Novel viral vectors in infectious diseases

Vaccine delivery systems and administration routes: Advanced biotechnological techniques to improve the immunization efficacy

Since the first use of vaccine tell the last COVID-19 pandemic caused by spread of SARS-CoV-2 worldwide, the use of advanced biotechnological techniques has accelerated the development of different types and methods for immunization. The last pandemic showed that the nucleic acid-based vaccine, especially mRNA, has an advantage in terms of development time; however, it showed a very critical drawback namely, the higher costs when compared to other strategies, and its inability to protect against new variants. This showed the need of more improvement to reach a better delivery and efficacy. In this review we will describe different vaccine delivery systems including, the most used viral vector, and also variable strategies for delivering of nucleic acid-based vaccines especially lipid-based nanoparticles formulation, polymersomes, electroporation and also the new powerful tools for the delivery of mRNA, which is based on the use of cell-penetrating peptides (CPPs). Additionally, we will also discuss the main challenges associated with each system. Finlay, the efficacy and safety of the vaccines depends not only on the formulations and delivery systems, but also the dosage and route of administration are also important players, therefore we will see the different routes for the vaccine administration including traditionally routes (intramuscular, Transdermal, subcutaneous), oral inhalation or via nasal mucosa, and will describe the advantages and disadvantage of each administration route.

Mucosal T-cell responses to chronic viral infections: Implications for vaccine design

Mucosal surfaces that line the respiratory, gastrointestinal and genitourinary tracts are the major interfaces between the immune system and the environment. Their unique immunological landscape is characterized by the necessity of balancing tolerance to commensal microorganisms and other innocuous exposures against protection from pathogenic threats such as viruses. Numerous pathogenic viruses, including herpesviruses and retroviruses, exploit this environment to establish chronic infection. Effector and regulatory T-cell populations, including effector and resident memory T cells, play instrumental roles in mediating the transition from acute to chronic infection, where a degree of viral replication is tolerated to minimize immunopathology. Persistent antigen exposure during chronic viral infection leads to the evolution and divergence of these responses. In this review, we discuss advances in the understanding of mucosal T-cell immunity during chronic viral infections and how features of T-cell responses develop in different chronic viral infections of the mucosa. We consider how insights into T-cell immunity at mucosal surfaces could inform vaccine strategies: not only to protect hosts from chronic viral infections but also to exploit viruses that can persist within mucosal surfaces as vaccine vectors.

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.

The Quest for Immunity: Exploring Human Herpesviruses as Vaccine Vectors

Herpesviruses are large DNA viruses that have long been used as powerful gene therapy tools. In recent years, the ability of herpesviruses to stimulate both innate and adaptive immune responses has led to their transition to various applications as vaccine vectors. This vaccinology branch is growing at an unprecedented and accelerated rate. To date, human herpesvirus-based vectors have been used in vaccines to combat a variety of infectious agents, including the Ebola virus, foot and mouth disease virus, and human immunodeficiency viruses. Additionally, these vectors are being tested as potential vaccines for cancer-associated antigens. Thanks to advances in recombinant DNA technology, immunology, and genomics, numerous steps in vaccine development have been greatly improved. A better understanding of herpesvirus biology and the interactions between these viruses and the host cells will undoubtedly foster the use of herpesvirus-based vaccine vectors in clinical settings. To overcome the existing drawbacks of these vectors, ongoing research is needed to further advance our knowledge of herpesvirus biology and to develop safer and more effective vaccine vectors. Advanced molecular virology and cell biology techniques must be used to better understand the mechanisms by which herpesviruses manipulate host cells and how viral gene expression is regulated during infection. In this review, we cover the underlying molecular structure of herpesviruses and the strategies used to engineer their genomes to optimize capacity and efficacy as vaccine vectors. Also, we assess the available data on the successful application of herpesvirus-based vaccines for combating diseases such as viral infections and the potential drawbacks and alternative approaches to surmount them.

