Live attenuated and inactivated viral vaccine formulation and nasal delivery: potential and challenges

Thermostable vacuum foam dried Newcastle disease vaccine: Process optimization and pilot-scale study

Vacuum foam drying (VFD) has been shown to improve the thermostability and long-term shelf life of Newcastle Disease Virus (NDV). This study optimized the VFD process to improve the shelf life of NDV at laboratory-scale and then tested the optimized conditions at pilot-scale. The optimal NDV to T5 formulation ratio was determined to be 1:1 or 3:2. Using the 1:1 virus to formulation ratio, the optimal filling volumes were determined to be 13-17% of the vial capacity. The optimized VFD process conditions were determined to be at a shelf temperature of 25℃ with a minimum overall drying time of 44 h. The vaccine samples prepared using these optimized conditions at laboratory-scale exhibited virus titer losses of ≤ 1.0 log10 with residual moisture content (RMC) below 3%. Furthermore, these samples were transported for 97 days around China at ambient temperature without significant titer loss, thus demonstrating the thermostability of the NDV-VFD vaccine. Pilot-scale testing of the NDV-VFD vaccine at optimized conditions showed promising results for up-scaling the process as the RMC was below 3%. However, the virus titer loss was slightly above 1.0 log10 (approximately 1.1 log10). Therefore, the NDV-VFD process requires further optimization at pilot scale to obtain a titer loss of ≤ 1.0 log10. Results from this study provide important guidance for possible industrialization of NDV-VFD vaccine in the future. KEY POINTS: • The process optimization and scale-up test of thermostable NDV vaccine prepared through VFD is reported for the first time in this study. • The live attenuated NDV-VFD vaccine maintained thermostability for 97 days during long distance transportation in summer without cold chain conditions. • The optimized NDV-VFD vaccine preparations evaluated at pilot-scale maintained acceptable levels of infectivity after preservation at 37℃ for 90 days, which demonstrated the feasibility of the vaccine for industrialization.

Analysis of the Immunogenicity of African Swine Fever F317L Protein and Screening of T Cell Epitopes

The African swine fever virus (ASFV) encodes numerous proteins characterized by complex immune escape mechanisms. At present, the structure and function of these proteins, including the F317L protein, have yet to be fully elucidated. In this study, we examined the immunogenicity of the F317L protein. Mice were subcutaneously immunized with the F317L protein using initial and subsequent booster doses, and, at the 28th day post-treatment, we assessed the humoral and cellular immune responses of mice. The F317L protein stimulated production of specific antibodies and activated humoral immune responses. In addition, F317L stimulated the production of large amounts of IFN-γ by splenic lymphocytes, thereby activating cellular immune responses. Using informatics technology, we predicted and synthesized 29 F317L protein T cell epitopes, which were screened using IFN-γ ELISpot. Among these, the F25 (246SRRSLVNPWT255) peptide was identified as having a stronger stimulatory effect than the full-length protein. Collectively, our findings revealed that the ASFV F317L protein can stimulate both strong humoral and cellular immunity in mice, and that the F25 (246SRRSLVNPWT255) peptide may be a potential active T cell epitope. These findings will provide a reference for further in-depth studies of the F317L protein and screening of antigenic epitopes.

Recent progress and major gaps in the vaccine development for African swine fever

The swine industry across the globe is recently facing a devastating situation imparted by a highly contagious and deadly viral disease, African swine fever. The disease is caused by a DNA virus, the African swine fever virus (ASFV) of the genus Asfivirus. ASFV affects both wild boars and domestic pigs resulting in an acute form of hemorrhagic fever. Since the first report in 1921, the disease remains endemic in some of the African countries. However, the recent occurrence of ASF outbreaks in Asia led to a fresh and formidable challenge to the global swine production industry. Culling of the infected animals along with the implementation of strict sanitary measures remains the only options to control this devastating disease. Efforts to develop an effective and safe vaccine against ASF began as early as in the mid-1960s. Different approaches have been employed for the development of effective ASF vaccines including inactivated vaccines, subunit vaccines, DNA vaccines, virus-vectored vaccines, and live attenuated vaccines (LAVs). Inactivated vaccines are a non-feasible strategy against ASF due to their inability to generate a complete cellular immune response. However genetically engineered vaccines, such as subunit vaccines, DNA vaccines, and virus vector vaccines, represent tailored approaches with minimal adverse effects and enhanced safety profiles. As per the available data, gene deleted LAVs appear to be the most potential vaccine candidates. Currently, a gene deleted LAV (ASFV-G-∆I177L), developed in Vietnam, stands as the sole commercially available vaccine against ASF. The major barrier to the goal of developing an effective vaccine is the critical gaps in the knowledge of ASFV biology and the immune response induced by ASFV infection. The precise contribution of various hosts, vectors, and environmental factors in the virus transmission must also be investigated in depth to unravel the disease epidemiology. In this review, we mainly focus on the recent progress in vaccine development against ASF and the major gaps associated with it.

Design Rules for the Sequestration of Viruses into Polypeptide Complex Coacervates

Encapsulation is a strategy that has been used to facilitate the delivery and increase the stability of proteins and viruses. Here, we investigate the encapsulation of viruses via complex coacervation, which is a liquid-liquid phase separation resulting from the complexation of oppositely charged polymers. In particular, we utilized polypeptide-based coacervates and explored the effects of peptide chemistry, chain length, charge patterning, and hydrophobicity to better understand the effects of the coacervating polypeptides on virus incorporation. Our study utilized two nonenveloped viruses, porcine parvovirus (PPV) and human rhinovirus (HRV). PPV has a higher charge density than HRV, and they both appear to be relatively hydrophobic. These viruses were compared to characterize how the charge, hydrophobicity, and patterning of chemistry on the surface of the virus capsid affects encapsulation. Consistent with the electrostatic nature of complex coacervation, our results suggest that electrostatic effects associated with the net charge of both the virus and polypeptide dominated the potential for incorporating the virus into a coacervate, with clustering of charges also playing a significant role. Additionally, the hydrophobicity of a virus appears to determine the degree to which increasing the hydrophobicity of the coacervating peptides can enhance virus uptake. Nonintuitive trends in uptake were observed with regard to both charge patterning and polypeptide chain length, with these parameters having a significant effect on the range of coacervate compositions over which virus incorporation was observed. These results provide insights into biophysical mechanisms, where sequence effects can control the uptake of proteins or viruses into biological condensates and provide insights for use in formulation strategies.

MA, Tovar-Rosero YY, Oñate AA, O'Ryan M. Two centuries of vaccination: historical and conceptual approach and future perspectives

Over the past two centuries, vaccines have been critical for the prevention of infectious diseases and are considered milestones in the medical and public health history. The World Health Organization estimates that vaccination currently prevents approximately 3.5-5 million deaths annually, attributed to diseases such as diphtheria, tetanus, pertussis, influenza, and measles. Vaccination has been instrumental in eradicating important pathogens, including the smallpox virus and wild poliovirus types 2 and 3. This narrative review offers a detailed journey through the history and advancements in vaccinology, tailored for healthcare workers. It traces pivotal milestones, beginning with the variolation practices in the early 17th century, the development of the first smallpox vaccine, and the continuous evolution and innovation in vaccine development up to the present day. We also briefly review immunological principles underlying vaccination, as well as the main vaccine types, with a special mention of the recently introduced mRNA vaccine technology. Additionally, we discuss the broad benefits of vaccines, including their role in reducing morbidity and mortality, and in fostering socioeconomic development in communities. Finally, we address the issue of vaccine hesitancy and discuss effective strategies to promote vaccine acceptance. Research, collaboration, and the widespread acceptance and use of vaccines are imperative for the continued success of vaccination programs in controlling and ultimately eradicating infectious diseases.

