Baculovirus surface display of the HA protein of H5N2 avian influenza virus and its immunogenicity against a lethal challenge with H5N1 virus in chickens

Development of Polycistronic Baculovirus Surface Display Vectors to Simultaneously Express Viral Proteins of Porcine Reproductive and Respiratory Syndrome and Analysis of Their Immunogenicity in Swine

To simultaneously express and improve expression levels of multiple viral proteins of a porcine reproductive and respiratory syndrome virus (PRRSV), polycistronic baculovirus surface display vectors were constructed and characterized. We engineered polycistronic baculovirus surface display vectors, namely, pBacDual Display EGFP(BacDD)-2GP2-2GP4 and pBacDD-4GP5N34A/N51A (mtGP5), which simultaneously express and display the ectodomain of His-tagged GP2-gp64TM-CTD, His-tagged GP4-gp64TM-CTD, and His-tagged mtGP5-gp64TM-CTD fusion proteins of PRRSV on cell membrane of Sf-9 cells. Specific pathogen-free (SPF) pigs were administered intramuscularly in 2 doses at 21 and 35 days of age with genetic recombinant baculoviruses-infected cells. Our results revealed a high level of ELISA-specific antibodies, neutralizing antibodies, IL-4, and IFN-γ in SPF pigs immunized with the developed PRRSV subunit vaccine. To further assess the co-expression efficiency of different gene combinations, pBacDD-GP2-GP3-2GP4 and pBacDD-2mtGP5-2M constructs were designed for the co-expression of the ectodomain of His-tagged GP2-gp64TM-CTD, His-tagged GP3-gp64TM-CTD, and His-tagged GP4-gp64TM-CTD proteins as well as the ectodomain of His-tagged mtGP5-gp64TM-CTD and His-tagged M-gp64TM-CTD fusion proteins of PRRSV. To develop an ELISA assay for detecting antibodies against PRRSV proteins, the sequences encoding the ectodomain of the GP2, GP3, GP4, mtGP5, and M of PRRSV were amplified and subcloned into the pET32a vector and expressed in E. coli. In this work, the optimum conditions for expressing PRRSV proteins were evaluated, and the results suggested that 4 × 105 of Sf-9 cells supplemented with 7% fetal bovine serum and infected with the recombinant baculoviruses at an MOI of 20 for three days showed a higher expression levels of the protein. Taken together, the polycistronic baculovirus surface display system is a useful tool to increase expression levels of viral proteins and to simultaneously express multiple viral proteins of PRRSV for the preparation of subunit vaccines.

Influenza H7N9 Virus Hemagglutinin with T169A Mutation Possesses Enhanced Thermostability and Provides Effective Immune Protection against Lethal H7N9 Virus Challenge in Chickens

H7N9 avian influenza virus (AIV) has caused huge losses in the poultry industry and impacted human public health security, and still poses a potential threat. Currently, immune prevention and control of avian influenza relies on traditional inactivated vaccines; however, they have some limitations and genetically engineered avian influenza subunit vaccines may be potential candidate vaccines. In this study, a T169A mutation in the HA protein derived from H7N9 AIV A/Chicken/Guangdong/16876 (H7N9-16876) was generated using the baculovirus expression system (BVES). The results showed that the mutant (HAm) had significantly increased thermostability compared with the wild-type HA protein (HA-WT). Importantly, immunizing chickens with HAm combined with ISA 71VG elicited higher cross-reactive hemagglutination inhibition (HI) antibody responses and cytokine (IFN-γ and IL-4) secretion. After a lethal challenge with heterologous H7N9 AIV, the vaccine conferred chickens with 100% (10/10) clinical protection and effectively inhibited viral shedding, with 90% (9/10) of the chickens showing no virus shedding. The thermostability of HAm may represent an advantage in practical vaccine manufacture and application. In general, the HAm generated in this study represents a promising subunit vaccine candidate for the prevention and control of H7N9 avian influenza.

