Virus-like particles: potential veterinary vaccine immunogens

Virus-like particle (VLP) composed of outer shell but no genome of virus mimics the natural configuration of authentic virion and has no characteristics of self-replication. A close resemblance to native viruses in molecular scaffolds and an absence of genomes make VLPs effectively elicit both humoral and cell-mediated immune responses even with no requirement of adjuvant for vaccines. As effective immunogens, characterized by high immunogenicity and safety, VLPs have been employed in production of human vaccines, such as the licensed vaccines of hepatitis B virus and human papillomavirus. However, there has been no report of licensed veterinary VLP vaccine worldwide as yet. Despite the wide application in vaccination, both the conventional inactivated and live attenuated vaccines for animals are subject to potential limitations due to incomplete inactivation and reversion to virulence. Therefore, those conventional vaccines may, to some extent, be replaced with the VLP-based vaccines conferring higher protection and safety to vaccinated animals. Here, we review the current status of VLPs as veterinary vaccines, and discuss the characteristics and problems associated with generating VLPs for different animal viruses.     

昆虫杆状病毒表达系统生产流感疫苗的研究进展

综述了昆虫杆状病毒表达系统生产流感疫苗的研究进展,同时分析了昆虫杆状病毒表达系统表达流感病毒样颗粒用于流感疫苗的优势和前景,以期为兽用流感病毒VLPs疫苗研发提供参考。     

Present and future of veterinary viral vaccinology: a review

This review deals briefly with some key developments in veterinary vaccinology, lists the types of vaccines that are used for vaccinations commonly performed in food animals as well as in companion animals, and indicates that the practising veterinarian can select the best vaccine by comparing the results of efficacy studies. Diva (Differentiating Infected from Vaccinated Animals; also termed marker) vaccines and companion diagnostic tests have been developed that can be used for progammes aimed to control or eradicate virus infections. Vaccine-induced herd immunity, which can be measured relatively easily when diva vaccines are used, is a crucial issue in such programmes. Current vaccine research follows many routes towards novel vaccines, which can be divided into non-replicating ('killed') and replicating ('live') vaccines. Promising trends are the development of DNA vaccination, vector vaccines, and attenuation of DNA and RNA viruses by DNA technology. The lack of (in vitro) correlates of vaccine protection markedly hampers progress in vaccine research. Various characteristics of an 'ideal' vaccine are listed, such as multivalency and the induction of lifelong immunity after one non-invasive administration in animals with maternal immunity. Future research should be aimed at developing vaccines that approach the ideal as closely as possible and which are directed against diseases not yet controlled by vaccination and against newly emerging diseases.     

The application of nucleic acid vaccines in veterinary medicine

Nucleic acid immunisation entails the delivery of DNA (or RNA) encoding a vaccine antigen to the recipient. The DNA is taken up by host cells and transcribed to mRNA, from which the vaccine proteins are then translated. The expressed proteins are recognised as foreign by the host immune system and elicit an immune response, which may have both cell-mediated and humoral components. DNA vaccines offer a number of advantages over conventional vaccines, including ease of production, stability and cost. They also allow the production of vaccines against organisms which are difficult or dangerous to culture in the laboratory. This review describes the principles of DNA vaccination and the application of DNA vaccines to veterinary species. Although a great deal of developmental work is required before the technology can give rise to commercial vaccines in domestic animals, there is ongoing research in many fields and it is expected that a number of exciting developments will arise in the next decade.     

Bluetongue vaccines in Europe

The article reviews the history, present status and the future of BT vaccines in Europe. So far, an attenuated (modified live viruses, MLV) and inactivated virus vaccines against BT were developed and used in the field. Moreover, the virus-like particles (VLPs) produced from recombinant baculovirus, and live recombinant vaccinia or canarypox virus-vectored vaccines were tested in the laboratory. The main aims of BT vaccination strategy are: to prevent clinical disease, to reduce the spread of the BTV in the environment and to protect movement of susceptible animals between affected and free zones. Actually, all of the most recent European BT vaccination campaigns have used exclusively inactivated vaccines. The use of inactivated vaccines avoid risk associated with the use of live-attenuated vaccines, such as reversion to virulence, reassortment of genes with field strain, teratogenicity and insufficient attenuation leading to clinical disease. The mass vaccinations of all susceptible animals are the most efficient veterinary method to fight against BT and successful control of disease. The vaccination of livestock has had a major role in reducing BTV circulation and even in eradicating the virus from most areas of Europe.     