DNA Nanostructures: Self-Adjuvant Carriers for Highly Efficient Subunit Vaccines

Subunit vaccines based on antigen proteins or epitopes of pathogens or tumors show advantages in immunological precision and high safety, but are often limited by their low immunogenicity. Adjuvants can boost immune responses by stimulating immune cells or promoting antigen uptake by antigen presenting cells (APCs), yet existing clinical adjuvants struggle in simultaneously achieving these dual functions. Additionally, the spatial organization of antigens might be crucial to their immunogenicity. Hence, superior adjuvants should potently stimulate the immune system, precisely arrange antigens, and effectively deliver antigens to APCs. Recently, precisely organizing and delivering antigens with the unique editability of DNA nanostructures has been proposed, presenting unique abilities in significantly improving the immunogenicity of antigens. In this minireview, we will discuss the principles behind using DNA nanostructures as self-adjuvant carriers and review the latest advancements in this field. The potential and challenges associated with self-adjuvant DNA nanostructures will also be discussed.

Transcriptome Analysis of Peritoneal Cells Reveals the Early Immune Response of Flounder (Paralichthys olivaceus) to Inactivated Vibrio anguillarum Immunization

Vibrio anguillarum (V. anguillarum) is a bacterium that seriously harms flounder and other aquaculture species. Vaccination is an effective means of preventing vibriosis and is mainly administered by intraperitoneal injection. Effective antigen processing at the initial stage of immunization is essential to elicit adaptive immune responses and improve vaccine efficacy. To understand the early immune response of flounder caused by inactivated V. anguillarum, we detected the transcriptome profiles of the cells in the peritoneal cavity (PoPerCs) after inactivated V. anguillarum immunization. More than 10 billion high-quality reads were obtained, of which about 89.33% were successfully mapped to the reference genome of flounder. A total of 1985, 3072, 4001, and 5476 differentially expressed genes were captured at 6, 12, 24, and 48 h post immunization, respectively. The hub module correlated with the immunization time was identified by WGCNA. GO and KEGG analysis showed that hub module genes were abundantly expressed in various immune-related aspects, including the response to stimuli, the immune system process, signal transducer activity, autophagy, the NOD-like receptor signaling pathway, the toll-like receptor signaling pathway, the T cell receptor signaling pathway, and Th17 cell differentiation. Additionally, genes related to Th cell differentiation are presented as heatmaps. These genes constitute a complex immune regulatory network, mainly involved in pathogen recognition, antigen processing and presentation, and Th cell differentiation. The results of this study provide the first transcriptome profile of PoPerCs associated with inactivated V. anguillarum immunity and lay a solid foundation for further studies on effective V. anguillarum vaccines.

An investigation of excipients for a stable Orf viral vector formulation

The Orf virus (ORFV) is a promising candidate for vector vaccines as well as for immunomodulatory and oncolytic therapies. However, few publications are available on its infectivity degradation or on suitable additives for prolonging its viral stability. In this study, the non-supplemented ORFV itself showed a very high stability at storage temperatures up to 28 °C, with a linear titer loss of 0.10 log infectious particles per day at 4 °C over a period of five weeks. To prolong this inherent stability, thirty additives, i.e., detergents, sugars, proteins, salts, and buffers as well as amino acids, were tested for their time- and temperature-dependent influence on the ORFV infectivity. A stabilizing effect on the infectivity was identified for the addition of all tested proteins, i.e., gelatine, bovine serum albumin, and recombinant human serum albumin (rHSA), of several sugars, i.e., mannitol, galactose, sucrose, and trehalose, of amino acids, i.e., arginine and proline, of the detergent Pluronic F68, and of the salt Na2SO4. The infectivity preservation was especially pronounced for proteins in liquid and frozen formulations, sugars in frozen state, and arginine und Pluronic in liquid formulations at high storage temperatures (37 °C). The addition of 1% rHSA with and without 5% sucrose was evaluated as a very stable formulation with a high safety profile and economic validity at storage temperatures up to 28 °C. At increased temperatures, the supplementation with 200 mM arginine performed better than with rHSA. In summary, this comprehensive data provides different options for a stable ORFV formulation, considering temperature, storage time, economic aspects, and downstream processing integrity.

An attenuated strain of cyprinid herpesvirus 2 as a vaccine candidate against herpesviral hematopoietic necrosis disease in gibel carp, Carassius auratus gibelio

Herpesviral hematopoietic necrosis disease causes by cyprinid herpesvirus 2 (CyHV-2) infection is a high mortality disease that leads to great economic damage to gibel carp, Carassius auratus gibelio aquaculture. In this study, an attenuated strain of CyHV-2 G-RP7 was achieved by subculture on RyuF-2 cells derived from the fin of Ryukin-variety goldfish and GiCF cells derived from fin of gibel carp. As the attenuated vaccine candidate, there are no clinical symptoms of gibel carp that immersion or intraperitoneal injection with G-RP7 strain. The protection rates of G-PR7 to gibel carp by immersion and intraperitoneal injection were 92% and 100%, respectively. In the test for virulence reversion, the candidate was propagated through gibel carp six times by intraperitoneal injection with kidney and spleen homogenate of the inoculated fish. During in vivo passages in gibel carp, no abnormality and mortality of the inoculated fish were observed, and the virus DNA copies maintain a low level from the first passage to the sixth passage. The dynamic of virus DNA in each tissue of G-RP7 vaccination fish increased within 1, 3, and 5 days post-immunization, and subsequently decreased and stabilized within 7 and 14 days. In addition, the increase of anti-virus antibody titer was detected both immersion and injection immunization fish 21 days after vaccination by ELISA. These results demonstrated that G-RP7 can be a promising live attenuated vaccine candidate against the disease.

