Virus-like particles as immunogens

Viral vector- and virus-like particle-based vaccines against infectious diseases: A minireview

To overcome the limitations of conventional vaccines, new platforms for vaccine design have emerged such as those based on viral vectors and virus-like particles (VLPs). Viral vector vaccines are highly efficient and the onset of protection is quick. Many recombinant vaccine candidates for humans are based on viruses belonging to different families such as Adenoviridae, Retroviridae, Paramyxoviridae, Rhabdoviridae, and Parvoviridae. Also, the first viral vector vaccine licensed for human vaccination was the Japanese encephalitis virus vaccine. Since then, several viral vectors have been approved for vaccination against the viruses of Lassa fever, Ebola, hepatitis B, hepatitis E, SARS-CoV-2, and malaria. VLPs are nanoparticles that mimic viral particles formed from the self-assembly of structural proteins and VLP-based vaccines against hepatitis B and E viruses, human papillomavirus, and malaria have been commercialized. As evidenced by the accelerated production of vaccines against COVID-19, these new approaches are important tools for vaccinology and for generating rapid responses against pathogens and emerging pandemic threats.

GB and gH/gL fusion machinery: a promising target for vaccines to prevent Epstein-Barr virus infection

Epstein‒Barr virus (EBV) is a double-stranded DNA virus belonging to the family Orthoherpesviridae that is associated with the development of various tumors, such as lymphoma, nasopharyngeal carcinoma, and gastric cancer. There are no uniformly effective treatments for human EBV infection, and vaccines and immunotherapies are currently the main research directions. The glycoproteins gB and gH/gL are surface glycoproteins that are common to all herpesviruses, with subtle differences in structure and function between different viruses. The core membrane fusion machinery constituted by EBV gB and gH/gL is an important target of neutralizing antibodies in epithelial EBV infection due to its essential role in the fusion of viral and target cell membranes. In this article, we review the main modes of EBV infection, the structure and function of the core fusion machinery gB and gH/gL, and the development of neutralizing antibodies and prophylactic vaccines based on this target.

Progress in research and development of preventive vaccines for children in China

The infant and child stage is an important stage for the continuation and development of human society. The initial years of life have a lasting impact on a child's future. Children under the age of 5 have an immature immune system, especially infants and young children under 6 months of age. At this stage, the population has a low immunity to pathogen infections, making them vulnerable to bacteria and viruses. Vaccination can enhance the immunity of infants and children to specific diseases, reduce the transmission rate of infectious diseases, and promote the development of global public health. This article summarizes the current application status of Rotavirus (RV) vaccine, Hand-foot -mouth disease (HFMD) vaccine, and Pneumococcal Conjugate Vaccine (PCV) in China, as well as the research progress of clinical trial vaccine, laying a foundation for subsequent vaccine development.

Analyzing atomic force microscopy images of virus-like particles by expectation-maximization

Analysis of virus-like particles (VLPs) is an essential task in optimizing their implementation as vaccine antigens for virus-initiated diseases. Interrogating VLP collections for elasticity by probing with a rigid atomic force microscopy (AFM) tip is a potential method for determining VLP morphological changes. During VLP morphological change, it is not expected that all VLPs would be in the same state. This leads to the open question of whether VLPs may change in a continuous or stepwise fashion. For continuous change, the statistical distribution of observed VLP properties would be expected as a single distribution, while stepwise change would lead to a multimodal distribution of properties. This study presents the application of a Gaussian mixture model (GMM), fit by the Expectation-Maximization (EM) algorithm, to identify different states of VLP morphological change observed by AFM imaging.

Cutaneous adverse reactions associated with COVID-19 vaccines: Current evidence and potential immune mechanisms

As the number of vaccinated individuals has increased, there have been increasing reports of cutaneous hypersensitivity reactions. The main COVID-19 vaccines administered include messenger ribonucleic acid vaccines, non-replicating viral vector vaccines, inactivated whole-virus vaccines, and protein-based vaccines. These vaccines contain active components such as polyethylene glycol, polysorbate 80, aluminum, tromethamine, and disodium edetate dihydrate. Recent advances in understanding the coordination of inflammatory responses by specific subsets of lymphocytes have led to a new classification based on immune response patterns. We categorize these responses into four patterns: T helper (Th)1-, Th2-, Th17/22-, and Treg-polarized cutaneous inflammation after stimulation of COVID-19 vaccines. Although the association between COVID-19 vaccination and these cutaneous adverse reactions remains controversial, the occurrence of rare dermatoses and their short intervals suggest a possible relationship. Despite the potential adverse reactions, the administration of COVID-19 vaccines is crucial in the ongoing battle against severe acute respiratory syndrome coronavirus 2.

Role of Natural Binding Proteins in Therapy and Diagnostics

This review systematically investigates the critical role of natural binding proteins (NBPs), encompassing DNA-, RNA-, carbohydrate-, fatty acid-, and chitin-binding proteins, in the realms of oncology and diagnostics. In an era where cancer continues to pose significant challenges to healthcare systems worldwide, the innovative exploration of NBPs offers a promising frontier for advancing both the diagnostic accuracy and therapeutic efficacy of cancer management strategies. This manuscript provides an in-depth examination of the unique mechanisms by which NBPs interact with specific molecular targets, highlighting their potential to revolutionize cancer diagnostics and therapy. Furthermore, it discusses the burgeoning research on aptamers, demonstrating their utility as 'nucleic acid antibodies' for targeted therapy and precision diagnostics. Despite the promising applications of NBPs and aptamers in enhancing early cancer detection and developing personalized treatment protocols, this review identifies a critical knowledge gap: the need for comprehensive studies to understand the diverse functionalities and therapeutic potentials of NBPs across different cancer types and diagnostic scenarios. By bridging this gap, this manuscript underscores the importance of NBPs and aptamers in paving the way for next-generation diagnostics and targeted cancer treatments.