动物细胞悬浮培养技术在兽用疫苗生产领域中的应用

近年来,动物细胞悬浮培养技术备受关注,该技术已广泛应用于各类生物制品及兽用疫苗的研究和生产过程中。细胞悬浮培养生产兽用疫苗既能降低成本, 也能提高产品质量。以生物反应器技术为基础的细胞悬浮培养技术平台正逐步被建立起来且日趋成熟,成为推动兽用疫苗生产快速发展的主要动力。文章介绍了细胞悬浮培养技术,并就该技术在兽用疫苗生产中的应用进行了论述。     

Production of viral vaccines for veterinary use

This review provides inside information on the production of vaccines for veterinary use. The vaccines against rinderpest as well as foot and mouth disease are considered milestones in the history of veterinary vaccine production. Modern vaccines are based on the scientific progress in virology, cell biology and immunology. While naturally occurring attenuated viruses or viruses obtained after passage in different animal species or cell culture were used as vaccine strains in the early vaccines, nowadays targeted mutagenesis can be applied to generate vaccine virus strains. In principle, the antigen production process is the same for live and inactivated vaccines. The vaccine virus is usually grown in cell culture, either in roller bottles or bioreactors. Most live vaccines are freeze-dried in order to enable storage in the refridgerator for a longer period. To this end, a so-called stabilizer is added to the culture medium. The inactivation of the vaccine virus for the production of killed vaccines is done by physical or chemical treatments that lead to denaturation of the proteins or damage of the nucleic acids. The inactivated antigen may be further purified and mixed with an adjuvant. The quality standards for vaccines are layed down in international regulations and laws. Numerous tests are performed during the different production steps and on the final product in order to warrant the quality of each batch.     

A simplified roller bottle platform for the production of a new generation VLPs rabies vaccine for veterinary applications

Rabies is a neglected disease with an estimated annual mortality of 55,000 human deaths, affecting mainly low-income countries. Over 95% of these cases result from virus transmission through the bite of infected dogs and for this reason there is a real need for a cheap and effective rabies veterinary vaccine to be used in mass vaccination campaigns. In this work, we describe the establishment of a simple platform for the production of a virus-like particles based rabies vaccine using mammalian cells and roller bottles as culture system. Adherent cells were cultured during more than 15 days and VLPs were continuously produced and secreted to the culture supernatant. Immunogenicity and protective efficacy of VLPs were tested through rabies virus neutralizing antibody test and NIH potency test. These viral particles induced high titer of long lasting neutralizing antibodies and protected mice against active virus challenge. Therefore, this development represents a promising platform for the production of a new generation and virus-free rabies vaccine candidate for veterinary applications.     

新城疫病毒样颗粒研究进展

新城疫(Newcastle disease,ND)是由新城疫病毒(Newcastle disease virus,NDV)引起的一种急性、高度接触性禽类烈性传染病,以呼吸道、消化道及神经系统症状为主要特征,在易感家禽中死亡率高达100%,给中国及世界养禽业和贸易往来带来了严重的经济损失。病毒样颗粒(virus-like particles,VLPs)是由病毒蛋白在感染过程中体外表达或自发组装而形成的不含病毒基因组、不能复制、不具有感染能力的病毒样蛋白颗粒。VLPs适宜的大小及独特的表面结构可被天然免疫细胞和分子有效识别,诱导良好的先天性免疫应答和适应性免疫应答,且VLPs不含病毒的感染性核酸,安全性较高,近年来成为疫苗领域中的研究热点。树突状细胞(dendritic cells,DCs)作为专职抗原递呈细胞,在连接天然免疫与适应性免疫之间具有独特功能,是目前抗原递呈能力最强的专职免疫细胞。成熟DCs (mature DCs,mDCs)迁移至次级淋巴组织能刺激初始型T细胞活化和增殖,被认为是特异性免疫应答的始动者,体外培养的不成熟DCs (immature DCs,imDCs) 也可辅助增强抗原递呈能力。NDV-VLPs主要是以NDV-M蛋白为骨架,来装配HN、F和NP蛋白,可表现出与活的NDV颗粒相似的外观和免疫原性。可见通过NDV-VLPs制成的疫苗同样具备安全、稳定、可刺激体液和细胞免疫应答、作为载体表达其他抗原及可设计成区分自然感染与免疫接种等诸多优点。文章主要就NDV-VLPs的相关内容展开探讨,以期为后续研究提供参考。     