Nonclinical safety assessment and immunogenicity of rVSVInd(GML)-mspSGtc vaccine for SARS-CoV-2 in rabbits

The worldwide health, economic, and societal consequences of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic have been devastating. The primary strategy to prevent new infectious diseases is to vaccinate the majority of people worldwide. However, the significant hurdles that are faced include vaccine safety concerns and vaccine reluctance. Among the various types of vaccines, the recombinant vesicular stomatitis virus (rVSV) is a promising candidate owing to its safety and efficacy. Therefore, we investigated the toxicity, immunogenicity, and local tolerance of the rVSVInd(GML)-mspSGtc vaccine against SARS-CoV-2. New Zealand White (NZW) rabbits were administered single or three repeated intramuscular injections of rVSVInd(GML)-mspSGtc every 2 weeks, followed by a 4-week recovery period. Male and female rabbits were randomly assigned into three groups: a control group and two dose-level groups (1 × 109 and 4 × 109 PFU/mL). Treatment-related changes included a temporary increase in body temperature and local inflammation at the injection site. These findings indicated recovery or a trend toward recovery, with no overt systemic toxicity. Immunogenicity analysis results suggested that rVSVInd(GML)-mspSGtc elicited a robust dose-dependent immune response in terms of neutralizing antibodies and IgG antibodies against the SARS-CoV-2 spike protein. In addition, the immune response intensity was increased by repeated vaccine administration. In conclusion, both the approximate lethal dose and the no observed adverse effect level for rVSVInd(GML)-mspSGtc exceeded 4 × 109 PFU/mL in NZW rabbits. Overall, rVSVInd(GML)-mspSGtc induced no adverse effects at the maximum dosage tested; however, its efficacy warrants further clinical evaluation.

The Application of Mesenchymal Stem Cells in Future Vaccine Synthesis

Vaccines have significant potential in treating and/or preventing diseases, yet there remain challenges in developing effective vaccines against some diseases, such as AIDS and certain tumors. Mesenchymal stem cells (MSCs), a subset of cells with low immunogenicity, high proliferation potential, and an abundant source of extracellular vesicles (EVs), represent one of the novel and promising vaccine platforms. This review describes the unique features and potential mechanisms of MSCs as a novel vaccine platform. We also cover aspects such as the safety and stability of MSCs that warrant future in-depth studies.

Comparison of heterologous prime-boost immunization strategies with DNA and recombinant vaccinia virus co-expressing GP3 and GP5 of European type porcine reproductive and respiratory syndrome virus in pigs

Vaccination is principally used to control and treat porcine reproductive and respiratory syndrome virus (PRRSV) infection. This study investigated immunogenicity and protective efficacy of heterologous prime-boost regimens in pigs, including recombinant DNA and vaccinia virus vectors coexpressing PRRSV European genotype (EU) isolate GP3 and GP5: group A, pVAX1-EU-GP3-GP5 prime and rddVTT-EU-GP3-GP5 boost; group B, rddVTT-EU-GP3-GP5 prime and pVAX1-EU-GP3-GP5 boost; group C, empty vector pVAX1; group D, E3L gene-deleted vaccinia virus E3L- VTT. Vaccine efficacy was tested in an EU-type PRRSV (Lelystad virus strain) challenge pig model based on evaluating PRRSV-specific antibody responses, neutralizing antibodies, cytokines, T lymphocyte proliferation, CD4+ and CD8+ T lymphocytes, clinical symptoms, viremia and tissue virus loads. Plasmid DNA was delivered as chitosan-DNA nanoparticles, and Quil A (Quillaja) was used to increase vaccine efficiency. All piglets were boosted 21 days post the initial inoculation (dpi) and then challenged 14 days later. At 14, 21, 28 and 35 dpi, groups A and B developed significantly higher PRRSV-specific antibody responses compared with control groups C and D. Two weeks after the boost, significant differences in neutralizing antibody and IFN-γ levels were observed between groups A, C, D and B. At 49 dpi, groups A and B had markedly increased peripheral blood CD3+CD4+ T cell levels. Following virus challenge, group A showed viremia, but organ virus loads were lower than those in other groups. Thus, a heterologous prime-boost vaccine regimen (rddVTT-EU-GP3-GP5 prime, pVAX1-EU-GP3-GP5 boost) can improve humoral- and cell-mediated immune responses to provide resistance to EU-type PRRSV infection in vivo.

Modeling the dynamics of COVID-19 with real data from Thailand

In recent years, COVID-19 has evolved into many variants, posing new challenges for disease control and prevention. The Omicron variant, in particular, has been found to be highly contagious. In this study, we constructed and analyzed a mathematical model of COVID-19 transmission that incorporates vaccination and three different compartments of the infected population: asymptomatic [Formula: see text], symptomatic [Formula: see text], and Omicron [Formula: see text]. The model is formulated in the Caputo sense, which allows for fractional derivatives that capture the memory effects of the disease dynamics. We proved the existence and uniqueness of the solution of the model, obtained the effective reproduction number, showed that the model exhibits both endemic and disease-free equilibrium points, and showed that backward bifurcation can occur. Furthermore, we documented the effects of asymptomatic infected individuals on the disease transmission. We validated the model using real data from Thailand and found that vaccination alone is insufficient to completely eradicate the disease. We also found that Thailand must monitor asymptomatic individuals through stringent testing to halt and subsequently eradicate the disease. Our study provides novel insights into the behavior and impact of the Omicron variant and suggests possible strategies to mitigate its spread.