Optimized production of full-length PCV2d virus-like particles in Escherichia coli: A cost-effective and high-yield approach for potential vaccine antigen development

Porcine circovirus type 2 (PCV2) is a globally prevalent infectious pathogen affecting swine, with its capsid protein (Cap) being the sole structural protein critical for vaccine development. Prior research has demonstrated that PCV2 Cap proteins produced in Escherichia coli (E. coli) can form virus-like particles (VLPs) in vitro, and nuclear localization signal peptides (NLS) play a pivotal role in stabilizing PCV2 VLPs. Recently, PCV2d has emerged as an important strain within the PCV2 epidemic. In this study, we systematically optimized the PCV2d Cap protein and successfully produced intact PCV2d VLPs containing NLS using E. coli. The recombinant PCV2d Cap protein was purified through affinity chromatography, yielding 7.5 mg of recombinant protein per 100 ml of bacterial culture. We augmented the conventional buffer system with various substances such as arginine, β-mercaptoethanol, glycerol, polyethylene glycol, and glutathione to promote VLP assembly. The recombinant PCV2d Cap self-assembled into VLPs approximately 20 nm in diameter, featuring uniform distribution and exceptional stability in the optimized buffer. We developed the vaccine and immunized pigs and mice, evaluating the immunogenicity of the PCV2d VLPs vaccine by measuring PCV2-IgG, IL-4, TNF-α, and IFN-γ levels, comparing them to commercial vaccines utilizing truncated PCV2 Cap antigens. The HE staining and immunohistochemical tests confirmed that the PCV2 VLPs vaccine offered robust protection. The results revealed that animals vaccinated with the PCV2d VLPs vaccine exhibited high levels of PCV2 antibodies, with TNF-α and IFN-γ levels rapidly increasing at 14 days post-immunization, which were higher than those observed in commercially available vaccines, particularly in the mouse trial. This could be due to the fact that full-length Cap proteins can assemble into more stable PCV2d VLPs in the assembling buffer. In conclusion, our produced PCV2d VLPs vaccine elicited stronger immune responses in pigs and mice compared to commercial vaccines. The PCV2d VLPs from this study serve as an excellent candidate vaccine antigen, providing insights for PCV2d vaccine research.

Self-Assembling E2-Based Nanoparticles Improve Vaccine Thermostability and Protective Immunity against CSFV

Classical swine fever virus (CSFV) is a highly contagious pathogen causing significant economic losses in the swine industry. Conventional inactivated or attenuated live vaccines for classical swine fever (CSF) are effective but face biosafety concerns and cannot distinguish vaccinated animals from those infected with the field virus, complicating CSF eradication efforts. It is noteworthy that nanoparticle (NP)-based vaccines resemble natural viruses in size and antigen structure, and offer an alternative tool to circumvent these limitations. In this study, we developed an innovative vaccine delivery scaffold utilizing self-assembled mi3 NPs, which form stable structures carrying the CSFV E2 glycoprotein. The expressed yeast E2-fused protein (E2-mi3 NPs) exhibited robust thermostability (25 to 70 °C) and long-term storage stability at room temperature (25 °C). Interestingly, E2-mi3 NPs made with this technology elicited enhanced antigen uptake by RAW264.7 cells. In a rabbit model, the E2-mi3 NP vaccine against CSFV markedly increased CSFV-specific neutralizing antibody titers. Importantly, it conferred complete protection in rabbits challenged with the C-strain of CSFV. Furthermore, we also found that the E2-mi3 NP vaccines triggered stronger cellular (T-lymphocyte proliferation, CD8+ T-lymphocytes, IFN-γ, IL-2, and IL-12p70) and humoral (CSFV-specific neutralizing antibodies, CD4+ T-lymphocytes, and IL-4) immune responses in pigs than the E2 vaccines. To sum up, these structure-based, self-assembled mi3 NPs provide valuable insights for novel antiviral strategies against the constantly infectious agents.

Virus-like particles (VLPs): A promising platform for combating against Newcastle disease virus

The global poultry industry plays a pivotal role in providing eggs and meat for human consumption. However, outbreaks of viral disease, especially Newcastle virus disease (NDV), within poultry farms have detrimental effects on various zootechnical parameters, such as body weight gain, feed intake, feed conversion ratio, as well as the quality of egg and meat production. Cases of vaccine failure have been reported in regions where highly pathogenic strains of NDV are prevalent. To tackle this challenge, virus-like particles (VLPs) have emerged as a potential solution. VLPs closely resemble natural viruses, offering biocompatibility and immune-stimulating properties that make them highly promising for therapeutic applications against NDV. Hence, this review emphasizes the significance of NDV and the need for effective treatments. The manuscript will contain several key aspects, starting with an exploration of the structure and properties of NDV. Subsequently, the paper will delve into the characteristics and benefits of VLPs compared to conventional drug delivery systems. A comprehensive analysis of VLPs as potential vaccine candidates targeting NDV will be presented, along with a discussion on strategies for loading cargo into these NDV-targeting VLPs. The review will also examine various expression systems utilized in the production of NDV-targeting VLPs. Additionally, the manuscript will address future prospects and challenges in the field, concluding with recommendations for further research.

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.

Mammalian cells-based platforms for the generation of SARS-CoV-2 virus-like particles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19. Though many COVID-19 vaccines have been developed, most of them are delivered via intramuscular injection and thus confer relatively weak mucosal immunity against the natural infection. Virus-Like Particles (VLPs) are self-assembled nanostructures composed of key viral structural proteins, that mimic the wild-type virus structure but are non-infectious and non-replicating due to the lack of viral genetic material. In this study, we efficiently generated SARS-CoV-2 VLPs by co-expressing the four SARS-CoV-2 structural proteins, specifically the membrane (M), small envelope (E), spike (S) and nucleocapsid (N) proteins. We show that these proteins are essential and sufficient for the efficient formation and release of SARS-CoV-2 VLPs. Moreover, we used lentiviral vectors to generate human cell lines that stably produce VLPs. Because VLPs can bind to the virus natural receptors, hence leading to entry into cells and viral antigen presentation, this platform could be used to develop novel vaccine candidates that are delivered intranasally.

Translational Challenges and Prospective Solutions in the Implementation of Biomimetic Delivery Systems

Biomimetic delivery systems (BDSs), inspired by the intricate designs of biological systems, have emerged as a groundbreaking paradigm in nanomedicine, offering unparalleled advantages in therapeutic delivery. These systems, encompassing platforms such as liposomes, protein-based nanoparticles, extracellular vesicles, and polysaccharides, are lauded for their targeted delivery, minimized side effects, and enhanced therapeutic outcomes. However, the translation of BDSs from research settings to clinical applications is fraught with challenges, including reproducibility concerns, physiological stability, and rigorous efficacy and safety evaluations. Furthermore, the innovative nature of BDSs demands the reevaluation and evolution of existing regulatory and ethical frameworks. This review provides an overview of BDSs and delves into the multifaceted translational challenges and present emerging solutions, underscored by real-world case studies. Emphasizing the potential of BDSs to redefine healthcare, we advocate for sustained interdisciplinary collaboration and research. As our understanding of biological systems deepens, the future of BDSs in clinical translation appears promising, with a focus on personalized medicine and refined patient-specific delivery systems.

