Large-scale production and purification of VLP-based vaccines

Chromatography media and purification processes for complex and super-large biomolecules: A review

The biopharmaceutical industry has been one of the most dynamic industries in the world. New biopharmaceuticals are constantly developed, especially for complex and super-large biomolecules including antibodies, virus-like particles (VLPs), viral vectors, DNA, mRNA, and are very promising in drugs, vaccines, cell and gene therapy. Due to complex and unstable structures, as well as low concentration, it is very difficult to purify these complex and super-large biomolecules. Chromatography is the most widely used purification technique in bioseparation, and chromatography media is the key material. This review gives a comprehensive analysis of chromatography media and purification processes for complex and super-large biomolecules. A detailed summary of tailor-made chromatography media is first provided, including particle size and its uniformity, pore structure, spacer arm and polymer grafting, and new ligands and special separation mechanisms. Then the current choices and trends of purification processes for vaccines, VLPs, DNA, mRNA, antibodies and modified therapeutic proteins are reviewed. Finally, a brief overview of continuous biochromatography and computer-assisted chromatographic method development is provided. We hope this review will provide some useful guidance for design of chromatography media and purification of complex biopharmaceuticals.

Recent Advances in Antiviral Drug Delivery Strategies

Viral infectious diseases have long posed significant challenges to public health, leading to substantial morbidity and mortality worldwide. Recent outbreaks, including those caused by coronaviruses, have highlighted the urgent need for more effective antiviral treatments. Existing therapies, while numerous, face limitations such as drug resistance, toxicity, poor bioavailability, and non-specific targeting, which hinder their effectiveness against new and emerging viruses. This review focuses on the latest advances in nanoplatform technologies designed to enhance drug solubility, provide sustained or targeted delivery, and improve the efficacy of antiviral therapies. Additionally, we explore how these technologies can be integrated with novel strategies like genetic modulation to combat viral infections more effectively. The review also discusses the potential of these innovations in addressing the challenges posed by current antiviral therapies and their implications for future clinical applications.

Self-assembling of coiled-coil peptides into virus-like particles: Basic principles, properties, design, and applications with special focus on vaccine design and delivery

Self-assembling peptide nanoparticles (SAPN) based delivery systems, including virus-like particles (VLP), have shown great potential for becoming prominent in next-generation vaccine and drug development. The VLP can mimic properties of natural viral capsid in terms of size (20-200 nm), geometry (i.e., icosahedral structures), and the ability to generate a robust immune response (with multivalent epitopes) through activation of innate and/or adaptive immune signals. In this regard, coiled-coil (CC) domains are suitable building blocks for designing VLP because of their programmable interaction specificity, affinity, and well-established sequence-to-structure relationships. Generally, two CC domains with different oligomeric states (trimer and pentamer) are fused to form a monomeric protein through a short, flexible spacer sequence. By using combinations of symmetry axes (2-, 3- and 5- folds) that are unique to the geometry of the desired protein cage, it is possible, in principle, to assemble well-defined protein cages like VLP. In this review, we have discussed the crystallographic rules and the basic principles involved in the design of CC-based VLP. It also explored the functions of numerous noncovalent interactions in generating stable VLP structures, which play a crucial role in improving the properties of vaccine immunogenicity, drug delivery, and 3D cell culturing.

Influenza Neuraminidase Virus-Like Particle-Based Nanocarriers as a New Platform for the Delivery of Small-Peptide Antigens

A new and simple platform to produce a nanocarrier for small-peptide antigen delivery was developed. Virus-like particles (VLPs) were of interest due to their good cell-penetrating properties and ability to protect target molecules from degradation. In this study, the VLP that was entirely formed by influenza neuraminidase (NA), NA-VLPs, was employed. The platform construction includes the genetic engineering of target peptides into the NA structure immediately above its stalk, at the bottom of the NA head, by an overlap extension PCR. The resulting chimeric gene is next expressed in stably transformed insect cells. The recombinant NA protein produced by the insect cells is then naturally assembled into the NA-VLPs that display those peptides on their surfaces. For the platform demonstration, Angiotensin II (AngII) octapeptide hormones that raise blood pressure were chosen as a model peptide antigen. The NA-VLPs displaying AngII peptides were successfully produced by the stably transformed insect cells. The AngII octapeptides were successfully delivered by the NA-AngII VLPs as the anti-AngII antibodies were raised in hypertensive rats. The antibodies effectively neutralized the AngII peptide hormone in these rats, as demonstrated by the decrease in systolic blood pressure of the immunized rats. Thus, NA-VLP nanocarriers represent a promising platform for delivering small-peptide antigens to stimulate antibody production.

Critical parameters on Zika virus-like particles' generation

The Zika virus became a global threat in 2015 due to its association with microcephaly. Preventing its spread depends on developing vaccines, with virus-like particles (VLP) being a promising approach, especially because of their safety profile and high immunogenicity. This study focused on the production of Zika VLP using Sf9 cells and the baculovirus expression system, evaluating cell growth kinetics, nutrient consumption, and metabolite production in Sf-900™ III medium. As a methodology, this study includes bioreactor experiments, cell density and viability quantification, nutrient and metabolite analysis, Dot Blot, Western Blot, and transmission electron microscopy. Among the critical conditions tested are culture medium supplementation with 0.028 mM cholesterol/ 6 nM bovine serum albumin, multiplicity of infection (MOI= 0.2 or 2), and dissolved oxygen tension (DOT= 5 or 30 % air saturation). As a result, in the growth phase, Sf9 cells achieved rapid exponential growth, with doubling times ranging from 22.8 to 35.4 hours and standard nutrient consumption and metabolite generation profiles for this cell line. The infection phase recorded cell death rates between 8200 and 12600 cells mL⁻¹ h⁻¹ , with higher VLP production under low MOI (0.2) and low DOT (5 %). These conditions also reduced protein degradation and nutrient consumption. The produced VLP ranged from 32 to 73 nm in size, with smaller sizes observed under low MOI conditions. Finally, controlling the DOT at 5 % air saturation without cholesterol/albumin supplementation increased VLP production without the need to raise the viral load, highlighting the importance of choosing the appropriate combination of critical parameters (MOI, DOT, and medium supplementation) as key factors in optimizing the upstream process. This finding impacts substantially upstream stage efficiency and economy, which could be useful for future scaling up to the commercial manufacturing scale.

Development of Methods to Produce SARS CoV-2 Virus-Like Particles at Scale

The devastating global toll precipitated by the SARS CoV-2 outbreak and the profound impact of vaccines in stemming that outbreak has established the need for molecular platforms capable of rapidly delivering effective, safe and accessible medical interventions in pandemic preparedness. We describe a simple, efficient and adaptable process to produce SARS CoV-2 virus-like particles (VLPs) that can be readily scaled for manufacturing. A rapid but gentle method of tangential flow filtration using a 100 kDa semi-permeable membrane concentrates and buffer exchanges 0.5 L of SARS CoV-2 VLP containing supernatant into low salt and optimal pH for anion exchange chromatography. VLPs are washed, eluted under high salt, dialyzed into physiological buffer, sterile filtered and aliquoted for storage at -80°C. Purification is completed in less than 2 days. A simple quality control process includes Western blot for coincident detection of Spike, Membrane and Envelope protein as a proxy for intact VLP, ELISA to detect conformationally sensitive Spike using readily available anti-Spike and/or anti-RBD antibodies, and negative stain and immunogold electron microscopy to validate particulate, Spike crowned VLPs. This process to produce SARS CoV-2 VLPs for preclinical studies serves as a roadmap for preparation of more distantly related VLPs for pandemic preparedness.

