转基因植物疫苗的研究进展

近些年,随着遗传技术和植物基因工程的发展进步,疫苗（亚单位疫苗、活载体疫苗和核酸疫苗等）的研究迅速发展起来。尤其是利用转基因植物技术生产植物疫苗的研究受到了广泛的关注,在转基因植物（蔬菜、水果、农作物）的可食用部位表达抗原生产人或动物治疗用重组蛋白和疫苗的技术为可食性疫苗的研制开辟了新途径,展现了诱人的开发前景。植物来源的疫苗具有很多优势,如生产成本低、易于保存、免疫接种方便、甚至不需提取纯化等处理而直接食用。目前已有很多转基因植物疫苗产品投入开发和生产。文章综述了近几年转基因植物疫苗在表达系统、生产、生物安全／管理、公众健康等方面的研究进展,对转基因植物疫苗存在的问题进行了分析,并对其研究前景提出了展望。     

Plants as bioreactors for the production of vaccine antigens

Plants have been identified as promising expression systems for commercial production of vaccine antigens. In phase I clinical trials several plant-derived vaccine antigens have been found to be safe and induce sufficiently high immune response. Thus, transgenic plants, including edible plant parts are suggested as excellent alternatives for the production of vaccines and economic scale-up through cultivation. Improved understanding of plant molecular biology and consequent refinement in the genetic engineering techniques have led to designing approaches for high level expression of vaccine antigens in plants. During the last decade, several efficient plant-based expression systems have been examined and more than 100 recombinant proteins including plant-derived vaccine antigens have been expressed in different plant tissues. Estimates suggest that it may become possible to obtain antigen sufficient for vaccinating millions of individuals from one acre crop by expressing the antigen in seeds of an edible legume, like peanut or soybean. In the near future, a plethora of protein products, developed through ‘naturalized bioreactors’ may reach market. Efforts for further improvements in these technologies need to be directed mainly towards validation and applicability of plant-based standardized mucosal and edible vaccines, regulatory pharmacology, formulations and the development of commercially viable GLP protocols. This article reviews the current status of developments in the area of use of plants for the development of vaccine antigens.     

Recent advances and safety issues of transgenic plant-derived vaccines

Transgenic plant-derived vaccines comprise a new type of bioreactor that combines plant genetic engineering technology with an organism's immunological response. This combination can be considered as a bioreactor that is produced by introducing foreign genes into plants that elicit special immunogenicity when introduced into animals or human beings. In comparison with traditional vaccines, plant vaccines have some significant advantages, such as low cost, greater safety, and greater effectiveness. In a number of recent studies, antigen-specific proteins have been successfully expressed in various plant tissues and have even been tested in animals and human beings. Therefore, edible vaccines of transgenic plants have a bright future. This review begins with a discussion of the immune mechanism and expression systems for transgenic plant vaccines. Then, current advances in different transgenic plant vaccines will be analyzed, including vaccines against pathogenic viruses, bacteria, and eukaryotic parasites. In view of the low expression levels for antigens in plants, high-level expression strategies of foreign protein in transgenic plants are recommended. Finally, the existing safety problems in transgenic plant vaccines were put forward will be discussed along with a number of appropriate solutions that will hopefully lead to future clinical application of edible plant vaccines.     

植物性口服疫苗研究进展

利用转基因植物作为生物反应器生产疫苗是近几年发展起来的一个崭新的领域 ,并取得了许多成就。就植物性口服疫苗的最新研究进展进行了综述 ,并展望了这一领域的发展前景与存在问题。     

Application of chitosan microspheres for nasal delivery of vaccines

Nasal vaccines offer several benefits, such as highly vascular mucous membranes, low enzymatic degradation compared to oral vaccines, and greater acceptability to patients. Nasal vaccines, however, have to overcome several limitations, including mucociliary clearance and the inefficient uptake of soluble antigens. Therefore, nasal vaccines require potent adjuvants and delivery systems to enhance their immunogenicity and to protect their antigens. Chitosan is a cheap, biocompatible, biodegradable, mucoadhesive, and nontoxic natural polymer. Chitosan microspheres have been investigated to determine whether they allow the controlled release of drugs and vaccines. They have figured in various studies on the vaccine delivery system through the nasal route. Several researchers have developed modified chitosan microspheres through their concomitant use with adjuvants or immunomodulators for an additive and a synergistic effect, and through the mannosylation of chitosan for receptor-mediated targeting antigen-presenting cells. The results of the recent researches on chitosan microspheres used as a nasal vaccine delivery system are discussed in this review.     

