Influenza virus-like particles elicit broader immune responses than whole virion inactivated influenza virus or recombinant hemagglutinin

Vaccine efficacy induced by 2020-2021 seasonal influenza-derived H3N1 virus-like particles co-expressing M2e5x or N2

Influenza A matrix protein 2 (M2e) and neuraminidase (NA) antigens are known to play important roles in mounting a broad range of protection. Nonetheless, the protective efficacy of the VLP vaccines co-expressing both M2e and NA antigens has not been explored. In this study, we generated 2020/2021 seasonal influenza H3N1 VLPs that co-expressed either M2e5x (H3N1M2e5x) or N2 (H3N1N2 VLP) antigens. The protective efficacy of these VLPs was assessed by challenge infection with heterologous H3N2 and heterosubtypic H1N1 and H5N1 viruses in mice. Both VLP formulations induced cross-protection against distinct viruses, H3N1M2e5x VLPs elicited higher levels of cross-reactive IgG in sera against H1N1 and H5N1 viruses than H3N1N2 VLPs. Compared to H3N1N2 VLPs, H3N1M2e5x VLPs also induced substantially enhanced germinal center B cell responses while inhibiting IFN-γ production in the lungs. Importantly, H3N1M2e5x VLPs significantly reduced the lung virus titers upon H1N1, H3N2, and H5N1 challenge infections. These results indicated that VLPs comprising the M2e5x antigen are a promising vaccine design strategy that could aid in the pursuit of a universal influenza vaccine.

Viral nanoparticles: Current advances in design and development

Viral nanoparticles (VNPs) are self-assembling, adaptable delivery systems for vaccines and other therapeutic agents used in a variety of biomedical applications. The potential of viruses to invade and infect various hosts and cells renders them suitable as potential nanocarriers, possessing distinct functional characteristics, immunogenic properties, and improved biocompatibility and biodegradability. VNPs are frequently produced through precise genetic or chemical engineering, which involves adding diverse sequences or functional payloads to the capsid protein (CP). Several spherical and helical plant viruses, bacteriophages, and animal viruses are currently being used as VNPs, or non-infectious virus-like particles (VLPs). In addition to their broad use in cancer therapy, vaccine technology, diagnostics, and molecular imaging, VNPs have made important strides in the realms of tissue engineering, biosensing, and antimicrobial prophylaxis. They are also being used in energy storage cells due to their binding and piezoelectric properties. The large-scale production of VNPs for research, preclinical testing, and clinical use is fraught with difficulties, such as those relating to cost-effectiveness, scalability, and purity. Consequently, many plants- and microorganism-based platforms are being developed, and newer viruses are being explored. The goal of the current review is to provide an overview of these advances.

Development of Virus-like Particle Plant-Based Vaccines against Avian H5 and H9 Influenza A Viruses

Avian influenza A virus (AIV) is a significant cause of mortality in poultry, causing substantial economic loss, particularly in developing countries, and has zoonotic potential. For example, highly pathogenic avian influenza (HPAI) viruses of the H5 subtype have been circulating in Egypt for around two decades. In the last decade, H5N1 viruses of clade 2.2.1 have been succeeded by the antigenically distinct H5N8 clade 2.3.4.4b viruses. Furthermore, H9N2 viruses co-circulate with the H5N8 viruses in Egyptian poultry. It is widely recognised that effective vaccination against IAV requires a close antigenic match between the vaccine and viruses circulating in the field. Therefore, approaches to develop cost-effective vaccines that can be rapidly adapted to local virus strains are required for developing countries such as Egypt. In this project, the haemagglutinin (HA) proteins of Egyptian H5 and H9 viruses were expressed by transient transfection of plants (Nicotiana benthamiana). The formation of virus-like particles (VLPs) was confirmed by transmission electron microscopy. Mice were immunised with four doses of either H5 or H9 VLPs with adjuvant. Antibody and cellular immune responses were measured against the corresponding recombinant protein using ELISA and enzyme-linked immunosorbent assay (ELISpot), respectively. Chickens were immunised with one dose of H5 VLPs, eliciting HA-specific antibodies measured by ELISA and a pseudotyped virus neutralisation test using a heterologous H5 HA. In conclusion, plant-based VLP vaccines have potential for producing an effective vaccine candidate within a short time at a relatively low cost.

Viral protein-based nanoparticles (part 2): Pharmaceutical applications

Viral protein nanoparticles (ViP NPs) such as virus-like particles and virosomes are structures halfway between viruses and synthetic nanoparticles. The biological nature of ViP NPs endows them with the biocompatibility, biodegradability, and functional properties that many synthetic nanoparticles lack. At the same time, the absence of a viral genome avoids the safety concerns of viruses. Such characteristics of ViP NPs offer a myriad of opportunities for theirapplication at several points across disease development: from prophylaxis to diagnosis and treatment. ViP NPs present remarkable immunostimulant properties, and thus the vaccination field has benefited the most from these platforms capable of overcoming the limitations of both traditional and subunit vaccines. This was reflected in the marketing authorization of several VLP- and virosome-based vaccines. Besides, ViP NPs inherit the ability of viruses to deliver their cargo to target cells. Because of that, ViP NPs are promising candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze the pharmaceutical applications of ViP NPs, describing the products that are commercially available or under clinical evaluation, but also the advances that scientists are making toward the implementation of ViP NPs in other areas of major pharmaceutical interest.

Nanoadjuvants: Promising Bioinspired and Biomimetic Approaches in Vaccine Innovation

Adjuvants are the important part of vaccine manufacturing as they elicit the vaccination effect and enhance the durability of the immune response through controlled release. In light of this, nanoadjuvants have shown unique broad spectrum advantages. As nanoparticles (NPs) based vaccines are fast-acting and better in terms of safety and usability parameters as compared to traditional vaccines, they have attracted the attention of researchers. A vaccine nanocarrier is another interesting and promising area for the development of next-generation vaccines for prophylaxis. This review looks at the various nanoadjuvants and their structure-function relationships. It compiles the state-of-art literature on numerous nanoadjuvants to help domain researchers orient their understanding and extend their endeavors in vaccines research and development.

The production of Newcastle disease virus-like particles in Nicotiana benthamiana as potential vaccines

Newcastle disease (ND) is a highly contagious viral respiratory and neurological disease that has a severe impact on poultry production worldwide. In the present study, an expression platform was established for the transient production in N.bethamiana of ND virus-like particles (VLPs) for use as vaccines against ND. The expression of the ND Fusion (F) and/or Hemagglutinin-neuraminidase (HN) proteins of a genotype VII.2 strain formed ND VLPs in planta as visualized under the transmission electron microscope, and HN-containing VLPs agglutinated chicken erythrocytes with hemagglutination (HA) titres of up to 13 log2.The immunogenicity of the partially-purified ND VLPs was confirmed in specific-pathogen-free White leghorn chickens. Birds receiving a single intramuscular immunization with 1024 HA units (10 log2) of the F/HN ND VLPs administered with 20% [v/v] Emulsigen®-P adjuvant, seroconverted after 14 days with F- and HN-specific antibodies at ELISA titres of 5705.17 and HI geometric mean titres (GMTs) of 6.2 log2, respectively. Furthermore, these ND-specific antibodies successfully inhibited viral replication in vitro of two antigenically closely-related ND virus isolates, with virus-neutralization test GMTs of 3.47 and 3.4, respectively. Plant-produced ND VLPs have great potential as antigen-matched vaccines for poultry and other avian species that are highly immunogenic, cost-effective, and facilitate prompt updating to ensure improved protection against emerging ND field viruses.