Chemometrics and analytical blank on the at-line monitoring of Zika-VLP production using near-infrared spectroscopy

The Zika disease caused by the Zika virus was declared a Public Health Emergency by the World Health Union (WHO), with microcephaly as the most critical consequence. Aiming to reduce the spread of the virus, biopharmaceutical organizations invest in vaccine research and production, based on multiple platforms. A crescent vaccine production approach is based on virus-like particles (VLP), for not having genetic material in its composition, hypoallergenic and non-mutant character. For bioprocess, it is essential to have means of real-time monitoring, which can be assessed using process analysis techniques such as Near-infrared (NIR) spectroscopy, that can be combined with chemometric methods, like Partial-Least Squares (PLS) and Artificial Neural Networks (ANN) for prediction of biochemical variables. This work proposes a biochemical Zika VLP upstream production at-line monitoring model using NIR spectroscopy comparing sampling conditions (with or without cells), analytical blank (air, ultrapure water), and spectra pre-processing approaches. Seven experiments in a benchtop bioreactor using recombinant baculovirus/Sf9 insect cell platform in serum-free medium were performed to obtain biochemical and spectral data for chemometrics modeling (PLS and ANN), composed by a random data split (80 % calibration, 20 % validation) for cross-validation of the PLS models and 70 % training, 15 % testing, 15 % validation for ANN. The best models generated in the present work presented an average absolute error of 1.59 × 105 cell/mL for density of viable cells, 2.37 % for cell viability, 0.25 g/L for glucose, 0.007 g/L for lactate, 0.138 g/L for glutamine, 0.18 g/L for glutamate, 0,003 g/L for ammonium, and 0.014 g/L for potassium.

Dimming the corona: studying SARS-coronavirus-2 at reduced biocontainment level using replicons and virus-like particles

The coronavirus-induced disease 19 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections, has had a devastating impact on millions of lives globally, with severe mortality rates and catastrophic social implications. Developing tools for effective vaccine strategies and platforms is essential for controlling and preventing the recurrence of such pandemics. Moreover, molecular virology tools that facilitate the study of viral pathogens, impact of viral mutations, and interactions with various host proteins are essential. Viral replicon- and virus-like particle (VLP)-based systems are excellent examples of such tools. This review outlines the importance, advantages, and disadvantages of both the replicon- and VLP-based systems that have been developed for SARS-CoV-2 and have helped the scientific community in dimming the intensity of the COVID-19 pandemic.

SARS-CoV-2 spike-based virus-like particles incorporate influenza H1/N1 antigens and induce dual immunity in mice

A vaccine effective against both SARS-CoV-2 and influenza A (IAV) viruses could represent a cost-effective strategy to reduce their combined public health burden as well as potential complications arising from co-infection. Based on previous findings that full-length SARS-CoV-2 spike (S) expression can induce high-level, enveloped VLP (eVLP) production in CHO cells, we tested whether IAV H1N1 hemagglutinin (H1) and neuraminidase (N1) could also be displayed on these particles. We found that co-incorporation of the IAV surface antigens in spike VLPs (S-VLPs) was highly efficient: upon transient co-expression of S + H1 or S + H1 + N1 in CHO cells, the resulting VLPs contained similar amounts of the SARS-CoV-2 S and IAV antigens. The self-assembled bivalent (S/H1) and trivalent (S/H1/N1) VLPs released into the culture media were purified by single-step chromatography using a S-VLP affinity resin. Western blot analysis and immuno‑gold labeling transmission electron microscopy (TEM) of purified VLPs confirmed the coexistence of S, H1 and N1 antigens in the same particles. Finally, we demonstrated that two doses of adjuvanted bivalent and trivalent VLPs elicit specific functional antibodies and cellular immunity in a mouse model, suggesting potential for combined SARS-CoV-2/IAV vaccine development.

Experimental and molecular dynamics simulation studies on the physical properties of three HBc-VLP derivatives as nanoparticle protein vaccine candidates

Self-assembling virus-like particles (VLPs) are promising platforms for vaccine development. However, the unpredictability of the physical properties, such as self-assembly capability, hydrophobicity, and overall stability in engineered protein particles fused with antigens, presents substantial challenges in their downstream processing. We envision that these challenges can be addressed by combining more precise computer-aided molecular dynamics (MD) simulations with experimental studies on the modified products, with more to-date forcefield descriptions and larger models closely resembling real assemblies, realized by rapid advancement in computing technology. In this study, three chimeric designs based on the hepatitis B core (HBc) protein as model vaccine candidates were constructed to study and compare the influence of inserted epitopes as well as insertion strategy on HBc modifications. Large partial VLP models containing 17 chains for the HBc chimeric model vaccines were constructed based on the wild-type (wt) HBc assembly template. The findings from our simulation analysis have demonstrated good consistency with experimental results, pertaining to the surface hydrophobicity and overall stability of the chimeric vaccine candidates. Furthermore, the different impact of foreign antigen insertions on the HBc scaffold was investigated through simulations. It was found that separately inserting two epitopes into the HBc platform at the N-terminal and the major immunogenic regions (MIR) yields better results compared to a serial insertion at MIR in terms of protein structural stability. This study substantiates that an MD-guided design approach can facilitate vaccine development and improve its manufacturing efficiency by predicting products with extreme surface hydrophobicity or structural instability.

Virus-like particles in poultry disease: an approach to effective and safe vaccination

The poultry industry, a cornerstone of global food security, faces dynamic challenges exacerbated by viral diseases. This review traces the trajectory of poultry vaccination, evolving from traditional methods to the forefront of innovation Virus-Like Particle (VLP) vaccines. Vaccination has been pivotal in disease control, but traditional vaccines exhibit some limitations. This review examines the emergence of VLPs as a game-changer in poultry vaccination. VLPs, mimicking viruses without replication, offer a safer, targeted alternative with enhanced immunogenicity. The narrative encompasses VLP design principles, production methods, immunogenicity, and efficacy against major poultry viruses. Challenges and prospects are explored, presenting VLP vaccines as a transformative technique in poultry disease control. Understanding their potential empowers industry stakeholders to navigate poultry health management with precision, promising improved welfare, reduced economic losses, and heightened food safety.

