Self-Complementary AAV2 Factor IX for Hemophilia B

描述（由申请人提供）：该提案旨在开发一种血友病B核酸疗法，能够在治疗水平上介导因子IX （FIX）的多年表达，单次给药预计花费少于2年的传统重组FIX重复给药。我们的建议很大程度上受益于先前的血友病B基因治疗的独立人类临床试验的结果，该试验使用类似的腺相关病毒- (AAV-)血清型2载体为基础的靶向肝脏的FIX递送。该试验证明了衣壳或载体壳的相对安全性，在高于本文建议的剂量下不会引起症状性毒性。该研究达到了治疗水平（11 - 15%）的循环FIX蛋白（甚至6%的正常活动将表型严重转化为轻度出血性疾病），最高测试剂量提供了希望。然而，这种效果是短暂的，因为明显的免疫反应逐渐消除了转导细胞。重要的是，5和25倍低剂量的AAV2 FIX表现出更持久的转导，尽管没有证据表明可检测到循环因子。在不引发免疫介导的疗效丧失的情况下，显然无法在治疗窗口内获得表达，这阻碍了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有望有效地改变剂量-反应关系，从而使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，与之前人类临床试验中使用的传统单链AAV相比，我们结合了一种新的基因组结构，即自互补腺相关病毒（scAAV），可以改善表达。这些scAAV载体显著减少了在小鼠中实现持续转基因表达所需的载体负荷。使用肝脏特异性启动子（scAAV2- hfix）下带有优化FIX密码子序列的scAAV2，我们已经证明使用低15至20倍的病毒载体剂量对血友病小鼠进行校正。我们的初步临床前研究表明，循环FIX的治疗水平与之前临床试验中最低研究的临床剂量相当。该提案建立在广泛的临床前可行性数据和先前的临床经验基础上，概述了关键的临床前和临床研究，以支持这种一流方法的商业化，旨在满足B型血友病患者的重要医疗需求。研究目标的成功完成将支持与商业化合作伙伴合作进入II/III期测试。

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.