导读

基因治疗与表达载体构建是本期文章收录的主题。基因治疗是指向靶细胞引入正常有功能的基因,以纠正或补偿致病基因所产生的缺陷,从而达到治疗疾病的目的。其中将目的基因导入靶细胞并使之表达是其关键环节,因此介导的表达载体的选择便显得格外重要。基因治疗载体可分为病毒性载体和非病毒性载体。病毒性载体中反转录病毒载体对淋巴细胞、神经细胞、肝细胞、心肌细胞、肌细胞和多种肿瘤细胞均具有较高的转导效率;腺相关病毒载体被广泛用于治疗恶性肿瘤、自身免疫性疾病、感染性疾病及器官移植     

癌基因治疗传递系统研究的新进展

基因治疗的主要目的是开发和利用高效无毒的基因载体，包裹和传递外源性基因材料到靶细胞。病毒型基因载体包括逆转录病毒、腺病毒、单纯疱疹病毒、腺病毒相关病毒和痘病毒，基因传递效率高，但安全性差和基因载量低。非病毒载体包括阳离子聚合物、阳离子多肽和阳离子脂质体，基因传递效率比病毒载体低，但更安全、制备简单、基因包裹率高。     

一种基因递送的载体——人工病毒[英]

一种具有病毒样功能的人工病毒作为基因递送的载体用于基因治疗的研究正在进行中。虽然该技术尚处于实验室研究阶段，但有可能对将来的基因治疗产生巨大影响。全世界已进行过1000多次基因治疗临床试验，但成功率很低，而且，目前尚没有一个基因治疗的产品通过FDA批准。造成这种现象的很重要的一个原因是现有的基因治疗载体很难将目的DNA递送进靶细胞并在胞核内持续表达，即现有的技术如质粒等细胞的转染率很低。     

基因治疗在肾脏疾病中的应用进展

基因治疗是利用DNA重组和基因转移技术在基因水平对疾病进行治疗的一种方法。目前用作基因治疗载体的主要有病毒载体、细菌载体、人工载体和脂质体载体等。病毒载体常用的是逆转录病毒、腺病毒(Ad)、腺相关病毒(AAV)、慢病毒和单纯疱疹病毒(HSV)。细菌载体和人工载体则还处于研究阶段。     

多糖类材料在基因递释系统中的应用

基因治疗需要将外源正常基因导入靶细胞,以纠正或补偿因基因缺陷和异常引起的疾病,以达到治疗目的。为了增加外源性基因的转染效率,必须借助适宜的载体,现常用的载体分为病毒载体(如腺病毒载体)与非病毒载体。与病毒载体相比,非病毒载体如多糖类载体具有来源广泛,安全性高,无毒,生物相容性好,高度可修饰性等特点,具有广泛的应用前景。文章就多糖类材料在基因递释系统中的应用进行了综述。     

用于基因治疗和DNA疫苗的质粒DNA下游技术

基因治疗是将核酸导入人体细胞来改变基因组成而达到治疗目的的一种治疗战略。核酸是一种编码治疗性蛋白、破坏性蛋白或标记蛋白的双链DNA；它也可以是结合到宿主细胞靶序列上的反义RNA或单链DNA，通过阻滞mRNA或基因启动子来抑制基因的表达。第一个基因治疗产品一问世，很快便得到市场认可，预计该类产品的销售额到2010年将超过450亿美元。有效的基因治疗的先决条件是将核酸有效地传送到靶细胞。除了用反义疗法外，该核酸还必须到达细胞核。目前已经开发了能传递核酸的病毒载体和非病毒载体。尽管用病毒载体有许多优点，但是尚无足够…     

阳离子脂质体在基因转染载体中的研究进展

目前基因治疗面临的首要技术问题是基因药物的载体,用于基因治疗的载体主要分为两大类:病毒载体和非病毒载体.病毒载体可能在体内发生基因的重组或互补,因此具有较大的潜在危险,限制了它在临床基因治疗上的应用[1].非病毒载体中发展最为成熟的是阳离子脂质体(cationic liposomes,CL)载体,它具有可自然降解、无免疫原性、可重复转染等优点,迄今已有数十种阳离子脂质体被用于基因转染[2].该项技术目前已成为基因治疗的研究热点之一,现就其进展综述如下.     