Immunogenicity and protective potential of chimeric virus-like particles containing SARS-CoV-2 spike and H5N1 matrix 1 proteins

Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), has posed a constant threat to human beings and the world economy for more than two years. Vaccination is the first choice to control and prevent the pandemic. However, an effective SARS-CoV-2 vaccine against the virus infection is still needed. This study designed and prepared four kinds of virus-like particles (VLPs) using an insect expression system. Two constructs encoded wild-type SARS-CoV-2 spike (S) fused with or without H5N1 matrix 1 (M1) (S and SM). The other two constructs contained a codon-optimized spike gene and/or M1 gene (mS and mSM) based on protein expression, stability, and ADE avoidance. The results showed that the VLP-based vaccine could induce high SARS-CoV-2 specific antibodies in mice, including specific IgG, IgG1, and IgG2a. Moreover, the mSM group has the most robust ability to stimulate humoral immunity and cellular immunity than the other VLPs, suggesting the mSM is the best immunogen. Further studies showed that the mSM combined with Al/CpG adjuvant could stimulate animals to produce sustained high-level antibodies and establish an effective protective barrier to protect mice from challenges with mouse-adapted strain. The vaccine based on mSM and Al/CpG adjuvant is a promising candidate vaccine to prevent the COVID-19 pandemic.

A Single Vaccination of Chimeric Bivalent Virus-Like Particle Vaccine Confers Protection Against H9N2 and H3N2 Avian Influenza in Commercial Broilers and Allows a Strategy of Differentiating Infected from Vaccinated Animals

H9N2 and H3N2 are the two most important subtypes of low pathogenic avian influenza viruses (LPAIV) because of their ongoing threat to the global poultry industry and public health. Although commercially available inactivated H9N2 vaccines are widely used in the affected countries, endemic H9N2 avian influenza remains uncontrolled. In addition, there is no available avian H3N2 vaccine. Influenza virus-like particles (VLPs) are one of the most promising vaccine alternatives to traditional egg-based vaccines. In this study, to increase the immunogenic content of VLPs to reduce production costs, we developed chimeric bivalent VLPs (cbVLPs) co-displaying hemagglutinin (HA) and neuraminidase (NA) of H9N2 and H3N2 viruses with the Gag protein of bovine immunodeficiency virus (BIV) as the inner core using the Bac-to-Bac baculovirus expression system. The results showed that a single immunization of chickens with 40μg/0.3mL cbVLPs elicited an effective immune response and provided complete protection against H9N2 and H3N2 viruses. More importantly, cbVLPs with accompanying serological assays can successfully accomplish the strategy of differentiating infected animals from vaccinated animals (DIVA), making virus surveillance easier. Therefore, this cbVLP vaccine candidate would be a promising alternative to conventional vaccines, showing great potential for commercial development.

Review: A systematic review of virus-like particles of coronavirus: Assembly, generation, chimerism and their application in basic research and in the clinic

Virus-like particles (VLPs) are nano-scale particles that are morphologically similar to a live virus but which lack a genetic component. Since the pandemic spread of COVID-19, much focus has been placed on coronavirus (CoV)-related VLPs. CoVs contain four structural proteins, though the minimum requirement for VLP formation differs among virus species. CoV VLPs are commonly produced in mammalian and insect cell systems, sometimes in the form of chimeric VLPs that enable surface display of CoV epitopes. VLPs are an ideal model for virological research and have been applied as vaccines and diagnostic reagents to aid in clinical disease control. This review summarizes and updates the research progress on the characteristics of VLPs from different known CoVs, mainly focusing on assembly, in vitro expression systems for VLP generation, VLP chimerism, protein-based nanoparticles and their applications in basic research and clinical settings, which may aid in development of novel VLP vaccines against emerging coronavirus diseases such as SARS-CoV-2.

Strategies for fighting pandemic virus infections: Integration of virology and drug delivery

Respiratory viruses have sometimes resulted in worldwide pandemics, with the influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) being major participants. Long-term efforts have made it possible to control the influenza virus, but seasonal influenza continues to take many lives each year, and a pandemic influenza virus sometimes emerges. Although vaccines for coronavirus disease 2019 (COVID-19) have been developed, we are not yet able to coexist with the SARS-CoV-2. To overcome such viruses, it is necessary to obtain knowledge about international surveillance systems, virology, ecology and to determine that immune responses are effective. The information must then be transferred to drugs. Delivery systems would be expected to contribute to the rational development of drugs. In this review, virologist and drug delivery system (DDS) researchers discuss drug delivery strategies, especially the use of lipid-based nanocarriers, for fighting to respiratory virus infections.

Evaluation of the antigenic stability of influenza virus like particles after exposure to acidic or basic pH

Purpose

Virus-like particles (VLPs) are being developed as a promising vaccine platform and therapeutic delivery. Various strategies for effectively constructing VLPs have been studied, but relatively few studies have been done on various factors affecting storage. In this study, we investigated the antigenic changes of VLPs in an acidic or basic pH environment using influenza VLPs as an experimental model.

Materials and Methods

Influenza VLPs containing hemagglutination and M1 proteins were generated and their antigenicity and protective immunity in vitro and in vivo were evaluated after exposure to acidic (pH 4 and 5) or basic (pH 9 and 10) pH buffers.

Results

VLP exposed to basic pH showed similar levels of antigenicity to those stored in neutral pH, while antigenicity of VLP exposed to acidic pH was found to be significantly reduced compared to those expose neutral or basic pH. All groups of mice responded effectively to low concentrations of virus infections; however, VLP vaccine groups exposed to acid pH were found not to induce sufficient protective immune responses when a high concentration of influenza virus infection.

Conclusion

In order for VLP to be used as a more powerful vaccine platform, it should be developed in a strategic way to respond well to external changes such as acidic pH conditions.

COVID-19 Vaccine Platforms: Challenges and Safety Contemplations

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a pandemic as of March 2020, creating a global crisis and claiming millions of lives. To halt the pandemic and alleviate its impact on society, economy, and public health, the development of vaccines and antiviral agents against SARS-CoV-2 was a dire need. To date, various platforms have been utilized for SARS-CoV-2 vaccine development, and over 200 vaccine candidates have been produced, many of which have obtained the United States Food and Drug Administration (FDA) approval for emergency use. Despite this successful development and licensure, concerns regarding the safety and efficacy of these vaccines have arisen, given the unprecedented speed of vaccine development and the newly emerging SARS-CoV-2 strains and variants. In this review, we summarize the different platforms used for Coronavirus Disease 2019 (COVID-19) vaccine development, discuss their strengths and limitations, and highlight the major safety concerns and potential risks associated with each vaccine type.

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.

