Baculovirus stimulates antiviral effects in mammalian cells

The Magic Staff: A Comprehensive Overview of Baculovirus-Based Technologies Applied to Human and Animal Health

Baculoviruses are enveloped, insect-specific viruses with large double-stranded DNA genomes. Among all the baculovirus species, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied. Due to its characteristics regarding biosafety, narrow host range and the availability of different platforms for modifying its genome, AcMNPV has become a powerful biotechnological tool. In this review, we will address the most widespread technological applications of baculoviruses. We will begin by summarizing their natural cycle both in larvae and in cell culture and how it can be exploited. Secondly, we will explore the different baculovirus-based protein expression systems (BEVS) and their multiple applications in the pharmaceutical and biotechnological industry. We will focus particularly on the production of vaccines, many of which are either currently commercialized or in advanced stages of development (e.g., Novavax, COVID-19 vaccine). In addition, recombinant baculoviruses can be used as efficient gene transduction and protein expression vectors in vertebrate cells (e.g., BacMam). Finally, we will extensively describe various gene therapy strategies based on baculoviruses applied to the treatment of different diseases. The main objective of this work is to provide an extensive up-to-date summary of the different biotechnological applications of baculoviruses, emphasizing the genetic modification strategies used in each field.

Baculovirus Vectors Induce the Production of Interferons in Swine: Their Potential in the Development of Antiviral Strategies

The huge variety of viruses affecting swine represents a global threat. Since vaccines against highly contagious viruses last several days to induce protective immune responses, antiviral strategies for rapid control of outbreak situations are needed. The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an insect virus, has been demonstrated to be an effective vaccine vector for mammals. Besides the ability to display or transduce heterologous antigens, it also induces strong innate immune responses and provides IFN-mediated protection against lethal challenges with viruses like foot-and-mouth disease virus (FMDV) in mice. Thus, the aim of this study was to evaluate the ability of AcMNPV to induce IFN production and elicit antiviral activity in porcine peripheral blood mononuclear cells (PBMCs). Our results demonstrated that AcMNPV induced an IFN-α-mediated antiviral activity in PBMCs in vitro. Moreover, the inoculation of AcMNPV in piglets led to the production of type I and II IFNs in sera from inoculated animals and antiviral activities against vesicular stomatitis virus (VSV) and FMDV measured by in vitro assays. Finally, it was demonstrated that the pseudotyping of AcMNPV with VSV-G protein, but not the enrichment of the AcMNPV genome with specific immunostimulatory CpG motifs for the porcine TLR9, improved the ability to induce IFN-α production in PBMCs in vitro. Together, these results suggest that AcMNPV is a promising tool for the induction of IFNs in antiviral strategies, with the potential to be biotechnologically improved.

Solutions against emerging infectious and noninfectious human diseases through the application of baculovirus technologies

Abstract

Baculoviruses are insect pathogens widely used as biotechnological tools in different fields of life sciences and technologies. The particular biology of these entities (biosafety viruses 1; large circular double-stranded DNA genomes, infective per se; generally of narrow host range on insect larvae; many of the latter being pests in agriculture) and the availability of molecular-biology procedures (e.g., genetic engineering to edit their genomes) and cellular resources (availability of cell lines that grow under in vitro culture conditions) have enabled the application of baculoviruses as active ingredients in pest control, as systems for the expression of recombinant proteins (Baculovirus Expression Vector Systems—BEVS) and as viral vectors for gene delivery in mammals or to display antigenic proteins (Baculoviruses applied on mammals—BacMam). Accordingly, BEVS and BacMam technologies have been introduced in academia because of their availability as commercial systems and ease of use and have also reached the human pharmaceutical industry, as incomparable tools in the development of biological products such as diagnostic kits, vaccines, protein therapies, and—though still in the conceptual stage involving animal models—gene therapies. Among all the baculovirus species, the Autographa californica multiple nucleopolyhedrovirus has been the most highly exploited in the above utilities for the human-biotechnology field. This review highlights the main achievements (in their different stages of development) of the use of BEVS and BacMam technologies for the generation of products for infectious and noninfectious human diseases.

Key points

• Baculoviruses can assist as biotechnological tools in human health problems.

• Vaccines and diagnosis reagents produced in the baculovirus platform are described.

• The use of recombinant baculovirus for gene therapy–based treatment is reviewed.

Baculoviruses in Gene Therapy and Personalized Medicine

This review will outline the role of baculoviruses in gene therapy and future potential in personalized medicine. Baculoviruses are a safe, non-toxic, non-integrative vector with a large cloning capacity. Baculoviruses are also a highly adaptable, low-cost vector with a broad tissue and host tropism due to their ability to infect both quiescent and proliferating cells. Moreover, they only replicate in insect cells, not mammalian cells, improving their biosafety. The beneficial properties of baculoviruses make it an attractive option for gene delivery. The use of baculoviruses in gene therapy has advanced significantly, contributing to vaccine production, anti-cancer therapies and regenerative medicine. Currently, baculoviruses are primarily used for recombinant protein production and vaccines.  This review will also discuss methods to optimize baculoviruses protein production and mammalian cell entry, limitations and potential for gene therapy and personalized medicine. Limitations such as transient gene expression, complement activation and virus fragility are discussed in details as they can be overcome through further genetic modifications and other methods. This review concludes that baculoviruses are an excllent candidate for gene therapy, personalized medicine and other biotherapeutic applications.

Evaluation of the Nucleopolyhedrovirus of Anticarsia gemmatalis as a Vector for Gene Therapy in Mammals

BACKGROUND

Baculoviruses are insect pathogens with important biotechnological applications that transcend their use as biological controllers of agricultural pests. One species, Autographa californica multiple nucleopolhyedrovirus (AcMNPV), has been extensively exploited as a molecular platform to produce recombinant proteins and as a delivery vector for genes in mammals because it can transduce a wide range of mammalian cells and tissues without replicating or producing progeny.

METHOD

To investigate if the budded virions of Anticarsia gemmatalis multiple nucleopolhyedrovirus (AgMNPV) species has the same ability, the viral genome was modified by homologous recombination into susceptible insect cells to integrate reporter genes and then it was evaluated on mammalian cell lines in a comparative form with respect to equivalent viruses derived from AcMNPV. Besides, the replicative capacity of AgMNPV´s virions in mammals was determined.

RESULTS

The experiments carried out showed that the recombinant variant of AgMNPV transduces and support the expression of delivered genes but not replicates in mammalian cells.

CONCLUSION

Consequently, this insect pathogen is proposed as an alternative to non-infectious viruses in humans to explore new approaches in gene therapy and other applications based on the use of mammalian cells.