Delivery of gene editing therapeutics

For the past decades, gene editing demonstrated the potential to attenuate each of the root causes of genetic, infectious, immune, cancerous, and degenerative disorders. More recently, Clustered Regularly Interspaced Short Palindromic Repeats-CRISPR-associated protein 9 (CRISPR-Cas9) editing proved effective for editing genomic, cancerous, or microbial DNA to limit disease onset or spread. However, the strategies to deliver CRISPR-Cas9 cargos and elicit protective immune responses requires safe delivery to disease targeted cells and tissues. While viral vector-based systems and viral particles demonstrate high efficiency and stable transgene expression, each are limited in their packaging capacities and secondary untoward immune responses. In contrast, the nonviral vector lipid nanoparticles were successfully used for as vaccine and therapeutic deliverables. Herein, we highlight each available gene delivery systems for treating and preventing a broad range of infectious, inflammatory, genetic, and degenerative diseases. STATEMENT OF SIGNIFICANCE: CRISPR-Cas9 gene editing for disease treatment and prevention is an emerging field that can change the outcome of many chronic debilitating disorders.

A Bioreactor-Based Yellow Fever Virus-like Particle Production Process with Integrated Process Analytical Technology Based on Transient Transfection

Yellow Fever (YF) is a severe disease that, while preventable through vaccination, lacks rapid intervention options for those already infected. There is an urgent need for passive immunization techniques using YF-virus-like particles (YF-VLPs). To address this, we successfully established a bioreactor-based production process for YF-VLPs, leveraging transient transfection and integrating Process Analytical Technology. A cornerstone of this approach was the optimization of plasmid DNA (pDNA) production to a yield of 11 mg/L using design of experiments. Glucose, NaCl, yeast extract, and a phosphate buffer showed significant influence on specific pDNA yield. The preliminary work for VLP-production in bioreactor showed adjustments to the HEK cell density, the polyplex formation duration, and medium exchanges effectively elevated transfection efficiencies. The additive Pluronic F-68 was neutral in its effects, and anti-clumping agents (ACA) adversely affected the transfection process. Finally, we established the stirred-tank bioreactor process with integrated dielectric spectroscopy, which gave real-time insight in relevant process steps, e.g., cell growth, polyplex uptake, and harvest time. We confirmed the presence and integrity of YF-VLP via Western blot, imaging flow cytometry measurement, and transmission electron microscopy. The YF-VLP production process can serve as a platform to produce VLPs as passive immunizing agents against other neglected tropical diseases.

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.

Engineering Materials and Devices for the Prevention, Diagnosis, and Treatment of COVID-19 and Infectious Diseases

Following the global spread of COVID-19, scientists and engineers have adapted technologies and developed new tools to aid in the fight against COVID-19. This review discusses various approaches to engineering biomaterials, devices, and therapeutics, especially at micro and nano levels, for the prevention, diagnosis, and treatment of infectious diseases, such as COVID-19, serving as a resource for scientists to identify specific tools that can be applicable for infectious-disease-related research, technology development, and treatment. From the design and production of equipment critical to first responders and patients using three-dimensional (3D) printing technology to point-of-care devices for rapid diagnosis, these technologies and tools have been essential to address current global needs for the prevention and detection of diseases. Moreover, advancements in organ-on-a-chip platforms provide a valuable platform to not only study infections and disease development in humans but also allow for the screening of more effective therapeutics. In addition, vaccines, the repurposing of approved drugs, biomaterials, drug delivery, and cell therapy are promising approaches for the prevention and treatment of infectious diseases. Following a comprehensive review of all these topics, we discuss unsolved problems and future directions.

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.

Exploring FeLV-Gag-Based VLPs as a New Vaccine Platform-Analysis of Production and Immunogenicity

Feline leukemia virus (FeLV) is one of the most prevalent infectious diseases in domestic cats. Although different commercial vaccines are available, none of them provides full protection. Thus, efforts to design a more efficient vaccine are needed. Our group has successfully engineered HIV-1 Gag-based VLPs that induce a potent and functional immune response against the HIV-1 transmembrane protein gp41. Here, we propose to use this concept to generate FeLV-Gag-based VLPs as a novel vaccine strategy against this retrovirus. By analogy to our HIV-1 platform, a fragment of the FeLV transmembrane p15E protein was exposed on FeLV-Gag-based VLPs. After optimization of Gag sequences, the immunogenicity of the selected candidates was evaluated in C57BL/6 and BALB/c mice, showing strong cellular and humoral responses to Gag but failing to generate anti-p15E antibodies. Altogether, this study not only tests the versatility of the enveloped VLP-based vaccine platform but also sheds light on FeLV vaccine research.

Application of Traditional Vaccine Development Strategies to SARS-CoV-2

Over the past 150 years, vaccines have revolutionized the relationship between people and disease. During the COVID-19 pandemic, technologies such as mRNA vaccines have received attention due to their novelty and successes. However, more traditional vaccine development platforms have also yielded important tools in the worldwide fight against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A variety of approaches have been used to develop COVID-19 vaccines that are now authorized for use in countries around the world. In this review, we highlight strategies that focus on the viral capsid and outwards, rather than on the nucleic acids inside. These approaches fall into two broad categories: whole-virus vaccines and subunit vaccines. Whole-virus vaccines use the virus itself, in either an inactivated or an attenuated state. Subunit vaccines contain instead an isolated, immunogenic component of the virus. Here, we highlight vaccine candidates that apply these approaches against SARS-CoV-2 in different ways. In a companion article (H. M. Rando, R. Lordan, L. Kolla, E. Sell, et al., mSystems 8:e00928-22, 2023, https://doi.org/10.1128/mSystems.00928-22), we review the more recent and novel development of nucleic acid-based vaccine technologies. We further consider the role that these COVID-19 vaccine development programs have played in prophylaxis at the global scale. Well-established vaccine technologies have proved especially important to making vaccines accessible in low- and middle-income countries. Vaccine development programs that use established platforms have been undertaken in a much wider range of countries than those using nucleic acid-based technologies, which have been led by wealthy Western countries. Therefore, these vaccine platforms, though less novel from a biotechnological standpoint, have proven to be extremely important to the management of SARS-CoV-2. IMPORTANCE The development, production, and distribution of vaccines is imperative to saving lives, preventing illness, and reducing the economic and social burdens caused by the COVID-19 pandemic. Vaccines that use cutting-edge biotechnology have played an important role in mitigating the effects of SARS-CoV-2. However, more traditional methods of vaccine development that were refined throughout the 20th century have been especially critical to increasing vaccine access worldwide. Effective deployment is necessary to reducing the susceptibility of the world's population, which is especially important in light of emerging variants. In this review, we discuss the safety, immunogenicity, and distribution of vaccines developed using established technologies. In a separate review, we describe the vaccines developed using nucleic acid-based vaccine platforms. From the current literature, it is clear that the well-established vaccine technologies are also highly effective against SARS-CoV-2 and are being used to address the challenges of COVID-19 globally, including in low- and middle-income countries. This worldwide approach is critical for reducing the devastating impact of SARS-CoV-2.