靶向基因转移系统的研究进展

基因治疗已在治疗多种人类重大疾病如遗传病、肿瘤等方面显示出良好的应用前景,但也面临着巨大的挑战,主要是如何选择安全、高效、靶向的载体系统。基因治疗的靶向性研究近年来取得了许多新的进展,如应用重组病毒载体,借助抗体或配体将治疗基因定向导入靶细胞。纳米生物材料由于其良好的生物安全性,可方便有效地实现基因的靶向性及高效表达,成为制备高效、靶向的基因治疗载体系统的良好介质,在基因治疗载体系统中日益受到广泛重视。本文综述了目前国内外在靶向基因转移系统中的最新研究进展。     

肝癌的基因治疗

<正>相对于传统的疾病治疗方法,基因治疗是一种全新的理念。这种治疗理念是将外源基因通过各种特殊处理的载体导入到机体细胞内,从而发挥目的基因的治疗效果。目前,基因治疗肝癌的过程中,实验经常使用到病毒载体和非病毒载体。载体包裹目的基因转染癌细胞,使得癌细胞受到杀伤或者生长抑制。常使用的基因治疗策略有:①直接或者间接地诱导癌细胞凋亡;②激活机体的免疫系统杀伤肿瘤细胞;③抑制肿瘤组织血管生成。随着对基因表达技术的深入研究,现在的基因治疗已经逐步发展成为一种"载体具有靶向性、基因表达具有选择性"的基本模式[1]。     

肝细胞癌的靶向基因治疗

靶向基因治疗技术的发展和应用为肝癌治疗提供了新的手段，具备广阔的临床应用前景。基因治疗必需具备遗传物质和目的基因载体两个条件。载体分为病毒载体和外病毒载体，而遗传物质则可根据相应的治疗目的加以选择。     

Evolving phage vectors for cell targeted gene delivery

We adapted filamentous phage vectors for targeted gene delivery to mammalian cells by inserting a mammalian reporter gene expression cassette (GFP) into the vector backbone and fusing the pIII coat protein to a cell targeting ligand (i.e. FGF2, EGF). Like transfection with animal viral vectors, targeted phage gene delivery is concentration, time, and ligand dependent. Importantly, targeted phage particles are specific for the appropriate target cell surface receptor. Phage have distinct advantages over existing gene therapy vectors because they are simple, economical to produce at high titer, have no intrinsic tropism for mammalian cells, and are relatively simple to genetically modify and evolve. Initially transduction by targeted phage particles was low resulting in foreign gene expression in 1-2% of transfected cells. We increased transduction efficiency by modifying both the transfection protocol and vector design. For example, we stabilized the display of the targeting ligand to create multivalent phagemid-based vectors with transduction efficiencies of up to 45% in certain cell lines when combined with genotoxic treatment. Taken together, these studies establish that the efficiency of phage-mediated gene transfer can be significantly improved through genetic modification. We are currently evolving phage vectors with enhanced cell targeting, increased stability, reduced immunogenicity and other properties suitable for gene therapy.     

Assaying extrachromosomal gene therapy vectors that carry replication/persistence elements

Persistence in the cell is a desirable property for most gene therapy vectors. For extrachromosomal vectors, persistence is limited in most cell types. To address this problem, we have developed vectors with the ability to replicate and be retained in the nucleus. These properties are conferred by specific elements present on the vectors and derived from genomic DNA and from Epstein–Barr virus. In order to begin evaluation of these vectors for use in gene therapy, we developed and present here two assays that measure the persistence of vector DNA in tissue culture cells under rapidly dividing and slowly dividing conditions. Our results indicate that inclusion of DNA replication and nuclear retention elements on a vector increases persistence of vector DNA in slowly dividing cells by at least 500%. Further improvement of the system is discussed.     