Unraveling the Genome-Wide Impact of Recombinant Baculovirus Infection in Mammalian Cells for Gene Delivery

Baculovirus expression systems have been widely used to produce recombinant mammalian proteins owing to the lack of viral replication in vertebrates. Although several lines of evidence have demonstrated impacts of baculovirus infection in mammalian hosts, genome-wide effects have not been fully elucidated. Here, we provide comparative transcriptome profiles of baculovirus and host-immune response genes in recombinant baculovirus-infected mammalian and insect cells. Specifically, to decipher the impacts of baculovirus infection in mammalian cells, we conducted total RNA-seq on human 293TT cells and insect Sf9 cells infected with recombinant baculovirus. We found that baculovirus genes were rarely expressed under the control of baculoviral promoters in 293TT cells. Although some baculovirus early genes, such as PE38 and IE-01, showed limited expression in 293TT cells, baculoviral late genes were mostly silent. We also found modest induction of a small number of mammalian immune response genes associated with Toll-like receptors, cytokine signaling, and complement in baculovirus-infected 293TT cells. These comprehensive transcriptome data will contribute to improving recombinant baculovirus as tools for gene delivery, gene therapy, and vaccine development.

Baculovirus Transduction in Mammalian Cells Is Affected by the Production of Type I and III Interferons, Which Is Mediated Mainly by the cGAS-STING Pathway

The baculovirus Autographa californica multiple nucleopolyhedrovirus is an insect virus with a circular double-stranded DNA genome, which, among other multiple biotechnological applications, is used as an expression vector for gene delivery in mammalian cells. Nevertheless, the nonspecific immune response triggered by viral vectors often suppresses transgene expression. To understand the mechanisms involved in that response, in the present study, we studied the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway by using two approaches: the genetic edition through CRISPR/Cas9 technology of genes encoding STING or cGAS in NIH/3T3 murine fibroblasts and the infection of HEK293 and HEK293 T human epithelial cells, deficient in cGAS and in cGAS and STING expression, respectively. Overall, our results suggest the existence of two different pathways involved in the establishment of the antiviral response, both dependent on STING expression. Particularly, the cGAS-STING pathway resulted in the more relevant production of beta interferon (IFN-β) and IFN-λ1 in response to baculovirus infection. In human epithelial cells, IFN-λ1 production was also induced in a cGAS-independent and DNA-protein kinase (DNA-PK)-dependent manner. Finally, we demonstrated that these cellular responses toward baculovirus infection affect the efficiency of transduction of baculovirus vectors.IMPORTANCE Baculoviruses are nonpathogenic viruses that infect mammals, which, among other applications, are used as vehicles for gene delivery. Here, we demonstrated that the cytosolic DNA sensor cGAS recognizes baculoviral DNA and that the cGAS-STING axis is primarily responsible for the attenuation of transduction in human and mouse cell lines through type I and type III IFNs. Furthermore, we identified DNA-dependent protein kinase (DNA-PK) as a cGAS-independent and alternative DNA cytosolic sensor that contributes less to the antiviral state in baculovirus infection in human epithelial cells than cGAS. Knowledge of the pathways involved in the response of mammalian cells to baculovirus infection will improve the use of this vector as a tool for gene therapy.

Baculovirus AcMNPV induces type I interferons and NK/NKT cells-mediated protection against foot-and-mouth disease virus in mice

Foot-and-mouth disease is a viral illness that affects cloven-hoofed animals causing serious economic losses. Inactivated vaccines against its causative agent, foot-and-mouth disease virus (FMDV), require approximately seven days to induce protection. Therefore, antiviral strategies are needed to provide earlier protection and to stop the spread of this highly contagious virus during outbreak situations. In this way, our group has previously demonstrated that the baculovirus (BV) Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an insect virus with immunostimulant effects, induces a nonspecific antiviral status that protects C57BL/6 mice against a lethal challenge with FMDV A/Arg/01 at 3 hours or 3 days post inoculation. In this work, we studied the immunological mechanisms involved in this protection. Firstly, we compared the protection elicited by AcMNPV in wild type mice and in knock-out mice lacking the subunit IFNAR1 of the receptor for type I interferons (IFNs). Our results showed that type I IFNs are key to prevent the death of the animals after the FMDV challenge. On the other hand, we evaluated the role of NK and NKT cells by depleting these cell subsets with anti-NK1.1 monoclonal antibody. These cells proved to be necessary for the induction of IFN-γ by AcMNPV and to prevent the onset of a severe disease after the FMDV challenge. We propose BV as a novel tool for the development of antiviral strategies because of the high levels of IFNs induced and the NK/NKT cells-mediated immune response elicited.

Baculovirus-Derived Vectors for Immunization and Therapeutic Applications

Baculoviruses are arthropod-specific, enveloped viruses with circular, supercoiled double-stranded deoxyribonucleic acid genomes. While many viruses are studied to seek solutions for their adverse impact on human, veterinary, and plant health, the study of baculoviruses was stimulated initially by their potential utility to control insect pests. Later, the utility of baculovirus as gene expression vectors was evidenced leading to numerous applications. Several strategies are employed to obtain recombinant viruses that express large quantities of heterologous proteins. A major step forward was the development of bacmid technology (the construction of bacterial artificial chromosomes containing the genome of the baculovirus) which allows the manipulation of the baculovirus genome in bacteria. With this technology, foreign genes can be introduced into the bacmid by homologous and site-directed recombination or by transposition. Baculoviruses have been used to explore fundamental questions in molecular biology such as the nature of programmed cell-death. Moreover, the ability of baculoviruses to transduce mammalian cells led to the consideration of their use as gene-therapy and vaccine vectors. Strategies for genetic engineering of baculoviruses have been developed to meet the requirements of new application areas. Display of foreign proteins on the surface of virions or in nucleocapsid structures, the assembly of expressed proteins to form virus-like particles or protein complexes have been explored and validated as vaccines. The aim of this chapter is to update the areas of application of the baculoviruses in protein expression, alternative vaccine designs and gene therapy of infectious diseases and genetic disorders. Finally, we review the baculovirus-derived products on the market and in the pipeline for biomedical and veterinary use.

Recombinant baculovirus expressing the FrC-OVA protein induces protective antitumor immunity in an EG7-OVA mouse model

Background

The baculovirus (BV) Autographa californica multiple nuclear polyhedrosis virus has been used in numerous protein expression systems because of its ability to infect insect cells and serves as a useful vaccination vector with several benefits, such as its low clinical risks and posttranslational modification ability. We recently reported that dendritic cells (DCs) infected with BV stimulated antitumor immunity. The recombinant BV (rBV) also strongly stimulated peptide-specific T-cells and antitumor immunity. In this study, the stimulation of an immune response against EG7-OVA tumors in mice by a recombinant baculovirus-based combination vaccine expressing fragment C-ovalbumin (FrC-OVA-BV; rBV) was evaluated.