Pharming vaccines for hepatitis and cytomegalovirus: Towards the development of multivalent and subunit vaccines for oral delivery of antigens

A plant based high fidelity vaccine production system is being developed with emphasis on producing antigens capable of being orally delivered in multivalent or subunit plant packets. Plant-based edible vaccines may provide an attractive, safe and inexpensive alternative to conventional vaccine production. Edible plant tissues are not normally antigenic in nature. However, foreign antigens from common infectious organisms like hepatitis-B virus (HBV) can be produced along with naturally occurring storage proteins in DNA-transformed plants. Upon administration via the oral route, these transgenic plant tissues may mobilize the protective humoral and mucosal immune responses to challenge the natural infectious agent. When tobacco, carrot and rice plants were transformed with the truncated version of the HBV nucleocapsid gene expression construct, non-infective hepatitis B viral core particles were observed via electron microscopy. A second plant codon-optimised HBV expression construct was designed that included the extensin signal sequence for augmented HBV particle accumulation. Upon transformation of tobacco plants with the codon-optimised construct, over 4 times more transgenic plants with high levels of expression of the HBV nucleocapsid protein were generated in comparison with a similar vector containing the unmodified wild-type HBV gene codon sequence. Further analysis via Western blotting confirmed the presence of the viral antigen in the total protein extracts from transgenic tobacco leaves and seeds. Electron microscopy showed that the expressed protein self-assembled into viral-like particles of 25–30 nm in diameter. To develop an edible subunit vaccine in plant seeds, a third plant transformation construct was used for the synthesis of the human cytomegalovirus glycoprotein B (HCMV gB) subunit. The gB protein derived from tobacco seeds retained critical structural features including epitopes for neutralizing antibodies and was targeted to the protein storage vesicles of tobacco seed endosperm. Two different strains of mice were orally immunized with tobacco seeds containing low concentrations of HCMV gB, with varying dosages, but without adjuvant. No anti-gB response was detected in intestinal or serum samples. However, a systemic immune response to normal tobacco seed proteins was observed in both strains of mice. While higher expression levels of antigens in seeds must be achieved, seeds may provide an effective and immunostimulatory vehicle for delivering edible vaccines to the intestinal mucosa. One of the outstanding challenges includes defining optimum conditions of antigen presentation, dosage and immunization schedules that will induce strong mucosal and/or systemic immune responses in heterogeneous populations. Here we review the different strategies being employed to produce specific oral antigens in plant tissues.     

A banana or a syringe: journey to edible vaccines

Constant emergence of diseases, along with the expanding size of world population creates demands for newer vaccines which can meet the challenges that conventional vaccines have not been able to overcome. The application of transgenic plants in the production of pharmaceuticals has led to the new approach of plant-based, orally-delivered vaccines. In recent years a number of recombinant vaccine antigens have been expressed in different plant tissues. The review highlights the generation of edible vaccines, their mode of action and their clinical application in various human diseases. Though the road ahead seems promising, there are several constraints which restrict the success and public acceptability of these vaccines. These include problems of choice of plants, storage, delivery, dosage, safety, public perception, quality control and licensing.     

植物口服疫苗的研究进展

植物口服疫苗是通过转基因植物生产,通过口服的方式预防疾病的生物制品.作为一种新型疫苗,其研究开始于三十几年前.由于植物口服疫苗可以最大程度地降低传统疫苗的潜在风险,在疫苗生产中具有优势,因此拥有良好的商业生产前景.植物疫苗价格低廉,生产过程安全,可产生与注射疫苗相似效价效果,无论是在控制养殖业抗生素滥用的情况下作为替代...     

Edible plant vaccines: applications for prophylactic and therapeutic molecular medicine

The use of edible plants for the production and delivery of vaccine proteins could provide an economical alternative to fermentation systems. Genes encoding bacterial and viral antigens are faithfully expressed in edible tissues to form immunogenic proteins. Studies in animals and humans have shown that ingestion of transgenic plants containing vaccine proteins causes production of antigen-specific antibodies in serum and mucosal secretions. In general, the technology is limited by low expression levels for nuclear-integrated transgenes, but recent progress in plant organelle transformation shows promise for enhanced expression. The stability and immunogenicity of orally delivered antigens vary greatly, which necessitates further study on protein engineering to enhance mucosal delivery. These issues are discussed with regard to the further development of plant-based vaccine technology.     

Transgenic plants as factories for biopharmaceuticals

Plants have considerable potential for the production of biopharmaceutical proteins and peptides because they are easily transformed and provide a cheap source of protein. Several biotechnology companies are now actively developing, field testing, and patenting plant expression systems, while clinical trials are proceeding on the first biopharmaceuticals derived from them. One transgenic plant-derived biopharmaceutical, hirudin, is now being commercially produced in Canada for the first time. Product purification is potentially an expensive process, and various methods are currently being developed to overcome this problem, including oleosin-fusion technology, which allows extraction with oil bodies. In some cases, delivery of a biopharmaceutical product by direct ingestion of the modified plant potentially removes the need for purification. Such biopharmaceuticals and edible vaccines can be stored and distributed as seeds, tubers, or fruits, making immunization programs in developing countries cheaper and potentially easier to administer. Some of the most expensive biopharmaceuticals of restricted availability, such as glucocerebrosidase, could become much cheaper and more plentiful through production in transgenic plants.     