Prospects and problems of gene therapy: an update

The gene therapy approach can vary from delivering extra copies of a gene, through modifications of a genome using the properties of ribozymes or chimeraplasts, to injection of modified cells. For the treatment of genetic deficits the ultimate goal would be the repair of the mutated gene in the target tissue(s). The techniques required for such an approach are emerging, albeit slowly. Therefore, delivery of an extra copy of a normal gene in a specific vector remains the predominant approach. Moreover, this method finds wider applications in gene therapy relating to disorders other than heritable defects, e.g., malignancies, cardiovascular diseases and infections. The major and most intensive areas of research are: i) vectors and delivery methods, ii) regulation of transgene expression and iii) stability of expression. Targeting of the therapeutic gene is being accomplished by using viral vectors or non-viral delivery systems, either ex vivo or in vivo. The choice of vectors and delivery routes depends on the nature of the target cells and the required levels and stability of expression. Although there have been the first positive clinical results and significant technical achievements over the past 2 years, there are still obstacles to the development of effective clinical products and these remain largely unchanged. The most important barriers are the low levels and stability of expression and immune responses to vectors and/or gene products. The safety aspects of gene therapy have become painfully evident with the first death conclusively linked to gene therapy. The progress in AAV and lentiviral vectors, improved regulation of transgene expression and advances in stem cell technology are among the recent most exciting developments.     

Basic study for next-generation gene therapy products

Successful gene therapy depends largely on vectors that can efficiently deliver the therapeutic genes into the target tissues and cells. Recombinant adenovirus (Ad) vectors continue to be the preferred vectors for gene therapy because they can easily be grown to high titers and can efficiently transfer genes into both dividing and nondividing cells. However, there are some limitations such as the time-consuming and labor-intensive procedures for vector construction, coxsackievirus-adenovirus receptor (CAR)-dependent gene transfer, immunologic side effects, lack of tissue specificity, lack of regulation of gene expression, etc. In this paper, I review our approach to the development of advanced recombinant Ad vectors. The next generation of Ad vectors have not only become promising vectors for gene therapy but also important tools for gene transfer into mammalian cells.     

Recombinant adeno-associated virus: formulation challenges and strategies for a gene therapy vector

Recombinant adeno-associated virus (AAV)-based vectors capable of expressing therapeutic gene products in vivo have shown significant promise for human gene therapy. One challenge facing the field is the development of vector formulations to achieve optimal vector safety, stability and efficacy. Formulation challenges for AAV vectors can be divided into those relating to maintaining vector activity during purification and storage, and those relating to efficient target tissue transduction in vivo. AAV vectors are potentially susceptible to loss of activity through aggregation, proteolysis and oxidation, as well as through non-specific binding to product contact materials used for vector purification and storage. These deleterious changes need to be thoroughly characterized, and the conditions and excipients to prevent them need to be identified. For in vivo administration, major vector formulation challenges include optimization of efficiency and specificity of target tissue transduction, and the ability to overcome host immune responses.     

Retroviral vector-mediated gene therapy for metabolic diseases: an update

Retroviral vectors have been used for several decades for the transfer of therapeutic genes to various cells or organs including the liver. Initial studies aimed at treating inherited liver deficiencies were carried out with murine oncoretroviral vectors either delivered directly to the organ or using an ex vivo strategy that entailed harvest of the hepatocytes, transduction during a culture phase and further reinfusion to the patient. However, although a clinical trial was performed in the early 1990s, a complete cure of animal models of metabolic diseases was rarely achieved. The advent of lentiviral vectors derived from HIV1 profoundly changed the field and this vector type now appears to be of the most attractive for liver directed gene therapy. Indeed, lentiviral vectors do not require complete cell division to transduce the target cells. There are however still bottlenecks that limit the clinical development of gene therapy using retroviral vectors. In the present review we will specifically focus on specific aspects such as the risk of insertional mutagenesis, the potential requirement of cell cycle activation to enhance transduction and the major issue of an immune response directed against the transgene as well as some specific aspects of ex vivo gene transfer. Finally we will briefly consider the future developments of these vectors made possible by the availability of new techniques in cell and molecular biology.     

Conditionally replicative adenoviruses for cancer therapy

The delineation of the genetic etiology of cancer makes gene therapy a rational approach for the molecular treatment of cancer. Many gene delivery systems have been developed, with viral vectors being the most effective. Underlying cancer gene therapy protocols is the recognition that quantitative tumor transduction cannot be achieved with the vector systems available at the present time. One way to overcome this problem could be to amplify the transduction efficiency through the use of vectors capable of replicating specifically in tumor cells. We are currently developing an adenoviral vector in which viral replication will be restricted to the target tumor cells by limiting the expression of viral genes essential for the virus replication only to the tumor cells of interest.