Results

We constructed an rBV expressing fragment C (FrC) of tetanus toxin containing a promiscuous MHC II-binding sequence and a p30-ovalbumin (OVA) peptide that functions in the MHC I pathway. The results showed that rBV activated the CD8⁺ T-cell-mediated response much more efficiently than the wild-type BV (wtBV). Experiments with EG7-OVA tumor mouse models showed that rBV significantly decreased tumor volume and increased survival compared with those in the wild-type BV or FrC-OVA DNA vaccine groups. In addition, a significant antitumor effect of classic prophylactic or therapeutic vaccinations was observed for rBV against EG7-OVA-induced tumors compared with that in the controls.

Conclusion

Our findings showed that FrC-OVA-BV (rBV) induced antitumor immunity, paving the way for its use in BV immunotherapy against malignancies.

Characterization of protective humoral and cellular immune responses against RHDV2 induced by a new vaccine based on recombinant baculovirus

Rabbit hemorrhagic disease (RHD) is a lethal disease in rabbits caused by RHD virus (RHDV). Protection is only possible through vaccination. A new virus variant (RHDV2) which emerged in 2010 in France differed from the classical RHDV1 variant in certain aspects and vaccines against RHDV1 induced limited cross protection only. In a previous study, we designed a recombinant baculovirus based RHDV2-VP1 vaccine, which provided a protective immunity in rabbits against RHDV2. In the present study this newly created vaccine is characterized with regard to onset and duration of protection, and possible cross protection against classical RHDV1. Furthermore, humoral and cellular immune mechanisms in vaccinated and infected rabbits were analyzed. In all experiments, the recombinant vaccine was compared to a conventional liver-based RHDV2 vaccine. The RHDV2-VP1 vaccine induced a protective immune response already seven days after single vaccination and fully protected for at least 14 months. A booster vaccination 21 days after the first had a negative influence on long-term protection. The cross protection provided by the RHDV2-VP1 vaccine against classical RHDV1 was limited since only 50% of vaccinated rabbits survived the infection. Conclusively, the new, baculovirus-based RHDV2-VP1 vaccine has the potential to protect rabbits against the infection with RHDV2, blocks completely the disease progression and prevents the spread of RHDV2 at the population level.

Baculovirus as a Tool for Gene Delivery and Gene Therapy

Based on its ability to express high levels of protein, baculovirus has been widely used for recombinant protein production in insect cells for more than thirty years with continued technical improvements. In addition, baculovirus has been successfully applied for foreign gene delivery into mammalian cells without any viral replication. However, several CpG motifs are present throughout baculoviral DNA and induce an antiviral response in mammalian cells, resulting in the production of pro-inflammatory cytokines and type I interferon through a Toll-like receptor (TLR)-dependent or -independent signaling pathway, and ultimately limiting the efficiency of transgene expression. On the other hand, by taking advantage of this strong adjuvant activity, recombinant baculoviruses encoding neutralization epitopes can elicit protective immunity in mice. Moreover, immunodeficient cells, such as hepatitis C virus (HCV)- or human immunodeficiency virus (HIV)-infected cells, are more susceptible to baculovirus infection than normal cells and are selectively eliminated by the apoptosis-inducible recombinant baculovirus. Here, we summarize the application of baculovirus as a gene expression vector and the mechanism of the host innate immune response induced by baculovirus in mammalian cells. We also discuss the future prospects of baculovirus vectors.

Production of biologically active feline interferon beta in insect larvae using a recombinant baculovirus

Feline interferon beta is a cytokine that belongs to the type I IFN family, with antitumor, antiviral and immunomodulatory functions. In this work, recombinant feline interferon beta (rFeIFNβ) was expressed in insect larvae that constitute important agronomic plagues. rFeIFNβ accumulated in the hemolymph of Spodoptera frugiperda larvae infected with recombinant baculovirus and was purified by Blue-Sepharose chromatography directly from larval homogenates on day 4 post-infection. rFeIFNβ was recovered after purification with a specific activity of 1 × 10⁶ IU mg^-1. By this method, we obtained 8.9 × 10⁴ IU of purified rFeIFNβ per larva. The product was biologically active in vitro, with an antiviral activity of 9.5 × 10⁴ IU mL^-1, as well as a potent antitumor activity comparable to that of the commercial FeIFNω. The glycosylation of rFeIFNβ was confirmed by peptide-N-glycosidase F digestion. Our findings provide a cost-effective platform for large-scale rFeIFNβ production in laboratory research or veterinary medicine applications.

Dendritic cell-based cancer immunotherapy for pancreatic cancer

Pancreatic cancer (PC) is a lethal disease and remains one of the most resistant cancers to traditional therapies. New therapeutic modalities are urgently needed, particularly immunotherapy, which has shown promise in numerous animal model studies. Dendritic cell (DC)-based immunotherapy has been used in clinical trials for various cancers, including PC, because DCs are the most potent antigen-presenting cell (APC), which are capable of priming naive T cells and stimulating memory T cells to generate antigen-specific responses. In this paper, we review the preclinical and clinical efforts towards the application of DCs for PC.

Live baculovirus acts as a strong B and T cell adjuvant for monomeric and oligomeric protein antigens

Recombinant proteins produced by baculovirus (BV) expression systems contain residual BV after crude purification. We studied adjuvant effect of BV on antibody and T cell responses against two model antigens, monomeric ovalbumin (OVA) protein and oligomeric norovirus (NoV) virus-like particles (VLPs). BALB/c mice were immunized intradermally with OVA alone or OVA formulated with live or inactivated BV, and VLP formulations comprised of chromatographically purified NoV GII.4 VLPs alone or mixed with BV, or of crude purified VLPs containing BV impurities from expression system. Live BV improved immunogenicity of NoV VLPs, sparing VLP dose up to 10-fold. Moreover, soluble OVA protein induced IgG2a antibodies and T cell response only when co-administered with live BV. BV adjuvant effect was completely abrogated by removal or inactivation of BV. These findings support the usage of crude purified proteins containing residual BV as vaccine antigens.

Two Distinctive Phenotypes of AcMNPV Display Different Immune Abilities and Intracellular Destiny

The budded phenotype (BV) of the baculovirus AcMNPV has been demonstrated to have strong immunostimulatory properties that are relevant for the development of vaccines and antiviral therapies. Although the occluded phenotype (ODV) shares the main structural proteins and its genome with BV, it has been poorly studied in mammals. In this study, we assessed the capacity of ODV to induce immune responses in mice. In contrast to BVs, ODVs failed to promote the secretion of IFN-gamma, IL-6 and Il-12 and to induce antiviral activity against VSV in the short term. Furthermore, ODVs were unable to induce cellular immunity against a coadministered antigen 7 days after inoculation. By analyzing the interaction of ODVs with BMDCs, we observed that although ODVs entered the cells reaching late and acidic endosomes, they did not induce their maturation. Finally, we also analyzed if BVs and ODVs followed different routes in the cell during the infection. BVs, but not ODVs, colocalized with the protein ovalbumin in compartments with the presence of proteases. The results suggest that structural differences could be responsible for their different destinies in the dendritic cell and this could lead to a different impact on the immune response.

