The large-scale production of an artificial influenza virus-like particle vaccine in silkworm pupae

Effective expression and characterization of the receptor binding domains in SARS-CoV-2 Spike proteins from original strain and variants of concern using Bombyx mori nucleopolyhedrovirus in silkworm

A new coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is responsible for the global pandemic of COVID-19 in 2020. Through structural analysis, it was found that several amino acid residues in the human angiotensin-converting enzyme-2 (hACE2) receptor directly interact with those in the receptor binding domain (RBD) of the spike glycoprotein (S-protein). Various cell lines, including HEK293, HeLa cells, and the baculovirus expression vector system (BEVS) with the insect cell line Sf9, have been utilized to produce the RBD. In this study, we investigated the use of Bombyx mori nucleopolyhedrovirus (BmNPV) and BEVS. For efficient production of a highly pure recombinant RBD protein, we designed it with two tags (His tag and STREP tag) at the C-terminus and a solubilizing tag (SUMO) at the N-terminus. After expressing the protein using BmNPV and silkworm and purifying it with a HisTrap excel column, the eluted protein was digested with SUMO protease and further purified using a Strep-Tactin Superflow column. As a result, we obtained the RBD as a monomer with a yield of 2.6 mg/10 mL serum (equivalent to 30 silkworms). The RBD showed an affinity for the hACE2 receptor. Additionally, the RBDs from the Alpha, Beta, Gamma, Delta, and Omicron variants were expressed and purified using the same protocol. It was found that the RBD from the Alpha, Beta, Gamma, and Delta variants could be obtained with yields of 1.4-2.6 mg/10 mL serum and had an affinity to the hACE2 receptor.

The potential of a universal influenza virus-like particle vaccine expressing a chimeric cytokine

The efficacy of the current influenza vaccines is frequently reduced because of antigenic drift, a trade-off of developing improved vaccines with broad cross-protective activity against influenza A viruses. In this study, we have successfully constructed a chimeric cytokine (CC) comprising the M2 protein, influenza A neuraminidase stalk, and interleukin-12. We produced virus-like particles (VLPs) containing CC and influenza hemagglutinin (HA) proteins using a baculovirus system in Eri silkworm pupae. The protective efficacy of the CCHA-VLP vaccine was evaluated in mice. The CCFkH5HA-VLP vaccine increased the survival rates of BALB/c mice, infected with a lethal dose of PRH1 and HKH5 viruses, to 80% and 100%, respectively. The results suggested that CCHA-VLP successfully induced potent cross-reactive protective immunity against infection with homologous and heterologous subtypes of the influenza A virus. This is the first study to design a CC-containing HA-VLP vaccine and validate its protective efficacy.

Examining the Interactions of GalahadTM Compound with Viruses to Develop a Novel Inactivated Influenza A Virus Vaccine

Galahad™ is a proanthocyanidin complexed with polysaccharides that inactivates viruses and indicates potential for an innovative approach to making protective vaccines. The polysaccharide portion of Galahad™ consists mainly of arabinan and arabinogalactan. In a seven-day toxicity study in rats, it was not toxic even when tested undiluted. Galahad™ inactivated a wide range of DNA and RNA viruses including adenoviruses, corona viruses such as SARS-CoV-2, and influenza viruses. Electron microscopy studies showed that exposure to Galahad™ caused extensive clumping of virions followed by lack of detection of virions after longer periods of exposure. Based on the viral inactivation data, the hypotheses tested is that Galahad™ inactivation of virus can be used to formulate a protective inactivated virus vaccine. To evaluate this hypothesis, infectious influenza A virus (H5N1, Duck/MN/1525/81) with a titer of 10^5.7 CCID₅₀/0.1 ml was exposed for 10 min to Galahad™. This treatment caused the infectious virus titer to be reduced to below detectable limits. The Galahad™ -inactivated influenza preparation without adjuvant or preservative was given to BALB/c mice using a variety of routes of administration and dosing regimens. The most protective route of administration and dosing regimen was when mice were given the vaccine twice intranasally, the second dose coming 14 days after the primary vaccine dose. All the mice receiving this vaccine regimen survived the virus challenge while only 20% of the mice receiving placebo survived. This suggests that a Galahad™-inactivated influenza virus vaccine can elicit a protective immune response even without the use of an adjuvant. This technology should be investigated further for its potential to make effective human vaccines.

