Mosquito Cell-Derived Japanese Encephalitis Virus-Like Particles Induce Specific Humoral and Cellular Immune Responses in Mice

Identifying Key Drivers of Efficient B Cell Responses: On the Role of T Help, Antigen-Organization, and Toll-like Receptor Stimulation for Generating a Neutralizing Anti-Dengue Virus Response

T help (Th), stimulation of toll-like receptors (pathogen-associated molecular patterns, PAMPs), and antigen organization and repetitiveness (pathogen-associated structural patterns, PASPs) were shown numerous times to be important in driving B-cell and antibody responses. In this study, we dissected the individual contributions of these parameters using newly developed "Immune-tag" technology. As model antigens, we used eGFP and the third domain of the dengue virus 1 envelope protein (DV1 EDIII), the major target of virus-neutralizing antibodies. The respective proteins were expressed alone or genetically fused to the N-terminal fragment of the cucumber mosaic virus (CMV) capsid protein-nCMV, rendering the antigens oligomeric. In a step-by-step manner, RNA was attached as a PAMP, and/or a universal Th-cell epitope was genetically added for additional Th. Finally, a PASP was added to the constructs by displaying the antigens highly organized and repetitively on the surface of CMV-derived virus-like particles (CuMV VLPs). Sera from immunized mice demonstrated that each component contributed stepwise to the immunogenicity of both proteins. All components combined in the CuMV VLP platform induced by far the highest antibody responses. In addition, the DV1 EDIII induced high levels of DENV-1-neutralizing antibodies only if displayed on VLPs. Thus, combining multiple cues typically associated with viruses results in optimal antibody responses.

Artificial Feeding Systems for Vector-Borne Disease Studies

This review examines the advancements and methodologies of artificial feeding systems for the study of vector-borne diseases, offering a critical assessment of their development, advantages, and limitations relative to traditional live host models. It underscores the ethical considerations and practical benefits of such systems, including minimizing the use of live animals and enhancing experimental consistency. Various artificial feeding techniques are detailed, including membrane feeding, capillary feeding, and the utilization of engineered biocompatible materials, with their respective applications, efficacy, and the challenges encountered with their use also being outlined. This review also forecasts the integration of cutting-edge technologies like biomimicry, microfluidics, nanotechnology, and artificial intelligence to refine and expand the capabilities of artificial feeding systems. These innovations aim to more accurately simulate natural feeding conditions, thereby improving the reliability of studies on the transmission dynamics of vector-borne diseases. This comprehensive review serves as a foundational reference for researchers in the field, proposing a forward-looking perspective on the potential of artificial feeding systems to revolutionize vector-borne disease research.

Virus-like Particle Vaccines and Platforms for Vaccine Development

Virus-like particles (VLPs) have gained a lot of interest within the past two decades. The use of VLP-based vaccines to protect against three infectious agents-hepatitis B virus, human papillomavirus, and hepatitis E virus-has been approved; they are very efficacious and offer long-lasting immune responses. Besides these, VLPs from other viral infectious agents (that infect humans, animals, plants, and bacteria) are under development. These VLPs, especially those from human and animal viruses, serve as stand-alone vaccines to protect against viruses from which the VLPs were derived. Additionally, VLPs, including those derived from plant and bacterial viruses, serve as platforms upon which to display foreign peptide antigens from other infectious agents or metabolic diseases such as cancer, i.e., they can be used to develop chimeric VLPs. The goal of chimeric VLPs is to enhance the immunogenicity of foreign peptides displayed on VLPs and not necessarily the platforms. This review provides a summary of VLP vaccines for human and veterinary use that have been approved and those that are under development. Furthermore, this review summarizes chimeric VLP vaccines that have been developed and tested in pre-clinical studies. Finally, the review concludes with a snapshot of the advantages of VLP-based vaccines such as hybrid/mosaic VLPs over conventional vaccine approaches such as live-attenuated and inactivated vaccines.

Development of a Novel Chikungunya Virus-Like Replicon Particle for Rapid Quantification and Screening of Neutralizing Antibodies and Antivirals