Lessons from the cat: development of vaccines against lentiviruses

Feline immunodeficiency virus (FIV) is a natural infection of domestic cats, which produces a disease with many similarities to human immunodeficiency virus (HIV) infection in man. The virus is an important cause of morbidity and mortality in pet cats worldwide. As such an effective vaccine is desirable both for its use in veterinary medicine and also as a model for the development of an HIV vaccine. A large number of candidate vaccines have been tested against feline immunodeficiency virus. These include inactivated virus and infected cell vaccines, DNA and viral vectored vaccines, subunit and peptide vaccines and vaccines using bacterial vectors. Ultimately, the development of inactivated virus and infected cell vaccines led to the release of the first licensed vaccine against FIV, in 2002. This review highlights some of the difficulties associated with the development of lentiviral vaccines and some of the lessons that have been learned in the FIV model that are of particular relevance to the development of HIV vaccines.     

纳米疫苗在禽流感防控中的研究进展

禽流感病毒(Avian influenza virus, AIV)因其具有变异性强、亚型种类多、感染宿主多样性等特点,对畜牧业发展及公共卫生安全具有巨大的影响。目前,传统灭活疫苗在预防禽流感中虽起着重要作用,但仍存在免疫失败、多次接种及易出现不良反应等弊端,因此,研制新型疫苗来弥补传统疫苗的不足非常有必要。纳米颗粒疫苗具有包裹性好、结构稳定、靶向性高和免疫原性强等优点,可作为新型流感病毒疫苗的候选。笔者首先介绍了禽流感难以防控的原因及纳米疫苗的特点,然后对病毒样颗粒疫苗、自组装蛋白疫苗、聚合物纳米颗粒疫苗、无机纳米颗粒疫苗及纳米颗粒的毒性机制方面进行综述,概述了近年来AIV纳米颗粒疫苗的研究进展,并简述了采用不同抗原、不同纳米材料及不同给药方式对免疫效果的影响,结合目前纳米疫苗的研究,预测了未来纳米颗粒疫苗可作为AIV防控的一种新途径,对禽流感纳米疫苗在兽医临床的应用前景进行了分析和展望。     

FIV vaccine development and its importance to veterinary and human medicine: a review FIV vaccine 2002 update and review

Feline immunodeficiency virus (FIV) is a natural infection of domestic cats that results in acquired immunodeficiency syndrome resembling human immunodeficiency virus (HIV) infection in humans. The worldwide prevalence of FIV infection in domestic cats has been reported to range from 1 to 28%. Hence, an effective FIV vaccine will have an important impact on veterinary medicine in addition to being used as a small animal AIDS model for humans. Since the discovery of FIV reported in 1987, FIV vaccine research has pursued both molecular and conventional vaccine approaches toward the development of a commercial product. Published FIV vaccine trial results from 1998 to the present have been compiled to update the veterinary clinical and research communities on the immunologic and experimental efficacy status of these vaccines. A brief report is included on the outcome of the 10 years of collaborative work between industry and academia which led to recent USDA approval of the first animal lentivirus vaccine, the dual-subtype FIV vaccine. The immunogenicity and efficacy of the experimental prototype, dual-subtype FIV vaccine and the efficacy of the currently approved commercial, dual-subtype FIV vaccine (Fel-O-Vax FIV) are discussed. Potential cross-reactivity complications between commercial FIV diagnostic tests, Idexx Snap Combo Test and Western blot assays, and sera from previously vaccinated cats are also discussed. Finally, recommendations are made for unbiased critical testing of new FIV vaccines, the currently USDA approved vaccine, and future vaccines in development.     