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Discovery of novel virus-inactivating agent: polysaccharide/catechin (Galahad™).

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Non-toxic: inactivates/lowers titers in 25 viruses, including Avian H5N1, COVID-19.

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Agent used to make whole virus vaccine; tested in 400 animal mouse model.

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Galahad™-inactivated vaccine 100% successful intranasally vs. lethal H5N1 challenge.

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Platform offers possible benefits—in time, cost, & mass distribution.

Silkworm Pupae: A Functional Food with Health Benefits for Humans

Silkworm pupae are insects that are beneficial to human health, not only for their high nutritional value but, more importantly, for the variety of pharmacological functions they can perform when consumed. Currently, there is a lot of interest in the pharmaceutical applications of silkworm pupae. In recent years, the biological functions of domestic silkworm pupae have gradually been identified and confirmed, especially for their beneficial effects on human health. Studies have found that silkworm pupae have positive effects on liver protection, immune enhancement, antiapoptosis, antitumour, antibacterial, regulation of blood glucose and blood lipids, and lowering of blood pressure. However, the pharmacological mechanisms and systemic safety of silkworm pupae have not been systematically evaluated. In this paper, the nutritional composition of the pupae of the domestic silkworm is first summarised. The pharmacological functions of silkworm pupae and their components are then classified, and their mechanisms of occurrence are described. In addition, we provide a preliminary evaluation of the safety of silkworm pupae, analyse their application prospects, and suggest future directions for further pharmacological function studies. The aim is to generate interest in the promotion of human health through the use of silkworm pupae.

Optimization of SARS-CoV-2 Spike Protein Expression in the Silkworm and Induction of Efficient Protective Immunity by Inoculation With Alum Adjuvants

The newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing a spread of coronavirus disease 2019 (COVID-19) globally. In order to end the COVID-19 pandemic, an effective vaccine against SARS-CoV-2 must be produced at low cost and disseminated worldwide. The spike (S) protein of coronaviruses plays a pivotal role in the infection to host cells. Therefore, targeting the S protein is one of the most rational approaches in developing vaccines and therapeutic agents. In this study, we optimized the expression of secreted trimerized S protein of SARS-CoV-2 using a silkworm-baculovirus expression vector system and evaluated its immunogenicity in mice. The results showed that the S protein forming the trimeric structure was the most stable when the chicken cartilage matrix protein was used as the trimeric motif and could be purified in large amounts from the serum of silkworm larvae. The purified S protein efficiently induced antigen-specific antibodies in mouse serum without adjuvant, but its ability to induce neutralizing antibodies was low. After examining several adjuvants, the use of Alum adjuvant was the most effective in inducing strong neutralizing antibody induction. We also examined the adjuvant effect of paramylon from Euglena gracilis when administered with the S protein. Our results highlight the effectiveness and suitable construct design of the S protein produced in silkworms for the subunit vaccine development against SARS-CoV-2.

Single Dose of Bivalent H5 and H7 Influenza Virus-Like Particle Protects Chickens Against Highly Pathogenic H5N1 and H7N9 Avian Influenza Viruses

Both H5N1 and H7N9 subtype avian influenza viruses cause enormous economic losses and pose considerable threats to public health. Bivalent vaccines against both two subtypes are more effective in control of H5N1 and H7N9 viruses in poultry and novel egg-independent vaccines are needed. Herein, H5 and H7 virus like particle (VLP) were generated in a baculovirus expression system and a bivalent H5+H7 VLP vaccine candidate was prepared by combining these two antigens. Single immunization of the bivalent VLP or commercial inactivated vaccines elicited effective antibody immune responses, including hemagglutination inhibition, virus neutralizing and HA-specific IgG antibodies. All vaccinated birds survived lethal challenge with highly pathogenic H5N1 and H7N9 viruses. Furthermore, the bivalent VLP significantly reduced viral shedding and virus replication in chickens, which was comparable to that observed for the commercial inactivated vaccine. However, the bivalent VLP was better than the commercial vaccine in terms of alleviating pulmonary lesions caused by H7N9 virus infection in chickens. Therefore, our study suggests that the bivalent H5+H7 VLP vaccine candidate can serve as a critical alternative for the traditional egg-based inactivated vaccines against H5N1 and H7N9 avian influenza virus infection in poultry.