Advancements in Functional Nanomaterials Inspired by Viral Particles

Virus-like particles (VLPs) are nanostructures composed of one or more structural proteins, exhibiting stable and symmetrical structures. Their precise compositions and dimensions provide versatile opportunities for modifications, enhancing their functionality. Consequently, VLP-based nanomaterials have gained widespread adoption across diverse domains. This review focuses on three key aspects: the mechanisms of viral capsid protein self-assembly into VLPs, design methods for constructing multifunctional VLPs, and strategies for synthesizing multidimensional nanomaterials using VLPs. It provides a comprehensive overview of the advancements in virus-inspired functional nanomaterials, encompassing VLP assembly, functionalization, and the synthesis of multidimensional nanomaterials. Additionally, this review explores future directions, opportunities, and challenges in the field of VLP-based nanomaterials, aiming to shed light on potential advancements and prospects in this exciting area of research.

Virus-like Particles as Vaccines for Allergen-Specific Therapy: An Overview of Current Developments

Immune engineering and modulation are the basis of a novel but powerful tool to treat immune diseases using virus-like particles (VLPs). VLPs are formed by the viral capsid without genetic material making them non-infective. However, they offer a wide variety of possibilities as antigen-presenting platforms, resulting in high immunogenicity and high efficacy in immune modulation, with low allergenicity. Both animal and plant viruses are being studied for use in the treatment of food allergies. These formulations are combined with adjuvants, T-stimulatory epitopes, TLR ligands, and other immune modulators to modulate or enhance the immune response toward the presented allergen. Here, the authors present an overview of VLP production systems, their immune modulation capabilities, and the applicability of actual VLP-based formulations targeting allergic diseases.

Cross-protection against influenza viruses by chimeric M2e-H3 stalk protein or multi-subtype neuraminidase plus M2e virus-like particle vaccine in ferrets

Current influenza vaccine is not effective in providing cross-protection against variants. We evaluated the immunogenicity and efficacy of multi-subtype neuraminidase (NA) and M2 ectodomain virus-like particle (m-cNA-M2e VLP) and chimeric M2e-H3 stalk protein vaccines (M2e-H3 stalk) in ferrets. Our results showed that ferrets with recombinant m-cNA-M2e VLP or M2e-H3 stalk vaccination induced multi-vaccine antigen specific IgG antibodies (M2e, H3 stalk, NA), NA inhibition, antibody-secreting cells, and IFN-γ secreting cell responses. Ferrets immunized with either m-cNA-M2e VLP or M2e-H3 stalk vaccine were protected from H1N1 and H3N2 influenza viruses by lowering viral titers in nasal washes, trachea, and lungs after challenge. Vaccinated ferret antisera conferred broad humoral immunity in naïve mice. Our findings provide evidence that immunity to M2e and HA-stalk or M2e plus multi-subtype NA proteins induces cross-protection in ferrets.

Production of norovirus-, rotavirus-, and enterovirus-like particles in insect cells is simplified by plasmid-based expression

Insect cells have long been the main expression host of many virus-like particles (VLP). VLPs resemble the respective viruses but are non-infectious. They are important in vaccine development and serve as safe model systems in virus research. Commonly, baculovirus expression vector system (BEVS) is used for VLP production. Here, we present an alternative, plasmid-based system for VLP expression, which offers distinct advantages: in contrast to BEVS, it avoids contamination by baculoviral particles and proteins, can maintain cell viability over the whole process, production of alphanodaviral particles will not be induced, and optimization of expression vectors and their ratios is simple. We compared the production of noro-, rota- and entero-VLP in the plasmid-based system to the standard process in BEVS. For noro- and entero-VLPs, similar yields could be achieved, whereas production of rota-VLP requires some further optimization. Nevertheless, in all cases, particles were formed, the expression process was simplified compared to BEVS and potential for the plasmid-based system was validated. This study demonstrates that plasmid-based transfection offers a viable option for production of noro-, rota- and entero-VLPs in insect cells.

Advances in virus-like particle-based SARS-CoV-2 vaccines

The Coronavirus Disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has incurred devastating human and economic losses. Vaccination remains the most effective approach for controlling the COVID-19 pandemic. Nonetheless, the sustained evolution of SARS-CoV-2 variants has provoked concerns among the scientific community regarding the development of next-generation COVID-19 vaccines. Among these, given their safety, immunogenicity, and flexibility to display varied and native epitopes, virus-like particle (VLP)-based vaccines represent one of the most promising next-generation vaccines. In this review, we summarize the advantages and characteristics of VLP platforms, strategies for antigen display, and current clinical trial progress of SARS-CoV-2 vaccines based on VLP platforms. Importantly, the experience and lessons learned from the development of SARS-CoV-2 VLP vaccines provide insights into the development of strategies based on VLP vaccines to prevent future coronavirus pandemics and other epidemics.

Tailored Viral-like Particles as Drivers of Medical Breakthroughs

Despite the recognized potential of nanoparticles, only a few formulations have progressed to clinical trials, and an even smaller number have been approved by the regulatory authorities and marketed. Virus-like particles (VLPs) have emerged as promising alternatives to conventional nanoparticles due to their safety, biocompatibility, immunogenicity, structural stability, scalability, and versatility. Furthermore, VLPs can be surface-functionalized with small molecules to improve circulation half-life and target specificity. Through the functionalization and coating of VLPs, it is possible to optimize the response properties to a given stimulus, such as heat, pH, an alternating magnetic field, or even enzymes. Surface functionalization can also modulate other properties, such as biocompatibility, stability, and specificity, deeming VLPs as potential vaccine candidates or delivery systems. This review aims to address the different types of surface functionalization of VLPs, highlighting the more recent cutting-edge technologies that have been explored for the design of tailored VLPs, their importance, and their consequent applicability in the medical field.

Efficient Production of Enterovirus 71 (EV71) Virus-like Particles by Controlling Promoter Strength in Insect Cells

This study was conducted to efficiently produce virus-like particles (VLPs) of enterovirus 71 (EV71), a causative virus of hand, foot, and mouth disease (HFMD). The expression level of the P1 precursor, a structural protein of EV71, was modified to increase VLP production, and the optimal expression level and duration of the 3CD protein for P1 cleavage were determined. The expression level and duration of 3CD were controlled by the p10 promoter, which was weakened by repeated burst sequence (BS) applications, as well as the OpIE2 promoter, which was weakened by the insertion of random untranslated region sequences of various lengths. The cleavage and production efficiency of the P1 precursor were compared based on the expression time and level of 3CD, revealing that the p10-BS5 promoter with four repeated BSs was the most effective. When P1 and 3CD were expressed using the hyperexpression vector and the p10-BS5 promoter, high levels of structural protein production and normal HFMD-VLP formation were observed, respectively. This study suggests that the production efficiency of HFMD-VLPs can be significantly enhanced by increasing the expression of the P1 precursor and controlling the amount and duration of 3CD expression.