Nano-adjuvanted dry powder vaccine for the mucosal immunization against airways pathogens

Nasal vaccination has been shown to provide optimal protection against respiratory pathogens. However, mucosal vaccination requires the implementation of specific immunization strategies to improve its effectiveness. Nanotechnology appears a key approach to improve the effectiveness of mucosal vaccines, since several nanomaterials provide mucoadhesion, enhance mucosal permeability, control antigen release and possess adjuvant properties. Mycoplasma hyopneumoniae is the main causative agent of enzootic pneumonia in pigs, a respiratory disease responsible for considerable economic losses in the pig farming worldwide. The present work developed, characterized, and tested in vivo an innovative dry powder nasal vaccine, obtained from the deposition on a solid carrier of an inactivated antigen and a chitosan-coated nanoemulsion, as an adjuvant. The nanoemulsion was obtained through a low-energy emulsification technique, a method that allowed to achieve nano droplets in the order of 200 nm. The oil phase selected was alpha-tocopherol, sunflower oil, and poly(ethylene glycol) hydroxystearate used as non-ionic tensioactive. The aqueous phase contained chitosan, which provides a positive charge to the emulsion, conferring mucoadhesive properties and favoring interactions with inactivated M. hyopneumoniae. Finally, the nanoemulsion was layered with a mild and scalable process onto a suitable solid carrier (i.e., lactose, mannitol, or calcium carbonate) to be transformed into a solid dosage form for administration as dry powder. In the experimental study, the nasal vaccine formulation with calcium carbonate was administered to piglets and compared to intramuscular administration of a commercial vaccine and of the dry powder without antigen, aimed at evaluating the ability of IN vaccination to elicit an in vivo local immune response and a systemic immune response. Intranasal vaccination was characterized by a significantly higher immune response in the nasal mucosa at 7 days post-vaccination, elicited comparable levels of Mycoplasma-specific IFN-γ secreting cells and comparable, if not higher, responsiveness of B cells expressing IgA and IgG in peripheral blood mononuclear cells, with those detected upon a conventional intramuscular immunization. In conclusion, this study illustrates a simple and effective strategy for the development of a dry powder vaccine formulation for nasal administration which could be used as alternative to current parenteral commercial vaccines.

Recent advances in respiratory immunization: A focus on COVID-19 vaccines

The development of vaccines has always been an essential task worldwide since vaccines are regarded as powerful weapons in protecting the global population. Although the vast majority of currently authorized human vaccinations are administered intramuscularly or subcutaneously, exploring novel routes of immunization has been a prominent area of study in recent years. This is particularly relevant in the face of pandemic diseases, such as COVID-19, where respiratory immunization offers distinct advantages, such as inducing systemic and mucosal responses to prevent viral infections in both the upper and lower respiratory tracts and also leading to higher patient compliance. However, the development of respiratory vaccines confronts challenges due to the physiological barriers of the respiratory tract, with most of these vaccines still in the research and development stage. In this review, we detail the structure of the respiratory tract and the mechanisms of mucosal immunity, as well as the obstacles to respiratory vaccination. We also examine the considerations necessary in constructing a COVID-19 respiratory vaccine, including the dosage form of the vaccines, potential excipients and mucosal adjuvants, and delivery systems and devices for respiratory vaccines. Finally, we present a comprehensive overview of the COVID-19 respiratory vaccines currently under clinical investigation. We hope this review can provide valuable insights and inspiration for the future development of respiratory vaccinations.

In Vitro Comparison of Local Nasal Vaccine Delivery and Correlation with Device Spray Performance

PURPOSE

This study is the first vaccine candidate in vitro investigation with a focus on finding a correlation between the spray characteristics and the delivery efficiency of the local deposition in the nasal airways of infants under 24 months using various intranasal devices.

METHODS

In vitro tests were developed to measure the spray characteristics of four intranasal delivery devices and how they regionally deliver a candidate vaccine formulation matrix in five nasal airway replicas (3 to 24 months). The correlation between the spray performance, geometric parameters, and delivery efficiency were assessed.

RESULTS

All four devices performed consistently in terms of spray characteristics and were capable of delivering a high percentage of the candidate vaccine to the target areas, with a minimum delivery efficiency of 80%. Moreover, the delivery efficiency was affected by either the spray droplet size distribution or the distance between the nozzle tip and the internal nasal valve. Correlations between the spray performance and the in vitro local dose deposition were established.

CONCLUSION

The infant nasal model tests can be complementary to device spray performance evaluation. In the absence of in vivo correlations, they can also facilitate the process of new product development by estimating delivery a priori.

Recent advancement, immune responses, and mechanism of action of various vaccines against intracellular bacterial infections

Emerging and re-emerging bacterial infections are a serious threat to human and animal health. Extracellular bacteria are free-living, while facultative intracellular bacteria replicate inside eukaryotic host cells. Many serious human illnesses are now known to be caused by intracellular bacteria such as Salmonella enterica, Escherichia coli, Staphylococcus aureus, Rickettsia massiliae, Chlamydia species, Brucella abortus, Mycobacterium tuberculosis and Listeria monocytogenes, which result in substantial morbidity and mortality. Pathogens like Mycobacterium, Brucella, MRSA, Shigella, Listeria, and Salmonella can infiltrate and persist in mammalian host cells, particularly macrophages, where they proliferate and establish a repository, resulting in chronic and recurrent infections. The current treatment for these bacteria involves the application of narrow-spectrum antibiotics. FDA-approved vaccines against obligate intracellular bacterial infections are lacking. The development of vaccines against intracellular pathogenic bacteria are more difficult because host defense against these bacteria requires the activation of the cell-mediated pathway of the immune system, such as CD8+ T and CD4+ T. However, different types of vaccines, including live, attenuated, subunit, killed whole cell, nano-based and DNA vaccines are currently in clinical trials. Substantial development has been made in various vaccine strategies against intracellular pathogenic bacteria. This review focuses on the mechanism of intracellular bacterial infection, host immune response, and recent advancements in vaccine development strategies against various obligate intracellular bacterial infections.

Tilapia Lake Virus Vaccine Development: A Review on the Recent Advances

Tilapia tilapinevirus (or tilapia lake virus, TiLV) is a recently emerging virus associated with a novel disease affecting and decimating tilapia populations around the world. Since its initial identification, TiLV has been reported in 17 countries, often causing mortalities as high as 90% in the affected populations. To date, no therapeutics or commercial vaccines exist for TiLV disease control. Tilapia exposed to TiLV can develop protective immunity, suggesting that vaccination is achievable. Given the important role of vaccination in fish farming, several vaccine strategies are currently being explored and put forward against TiLV but, a comprehensive overview on the efficacy of these platforms is lacking. We here present these approaches in relation with previously developed fish vaccines and discuss their efficacy, vaccine administration routes, and the various factors that can impact vaccine efficacy. The overall recent advances in TiLV vaccine development show different but promising levels of protection. The field is however hampered by the lack of knowledge of the biology of TiLV, notably the function of its genes. Further research and the incorporation of several approaches including prime-boost vaccine regimens, codon optimization, or reverse vaccinology would be beneficial to increase the effectiveness of vaccines targeting TiLV and are further discussed in this review.

Mucus adhesion vs. mucus penetration? Screening nanomaterials for nasal inhalation by MD simulation

Nanocarrier-aided drug delivery techniques have improved the absorption and permeability of drugs in nose-to-brain delivery. However, the molecular properties of nanocarriers during the delivery process are of great interest; in particular, the characteristics when penetrating barriers in vivo are crucial for the screening and optimization of materials for nasal inhalation. In this study, we have focused on two types of delivery systems: mucoadhesive nanoparticles (MAPs) and mucopenetrating nanoparticles (MPPs); both have been widely used for mucosal delivery, although a method for selecting the more effective type of drug carriers for mucosal delivery has not been established. Molecular dynamics (MD) simulations were used to reveal the all-atom dynamic characteristics of the interaction between different delivery systems and the nasal mucus protein MUC5AC. Among the systems tested, hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) had the strongest interaction with mucin, suggesting it had better mucoadhesive performance, and that it interacted with MUC5AC more strongly than unmodified chitosan. In contrast, the mucus-penetrating material polyethylene glycol-poly lactic acid-co-glycolic acid (PEG-PLGA), had almost no interaction with MUC5AC. The results of the MD simulations were verified by in vitro experiments on nanoparticles (NPs) and mucin binding. The drug delivery performance of the four types of NPs, analyzed by in vitro and ex vivo mucosal penetration, were all generally consistent with the properties of the material predicted from the MD simulation. These clues to the molecular mechanism of MAPs and MPPs may provide useful insight into the screening and optimization of nanomaterials suitable for nasal inhalation.

