1 Department of Gene Therapy & Regenerative Medicine, Free University of Brussels (VUB) , Brussels, Belgium.
2 Center for Molecular & Vascular Biology, Department of Cardiovascular Sciences, University of Leuven , Leuven, Belgium .
Hum Gene Ther. 2017 Nov;28(11):1013-1023. doi: 10.1089/hum.2017.116. Epub 2017 Aug 3.
Hemophilia A and B are congenital, X-linked bleeding disorders caused by mutations in the genes encoding for the blood clotting factor VIII (FVIII) or factor IX (FIX), respectively. Since the beginning of gene therapy, hemophilia has been considered an attractive disease target that served as a trailblazer for the field at large. Different technologies have been explored to efficiently and safely deliver the therapeutic FVIII and FIX genes into the patients' cells. Currently, the most promising vectors for hemophilia gene therapy are adeno-associated viral vectors (AAVs) and lentiviral vectors. More recently, gene editing approaches based on designer nucleases or CRISPR/Cas, have also been considered to minimize risks associated with random vector integration and insertional mutagenesis though off-target issues would have to be carefully and comprehensively assessed. In the past two decades, several phase 1 hemophilia gene therapy clinical trials have been initiated with varying success. In particular, the early gene therapy clinical trials in hemophilia B patients based on AAV showed either transient or subtherapeutic clotting factor expression levels. This could be ascribed, at least in part, to suboptimal vector design and/or inadvertent immune consequences triggering hepatic inflammation. Hence, there was an unmet need to further increase vector safety and efficacy in future trials, preferably by using lower vector doses. It is particularly encouraging that sustained therapeutic FVIII and FIX expression levels have recently been attained after gene therapy in patients with severe hemophilia paving the way towards pivotal trials and commercialization. Nevertheless, transient liver toxicity still occurs and the use of transient immunosuppression was still required to curtail inadvertent immune responses, especially at high vector doses. To further boost clotting factor expression levels, codon-usage optimized synthetic FVIII or FIX transgenes have been employed. Alternatively, we and others have shown that the incorporation of hyperactive gain-of-function R338L mutation in the FIX gene substantially increased the overall efficacy. It is inevitable that the continued improvements in vector engineering and new insights in the vector-patient interactions will further benefit the development of a safe and effective cure for hemophilia A and B.
A 型和 B 型血友病分别是由凝血因子 VIII（FVIII）或凝血因子 IX（FIX）基因的突变引起的先天性 X 连锁出血性疾病。自基因治疗开始以来，血友病一直被认为是一个有吸引力的疾病靶点，为整个领域开辟了道路。已经探索了不同的技术来有效地将治疗性 FVIII 和 FIX 基因递送到患者的细胞中。目前，用于血友病基因治疗的最有前途的载体是腺相关病毒（AAV）和慢病毒载体。最近，基于设计的核酸酶或 CRISPR/Cas 的基因编辑方法也被认为可以最大限度地降低与随机载体整合和插入突变相关的风险，尽管脱靶问题需要仔细和全面地评估。在过去的二十年中，已经启动了几项不同成功的血友病基因治疗 1 期临床试验。特别是，基于 AAV 的血友病 B 患者早期基因治疗临床试验显示出短暂或低于治疗水平的凝血因子表达。这至少部分归因于不理想的载体设计和/或意外的免疫后果引发的肝炎症。因此，需要进一步提高未来试验中的载体安全性和疗效，最好是使用较低的载体剂量。最近，在严重血友病患者接受基因治疗后，持续获得了治疗性 FVIII 和 FIX 表达水平，这令人鼓舞，为关键性试验和商业化铺平了道路。然而，仍然存在短暂的肝毒性，仍然需要使用短暂的免疫抑制来抑制意外的免疫反应，特别是在高载体剂量时。为了进一步提高凝血因子的表达水平，已经使用了密码子优化的合成 FVIII 或 FIX 转基因。或者，我们和其他人已经表明，FIX 基因中引入高活性功能获得性 R338L 突变大大提高了整体疗效。不可避免的是，载体工程的持续改进和对载体-患者相互作用的新见解将进一步促进 A 型和 B 型血友病的安全有效治疗的发展。