Protection induced by early stage vaccination with pandemic influenza virus-like particles

The 2009 worldwide influenza pandemic emphasized the need for new approaches to develop emergency vaccines. In this study, a virus-like particle vaccine comprised of hemagglutinin (HA) and M1 from the pandemic influenza virus A/California/04/09 were used and its ability to induce protective immunity during the early stage of vaccination was assessed in a mouse model. A single intramuscular vaccination with virus-like particles (VLPs) provided protection on days 4 and 7 post-vaccination against lethal virus challenge with only moderate body weight loss. VLP vaccination induced significantly higher IgG antibody responses and high hemagglutinin inhibition (HAI) titers on day 4 post-vaccination. A predominant IgG2a antibody response and viral neutralizing antibodies were induced on day 7. These immune responses were closely correlated with protection. Lung virus titers decreased significantly on day 7 compared to those on day 4 post-vaccination. The lung virus titer on day 4 post-vaccination also decreased significantly compared to that of the naïve control. These results demonstrate that VLP vaccination confers effective protection during the early stage after vaccination in a mouse model.

Local Immune Stimulation by Intravesical Instillation of Baculovirus to Enable Bladder Cancer Therapy

Intravesical instillation of Bacillus Calmette-Guérin is currently used as adjuvant therapy for superficial, non-muscle invasive bladder cancer (NMIBC). However, nearly 40% of patients with NMIBC will fail Bacillus Calmette-Guérin therapy. In an attempt to investigate the feasibility of using insect baculovirus-based vectors for bladder cancer therapy, we observed that intravesical instillation of baculoviruses without transgene up-regulated a set of Th1-type of cytokines and increased the survival rate of mice bearing established orthotopic bladder tumors. When baculoviral vectors were used to co-deliver the mouse CD40 ligand and IL-15 genes through intravesical instillation, the immunogene therapy triggered significantly increased bladder infiltrations of inflammatory monocytes, CD4⁺, CD8⁺ and γδ T lymphocytes. All treated animals survived beyond 12 months whereas control animals died around 2 months after tumor inoculation. We conclude that direct intravesical instillation of baculoviral gene transfer vectors holds the potential to be a novel therapeutic modality for NMIBC.

Immunomodulatory effect of baculovirus in chickens: How it modifies the immune response against infectious bursal disease virus

Several reports have shown that baculoviruses (BVs) have strong adjuvant properties on the mammalian immune system. Recent studies of our group demonstrated the ability of BV to stimulate the innate immunity in chickens. In this investigation, we aimed to assess the potential antiviral effect of BV given both, before and after infectious bursal disease virus (IBDV). In the first case, specific pathogen free chickens were intravenously inoculated with 5 × 10(7) pfu of Autographa californica nuclear polyhedrosis virus and 3 h later were orally administered 2.5 × 10(5) egg infectious doses 50 of IBDV. In the second case, chickens received IBDV 3 h before BV inoculation. Five days later, chickens were bled and euthanized. RNA from the bursa was analyzed for cytokine production. Also, bursae were used for virus recovery, and processed for lymphocyte isolation. The results showed that the administration of BV 3 h after the inoculation with IBDV produced important changes in the effect that IBDV causes in the bursa. BV reduced the infiltration of T lymphocytes, decreased the expression pattern of IL-6 and IFN-γ and inhibited IBDV replication. The results herein presented demonstrate that this Lepidopteran virus shows antiviral activity in chickens under experimental conditions. Investigations under field conditions have to be done to probe this strategy as a valuable sanitary tool for the treatment and prevention of chicken diseases.

Baculovirus Displaying Hemagglutinin Elicits Broad Cross-Protection against Influenza in Mice

The widespread influenza virus infection further emphasizes the need for novel vaccine strategies that effectively reduce the impact of epidemic as well as pandemic influenza. Conventional influenza vaccines generally induce virus neutralizing antibody responses which are specific for a few antigenically related strains within the same subtype. However, antibodies directed against the conserved stalk domain of HA could neutralize multiple subtypes of influenza virus and thus provide broad-spectrum protection. In this study, we designed and constructed a recombinant baculovirus-based vaccine, rBac-HA virus, that expresses full-length HA of pandemic H1N1 influenza virus (A/California/04/09) on the viral envelope. We demonstrated that repeated intranasal immunizations with rBac-HA virus induced HA stalk-specific antibody responses and protective immunity against homologous as well as heterosubtypic virus challenge. The adoptive transfer experiment shows that the cross-protection is conferred by the immune sera which contain HA stalk-specific antibodies. These results warrant further development of rBac-HA virus as a broad-protective vaccine against influenza. The vaccine induced protection against infection with the same subtype as well as different subtype, promising a potential universal vaccine for broad protection against different subtypes to control influenza outbreaks including pandemic.

Recent Progress towards Novel EV71 Anti-Therapeutics and Vaccines

Enterovirus 71 (EV71) is a group of viruses that belongs to the Picornaviridae family, which also includes viruses such as polioviruses. EV71, together with coxsackieviruses, is widely known for its association with Hand Foot Mouth Disease (HFMD), which generally affects children age five and below. Besides HFMD, EV71 can also trigger more severe and life-threatening neurological conditions such as encephalitis. Considering the lack of a vaccine and antiviral drug against EV71, together with the increasing spread of these viruses, the development of such drugs and vaccines becomes the top priority in protecting our younger generations. This article, hence, reviews some of the recent progress in the formulations of anti-therapeutics and vaccine generation for EV71, covering (i) inactivated vaccines; (ii) baculovirus-expressed vaccines against EV71; (iii) human intravenous immunoglobulin (IVIg) treatment; and (iv) the use of monoclonal antibody therapy as a prevention and treatment for EV71 infections.