Vaccines for African swine fever: an update

African swine fever (ASF) is a fatal infectious disease of swine caused by the African swine fever virus (ASFV). Currently, the disease is listed as a legally notifiable disease that must be reported to the World Organization for Animal Health (WOAH). The economic losses to the global pig industry have been insurmountable since the outbreak of ASF. Control and eradication of ASF are very critical during the current pandemic. Vaccination is the optimal strategy to prevent and control the ASF epidemic, but since inactivated ASFV vaccines have poor immune protection and there aren't enough cell lines for efficient in vitro ASFV replication, an ASF vaccine with high immunoprotective potential still remains to be explored. Knowledge of the course of disease evolution, the way of virus transmission, and the breakthrough point of vaccine design will facilitate the development of an ASF vaccine. In this review, the paper aims to highlight the recent advances and breakthroughs in the epidemic and transmission of ASF, virus mutation, and the development of vaccines in recent years, focusing on future directions and trends.

Induction of attenuated Nocardia seriolae and their use as live vaccine trials against fish nocardiosis

Nocardia seriolae, a Gram-positive facultative intercellular pathogen, has been identified as the causative agent of fish nocardiosis, causing substantial mortality and morbidity of a wide range of fish species. Looking into that fact, the effective vaccine against this pathogen is urgently needed to control the significant losses in aquaculture practices. In order to induct attenuated strains for developing the potential live vaccines, the mutagenic N. seriolae strain S-250 and U-20 were obtained from wild-type strain ZJ0503 through continuous passaging and ultraviolet (UV) irradiation, respectively. Additionally, the biological characteristic, virulence, stability, mediating immune response and supplying protective efficacy to hybrid snakehead of the S-250 and U-20 strains were determined in the present study. The results showed that U-20 strain displayed dramatic changes in morphological characteristic and significant decreased in the virulence to hybrid snakehead, while that of S-250 strain had no obvious different in comparison to ZJ0503 strain. When hybrid snakehead were intraperitoneally injected with ZJ0503, S-250 and U-20 strains at their respective sub-clinical dosage, the non-specific immunity parameters (serum LYZ, POD, ACP, AKP and SOD activities), specific antibody (IgM) titers production and immune-related genes (CC1, CC2, IL-1β, IL-8, TNFα, IFNγ, MHCIα, MHCIIα, CD4, CD8α, TCRα and TCRβ) expression were up-regulated, indicating that they were able to trigger humoral and cell-mediated immune responses. Furthermore, the protective efficacy in hybrid snakehead after vaccination with ZJ0503, S-250 and U-20 strains, in terms of relative percentage survival (RPS), were 28.85%, 56.89% and 89.65% respectively. Taken together, two attenuated N. seriolae strains S-250 and U-20 were obtained successfully and they could elicit strong immune response and supply protective efficacy to hybrid snakehead against N. seriolae, which suggested that these two attenuated strains were the potential candidates for live vaccine development to control fish nocardiosis in aquaculture.

Mucosal delivery of nanovaccine strategy against COVID-19 and its variants

Despite the global administration of approved COVID-19 vaccines (e.g., ChAdOx1 nCoV-19®, mRNA-1273®, BNT162b2®), the number of infections and fatalities continue to rise at an alarming rate because of the new variants such as Omicron and its subvariants. Including COVID-19 vaccines that are licensed for human use, most of the vaccines that are currently in clinical trials are administered via parenteral route. However, it has been proven that the parenteral vaccines do not induce localized immunity in the upper respiratory mucosal surface, and administration of the currently approved vaccines does not necessarily lead to sterilizing immunity. This further supports the necessity of a mucosal vaccine that blocks the main entrance route of COVID-19: nasal and oral mucosal surfaces. Understanding the mechanism of immune regulation of M cells and dendritic cells and targeting them can be another promising approach for the successful stimulation of the mucosal immune system. This paper reviews the basic mechanisms of the mucosal immunity elicited by mucosal vaccines and summarizes the practical aspects and challenges of nanotechnology-based vaccine platform development, as well as ligand hybrid nanoparticles as potentially effective target delivery agents for mucosal vaccines.

Chitosan-Based Nanomaterial as Immune Adjuvant and Delivery Carrier for Vaccines

With the support of modern biotechnology, vaccine technology continues to iterate. The safety and efficacy of vaccines are some of the most important areas of development in the field. As a natural substance, chitosan is widely used in numerous fields-such as immune stimulation, drug delivery, wound healing, and antibacterial procedures-due to its good biocompatibility, low toxicity, biodegradability, and adhesion. Chitosan-based nanoparticles (NPs) have attracted extensive attention with respect to vaccine adjuvants and delivery systems due to their excellent properties, which can effectively enhance immune responses. Here, we list the classifications and mechanisms of action of vaccine adjuvants. At the same time, the preparation methods of chitosan, its NPs, and their mechanism of action in the delivery system are introduced. The extensive applications of chitosan and its NPs in protein vaccines and nucleic acid vaccines are also introduced. This paper reviewed the latest research progress of chitosan-based NPs in vaccine adjuvant and drug delivery systems.

Susceptibility to SARS-CoV-2 Omicron following ChAdOx1 nCoV-19 and BNT162b2 versus CoronaVac vaccination

The emergence of SARS-CoV-2 variants raises concerns of reduced COVID-19 vaccine efficacy. We investigated the humoral immunity in uninfected and previously infected ChAdOx1 nCoV-19, BNT162b2 and CoronaVac vaccinees, who have received complete regimes of vaccines by means of a SARS-CoV-2 surrogate virus blocking test. The ChAdOx1 nCoV-19 (p = 0.0013) and BNT162b2 (p = 0.0005) vaccines induced significant higher blocking activity with longer durability against the Spike (S) protein receptor binding domain (RBD) of wild type SARS-CoV-2 than the CoronaVac vaccine in uninfected vaccinees. Prior infection improved protection in the CoronaVac vaccinees. Subsequent investigation on the breadth of SARS-CoV-2 vaccine-induced antibody blocking responses, revealed that all vaccine platforms cross-protected uninfected vaccinees against all variant of concerns, except Omicron. Prior infection protected the ChAdOx1 nCoV-19 and BNT162b2 vaccinees against Omicron but not CoronaVac vaccinees. Our study suggests that vaccines that induce broader sterilizing immunity are essential to fight against fast-emerging variants.