Baculovirus Display of Peptides and Proteins for Medical Applications

Baculoviridae is a large family of arthropod-infective viruses. Recombinant baculoviruses have many applications, the best known is as a system for large scale protein production in combination with insect cell cultures. More recently recombinant baculoviruses have been utilized for the display of proteins of interest with applications in medicine. In the present review we analyze the different strategies for the display of proteins and peptides on the surface of recombinant baculoviruses and provide some examples of the different proteins displayed. We analyze briefly the commercially available systems for recombinant baculovirus production and display and discuss the future of this emerging and powerful technology.

An ambient-temperature stable nanoparticle-based vaccine for nasal application that confers long-lasting immunogenicity to carried antigens

Polyhedrins are viral proteins present in a large family of baculoviruses that form occlusion bodies (polyhedra). These structures protect the virus particles from the outside environment until they are ingested by susceptible insects. Occluded viruses can sustain inclement weather for long periods of time. Therefore, the polyhedra is a natural preservative that keeps the viral structure intact at ambient temperature for years. In a previous study we identified the first 110 amino acids from polyhedrin (PH(1-110)) as a good candidate to carry antigens of interest. As a proof of concept, we produced a fusion protein with PH(1-110) and the green fluorescent protein (PH(1-110)GFP). The fusion protein associates spontaneously during its synthesis resulting in the formation of nanoparticles. Nasal immunization with these nanoparticles and in the absence of any adjuvant, results in a robust immune response with the production of IgG immunoglobulins that remained elevated for months and that selectively recognize the GFP but not PH(1-110). These results indicate that PH(1-110) is poorly immunogenic but capable of enhancing the immune response to GFP.

The cytoplasmic tail substitution increases the assembly efficiency of Ebola virus glycoprotein on the budded virus of Bombyx mori nucleopolyhedrovirus

Glycoprotein (GP_1,2) of the Ebola virus (EBOV) is the key membrane fusion protein, which is a key candidate protein for vaccine preparations. Previously, GP_1,2 was expressed by Bombyx mori nucleopolyhedrovirus (BmNPV) expression vector system; however, few GP_1,2 was incorporated into budded virus (BV) of BmNPV. To improve the incorporation efficiency of GP_1,2 into the virion, the GP_1,2 fusion with the cytoplasmic tail of GP64 of BmNPV was expressed in BmN cells by the BmNPV expression system. The BV was purified by ultracentrifugation, and GP_1,2 expression in BV was detected by the antibody. The result indicated that a 532% increase in the relative GP_1,2 densitometry signal was observed in constructs utilizing the GP64 C-terminal domain; moreover, the substitution of GP_1,2 native signal peptide with GP64 signal peptide increased the incorporation efficiency by 34.6% in the relative GP_1,2 densitometry signal. We revealed that the application of the cytoplasmic tail of BmNPV GP64 significantly increased the incorporation rate of GP_1,2 into the BV envelope. This study lays a foundation for GP_1,2 vaccine development.

Baculovirus Display of Varicella-Zoster Virus Glycoprotein E Induces Robust Humoral and Cellular Immune Responses in Mice

Varicella-zoster virus (VZV) is the causative agent of varicella and herpes zoster (HZ) and can pose a significant challenge to human health globally. The initial VZV infection-more common in children-causes a self-limiting chicken pox. However, in later life, the latent VZV can become reactivated in these patients, causing HZ and postherpetic neuralgia (PHN), a serious and painful complication. VZV glycoprotein E (gE) has been developed into a licensed subunit vaccine against HZ (Shingrix). However, its efficacy relies on the concomitant delivery of a robust adjuvant (AS01B). Here, we sought to create a new immunogen for vaccine design by displaying the VZV-gE on the baculovirus surface (Bac-gE). Correct localization and display of gE on the engineered baculovirus was verified by flow cytometry and immune electron microscopy. We show that Bac-gE provides excellent antigenicity against VZV and induces not only stronger gE-specific CD4+ and CD8+ T cell responses but also higher levels of VZV-specific neutralizing antibodies as compared with other vaccine strategies in mice. Collectively, we show that the baculovirus display of VZV-gE confers ideal humoral and cellular immune responses required for HZ vaccine development, paving the way for a baculovirus-based vaccine design.