Production of a promising modular proteinaceous self-assembled delivery system for vaccination

Recently, there have been enormous advances in nano-delivery materials, especially safer and more biocompatible protein-based nanoparticles. Generally, proteinaceous nanoparticles (such as ferritin and virus-like particles) are self-assembled from some natural protein monomers. However, to ensure their capability of assembly, it is difficult to upgrade the protein structure through major modifications. Here, we have developed an efficient orthogonal modular proteinaceous self-assembly delivery system that could load antigens with an attractive coupling strategy. In brief, we constructed a nanocarrier by fusing two orthogonal domains-a pentameric cholera toxin B subunit and a trimer forming peptide-and an engineered streptavidin monomer for binding biotinylated antigens. After successfully preparing the nanoparticles, the receptor-binding domain of SARS-CoV-2 spike protein and influenza virus haemagglutination antigen are used as model antigens for further evaluation. We found that the biotinylated antigen is able to bind to the nanoparticles with high affinity and achieve efficient lymph node drainage when loaded on the nanoparticles. Then, T cells are greatly activated and the formation of germinal centers is observed. Experiments of two mouse models demonstrate the strong antibody responses and prophylactic effects of these nanovaccines. Thus, we establish a proof-of-concept for the delivery system with the potential to load diverse antigen cargos to generate high-performance nanovaccines, thereby offering an attractive platform technology for nanovaccine preparation.

Role of MHC class I pathways in Mycobacterium tuberculosis antigen presentation

MHC class I antigen processing is an underappreciated area of nonviral host–pathogen interactions, bridging both immunology and cell biology, where the pathogen’s natural life cycle involves little presence in the cytoplasm. The effective response to MHC-I foreign antigen presentation is not only cell death but also phenotypic changes in other cells and stimulation of the memory cells ready for the next antigen reoccurrence. This review looks at the MHC-I antigen processing pathway and potential alternative sources of the antigens, focusing on Mycobacterium tuberculosis (Mtb) as an intracellular pathogen that co-evolved with humans and developed an array of decoy strategies to survive in a hostile environment by manipulating host immunity to its own advantage. As that happens via the selective antigen presentation process, reinforcement of the effective antigen recognition on MHC-I molecules may stimulate subsets of effector cells that act earlier and more locally. Vaccines against tuberculosis (TB) could potentially eliminate this disease, yet their development has been slow, and success is limited in the context of this global disease’s spread. This review’s conclusions set out potential directions for MHC-I-focused approaches for the next generation of vaccines.

Recent Advances in the Development of Adenovirus-Vectored Vaccines for Parasitic Infections

Vaccines against parasites have lagged centuries behind those against viral and bacterial infections, despite the devastating morbidity and widespread effects of parasitic diseases across the globe. One of the greatest hurdles to parasite vaccine development has been the lack of vaccine strategies able to elicit the complex and multifaceted immune responses needed to abrogate parasitic persistence. Viral vectors, especially adenovirus (AdV) vectors, have emerged as a potential solution for complex disease targets, including HIV, tuberculosis, and parasitic diseases, to name a few. AdVs are highly immunogenic and are uniquely able to drive CD8+ T cell responses, which are known to be correlates of immunity in infections with most protozoan and some helminthic parasites. This review presents recent developments in AdV-vectored vaccines targeting five major human parasitic diseases: malaria, Chagas disease, schistosomiasis, leishmaniasis, and toxoplasmosis. Many AdV-vectored vaccines have been developed for these diseases, utilizing a wide variety of vectors, antigens, and modes of delivery. AdV-vectored vaccines are a promising approach for the historically challenging target of human parasitic diseases.