Neuraminidase in Virus-like Particles Contributes to the Protection against High Dose of Avian Influenza Virus Challenge Infection

Neuraminidase is an important target for influenza vaccination. In this study, we generated avian influenza VLPs, expressing hemagglutinin (HA), neuraminidase (NA), HA and NA co-expressed (HANA), to evaluate the protective role of NA against a high (10LD₅₀) and low (2LD₅₀) dose of avian influenza virus challenge infections. A single immunization with HANA VLPs elicited the highest level of virus-specific IgG, IgG1, and IgG2a responses from the sera post-vaccination and the lungs post-challenge-infection. Potent antibody-secreting cell responses were observed from the spleens and lungs of HANA-VLP-immunized mice post-challenge-infection. HANA VLPs induced the highest CD4⁺ T cell, CD8⁺ T cell, and germinal center B cells, while strongly limiting inflammatory cytokine production in the lungs compared to other VLP immunization groups. In correlation with these findings, the lowest bodyweight losses and lung virus titers were observed from HANA VLP immunization, and all of the immunized mice survived irrespective of the challenge dose. Contrastingly, VLPs expressing either HA or NA alone failed to elicit complete protection. These results indicated that NA in VLPs played a critical role in inducing protection against a high dose of the challenge infection.

The contribution of bovines to human health against viral infections

In the last 40 years, novel viruses have evolved at a much faster pace than other pathogens. Viral diseases pose a significant threat to public health around the world. Bovines have a longstanding history of significant contributions to human nutrition, agricultural, industrial purposes, medical research, drug and vaccine development, and livelihood. The life cycle, genomic structures, viral proteins, and pathophysiology of bovine viruses studied in vitro paved the way for understanding the human counterparts. Calf model has been used for testing vaccines against RSV, papillomavirus vaccines and anti-HCV agents were principally developed after using the BPV and BVDV model, respectively. Some bovine viruses-based vaccines (BPIV-3 and bovine rotaviruses) were successfully developed, clinically tried, and commercially produced. Cows, immunized with HIV envelope glycoprotein, produced effective broadly neutralizing antibodies in their serum and colostrum against HIV. Here, we have summarized a few examples of human viral infections for which the use of bovines has contributed to the acquisition of new knowledge to improve human health against viral infections covering the convergence between some human and bovine viruses and using bovines as disease models. Additionally, the production of vaccines and drugs, bovine-based products were covered, and the precautions in dealing with bovines and bovine-based materials.

H7N9 influenza virus-like particle based on BEVS protects chickens from lethal challenge with highly pathogenic H7N9 avian influenza virus

H7N9 avian influenza virus poses a dual threat to both poultry industry and public health. Therefore, it is highly urgent to develop an effective vaccine to reduce its pandemic potential. Virus-like particles (VLP) represent an effective approach for pandemic vaccine development. In this study, a recombinant baculovirus co-expressing the HA, NA and M1 genes of the H7N9 virus was constructed for generation of H7N9 VLP. Single immunization of chickens with 15 μg of the VLP or the commercial whole virus inactivated vaccine stimulates high hemagglutination inhibition, virus neutralizing and HA-specific IgY antibodies. Moreover, the antiserum had a good cross-reactivity with H7N9 field strains isolated in different years. Within 14 days after a lethal challenge with highly pathogenic (HP) H7N9 virus, no clinical symptoms and death were observed in the vaccinated chickens, and no virus was recovered from the organs. Compared to the non-vaccinated chickens, H7N9 VLP significantly reduced the proportion of animals shedding virus. Only 30 % of the VLP-vaccinated birds shed virus, whereas virus shedding was detected in 50 % of the chickens immunized with the commercial vaccine. Moreover, both vaccines dramatically alleviated pulmonary lesions caused by HP H7N9 virus, with a greater degree observed for the VLP. Altogether, our results indicated that the H7N9 VLP vaccine candidate confers a complete clinical protection against a lethal challenge with HP H7N9 virus, significantly inhibits virus shedding and abolishes viral replication in chickens. The VLP generated in this study represents a promising alternative strategy for the development of novel H7N9 avian influenza vaccines for chickens.

Virus-like particle preparation is improved by control over capsomere-DNA interactions during chromatographic purification

Expression of viral capsomeres in bacterial systems and subsequent in vitro assembly into virus-like particles is a possible pathway for affordable future vaccines. However, purification is challenging as viral capsomeres show poor binding to chromatography media. In this study, the behavior of capsomeres in unfractionated bacterial lysate was compared with that for purified capsomeres, with or without added microbial DNA, to better understand reasons for poor bioprocess behavior. We show that aggregates or complexes form through the interaction between viral capsomeres and DNA, especially in bacterial lysates rich in contaminating DNA. The formation of these complexes prevents the target protein capsomeres from accessing the pores of chromatography media. We find that protein-DNA interactions can be modulated by controlling the ionic strength of the buffer and that at elevated ionic strengths the protein-DNA complexes dissociate. Capsomeres thus released show enhanced bind-elute behavior on salt-tolerant chromatography media. DNA could therefore be efficiently removed. We believe this is the first report of the use of an optimized salt concentration that dissociates capsomere-DNA complexes yet enables binding to salt-tolerant media. Post purification, assembly experiments indicate that DNA-protein interactions can play a negative role during in vitro assembly, as DNA-protein complexes could not be assembled into virus-like particles, but formed worm-like structures. This study reveals that the control over DNA-protein interaction is a critical consideration during downstream process development for viral vaccines.

Engineered Nanoparticle Applications for Recombinant Influenza Vaccines

Influenza viruses cause seasonal epidemics and represent a pandemic risk. With current vaccine methods struggling to protect populations against emerging strains, there is a demand for a next-generation flu vaccine capable of providing broad protection. Recombinant biotechnology, combined with nanomedicine techniques, could address this demand by increasing immunogenicity and directing immune responses toward conserved antigenic targets on the virus. Various nanoparticle candidates have been tested for use in vaccines, including virus-like particles, protein and carbohydrate nanoconstructs, antigen-carrying lipid particles, and synthetic and inorganic particles modified for antigen presentation. These methods have yielded some promising results, including protection in animal models against antigenically distinct influenza strains, production of antibodies with broad reactivity, and activation of potent T cell responses. Based on the evidence of current research, it is feasible that the next generation of influenza vaccines will combine recombinant antigens with nanoparticle carriers.

COVID-19: Coronavirus Vaccine Development Updates

Coronavirus Disease 2019 (COVID-19) is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), a newly emerged coronavirus, and has been pandemic since March 2020 and led to many fatalities. Vaccines represent the most efficient means to control and stop the pandemic of COVID-19. However, currently there is no effective COVID-19 vaccine approved to use worldwide except for two human adenovirus vector vaccines, three inactivated vaccines, and one peptide vaccine for early or limited use in China and Russia. Safe and effective vaccines against COVID-19 are in urgent need. Researchers around the world are developing 213 COVID-19 candidate vaccines, among which 44 are in human trials. In this review, we summarize and analyze vaccine progress against SARS-CoV, Middle-East respiratory syndrome Coronavirus (MERS-CoV), and SARS-CoV-2, including inactivated vaccines, live attenuated vaccines, subunit vaccines, virus like particles, nucleic acid vaccines, and viral vector vaccines. As SARS-CoV-2, SARS-CoV, and MERS-CoV share the common genus, Betacoronavirus, this review of the major research progress will provide a reference and new insights into the COVID-19 vaccine design and development.