The application of biotechnology to the control of foot-and-mouth disease virus.

Biotechnology, which less than 10 years ago was heralded as an alternative to epidemiology in providing the answers to the control of foot-and-mouth disease (FMD), has not fulfilled its initial promise. Instead it is now complementing epidemiology by providing extremely sensitive and specific tools for identifying and characterizing strains of FMD virus in diagnostic material. Considerable advances in our understanding of the evolution of the virus in different field situations has been made possible by the development and application of polymerase chain reaction and nucleotide sequencing techniques. The individual genes of FMD virus can now be cloned into a number of vectors and separately expressed and studied in isolation from the other viral proteins. Biotechnology has not provided a safe and effective vaccine to replace the conventional tissue culture derived vaccine that would have made FMD a disease of the past. FMD remains the most economically significant animal disease having a major influence on the international trade of animals and their products. The world distribution of FMD has remained almost unchanged over the last 20 years and a balance has been maintained between improved surveillance and diagnostic technology and the ever increasing legal and illegal international movement of animals and reduction in veterinary resources. Research continues on peptide, recombinant and vector expressed virus protein vaccines which could at any time yield a breakthrough, not only for FMD control but, using similar technology, for control of other viral diseases, human and animal. Until this occurs, control and eradication of FMD still relies on classical epidemiological techniques, making use of new biotechnological methods.     

Equine influenza vaccine efficacy: the significance of antigenic variation

To investigate the level of cross-protection induced by equine influenza H3N8 vaccines derived from different lineages, two studies have been carried out with ponies vaccinated with 'American-like' and 'European-like' vaccines and experimentally challenged with a European-like strain. The results demonstrated that equine influenza vaccines clearly protect against challenge with homologous virus if serum antibody titres are sufficiently high. On the other hand, protection is incomplete even when animals vaccinated with heterologous strains have comparative antibody levels. Nevertheless, the protection afforded by heterologous viruses can be improved by stimulating high levels of antibody. It would be advisable to update equine influenza vaccine strains regularly so that they contain similar strains to variants that are circulating in the field.     

Production and immunogenicity of chimeric virus-like particles containing the spike glycoprotein of infectious bronchitis virus

Infectious bronchitis virus (IBV) poses a severe threat to the poultry industry and causes heavy economic losses worldwide. Vaccination is the most effective method of preventing infection and controlling the spread of IBV, but currently available inactivated and attenuated virus vaccines have some disadvantages. We developed a chimeric virus-like particle (VLP)-based candidate vaccine for IBV protection. The chimeric VLP was composed of matrix 1 protein from avian influenza H5N1 virus and a fusion protein neuraminidase (NA)/spike 1 (S1) that was generated by fusing IBV S1 protein to the cytoplasmic and transmembrane domains of NA protein of avian influenza H5N1 virus. The chimeric VLPs elicited significantly higher S1-specific antibody responses in intramuscularly immunized mice and chickens than inactivated IBV viruses. Furthermore, the chimeric VLPs induced significantly higher neutralization antibody levels than inactivated H120 virus in SPF chickens. Finally, the chimeric VLPs induced significantly higher IL-4 production in mice. These results demonstrate that chimeric VLPs have the potential for use in vaccines against IBV infection.     

Viruses as vectors

Traditional vaccines against diseases caused by viruses are based on live attenuated viruses or killed virus preparations. Through the application of molecular biology it is now possible to consider several new approaches to making vaccines, which may combine increased efficacy with greater safety. One of these approaches is to manipulate genetically a virus so that it carries and expresses a foreign gene (or part of a gene) which codes for a protective antigen for another disease. Adeno-, polio- and herpesviruses have been engineered to act as vectors in this way but vaccinia virus remains the main candidate for a recombinant virus vector for vaccine use. The broad host-range of vaccinia virus has made it an effective vector for the analysis of expression of "foreign" antigens as well as a tool for the dissection of the host animal's immune system. For practical purposes in veterinary vaccines, recombinant viruses based on other poxviruses, with more restricted host-ranges, may have certain advantages. Work on the development of recombinant avipoxviruses and capripoxviruses as prototype vaccines for use in poultry and ruminants, respectively, is discussed and illustrated.     