CHO cells for virus-like particle and subunit vaccine manufacturing

Chinese Hamster Ovary (CHO) cells, employed primarily for manufacturing monoclonal antibodies and other recombinant protein (r-protein) therapeutics, are emerging as a promising host for vaccine antigen production. This is exemplified by the recently approved CHO cell-derived subunit vaccines (SUV) against respiratory syncytial virus (RSV) and varicella-zoster virus (VZV), as well as the enveloped virus-like particle (eVLP) vaccine against hepatitis B virus (HBV). Here, we summarize the design, production, and immunogenicity features of these vaccine and review the most recent progress of other CHO-derived vaccines in pre-clinical and clinical development. We also discuss the challenges associated with vaccine production in CHO cells, with a focus on ensuring viral clearance for eVLP products.

In situ bio-mineralized Mn nanoadjuvant enhances anti-influenza immunity of recombinant virus-like particle vaccines

Virus like particles (VLPs) have been well recognized as one of the most important vaccine platforms due to their structural similarity to natural viruses to induce effective humoral and cellular immune responses. Nevertheless, lack of viral nucleic acids in VLPs usually leads the vaccine candidates less efficient in provoking innate immune against viral infection. Here, we constructed a biomimetic dual antigen hybrid influenza nanovaccines THM-HA@Mn with robust immunogenicity via in situ synthesizing a stimulator of interferon genes (STING) agonist Mn3O4 inside the cavity of a recombinant Hepatitis B core antigen VLP (HBc VLP) having fused SpyTag and influenza M2e antigen peptides (Tag-HBc-M2e, THM for short), followed by conjugating a recombinant hemagglutinin (rHA) antigen on the surface of the nanoparticles through SpyTag/SpyCatcher ligating. Such inside Mn3O4 immunostimulator-outside rHA antigen design, together with the chimeric M2e antigen on the HBc skeleton, enabled the synthesized hybrid nanovaccines THM-HA@Mn to well imitate the spatial distribution of M2e/HA antigens and immunostimulant in natural influenza virus. In vitro cellular experiments indicated that compared with the THM-HA antigen without Mn3O4 and a mixture vaccine consisting of THM-HA + MnOx, the THM-HA@Mn hybrid nanovaccines showed the highest efficacies in dendritic cells uptake and in promoting BMDC maturation, as well as inducing expression of TNF-α and type I interferon IFN-β. The THM-HA@Mn also displayed the most sustained antigen release at the injection site, the highest efficacies in promoting the DC maturation in lymph nodes and germinal center B cells activation in the spleen of the immunized mice. The co-delivery of immunostimulant and antigens enabled the THM-HA@Mn nanovaccines to induce the highest systemic antigen-specific antibody responses and cellular immunogenicity in mice. Together with the excellent colloid dispersion stability, low cytotoxicity, as well as good biosafety, the synthetic hybrid nanovaccines presented in this study offers a promising strategy to design VLP-based vaccine with robust natural and adaptive immunogenicity against emerging viral pathogens.

Effects of ultra-filtration purification of infectious bursal disease virus on immune responses and cytokine activation in specific pathogen free chickens

Purification is an important step in the production of viral vaccines that strongly affects product recovery and subsequent immune responses. The present study was carried out with the aim of improving the purification of infectious bursal disease virus (IBDV) by the tangential flow filtration (TFF) method. Then, the effect of the purified virus on the induction of immune responses against IBDV in specific pathogen free (SPF) chickens was investigated. The IBD07IR strain was propagated in embryonated SPF eggs. The virus was purified using a 100 kDa cassette. The quality of the recovered viruses was evaluated by titration. A total number of 60 SPF chickens were randomly divided into three groups (n = 20) and received the concentrated viral antigen, commercial live IBDV vaccine and phosphate-buffered saline at the age of 3 weeks by eye drop method. The bursa of Fabricius was examined histopathologically for possible changes. Sera were collected at 1-week intervals from day 0 until the end of 6 weeks after vaccination. The IBDV-specific antibody levels, induction of cell-mediated immunity and mRNA expression levels of cytokines were evaluated. The results showed that despite a relative raise in virus titer from 7.66 to 8.17 embryo infectious dose (EID)50 mL-1 following purification, both the purified IBDV and commercial vaccine are able to induce strong immune responses against the virus. Within a context of egg-based IBDV vaccine production, a single-step TFF can be applied for the relatively purification. This platform requires a further study in the selection of multiple membranes to optimize the operating conditions and final product.

Purification and Quality Control of Recombinant Proteins Expressed in Mammalian Cells: A Practical Review

In the recent years, there has been a rapid development of new technologies and strategies when it comes to protein purification and quality control (QC), but the basic technologies for these processes go back a long way, with many improvements over the past few decades. The purpose of this chapter is to review these approaches, as well as some other topics such as the advantages and disadvantages of various purification methods for intracellular or extracellular proteins, the most effective and widely used genetically engineered affinity tags, solubility-enhancing tags, and specific proteases for removal of nontarget sequences. Affinity chromatography (AC), like Protein A or G resins for the recovery of antibodies or Fc fusion proteins or immobilized metals for the recovery of histidine-tagged proteins, will be discussed along with other conventional chromatography techniques: ion exchange (IEC), hydrophobic exchange (HEC), mixed mode (MMC), size exclusion (SEC), and ultrafiltration (UF) systems. How to select and combine these different technologies for the purification of any given protein and the minimal criteria for QC characterization of the purity, homogeneity, identity, and integrity of the final product will be presented.

Virus-like particles as powerful vaccination strategy against human viruses

Nowadays, viruses are not only seen as causative agents of viral infectious diseases but also as valuable research materials for various biomedical purposes, including recombinant protein production. When expressed in living or cell-free expression systems, viral structural proteins self-assemble into virus-like particles (VLPs). Mimicking the native form and size of viruses and lacking the genetic material, VLPs are safe and highly immunogenic and thus can be exploited to develop antiviral vaccines. Some vaccines based on VLPs against various infectious pathogens have already been licenced for human use and are available in the commercial market, the latest of which is a VLP-based vaccine to protect against the novel Coronavirus. Despite the success and popularity of VLP subunit vaccines, many more VLPs are still in different stages of design, production, and approval. There are still many challenges that require to be addressed in the future before this surface display system can be widely used as an effective vaccine strategy in combating infectious diseases. In this review, we highlight the use of structural viral proteins to produce VLPs, emphasising their intrinsic properties, structural classification, and main expression host systems. We also compiled the recent scientific literature about VLP-based vaccines to underline the recent advances in their application as a vaccine strategy for preventing and fighting virulent human pathogens. Finally, we presented the key challenges and possible solutions for VLP-based vaccine production.