An optimized messenger RNA vaccine candidate protects non-human primates from Zika virus infection

Zika virus (ZIKV), an arbovirus transmitted by mosquitoes, was identified as a cause of congenital disease during a major outbreak in the Americas in 2016. Vaccine design strategies relied on limited available isolate sequence information due to the rapid response necessary. The first-generation ZIKV mRNA vaccine, mRNA-1325, was initially generated and, as additional strain sequences became available, a second mRNA vaccine, mRNA-1893, was developed. Herein, we compared the immune responses following mRNA-1325 and mRNA-1893 vaccination and reported that mRNA-1893 generated comparable neutralizing antibody titers to mRNA-1325 at 1/20th of the dose and provided complete protection from ZIKV challenge in non-human primates. In-depth characterization of these vaccines indicated that the observed immunologic differences could be attributed to a single amino acid residue difference that compromised mRNA-1325 virus-like particle formation.

Nanoparticles as a Delivery System of Antigens for the Development of an Effective Vaccine against Toxoplasma gondii

Nanoparticles include particles ranging in size from nanometers to micrometers, whose physicochemical characteristics are optimized to make them appropriate delivery vehicles for drugs or immunogens important in the fight and/or prevention of infectious diseases. There has been a rise in the use of nanoparticles in preventive vaccine formulations as immunostimulatory adjuvants, and as vehicles for immunogen delivery to target immune cells. Toxoplasma is important worldwide, and may cause human toxoplasmosis. In immunocompetent hosts, infection is usually asymptomatic, but in immunocompromised patients it can cause serious neurological and ocular consequences, such as encephalitis and retinochoroiditis. Primary infection during pregnancy may cause abortion or congenital toxoplasmosis. Currently, there is no effective human vaccine against this disease. Evidence has emerged from several experimental studies testing nanovaccines showing them to be promising tools in the prevention of experimental toxoplasmosis. For the present study, a literature review was carried out on articles published over the last 10 years through the PubMed database, pertaining to in vivo experimental models of T. gondii infection where nanovaccines were tested and protection and immune responses evaluated. This review aims to highlight the way forward in the search for an effective vaccine for toxoplasmosis.

Effect of Antigen Structure in Subunit Vaccine Nanoparticles on Humoral Immune Responses

Subunit vaccines offer numerous attractive features, including good safety profiles and well-defined components with highly characterized properties because they do not contain whole pathogens. However, vaccine platforms based on one or few selected antigens are often poorly immunogenic. Several advances have been made in improving the effectiveness of subunit vaccines, including nanoparticle formulation and/or co-administration with adjuvants. Desolvation of antigens into nanoparticles is one approach that has been successful in eliciting protective immune responses. Despite this advance, damage to the antigen structure by desolvation can compromise the recognition of conformational antigens by B cells and the subsequent humoral response. Here, we used ovalbumin as a model antigen to demonstrate enhanced efficacy of subunit vaccines by preserving antigen structures in nanoparticles. An altered antigen structure due to desolvation was first validated by GROMACS and circular dichroism. Desolvant-free nanoparticles with a stable ovalbumin structure were successfully synthesized by directly cross-linking ovalbumin or using ammonium sulfate to form nanoclusters. Alternatively, desolvated OVA nanoparticles were coated with a layer of OVA after desolvation. Vaccination with salt-precipitated nanoparticles increased OVA-specific IgG titers 4.2- and 22-fold compared to the desolvated and coated nanoparticles, respectively. In addition, enhanced affinity maturation by both salt precipitated and coated nanoparticles was displayed in contrast to desolvated nanoparticles. These results demonstrate both that salt-precipitated antigen nanoparticles are a potential new vaccine platform with significantly improved humoral immunity and a functional value of preserving antigen structures in vaccine nanoparticle design.

Protein-based nano-vaccines against SARS-CoV-2: Current design strategies and advances of candidate vaccines

The outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has shaken the global health system. Various nanotechnology-based strategies for vaccine development have played pivotal roles in fighting against SARS-CoV-2. Among them, the safe and effective protein-based nanoparticle (NP) platforms display a highly repetitive array of foreign antigens on their surface, which is urgent for improving the immunogenicity of vaccines. These platforms greatly improved antigen uptake by antigen presenting cells (APCs), lymph node trafficking, and B cell activation, due to the optimal size, multivalence, and versatility of NPs. In this review, we summarize the advances of protein-based NP platforms, strategies of antigen attachment, and the current progress of clinical and preclinical trials in the development of SARS-CoV-2 vaccines based on protein-based NP platforms. Importantly, the lessons learnt and design approaches developed for these NP platforms against SARS-CoV-2 also provide insights into the development of protein-based NP strategies for preventing other epidemic diseases.

Immunogenic Properties and Antigenic Similarity of Virus-like Particles Derived from Human Polyomaviruses

Polyomaviruses (PyVs) are highly prevalent in humans and animals. PyVs cause mild illness, however, they can also elicit severe diseases. Some PyVs are potentially zoonotic, such as simian virus 40 (SV40). However, data are still lacking about their biology, infectivity, and host interaction with different PyVs. We investigated the immunogenic properties of virus-like particles (VLPs) derived from viral protein 1 (VP1) of human PyVs. We immunised mice with recombinant HPyV VP1 VLPs mimicking the structure of viruses and compared their immunogenicity and cross-reactivity of antisera using a broad spectrum of VP1 VLPs derived from the PyVs of humans and animals. We demonstrated a strong immunogenicity of studied VLPs and a high degree of antigenic similarity between VP1 VLPs of different PyVs. PyV-specific monoclonal antibodies were generated and applied for investigation of VLPs phagocytosis. This study demonstrated that HPyV VLPs are highly immunogenic and interact with phagocytes. Data on the cross-reactivity of VP1 VLP-specific antisera revealed antigenic similarities among VP1 VLPs of particular human and animal PyVs and suggested possible cross-immunity. As the VP1 capsid protein is the major viral antigen involved in virus-host interaction, an approach based on the use of recombinant VLPs is relevant for studying PyV biology regarding PyV interaction with the host immune system.

Virus-like nanoparticles as enzyme carriers for Enzyme Replacement Therapy (ERT)

Enzyme replacement therapy (ERT) has been used to treat a few of the many existing diseases which are originated from the lack of, or low enzymatic activity. Exogenous enzymes are administered to contend with the enzymatic activity deficiency. Enzymatic nanoreactors based on the enzyme encapsulation inside of virus-like particles (VLPs) appear as an interesting alternative for ERT. VLPs are excellent delivery vehicles for therapeutic enzymes as they are biodegradable, uniformly organized, and porous nanostructures that transport and could protect the biocatalyst from the external environment without much affecting the bioactivity. Consequently, significant efforts have been made in the production processes of virus-based enzymatic nanoreactors and their functionalization, which are critically reviewed. The use of virus-based enzymatic nanoreactors for the treatment of lysosomal storage diseases such as Gaucher, Fabry, and Pompe diseases, as well as potential therapies for galactosemia, and Hurler and Hunter syndromes are discussed.