The current state of veterinary vaccines: is there hope for the future?

This article is an overview and assessment of available veterinary vaccines, placed in a historical context. A more complete presentation of the main tenets of the symposium talk at Agenda for Action: Veterinary Medicine's Role in Biodefense and Public Health is published elsewhere.' The symposium presentation contained a critical evaluation of the current state of the field of veterinary vaccines for both food and companion animals and of promises for future vaccine development. There is considerable variability in safety and sustained efficacy among veterinary vaccines, especially those developed for companion animals. Standardization of vaccines and vaccinal strains and detailed knowledge of their safety, efficacy, and potency and of the duration of immunity are needed before rational recommendations can truly be made. It is proposed that the establishment of an international vaccine advisory committee be supported, which would function to apprise the veterinary profession of the current status of vaccines and their use, and that a system for reporting vaccine adverse events, similar to that for humans, should be established.     

Prospects for molecular vaccines in veterinary parasitology

Despite the profound developments in recombinant DNA technology there is only one marketed recombinant vaccine (for human viral hepatitis B). The development of others proceeds with great difficulty. Molecular vaccines against veterinary parasites are at the utmost pole of complexity in the spectrum of potential vaccines since these parasites are complex eukaryotic organisms, often dwelling at mucosal surfaces where anamnestic responses are problematic, where the immunogenicity of the parasite components is poorly understood and where the effector mechanisms of immunity are unresolved. Cloning a "protective" gene is only the first step, and perhaps the easiest, in a long process which will be necessary to develop vaccines against parasites. Additional steps will involve comprehensive analyses of the immunological responses to ensure that vaccine antigens contain the correct epitopes to induce appropriate immune effector mechanisms for parasite elimination and immunological memory and that these responses are not genetically restricted. The great expectations for recombinant vaccinia-based vaccines must be modified substantially in the light of recent evidence indicating immunological and other constraints on this approach. The use of anti-idiotype vaccines is an underexplored opportunity for practical parasite vaccines since they have several potentially important advantages. The need to include T cell antigenic peptides in peptide vaccines to extend the range of genetic responsiveness and to induce anamnestic responses is now clear. New algorithms for the prediction of such sites exist and these can be tested experimentally with synthetic peptides. There are no major technical obstacles to the development of vaccines for parasites which cannot be overcome. However substantial long term basic research is needed over a range of disciplines to achieve this worthwhile objective.     

三个厂家猪瘟活疫苗免疫效果比较试验

在同一条件下对3个厂家生产的猪瘟细胞源活疫苗进行了免疫效果评价试验,并与猪瘟传代细胞苗免疫效果进行比较。结果发现3个厂家生产的猪瘟细胞源活疫苗存在一定差异,2个厂家的免疫效果较好,1个厂家的免疫效果较差。猪瘟传代细胞苗免疫效果优于猪瘟细胞源活疫苗,猪瘟传代细胞苗免疫1次,抗体合格率高,持续时间长,猪瘟细胞源活疫苗要免疫两次才能获得比较好的效果。同时,我们发现高致病性猪蓝耳病活疫苗（JXA1-R株）对猪瘟抗体产生有一定影响。     

Modern veterinary vaccines and the Shaman's apprentice

This paper is an overview and assessment of new, commercially available veterinary vaccines placed in a historical context. The authors critically evaluate the current state of the field of veterinary vaccines in both food and companion animals and the promises for future vaccine development. The authors maintain that there is considerable variability in safety and sustained efficacy among veterinary vaccines, especially those developed for companion animals. It is proposed that establishment of an international vaccine advisory committee be supported which would function to apprise the veterinary profession of the current status of vaccines and their use.