Establishment of the Risk of AAV Vector Integration

描述（由申请人提供）：重组腺相关病毒（rAAV）载体在许多靶组织中有效地传递治疗基因。它们已经变得非常流行，并广泛用于许多基因转移实验，包括代谢疾病和遗传疾病的基因治疗。由于rAAV载体是基于非致病性病毒产生的，因此多年来一直被认为是最安全的载体之一。然而，最近在小鼠和人类受试者中不可预测的逆转录病毒插入突变的报道，以及我们最近在对有限数量的rAAV整合事件的分析中发现，rAAV载体优先整合到活性基因中，这引起了人们对rAAV介导的插入突变的可能性的关注。因此，重新定义raav介导的基因治疗的风险是非常重要的。我们在这方面的长期目标是建立rAAV载体整合的风险，并开发最安全的rAAV载体系统。为了实现这些目标，我们提出三项探索性研究。首先，我们将开发一种新的高通量方法来分离rAAV载体在载体转导组织中的插入位点，并进行大规模的分析，以彻底了解rAAV载体的生物学和rAAV载体整合的后果。其次，考虑到rAAV优先整合到活性基因中，我们假设由于肝细胞损伤而持续再生的细胞可能存在细胞周期相关基因的表达失调，这些基因可能容易被rAAV载体整合，从而加速肝细胞的恶性转化。因此，我们将利用转基因小鼠模型评估rAAV载体对易患肝癌的病毒性肝炎的协同致癌潜力。第三，我们将探索使用突变Cre重组酶（保留IoxP位点结合的能力，但催化活性不高）来开发非整合rAAV载体系统。我们推测，表达突变体Cre和使用每个载体末端都有IoxP位点的rAAV载体，将促进分子内自循环，最终抑制rAAV载体基因组整合。我们将通过一系列的体外和体内实验来证明这种方法的原理。这些研究的结果将有助于深入了解rAAV载体整合的机制和插入突变的风险，并开发新的技术来避免不必要的载体基因组整合。

DESCRIPTION (provided by applicant): Recombinant adeno-associated virus (rAAV) vectors efficiently deliver therapeutic genes in many target tissues. They have become very popular and are widely used for many gene transfer experiments including gene therapy of metabolic diseases and genetic disorders. Since rAAV vectors are generated based on a non-pathogenic virus, they have been considered as one of the safest vectors for years. However, recent reports of unpredictable retroviral insertional mutagenesis in mice and human subjects, and our recent findings in an analysis of a limited number of rAAV integration events showing that rAAV vectors preferentially integrate into active genes, have raised concerns about the potential for rAAV-mediated insertional mutagenesis. Therefore, it is very important to re-define the risk of rAAV-mediated gene therapy. Our long-term objectives in this regard are to establish the risk of rAAV vector integration and to develop the safest rAAV vector systems. To achieve these goals, we propose three exploratory studies. First, we will develop a novel high-throughput method for isolation of rAAV vector insertion sites in vector-transduced tissues and carry out a large-scale analysis for thorough understanding of rAAV vector biology and consequences of rAAV vector integration. Second, considering that rAAV preferentially integrate into active genes, we assume that continuously regenerating cells due to hepatocellular injury may have dysregulated expression of cell cycle-related genes, which may be susceptible to rAAV vector integration, leading to accelerated malignant transformation of hepatocytes. Therefore, we will assess synergistic procarcinogenic potential of rAAV vectors using transgenic mouse models for viral hepatitis predisposed to liver cancer. Third, we will explore the use of mutant Cre recombinases (retaining the ability of IoxP site binding but catalytically inactive) to develop a non-integrating rAAV vector system. We hypothesize that expression of a mutant Cre and the use of rAAV vectors with a IoxP site at each vector end, will facilitate intramolecular selfcircularization and ultimately inhibit rAAV vector genome integration. We will establish proof of principle of this approach with a series of in vitro and in vivo experiments. The results from these proposed studies will lead to profound understanding of the mechanisms of rAAV vector integration and the risk of insertional mutagenesis, and to development of new technologies to avoid unwanted vector genome integration.