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ChAdOx1 nCoV-19, BNT162b2, and CoronaVac did not protect against Omicron variant

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Combination of prior infection and ChAdOx1 nCoV-19 or BNT162b2 cross-protected against Omicron variant

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The CoronaVac vaccine had no protective effect against Omicron regardless of infection status

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Prolonged target antigen exposure and target diversification are key for next SARS-CoV-2 vaccines

The Mucoadhesive Nanoparticle-Based Delivery System in the Development of Mucosal Vaccines

Mucosal tissue constitutes the largest interface between the body and the external environment, regulating the entry of pathogens, particles, and molecules. Mucosal immunization is the most effective way to trigger a protective mucosal immune response. However, the majority of the currently licensed vaccines are recommended to be administered by intramuscular injection, which has obvious shortcomings, such as high production costs, low patient compliance, and lack of mucosal immune response. Strategies for eliciting mucosal and systemic immune responses are being developed, including appropriate vaccine adjuvant, delivery system, and bacterial or viral vectors. Biodegradable mucoadhesive nanoparticles (NPs) are the most promising candidate for vaccine delivery systems due to their inherent immune adjuvant property and the ability to protect the antigen from degradation, sustain the release of loaded antigen, and increase the residence time of antigen at the administration site. The current review outlined the complex structure of mucosa, the mechanism of interaction between NPs and mucosa, factors affecting the mucoadhesion of NPs, and the application of the delivery system based on mucoadhesive NPs in the field of vaccines. Moreover, this review demonstrated that the biodegradable and mucoadhesive NP-based delivery system has the potential for mucosal administration of vaccines.

Spray dried powders for nasal delivery: Process and formulation considerations

Powders for nasal delivery have been recognized as advantageous dosage forms over liquids due to increased stability and residence time on nasal mucosa, with improved bioavailability. They can be manufactured by spray-drying, allowing the optimization of the particle properties that are critical to guarantee nasal deposition, as size and shape. It is also a scalable and flexible method already explored extensively in the pharmaceutical industry. However, it is important to understand how process parameters, particle physical properties and formulation considerations affect the product performance. Hence, this review aims to provide an overview of nasal powder formulation and processing through spray drying, with an emphasis on the variables that impact on performance. To this purpose, we describe the physical, biological and pharmacological phenomena prior to drug absorption as well as the most relevant powder properties. Formulation considerations including qualitative and quantitative composition are then reviewed, as well as manufacturing considerations including spray drying relevant parameters.

Fabrication of subunit nanovaccines by physical interaction

Vaccines can improve the quality of human life by preventing the burden of infectious diseases. Also, vaccination is becoming a powerful medication for preventing and treating tumors. Various vaccines have been developed based on the origin of the antigens. Herein, we focus on the subunit vaccines whose antigens are proteins or peptides. The advantage of subunit vaccines is safety for recipients; however, the immunogenicity of subunit antigens is relatively low. Nanoparticular delivery systems have been applied to improve the immunocompetence of subunit vaccines by targeting lymph nodes, and effectively present antigens to immune cells. Moreover, adding appropriate molecular adjuvants may strengthen the antigens to elicit immune response. In this perspective article, we first elucidate the characteristics of immunity induced by subunit nanovaccines and then summarize the strategies to fabricate subunit nanovaccines with delivering materials. Herein we highlight non-covalent interaction to fabricate nanoparticular subunit vaccines.

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

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

The race for a COVID-19 vaccine: where are we up to?

INTRODUCTION

A novel strain of coronavirus, SARS-CoV-2, has triggered a global pandemic of coronavirus disease (COVID-19) in late 2019. In January 2020, the WHO declared this pandemic a public health emergency. This pandemic has already caused over 5.3 million deaths from more than 272 million infections. The development of a successful vaccine is an urgent global priority to halt the spread of SARS-CoV-2 and prevent further fatalities. Researchers are fast-tracking this process, and there have already been significant developments in preclinical and clinical phases in a relatively short period of time. Some vaccines have been approved either for emergency use or mass application in recent months.

AREAS COVERED

Herein, we provide a general understanding of the fast-tracked clinical trial procedures and highlight recent successes in preclinical and clinical trials to generate a clearer picture of the progress of COVID-19 vaccine development.

EXPERT OPINION

A good number of vaccines have been rolled out within a short period a feat unprecedented in medical history. However, the emergence of new variants over time has appeared as a new threat, and the number of infections and casualties is still on the rise and this is going to be an ongoing battle.

Intranasal vaccine: Factors to consider in research and development

Most existing vaccines for human use are administered by needle-based injection. Administering vaccines needle-free intranasally has numerous advantages over by needle-based injection, but there are only a few intranasal vaccines that are currently approved for human use, and all of them are live attenuated influenza virus vaccines. Clearly, there are immunological as well as non-immunological challenges that prevent vaccine developers from choosing the intranasal route of administration. We reviewed current approved intranasal vaccines and pipelines and described the target of intranasal vaccines, i.e. nose and lymphoid tissues in the nasal cavity. We then analyzed factors unique to intranasal vaccines that need to be considered when researching and developing new intranasal vaccines. We concluded that while the choice of vaccine formulations, mucoadhesives, mucosal and epithelial permeation enhancers, and ligands that target M-cells are important, safe and effective intranasal mucosal vaccine adjuvants are needed to successfully develop an intranasal vaccine that is not based on live-attenuated viruses or bacteria. Moreover, more effective intranasal vaccine application devices that can efficiently target a vaccine to lymphoid tissues in the nasal cavity as well as preclinical animal models that can better predict intranasal vaccine performance in clinical trials are needed to increase the success rate of intranasal vaccines in clinical trials.

The Current Status of COVID-19 Vaccines

The current COVID-19 pandemic has substantially accelerated the demands for efficient vaccines. A wide spectrum of approaches includes live attenuated and inactivated viruses, protein subunits and peptides, viral vector-based delivery, DNA plasmids, and synthetic mRNA. Preclinical studies have demonstrated robust immune responses, reduced viral loads and protection against challenges with SARS-CoV-2 in rodents and primates. Vaccine candidates based on all delivery systems mentioned above have been subjected to clinical trials in healthy volunteers. Phase I clinical trials have demonstrated in preliminary findings good safety and tolerability. Evaluation of immune responses in a small number of individuals has demonstrated similar or superior levels of neutralizing antibodies in comparison to immunogenicity detected in COVID-19 patients. Both adenovirus- and mRNA-based vaccines have entered phase II and study protocols for phase III trials with 30,000 participants have been finalized.

Mucosal immunoglobulins of teleost fish: A decade of advances

Immunoglobulins (Igs) are complex glycoproteins that play critical functions in innate and adaptive immunity of all jawed vertebrates. Given the unique characteristics of mucosal barriers, secretory Igs (sIgs) have specialized to maintain homeostasis and keep pathogens at bay at mucosal tissues from fish to mammals. In teleost fish, the three main IgH isotypes, IgM, IgD and IgT/Z can be found in different proportions at the mucosal secretions of the skin, gills, gut, nasal, buccal, and pharyngeal mucosae. Similar to the role of mammalian IgA, IgT plays a predominant role in fish mucosal immunity. Recent studies in IgT have illuminated the primordial role of sIgs in both microbiota homeostasis and pathogen control at mucosal sites. Ten years ago, IgT was discovered to be an immunoglobulin class specialized in mucosal immunity. Aiming at this 10-year anniversary, the goal of this review is to summarize the current status of the field of fish Igs since that discovery, while identifying knowledge gaps and future avenues that will move the field forward in both basic and applied science areas.