In vivo study of immunogenicity and kinetic characteristics of a quantum dot-labelled baculovirus

Nanomaterials conjugated with biomacromolecules, including viruses, have great potential for in vivo applications. Therefore, it is important to evaluate the safety of nanoparticle-conjugated macromolecule biomaterials (Nano-mbio). Although a number of studies have assessed the risks of nanoparticles and macromolecule biomaterials in living bodies, only a few of them investigated Nano-mbios. Here we evaluated the in vivo safety profile of a quantum dot-conjugated baculovirus (Bq), a promising new Nano-mbio, in mice. Each animal was injected twice intraperitoneally with 50 μg virus protein labelled with around 3*10(-5)nmol conjugated qds. Control animals were injected with PBS, quantum dots, baculovirus, or a mixture of quantum dots and baculovirus. Blood, tissues and body weight were analysed at a series of time points following both the first and the second injections. It turned out that the appearance and behaviour of the mice injected with Bq were similar to those injected with baculovirus alone. However, combination of baculovirus and quantum dot (conjugated or simply mixed) significantly induced stronger adaptive immune responses, and lead to a faster accumulation and longer existence of Cd in the kidneys. Thus, despite the fact that both quantum dot and baculovirus have been claimed to be safe in vivo, applications of Bq in vivo should be cautious. To our knowledge, this is the first study examining the interaction between a nanoparticle-conjugated virus and a living body from a safety perspective, providing a basis for in vivo application of other Nano-mbios.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

Antitumor effects of baculovirus-infected dendritic cells against human pancreatic carcinoma

Recently, we showed that baculovirus (BV)-infected dendritic cells (DCs) (BV-DCs) induced antitumor immunity against established tumors in mice. These antitumor effects were CD8(+) T-cell and natural killer (NK) cell dependent but CD4(+) T-cell independent. In the current study, we examined the antitumor effect of BV-DCs on human pancreatic cancer cells (AsPC-1). After treatment with BV-infected bone marrow-derived dendritic cells (BMDCs), human pancreatic tumors caused by AsPC-1 cells in a nude mouse model were significantly reduced in size, and the survival of the mice was improved compared with that of non-immature BMDC (iDC)- and BV-DC-immunized mice. We also found that wild-type BV could activate human DCs (HDCs) and that NK cells were activated by BV-infected HDCs (BHDCs). Our findings show that BV-DCs can induce antitumor immunity, which paves the way for the use of this technique as an effective tool for DC immunotherapy against malignancies.

Innate immune response induced by baculovirus attenuates transgene expression in mammalian cells

The baculovirus Autographa californica nucleopolyhedrovirus (AcNPV) has been widely used to achieve a high level of foreign gene expression in insect cells, as well as for efficient gene transduction into mammalian cells without any replication. In addition to permitting efficient gene delivery, baculovirus has been shown to induce host innate immune responses in various mammalian cells and in mice. In this study, we examined the effects of the innate immune responses on gene expression by recombinant baculoviruses in cultured cells. The reporter gene expression in IRF3-deficient mouse embryonic fibroblasts (MEFs) infected with the recombinant baculovirus was shown to be enhanced in accordance with the suppression of beta interferon (IFN-β) production. Furthermore, efficient gene transduction by the recombinant baculovirus was achieved in MEFs deficient for stimulator of interferon genes (STING), TANK binding kinase 1 (TBK1), IFN regulatory factor 3 (IRF3), or IFN-β promoter stimulator 1 (IPS-1), but not in those deficient for IRF7, MyD88, or Z-DNA binding protein 1 (ZBP1)/DAI. Enhancement of gene expression by the recombinant baculovirus was also observed in human hepatoma cell lines replicating hepatitis C virus (HCV), in which innate immunity was impaired by the cleavage of IPS-1 by the viral protease. In addition, infection with the recombinant baculovirus expressing the BH3-only protein, BIMS, a potent inducer of apoptosis, resulted in a selective cell death in the HCV replicon cells. These results indicate that innate immune responses induced by infection with baculovirus attenuate transgene expression, and this characteristic might be useful for a selective gene transduction into cells with impaired innate immunity arising from infection with various viruses.

Intradermal immunization with combined baculovirus and tumor cell lysate induces effective antitumor immunity in mice

Although tumor lysate contains all the potential helper and killer epitopes capable of stimulating T cells, it is difficult to use as a cancer vaccine because it suppresses dendritic cell (DC) function. We report that wild-type baculovirus possesses an adjuvant effect to improve the immunogenicity of tumor lysate. When mice were administered CT26 tumor cell lysate combined with baculovirus intradermally, antitumor immunity was induced and rejection of CT26 tumor growth was observed in 40% of the immunized mice. In contrast, such antitumor immunity was not elicited in mice inoculated with tumor cell lysate or baculovirus alone. In tumor-bearing mice, which had previously received the combined baculovirus and tumor lysate vaccine, the established tumors were completely eradicated by administering a booster dose of the combined vaccine. This antitumor effect was attributed to tumor-specific T cell immunity mediated primarily by CD8⁺ T cells. Baculovirus also strongly activated DCs loaded with tumor lysate. Increased interleukin (IL)-6 and IL-12p70 production were also observed in DCs co-cultured with tumor cell lysate and baculovirus. Our study demonstrates that combined baculovirus and tumor lysate vaccine can effectively stimulate DCs to induce acquired antitumor immunity.

Immunological effects of Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) by stimulation of mice in vivo and in vitro

Baculoviruses are highly specific and only capable of replication in arthropod hosts. The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied baculovirus at the molecular level and the Anticarsia gemnatalis multiple nucleopolyhedrovirus (AgMNPV) is the most used viral insecticide worldwide. AcMNPV have also been shown to stimulate the mammalian immune response acting as an adjuvant. In order to evaluate the effects of AgMNPV in modulating macrophage and lymphocyte activation, we have stimulated these cells in vitro and inoculated BALB/c mice intranasally with the two viral phenotypes (PIBs and BVs) and compared with the response induced by the same phenotypes of AcMNPV. Our results showed that baculoviruses are able to modulate mammalian immune response; in vitro they increase phagocytosis, NO2 production and Th1 cells response. In vivo, AgMNPV BVs or PIBs do not induce an inflammatory reaction in normal lung but during a fungal lung infection they can change the type of adaptive response developed. Considering our data, AgMNPV can be considered more useful as a vaccine vector or immune adjuvant than AcMNPV.

Intranasal immunization of baculovirus displayed hemagglutinin confers complete protection against mouse adapted highly pathogenic H7N7 reassortant influenza virus

Background

Avian influenza A H7N7 virus poses a pandemic threat to human health because of its ability for direct transmission from domestic poultry to humans and from human to human. The wide zoonotic potential of H7N7 combined with an antiviral immunity inhibition similar to pandemic 1918 H1N1 and 2009 H1N1 influenza viruses is disconcerting and increases the risk of a putative H7N7 pandemic in the future, underlining the urgent need for vaccine development against this virus.

Methodology/Principal Findings

In this study, we developed a recombinant vaccine by expressing the H7N7-HA protein on the surface of baculovirus (Bac-HA). The protective efficacy of the live Bac-HA vaccine construct was evaluated in a mouse model by challenging mice immunized intranasally (i.n.) or subcutaneously (s.c.) with high pathogenic mouse adapted H7N7 reassorted strain. Although s.c. injection of live Bac-HA induced higher specific IgG than i.n. immunization, the later resulted in an elevated neutralization titer. Interestingly, 100% protection from the lethal viral challenge was only observed for the mice immunized intranasally with live Bac-HA, whereas no protection was achieved in any other s.c. or i.n. immunized mice groups. In addition, we also observed higher mucosal IgA as well as increased IFN-γ and IL-4 responses in the splenocytes of the surviving mice coupled with a reduced viral titer and diminished histopathological signs in the lungs.

