Self-Complementary AAV2 Factor IX for Hemophilia B

描述（由申请方提供）：本提案旨在开发一种血友病B核酸疗法，该疗法能够通过单次给药介导治疗水平的因子IX（FIX）的多年表达，预计重组FIX传统重复给药的成本低于2年。我们的提案极大地受益于先前使用类似的基于腺相关病毒-（AAV-）血清型-2载体的FIX靶向肝脏递送的血友病B基因治疗的独立人体临床试验的结果。该试验证明了衣壳或载体壳的相对安全性，在高于本文提出的剂量下不引起症状性毒性。该研究实现了循环FIX蛋白的治疗水平（11 - 15%）（即使6%的正常活性也可将表型重度出血性疾病转化为轻度出血性疾病），最高试验剂量提供了希望。然而，这种效应是短暂的，因为明显的免疫应答逐渐消除了转导的细胞。重要的是，5倍和25倍低剂量的AAV 2 FIX表现出更持久的转导，尽管没有证据表明存在可检测的循环因子。在治疗窗口中明显不能获得表达而不触发免疫介导的功效丧失阻碍了这种先前方法的进一步发展。AskBio在AAV介导的基因治疗方面的专有进展提供了有效改变剂量-反应关系的希望，使得治疗窗口不再需要与触发CTL反应相关的病毒载量。具体而言，可行性研究表明，与先前人类临床试验中使用的传统单链AAV相比，我们掺入了一种新的基因组结构，即自互补腺相关病毒（scAAV），从而改善了表达。这些scAAV载体显著最小化了在小鼠中实现持续转基因表达所需的载体负载。使用在肝脏特异性启动子下具有优化的FIX密码子序列的scAAV 2（scAAV 2-hFIX），我们已经显示了使用15- 20倍低的病毒载体剂量对血友病小鼠的校正。我们的初步临床前研究表明，在与既往临床试验中耐受良好的最低研究临床剂量相当的剂量下，循环FIX的治疗水平。该提案基于广泛的临床前可行性数据以及既往临床经验，概述了关键的临床前和临床研究，以支持这种旨在满足血友病B患者重大医疗需求的一流方法的商业化。成功完成拟议的研究目标将支持与商业化合作伙伴合作进入II/III期测试。 公共卫生相关性：该提案旨在推进Asklepios Biopharmacology开发血友病B基因疗法。这种治疗性基因替代旨在产生稳定的长期凝血因子IX水平，而无需重新给药，具有持久正常化受影响个体凝血功能的潜力。患者负担减轻、不依从和血液制品暴露预计与发病率和死亡率降低相关-仅在美国，血友病B患者的生活质量大幅改善。

DESCRIPTION (provided by applicant): This proposal is designed to develop a hemophilia B nucleic-acid therapy capable of mediating multi-year expression of Factor IX (FIX) at therapeutic levels from a single administration that is anticipated to cost less than 2 years of traditional repeated administration of recombinant FIX. Our proposal benefits greatly from the findings of a previous independent human clinical trial of gene therapy for hemophilia B using similar adeno- associated virus- (AAV-) serotype-2 vector-based delivery of FIX targeting liver. This trial demonstrated the relative safety of the capsid, or vector shell, in not eliciting symptomatic toxicities at doses higher than proposed herein. The study achieved therapeutic levels (11 - 15%) of circulating FIX protein (even 6% of normal activity converts phenotypically severe to mild bleeding disorders) with the highest tested dose offered promise. However, the effect was transient as an apparent immune response gradually eliminated transduced cells. Importantly, 5- and 25-fold lower doses of AAV2 FIX demonstrated more durable transduction, though without evidence for detectable circulating factor. The apparent inability to attain expression in a therapeutic window without triggering an immune-mediated loss of efficacy has hindered the further development of this previous approach. AskBio's proprietary advances in AAV-mediated gene therapy offer the promise to effectively shift the dose-response relation so that the therapeutic window no longer requires a viral load associated with triggering a CTL response. Specifically, feasibility studies demonstrate improved expression from our incorporation of a novel genomic structure, self-complementary adeno-associated virus (scAAV) in contrast to the traditional single-strand AAV used in previous human clinical trials. These scAAV vectors significantly minimize the vector load required to achieve sustained transgene expression in mice. Using scAAV2 with an optimized FIX codon sequence under a liver-specific promoter (scAAV2-hFIX), we have shown correction of hemophilic mice using 15- to 20-fold lower viral vector doses. Our preliminary preclinical studies demonstrate therapeutic levels of circulating FIX at doses comparable to the lowest investigated clinical doses shown to be well tolerated in the previous clinical trial. This proposal builds upon both extensive preclinical feasibility data as well as previous clinical experience to outline critical preclinical and clinical studies to support the commercialization of this first-in-class approach designed to meet the significant medical needs of Hemophilia B patients. Successful completion of the research aims proposed will support advancement into Phase II/III testing in collaboration with a commercialization partner. PUBLIC HEALTH RELEVANCE: This proposal intends to advance Asklepios Biopharmaceutical's development of a gene therapy for Hemophilia B. Designed to generate stable long-term production of blood-coagulation factor-IX levels without the need for re-administration, this therapeutic gene replacement offers the potential to durably normalize blood-coagulation in affected individuals. Reduced patient burden, non-compliance, and exposure to blood products are expected to correlate with reductions in morbidity and mortality - as well as a vastly improved quality of life for Hemophilia B patients in the U.S. alone.