Oral and Subcutaneous Immunization with a Plant-Produced Mouse-Specific Zona Pellucida 3 Peptide Presented on Hepatitis B Core Antigen Virus-like Particles

A short mouse-specific peptide from zona pellucida 3 (mZP3, amino acids 328-342) has been shown to be associated with antibody-mediated contraception. In this study, we investigated the production of mZP3 in the plant, as an orally applicable host, and examined the immunogenicity of this small peptide in the BALB/c mouse model. The mZP3 peptide was inserted into the major immunodominant region of the hepatitis B core antigen and was produced in Nicotiana benthamiana plants via Agrobacterium-mediated transient expression. Soluble HBcAg-mZP3 accumulated at levels up to 2.63 mg/g leaf dry weight (LDW) containing ~172 µg/mg LDW mZP3 peptide. Sucrose gradient analysis and electron microscopy indicated the assembly of the HBcAg-mZP3 virus-like particles (VLPs) in the soluble protein fraction. Subcutaneously administered mZP3 peptide displayed on HBcAg VLPs was immunogenic in BALB/c mice at a relatively low dosage (5.5 µg mZP3 per dose) and led to the generation of mZP3-specific antibodies that bound to the native zona pellucida of wild mice. Oral delivery of dried leaves expressing HBcAg-mZP3 also elicited mZP3-specific serum IgG and mucosal IgA that cross-reacted with the zona pellucida of wild mice. According to these results, it is worthwhile to investigate the efficiency of plants producing HBcAg-mZP3 VLPs as immunogenic edible baits in reducing the fertility of wild mice through inducing antibodies that cross-react to the zona pellucida.

Plant-made pharmaceuticals: exploring studies for the production of recombinant protein in plants and assessing challenges ahead

The production of pharmaceutical compounds in plants is attracting increasing attention, as plant-based systems can be less expensive, safer, and more scalable than mammalian, yeast, bacterial, and insect cell expression systems. Here, we review the history and current status of plant-made pharmaceuticals. Producing pharmaceuticals in plants requires pairing the appropriate plant species with suitable transformation technology. Pharmaceuticals have been produced in tobacco, cereals, legumes, fruits, and vegetables via nuclear transformation, chloroplast transformation, transient expression, and transformation of suspension cell cultures. Despite this wide range of species and methods used, most such efforts have involved the nuclear transformation of tobacco. Tobacco readily generates large amounts of biomass, easily accepts foreign genes, and is amenable to stable gene expression via nuclear transformation. Although vaccines, antibodies, and therapeutic proteins have been produced in plants, such pharmaceuticals are not readily utilized by humans due to differences in glycosylation, and few such compounds have been approved due to a lack of clinical data. In addition, achieving an adequate immune response using plant-made pharmaceuticals can be difficult due to low rates of production compared to other expression systems. Various technologies have recently been developed to help overcome these limitations; however, plant systems are expected to increasingly become widely used expression systems for recombinant protein production.

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.

Vaccines against Group B Coxsackieviruses and Their Importance

The group B coxsackieviruses (CVBs) exist in six serotypes (CVB1 to CVB6). Disease associations have been reported for most serotypes, and multiple serotypes can cause similar diseases. For example, CVB1, CVB3, and CVB5 are generally implicated in the causation of myocarditis, whereas CVB1 and CVB4 could accelerate the development of type 1 diabetes (T1D). Yet, no vaccines against these viruses are currently available. In this review, we have analyzed the attributes of experimentally tested vaccines and discussed their merits and demerits or limitations, as well as their impact in preventing infections, most importantly myocarditis and T1D.

Application of Traditional Vaccine Development Strategies to SARS-CoV-2

Over the past 150 years, vaccines have revolutionized the relationship between people and disease. During the COVID-19 pandemic, technologies such as mRNA vaccines have received attention due to their novelty and successes. However, more traditional vaccine development platforms have also yielded important tools in the worldwide fight against the SARS-CoV-2 virus. A variety of approaches have been used to develop COVID-19 vaccines that are now authorized for use in countries around the world. In this review, we highlight strategies that focus on the viral capsid and outwards, rather than on the nucleic acids inside. These approaches fall into two broad categories: whole-virus vaccines and subunit vaccines. Whole-virus vaccines use the virus itself, either in an inactivated or attenuated state. Subunit vaccines contain instead an isolated, immunogenic component of the virus. Here, we highlight vaccine candidates that apply these approaches against SARS-CoV-2 in different ways. In a companion manuscript, we review the more recent and novel development of nucleic-acid based vaccine technologies. We further consider the role that these COVID-19 vaccine development programs have played in prophylaxis at the global scale. Well-established vaccine technologies have proved especially important to making vaccines accessible in low- and middle-income countries. Vaccine development programs that use established platforms have been undertaken in a much wider range of countries than those using nucleic-acid-based technologies, which have been led by wealthy Western countries. Therefore, these vaccine platforms, though less novel from a biotechnological standpoint, have proven to be extremely important to the management of SARS-CoV-2.

SARS-CoV-2 and its new variants: a comprehensive review on nanotechnological application insights into potential approaches

SARS-CoV-2 (COVID-19) spreads and develops quickly worldwide as a new global crisis which has left deep socio-economic damage and massive human mortality. This virus accounts for the ongoing outbreak and forces an urgent need to improve antiviral therapeutics and targeted diagnosing tools. Researchers have been working to find a new drug to combat the virus since the outbreak started in late 2019, but there are currently no successful drugs to control the SARS-CoV-2, which makes the situation riskier. Very recently, new variant of SARS-CoV-2 is identified in many countries which make the situation very critical. No successful treatment has yet been shown although enormous international commitment to combat this pandemic and the start of different clinical trials. Nanomedicine has outstanding potential to solve several specific health issues, like viruses, which are regarded a significant medical issue. In this review, we presented an up-to-date drug design strategy against SARS-CoV-2, including the development of novel drugs and repurposed product potentials were useful, and successful drugs discovery is a constant requirement. The use of nanomaterials in treatment against SARS-CoV-2 and their use as carriers for the transport of the most frequently used antiviral therapeutics are discussed systematically here. We also addressed the possibilities of practical applications of nanoparticles to give the status of COVID-19 antiviral systems.