Conclusion

Our results indicated that protection from high pathogenic H7N7 (NL/219/03) virus requires both mucosal and systemic immune responses in mice. The balance between Th1 and Th2 cytokines is also required for the protection against the H7N7 pathogen. Intranasal administration of live Bac-HA induced all these immune responses and protected the mice from lethal viral challenge. Therefore, live Bac-HA is an effective vaccine candidate against H7N7 viral infections.

Recombinant monovalent llama-derived antibody fragments (VHH) to rotavirus VP6 protect neonatal gnotobiotic piglets against human rotavirus-induced diarrhea

Group A Rotavirus (RVA) is the leading cause of severe diarrhea in children. The aims of the present study were to determine the neutralizing activity of VP6-specific llama-derived single domain nanoantibodies (VHH nanoAbs) against different RVA strains in vitro and to evaluate the ability of G6P[1] VP6-specific llama-derived single domain nanoantibodies (VHH) to protect against human rotavirus in gnotobiotic (Gn) piglets experimentally inoculated with virulent Wa G1P[8] rotavirus. Supplementation of the daily milk diet with 3B2 VHH clone produced using a baculovirus vector expression system (final ELISA antibody -Ab- titer of 4096; virus neutralization -VN- titer of 256) for 9 days conferred full protection against rotavirus associated diarrhea and significantly reduced virus shedding. The administration of comparable levels of porcine IgG Abs only protected 4 out of 6 of the animals from human RVA diarrhea but significantly reduced virus shedding. In contrast, G6P[1]-VP6 rotavirus-specific IgY Abs purified from eggs of hyperimmunized hens failed to protect piglets against human RVA-induced diarrhea or virus shedding when administering similar quantities of Abs. The oral administration of VHH nanoAb neither interfered with the host's isotype profiles of the Ab secreting cell responses to rotavirus, nor induced detectable host Ab responses to the treatment in serum or intestinal contents. This study shows that the oral administration of rotavirus VP6-VHH nanoAb is a broadly reactive and effective treatment against rotavirus-induced diarrhea in neonatal pigs. Our findings highlight the potential value of a broad neutralizing VP6-specific VHH nanoAb as a treatment that can complement or be used as an alternative to the current strain-specific RVA vaccines. Nanobodies could also be scaled-up to develop pediatric medication or functional food like infant milk formulas that might help treat RVA diarrhea.

Group A rotavirus (RVA) is the most common cause of severe diarrhea in human infants worldwide. Live-attenuated rotavirus vaccines are available to prevent rotavirus diarrhea in children, although their efficacy in impoverished areas has been questioned, in addition to not being suitable for children suffering from immune deficiencies. Since no rotavirus-specific treatments are available as an alternative, we investigated llama-derived single-chain antibody fragments (VHH) as preventive therapy and a potential treatment option. Gnotobiotic piglets were chosen as an animal model because their gastrointestinal physiology and mucosal immune system resemble that of human infants. We evaluated the broad neutralizing activity of a VHH clone (3B2) to different genotypes of RVA circulating in humans, and tested the efficacy of oral administration of 3B2 VHH as a functional milk to prevent the diarrhea induced by one of the most prevalent human RVA strains (G1P[8]). Supplementation of the milk diet with 3B2 twice a day for 9 days conferred full protection against rotavirus-associated diarrhea and significantly reduced virus shedding in gnotobiotic piglets experimentally inoculated with a human RVA. This study demonstrates the potential application of VHH to prevent rotavirus-induced diarrhea, and suggests that VHHs should be further investigated as a suitable treatment for gastroenteritis.

Viral-mediated gene delivery for cell-based assays in drug discovery

BACKGROUND

Adenovirus, retrovirus and lentivirus-based vectors, originally engineered and optimized for in vivo and ex vivo gene therapy, have become increasingly useful for viral-mediated gene delivery to support in vitro cell-based assays. Viral vectors underpin functional genomics screening of cDNA, shRNA and aptamer libraries, are used for a variety of target validation studies and importantly, for high-throughput cell-based drug discovery and compound profiling assays. The baculovirus/insect cell expression system had gained prevalence as a tool for recombinant protein production when it was observed that recombinant baculovirus vectors too could serve as efficient gene delivery vehicles for a wide range of mammalian cells. Although the use of baculovirus vectors in vivo has lagged behind retroviral, adenoviral and lentiviral vectors, they have gained prominence for development of in vitro cell-based assays due to the ease of generation, broad host range and excellent biosafety profile. There is an increasing emphasis on cell-based assays in high-throughput automated drug discovery laboratories and a variety of commercially available viral-vectors can be used for supporting these assays.

OBJECTIVE

We compare and contrast the current viral-mediated gene delivery vector systems and highlight their suitability for cell-based drug discovery assays.

CONCLUSION

Viral-mediated gene delivery is increasingly being used in support of genome scale target validation studies and cell-based assay development for specific drug target genes such as ion channels, G protein-coupled receptors and intracellular enzymes. The choice of a delivery system over another for a particular application is largely dictated by the cell types and cell lines in use, virus cellular tropism, assay throughput, safety requirements and ease/cost of reagent generation.

Cross-protective efficacy of bivalent recombinant baculoviral vaccine against heterologous influenza H5N1 challenge

The present study demonstrates the cross-protective efficacy of baculovirus displayed HAs of A/Indonesia/669/06 and A/Anhui/01/05 against heterologous H5N1 challenges in a mouse model. Mice orally or subcutaneously immunized with live bivalent-BacHA vaccine significantly induced higher HA-specific humoral and cellular immune responses when compared with inactivated bivalent-BacHA. In addition, oral administration of live bivalent-BacHA vaccine was able to induce significant level of antigen-specific mucosal IgA levels. Microneutralization assay indicated that live bivalent-BacHA vaccine was able to induce strong cross-clade neutralization titer against distinct H5N1 clades (1, 2.1.3, 2.2.1.1, 2.3.2, 2.3.4, 4, 7 and 9). The production of both interferon-gamma (IFN-γ) and interleukin-4 (IL-4) by splenocytes from vaccinated mice indicated that mice vaccinated orally or subcutaneously with live bivalent-BacHA stimulated both IFN-γ secreting Th1 cells and IL-4 secreting Th2 cells, whereas mice immunized subcutaneously with inactive adjuvanted bivalent-BacHA stimulated only IL-4 secreting Th2 cells. Cross-protective immunity study also showed that mice immunized either orally or subcutaneously with live bivalent-BacHA were completely protected against 5MLD50 of clade 1 and clade 2.2.1.1 H5N1 viral infections. The protective immune response elicited by bivalent-BacHA vaccine against H5N1 variants demonstrates the possibility of protection against a broad range of H5N1 strains.