Vaccines and global health

Vaccines have made a major contribution to global health in recent decades but they could do much more. In November 2011, a Royal Society discussion meeting, 'New vaccines for global health', was held in London to discuss the past contribution of vaccines to global health and to consider what more could be expected in the future. Papers presented at the meeting reviewed recent successes in the deployment of vaccines against major infections of childhood and the challenges faced in developing vaccines against some of the world's remaining major infectious diseases such as human immunodeficiency virus (HIV), malaria and tuberculosis. The important contribution that development of more effective veterinary vaccines could make to global health was also addressed. Some of the social and financial challenges to the development and deployment of new vaccines were reviewed. The latter issues were also discussed at a subsequent satellite meeting, 'Accelerating vaccine development', held at the Kavli Royal Society International Centre. Delegates at this meeting considered challenges to the more rapid development and deployment of both human and veterinary vaccines and how these might be addressed. Papers based on presentations at the discussion meeting and a summary of the main conclusions of the satellite meeting are included in this issue of Philosophical Transactions of the Royal Society B.     

Successful oral prime-immunization with VP60 from rabbit haemorrhagic disease virus produced in transgenic plants using different fusion strategies

Expression levels of vaccine antigens in transgenic plants have important consequences in their use as edible vaccines. The major structural protein VP60 from the rabbit haemorrhagic disease virus (RHDV) has been produced in transgenic plants using different strategies to compare its accumulation in plant tissues. The highest expressing plants were those presenting stable, complex, high-density structures formed by VP60, suggesting the importance of multisubunit structures for the stability of this protein in plant cells. Mice fed with leaves of transgenic plants expressing VP60 were primed to a subimmunogenic baculovirus-derived vaccine single dose. This indicates that plants expressing VP60 antigen may be a new means for oral RHDV immunization.     

The Expression of Mycobacterium tuberculosis MPT64 Protein in Transgenic Carrots

Oral vaccines produced by transgenic plants would change the traditional means of production and inoculation of vaccines and the cost of vaccine production would be reduced greatly. In the experiments, hypocotyls and cotyledons of carrot (Daucus carota L.var.sativa)were infected with Agrobacterium tumefaciens (Smith et Townsend) Conn LBA4404 containing Mycobacterium tuberculosis (Zopf) Lehmann et Neumann MPT64 gene under the control of the 35S promoter of cauliflower mosaic virus. After two days coculture, the explants were transferred to MS selection media which contained different concentrations of kanamycin and carbenicillin. The regenerated plants with kanamycin resistance were obtained through somatic embryogenesis from the embryogenic calli formed on the selection media. Some of the plants have been transplanted and grew well in phytotron. PCR and Southern blot analyses of carrot DNA confirmed that the MPT64 gene has been introduced into the plant genome. The results of Western blot showed that the MPT64 protein have been expressed in some transgenic plants. Therefore, the transgenic plants should provide a valuable tool for the development of edible oral vaccines.     

转基因植物疫苗的研究进展

利用转基因植物作为生物反应器生产疫苗是一个新兴的技术领域,它具有生产简便、成本低廉,不需要冷藏和低温运输,安全性好,无外源性病原污染等优点。概述当前转基因植物疫苗的研究进展,并就转基因植物疫苗的作用机理及原理方法进行了介绍。     

Oral hepatitis B vaccine candidates produced and delivered in plant material

Hepatitis B is a major global health problem; approximately two billion people are infected with the virus worldwide, despite the fact that safe and efficacious vaccines have been developed and used for nearly 20 years. Prohibitive costs for vaccine purchase and administration restrict uptake in many developing nations. Agencies such as the Global Alliance for Vaccination and Immunization are helping to make current vaccines more available, but reduced costs would greatly aid this effort. Oral delivery is an option to reduce the expense of administering hepatitis B vaccines. It may also improve compliance, and orally delivered vaccines may be more efficacious among poor responders to current vaccines. However, to induce protective efficacy, oral administration may require encapsulation of antigen and delivery of large doses. Plant-based expression systems offer an oral delivery alternative with low production costs, and they also encapsulate the antigen. Some plant-based systems also stabilize antigen and therefore reduce storage and distribution costs. The hepatitis B major surface antigen has been expressed in several plant systems. A variety of regulatory sequences and subcellular targets have been used to achieve expression suitable for early stage clinical trials. However, further increase in expression will be necessary for practical and efficacious products. Appropriate processing can yield palatable products with uniform antigen concentration. The antigen expressed in plant systems shows extensive disulphide cross-linking and oligomerization and forms virus-like particles. Oral delivery of the antigen in plant material can induce a serum antibody response, prime the immune system for a subsequent injection of antigen and give a boosted response to a prior injection. Small scale clinical trials in which the antigen has been delivered orally in edible plant material indicate safety and immunogenicity.     