Plant-Based Vaccines: The Way Ahead?

Severe virus outbreaks are occurring more often and spreading faster and further than ever. Preparedness plans based on lessons learned from past epidemics can guide behavioral and pharmacological interventions to contain and treat emergent diseases. Although conventional biologics production systems can meet the pharmaceutical needs of a community at homeostasis, the COVID-19 pandemic has created an abrupt rise in demand for vaccines and therapeutics that highlight the gaps in this supply chain's ability to quickly develop and produce biologics in emergency situations given a short lead time. Considering the projected requirements for COVID-19 vaccines and the necessity for expedited large scale manufacture the capabilities of current biologics production systems should be surveyed to determine their applicability to pandemic preparedness. Plant-based biologics production systems have progressed to a state of commercial viability in the past 30 years with the capacity for production of complex, glycosylated, "mammalian compatible" molecules in a system with comparatively low production costs, high scalability, and production flexibility. Continued research drives the expansion of plant virus-based tools for harnessing the full production capacity from the plant biomass in transient systems. Here, we present an overview of vaccine production systems with a focus on plant-based production systems and their potential role as "first responders" in emergency pandemic situations.

AIV polyantigen epitope expressed by recombinant baculovirus induces a systemic immune response in chicken and mouse models

BACKGROUND

The protective efficacy of avian influenza virus (AIV) vaccines is unsatisfactory due to the presence of various serotypes generated by genetic reassortment. Thus, immunization with a polyantigen chimeric epitope vaccine may be an effective strategy for protecting poultry from infection with different AIV subtypes.

METHODS

Baculovirus has recently emerged as a novel and attractive gene delivery vehicle for animal cells. In the present study, a recombinant baculovirus BmNPV-CMV/THB-P10/CTLT containing a fused codon-optimized sequence (CTLT) of T lymphocyte epitopes from H1HA, H9HA, and H7HA AIV subtypes, and another fused codon-optimized sequence (THB) of Th and B cell epitopes from H1HA, H9HA, and H7HA AIV subtypes, driven by a baculovirus P10 promoter and cytomegalovirus CMV promoter, respectively, was constructed.

RESULTS

Western blotting and cellular immunofluorescence demonstrated that the CTLT (THB) can be expressed in rBac-CMV/THB-P10/CTLT-infected silkworm cells (mammalian HEK293T cells). Furthermore, the recombinant virus, rBac-CMV-THB-CTLT, was used to immunize both chickens and mice.

CONCLUSIONS

The results of an indirect ELISA, immunohistochemistry, and T lymphocyte proliferation assay indicated that specific humoral and cellular responses were detected in both chicken and mice. These results suggest that rBac-CMV/THB-P10/CTLT can be developed as a potential vaccine against different AIV subtypes.

Protective Immunity against SARS Subunit Vaccine Candidates Based on Spike Protein: Lessons for Coronavirus Vaccine Development

The recent outbreak of the novel coronavirus disease, COVID-19, has highlighted the threat that highly pathogenic coronaviruses have on global health security and the imminent need to design an effective vaccine for prevention purposes. Although several attempts have been made to develop vaccines against human coronavirus infections since the emergence of Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) in 2003, there is no available licensed vaccine yet. A better understanding of previous coronavirus vaccine studies may help to design a vaccine for the newly emerged virus, SARS-CoV-2, that may also cover other pathogenic coronaviruses as a potentially universal vaccine. In general, coronavirus spike protein is the major antigen for the vaccine design as it can induce neutralizing antibodies and protective immunity. By considering the high genetic similarity between SARS-CoV and SARS-CoV-2, here, protective immunity against SARS-CoV spike subunit vaccine candidates in animal models has been reviewed to gain advances that can facilitate coronavirus vaccine development in the near future.

Nanomaterials and Nanotechnology-Associated Innovations against Viral Infections with a Focus on Coronaviruses

Viral infections have recently emerged not only as a health threat to people but rapidly became the cause of universal fatality on a large scale. Nanomaterials comprising functionalized nanoparticles (NPs) and quantum dots and nanotechnology-associated innovative detection methods, vaccine design, and nanodrug production have shown immense promise for interfacing with pathogenic viruses and restricting their entrance into cells. These viruses have been scrutinized using rapid diagnostic detection and therapeutic interventional options against the caused infections including vaccine development for prevention and control. Coronaviruses, namely SARS-CoV, MERS-CoV, and SARS-CoV-2, have endangered human life, and the COVID-19 (caused by SARS-CoV-2) outbreak has become a perilous challenge to public health globally with huge accompanying morbidity rates. Thus, it is imperative to expedite the drug and vaccine development efforts that would help mitigate this pandemic. In this regard, smart and innovative nano-based technologies and approaches encompassing applications of green nanomedicine, bio-inspired methods, multifunctional bioengineered nanomaterials, and biomimetic drug delivery systems/carriers can help resolve the critical issues regarding detection, prevention, and treatment of viral infections. This perspective review expounds recent nanoscience advancements for the detection and treatment of viral infections with focus on coronaviruses and encompasses nano-based formulations and delivery platforms, nanovaccines, and promising methods for clinical diagnosis, especially regarding SARS-CoV-2.

Influenza Virus Like Particles (VLPs): Opportunities for H7N9 Vaccine Development

In the midst of the ongoing COVID-19 coronavirus pandemic, influenza virus remains a major threat to public health due to its potential to cause epidemics and pandemics with significant human mortality. Cases of H7N9 human infections emerged in eastern China in 2013 and immediately raised pandemic concerns as historically, pandemics were caused by the introduction of new subtypes into immunologically naïve human populations. Highly pathogenic H7N9 cases with severe disease were reported recently, indicating the continuing public health threat and the need for a prophylactic vaccine. Here we review the development of recombinant influenza virus-like particles (VLPs) as vaccines against H7N9 virus. Several approaches to vaccine development are reviewed including the expression of VLPs in mammalian, plant and insect cell expression systems. Although considerable progress has been achieved, including demonstration of safety and immunogenicity of H7N9 VLPs in the human clinical trials, the remaining challenges need to be addressed. These challenges include improvements to the manufacturing processes, as well as enhancements to immunogenicity in order to elicit protective immunity to multiple variants and subtypes of influenza virus.

Immune Imprinting in the Influenza Ferret Model

The initial exposure to influenza virus usually occurs during childhood. This imprinting has long-lasting effects on the immune responses to subsequent infections and vaccinations. Animal models that are used to investigate influenza pathogenesis and vaccination do recapitulate the pre-immune history in the human population. The establishment of influenza pre-immune ferret models is necessary for understanding infection and transmission and for designing efficacious vaccines.