Chikungunya fever is a mosquito-transmitted infectious disease that induces rash, myalgia, and persistent incapacitating arthralgia. At present, no vaccines or antiviral therapies specific to Chikungunya virus (CHIKV) infection have been approved, and research is currently restricted to biosafety level 3 containment. CHIKV-like replicon particles (VRPs) are single-cycle infectious particles containing viral structure proteins, as well as a defective genome to provide a safe surrogate for living CHIKV to facilitate the testing of vaccines and antivirals. However, inefficient RNA transfection and the potential emergence of the competent virus through recombination in mammalian cells limit VRP usability. This study describes a transfection-free system for the safe packaging of CHIK VRP with all necessary components via transduction of mosquito cell lines using a single baculovirus vector. We observed the release of substantial quantities of mosquito cell-derived CHIK VRP (mos-CHIK VRP) from baculovirus-transduced mosquito cell lines. The VRPs were shown to recapitulate viral replication and subgenomic dual reporter expression (enhanced green fluorescent protein [eGFP] and luciferase) in infected host cells. Interestingly, the rapid expression kinetics of the VRP-expressing luciferase reporter (6 h) makes it possible to use mos-CHIK VRPs for the rapid quantification of VRP infection. Treatment with antivirals (suramin or 6-azauridine) or neutralizing antibodies (monoclonal antibodies [MAbs] or patient sera) was shown to inhibit mos-CHIK VRP infection in a dose-dependent manner. Ease of manufacture, safety, scalability, and high throughput make mos-CHIK VRPs a highly valuable vehicle for the study of CHIKV biology, the detection of neutralizing (NT) antibody activity, and the screening of antivirals against CHIKV. IMPORTANCE This study proposes a transfection-free system that enables the safe packaging of CHIK VRPs with all necessary components via baculovirus transduction. Those mosquito cell-derived CHIK VRP (mos-CHIK VRPs) were shown to recapitulate viral replication and subgenomic dual reporter (enhanced green fluorescent protein [eGFP] and luciferase) expression in infected host cells. Rapid expression kinetics of the VRP-expressing luciferase reporter (within hours) opens the door to using mos-CHIK VRPs for the rapid quantification of neutralizing antibody and antiviral activity against CHIKV. To the best of our knowledge, this is the first study to report a mosquito cell-derived alphavirus VRP system. Note that this system could also be applied to other arboviruses to model the earliest event in arboviral infection in vertebrates.

Virus-like particles vaccines based on glycoprotein E0 and E2 of bovine viral diarrhea virus induce Humoral responses

Bovine viral diarrhea/mucosal disease (BVD/MD) is a viral infectious disease that seriously endangers the health of cattle herds and brings serious economic losses to the global cattle industry. Virus-like particles (VLPs) are empty shell structures without viral nucleic acid, which are similar to natural virus particles in morphology and structure. Because of their strong immunogenicity and biological activity, some of them have been used as vaccines in clinical trials. In this study, we developed a strategy to generate BVDV (E0 + E2, E2 + E2) VLPs using an insect baculovirus expression vector system (BEVS). The VLPs obtained were detected by immunofluorescence assay (IFA), western blotting analyses and transmission electron microscope (TEM), and the results showed that VLPs of high purity were obtained. Mice immunized with VLPs (15  μg) and Freund's adjuvant (100  μl) elicited higher BVDV-neutralizing antibody in comparison with Freund's adjuvant control (p < 0.0001), and even on day 21 or 35 post-prime immunization, the neutralizing antibody levels of mice immunized with E0 + E2 or E2 + E2 VLPs were significantly higher compared with inactivated vaccine (p < 0.05). A subsequent challenge reveals that the viral loads of livers, kidneys, spleens, lungs and small intestines were significantly lower compared with control (p < 0.0001), and the viral loads of mice immunized with E0 + E2 or E2 + E2 VLPs in the small intestines were significantly lower compared with inactivated vaccine (p < 0.05). Thus, VLPs are a promising candidate vaccine and warrants further clinical evaluation.

Japanese encephalitis genotype I virus-like particles stably expressed in BHK-21 cells serves as potential antigen in JE IgM ELISA

Abstract

Japanese encephalitis virus (JEV) is one of the leading causes of epidemic encephalitis in South Asian countries. Due to the short-term viremia, detecting IgM antibodies by ELISA is treated as the front-line diagnostic assay. Co-circulation and multiple exposures to antigenically cross-reactive flaviviruses in India pose a challenge in serodiagnosis. Replacing the whole virus antigen currently used in the JE IgM detection kits (ELISA) may improve the specificity and sensitivity of the existing JE MAC ELISA kits. For this purpose, we developed a stably transfected cell clone, BHK-IE6, which expresses a high amount of VLPs up to 37 µg/ml and is consistent in expression up to 40 passages. For the expression of VLPs in the secretory form, we cloned the JEV G-I prM-E coding gene along with the C-terminal signal sequence of capsid protein in the BHK-21 cells using the pcDNA3.1 + mammalian expression vector. The immune assays performed demonstrated its immune reactivity equivalent to the parental JEV strain. Simultaneously performed ELISAs using the whole virus antigen and newly developed antigen gave comparable results for JE positive and negative samples, which established the utility of developed JEV E-VLP as an antigen. Reduced cross-reactivity and increased specificity were observed when tested with dual positive sera for anti-JEV and DENV antibodies. These findings confirm the efficiency and reliability of newly developed recombinant E-VLP antigen expressed by the BHK-IE6 cell clone as an antigen in serodiagnostic assays. The implementation and progress in developing cross-reactivity-reduced antigens would improve serodiagnosis and disease burden estimates of flavivirus infection.

