Clinical trial of self complementary AAV8-mediated gene transfer for hemophilia B

描述（由申请人提供）： 我们提出了一项开放标签、剂量递增、I/II期研究，其中将单剂量的新型自身互补AAV载体scAAV 2/8 LP 1 hFIXco施用到患有重度血友病B的成人受试者的外周静脉中。血友病B（HB）是一种X-连锁隐性出血性疾病，由因子IX（FIX）基因缺陷引起，该基因编码对适当纤维蛋白凝块形成至关重要的丝氨酸蛋白酶。在临床上，该疾病的特征是频繁的自发性出血，最常见的是进入关节和软组织等部位，但也可能发生在大脑中，并可能危及生命。我们在鼠模型和恒河猴中的广泛研究表明，与先前临床试验中评价的载体相比，scAAV 2/8 LP 1 hFIXco载体在这些动物中以相对低的剂量建立了FIX的治疗水平。这项研究与以前使用AAV载体的HB临床试验在三个重要方面不同。首先，将使用AAV8假型化载体代替AAV2，主要是因为在人中对该AAV血清型的预先存在的免疫性的普遍性显著较低。第二个差异涉及使用含有自身互补基因组的载体，由于其在靶组织中快速形成稳定的、转录活性的双链线性分子的能力，提供了以较低剂量的载体潜在地介导有效的治疗性基因转移的独特机会。最后，因为载体的生物分布主要是肝脏，而不管施用途径如何，scAAV颗粒将通过外周静脉施用。我们建议测试三个剂量水平：每公斤体重2x1010、6x1010和2x1011个载体基因组。本研究的主要目的是评估该载体全身给药的安全性，而次要目的是1）确定达到正常水平3%或以上的hFIX稳定表达所需的载体颗粒剂量; 2）描述对hFIX转基因产物和AAV衣壳蛋白的免疫应答; 3）获得病毒脱落到各种体液中。招募仅限于确诊为hFIX基因错义突变导致的重度HB的成人（≥ 18岁）。在入组下一位患者之前，将在载体给药后观察患者至少42天。将根据安全性（主要）和疗效（次要）标准进行剂量递增。免疫抑制不会常规给予;相反，只有当患者发生急性，显著的转氨酶升高（ALT或胆红素> 10倍正常值）或持续（> 16周）ALT或胆红素升高时才给予免疫抑制。发生以下任何一种情况将导致立即暂停试验：1）在给定剂量水平下，1例患者发生IV级毒性或2例患者发生III级毒性。2)1例受试者基因转移后产生FIX中和抗体。5)患者在基因转移后的任何时间点死亡，可能、很可能或肯定与研究药物相关。目前血友病B治疗的不足之处激发了人们对替代治疗方法的兴趣，包括基因转移。成功的AAV介导的血友病B基因转移为患有这种疾病的患者提供了有效的终身预防出血及其并发症的潜力。此外，从这项研究中获得的信息将是重要的，在规划其他未来的战略与AAV载体，其中影响肝脏的其他疾病，如溶酶体贮积症和尿素循环障碍，是目标。

DESCRIPTION (provided by applicant): We propose an open label, dose-escalation, phase I/II study in which a single dose of the novel self- complementary AAV vector, scAAV2/8 LP1 hFIXco, will be administered into a peripheral vein of adult subjects with severe hemophilia B. Hemophilia B (HB) is an X-linked recessive bleeding disorder that results from a defect in the factor IX (FIX) gene which encodes a serine protease critical for appropriate fibrin clot formation. Clinically the disease is characterized by frequent spontaneous bleeding, most commonly into such sites as joints and soft tissues, but which can also occur in the brain and potentially be life threatening. Our extensive studies in murine models and rhesus macaques have shown that scAAV2/8 LP1 hFIXco vector establishes therapeutic levels of FIX at relatively low doses in these animals, compared to vectors evaluated in previous clinical trials. This study differs from previous HB clinical trials with AAV vectors in three important aspects. Firstly, an AAV8 pseudotyped vector will be used instead of AAV2, primarily because of the substantially lower prevalence of pre-existing immunity to this AAV serotype in humans. The second difference relates to the use of a vector containing a self-complementary genome which, because of its ability to rapidly form stable, transcriptionally active, double stranded linear molecules in target tissues, offers the unique opportunity to mediate efficient therapeutic gene transfer potentially at lower doses of vector. Finally, because the biodistribution of vector is predominantly to the liver regardless of the route of administration, scAAV particles will be administered via a peripheral vein. We propose to test three dose levels: 2x1010, 6x1010 and 2x1011 vector genomes per kilogram body weight. The primary objective of the study is to assess the safety of systemic administration of this vector while the secondary objectives are 1) to determine the dose of vector particles required to achieve stable expression of hFIX at or above 3% of normal; 2) to describe the immune responses to the hFIX transgene product and AAV capsid proteins and 3) to access viral shedding into various body fluids. Recruitment will be limited to adults (greater than or equal to 18 years of age) with a confirmed diagnosis of severe HB resulting from a missense mutation in the hFIX gene. Patients will be observed for at least 42 days following vector administration before enrollment of the next patient. Dose escalation will proceed based on safety (primary) and efficacy (secondary) criteria. Immunosupression will not be given routinely; rather, only if a patient develops acute, significant transaminitis (ALT or bilirubin >10X normal) or persistent (>16 weeks) ALT or bilirubin elevation. The occurrence of any of the following will result in immediate suspension of the trial: 1) The occurrence of Grade IV toxicity in one patient or Grade III toxicity in two patients at a given dose level. 2) The development of neutralizing antibodies to FIX following gene transfer in one subject. 5) Death of a patient at any time point after gene transfer that is possibly, probably, or definitely related to the study agent. The inadequacies of current therapy for hemophilia B have fuelled interest in alternative treatment approaches, including gene transfer. Successful AAV-mediated gene transfer for hemophilia B offers the potential of effective lifetime prevention of bleeding and its complications for patients with this disorder. In addition, the information gained from this study will be important in planning additional future strategies with AAV vectors in which other disorders affecting the liver, such as lysosomal storage and urea cycle disorders, are targeted.