Strategies for enhancing immunity against avian influenza virus in chickens: A review

Poultry infection with avian influenza viruses (AIV) is a continuous source of concern for poultry production and human health. Uncontrolled infection and transmission of AIV in poultry increases the potential for viral mutation and reassortment, possibly resulting in the emergence of zoonotic viruses. To this end, implementing strategies to disrupt the transmission of AIVs in poultry, including a wide array of traditional and novel methods, is much needed. Vaccination of poultry is a targeted approach to reduce clinical signs and shedding in infected birds. Strategies aimed at enhancing the effectiveness of AIV vaccines are multi-pronged and include methods directed towards eliciting immune responses in poultry. Strategies include producing vaccines of greater immunogenicity via vaccine type and adjuvant application and increasing bird responsiveness to vaccines by modification of the gastrointestinal tract (GIT) microbiome and dietary interventions. This review provides an in-depth discussion of recent findings surrounding novel AIV vaccines for poultry, including reverse genetics vaccines, vectors, protein vaccines and virus like particles, highlighting their experimental efficacy among other factors such as safety and potential for use in the field. In addition to the type of vaccine employed, vaccine adjuvants also provide an effective way to enhance AIV vaccine efficacy, therefore, research on different types of vaccine adjuvants and vaccine adjuvant delivery strategies is discussed. Finally, the poultry gastrointestinal microbiome is emerging as an important factor in the effectiveness of prophylactic treatments. In this regard, current findings on the effects of the chicken GIT microbiome on AIV vaccine efficacy are summarized here.

Development and application of reverse genetic technology for the influenza virus

Influenza virus is a common virus in people's daily lives, and it has certain infectivity in humans and animals. Influenza viruses have the characteristics of a high mutation rate and wide distribution. Reverse genetic technology is primarily used to modify viruses at the DNA level through targeted modification of the virus cDNA. Genetically modified influenza viruses have a unique advantage when researching the transmission and pathogenicity of influenza. With the continuous development of oncolytic viruses in recent years, studies have found that influenza viruses also have certain oncolytic activity. Influenza viruses can specifically recognize tumor cells; activate cytotoxic T cells, NK cells, dendritic cells, etc.; and stimulate the body to produce an immune response, thereby killing tumor cells. This article will review the development and application of influenza virus reverse genetic technology.

Construction of polycistronic baculovirus surface display vectors to express the PCV2 Cap(d41) protein and analysis of its immunogenicity in mice and swine

To increase expression levels of the PCV2 Cap(d41) protein, novel baculovirus surface display vectors with multiple expression cassettes were constructed to create recombinant baculoviruses BacSC-Cap(d41), BacDD-2Cap(d41), BacDD-3Cap(d41), and BacDD-4Cap(d41). Our results reveal that the recombinant baculovirus BacDD-4Cap(d41) was able to express the highest levels of Cap(d41) protein. Optimum conditions for expressing the PCV2 Cap(d41) protein were determined, and our results show that 107 of Sf-9 infected with the recombinant baculovirus BacDD-4Cap(d41) at an MOI of 5 for 3 days showed the highest level of protein expression. Mice immunized with the 4Cap(d41) vaccine which was prepared from the recombinant baculovirus-infected cells (107) elicited higher ELISA titers compared to the Cap (d41) vaccine. The 4Cap(d41) vaccine could elicit anti-PCV2 neutralizing antibodies and IFN-γ in mice, as confirmed by virus neutralization test and IFN-γ ELISA. Moreover, the swine lymphocyte proliferative responses indicated that the 4Cap(d41) vaccine was able to induce a clear cellular immune response. Flow cytometry analysis showed that the percentage of CD4+ T cells and CD4+/CD8+ ratio was increased significantly in SPF pigs immunized with the 4Cap(d41) vaccine. Importantly, the 4Cap(d41) vaccine induced an IFN-γ response, further confirming that its effect is through cellular immunity in SPF pigs. An in vivo challenge study revealed that the 4Cap(d41) and the commercial vaccine groups significantly reduce the viral load of vaccinated pigs as compared with the CE negative control group. Taken together, we have successfully developed a 4Cap(d41) vaccine that may be a potential subunit vaccine for preventing the disease associated with PCV2 infections.