Key points

• pcDNA3.1/JE-Sig-prM-E plasmid transfected BHK-21 cells stably express VLPs.

• Sodium butyrate induction enhanced the extracellular expression of VLPs.

• Application of JEV-E VLPs increases the specificity of JE IgM ELISA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11825-1.

Virus-Like Particles: Revolutionary Platforms for Developing Vaccines Against Emerging Infectious Diseases

Virus-like particles (VLPs) are nanostructures that possess diverse applications in therapeutics, immunization, and diagnostics. With the recent advancements in biomedical engineering technologies, commercially available VLP-based vaccines are being extensively used to combat infectious diseases, whereas many more are in different stages of development in clinical studies. Because of their desired characteristics in terms of efficacy, safety, and diversity, VLP-based approaches might become more recurrent in the years to come. However, some production and fabrication challenges must be addressed before VLP-based approaches can be widely used in therapeutics. This review offers insight into the recent VLP-based vaccines development, with an emphasis on their characteristics, expression systems, and potential applicability as ideal candidates to combat emerging virulent pathogens. Finally, the potential of VLP-based vaccine as viable and efficient immunizing agents to induce immunity against virulent infectious agents, including, SARS-CoV-2 and protein nanoparticle-based vaccines has been elaborated. Thus, VLP vaccines may serve as an effective alternative to conventional vaccine strategies in combating emerging infectious diseases.

Nanoparticular CpG-adjuvanted SARS-CoV-2 S1 protein elicits broadly neutralizing and Th1-biased immunoreactivity in mice

The spike (S) protein is a leading vaccine candidate against SARS-CoV-2 infection. The S1 domain of S protein, which contains a critical receptor-binding domain (RBD) antigen, potentially induces protective immunoreactivities against SARS-CoV-2. In this study, we presented preclinical evaluations of a novel insect cell-derived SARS-CoV-2 recombinant S1 (rS1) protein as a potent COVID-19 vaccine candidate. The native antigenicity of rS1 was characterized by enzyme-linked immunosorbent assay with a neutralizing monoclonal antibody targeting the RBD antigen. To improve its immunogenicity, rS1-adjuvanted with fucoidan/trimethylchitosan nanoparticles (FUC-TMC NPs) and cytosine-phosphate-guanosine-oligodeoxynucleotides (CpG-ODNs) were investigated using a mouse model. The S1-specific immunoglobulin G (IgG) titers, FluoroSpot assay, pseudovirus- and prototype SARS-CoV-2-based neutralization assays were assessed. The results showed that the rS1/CpG/ FUC-TMC NPs (rS1/CpG/NPs) formulation induced a broad-spectrum IgG response with potent, long-lasting, and cross-protective neutralizing activity against the emerging SARS-CoV-2 variant of concern, along with a Th1-biased cellular response. Thus, the rS1/CpG/NPs formulation presents a promising vaccination approach against COVID-19.

Induction of Robust and Specific Humoral and Cellular Immune Responses by Bovine Viral Diarrhea Virus Virus-Like Particles (BVDV-VLPs) Engineered with Baculovirus Expression Vector System

Bovine viral diarrhea virus (BVDV) is an important animal pathogen that affects cattle. Infections caused by the virus have resulted in substantial economic losses and outbreaks of BVDV are reported globally. Virus-like particles (VLPs) are promising vaccine technology largely due to their safety and strong ability to elicit robust immune responses. In this study, we developed a strategy to generate BVDV-VLPs using a baculovirus expression vector system (BEVS). We were able to assemble BVDV-VLPs composed of dimerized viral proteins E2 and E^rns, and the VLPs were spherical particles with the diameters of about 50 nm. Mice immunized with 15 μg of VLPs adjuvanted with ISA201 elicited higher levels of E2-specific IgG, IgG1, and IgG2a antibodies as well as higher BVDV-neutralizing activity in comparison with controls. Re-stimulation of the splenocytes collected from mice immunized with VLPs led to significantly increased levels of CD3⁺CD4⁺T cells and CD3⁺CD8⁺T cells. In addition, the splenocytes showed dramatically enhanced proliferation and the secretion of Th1-associated IFN-γ and Th2-associated IL-4 compared to that of the unstimulated control group. Taken together, our data indicate that BVDV-VLPs efficiently induced BVDV-specific humoral and cellular immune responses in mice, showing a promising potential of developing BVDV-VLP-based vaccines for the prevention of BVDV infections.