Multivalent viral particles elicit safe and efficient immunoprotection against Nipah Hendra and Ebola viruses

Experimental vaccines for the deadly zoonotic Nipah (NiV), Hendra (HeV), and Ebola (EBOV) viruses have focused on targeting individual viruses, although their geographical and bat reservoir host overlaps warrant creation of multivalent vaccines. Here we explored whether replication-incompetent pseudotyped vesicular stomatitis virus (VSV) virions or NiV-based virus-like particles (VLPs) were suitable multivalent vaccine platforms by co-incorporating multiple surface glycoproteins from NiV, HeV, and EBOV onto these virions. We then enhanced the vaccines' thermotolerance using carbohydrates to enhance applicability in global regions that lack cold-chain infrastructure. Excitingly, in a Syrian hamster model of disease, the VSV multivalent vaccine elicited safe, strong, and protective neutralizing antibody responses against challenge with NiV, HeV, or EBOV. Our study provides proof-of-principle evidence that replication-incompetent multivalent viral particle vaccines are sufficient to provide protection against multiple zoonotic deadly viruses with high pandemic potential.

Virus-like particle - mediated delivery of the RIG-I agonist M8 induces a type I interferon response and protects cells against viral infection

Virus-Like Particles (VLPs) are nanostructures that share conformation and self-assembly properties with viruses, but lack a viral genome and therefore the infectious capacity. In this study, we produced VLPs by co-expression of VSV glycoprotein (VSV-G) and HIV structural proteins (Gag, Pol) that incorporated a strong sequence-optimized 5'ppp-RNA RIG-I agonist, termed M8. Treatment of target cells with VLPs-M8 generated an antiviral state that conferred resistance against multiple viruses. Interestingly, treatment with VLPs-M8 also elicited a therapeutic effect by inhibiting ongoing viral replication in previously infected cells. Finally, the expression of SARS-CoV-2 Spike glycoprotein on the VLP surface retargeted VLPs to ACE2 expressing cells, thus selectively blocking viral infection in permissive cells. These results highlight the potential of VLPs-M8 as a therapeutic and prophylactic vaccine platform. Overall, these observations indicate that the modification of VLP surface glycoproteins and the incorporation of nucleic acids or therapeutic drugs, will permit modulation of particle tropism, direct specific innate and adaptive immune responses in target tissues, and boost immunogenicity while minimizing off-target effects.

Development and Efficacy Evaluation of a Novel Nano-Emulsion Adjuvant for a Foot-and-Mouth Disease Virus-like Particles Vaccine Based on Squalane

The successful development of foot-and-mouth disease virus-like particles (FMD-VLPs) has opened a new direction for researching a novel subunit vaccine for foot-and-mouth disease (FMD). Therefore, it is urgent to develop an adjuvant that is highly effective and safe to facilitate a better immune response to be pair with the FMD-VLP vaccine. In this research, we prepared a new nano-emulsion adjuvant based on squalane (SNA) containing CpG using the pseudo-ternary phase diagram method and the phase transformation method. The SNA consisted of Span85, Tween60, squalane, polyethene glycol-400 (PEG400) and CpG aqueous solution. The average particle diameter of the SNA was about 95 nm, and it exhibited good resistance to centrifugation, thermal stability, and biocompatibility. Then, SNA was emulsified as an adjuvant to prepare foot-and-mouth disease virus-like particles vaccine, BALB/c mice and guinea pigs were immunized, and we evaluated the immunization effect. The immunization results in mice showed that the SNA-VLPs vaccine significantly increased specific antibody levels in mice within 4 weeks, including higher levels of IgG1 and IgG2a. In addition, it increased the levels of IFN-γ and IL-1β in the immune serum of mice. Meanwhile, guinea pig-specific and neutralizing antibodies were considerably increased within 4 weeks when SNA was used as an adjuvant, thereby facilitating the proliferation of splenic lymphocytes. More importantly, in guinea pigs immunized with one dose of SNA-VLPs, challenged with FMDV 28 days after immunization, the protection rate can reach 83.3%, which is as high as in the ISA-206 control group. In conclusion, the novel squalane nano-emulsion adjuvant is an effective adjuvant for the FMD-VLPs vaccine, indicating a promising adjuvant for the future development of a novel FMD-VLPs vaccine.

Norovirus-VLPs expressing pre-erythrocytic malaria antigens induce functional immunity against sporozoite infection

Despite the development of prophylactic anti-malarial drugs and practices to prevent infection, malaria remains a health concern. Preclinical testing of novel malaria vaccine strategies achieved through rational antigen selection and novel particle-based delivery platforms is yielding encouraging results. One such platform, self-assembling virus-like particles (VLP) is safer than attenuated live viruses, and has been approved as a vaccination tool by the FDA. We explore the use of Norovirus sub-viral particles lacking the natural shell (S) domain forming the interior shell but that retain the protruding (P) structures of the native virus as a vaccine vector. Epitope selection and their surface display has the potential to focus antigen specific immune responses to crucial epitopes. Recombinant P-particles displaying epitopes from two malaria antigens, Plasmodium falciparum (Pf) CelTOS and Plasmodium falciparum (Pf) CSP, were evaluated for immunogenicity and their ability to confer protection in a murine challenge model. Immune responses induced in mice resulted either in sterile protection (displaying PfCelTOS epitopes) or in antibodies with functional activity against sporozoites (displaying PfCSP epitopes) in an in vitro liver-stage development assay (ILSDA). These results are encouraging and support further evaluation of this platform as a vaccine delivery system.

Generation of a Soluble African Horse Sickness Virus VP7 Protein Capable of Forming Core-like Particles

A unique characteristic of the African horse sickness virus (AHSV) major core protein VP7 is that it is highly insoluble, and spontaneously forms crystalline particles in AHSV-infected cells and when expressed in vitro. The aggregation of AHSV VP7 into these crystals presents many problems in AHSV vaccine development, and it is unclear whether VP7 aggregation affects AHSV assembly or contributes to AHSV pathogenesis. Here, we set out to abolish VP7 self-assembly by targeting candidate amino acid regions on the surface of the VP7 trimer via site-directed mutagenesis. It was found that the substitution of seven amino acids resulted in the complete disruption of AHSV VP7 self-assembly, which abolished the formation of VP7 crystalline particles and converted VP7 to a fully soluble protein still capable of interacting with VP3 to form core-like particles. This work provides further insight into the formation of AHSV VP7 crystalline particles and the successful development of AHSV vaccines. It also paves the way for future research by drawing comparisons with similar viral phenomena observed in human virology.

Virus-Like Particle-Templated Silica-Adjuvanted Nanovaccines with Enhanced Humoral and Cellular Immunity

Virus-like particles (VLPs) are self-assembled viral proteins that represent a superior form of antigens in vaccine formulations. To enhance immunogenicity, adjuvants, especially the aluminum salts (Alum), are essentially formulated in VLP vaccines. However, Alum only induce biased humoral immune responses that limits further applications of VLP-based vaccines. To stimulate more balanced immunity, we, herein, develop a one-step strategy of using VLPs as the biotemplates to synthesize raspberry-like silica-adjuvanted VLP@Silica nanovaccines. Hepatitis B surface antigen (HBsAg) VLPs and human papillomavirus type 18 (HPV 18) VLPs are selected as model templates. Circular dichroism (CD) and affinity analyses demonstrate that HBsAg VLPs in the nanovaccines maintain their secondary structure and immunogenicity, respectively. VLP@Silica promote silica dissolution-induced lysosomal escape and cytosolic delivery of antigens, and enhance the secretion of both Th1 and Th2 type cytokines in murine bone marrow-derived dendritic cells (BMDCs). Additionally, they could improve antigen trafficking and mediate DC activation in draining lymph nodes (DLNs). Vaccination study demonstrate that both HBsAg VLP@Silica and HPV 18 VLP@Silica nanovaccines induce enhanced antigen-specific antibody productions and T-cell mediated adaptive immune responses. This design strategy can utilize VLPs derived from a diversity of viruses or their variants as templates to construct both prophylactic and therapeutic vaccines with improved immunogenicity.