轮状病毒外壳蛋白VP7在转基因番茄果实中的特异表达

将轮状病毒外壳蛋白VP7基因克隆到含有番茄果实特异性启动子TFP的植物表达载体pTF ,并转化到根癌农杆菌 (Agrobacteriumtumefaciens)菌株EHA10 5中 ,采用叶盘转化法转化番茄 (LycopersiconesculentumMill.)栽培品种TX0 0 14 ,获得了转基因植株。经PCR、PCR Southernblot和Southernblot分析表明VP7基因已整合到转基因番茄植株的核基因组中 ,RT PCR、Westernblot结果表明VP7蛋白在果实中获得了特异表达     

植物中表达口蹄疫病毒抗原研究进展

口蹄疫(foot-and-mouth disease,FMD)是由口蹄疫病毒(foot-and-mouth disease virus,FMDV)引起的一种急性、烈性、高度接触性传染病,严重危害畜牧养殖业健康发展。口蹄疫灭活疫苗是口蹄疫防控的主导产品,为控制口蹄疫流行起到了重要作用;但是也存在抗原不稳定、在生产制备过程中存在因病毒灭活不彻底而散毒的风险、生产成本较高等问题。与传统的微生物和动物生物反应器相比,通过转基因技术以植物作为生物反应器生产抗原蛋白,具有成本低廉、安全便捷、易于储运等一些优势,且无需蛋白提取纯化过程,可直接食用免疫;但也存在着表达量低、控制性差等问题。因此,通过植物生物反应器表达口蹄疫病毒抗原蛋白,可能是一种具有一定优势但仍需不断优化的疫苗生产手段。本文综述了在植物中表达活性蛋白的主要策略,以及通过植物生物反应器表达口蹄疫病毒抗原蛋白的研究进展,并讨论了目前面临的问题与挑战,以期为相关工作提供一定的借鉴和参考。     

转基因番木瓜作为抗结核植物口服疫苗的初步研究

转基因植物疫苗的研制,可改变传统的疫苗接种方式和接种手段,大大降低疫苗的生产成本,具有广阔的应用前景。结核病的泛滥使抗结核的免疫预防急需开发新型的疫苗,研制抗结核的转基因植物疫苗具有重大的理论和实践意义。本文对具有良好免疫原性的结核杆菌分泌蛋白ESAT—6基因,进行了修饰改造,构建了带潮霉素选择抗性基因的植物表达载体和根癌农杆菌工程菌;采用叶盘法转化热带水果番木瓜,获得了13株抗性植株,通过PCR、Southern blot和RNA dot blot分子检测,确认了4株为转基因植株。番木瓜ESAT—6转基因植株的获得,为进一步的结核病植物口服疫苗的免疫研究和新型抗结核疫苗的研制与开发奠定了基础。     

转基因植物疫苗研究策略

利用转基因植物作为生物反应器生产疫苗受到越来越多的关注。对转基因植物疫苗的研究、生产策略进行了介绍 ,重点对提高植物疫苗表达所采用的生物技术策略进行综述 ,探讨转基因植物疫苗的发展及面临的问题。     

Chloroplast-derived vaccines against human diseases: achievements, challenges and scopes

Infectious diseases represent a continuously growing menace that has severe impact on health of the people worldwide, particularly in the developing countries. Therefore, novel prevention and treatment strategies are urgently needed to reduce the rate of these diseases in humans. For this reason, different options can be considered for the production of affordable vaccines. Plants have been proved as an alternative expression system for various compounds of biological importance. Particularly, plastid genetic engineering can be potentially used as a tool for cost-effective vaccine production. Antigenic proteins from different viruses and bacteria have been expressed in plastids. Initial immunological studies of chloroplast-derived vaccines have yielded promising results in animal models. However, because of certain limitations, these vaccines face many challenges on production and application level. Adaptations to the novel approaches are needed, which comprise codon usage and choice of proven expression cassettes for the optimal yield of expressed proteins, use of inducible systems, marker gene removal, selection of specific antigens with high immunogenicity and development of tissue culture systems for edible crops to prove the concept of low-cost edible vaccines. As various aspects of plant-based vaccines have been discussed in recent reviews, here we will focus on certain aspects of chloroplast transformation related to vaccine production against human diseases.