Phase I/II clinical trial evaluating AAV-mediated gene therapy for a severe paediatric metabolic liver disease: Ornithine Transcarbamylase deficiency

鸟氨酸转甲氨基酰基酶缺乏症（OTCD）是一种罕见的x连锁遗传疾病，其特征是完全或部分缺乏鸟氨酸转甲氨基酰基酶（OTC）。OTC是尿素循环的关键元素，肝脏分解并从体内去除多余的氮。OTCD患者在血液中以过量氨（高氨血症）的形式积累氮。氨是有毒的，患者会出现“高氨失代偿”，症状包括呕吐、自主运动受损和进行性嗜睡。如果不及时治疗，可能会发展为昏迷和危及生命的并发症。患有严重强迫症的男性在出生后几天内出现症状。除了显著的死亡风险外，过量氨的神经毒性效应还会导致长期的神经异常，如智力残疾、发育迟缓和脑瘫。与较轻形式的这种疾病（可能在以后的男女儿童和成人中出现）一样，婴儿用氨清除药物和饮食干预进行治疗，但仍会发生高氨血症失代偿。新生儿发病的OTCD患者需要肝移植（LT）来维持长期生存。虽然肝移植可以挽救生命，但这种干预的机会仍然有限，并不是没有死亡和发病的风险。外科手术已经取得了进展，以方便获得供体肝组织，包括“活体供体部分肝移植”和“减少肝移植”，即婴儿和儿童接受成人肝脏的一部分。然而，患者及其家属仍然面临着终身免疫抑制和医学随访的挑战。欧洲指南推荐对年龄在3 - 12个月的严重表型患者进行肝移植，因为在这种代谢不稳定的患者中进行新生儿移植被认为风险太大。在过去的十年里，英国15名儿科强迫症患者中，只有4名是这个年龄段的。其他的都超过3岁，都有长期的神经损伤。我们开发了一种基于腺相关病毒（AAV）的基因疗法（AAV- lk03 -OTC），以特异性靶向肝脏并恢复AAV的功能表达。我们的方法包括对OTCD婴儿进行单次基因治疗，以提供肝脏代谢的立即正常化，从而降低高氨失代偿引起的急性死亡风险。这种治疗将作为“移植的桥梁”，使儿科患者能够在代谢稳定的情况下继续生长，直到移植成为可能，同时也最大限度地减少与高氨血症相关的长期神经系统发病率。我们的实验室实验证明了AAV- lk03 -OTC比其他AAV靶向肝细胞的能力增强，并引起功能性OTC的表达升高。我们已经证明AAV-LK03-OTC可以恢复这种遗传性疾病的实验小鼠模型的肝功能，目前正在动物研究中测试AAV-LK03-OTC的安全性。最近其他病毒基因疗法进入早期临床试验（例如AAV8治疗B型血友病）的成功，以及对肝细胞的靶向性增加（AAV-LK03比AAV8对肝细胞的转化多10倍），增强了对该方法安全性的信心。我们现在将把我们的临床前研究结果转化为评估AAV-LK03-OTC的安全性和有效性的I/II期剂量寻找临床试验。由于儿童是OTCD人群中最大的未满足需求，我们的目标是在英国招募12名儿科患者，为这种变革性先进疗法的后期开发和商业化提供早期临床数据。该项目旨在为儿科OTCD患者的临床管理提供一个阶段性的改变，并提供适用于许多其他肝脏遗传代谢疾病的关键基因治疗证据。

Ornithine transcarbamylase deficiency (OTCD) is a rare X-linked genetic disorder characterized by complete or partial lack of the enzyme ornithine transcarbamylase (OTC). OTC is a key element of the urea cycle, whereby the liver breaks down and removes surplus nitrogen from the body. OTCD patients accumulate nitrogen in the form of excess ammonia (hyperammonemia) in the blood. Ammonia is toxic and patients suffer 'hyperammonaemic decompensations' with symptoms including vomiting, impaired voluntary movement, and progressive lethargy. If left untreated these may progress to coma and life-threatening complications. Symptoms present within a few days of birth of males with severe OTCD. As well as significant risk of mortality, the neurotoxic effects of excess ammonia result in longer-term neurological abnormalities such as intellectual disability, developmental delays, and cerebral palsy. As with milder forms of this disease (which may present later in both male and female children and adults), infants are managed with ammonia-scavenging drugs and dietary intervention, however hyperammonaemic decompensations still occur. Neonatal-onset OTCD patients require liver transplantation (LT) for long-term survival. Whilst LT can be life-saving, opportunity for this intervention remains limited and not without risk of mortality and morbidity. Advances have been made in surgical practices to facilitate access to donor liver tissue, including 'living-donor partial liver grafts' and 'reduced-liver transplantation' whereby infants and children receive a portion of an adult liver. However, both the patient and their family still remain with the challenge of life-long immunosuppression and medical follow-up. European guidelines recommend LT for those patients with severe phenotype, aged between 3 and 12 months as neonatal transplant in such metabolically unstable patients is considered too great a risk. Of 15 paediatric OTCD patients transplanted in the UK this past decade, there were only 4 of this age. All others were over 3 years old and all had long-term neurological impairment. We have developed an Adeno associated virus (AAV)-based gene therapy (AAV-LK03-OTC) to specifically target the liver and restore functional expression of OTC. Our approach encompasses the single administration of gene therapy to OTCD infants to provide immediate normalisation of liver metabolism, thereby reducing acute risk of mortality from hyperammonaemic decompensations. Such treatment would serve as a 'bridge-to-transplant' enabling paediatric patients to continue to grow in a metabolically stable condition until such time that transplantation is possible, also minimising longer-term neurological morbidity associated with hyperammonaemia. Our laboratory experiments have demonstrated the enhanced ability of AAV-LK03-OTC to target liver cells over other AAV, and to elicit elevated expression of functional OTC. We have demonstrated that AAV-LK03-OTC restores liver function in experimental mouse models of this genetic disease and are currently testing the safety of AAV-LK03-OTC in animal studies. Recent success with other viral gene therapies advanced to early clinical trials (e.g. AAV8 for Haemophilia B) and the increased targeting to liver cells (AAV-LK03 >10-fold more transformation of liver cells than AAV8) reinforce confidence in this approach as being safe. We will now translate our pre-clinical findings to conduct a Phase I/II dose-finding clinical trial assessing the safety and efficacy of AAV-LK03-OTC. As children are the OTCD population with greatest unmet need, we aim to recruit 12 paediatric patients in the UK to provide early clinical data for later stage development and commercialisation of this transformative advanced therapy. This project aims to deliver a step-change in the clinical management of paediatric OTCD patients and provide critical gene therapy evidence applicable to many other liver-inherited metabolic diseases.