COVID-19: Insights into Potential Vaccines

People around the world ushered in the new year 2021 with a fear of COVID-19, as family members have lost their loved ones to the disease. Millions of people have been infected, and the livelihood of many has been jeopardized due to the pandemic. Pharmaceutical companies are racing against time to develop an effective vaccine to protect against COVID-19. Researchers have developed various types of candidate vaccines with the release of the genetic sequence of the SARS-CoV-2 virus in January. These include inactivated viral vaccines, protein subunit vaccines, mRNA vaccines, and recombinant viral vector vaccines. To date, several vaccines have been authorized for emergency use and they have been administered in countries across the globe. Meanwhile, there are also vaccine candidates in Phase III clinical trials awaiting results and approval from authorities. These candidates have shown positive results in the previous stages of the trials, whereby they could induce an immune response with minimal side effects in the participants. This review aims to discuss the different vaccine platforms and the clinical trials of the candidate vaccines.

Evaluation of Intranasal Vaccine Delivery Using Anatomical Replicas of Infant Nasal Airways

PURPOSE

Nasal delivery is a favorable route for vaccination against most respiratory infections, as antigen deposited in the nasal turbinate and Waldeyer's ring areas induce mucosal and systemic immune responses. However, little is known about the nasal distribution of the vaccines, specifically for infants.

METHODS

Anatomical nasal replicas of five subjects, 3-24 months, were developed to assess local intranasal vaccine delivery using MAD Nasal™ device, and understand impact of breathing conditions and administration parameters. High performance liquid chromatography was used to quantify the deposition pattern and determine the delivery efficiency.

RESULTS

The delivery efficiency on average for all models was found to be 86.57±14.23%. There were no significant differences in the total delivery efficiency between the models in all cases. However, the regional deposition pattern was altered based on the model and subsequent administration. Furthermore, removing the foam tip from the MAD Nasal™ device, to study the impact of insertion length, did not significantly increase the efficiency within the two models tested, 5- and 16-month.

CONCLUSION

Incorporating nasal replicas in testing provided a benchmark to determine the efficiency of a common intranasal vaccine delivery combination product. This proposed platform would allow comparing other potential nasal vaccine delivery devices.

The Science is There: Key Considerations for Stabilizing Viral Vector-Based Covid-19 Vaccines

Once Covid-19 vaccines become available, 5–10 billion vaccine doses should be globally distributed, stored and administered. In this commentary, we discuss how this enormous challenge could be addressed for viral vector-based Covid-19 vaccines by learning from the wealth of formulation development experience gained over the years on stability issues related to live attenuated virus vaccines and viral vector vaccines for other diseases. This experience has led –over time– to major improvements on storage temperature, shelf-life and in-use stability requirements. First, we will cover work on ‘classical’ live attenuated virus vaccines as well as replication competent viral vector vaccines. Subsequently, we address replication deficient viral vector vaccines. Freeze drying and storage at 2–8 °C with a shelf life of years has become the norm. In the case of pandemics with incredibly high and urgent product demands, however, the desire for rapid and convenient distribution chains combined with short end-user storage times require that liquid formulations with shelf lives of months stored at 2–8 °C be considered. In confronting this “perfect storm” of Covid-19 vaccine stability challenges, understanding the many lessons learned from decades of development and manufacturing of live virus-based vaccines is the shortest path for finding promising and rapid solutions.

Assessment of a natural grass carp reovirus genotype II avirulent strain GD1108 shows great potential as an avirulent live vaccine

Vaccine immunization is currently the only effective way to prevent and control the grass carp haemorrhagic disease, and the primary pathogen in these infections is grass carp reovirus genotype II (GCRV-II) for which there is no commercial vaccine. In this study, we evaluated the safety of the GCRV-II avirulent strain GD1108 which isolated in the early stage of the laboratory through continuously passed in grass carp. The immunogenicity and protective effects were evaluated after immunization by injection and immersion. The avirulent strain GD1108 could infect and replicate in the fish which did not revert to virulence after continuous passage. No adverse side effects were observed and the vaccine strain did not spread horizontally among fish. Two routes of immunization induced high serum antibody titers of OD_450nm value were 0.79 and 0.76 and neutralization titers of 320 and 320 for the injection and immersion routes of inoculation, respectively. The expression of immune-related genes increased after immunization and the levels were statistically significant. Challenge of immunized fish with a virulent GCRV-II strain resulted in protection rates of 93.88% and 76.00% for the injection and immersion routes, respectively. The avirulent strain GD1108 revealed good safety and immunogenicity via two different inoculation routes. Although the injection route provided the best immune effect, two pathways provided protection against infection with virulent GCRV-II strains in various degrees. These results indicated that the avirulent strain GD1108 can be used for the development and application as live vaccine.

African swine fever: Etiology, epidemiological status in Korea, and perspective on control

African swine fever (ASF), caused by the ASF virus, a member of the Asfarviridae family, is one of the most important diseases in the swine industry due to its clinical and economic impacts. Since the first report of ASF a century ago, ample information has become available, but prevention and treatment measures are still inadequate. Two waves of epizootic outbreaks have occurred worldwide. While the first wave of the epizootic outbreak was controlled in most of the infected areas, the second wave is currently active in the European and Asian continents, causing severe economic losses to the pig industry. There are different patterns of spreading in the outbreaks between those in European and Asian countries. Prevention and control of ASF are very difficult due to the lack of available vaccines and effective therapeutic measures. However, recent outbreaks in South Korea have been successfully controlled on swine farms, although feral pigs are periodically being found to be positive for the ASF virus. Therefore, we would like to share our story regarding the preparation and application of control measures. The success in controlling ASF on farms in South Korea is largely due to the awareness and education of swine farmers and practitioners, the early detection of infected animals, the implementation of strict control policies by the government, and widespread sharing of information among stakeholders. Based on the experience gained from the outbreaks in South Korea, this review describes the current understanding of the ASF virus and its pathogenic mechanisms, epidemiology, and control.

Current State of Global African Swine Fever Vaccine Development under the Prevalence and Transmission of ASF in China

African swine fever (ASF) is a highly lethal contagious disease of swine caused by African swine fever virus (ASFV). At present, it is listed as a notifiable disease reported to the World Organization for Animal Health (OIE) and a class one animal disease ruled by Chinese government. ASF has brought significant economic losses to the pig industry since its outbreak in China in August 2018. In this review, we recapitulated the epidemic situation of ASF in China as of July 2020 and analyzed the influencing factors during its transmission. Since the situation facing the prevention, control, and eradication of ASF in China is not optimistic, safe and effective vaccines are urgently needed. In light of the continuous development of ASF vaccines in the world, the current scenarios and evolving trends of ASF vaccines are emphatically analyzed in the latter part of the review. The latest research outcomes showed that attempts on ASF gene-deleted vaccines and virus-vectored vaccines have proven to provide complete homologous protection with promising efficacy. Moreover, gaps and future research directions of ASF vaccine are also discussed.

Development of vaccines for SARS-CoV-2

COVID-19 emerged in late 2019 and has rapidly spread through many countries globally. The causative SARS-CoV-2 virus was not known until recently, and there is little or no natural immunity in human populations. There is an urgent need for vaccines and drugs to combat this new pandemic. In just a few months, huge efforts and resources by government, academia, and industry have been thrown into the race to develop a vaccine. This brief review summarizes and discusses the array of technologies being applied to vaccine development, highlighting the strengths and weaknesses of the various approaches.