Enhanced Therapeutic Efficacy of Immunostimulatory CpG-ODN by Silencing SOCS-1 with Polysaccharide/miR-155 Complexes

For the induction of antigen-specific immune responses, adjuvants as well as antigens are essential. CpG-ODN is a potent agonist of toll-like receptor 9 (TLR9) and is known as an adjuvant to induce cellular immune responses. We previously developed a therapeutic oligonucleotide delivery system based on the formation of a complex between schizophyllan (SPG), a kind of β-1,3-glucan, and poly(dA), which actively delivered CpG-ODN to antigen-presenting cells (APCs) in the draining lymph nodes and induced antigen-specific immune responses. However, unfortunately, the signaling pathway of TLR9 is negatively regulated by an intracellular protein called suppressor of cytokine signaling-1 (SOCS-1), which suppresses the adjuvant effect of CpG-ODN. To solve this, we focused on microRNA-155 (miR-155), which regulates innate and autoimmune processes by targeting SOCS-1. In this study, we proposed a strategy of combining miR-155 and CpG-ODN, each complexed with SPG (denoted as SPG/miR-155 and SPG/CpG, respectively), to induce a more potent immune response. As a result, we showed that the efficient delivery of miR-155 to APCs by a complex form could induce much more potent cellular immune responses than SPG/CpG alone. Furthermore, the mice treated with the combination of SPG/miR-155 and SPG/CpG showed a long delay in tumor growth occurrence and improved survival after tumor inoculation. These results indicate the possibility of therapeutic strategies for cancer.

Adenoviral Vector-Based Vaccine Platform for COVID-19: Current Status

The coronavirus disease (COVID-19) breakout had an unimaginable worldwide effect in the 21st century, claiming millions of lives and putting a huge burden on the global economy. The potential developments in vaccine technologies following the determination of the genetic sequence of SARS-CoV-2 and the increasing global efforts to bring potential vaccines and therapeutics into the market for emergency use have provided a small bright spot to this tragic event. Several intriguing vaccine candidates have been developed using recombinant technology, genetic engineering, and other vaccine development technologies. In the last decade, a vast amount of the vaccine development process has diversified towards the usage of viral vector-based vaccines. The immune response elicited by such vaccines is comparatively higher than other approved vaccine candidates that require a booster dose to provide sufficient immune protection. The non-replicating adenoviral vectors are promising vaccine carriers for infectious diseases due to better yield, cGMP-friendly manufacturing processes, safety, better efficacy, manageable shipping, and storage procedures. As of April 2022, the WHO has approved a total of 10 vaccines around the world for COVID-19 (33 vaccines approved by at least one country), among which three candidates are adenoviral vector-based vaccines. This review sheds light on the developmental summary of all the adenoviral vector-based vaccines that are under emergency use authorization (EUA) or in the different stages of development for COVID-19 management.

Precision-engineering of subunit vaccine particles for prevention of infectious diseases

Vaccines remain the best approach for the prevention of infectious diseases. Protein subunit vaccines are safe compared to live-attenuated whole cell vaccines but often show reduced immunogenicity. Subunit vaccines in particulate format show improved vaccine efficacy by inducing strong immune responses leading to protective immunity against the respective pathogens. Antigens with proper conformation and function are often required to induce functional immune responses. Production of such antigens requiring post-translational modifications and/or composed of multiple complex domains in bacterial hosts remains challenging. Here, we discuss strategies to overcome these limitations toward the development of particulate vaccines eliciting desired humoral and cellular immune responses. We also describe innovative concepts of assembling particulate vaccine candidates with complex antigens bearing multiple post-translational modifications. The approaches include non-covalent attachments (e.g. biotin-avidin affinity) and covalent attachments (e.g. SpyCatcher-SpyTag) to attach post-translationally modified antigens to particles.

A Structural View at Vaccine Development against M. tuberculosis

Tuberculosis (TB) is still the leading global cause of death from an infectious bacterial agent. Limiting tuberculosis epidemic spread is therefore an urgent global public health priority. As stated by the WHO, to stop the spread of the disease we need a new vaccine, with better coverage than the current Mycobacterium bovis BCG vaccine. This vaccine was first used in 1921 and, since then, there are still no new licensed tuberculosis vaccines. However, there is extremely active research in the field, with a steep acceleration in the past decades, due to the advance of technologies and more rational vaccine design strategies. This review aims to gather latest updates in vaccine development in the various clinical phases and to underline the contribution of Structural Vaccinology (SV) to the development of safer and effective antigens. In particular, SV and the development of vaccine adjuvants is making the use of subunit vaccines, which are the safest albeit the less antigenic ones, an achievable goal. Indeed, subunit vaccines overcome safety concerns but need to be rationally re-engineered to enhance their immunostimulating effects. The larger availability of antigen structural information as well as a better understanding of the complex host immune response to TB infection is a strong premise for a further acceleration of TB vaccine development.