Efficacy of a plant-produced virus-like particle vaccine in chickens challenged with Influenza A H6N2 virus

The efficacy, safety, speed, scalability and cost-effectiveness of producing hemagglutinin-based virus-like particle (VLP) vaccines in plants are well-established for human influenza, but untested for the massive poultry influenza vaccine market that remains dominated by traditional egg-grown oil-emulsion whole inactivated virus vaccines. For optimal efficacy, a vaccine should be closely antigenically matched to the field strain, requiring that influenza A vaccines be updated regularly. In this study, an H6 subtype VLP transiently expressed in Nicotiana benthamiana was formulated into a vaccine and evaluated for efficacy in chickens against challenge with a heterologous H6N2 virus. A single dose of the plant-produced H6 VLP vaccine elicited an immune response comparable to two doses of a commercial inactivated H6N2 vaccine, with mean hemagglutination inhibition titres of 9.3 log2 and 8.8 log2 , respectively. Compared to the non-vaccinated control, the H6 VLP vaccine significantly reduced the proportion of shedders and the magnitude of viral shedding by >100-fold in the oropharynx and >6-fold in the cloaca, and shortened oropharyngeal viral shedding by at least a week. Despite its potency, the cost of the antigenic mismatch between the inactivated H6N2 vaccine and challenge strain was evident not only in this vaccine's failure to reduce viral shedding compared to the non-vaccinated group, but its apparent exacerbation of oropharyngeal viral shedding until 21 days post-challenge. We estimate that a kilogram of plant leaf material can produce H6 VLP vaccines sufficient for between 5000 and 30 000 chickens, depending on the effective dose and whether one or two immunizations are administered.

Off-target effects of an insect cell-expressed influenza HA-pseudotyped Gag-VLP preparation in limiting postinfluenza Staphylococcus aureus infections

Clinical and historical data underscore the ability of influenza viruses to ally with Staphylococcus aureus and predispose the host for secondary bacterial pneumonia, which is a leading cause of influenza-associated mortality. This is fundamental because no vaccine for S. aureus is available and the number of antibiotic-resistant strains is alarmingly rising. Hence, this leaves influenza vaccination the only strategy to prevent postinfluenza staphylococcal infections. In the present work, we assessed the off-target effects of a Tnms42 insect cell-expressed BEI-treated Gag-VLP preparation expressing the HA of A/Puerto Rico/8/1934 (H1N1) in preventing S. aureus superinfection in mice pre-infected with a homologous or heterologous H1N1 viral challenge strain. Our results demonstrate that matched anti-hemagglutinin immunity elicited by a VLP preparation may suffice to prevent morbidity and mortality caused by lethal secondary bacterial infection. This effect was observed even when employing a single low antigen dose of 50 ng HA per animal. However, induction of anti-hemagglutinin immunity alone was not helpful in inhibiting heterologous viral replication and subsequent bacterial infection. Our results indicate the potential of the VLP vaccine approach in terms of immunogenicity but suggest that anti-HA immunity should not be considered as the sole preventive method for combatting influenza and postinfluenza bacterial infections.

Progress in the development of virus-like particle vaccines against respiratory viruses

Introduction: Influenza virus, human respiratory syncytial virus (RSV), and human metapneumovirus (HMPV) are important human respiratory pathogens. Recombinant virus-like particle (VLP) vaccines are suggested to be potential promising platforms to protect against these respiratory viruses. This review updates important progress in the development of VLP vaccines against respiratory viruses.Areas Covered: This review summarizes progress in developing VLP and nanoparticle-based vaccines against influenza virus, RSV, and HMPV. The PubMed was mainly used to search for important research articles published since 2010 although earlier key articles were also referenced. The research area covered includes VLP and nanoparticle platform vaccines against seasonal, pandemic, and avian influenza viruses as well as RSV and HMPV respiratory viruses. The production methods, immunogenic properties, and vaccine efficacy of respiratory VLP vaccines in preclinical animal models and clinical studies were reviewed in this article.Expert opinion: Previous and current preclinical and clinical studies suggest that recombinant VLP and nanoparticle vaccines are expected to be developed as promising alternative platforms against respiratory viruses in future. Therefore, continued research efforts are warranted.

Nanoparticles in influenza subunit vaccine development: Immunogenicity enhancement

The threat of novel influenza infections has sparked research efforts to develop subunit vaccines that can induce a more broadly protective immunity by targeting selected regions of the virus. In general, subunit vaccines are safer but may be less immunogenic than whole cell inactivated or live attenuated vaccines. Hence, novel adjuvants that boost immunogenicity are increasingly needed as we move toward the era of modern vaccines. In addition, targeting, delivery, and display of the selected antigens on the surface of professional antigen-presenting cells are also important in vaccine design and development. The use of nanosized particles can be one of the strategies to enhance immunogenicity as they can be efficiently recognized by antigen-presenting cells. They can act as both immunopotentiators and delivery system for the selected antigens. This review will discuss on the applications, advantages, limitations, and types of nanoparticles (NPs) used in the preparation of influenza subunit vaccine candidates to enhance humoral and cellular immune responses.

The Potential of Influenza HA-Specific Immunity in Mitigating Lethality of Postinfluenza Pneumococcal Infections

Influenza virus infections pre-dispose an individual to secondary pneumococcal infections, which represent a serious public health concern. Matching influenza vaccination was demonstrated helpful in preventing postinfluenza bacterial infections and associated illnesses in humans. Yet, the impact of influenza hemagglutinin (HA)-specific immunity alone in this dual-infection scenario remains elusive. In the present study, we assessed the protective effect of neutralizing and non-neutralizing anti-hemagglutinin immunity in a BALB/c influenza-pneumococcus superinfection model. Our immunogens were insect cell-expressed hemagglutinin-Gag virus-like particles that had been differentially-treated for the inactivation of bioprocess-related baculovirus impurities. We evaluated the potential of several formulations to restrain the primary infection with vaccine-matched or -mismatched influenza strains and secondary bacterial replication. In addition, we investigated the effect of anti-HA immunity on the interferon status in mouse lungs prior to bacterial challenge. In our experimental setup, neutralizing anti-HA immunity provided significant but incomplete protection from postinfluenza bacterial superinfection, despite effective control of viral replication. In view of this, it was surprising to observe a survival advantage with non-neutralizing adaptive immunity when using a heterologous viral challenge strain. Our findings suggest that both neutralizing and non-neutralizing anti-HA immunity can reduce disease and mortality caused by postinfluenza pneumococcal infections.

Process development for pandemic influenza VLP vaccine production using a baculovirus expression system

Background

Influenza viruses cause hundreds of thousands of respiratory diseases worldwide each year, and vaccination is considered the most effective approach for preventing influenza annual epidemics or pandemics. Since 1950, chicken embryonated eggs have been used as the main method for producing seasonal influenza vaccines. However, this platform has the main drawback of a lack of scale-up flexibility, and thus, egg-based vaccine manufacturers cannot supply sufficient doses within a short period for use for pandemic prevention. As a result, strategies for reducing the manufacturing time and increasing production capacity are urgently needed. Non-virion vaccine methods have been considered an alternative strategy against an influenza pandemic, and the purpose of maintaining an immunogenic capsule structure with infectious properties appears to be met by the virus-like particle (VLP) platform.

