FIV Vectors for the Treatment of Hemophilia A

描述（由申请人提供）：尽管包括我们在内的几个实验室已经在动物模型中证明了基因治疗A型血友病的可行性，但在临床中没有观察到转基因在治疗水平上的长期表达。血友病患者缺乏足够表达水平的因子VIII （FVIII）表明需要进一步改进当前的基因传递系统以产生治疗产品。在该项目的一期研究中，我们开始了一项研究来解决FVIII表达水平和持续时间的问题，研究结果表明，FVIII的表达受不稳定mRNA、与内质网（ER）伴侣的相互作用以及通过与甘露糖结合凝集素LMAN1的相互作用促进ER向高尔基转运的要求所限制。在基因治疗应用中表达FVIII的载体通常使用B结构域缺失（BDD） cDNA，其中该结构域的编码序列被删除以产生用于蛋白质生产和基因转移的较短结构。值得注意的是，BDD FVIII在细胞内的表达与整个FVIII分子具有相同的局限性。然而，在短B结构域间隔中包含几种天冬酰胺连接的低聚糖增加了内质网到高尔基体的运输，导致体外和体内分泌的功能性FVIII水平比全长或B结构域缺失的FVIII高15- 25倍。在血友病犬中添加部分B结构域可以显著提高治疗性FVIII的产生，这是与人类疾病最相关的动物模型，也是临床研究的先决条件。我们构建并测试了两个含有添加不同长度B结构域的犬FVIII的FIV载体。构建物是用犬FVIII基因序列制备的，以减少引入血友病犬时复杂的跨物种因素。在第一阶段，优化了制备高滴度病毒的参数，并分析了VSV- G和GP64假型载体的先天免疫应答。I期目的的完成使本项目能够在血友病小鼠和犬中进行FVIII的表达水平和持续时间研究，并选择最有利的FVIII cDNA进行安全和长期表达。在这项II期研究中，目的是评估不含B结构域或含有两种不同长度B结构域的犬FVIII的FIV传递的表达水平、持续时间和临床效益。此外，可能进一步显著提高转导细胞FVIII产量的其他元件将被纳入转移载体并进行测试。该第二阶段还包括开发方法，为这些和后续研究提供更多的病毒载体，这些研究将需要大量的载体。

DESCRIPTION (provided by applicant): Although several labs including ours have demonstrated the feasibility of gene therapy for hemophilia A in animal models, long-term expression of the transgene at therapeutic levels was not observed in the clinic. The lack of sufficient expression levels Factor VIII (FVIII) in hemophilic patients indicates that further improvements of the current gene delivery systems are needed to generate a therapeutic product. In the Phase I of this project we initiated a study to address the issues of FVIII expression level and duration based on findings showing that FVIII expression is limited by unstable mRNA, interaction with endoplasmic reticulum (ER) chaperones, and a requirement for facilitated ER to Golgi transport through interaction with the mannose- binding lectin LMAN1. Vectors for FVIII expression in gene therapy applications typically have used a B domain deleted (BDD) cDNA in which the coding sequence for this domain is removed to yield a shorter construct for protein production and gene transfer. Of note, the expression of BDD FVIII within the cell has the same limitations as the whole FVIII molecule. However, the inclusion of several asparagine-linked oligosaccharides within a short B-domain spacer increased ER to Golgi transport resulting in secretion of functional FVIII at levels 15- to 25-fold higher than full-length or B domain deleted FVIII both in vitro and in vivo. Phase I initiated the testing of the hypothesis that therapeutic FVIII production can be significantly enhanced by addition of parts of the B domain in hemophilic dogs, the most relevant animal model to the human disease and a prerequisite test for clinical studies, Two FIV vectors were constructed and tested which contain canine FVIII with different lengths of the B domain added. The constructs were prepared with the canine FVIII genetic sequence to reduce complicating cross-species factors when introduced into the hemophilic dog. Also, in Phase I the parameters for preparing high titer virus were optimized and the innate immune response to VSV- G and GP64 pseudotyped vectors were analyzed. The completion of the Phase I aims puts the project in position to conduct the FVIII expression level and duration studies in hemophilic mice and dogs and to select the most favorable FVIII cDNA for safe and long term expression. In this Phase II study the aims are to evaluate expression level, duration and clinical benefit from FIV delivery of canine FVIII with no B domain or with two different lengths of the B domain included. Also, additional elements that may further enhance FVIII production significantly from transduced cells will be incorporated into the transfer vector and tested. This Phase II also includes the development of methods to provide increased production of the virus vector for these and subsequent studies, which will require large amounts of the vector. PUBLIC HEALTH RELEVANCE: Clinical application of Factor VIII gene therapies to hemophilia A patients have suffered from insufficient production of Factor VIII. Using an FIV lentiviral vector capable of long-term expression in host cells, Factor VIII gene sequences with improvements designed to overcome the problem of poor expression will be tested in hemophilic dogs, the animal model which closely resembles the human disease. The goal is to advance the best product as determined from this study toward application in the clinic to human patients.