Comparison of Chicken Immune Responses after Inoculation with H5 Avian Influenza Virus-like Particles Produced by Insect Cells or Pupae

Introduction

Novel clade 2.3.4.4 H5 highly pathogenic avian influenza virus (HPAIV) outbreaks have occurred since early 2015 in Taiwan and impacted the island economically, like they have many countries. This research investigates the immunogenicity of two HPAIV-like particles to assess their promise as vaccine candidates.

Material and Methods

The haemagglutinin (HA) gene derived from clade 2.3.4.4 H5 HPAIV and matrix protein 1 (M1) gene were cloned into the pFastBac Dual baculovirus vector. The resulting recombinant viruses were expressed in Spodoptera frugiperda moth (Sf)21 cells and silkworm pupae to generate Sf21 virus-like particles (VLP) and silkworm pupa VLP. Two-week-old specific pathogen–free chickens were immunised and their humoral and cellular immune responses were analysed.

Results

The silkworm pupa VLP had higher haemagglutination competence. Both VLP types elicited haemagglutination inhibition antibodies, anti-HA antibodies, splenic interferon gamma (IFN-γ) and interleukin 4 (IL-4) mRNA expression, and CD4⁺/CD8⁺ ratio elevation. However, chickens receiving silkworm pupa VLP exhibited a significantly higher anti-HA antibody titre in ELISA after vaccination. Although Sf21 VLP recipients expressed more IFN-γ and IL-4, the increase in IFN-γ did not significantly raise the CD4⁺/CD8⁺ ratio and the increase in IL-4 did not promote anti-HA antibodies.

Conclusion

Both VLP systems possess desirable immunogenicity in vivo. However, in respect of immunogenic efficacy and the production cost, pupa VLP may be the superior vaccine candidate against clade 2.3.4.4 H5 HPAIV infection.

Interleukin 12-containing influenza virus-like-particle vaccine elevate its protective activity against heterotypic influenza virus infection

To produce monovalent and bivalent influenza vaccines composed of virus-like particles (VLPs) containing hemagglutinin (HA), we generated four recombinant Baculoviruses derived from Bombyx mori nuclear polyhedrosis virus (BmNPV) and Autographa california nuclear polyhedrosis virus (AcNPV). Monovalent Fukushima (A/tufted duck/Fukushima/16/2011 [H5N1]) (FkH5) and Anhui (A/Anhui/1/2013 [H7N9]) (AnH7) VLP influenza vaccines were produced in silkworm pupae infected with FkH5-BmNPV or AnH7-BmNPV. To produce a bivalent FkH5 and AnH7 vaccine, the pupae were simultaneously inoculated with FkH5-BmNPV and AnH7-BmNPV. Then, interleukin (IL)-containing bivalent vaccines were produced by Eri silkworm pupae following triple infection with FkH5-AcNPV, AnH7-AcNPV, and IL-12-AcNPV. Fluorescent antibody tests in Sf9 cells triple-infected with FkH5-AcNPV, AnH7-AcNPV, and IL-12-AcNPV showed coexpression of FkH5, AnH7, and IL-12 antigens, suggesting the presence of VLPs containing all three antigens. We then performed competitive hemagglutination inhibition (CHI) tests to calculate the VLP vaccine constituents. Inoculation with two recombinant viruses led to the production of bivalent vaccines containing very similar amounts of the H5 and H7 antigens, suggesting that our dual infection system can be used to produce bivalent VLP vaccines. Immunisation of mice with our developed monovalent and bivalent VLP vaccines induced the production of HI antibody, which protected against a sublethal dose of influenza virus. These IL-12-containing vaccines tended to display increased protection against hetero-subtype influenza viruses.