Pseudotyping Improves the Yield of Functional SARS-CoV-2 Virus-like Particles (VLPs) as Tools for Vaccine and Therapeutic Development

Virus-like particles (VLPs) have been proposed as an attractive tool in SARS-CoV-2 vaccine development, both as (1) a vaccine candidate with high immunogenicity and low reactogenicity and (2) a substitute for live virus in functional and neutralization assays. Though multiple SARS-CoV-2 VLP designs have already been explored in Sf9 insect cells, a key parameter ensuring VLPs are a viable platform is the VLP spike yield (i.e., spike protein content in VLP), which has largely been unreported. In this study, we show that the common strategy of producing SARS-CoV-2 VLPs by expressing spike protein in combination with the native coronavirus membrane and/or envelope protein forms VLPs, but at a critically low spike yield (~0.04-0.08 mg/L). In contrast, fusing the spike ectodomain to the influenza HA transmembrane domain and cytoplasmic tail and co-expressing M1 increased VLP spike yield to ~0.4 mg/L. More importantly, this increased yield translated to a greater VLP spike antigen density (~96 spike monomers/VLP) that more closely resembles that of native SARS-CoV-2 virus (~72-144 Spike monomers/virion). Pseudotyping further allowed for production of functional alpha (B.1.1.7), beta (B.1.351), delta (B.1.617.2), and omicron (B.1.1.529) SARS-CoV-2 VLPs that bound to the target ACE2 receptor. Finally, we demonstrated the utility of pseudotyped VLPs to test neutralizing antibody activity using a simple, acellular ELISA-based assay performed at biosafety level 1 (BSL-1). Taken together, this study highlights the advantage of pseudotyping over native SARS-CoV-2 VLP designs in achieving higher VLP spike yield and demonstrates the usefulness of pseudotyped VLPs as a surrogate for live virus in vaccine and therapeutic development against SARS-CoV-2 variants.

An Overview of Recent Developments in the Application of Antigen Displaying Vaccine Platforms: Hints for Future SARS-CoV-2 VLP Vaccines

Recently, a great effort has been devoted to studying attenuated and subunit vaccine development against SARS-CoV-2 since its outbreak in December 2019. It is known that diverse virus-like particles (VLPs) are extensively employed as carriers to display various antigenic and immunostimulatory cargo modules for vaccine development. Single or multiple antigens or antigenic domains such as the spike or nucleocapsid protein or their variants from SARS-CoV-2 could also be incorporated into VLPs via either a genetic or chemical display approach. Such antigen display platforms would help screen safer and more effective vaccine candidates capable of generating a strong immune response with or without adjuvant. This review aims to provide valuable insights for the future development of SARS-CoV-2 VLP vaccines by summarizing the latest updates and perspectives on the vaccine development of VLP platforms for genetic and chemical displaying antigens from SARS-CoV-2.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

Downstream process design for Gag HIV-1 based virus-like particles

Virus-like particles-based vaccines have been gaining interest in recent years. The manufacturing of these particles includes their production by cell culture followed by their purification to meet the requirements of its final use. The presence of host cell extracellular vesicles represents a challenge for better virus-like particles purification, because both share similar characteristics which hinders their separation. The present study aims to compare some of the most used downstream processing technologies for capture and purification of virus-like particles. Four steps of the purification process were studied, including a clarification step by depth filtration and filtration, an intermediate step by tangential flow filtration or multimodal chromatography, a capture step by ion exchange, heparin affinity and hydrophobic interaction chromatography and finally, a polishing step by size exclusion chromatography. In each step, the yields were evaluated by percentage of recovery of the particles of interest, purity, and elimination of main contaminants. Finally, a complete purification train was implemented using the best results obtained in each step. A final concentration of 1.40 × 1010 virus-like particles (VLPs)/mL with a purity of 64% after the polishing step was achieved, with host cell DNA and protein levels complaining with regulatory standards, and an overall recovery of 38%. This work has resulted in the development of a purification process for HIV-1 Gag-eGFP virus-like particles suitable for scale-up.

Enhancing Anti-SARS-CoV-2 Neutralizing Immunity by Genetic Delivery of Enveloped Virus-like Particles Displaying SARS-CoV-2 Spikes

New vaccine delivery technologies, such as mRNA, have played a critical role in the rapid and efficient control of SARS-CoV-2, helping to end the COVID-19 pandemic. Enveloped virus-like particles (eVLPs) are often more immunogenic than protein subunit immunogens and could be an effective vaccine platform. Here, we investigated whether the genetic delivery of eVLPs could achieve strong immune responses in mice as previously reported with the immunization of in vitro purified eVLPs. We utilized Newcastle disease virus-like particles (NDVLPs) to display SARS-CoV-2 prefusion-stabilized spikes from the WA-1 or Beta variant (S-2P or S-2Pᵦ, respectively) and evaluated neutralizing murine immune responses achieved by a single-gene-transcript DNA construct for the WA-1 or Beta variant (which we named S-2P-NDVLP-1T and S-2Pᵦ-NDVLP-1T, respectively), by multiple-gene-transcript DNA constructs for the Beta variant (S-2Pᵦ-NDVLP-3T), and by a protein subunit-DNA construct for the WA-1 or Beta variant (S-2P-TM or S-2Pᵦ-TM, respectively). The genetic delivery of S-2P-NDVLP-1T or S-2Pᵦ-NDVLP-1T yielded modest neutralizing responses after a single immunization and high neutralizing responses after a second immunization, comparable to previously reported results in mice immunized with in vitro purified S-2P-NDVLPs. Notably, genetic delivery of S-2Pᵦ-NDVLP-3T yielded significantly higher neutralizing responses in mice after a second immunization than S-2Pᵦ-NDVLP-1T or S-2Pᵦ-TM. Genetic delivery also elicited high spike-specific T-cell responses. Collectively, these results indicate that genetic delivery can provide an effective means to immunize eVLPs and that a multiple-gene transcript eVLP platform may be especially efficacious and inform the design of improved vaccines.

Rotavirus Particle Disassembly and Assembly In Vivo and In Vitro

Rotaviruses (RVs) are non-enveloped multilayered dsRNA viruses that are major etiologic agents of diarrheal disease in humans and in the young in a large number of animal species. The viral particle is composed of three different protein layers that enclose the segmented dsRNA genome and the transcriptional complexes. Each layer defines a unique subparticle that is associated with a different phase of the replication cycle. Thus, while single- and double-layered particles are associated with the intracellular processes of selective packaging, genome replication, and transcription, the viral machinery necessary for entry is located in the third layer. This modular nature of its particle allows rotaviruses to control its replication cycle by the disassembly and assembly of its structural proteins. In this review, we examine the significant advances in structural, molecular, and cellular RV biology that have contributed during the last few years to illuminating the intricate details of the RV particle disassembly and assembly processes.

Evaluation of an inducible knockout system in insect cells based on co-infection and CRISPR/Cas9

Due to comparably high product titers and low production costs, the baculovirus/insect cell expression system is considered a versatile production platform in the biopharmaceutical industry. Its excellence in producing complex multimeric protein assemblies, including virus-like particles (VLPs), which are considered promising vaccine candidates to counter emerging viral threats, made the system even more attractive. However, the co-formation of budded baculovirus during VLP production poses a severe challenge to downstream processing. In order to reduce the amount of budded baculovirus in the expression supernatant we developed an inducible knockout system based on CRISPR/Cas9 and co-infection with two baculoviral vectors: one bringing along the Cas9 nuclease and the other one having incorporated the sequence for sgRNA expression. With our set-up high titer viruses can be generated separately, as only when both viruses infect cells simultaneously a knockout can occur. When budding essential genes gp64 and vp80 were targeted for knockout, we measured a reduction in baculovirus titer by over 90%. However, as a consequence, we also determined lower overall eYFP fluorescence intensity showing reduced recombinant protein production, indicating that further improvements in engineering as well as purification are required in order to ultimately minimize costs and timeframes for vaccine production utilizing the baculovirus/insect cell expression system.