Characterization and immunogenicity of norovirus capsid-derived virus-like particles purified by anion exchange chromatography

Recombinant baculovirus (BV) expression systems are widely applied in the production of viral capsid proteins and virus-like particles (VLPs) for use as immunogens and vaccine candidates. Traditional density gradient purification of VLPs does not enable complete elimination of BV-derived impurities, including live viruses, envelope glycoprotein gp64 and baculoviral DNA. We used an additional purification system based on ionic strength to purify norovirus (NoV) GII-4 capsid-derived VLPs. The anion exchange chromatography purification led to highly purified VLPs free from BV impurities with intact morphology. In addition, highly purified VLPs induced strong NoV-specific antibody responses in BALB/c mice. Here, we describe a method for NoV VLP purification and several methods for determining their purity, including quantitative PCR for BV DNA detection.

[Analysis of the application of host innate immune response to control and prevent infection]

The baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) has been widely used not only to achieve a high level of foreign gene expression in insect cells but also for efficient gene transduction into mammalian cells without any replication. In addition to the efficient gene delivery, baculovirus has been shown to induce host innate immune responses in various mammalian cells and in mice. The baculovirus has abundant CpG motifs in the viral genome and is capable of inducing pro-inflammatory cytokines and interferons (IFNs) through Toll-like receptor (TLR)-dependent and -independent signaling pathways in a cell-type-specific manner. The cytoplasmic helicase proteins RIG-I (retinoic-acid-inducible protein I) and MDA5 (melanoma-differentiation-associated gene 5) have been identified as viral dsRNA detectors and the adaptor IPS-1 (IFN-beta promoter stimulator-1) interacts with RIG-I and MDA5 to facilitate type-I IFN production mediated interferon regulatory factor 3 (IRF3) and 7 (IRF7). These helicases and IPS-1, however, were not essential for the type-I IFN and inflammatory cytokine responses to baculovirus. The baculovirus also has a strong adjuvant activity, and recombinant baculoviruses encoding neutralization epitopes elicit protective immunity in mice. This review deals with the current status of our knowledge of the induction of host innate immune responses by baculovirus and discusses the future prospects for baculovirus vectors.

Characterization of the immune responses elicited by baculovirus-based vector vaccines against influenza virus hemagglutinin

AIM

To compare the specific immune responses elicited by different baculovirus vectors in immunized mice.

METHODS

We constructed and characterized two recombinant baculoviruses carrying the expression cassette for the H5N1 influenza virus hemagglutinin (HA) gene driven by either an insect cell promoter (vAc-HA) or a dual-promoter active both in insect and mammalian cells (vAc-HA-DUAL). Virus without the HA gene (vAc-EGFP) was used as a control. These viruses were used to immunize mice subcutaneously and intraperitoneally. The production of total and specific antibodies was determined by ELISA and competitive ELISA. Cytokine production by the spleen cells of immunized mice was studied using the ELISPOT assay.

RESULTS

Both the vAc-HA and vAc-HA-DUAL vectors expressed HA proteins in insect Sf9 cells, and HA antigen was present in progeny virions. The vAc-HA-DUAL vector also mediated HA expression in virus-transduced mammalian cell lines (BHK and A547). Both vAc-HA and vAc-HA-DUAL exhibited higher transduction efficiencies than vAc-EGFP in mammalian cells, as shown by the expression of the reporter gene egfp. Additionally, both vAc-HA and vAc-HA-DUAL induced high levels of HA-specific antibody production in immunized mice; vAc-HA-DUAL was more efficient in inducing IFN-γ and IL-2 upon stimulation with specific antigen, whereas vAc-HA was more efficient in inducing IL-4 and IL-6.

CONCLUSION

Baculovirus vectors elicited efficient, specific immune responses in immunized mice. The vector displaying the HA antigen on the virion surface (vAc-HA) elicited a Th2-biased immune response, whereas the vector displaying HA and mediating HA expression in the cell (vAc-HA-DUAL) elicited a Th1-biased immune response.

Genetic modification of baculovirus expression vectors

As a protein expression vector, the baculovirus demonstrates many advantages over other vectors. With the development of biotechnology, baculoviral vectors have been genetically modified to facilitate high level expression of heterologous proteins in both insect and mammalian cells. These modifications include utilization of different promoters and signal peptides, deletion or replacement of viral genes for increasing protein secretion, integration of polycistronic expression cassette for producing protein complexes, and baculovirus pseudotyping, promoter accommodation or surface display for enhancing mammalian cell targeting gene delivery. This review summarizes the development and the current state of art of the baculovirus expression system. Further development of baculovirus expression systems will make them even more feasible and accessible for advanced applications.

Baculovirus GP64-mediated entry into mammalian cells

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) serves as an efficient viral vector, not only for abundant gene expression in insect cells, but also for gene delivery into mammalian cells. Lentivirus vectors pseudotyped with the baculovirus envelope glycoprotein GP64 have been shown to acquire more potent gene transduction than those with vesicular stomatitis virus (VSV) envelope glycoprotein G. However, there are conflicting hypotheses about the molecular mechanisms of the entry of AcMNPV. Moreover, the mechanisms of the entry of pseudotyped viruses bearing GP64 into mammalian cells are not well characterized. Determination of the entry mechanisms of AcMNPV and the pseudotyped viruses bearing GP64 is important for future development of viral vectors that can deliver genes into mammalian cells with greater efficiency and specificity. In this study, we generated three pseudotyped VSVs, NPVpv, VSVpv, and MLVpv, bearing envelope proteins of AcMNPV, VSV, and murine leukemia virus, respectively. Depletion of membrane cholesterol by treatment with methyl-β-cyclodextrin, which removes cholesterol from cellular membranes, inhibited GP64-mediated internalization in a dose-dependent manner but did not inhibit attachment to the cell surface. Treatment of cells with inhibitors or the expression of dominant-negative mutants for dynamin- and clathrin-mediated endocytosis abrogated the internalization of AcMNPV and NPVpv into mammalian cells, whereas inhibition of caveolin-mediated endocytosis did not. Furthermore, inhibition of macropinocytosis reduced GP64-mediated internalization. These results suggest that cholesterol in the plasma membrane, dynamin- and clathrin-dependent endocytosis, and macropinocytosis play crucial roles in the entry of viruses bearing baculovirus GP64 into mammalian cells.

Baculovirus-based Vaccine Displaying Respiratory Syncytial Virus Glycoprotein Induces Protective Immunity against RSV Infection without Vaccine-Enhanced Disease

Background

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract diseases in infancy and early childhood. Despite its importance as a pathogen, there is no licensed vaccine against RSV yet. The attachment glycoprotein (G) of RSV is a potentially important target for protective antiviral immune responses. Recombinant baculovirus has been recently emerged as a new vaccine vector, since it has intrinsic immunostimulatory properties and good bio-safety profile.