Purification and characterization of immunogenic recombinant virus-like particles of porcine circovirus type 2 expressed in silkworm pupae

Porcine circovirus type 2 (PCV2) is a primary causative agent of postweaningmultisystemic wasting syndrome (PMWS), which has a significant economic impact on the swine industry. The capsid protein (Cap) encoded by ORF2 of the viral genome has been used effectively as a vaccine against PCV2 infection. The Cap protein can spontaneously assemble into virus-like particles (VLPs) that are safe and highly immunogenic for vaccine applications. Several expression systems, including bacteria, yeast and insect cells, have been utilized to produce PCV2 VLPs. However, in some cases, the recombinant Cap (rCap) proteins produced in bacteria and yeast do not assemble spontaneously. In this study, we expressed rCap protein using a silkworm-baculovirus expression vector system (silkworm-BEVS) for mass production of PCV2 VLPs and established a simple three-step protocol for its purification from pupae: extraction by detergent, ammonium sulfate precipitation and anion exchange column chromatography. Size-exclusion chromatography (SEC) analysis and transmission electron microscope (TEM) observation showed that purified rCap proteins formed VLPs with a similar morphology to that of the original virus. Furthermore, the VLPs produced in silkworms were capable of inducing neutralizing antibodies against PCV2 in mice. Our results demonstrated that the silkworm system is a powerful tool for the production of PCV2 VLPs and will be useful for the development of a reliable and cost-effective PCV2 vaccine.

Virus-like particle vaccines: immunology and formulation for clinical translation

INTRODUCTION

Virus-like particle (VLP) vaccines face significant challenges in their translation from laboratory models, to routine clinical administration. While some VLP vaccines thrive and are readily adopted into the vaccination schedule, others are restrained by regulatory obstacles, proprietary limitations, or finding their niche amongst the crowded vaccine market. Often the necessity to supplant an existing vaccination regimen possesses an immediate obstacle for the development of a VLP vaccine, despite any preclinical advantages identified over the competition. Novelty, adaptability and formulation compatibility may prove invaluable in helping place VLP vaccines at the forefront of vaccination technology.

AREAS COVERED

The purpose of this review is to outline the diversity of VLP vaccines, VLP-specific immune responses, and to explore how modern formulation and delivery techniques can enhance the clinical relevance and overall success of VLP vaccines.

EXPERT COMMENTARY

The role of formation science, with an emphasis on the diversity of immune responses induced by VLP, is underrepresented amongst clinical trials for VLP vaccines. Harnessing such diversity, particularly through the use of combinations of select excipients and adjuvants, will be paramount in the development of VLP vaccines.

Functional growth inhibition of influenza A and B viruses by liquid and powder components of leaves from the subtropical plant Melia azedarach L

We evaluated the anti-influenza-virus effects of Melia components and discuss the utility of these components. The effects of leaf components of Melia azedarach L. on viruses were examined, and plaque inhibition tests were performed. The in vivo efficacy of M. azedarach L. was tested in a mouse model. Leaf components of Melia azedarach L. markedly inhibited the growth of various influenza viruses. In an initial screening, multiplication and haemagglutination (HA) activities of H1N1, H3N2, H5, and B influenza viruses were inactivated by the liquid extract of leaves of M. azedarach L. (MLE). Furthermore, plaque inhibition titres of H1N1, H3N2, and B influenza viruses treated with MLE ranged from 103.7 to 104.2. MLE possessed high plaque-inhibitory activity against pandemic avian H5N1, H7N9, and H9N2 vaccine candidate strains, with a plaque inhibition titre of more than 104.2. Notably, the buoyant density decreased from 1.175 to 1.137 g/cm3, and spikeless particles appeared. We identified four anti-influenza virus substances: pheophorbide b, pheophorbide a, pyropheophorbide a, and pheophytin a. Photomorphogenesis inside the envelope may lead to removal of HA and neuraminidase spikes from viruses. Thus, MLE could efficiently remove floating influenza virus in the air space without toxicity. Consistent with this finding, intranasal administration of MLE in mice significantly decreased the occurrence of pneumonia. Additionally, leaf powder of Melia (MLP) inactivated influenza viruses and viruses in the intestines of chickens. MLE and MLP may have applications as novel, safe biological disinfectants for use in humans and poultry.