Perspective vaccines for emerging viral diseases in farm animals

The world has watched the emergence of numerous animal viruses that may threaten animal health which were added to the perpetual growing list of animal pathogens. This emergence drew the attention of the experts and animal health groups to the fact that it has become necessary to work on vaccine development. The current review aims to explore the perspective vaccines for emerging viral diseases in farm animals. This aim was fulfilled by focusing on modern technologies as well as next generation vaccines that have been introduced in the field of vaccines, either in clinical developments pending approval, or have already come to light and have been applied to animals with acceptable results such as viral-vectored vaccines, virus-like particles, and messenger RNA-based platforms. Besides, it shed the light on the importance of differentiation of infected from vaccinated animals technology in eradication programs of emerging viral diseases. The new science of nanomaterials was explored to elucidate its role in vaccinology. Finally, the role of Bioinformatics or Vaccinomics and its assist in vaccine designing and developments were discussed. The reviewing of the published manuscripts concluded that the use of conventional vaccines is considered an out-of-date approach in eliminating emerging diseases. However, these types of vaccines are considered the suitable plan especially in countries with few resources and capabilities. Piloted vaccines that rely on genetic-based technologies with continuous analyses of current viruses should be the aim of future vaccinology. Smart genomics of emerging viruses will be the gateway to choosing appropriate vaccines, regardless of the evolutionary rates of viruses.

Gene-encoded nanoparticle vaccine platforms for in vivo assembly of multimeric antigen to promote adaptive immunity

Nanoparticle vaccines are a diverse category of vaccines for the prophylaxis or treatment of various diseases. Several strategies have been employed for their optimization, especially to enhance vaccine immunogenicity and generate potent B-cell responses. Two major modalities utilized for particulate antigen vaccines include using nanoscale structures for antigen delivery and nanoparticles that are themselves vaccines due to antigen display or scaffolding-the latter of which we will define as "nanovaccines." Multimeric antigen display has a variety of immunological benefits compared to monomeric vaccines mediated through potentiating antigen-presenting cell presentation and enhancing antigen-specific B-cell responses through B-cell activation. The majority of nanovaccine assembly is done in vitro using cell lines. However, in vivo assembly of scaffolded vaccines potentiated using nucleic acids or viral vectors is a burgeoning modality of nanovaccine delivery. Several advantages to in vivo assembly exist, including lower costs of production, fewer production barriers, as well as more rapid development of novel vaccine candidates for emerging diseases such as SARS-CoV-2. This review will characterize the methods for de novo assembly of nanovaccines in the host using methods of gene delivery including nucleic acid and viral vectored vaccines. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Size-selective downstream processing of virus particles and non-enveloped virus-like particles

Non-enveloped virus-like particles (VLPs) are versatile protein nanoparticles with great potential for biopharmaceutical applications. However, conventional protein downstream processing (DSP) and platform processes are often not easily applicable due to the large size of VLPs and virus particles (VPs) in general. The application of size-selective separation techniques offers to exploit the size difference between VPs and common host-cell impurities. Moreover, size-selective separation techniques offer the potential for wide applicability across different VPs. In this work, basic principles and applications of size-selective separation techniques are reviewed to highlight their potential in DSP of VPs. Finally, specific DSP steps for non-enveloped VLPs and their subunits are reviewed as well as the potential applications and benefits of size-selective separation techniques are shown.

Chimeric Human Papillomavirus-16 Virus-like Particles Presenting HIV-1 P18I10 Peptide: Expression, Purification, Bio-Physical Properties and Immunogenicity in BALB/c Mice

Human papillomavirus (HPV) vaccines based on HPV L1 virus-like particles (VLPs) are already licensed but not accessible worldwide. About 38.0 million people were living with HIV in 2020 and there is no HIV vaccine yet. Therefore, safe, effective, and affordable vaccines against both viruses are an urgent need. In this study, the HIV-1 P18I10 CTL peptide from the V3 loop of HIV-1 gp120 glycoprotein was inserted into the HPV16 L1 protein to construct chimeric HPV:HIV (L1:P18I10) VLPs. Instead of the traditional baculovirus expression vector/insect cell (BEVS/IC) system, we established an alternative mammalian 293F cell-based expression system using cost-effective polyethylenimine-mediated transfection for L1:P18I10 protein production. Compared with conventional ultracentrifugation, we optimized a novel chromatographic purification method which could significantly increase L1:P18I10 VLP recovery (~56%). Chimeric L1:P18I10 VLPs purified from both methods were capable of self-assembling to integral particles and shared similar biophysical and morphological properties. After BALB/c mice immunization with 293F cell-derived and chromatography-purified L1:P18I10 VLPs, almost the same titer of anti-L1 IgG (p = 0.6409) was observed as Gardasil anti-HPV vaccine-immunized mice. Significant titers of anti-P18I10 binding antibodies (p < 0.01%) and P18I10-specific IFN-γ secreting splenocytes (p = 0.0002) were detected in L1:P18I10 VLP-immunized mice in comparison with licensed Gardasil-9 HPV vaccine. Furthermore, we demonstrated that insertion of HIV-1 P18I10 peptide into HPV16 L1 capsid protein did not affect the induction in anti-L1 antibodies. All in all, we expected that the mammalian cell expression system and chromatographic purification methods could be time-saving, cost-effective, scalable platforms to engineer bivalent VLP-based vaccines against HPV and HIV-1.

Clinical Delivery of Circular RNA: Lessons Learned from RNA Drug Development

Circular RNAs (circRNA) represent a distinct class of covalently closed-loop RNA molecules, which play diverse roles in regulating biological processes and disease states. The enhanced stability of synthetic circRNAs compared to their linear counterparts has recently garnered considerable research interest, paving the way for new therapeutic applications. While clinical circRNA technology is still in its early stages, significant advancements in mRNA technology offer valuable insights into its potential future applications. Two primary obstacles that must be addressed are the development of efficient production methods and the optimization of delivery systems. To expedite progress in this area, this review aims to provide an overview of the current state of knowledge on circRNA structure and function, outline recent techniques for synthesizing circRNAs, highlight key delivery strategies and applications, and discuss the current challenges and future prospects in the field of circRNA-based therapeutics.

