAAV-MTM1 was delivered systemically maintained nearly normal strength in all four limbs, and normal respiratory function for more than 6 months surviving > 4 months longer than any untreated mutant dog in our colony. The positive observations in the murine and canine models drive us to focus on the development of systemic rAAV-MTM1 gene therapy. We hypothesize that modest levels of myotubularin will suffice to sustain long-term functionality of striated muscles throughout the body, including the vital respiratory muscles. We propose to utilize the canine system to test this hypothesis and to optimize vector selection (Aim 1) and dosing (Aim 2), while assessing potential safety concerns. Towards this end our Specific Aims are: Aim 1. Test systemic MTM1 gene replacement in the canine model using a novel rAAV vector (serotype 2i8) engineered for effective delivery to skeletal muscle while avoiding the liver Aim 2. Determine dose-response relationships for safety, efficacy, and immune response parameters over a period of at least 32 weeks after systemic MTM1 gene replacement in young XLMTM dogs