In vivo fate and intracellular trafficking of vaccine delivery systems

With the pandemic of severe acute respiratory syndrome coronavirus 2, vaccine delivery systems emerged as a core technology for global public health. Given that antigen processing takes place inside the cell, the intracellular delivery and trafficking of a vaccine antigen will contribute to vaccine efficiency. Investigations focusing on the in vivo behavior and intracellular transport of vaccines have improved our understanding of the mechanisms relevant to vaccine delivery systems and facilitated the design of novel potent vaccine platforms. In this review, we cover the intracellular trafficking and in vivo fate of vaccines administered via various routes and delivery systems. To improve immune responses, researchers have used various strategies to modulate vaccine platforms and intracellular trafficking. In addition to progress in vaccine trafficking studies, the challenges and future perspectives for designing next-generation vaccines are discussed.

A structural vaccinology approach for in silico designing of a potential self-assembled nanovaccine against Leishmania infantum

Visceral leishmaniasis (VL) remains a major public health problem across 98 countries. To date, VL has no effective drug. Vaccines, as the most successful breakthroughs in medicine, can promise an effective strategy to fight various diseases. More recently, self-assembled peptide nanoparticles (SAPNs) have attracted considerable attention in the field of vaccine design due to their multivalency. In this study, a SAPN nanovaccine was designed using various immunoinformatics methods. High-ranked epitopes were chosen from a number of antigens, including Leishmania-specific hypothetical protein (LiHy), Leishmania-specific antigenic protein (LSAP), histone H1, and sterol 24-c-methyltransferase (SMT). To facilitate the oligomerization process, pentameric and trimeric coiled-coil domains were employed. RpfE, a resuscitation-promoting factor of Mycobacterium tuberculosis, was added to induce strong immune responses. Pentameric and trimeric coiled-coil domains as well as eight immunodominant epitopes from antigenic proteins of Leishmania infantum, the causative agent of VL, were joined together using appropriate linkers. High-quality 3D structure of monomeric and oligomeric structures followed by refinement and validation processes demonstrated that the designed nanovaccine could be considered to be a promising medication against the parasite; however, experimental validation is essential to confirm the effectiveness of the nanovaccine.

Chimeric Virus-like Particle-Based COVID-19 Vaccine Confers Strong Protection against SARS-CoV-2 Viremia in K18-hACE2 Mice

Virus-like particles (VLPs) are highly immunogenic and versatile subunit vaccines composed of multimeric viral proteins that mimic the whole virus but lack genetic material. Due to the lack of infectivity, VLPs are being developed as safe and effective vaccines against various infectious diseases. In this study, we generated a chimeric VLP-based COVID-19 vaccine stably produced by HEK293T cells. The chimeric VLPs contain the influenza virus A matrix (M1) proteins and the SARS-CoV-2 Wuhan strain spike (S) proteins with a deletion of the polybasic furin cleavage motif and a replacement of the transmembrane and cytoplasmic tail with that of the influenza virus hemagglutinin (HA). These resulting chimeric S-M1 VLPs, displaying S and M1, were observed to be enveloped particles that are heterogeneous in shape and size. The intramuscular vaccination of BALB/c mice in a prime-boost regimen elicited high titers of S-specific IgG and neutralizing antibodies. After immunization and a challenge with SARS-CoV-2 in K18-hACE2 mice, the S-M1 VLP vaccination resulted in a drastic reduction in viremia, as well as a decreased viral load in the lungs and improved survival rates compared to the control mice. Balanced Th1 and Th2 responses of activated S-specific T-cells were observed. Moderate degrees of inflammation and viral RNA in the lungs and brains were observed in the vaccinated group; however, brain lesion scores were less than in the PBS control. Overall, we demonstrate the immunogenicity of a chimeric VLP-based COVID-19 vaccine which confers strong protection against SARS-CoV-2 viremia in mice.

Novel Noninvasive Approaches to the Treatment of Obesity: From Pharmacotherapy to Gene Therapy

Recent insights into the pathophysiologic underlying mechanisms of obesity have led to the discovery of several promising drug targets and novel therapeutic strategies to address the global obesity epidemic and its comorbidities. Current pharmacologic options for obesity management are largely limited in number and of modest efficacy/safety profile. Therefore, the need for safe and more efficacious new agents is urgent. Drugs that are currently under investigation modulate targets across a broad range of systems and tissues, including the central nervous system, gastrointestinal hormones, adipose tissue, kidney, liver, and skeletal muscle. Beyond pharmacotherapeutics, other potential antiobesity strategies are being explored, including novel drug delivery systems, vaccines, modulation of the gut microbiome, and gene therapy. The present review summarizes the pathophysiology of energy homeostasis and highlights pathways being explored in the effort to develop novel antiobesity medications and interventions but does not cover devices and bariatric methods. Emerging pharmacologic agents and alternative approaches targeting these pathways and relevant research in both animals and humans are presented in detail. Special emphasis is given to treatment options at the end of the development pipeline and closer to the clinic (ie, compounds that have a higher chance to be added to our therapeutic armamentarium in the near future). Ultimately, advancements in our understanding of the pathophysiology and interindividual variation of obesity may lead to multimodal and personalized approaches to obesity treatment that will result in safe, effective, and sustainable weight loss until the root causes of the problem are identified and addressed.

Recombinant Protein Technology in the Challenging Era of Coronaviruses

Coronaviruses have caused devastation in both human and animal populations, affecting both health and the economy. Amidst the emergence and re-emergence of coronaviruses, humans need to surmount the health and economic threat of coronaviruses through science and evidence-based approaches. One of these approaches is through biotechnology, particularly the heterologous production of biopharmaceutical proteins. This review article briefly describes the genome, general virion morphology, and key structural proteins of different coronaviruses affecting animals and humans. In addition, this review paper also presents the different systems in recombinant protein technology such as bacteria, yeasts, plants, mammalian cells, and insect/insect cells systems used to express key structural proteins in the development of countermeasures such as diagnostics, prophylaxis, and therapeutics in the challenging era of coronaviruses.