Overexpression of a virus-like particle influenza vaccine in Eri silkworm pupae, using Autographa californica nuclear polyhedrosis virus and host-range expansion

Ecological investigations of silkworms have revealed that Eri silkworms (Samia cynthia ricini) possess useful morphological and ecological characteristics for virus-like particle (VLP) production, namely non-seasonal breeding, longer lengths, and heavier weights than Bombyx mori silkworms. Furthermore, when vector DNA from Bombyx mori nuclear polyhedrosis virus (BmNPV), which is unable to replicate in Sf9 cells from Eri silkworms, was replaced with the Autographa californica nuclear polyhedrosis virus (AcNPV) vector, three improved AcNPV influenza virus recombinants capable of replication in Sf9 cells were obtained. Although VLP antigens produced previously in silkworms were not evaluated individually, the present recombinant Fukushima (FkH5) and Anhui (AnH7) VLP antigens were detected in tissue fluids and fat bodies of Eri silkworms. Here, we aimed to determine the function of the AcNPV vector and P143 gene by expressing recombinants in Sf9 cells and eri silkworm pupae. The FkH5 recombinant produced high yields of haemagglutinin (HA)-positive VLPs, showing a mean HA titre of 1.2 million. Similarly, high production of H7 HA VLPs was observed in the fat bodies of eri silkworm pupae. Antigenic analysis and electron microscopy examination of Eri-silkworm-produced H5 HA VLPs showed characteristic antigenicity and morphology similar to those of the influenza virus. Although FkH5 recombinants possessing the AcNPV vector did not replicate in Bm-N cells, the introduction of the helicase p143 gene from BmNPV resulted in their production in Bm-N and Sf9 cells.

Development of a Japanese encephalitis virus genotype V virus-like particle vaccine in silkworms

To counter the spread of multiple Japanese encephalitis virus (JEV) variants harboured in alternative host species and highly neurotoxic variants with new antigenicity, such as genotype V (Muar), methods for developing more effective and low-cost vaccines against a variety of epidemic JEV strains are required. Here, we successfully synthesized large amounts of a Muar virus-like particle (MVLP) vaccine for JEV in silkworm pupae by using a Bombyx mori nuclear polyhedrosis virus recombinant consisting of JEV codon-optimized envelope (E) DNA. In particular, histopathological examination suggested that MVLP was efficiently synthesized in body fat tissues as well as epithelial cells. Quantitative analysis indicated that one silkworm pupa produced 724.8 µg of E protein in the MVLP vaccine. Electron microscopic examination of purified MVLP vaccine defined a typical MVLP morphological structure. Detailed MVLP antigen assessment by immune-electron microscopy revealed that the majority of MVLPs were covered with approximately 10 nm projections. Boosted immunization with MVLP antigens in mice and rabbits tended to show improved plaque inhibition potency against homologous Muar and heterologous Nakayama, but less potency to Beijing-1 strains. Notably, mixed immune rabbit antisera against Nakayama and Muar VLP antigens led to an increase in the low antibody reaction to Beijing-1. Additionally, a stopgap divalent JEV vaccine consisting of MVLP and Nakayama VLP and its immune mouse serum significantly increased plaque inhibition titre against Muar, Nakayama and Beijing-1 strains. These findings suggested that low-cost MVLP vaccines prepared in silkworm pupae are suitable for providing simultaneous protection of individuals in developing countries against various JEV strains.

Non-protein biologic therapeutics

While the therapeutic biologics are dominated by therapeutic proteins, particularly monoclonal antibodies, a wide range of non-protein therapeutic biologics are rapidly gaining ground both in clinical studies and approved products. Many of these first-in-class therapies provide novel treatment modalities and address previously untreatable conditions or undruggable targets. In particular, novel treatments for rare genetic disorders and qualitatively different oncology therapeutics have been approved in the last two years. This review discusses recent advances in peptide, nucleic acid, carbohydrate, vaccine, and cell-based therapies as well as the manufacturing and commercialization challenges associated with these novel therapeutics.