Parenteral immunization of Salmonella Typhimurium ghosts with surface-displayed Escherichia coli flagellin enhancesTLR-5 mediated activation of immune responses that protect the chicken against Salmonella infection

The present study investigates the enhancement of immunogenicity and protection efficacy of Salmonella Typhimurium ghosts surface-displayed with FliC against chicken salmonellosis. The membrane-anchored FliC is a potential TLR-5 agonist, delivers an essential adjuvant effect for the ghost vaccine candidate. The present ghost plasmid pJHL184 construct carries a convergent dual promoter system that has the temperature-dependent induction of the phage lysis gene E and the target antigen FliC at the same time. Under permissible conditions of temperatures, less than 30 °C at the presence of 20 mM l-arabinose effectively suppresses expression of the lysis gene. Once the temperature is up-lifted to 42 °C without arabinose, cause the generation of ST ghosts expelling the cytoplasmic content. The addition of FliC adjuvant significantly enhanced the IgY response, cell-mediated immune responses, regulatory cytokine induction and subsequently enhanced protection against Salmonella challenge. Further, intramuscular immunization with ST ghosts displaying FliC induced particularly high CD8⁺ response demarcating its proficiency to elicit Type I immune responses. Further, ST ghosts displaying FliC caused an increase in both CD4⁺ and CD8⁺ response compared to the PBS control suggesting its capability to engage both cell-mediated and humoral immune responses essential for the elimination of Salmonella. Upon the virulent challenge, we could observe a significant reduction in challenged bacterial load on spleen, liver and cecum tissues in the ST ghosts surface-displaying FliC adjuvant. Our study suggests the biological incorporation of FliC on ST ghosts enhances vaccine immunogenic potency and acts as a safe and effective prevention strategy against chicken salmonellosis.

Salmonella enterica serovar Enteritidis ghosts displaying a surface FliC adjuvant elicit a robust immune response and effective protection against virulent challenge

Salmonella Enteritidis (SE) is one of the most common culprits of foodborne disease in humans due to its horizontal transmission from infected animals to humans. The development of a safe vaccine against Salmonella would be important for both farm animals and humans concerning disease containment. The SE ghosts carrying FliC were genetically constructed using a special ghost plasmid pJHL184 that co-expressed FliC and the phage lysis gene E. These SE ghosts were characterized by ghost generation efficacy by increasing the culture temperature to "42 °C" in the absence of L-arabinose. This temperature change led to an ghost generation with almost complete lysis of the SE host strain in 48 hs. The expression of FliC was confirmed by Western blot analysis. Also, indirect ELISA was used to prove FliC specific antibody generation in immunized mice. The parenteral adjuvant effect of the FliC antigen was demonstrated by immunizing mice with pJHL184::flC, pJHL184 alone, or PBS alone. The mice were intramuscularly immunized at six weeks of age (n = 8) and boosted after three weeks of primary inoculation. A total of 32 mice were equally divided into four groups. Each group was treated with pJHL-ghosts alone, ghost surface displaying FliC adjuvant, and compared to the PBS and naïve control groups. The immunized mice demonstrated greater IgG and IgA antibody responses than did the PBS control group. Furthermore, the addition of the ghosts to the FliC led to a significant increase in both the humoral and cell-mediated immune responses compared to those in the ghost alone group. Besides, the in vitro antigen uptake and presentation studies revealed efficient antigen presentation on the mouse macrophage cell surfaces. This finding further corroborated the potential efficacy of immune stimulation by SE ghosts. After the virulent challenge, we observed a significant reduction in the bacterial load in the spleen and liver tissues in SE ghosts surface, displaying FliC adjuvant. Our results demonstrate a safe and effective strategy to prevent salmonellosis. They also suggest that the surface expression of flagellin (FliC) significantly enhances antigen-specific humoral and cell-mediated immune responses. This FliC expression can also enhance the protective efficacy of the bacterial ghosts-based vaccine against virulent challenge.

A Review of Fish Vaccine Development Strategies: Conventional Methods and Modern Biotechnological Approaches

Fish immunization has been carried out for over 50 years and is generally accepted as an effective method for preventing a wide range of bacterial and viral diseases. Vaccination efforts contribute to environmental, social, and economic sustainability in global aquaculture. Most licensed fish vaccines have traditionally been inactivated microorganisms that were formulated with adjuvants and delivered through immersion or injection routes. Live vaccines are more efficacious, as they mimic natural pathogen infection and generate a strong antibody response, thus having a greater potential to be administered via oral or immersion routes. Modern vaccine technology has targeted specific pathogen components, and vaccines developed using such approaches may include subunit, or recombinant, DNA/RNA particle vaccines. These advanced technologies have been developed globally and appear to induce greater levels of immunity than traditional fish vaccines. Advanced technologies have shown great promise for the future of aquaculture vaccines and will provide health benefits and enhanced economic potential for producers. This review describes the use of conventional aquaculture vaccines and provides an overview of current molecular approaches and strategies that are promising for new aquaculture vaccine development.

A Measles Virus-Based Vaccine Candidate Mediates Protection against Zika Virus in an Allogeneic Mouse Pregnancy Model

The impact of the Zika virus (ZIKV) epidemic highlights the need for vaccines that reduce or prevent infection and reliably prevent teratogenic complications. The live-attenuated measles virus (MV) vaccine strains are a promising vaccine platform, since they induce robust humoral and cellular immune responses against additional antigens and have an excellent safety record. To explore its potential to protect against ZIKV, we compared a recombinant Schwarz strain MV that encodes ZIKV prM and soluble E proteins (MV-Zika-sE) with a prototypic alum-adjuvanted whole inactivated ZIKV particle vaccine. Analysis of MV-Zika-sE-infected cells confirmed antigen expression, and the virus replicated with vaccine strain characteristics. Immunized IFNAR-/--CD46Ge mice developed E protein-specific and neutralizing antibodies, and ZIKV E-specific cellular immune responses were observed by gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) and in vitro T cell proliferation assays. To analyze protective efficacy, vaccinated female mice were challenged with ZIKV after allogeneic mating. In MV-Zika-sE-vaccinated mice, weight gain was similar to that in uninfected mice, while no plasma viremia was detectable in the majority of the animals. In contrast, infected control animals gained less weight and experienced about 100-fold higher viremia over at least 3 days. Moreover, vaccination with MV-Zika-sE reduced the ZIKV load in different organs and the placentas and prevented infection of the fetus. Consequently, no fetal growth retardation, anemia, or death due to ZIKV infection was seen in MV-Zika-sE-vaccinated dams. In contrast, the inactivated ZIKV vaccine had little to no effect in our studies. Therefore, the MV-derived ZIKV vaccine is a promising candidate for further preclinical and clinical development.IMPORTANCE Zika virus (ZIKV) is a mosquito-borne flavivirus that causes a variety of neurological complications, including congenital birth defects. Despite the urgent need, no ZIKV vaccine has yet been licensed. Recombinant vaccine strain-derived measles viruses (MV) constitute a promising vector platform to induce immunity against foreign pathogens by expressing antigens from additional transcription units while at the same time possessing a remarkable safety profile. This concept has already been validated against different pathogens, including at least 3 other flaviviruses, and our data show that vaccination with MV expressing soluble ZIKV E protein significantly diminishes infection and prevents fetal loss or damage in an allogeneic mouse pregnancy model. It can thus be regarded as a promising emergency vaccine candidate with the potential for inclusion in routine vaccination settings in areas of endemicity to prevent teratogenic effects of circulating ZIKV during pregnancy, comparable to standard rubella virus vaccination.