Bio-mineralization of virus-like particles by metal-organic framework nanoparticles enhances the thermostability and immune responses of the vaccines

Virus-like particle (VLPs) vaccines have been extensively studied due to their good immunogenicity and safety; however, they highly rely on cold-chain storage and transportation. Nanotechnology of bio-mineralization as a useful strategy has been employed to improve the thermal stability and immunogenicity of VLPs. A zeolitic imidazole framework (ZIF-8), a core-shell structured nanocomposite, was applied to encapsulate foot-and-mouth disease virus (FMDV) VLPs. It was found that the ZIF-8 shell enhanced the heat resistance of VLPs and promoted their ability to be taken up by cells and escape from lysosomes. The VLPs-ZIF-8 easily activated antigen-presenting cells (APCs), triggered higher secretion levels of cytokines, and elicited stronger immune responses than VLPs alone even after being treated at 37 °C for 7 days. This platform has good potential in the development of VLP-based vaccine products without transportation.

A global survey in the developmental landscape of possible vaccination strategies for COVID-19

The development of COVID-19 vaccines was promptly regulated to ensure the best possible approach. By January 2022, 75 candidates reached preclinical evaluation in various animal models, 114 vaccines were in clinical trials on humans, and 48 were in the final testing stages. Vaccine platforms range from whole virus vaccines to nucleic acid vaccines, which are the most promising in prompt availability and safety. The USA and Europe have approved vaccines developed by Pfizer-BioNTech (BNT162b2) and Moderna (mRNa1273). So far, Pfizer-BioNTech, Moderna, Johnson & Johnson, AstraZeneca-University of Oxford, Sinopharm, Sinovac Biotech Gamaleya, Bharat Biotech, and Novavax have documented effective vaccines. Even with technological advances and a fast-paced development approach, many limitations and problems need to be overcome before a large-scale production of new vaccines can start. The Key is to ensure equal and fair distribution globally through regulatory measures. Recent studies link Bacillus Calmette-Guérin (BCG) vaccination programs and lower disease severity.

Toward rational vaccine engineering

Technological revolutions in several fields have pushed the boundaries of vaccine design and provided new avenues for vaccine development. Next-generation vaccine platforms have shown promise in targeting challenging antigens, for which traditional approaches have been ineffective. With advances in protein engineering, structural biology, computational biology and immunology, the structural vaccinology approach, which uses protein structure information to develop immunogens, holds promise for future vaccine design. In this review, we highlight various vaccine development strategies, along with their advantages and limitations. We discuss the rational vaccine design approach, which focuses on structure-based vaccine design. Finally, we discuss antigen engineering using the epitope-scaffold approach, gaps in structural vaccinology, and remaining challenges in vaccine design.

Characterization of Immune Response towards Generation of Universal Anti-HA-Stalk Antibodies after Immunization of Broiler Hens with Triple H5N1/NA-HA-M1 VLPs

(1) Background: Avian influenza viruses (AIVs) promptly evade preexisting immunity by constantly altering the immunodominant neutralizing antibody epitopes (antigenic drift) or by procuring new envelope serotypes (antigenic shift). As a consequence, the majority of antibodies elicited by infection or vaccination protect only against closely related strains. The immunodominance of the globular head of the main glycoprotein has been shown to mask the immunogenicity of the conserved regions located within the hemagglutinin (HA) protein. It has been shown that the broadly neutralizing universal antibodies recognize the HA2 domain in headless hemagglutinin (HA-stalk). Therefore, the HA-stalk is a highly conserved antigen, which makes it a good candidate to be used in universal vaccine development against AIVs. (2) Methods: Sf9 insect cells were used to produce triple H5N1/NA-HA-M1 influenza virus-like particles (VLPs) via co-expression of neuraminidase, hemagglutinin and matrix proteins from a tricistronic expression cassette. Purified influenza VLPs were used to immunize broiler hens. An in-depth characterization of the immune response was performed with an emphasis on the pool of elicited universal antibodies. (3) Results: Our findings suggest, that after vaccination with triple H5N1/NA-HA-M1 VLPs, hens generate a pool of broad-spectrum universal anti-HA-stalk antibodies. Furthermore, these universal antibodies are able to recognize the mammalian-derived HA-stalk recombinant proteins from homologous H5N1 and heterologous H7N9 AIVs as well as from the heterosubtypic human H1N1 influenza strain. (4) Conclusions: Our findings may suggest that highly pathogenic avian influenza H5 HA protein contain functional epitopes that are attractive targets for the generation of broad-spectrum antibodies against AIVs in their native hosts.

Protective effect of bivalent H1N1 and H3N2 VLP vaccines against Eurasian avian-like H1N1 and recent human-like H3N2 influenza viruses in a mouse model

Eurasian avian-like (EA) H1N1 swine influenza viruses (SIVs) are currently the most prevalent SIVs in Chinese swine populations, but recent human-like H3N2 SIV subtypes have also been frequently isolated. Hence, there is an urgent need to develop an effective vaccine against both EA H1N1 and recent human-like H3N2 infections. In this study, we utilized the baculovirus expression system to produce virus-like particles (VLPs) containing hemagglutinin protein (HA) and matrix protein (M1) based on A/Swine/Guangdong/YJ4/2014 (H1N1) and A/swine/Guangdong/L22/2010 (H3N2). An immunological experiment showed that in a mouse model, bivalent VLP vaccines against H1N1 and H3N2 can induce stronger humoral and cellular immune responses than whole influenza virus vaccines. Compared with monovalent inactivated vaccines that cannot offer protection against different SIV subtypes, monovalent H1N1 or H3N2 VLP vaccines can provide partial protection against lethal challenge by viruses of different subtypes. Meanwhile, bivalent VLP vaccines against H1N1 and H3N2 can provide full protection against lethal doses of homologous and heterologous viruses belonging to the EA H1N1 or recent human-like H3N2 lineage. These results suggest a promising approach to the development of vaccines against SIVs.

Downstream processing of virus-like particles with aqueous two-phase systems: applications and challenges

The advancement of recombinant virus-like particle-based vaccines has attracted global attention owing to substantially safety and high efficacy in provoking a protective immunity against various chronic and infectious diseases in humans and animals. A robust, low-cost and scalability separation and purification technology is of utmost importance in the downstream processing of recombinant virus-like particles to produce affordable and safe vaccines. Being a relatively simple, environmentally friendly and efficient biomolecules recovery approach, aqueous two-phase systems have received great attention from researchers worldwide. This review aims to highlight the challenges and outlook in addition to the current applications of aqueous two-phase systems in downstream processing of virus-like particles. The efforts will confidently reinforce scholars' knowledge and fill in the valuable research gap in the aspect of concerning recombinant virus-like particle-based vaccines development, particularly related to the virus-like particles downstream production processes. This article is protected by copyright. All rights reserved.