COVID-19 in early 2023: Structure, replication mechanism, variants of SARS-CoV-2, diagnostic tests, and vaccine & drug development studies

Coronavirus Disease-19 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome-coronaviruses-2 (SARS-CoV-2), a highly pathogenic and transmissible coronavirus. Most cases of COVID-19 have mild to moderate symptoms, including cough, fever, myalgias, and headache. On the other hand, this coronavirus can lead to severe complications and death in some cases. Therefore, vaccination is the most effective tool to prevent and eradicate COVID-19 disease. Also, rapid and effective diagnostic tests are critical in identifying cases of COVID-19. The COVID-19 pandemic has a dynamic structure on the agenda and contains up-to-date developments. This article has comprehensively discussed the most up-to-date pandemic situation since it first appeared. For the first time, not only the structure, replication mechanism, and variants of SARS-CoV-2 (Alpha, Beta, Gamma, Omicron, Delta, Epsilon, Kappa, Mu, Eta, Zeta, Theta, lota, Lambda) but also all the details of the pandemic, such as how it came out, how it spread, current cases, what precautions should be taken, prevention strategies, the vaccines produced, the tests developed, and the drugs used are reviewed in every aspect. Herein, the comparison of diagnostic tests for SARS-CoV-2 in terms of procedure, accuracy, cost, and time has been presented. The mechanism, safety, efficacy, and effectiveness of COVID-19 vaccines against SARS-CoV-2 variants have been evaluated. Drug studies, therapeutic targets, various immunomodulators, and antiviral molecules applied to patients with COVID-19 have been reviewed.

Virus-like particle-based nanocarriers as an emerging platform for drug delivery

New nanocarrier technologies are emerging, and they have great potential for improving drug delivery, targeting efficiency, and bioavailability. Virus-like particles (VLPs) are natural nanoparticles from animal and plant viruses and bacteriophages. Hence, VLPs present several great advantages, such as morphological uniformity, biocompatibility, reduced toxicity, and easy functionalisation. VLPs can deliver many active ingredients to the target tissue and have great potential as a nanocarrier to overcome the limitations associated with other nanoparticles. This review will focus primarily on the construction and applications of VLPs, particularly as a novel nanocarrier to deliver active ingredients. Herein, the main methods for the construction, purification, and characterisation of VLPs, as well as various VLP-based materials used in delivery systems are summarised. The biological distribution of VLPs in drug delivery, phagocyte-mediated clearance, and toxicity are also discussed.

Biomanufacturing Recombinantly Expressed Cripto-1 Protein in Anchorage-Dependent Mammalian Cells Growing in Suspension Bioreactors within a Three-Dimensional Hydrogel Microcarrier

Biotherapeutic soluble proteins that are recombinantly expressed in mammalian cells can pose a challenge when biomanufacturing in three-dimensional (3D) suspension culture systems. Herein, we tested a 3D hydrogel microcarrier for a suspension culture of HEK293 cells overexpressing recombinant Cripto-1 protein. Cripto-1 is an extracellular protein that is involved in developmental processes and has recently been reported to have therapeutic effects in alleviating muscle injury and diseases by regulating muscle regeneration through satellite cell progression toward the myogenic lineage. Cripto-overexpressing HEK293 cell lines were cultured in microcarriers made from poly (ethylene glycol)-fibrinogen (PF) hydrogels, which provided the 3D substrate for cell growth and protein production in stirred bioreactors. The PF microcarriers were designed with sufficient strength to resist hydrodynamic deterioration and biodegradation associated with suspension culture in stirred bioreactors for up to 21 days. The yield of purified Cripto-1 obtained using the 3D PF microcarriers was significantly higher than that obtained with a two-dimensional (2D) culture system. The bioactivity of the 3D-produced Cripto-1 was equivalent to commercially available Cripto-1 in terms of an ELISA binding assay, a muscle cell proliferation assay, and a myogenic differentiation assay. Taken together, these data indicate that 3D microcarriers made from PF can be combined with mammalian cell expression systems to improve the biomanufacturing of protein-based therapeutics for muscle injuries.

A lef5-deficient baculovirus expression system with no virion contamination and promoting secretion

The baculovirus expression system (BEVS) is widely used in biomanufacturing. However, massive late and very late genes are expressed during baculovirus infection of the host cell, and the protein aggregation has a significant negative impact on the intercellular environment of cells and organelle function. Baculovirus particle contamination also hinders the purification of particulate products. In this study, a novel baculovirus vector of deficient-lef5 (Ac-Δlef5) was established to prevent the production of baculovirus particles. It could transduce cells and replicate viral DNA but the expression of the late and very late genes was reduced so that no virus was packed and budded. The Ac-Δlef5 expression system was successfully used to express a secreted protein, thyroid peroxidase (TPO). Compared to wild-type baculovirus (Ac-wt), Ac-Δlef5 delayed the decline in cell viability and prolonged the harvest period from 4 to 6 days after infection. When expressed in the Ac-Δlef5 system, 98% of TPO was secreted extracellularly, which was about 1.8 times that of the Ac-wt system. Meanwhile, the transcription levels of protein folding-related genes were significantly increased. The results show that the Ac-Δlef5 system is a potential novel viral-free baculovirus expression system, which omits the virion removal operation in biomanufacturing.

Biochemical monitoring throughout all stages of rabies virus-like particles production by Raman spectroscopy using global models

This work aimed to quantify growth and biochemical parameters (viable cell density, Xv; cell viability, CV; glucose, lactate, glutamine, glutamate, ammonium, and potassium concentrations) in upstream stages to obtain rabies virus-like particles (rabies VLP) from insect cell-baculovirus system using on-line and off-line Raman spectra to calibrate global models with minimal experimental data. Five cultivations in bioreactor were performed. The first one comprised the growth of uninfected Spodoptera frugiperda (Sf9) cells, the second and third runs to obtain recombinant baculovirus (rBV) bearing Rabies G glycoprotein and matrix protein, respectively. The fourth one involved the generation of rabies VLP from rBVs and the last one was a repetition of the third one with cell inoculum infected by rBV. The spectra were acquired through a Raman spectrometer with a 785-nm laser source. The fitted Partial Least Square models for nutrients and metabolites were comparable with those previously reported for mammalian cell lines (Relative error < 15 %). However, the use of this chemometrics approach for Xv and CV was not as accurate as it was for other parameters. The findings from this work established the basis for bioprocess Raman spectroscopical monitoring using insect cells for VLP manufacturing, which are gaining ground in the pharmaceutical industry.

Protein-based nanocages for vaccine development

Protein nanocages have attracted considerable attention in various fields of nanomedicine due to their intrinsic properties, including biocompatibility, biodegradability, high structural stability, and ease of modification of their surfaces and inner cavities. In vaccine development, these protein nanocages are suited for efficient targeting to and retention in the lymph nodes and can enhance immunogenicity through various mechanisms, including excellent uptake by antigen-presenting cells and crosslinking with multiple B cell receptors. This review highlights the superiority of protein nanocages as antigen delivery carriers based on their physiological and immunological properties such as biodistribution, immunogenicity, stability, and multifunctionality. With a focus on design, we discuss the utilization and efficacy of protein nanocages such as virus-like particles, caged proteins, and artificial caged proteins against cancer and infectious diseases such as coronavirus disease 2019 (COVID-19). In addition, we summarize available knowledge on the protein nanocages that are currently used in clinical trials and provide a general outlook on conventional distribution techniques and hurdles faced, particularly for therapeutic cancer vaccines.