Recombinant expression of beak and feather disease virus capsid protein and assembly of virus-like particles in Nicotiana benthamiana

BACKGROUND

Beak and feather disease virus (BFDV) is an important disease causing agent affecting psittacines. BFDV is highly infectious and can present as acute, chronic or subclinical disease. The virus causes immunodeficiency and is often associated with secondary infections. No commercial vaccine is available and yields of recombinant BFDV capsid protein (CP) expressed in insect cells and bacteria are yet to be seen as commercially viable, although both systems produced BFDV CP that could successfully assemble into virus-like particles (VLPs). Plants as expression systems are increasingly becoming favourable for the production of region-specific and niche market products. The aim of this study was to investigate the formation and potential for purification of BFDV VLPs in Nicotiana benthamiana.

METHODS

The BFDV CP was transiently expressed in N. benthamiana using an Agrobacterium-mediated system and plant expression vectors that included a bean yellow dwarf virus (BeYDV)-based replicating DNA vector. Plant-produced BFDV CP was detected using immunoblotting. VLPs were purified using sucrose cushion and CsCl density gradient centrifugation and visualised using transmission electron microscopy.

RESULTS

In this study we demonstrate that the BFDV CP can be successfully expressed in N. benthamiana, albeit at relatively low yield. Using a purification strategy based on centrifugation we demonstrated that the expressed CP can self-assemble into VLPs that can be detected using electron microscopy. These plant-produced BFDV VLPs resemble those produced in established recombinant expression systems and infectious virions. It is possible that the VLPs are spontaneously incorporating amplicon DNA produced from the replicating BeYDV plant vector.

CONCLUSIONS

This is the first report of plant-made full-length BFDV CP assembling into VLPs. The putative pseudovirions could be used to further the efficacy of vaccines against BFDV.

Development of a Japanese encephalitis virus-like particle vaccine in silkworms using codon-optimised prM and envelope genes

We have successfully prepared a Japanese encephalitis virus (JEV) - Nakayama virus like particle (NVLP) vaccine using synthetic codon-optimized prM and E genes. The expression of the recombinant JEV Nakayama-BmNPV (JEV-NNPV) virus was determined in infected silkworm Bm-N cells by fluorescence and Western blot analysis. The recombinant was inoculated into silkworm pupae and the yield of Nakayama VLP (NVLP) reached a peak in the homogenates after 3 days. Additionally, in the peptide analysis of infected pupae homogenate, it appeared approximately 300-500 μg E protein/pupa were produced. When purified the above eluates on the discontinuous sucrose density gradient centrifugation, NVLP showed a strong hemagglutination (HA) activity by using chicken red blood cell in phosphate-buffered saline (PBS) free from Mg++ and Ca++ ions. The immune antisera against NVLP strain could efficiently neutralize the plaque formation of Nakayama, Beijing-1 and Muar strains, showing tendency of much higher reaction with heterologous Muar strain than homologous Nakayama strain. Our findings suggest that the JEV-NVLP may be useful for JEV epidemic control in many endemic areas of Asian countries as a widely effective and less expensive JE vaccine.

Quantitative analysis of the yield of avian H7 influenza virus haemagglutinin protein produced in silkworm pupae with the use of the codon-optimized DNA: A possible oral vaccine

