Production of Japanese Encephalitis Virus-Like Particles Using Insect Cell Expression Systems
Virus-like particles (VLPs) can be produced via the expression of virus surface proteins that self-assemble into particulate structures in recombinant protein expression systems. Expression of the DNA fragment encoding the Japanese encephalitis (JE) virus
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Introduction
1.1 Virus-Like Particles (VLPs) and Insect Cell Expression Systems
Structural viral proteins such as envelope and capsid proteins self-assemble into particulate structures similar to authentic virus particles or naturally occurring subviral particles. Based on this characteristic, the expression of such viral surface proteins in heterologous systems using recombinant DNA technology allows the production of VLPs [1–5]. VLPs are non-infectious and non-replicating because they are formed without incorporation of either the DNA or RNA of the virus. VLPs can induce strong humoral and cellular immune responses because of their densely repetitive display of viral antigens in an authentic conformation [1–5]. Therefore, VLPs offer a promising platform for the development of safe and efficacious vaccines and diagnostic antigens. VLPs can be rapidly manufactured on a large scale using recombinant protein production systems. A variety of expression systems, including bacterial, yeast, insect, mammalian, and plant cell systems and in vitro cell-free systems, are generally available for the production of recombinant proteins [5, 6]. Among them, the baculovirus–insect cell system has been employed extensively in the production of VLPs and subunit vaccines [4–11]. In the typical baculovirus–insect cell system, a recombinant nucleopolyhedrovirus (NPV) is generated, wherein the polyhedrin gene is replaced with a foreign gene of interest. The promoter for the polyhedrin gene is extremely strong, whereas the polyhedrin gene is essential neither for the infection nor for the replication of a baculovirus. Consequently, the infection of cultured lepidopteran insect cells, such as Spodoptera frugiperda Sf9 cells and Trichoplusia ni BTI-TN-5B1-4 (High Five) cells, with a recombinant baculovirus often leads to the expression of large quantities of foreign protein under the control of the polyhedrin promoter during the very late
Sunil Thomas (ed.), Vaccine Design: Methods and Protocols, Volume 2: Vaccines for Veterinary Diseases, Methods in Molecular Biology, vol. 1404, DOI 10.1007/978-1-4939-3389-1_25, © Springer Science+Business Media New York 2016
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Hideki Yamaji and Eiji Konishi
phase of infection. Host insect cells perform most of the posttranslational processing and modifications of higher eukaryotes [12]. The baculovirus–insect cell system is not hazardous to humans since baculoviruses are nonpathogenic to vertebrates and plants. In addition, insect cells do not support the growth of mammalian viruses (except for arboviruses) or mycoplasmas. Insect cells easily grow to a high cell density in suspension culture with a serum-free or animal-derived component-free medium. A human papillomaviruslike particle vaccine that has been approved for the prevention of cervical cancers is manufactured on an industrial scale using the baculovirus–insect cell system [8, 9, 13]. This system is also employed for the manufacture of a seasonal influenza vaccine that has been approved for use in the USA, and consists of recom
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