Diagnostic and Vaccination Approaches for Newcastle Disease Virus in Poultry: The Current and Emerging Perspectives

Newcastle disease (ND) is one of the most devastating diseases that considerably cripple the global poultry industry. Because of its enormous socioeconomic importance and potential to rapidly spread to naïve birds in the vicinity, ND is included among the list of avian diseases that must be notified to the OIE immediately upon recognition. Currently, virus isolation followed by its serological or molecular identification is regarded as the gold standard method of ND diagnosis. However, this method is generally slow and requires specialised laboratory with biosafety containment facilities, making it of little relevance under epidemic situations where rapid diagnosis is seriously needed. Thus, molecular based diagnostics have evolved to overcome some of these difficulties, but the extensive genetic diversity of the virus ensures that isolates with mutations at the primer/probe binding sites escape detection using these assays. This diagnostic dilemma leads to the emergence of cutting-edge technologies such as next-generation sequencing (NGS) which have so far proven to be promising in terms of rapid, sensitive, and accurate recognition of virulent Newcastle disease virus (NDV) isolates even in mixed infections. As regards disease control strategies, conventional ND vaccines have stood the test of time by demonstrating track record of protective efficacy in the last 60 years. However, these vaccines are unable to block the replication and shedding of most of the currently circulating phylogenetically divergent virulent NDV isolates. Hence, rationally designed vaccines targeting the prevailing genotypes, the so-called genotype-matched vaccines, are highly needed to overcome these vaccination related challenges. Among the recently evolving technologies for the development of genotype-matched vaccines, reverse genetics-based live attenuated vaccines obviously appeared to be the most promising candidates. In this review, a comprehensive description of the current and emerging trends in the detection, identification, and control of ND in poultry are provided. The strengths and weaknesses of each of those techniques are also emphasised.

Intranasal immunization with dry powder vaccines

Vaccination represents a cost-effective weapon for disease prevention and has proven to dramatically reduce the incidences of several diseases that once were responsible for significant mortality and morbidity worldwide. The nasal cavity constitutes the initial stage of the respiratory system and the first contact with inhaled pathogens. The intranasal (IN) route for vaccine administration is an attractive alternative to injection, due to the ease of administration as well as better patient compliance. Many published studies have demonstrated the safety and effectiveness of IN immunization with liquid vaccines. Currently, two liquid IN vaccines are available and both contain live attenuated influenza viruses. FluMist® was approved in 2003 in the United States, and Nasovac® H1N1 vaccine was approved in India in 2010. Preclinical studies showed that IN immunization with dry powder vaccines (DPVs) is feasible. Although there is not a commercially available DPV yet, DPVs have the inherent advantage of being relatively more stable than liquid vaccines. This review focuses on recent developments of DPVs as next-generation IN vaccines.

Alkyl polyglycoside, a highly promising adjuvant in intranasal split influenza vaccines

Influenza viral infections are significant global public health concerns due to the morbidity and mortality associated with acute respiratory disease, secondary complications, and pandemic threats; thus, continuous efforts have been made to develop potent influenza vaccines. In this study, 3 different mucosal adjuvants-alkyl polyglycoside (APG), gellan gum, and chitosan (CS)-were evaluated for their efficacy in intranasal A/H1N1 or B split influenza vaccines administered to BALB/c mice. Protective immunity was monitored by serum analysis for IgG, hemagglutination inhibition (HI), and neutralizing antibody levels, as well as mucosal IgA levels in nasal and pulmonary lavage fluids. Survival, body weight, lung viral titer, and pulmonary immunopathology were also examined following lethal influenza challenge. Notably, all adjuvants amplified the IgG and IgA immune responses (not detected in immunization of influenza B) and increased survival rate compared with controls administered adjuvant-free intranasal vaccines. Alternatively, intramuscular immunization stimulated IgG production, but had no effect on IgA levels. Our collective analysis identified that APG was the most effective intranasal adjuvant, as all mice survived influenza challenge with limited body weight loss, viral titer, and pulmonary pathology, similar to those observed with intramuscular vaccination. This evidence supports that APG can elicit both systemic and mucosal immunity, and may be an effective adjuvant in intranasal split influenza A/H1N1 and B vaccines.

Reverse Genetics Approaches for the Development of Influenza Vaccines

Influenza viruses cause annual seasonal epidemics and occasional pandemics of human respiratory disease. Influenza virus infections represent a serious public health and economic problem, which are most effectively prevented through vaccination. However, influenza viruses undergo continual antigenic variation, which requires either the annual reformulation of seasonal influenza vaccines or the rapid generation of vaccines against potential pandemic virus strains. The segmented nature of influenza virus allows for the reassortment between two or more viruses within a co-infected cell, and this characteristic has also been harnessed in the laboratory to generate reassortant viruses for their use as either inactivated or live-attenuated influenza vaccines. With the implementation of plasmid-based reverse genetics techniques, it is now possible to engineer recombinant influenza viruses entirely from full-length complementary DNA copies of the viral genome by transfection of susceptible cells. These reverse genetics systems have provided investigators with novel and powerful approaches to answer important questions about the biology of influenza viruses, including the function of viral proteins, their interaction with cellular host factors and the mechanisms of influenza virus transmission and pathogenesis. In addition, reverse genetics techniques have allowed the generation of recombinant influenza viruses, providing a powerful technology to develop both inactivated and live-attenuated influenza vaccines. In this review, we will summarize the current knowledge of state-of-the-art, plasmid-based, influenza reverse genetics approaches and their implementation to provide rapid, convenient, safe and more effective influenza inactivated or live-attenuated vaccines.

Novel antigen delivery systems

Vaccines represent the most relevant contribution of immunology to human health. However, despite the remarkable success achieved in the past years, many vaccines are still missing in order to fight important human pathologies and to prevent emerging and re-emerging diseases. For these pathogens the known strategies for making vaccines have been unsuccessful and thus, new avenues should be investigated to overcome the failure of clinical trials and other important issues including safety concerns related to live vaccines or viral vectors, the weak immunogenicity of subunit vaccines and side effects associated with the use of adjuvants. A major hurdle of developing successful and effective vaccines is to design antigen delivery systems in such a way that optimizes antigen presentation and induces broad protective immune responses. Recent advances in vector delivery technologies, immunology, vaccinology and system biology, have led to a deeper understanding of the molecular and cellular mechanisms by which vaccines should stimulate both arms of the adaptive immune responses, offering new strategies of vaccinations. This review is an update of current strategies with respect to live attenuated and inactivated vaccines, DNA vaccines, viral vectors, lipid-based carrier systems such as liposomes and virosomes as well as polymeric nanoparticle vaccines and virus-like particles. In addition, this article will describe our work on a versatile and immunogenic delivery system which we have studied in the past decade and which is derived from a non-pathogenic prokaryotic organism: the “E2 scaffold” of the pyruvate dehydrogenase complex from Geobacillus stearothermophilus.