Methods

We have constructed a recombinant baculovirus-based RSV vaccine, Bac-RSV/G, displaying G glycoprotein, and evaluated immunogenicity and protective efficacy by intranasal immunization of BALB/c mice with Bac-RSV/G.

Results

Bac-RSV/G efficiently provides protective immunity against RSV challenge. Strong serum IgG and mucosal IgA responses were induced by intranasal immunization with Bac-RSV/G. In addition to humoral immunity, G-specific Th17- as well as Th1-type T-cell responses were detected in the lungs of Bac-RSV/G-immune mice upon RSV challenge. Neither lung eosinophilia nor vaccine-induced weight loss was observed upon Bac-RSV/G immunization and subsequent RSV infection.

Conclusion

Our data demonstrate that intranasal administration of baculovirus-based Bac-RSV/G vaccine is efficient for the induction of protection against RSV and represents a promising prophylactic vaccination regimen.

Expression of an antiviral protein from Lonomia obliqua hemolymph in baculovirus/insect cell system

The control of viral infections, mainly those caused by influenza viruses, is of great interest in Public Health. Several studies have shown the presence of active properties in the hemolymph of arthropods, some of which are of interest for the development of new pharmacological drugs. Recently, we have demonstrated the existence of a potent antiviral property in the hemolymph of Lonomia obliqua caterpillars. The aim of this study was to produce an antiviral protein in a baculovirus/Sf9 cell system. The resulting bacmid contains the sequence coding for the antiviral protein previously described by our group. Total RNA from L. obliqua caterpillars was extracted with Trizol and used in the reverse transcription assay with oligo(d)T primer followed by polymerase chain reactions (RT-PCR) with specific primers for the cDNA coding for the antiviral protein, based on the sequence deposited in the GenBank database. Restriction sites were inserted in the cDNA for ligation in the donor plasmid pFastBac1™. The recombinant plasmid was selected in Escherichia coli DH5α and subsequently used in the transformation of E. coli DH10Bac for the construction of the recombinant bacmid. This bacmid was used for the expression of the antiviral protein in the baculovirus/Sf9 cell system. After identifying the protein by western blot, activity tests were performed, showing that the purified recombinant protein was able to significantly reduce viral replication (about 4 logs). Studies on the optimization of the expression system for the production of this antiviral protein in insect cells are in progress.

A pseudotype baculovirus expressing the capsid protein of foot-and-mouth disease virus and a T-cell immunogen shows enhanced immunogenicity in mice

Background

Foot-and-mouth disease (FMD) is a highly contagious disease of livestock which causes severe economic loss in cloven-hoofed animals. Vaccination is still a major strategy in developing countries to control FMD. Currently, inactivated vaccine of FMDV has been used in many countries with limited success and safety concerns. Development of a novel effective vaccine is must.

Methods

In the present study, two recombinant pseudotype baculoviruses, one expressing the capsid of foot-and-mouth disease virus (FMDV) under the control of a cytomegalovirus immediate early enhancer/promoter (CMV-IE), and the other the caspid plus a T-cell immunogen coding region under a CAG promoter were constructed, and their expression was characterized in mammalian cells. In addition, their immunogenicity in a mouse model was investigated. The humoral and cell-mediated immune responses induced by pseudotype baculovirus were compared with those of inactivated vaccine.

Results

Indirect immunofluorescence assay (IFA) and indirect sandwich-ELISA (IS-ELISA) showed both recombinant baculoviruses (with or without T-cell epitopes) were transduced efficiently and expressed target proteins in BHK-21 cells. In mice, intramuscular inoculation of recombinants with 1 × 10⁹ or 1 × 10¹⁰ PFU/mouse induced the production of FMDV-specific neutralizing antibodies and gamma interferon (IFN-γ). Furthermore, recombinant baculovirus with T-cell epitopes had better immunogenicity than the recombinant without T-cell epitopes as demonstrated by significantly enhanced IFN-γ production (P < 0.01) and higher neutralizing antibody titer (P < 0.05). Although the inactivated vaccine produced the highest titer of neutralizing antibodies, a lower IFN-γ expression was observed compared to the two recombinant pseudotype baculoviruses.

Conclusions

These results indicate that pseudotype baculovirus-mediated gene delivery could be a alternative strategy to develop a new generation of vaccines against FMDV infection.

Baculovirus expression systems for production of recombinant proteins in insect and mammalian cells

Baculovirus vector systems are extensively used for the expression of foreign gene products in insect and mammalian cells. New advances increase the possibilities and applications of the baculovirus expression system, which makes it possible to express multiple genes simultaneously within a single infected insect cell and to obtain multimeric proteins functionally similar to their natural analogs. Recombinant viruses with expression cassettes active in mammalian cells are used to deliver and express genes in mammalian cells in vitro and in vivo. Further improvement of the baculovirus expression system and its adaptation to specific target cells can open up a wide variety of applications. The review considers recent achievements in the use of modified baculoviruses to express recombinant proteins in eukaryotic cells, advantages and drawbacks of the baculovirus expression system, and ways to optimize the expression of recombinant proteins in both insect and mammalian cell lines.

Targeting of B and T lymphocyte associated (BTLA) prevents graft-versus-host disease without global immunosuppression

One-time treatment with an antibody against BTLA provides long-term protection against graft-versus-host disease without affecting effector T cell responses to tumors or pathogens.

Graft-versus-host disease (GVHD) causes significant morbidity and mortality in allogeneic hematopoietic stem cell transplantation (aHSCT), preventing its broader application to non–life-threatening diseases. We show that a single administration of a nondepleting monoclonal antibody specific for the coinhibitory immunoglobulin receptor, B and T lymphocyte associated (BTLA), permanently prevented GVHD when administered at the time of aHSCT. Once GVHD was established, anti-BTLA treatment was unable to reverse disease, suggesting that its mechanism occurs early after aHSCT. Anti-BTLA treatment prevented GVHD independently of its ligand, the costimulatory tumor necrosis factor receptor herpesvirus entry mediator (HVEM), and required BTLA expression by donor-derived T cells. Furthermore, anti-BTLA treatment led to the relative inhibition of CD4⁺ forkhead box P3⁻ (Foxp3⁻) effector T cell (T eff cell) expansion compared with precommitted naturally occurring donor-derived CD4⁺ Foxp3⁺ regulatory T cell (T reg cell) and allowed for graft-versus-tumor (GVT) effects as well as robust responses to pathogens. These results suggest that BTLA agonism rebalances T cell expansion in lymphopenic hosts after aHSCT, thereby preventing GVHD without global immunosuppression. Thus, targeting BTLA with a monoclonal antibody at the initiation of aHSCT therapy might reduce limitations imposed by histocompatibility and allow broader application to treatment of non–life-threatening diseases.