Results

An influenza H7N9-TW VLP production platform using insect cells, which included the expression of hemagglutinin (HA), NA, and M1 proteins, was established. To scale up H7N9-TW VLP production, several culture conditions were optimized to obtain a higher production yield. A high level of dissolved oxygen (DO) could be critical to H7N9-TW VLP production. If the DO was maintained at a high level, the HA titer obtained in the spinner flask system with ventilation was similar to that obtained in a shake flask. In this study, the HA titer in a 5-L bioreactor with a well-controlled DO level was substantially improved by 128-fold (from 4 HA units (HAU)/50 μL to 512 HAU/50 μL).

Conclusions

In this study, a multigene expression platform and an effective upstream process were developed. Notably, a high H7N9-TW VLP yield was achieved using a two-step production strategy while a high DO level was maintained. The upstream process, which resulted in high VLP titers, could be further used for large-scale influenza VLP vaccine production.

Peste des Petits Ruminants Virus-Like Particles Induce a Potent Humoral and Cellular Immune Response in Goats

Peste des petits ruminants is a highly contagious acute or subacute disease of small ruminants caused by the peste des petits ruminants virus (PPRV), and it is responsible for significant economic losses in animal husbandry. Vaccination represents the most effective means of controlling this disease, with virus-like particle (VLP) vaccines offering promising vaccine candidates. In this study, a PPRV VLP-based vaccine was developed using a baculovirus expression system, allowing for the simultaneous expression of the PPRV matrix (M), hemagglutinin (H), fusion (F) and nucleocapsid (N) proteins in insect cells. Immunization of mice and goats with PPRV VLPs elicited a robust neutralization response and a potent cellular immune response. Mouse studies demonstrated that VLPs induced a more robust IFN-γ response in CD4⁺ and CD8⁺ T cells than PPRV Nigeria 75/1 and recruited and/or activated more B cells and dendritic cells in inguinal lymph nodes. In addition, PPRV VLPs induced a strong Th1 class response in mice, as indicated by a high IgG2a to IgG1 ratio. Goat studies demonstrated that PPRV VLPs can induce the production of antibodies specific for F and H proteins and can also stimulate the production of virus neutralizing antibodies to the same magnitude as the PPRV Nigeria 75/1 vaccine. Higher amounts of IFN-γ in VLP-immunized animal serum suggested that VLPs also elicited a cellular immune response in goats. These results demonstrated that VLPs elicit a potent immune response against PPRV infection in small ruminants, making PPRV VLPs a potential candidate for PPRV vaccine development.

Induction of protective immune response to intranasal administration of influenza virus-like particles in a mouse model

Human influenza A viruses (IAVs) cause global pandemics and epidemics, which remains a nonignorable serious concern for public health worldwide. To combat the surge of viral outbreaks, new treatments are urgently needed. Here, we design a new vaccine based on virus-like particles (VLPs) and show how intranasal administration of this vaccine triggers protective immunity, which can be exploited for the development of new therapies. H1N1 VLPs were produced in baculovirus vectors and were injected into BALB/c mice by the intramuscular (IM) or intranasal (IN) route. We found that there were significantly higher inflammatory cell and lymphocyte concentrations in bronchoalveolar lavage samples and the lungs of IN immunized mice; however, the IM group had little signs of inflammatory responses. On the basis of our results, immunization with H1N1 influenza VLP elicited a strong T cell immunity in BALB/c mice. Despite T cell immunity amplification after both IN and IM vaccination methods in mice, IN-induced T cell responses were significantly more intense than IM-induced responses, and this was likely related to an increased number of both CD11b^high and CD103⁺ dendritic cells in mice lungs after IN administration of VLP. Furthermore, evaluation of interleukin-4 and interferon gamma cytokines along with several chemokine receptors showed that VLP vaccination via IN and IM routes leads to a greater CD4⁺ Th1 and Th2 response, respectively. Our findings indicated that VLPs represent a potential strategy for the development of an effective influenza vaccine; however, employing relevant routes for vaccination can be another important part of the universal influenza vaccine puzzle.

Immunosenescence Modulation by Vaccination

A decline in immune function is a hallmark of aging that leads to complicated illness from a variety of infectious diseases, cancer and other immune-mediated disorders, and may limit the ability to appropriately respond to vaccination. How vaccines might alter the senescent immune response and what are the immune correlates of protection will be addressed from the perspective of (1) stimulating a previously primed response as in the case of vaccines for seasonal influenza and herpes zoster, (2) priming the response to novel antigens such as pandemic influenza or West Nile virus, (3) vaccination against bacterial pathogens such as pneumococcus and pertussis, (4) vaccines against bacterial toxins such as tetanus and Clostridium difficile, and (5) vaccine approaches to mitigate effects of cytomegalovirus on immune senescence. New or improved vaccines developed over recent years demonstrate the considerable opportunity to improve current vaccines and develop new vaccines as a preventive approach to a variety of diseases in older adults. Strategies for selecting appropriate immunologic targets for new vaccine development and evaluating how vaccines may alter the senescent immune response in terms of potential benefits and risks in the preclinical and clinical trial phases of vaccine development will be discussed.

Biological characteristics and immunological properties in Muscovy ducks of H5N6 virus-like particles composed of HA-TM/HA-TMH3 and M1

Highly pathogenic avian influenza viruses (HPAIVs), including H5N6 strains, pose threats to the health of humans and poultry. Waterfowl play a crucial role as a reservoir of HPAIVs. Since current influenza vaccines induce poor antibody titres in waterfowl, there is an urgent need to develop an efficient vaccine against H5N6 infection. In this study, we constructed two H5N6 virus-like particles (VLPs) composed of matrix-1 (M1) and haemagglutinin of wildtype (HA-TM) or haemagglutinin with transmembrane domain replacement (HA-TM_H3) (designated as H5N6 VLPs-TM and H5N6 VLPs-TM_H3). Biological characteristics of the composed H5N6 VLPs were compared including localization, expression, contents of HA trimers, thermal stability, morphology and immunogenicity in Muscovy ducks. Our results indicate that the H5N6 VLPs-TM_H3 contained more HA trimers and presented better thermal stability. Moreover, Muscovy ducks immunized with H5N6 VLPs-TM_H3 produced higher titres of HI antibody and IFN-γ compared with those immunized with the same dose of H5N6 VLP-TM, thus providing a promising approach for the development of influenza virus vaccines for waterfowl. RESEARCH HIGHLIGHTS H5N6 VLPs-TM_H3 had more HA trimers and resisted higher temperature than H5N6 VLPs-TM H5N6 VLPs-TM_H3 induced higher titre of HI than H5N6 VLPs-TM in Muscovy ducks.