Advances in CRISPR-Cas9 for the Baculovirus Vector System: A Systematic Review

The baculovirus expression vector systems (BEVS) have been widely used for the recombinant production of proteins in insect cells and with high insert capacity. However, baculovirus does not replicate in mammalian cells; thus, the BacMam system, a heterogenous expression system that can infect certain mammalian cells, was developed. Since then, the BacMam system has enabled transgene expression via mammalian-specific promoters in human cells, and later, the MultiBacMam system enabled multi-protein expression in mammalian cells. In this review, we will cover the continual development of the BEVS in combination with CRPISPR-Cas technologies to drive genome-editing in mammalian cells. Additionally, we highlight the use of CRISPR-Cas in glycoengineering to potentially produce a new class of glycoprotein medicines in insect cells. Moreover, we anticipate CRISPR-Cas9 to play a crucial role in the development of protein expression systems, gene therapy, and advancing genome engineering applications in the future.

Virus-like particles containing a prefusion-stabilized F protein induce a balanced immune response and confer protection against respiratory syncytial virus infection in mice

Respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children worldwide. Currently, no licensed RSV vaccines are available. In this study, we explored stable prefusion conformation virus-like particles (Pre-F VLPs) as RSV vaccine candidates. RSV fusion (F) protein mutants were constructed to form stabilized Pre-F or postfusion (Post-F) configurations. VLPs containing Pre-F or Post-F protein were generated using a recombinant baculovirus (rBV)-insect cell expression system. The assembly and immunological properties of Pre-F or Post-F VLPs were investigated. Pre-F and Post-F VLPs contained antigenic sites Ø and I of pre- and postfusion conformations, respectively. Compared with Post-F VLPs, immunization with Pre-F VLPs elicited upregulation of IFN-γ, IL-2 and IL-10 and downregulation of IL-4 and IL-5 cytokine production in mice. A high percentage of CD25⁺ Foxp3⁺ cells or a low percentage of IL-17A-producing cells among CD4⁺ T cells was observed in the lungs of mice vaccinated with Pre-F VLPs. Importantly, immunization with Pre-F VLPs induced a high level of RSV neutralizing antibody and a balanced immune response, which protected mice against RSV infection without evidence of immunopathology. Our results suggested that Pre-F VLPs generated from rBV-insect cells represent promising RSV vaccine candidates.

Development of virus-like particles-based vaccines against coronaviruses

Severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are the most impactful coronaviruses in human history, especially the latter, which brings revolutionary changes to human vaccinology. Due to its high infectivity, the virus spreads rapidly throughout the world and was declared a pandemic in March 2020. A vaccine would normally take more than 10 years to be developed. As such, there is no vaccine available for SARS-CoV and MERS-CoV. Currently, 10 vaccines have been approved for emergency use by World Health Organization (WHO) against SARS-CoV-2. Virus-like particle (VLP)s are nanoparticles resembling the native virus but devoid of the viral genome. Due to their self-adjuvanting properties, VLPs have been explored extensively for vaccine development. However, none of the approved vaccines against SARS-CoV-2 was based on VLP and only 4% of the vaccine candidates in clinical trials were based on VLPs. In the current review, we focused on discussing the major advances in the development of VLP-based vaccine candidates against the SARS-CoV, MERS-CoV, and SARS-CoV-2, including those in clinical and pre-clinical studies, to give a comprehensive overview of the VLP-based vaccines against the coronaviruses.

Virus-like particle vaccinology, from bench to bedside

Virus-like particles (VLPs) have become key tools in biology, medicine and even engineering. After their initial use to resolve viral structures at the atomic level, VLPs were rapidly harnessed to develop antiviral vaccines followed by their use as display platforms to generate any kind of vaccine. Most recently, VLPs have been employed as nanomachines to deliver pharmaceutically active products to specific sites and into specific cells in the body. Here, we focus on the use of VLPs for the development of vaccines with broad fields of indications ranging from classical vaccines against viruses to therapeutic vaccines against chronic inflammation, pain, allergy and cancer. In this review, we take a walk through time, starting with the latest developments in experimental preclinical VLP-based vaccines and ending with marketed vaccines, which earn billions of dollars every year, paving the way for the next wave of prophylactic and therapeutic vaccines already visible on the horizon.

Virus-Like Particles as Nanocarriers for Intracellular Delivery of Biomolecules and Compounds

Virus-like particles (VLPs) are nanostructures assemble from viral proteins. Besides widely used for vaccine development, VLPs have also been explored as nanocarriers for cargo delivery as they combine the key advantages of viral and non-viral vectors. While it protects cargo molecules from degradation, the VLP has good cell penetrating property to mediate cargo passing the cell membrane and released into cells, making the VLP an ideal tool for intracellular delivery of biomolecules and drugs. Great progresses have been achieved and multiple challenges are still on the way for broad applications of VLP as delivery vectors. Here we summarize current advances and applications in VLP as a delivery vector. Progresses on delivery of different types of biomolecules as well as drugs by VLPs are introduced, and the strategies for cargo packaging are highlighted which is one of the key steps for VLP mediated intracellular delivery. Production and applications of VLPs are also briefly reviewed, with a discussion on future challenges in this rapidly developing field.

Separation and purification of highly infectious enterovirus A71 particles using a strong anion-exchange column

Virions produced from cell culture is the primary source for production of formalin-inactivated whole virus vaccines for enteroviruses. EV-A71 particles produced from culture system comprise two major types, the immature/empty (E)-particle and the mature/full (F)-particle, which both exhibit low isoelectric point (pI) values but have distinct differences in infectivity and immunogenicity. Although EV-A71 particles can conventionally be separated into E-particle and F-particle using sucrose gradient ultracentrifugation, this procedure is cumbersome and difficult to put into practice for vaccine production. Methods based on ion-exchange chromatography have been exploited to improve the purification efficacy; however, none of them are capable of separating the E- and F-particles efficiently. In this study, we aimed to develop an approach to isolate and purify the highly immunogenic mature EV-A71 particles. By applying a step gradient elution procedure, we successfully isolated the viral structure protein VP0-cleaved particles of EV-A71 from a mixture of cultured viral solution using the Q-membrane anion-exchange chromatography. The elution started with 0.1x phosphate buffered saline (PBS) solution while increasing the percentage of 1x PBS containing 1M NaCl in sequential steps. By this procedure, the VP0-cleaved mature particles and VP0-uncleaved immature particles of EV-A71 could be separated into different fractions in Q-membrane with gradually increased NaCl concentration in elution buffer. The purified VP0-cleaved particles were shown to have characteristics equivalent to those of the highly infectious F-particles of EV-A71. The overall recovery rate for the mature EV-A71 particles by Q-membrane is 56% and its purity was shown to be equivalent to those isolated by the sucrose gradient ultracentrifugation. Our approach provides a simple and efficient purification method for recovering mature, highly infectious virus particles from the EV-A71 culture bulk.