In this study, we aimed to quantitatively compare the increased production of three H7 influenza virus-like particle (VLP) haemagglutinin (HA) with the use of a codon-optimized single HA gene in silkworm pupae. Recombinant baculovirus (Korea H7-BmNPV) could produce 0.40 million HA units per pupa, corresponding to 1832μg protein. The yield of the HA produced in larva was estimated to be approximately 0.31 million HA units per larva, and there were no significant differences between the three HA proteins. We could establish efficient recovery system of HA production in larvae and pupae with the use of three cycles sonication methods. Next, we compared yields of HA proteins from three different H7 and two H5 recombinant baculoviruses based on the amount of mRNA synthesized in BmN cells, suggesting that mRNA synthesis may be also a useful indicator for the production of HA. Based on HA titres from four recombinants, the yield of HA had a great influence on the codon-optimized effect and the characteristics of the viral HA gene. The recombinant containing codon optimized HA DNA of A/tufted duck/Fukushima/16/2011 (H5N1) did produce more than one million HA units, although another recombinant including of the wild H5N1 strain failed to show HA activity. Electron microscopy revealed the presence of large VLP and small HA particle in the heavy and light fractions. The purified VLPs reacted with the authentic anti-H7 antibodies and the antibodies prepared after immunization with the VLP H7 antigen. Also H5 and H7VLPs could produce HI antibody in chickens and mice with oral immunization. The antibodies elicited with oral immunization were confirmed in fluorescent antibody analysis and western blotting in Korea H5-BmNPV and H7HA-BmNPV recombinant infected BmN cells. Taken together, these findings provided important insights into future oral vaccine development.

Expression and purification of virus like particles (VLPs) of foot-and-mouth disease virus in Eri silkworm (Samia cynthia ricini) larvae

Foot-and-mouth disease (FMD) is a highly contagious viral disease, which causes severe economic loss to livestock. Virus like particles (VLPs) produced by recombinant DNA technology are gaining importance because of their immunogenic properties and safety in developing a new vaccine for FMD. In the present study, a practical and economically feasible approach of expression, purification and characterization of VLPs of FMDV in Eri silkworm (Samia cynthia ricini) larvae was described. Although three lepidopteran insect larvae (Helicoverpa armigera, Spodoptera litura and Samia cynthia ricini) were tested for production of VLPs, expression was obtained only in Eri silkworm larvae. High titred recombinant baculovirus encoding the polyprotein P1-2A-3C of FMDV was prepared in Sf9 cells. Injection of recombinant baculovirus into hemocoel of Eri silkworm larvae resulted in increasing levels of expression of VLPs in the hemolymph from 3 to 7 days post infection (dpi) compared to low level expression by oral feeding. The VLPs reacted in Sandwich ELISA with serum raised against whole virus particles of FMDV type O/IND/R2/75 and protein banding pattern of 26, 37 and 47 kDa in Western blotting demonstrated their antigenic resemblance to native virus. Sucrose density gradient purified VLPs were used for immunization of rabbits and guinea pigs for assessing immunogenicity. Further, the reactivity of serum samples of rabbits and guinea pigs in Indirect-ELISA with titres (1.30-2.81 Log10) indicated that the VLPs were antigenic and immunogenic in nature. We demonstrate that Eri silkworm larvae could be used for production of VLPs of FMDV type O/IND/R2/75 for the first time. This approach could be useful for large scale production of recombinant VLPs for vaccine or diagnostic use in FMD control programme.

Inactivation of Bombyx mori macula-like virus under physical conditions

The Bombyx mori macula-like virus (BmMLV) is a member of the genus Maculavirus, family Tymoviridae, and contains a positive-sense single-stranded RNA genome. Previously, we reported that almost all B. mori-derived cell lines have already been contaminated with BmMLV via an unknown infection route. Since B. mori-derived cell lines are used for the baculovirus expression vector system, the invasion of BmMLV will cause a serious safety risk in the production of recombinant proteins. In this study, to determine the inactivation effectiveness of BmMLV, viruses were treated with various temperatures as well as gamma and ultraviolet (UV) light radiation. After these treatments, the virus solutions were inoculated into BmMLV-free BmVF cells. At 7 days postinoculation, the amount of virus in cells was evaluated by real-time reverse transcription PCR. Regarding heat treatment, conditions under 56°C for 3 h were tolerated, whereas infectivity disappeared after treatment at 75°C for 1 h. Regarding gamma radiation treatment, viruses were relatively stable at 1 kGy; however, their infectivity was entirely eliminated at a dose of 10 kGy. With 254 nm UV-C treatment, viruses were still active at less than 120 mJ/cm(2); however, their infectivity was completely lost at greater than 140 mJ/cm(2) UV-C radiation. These results provide quantitative evidence of the potential for BmMLV inactivation under a variety of physical conditions.