Nanoparticle Vaccines Against Infectious Diseases

Due to emergence of new variants of pathogenic micro-organisms the treatment and immunization of infectious diseases have become a great challenge in the past few years. In the context of vaccine development remarkable efforts have been made to develop new vaccines and also to improve the efficacy of existing vaccines against specific diseases. To date, some vaccines are developed from protein subunits or killed pathogens, whilst several vaccines are based on live-attenuated organisms, which carry the risk of regaining their pathogenicity under certain immunocompromised conditions. To avoid this, the development of risk-free effective vaccines in conjunction with adequate delivery systems are considered as an imperative need to obtain desired humoral and cell-mediated immunity against infectious diseases. In the last several years, the use of nanoparticle-based vaccines has received a great attention to improve vaccine efficacy, immunization strategies, and targeted delivery to achieve desired immune responses at the cellular level. To improve vaccine efficacy, these nanocarriers should protect the antigens from premature proteolytic degradation, facilitate antigen uptake and processing by antigen presenting cells, control release, and should be safe for human use. Nanocarriers composed of lipids, proteins, metals or polymers have already been used to attain some of these attributes. In this context, several physico-chemical properties of nanoparticles play an important role in the determination of vaccine efficacy. This review article focuses on the applications of nanocarrier-based vaccine formulations and the strategies used for the functionalization of nanoparticles to accomplish efficient delivery of vaccines in order to induce desired host immunity against infectious diseases.

How far have we reached in development of effective influenza vaccine?

Despite of ongoing research programs and numerous clinical trials, seasonal influenza epidemics remain a major concern globally. Vaccination remains the most effective method to prevent influenza infection. However, current flu vaccines have several limitations, including limited vaccine capacity, long production times, inconsistence efficacy in certain populations, and lack of a "universal" solution. Different next-generation approaches such as cell line-based culture, reverse genetics, and virus expression technology are currently under development to address the aforementioned challenges in conventional vaccine manufacture pipeline. Such approaches hope for safe and scalable production, induce broad-spectrum immunity, create premade libraries of vaccine strains, and target nonvariable regions of antigenic proteins for "universal" vaccination. Here, we discuss the process and challenges of the current influenza vaccine platform as well as new approaches that are being investigated. These developments indicate that an exciting future lies ahead in the influenza vaccine field.

Multi-clade H5N1 virus-like particles: Immunogenicity and protection against H5N1 virus and effects of beta-propiolactone

During the past decade, H5N1 highly pathogenic avian influenza (HPAI) viruses have diversified genetically and antigenically, suggesting the need for multiple H5N1 vaccines. However, preparation of multiple vaccines from live H5N1 HPAI viruses is difficult and economically not feasible representing a challenge for pandemic preparedness. Here we evaluated a novel multi-clade recombinant H5N1 virus-like particle (VLP) design, in which H5 hemagglutinins (HA) and N1 neuraminidase (NA) derived from four distinct clades of H5N1 virus were co-localized within the VLP structure. The multi-clade H5N1 VLPs were prepared by using a recombinant baculovirus expression system and evaluated for functional hemagglutination and neuraminidase enzyme activities, particle size and morphology, as well as for the presence of baculovirus in the purified VLP preparations. To remove residual baculovirus, VLP preparations were treated with beta-propiolactone (BPL). Immunogenicity and efficacy of multi-clade H5N1 VLPs were determined in an experimental ferret H5N1 HPAI challenge model, to ascertain the effect of BPL on immunogenicity and protective efficacy against lethal challenge. Although treatment with BPL reduced immunogenicity of VLPs, all vaccinated ferrets were protected from lethal challenge with influenza A/VietNam/1203/2004 (H5N1) HPAI virus, indicating that multi-clade VLP preparations treated with BPL represent a potential approach for pandemic preparedness vaccines.

Trigger factor assisted self-assembly of canine parvovirus VP2 protein into virus-like particles in Escherichia coli with high immunogenicity

Canine parvovirus (CPV) has been considered to be an important pathogen, which can cause acute infectious disease in canids. Although current vaccines are effective in preventing CPV infection, safety problems still remain unsolved. In this study, a subunit vaccine against CPV based on virus-like particles (VLPs) with good safety and immunogenicity is reported. Soluble CPV VP2 protein was produced by co-expression of chaperone trigger factor (Tf16) in Escherichia coli (E.coli), and assembled into CPV VLPs which could be affected by NaCl and pH. At 250 mM NaCl pH 8.0, the VLPs co-expressed with Tf16 had similar size (25 nm) and shape with the authentic virus capsid under the transmission electron microscopy (TEM), which is also in accordance with the dynamic light scattering (DLS) data. Immunization with these particles could induce high-titer hemagglutination inhibition (1:12288) and neutralizing antibodies (1:6144) in guinea pigs. Splenic cells of them could secrete IFN-γ and IL-4 after stimulation by CPV. Thus, the VLPs produced by the new approach with high yield and immunogenicity could be a potential candidate for CPV vaccine.

Intramuscular and intranasal immunization with an H7N9 influenza virus-like particle vaccine protects mice against lethal influenza virus challenge

The H7N9 influenza virus epidemic has been associated with a high mortality rate in China. Therefore, to prevent the H7N9 virus from causing further damage, developing a safe and effective vaccine is necessary. In this study, a vaccine candidate consisting of virus-like particles (VLPs) based on H7N9 A/Shanghai/2/2013 and containing hemagglutinin (HA), neuraminidase (NA), and matrix protein (M1) was successfully produced using a baculovirus (BV) expression system. Immunization experiments showed that strong humoral and cellular immune responses could be induced by the developed VLPs when administered via either the intramuscular (IM) or intranasal (IN) immunization routes. Notably, VLPs administered via both immunization routes provided 100% protection against lethal infection caused by the H7N9 virus. The IN immunization with 40μg of H7N9 VLPs induced strong lung IgA and lung tissue resident memory (TRM) cell-mediated local immune responses. These results provide evidence for the development of an effective preventive vaccine against the H7N9 virus based on VLPs administered through both the IM and IN immunization routes.

Sequential Immunizations with heterosubtypic virus-like particles elicit cross protection against divergent influenza A viruses in mice

Seasonal influenza vaccines have proven to be effective against well-matched viruses in healthy adults. However, rapid accumulation of mutations in the main antigenic surface proteins of influenza can compromise the efficiency of flu vaccines. Occasionally, influenza pandemics arise and present a different type of challenge to current seasonal vaccines. Novel vaccination strategies that can educate the host immune system to generate immune responses focusing on conserved epitopes on theses antigenic surface proteins are crucial for controlling and limiting influenza epidemics and pandemics. In this study, we have sequentially vaccinated mice with heterosubtypic influenza HA virus-like particles (VLPs) harboring H1, H8, and H13 from the HA phylogenetic group 1, or H3, H4, and H10 from the HA phylogenetic group 2, or in various combinations. The immunized animals were fully protected when challenged with lethal doses of heterosubtypic viruses from either phylogenetic group. Our vaccination approach demonstrates a promising strategy for the development of a ‘universal influenza vaccine’.

Large-Scale Transient Transfection of Suspension Mammalian Cells for VLP Production

Large-scale transient transfection of mammalian cell suspension cultures enables the production of biological products in sufficient quantity and under stringent quality attributes to perform accelerated in vitro evaluations and has the potential to support preclinical or even clinical studies. Here we describe the methodology to produce VLPs in a 3L bioreactor, using suspension HEK 293 cells and PEIPro as a transfection reagent. Cells are grown in the bioreactor to 1 × 10⁶ cells/mL and transfected with a plasmid DNA-PEI complex at a ratio of 1:2. Dissolved oxygen and pH are controlled and are online monitored during the production phase and cell growth and viability can be measured off line taking samples from the bioreactor. If the product is labeled with a fluorescent marker, transfection efficiency can be also assessed using flow cytometry analysis. Typically, the production phase lasts between 48 and 96 h until the product is harvested.

Developing a platform system for gene delivery: amplifying virus-like particles (AVLP) as an influenza vaccine

Delivery of a gene of interest to target cells is highly desirable for translational medicine, such as gene therapy, regenerative medicine, vaccine development, and studies of gene function. Parainfluenza virus 5 (PIV5), a paramyxovirus with a negative-sense RNA genome, normally infects cells without causing obvious cytopathic effect, and it can infect many cell types. To exploit these features of PIV5, we established a system generating self-amplifying, virus-like particles (AVLP). Using enhanced green fluorescent protein (EGFP) as a reporter, AVLP encoding EGFP (AVLP–EGFP) successfully delivered and expressed the EGFP gene in primary human cells, including stem cells, airway epithelial cells, monocytes, and T cells. To demonstrate the application of this system for vaccine development, we generated AVLPs to express the HA and M1 antigens from the influenza A virus strain H5N1 (AVLP–H5 and AVLP–M1H5). Immunization of mice with AVLP–H5 and AVLP–M1H5 generated robust antibody and cellular immune responses. Vaccination with a single dose of AVLP–H5 and M1H5 completely protected mice against lethal H5N1 challenge, suggesting that the AVLP-based system is a promising platform for delivery of desirable genes.

An ‘imitation virus’ can be used to deliver genetic material to target cells, with farreaching potential for medical application. The capacity to safely and affordably introduce genes into cells is highly-sought. A team led by the University of Georgia’s Biao He created a protein shell using parainfluenza virus 5 proteins, with the resultant particles possessing the ability to infect multiple types of cell and deliver desired genetic material. The team proved the utility of their system by using it to express immunity-promoting components of avian influenza virus in live mice—successfully vaccinating the animals, and enabling them to survive a subsequent lethal infection. His group also showed that their system is also able to deliver and express genes in human cells, prompting further research into this useful tool.

Induction of Antiviral Immune Response through Recognition of the Repeating Subunit Pattern of Viral Capsids Is Toll-Like Receptor 2 Dependent

Although viruses and viral capsids induce rapid immune responses, little is known about viral pathogen-associated molecular patterns (PAMPs) that are exhibited on their surface. Here, we demonstrate that the repeating protein subunit pattern common to most virus capsids is a molecular pattern that induces a Toll-like-receptor-2 (TLR2)-dependent antiviral immune response. This early antiviral immune response regulates the clearance of subsequent bacterial superinfections, which are a primary cause of morbidities associated with influenza virus infections. Utilizing this altered susceptibility to subsequent bacterial challenge as an outcome, we determined that multiple unrelated, empty, and replication-deficient capsids initiated early TLR2-dependent immune responses, similar to intact influenza virus or murine pneumovirus. These TLR2-mediated responses driven by the capsid were not dependent upon the capsid's shape, size, origin, or amino acid sequence. However, they were dependent upon the multisubunit arrangement of the capsid proteins, because unlike intact capsids, individual capsid subunits did not enhance bacterial clearance. Further, we demonstrated that even a linear microfilament protein built from repeating protein subunits (F-actin), but not its monomer (G-actin), induced similar kinetics of subsequent bacterial clearance as did virus capsid. However, although capsids and F-actin induced similar bacterial clearance, in macrophages they required distinct TLR2 heterodimers for this response (TLR2/6 or TLR2/1, respectively) and different phagocyte populations were involved in the execution of these responses in vivo Our results demonstrate that TLR2 responds to invading viral particles that are composed of repeating protein subunits, indicating that this common architecture of virus capsids is a previously unrecognized molecular pattern.IMPORTANCE Rapid and precise pathogen identification is critical for the initiation of pathogen-specific immune responses and pathogen clearance. Bacteria and fungi express common molecular patterns on their exteriors that are recognized by cell surface-expressed host pattern recognition receptors (PRRs) prior to infection. In contrast, viral molecular patterns are primarily nucleic acids, which are recognized after virus internalization. We found that an initial antiviral immune response is induced by the repeating subunit pattern of virus exteriors (capsids), and thus, induction of this response is independent of viral infection. This early response to viral capsids required the cell surface-expressed PRR TLR2 and allowed for improved clearance of subsequent bacterial infection that commonly complicates respiratory viral infections. Since the repeating protein subunit pattern is conserved across viral capsids, this suggests that it is not easy for a virus to change without altering fitness. Targeting this vulnerability could lead to development of a universal antiviral vaccine.

Production of virus-like particles for vaccines

Virus-like particles (VLPs) are nanostructures that resemble the structures of viruses. They are composed of one or more structural proteins that can be arranged in several layers and can also contain a lipid outer envelope. VLPs trigger a high humoral and cellular immune response due to their repetitive structures. A key factor regarding VLP safety is the lack of viral genomic material, which enhances safety during both manufacture and administration. Contemporary VLP production may take advantage of several systems, including bacterial, yeast, insect and mammalian cells. The choice of production platform depends on several factors, including cost and the need for post-translational modifications (PTMs), which can be essential in generating an optimal immune response. Some VLP-based vaccines designed to prevent several infectious diseases are already approved and on the market, with many others at the clinical trial or research stage. Interest in this technology has recently increased due to its advantages over classical vaccines. This paper reviews the state-of-the-art of VLP production systems and the newest generation of VLP-based vaccines now available.

Killed whole-HIV vaccine; employing a well established strategy for antiviral vaccines

The development of an efficient prophylactic HIV vaccine has been one of the major challenges in infectious disease research during the last three decades. Here, we present a mini review on strategies employed for the development of HIV vaccines with an emphasis on a well-established vaccine technology, the killed whole-virus vaccine approach. Recently, we reported an evaluation of the safety and the immunogenicity of a genetically modified and killed whole-HIV-1 vaccine designated as SAV001 [1]. HIV-1 Clade B NL4-3 was genetically modified by deleting the nef and vpu genes and substituting the coding sequence of the Env signal peptide with that of honeybee melittin to produce an avirulent and replication efficient HIV-1. This genetically modified virus (gmHIV-1 NL4-3 ) was propagated in a human T cell line followed by virus purification and inactivation by aldrithiol-2 and γ-irradiation. We found that SAV001 was well tolerated with no serious adverse events. HIV-1 NL4-3 -specific polymerase chain reaction showed no evidence of vaccine virus replication in participants receiving SAV001 and in human T cells infected in vitro. Furthermore, SAV001 with an adjuvant significantly increased the antibody response to HIV-1 structural proteins. Moreover, antibodies in the plasma from these vaccinations neutralized tier I and tier II of HIV-1 B, A, and D subtypes. These results indicated that the killed whole-HIV vaccine is safe and may trigger appropriate immune responses to prevent HIV infection. Utilization of this killed whole-HIV vaccine strategy may pave the way to develop an effective HIV vaccine.