Different Types of Vaccines against Pestiviral Infections: "Barriers" for "Pestis"

The genus Pestivirus of the family Flaviviridae mainly comprises classical swine fever virus (CSFV), bovine viral diarrhea virus 1 (BVDV-1), BVDV-2, border disease virus (BDV), and multiple new pestivirus species such as atypical porcine pestivirus (APPV), giraffe pestivirus, and antelope pestivirus. Pestiviruses cause infectious diseases, resulting in tremendous economic losses to animal husbandry. Different types of pestivirus vaccines have been developed to control and prevent these important animal diseases. In recent years, pestiviruses have shown great potential as viral vectors for developing multivalent vaccines. This review analyzes the advantages and disadvantages of various pestivirus vaccines, including live attenuated pestivirus strains, genetically engineered marker pestiviruses, and pestivirus-based multivalent vaccines. This review provides new insights into the development of novel vaccines against emerging pestiviruses, such as APPV and ovine pestivirus.

Vesicular stomatitis virus-based vaccine targeting plasmodium blood-stage antigens elicits immune response and protects against malaria with protein booster strategy

Merozoite invasion of the erythrocytes in humans is a key step in the pathogenesis of malaria. The proteins involved in the merozoite invasion could be potential targets for the development of malaria vaccines. Novel viral-vector-based malaria vaccine regimens developed are currently under clinical trials. Vesicular stomatitis virus (VSV) is a single-stranded negative-strand RNA virus widely used as a vector for virus or cancer vaccines. Whether the VSV-based malarial vaccine is more effective than conventional vaccines based on proteins involved in parasitic invasion is still unclear. In this study, we have used the reverse genetics system to construct recombinant VSVs (rVSVs) expressing apical membrane protein 1 (AMA1), rhoptry neck protein 2 (RON2), and reticulocyte-binding protein homolog 5 (RH5), which are required for Plasmodium falciparum invasion. Our results showed that VSV-based viral vaccines significantly increased Plasmodium-specific IgG levels and lymphocyte proliferation. Also, VSV-PyAMA1 and VSV-PyRON2sp prime-boost regimens could significantly increase the levels of IL-2 and IFN-γ-producing by CD4⁺ and CD8⁺ T cells and suppress invasion in vitro. The rVSV prime-protein boost regimen significantly increase Plasmodium antigen-specific IgG levels in the serum of mice compared to the homologous rVSV prime-boost. Furthermore, the protective efficacy of rVSV prime protein boost immunization in the mice challenged with P. yoelii 17XL was better compared to traditional antigen immunization. Together, our results show that VSV vector is a novel strategy for malarial vaccine development and preventing the parasitic diseases.

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.

COVID-19: Clinical status of vaccine development to date

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-induced COVID-19 is a complicated disease. Clinicians are continuously facing difficulties to treat infected patients using the principle of repurposing of drugs as no specific drugs are available to treat COVID-19. To minimize the severity and mortality, global vaccination is the only hope as a potential preventive measure. After a year-long global research and clinical struggle, 165 vaccine candidates have been developed and some are currently still in the pipeline. A total of 28 candidate vaccines have been approved for use and the remainder are in different phases of clinical trials. In this comprehensive report, the authors aim to demonstrate, classify and provide up-to-date clinical trial status of all the vaccines discovered to date and specifically focus on the approved candidates. Finally, the authors specifically focused on the vaccination of different types of medically distinct populations.

Viral Vector Vaccine Development and Application during the COVID-19 Pandemic

With the accumulation of mutations in SARS-CoV-2 and the continuous emergence of new variants, the importance of developing safer and effective vaccines has become more prominent in combating the COVID-19 pandemic. Both traditional and genetically engineered vaccines have contributed to the prevention and control of the pandemic. However, in recent years, the trend of vaccination research has gradually transitioned from traditional to genetically engineered vaccines, with the development of viral vector vaccines attracting increasing attention. Viral vector vaccines have several unique advantages compared to other vaccine platforms. The spread of Omicron has also made the development of intranasal viral vector vaccines more urgent, as the infection site of Omicron is more prominent in the upper respiratory tract. Therefore, the present review focuses on the development of viral vector vaccines and their application during the COVID-19 pandemic.

Vaccinia Virus Attenuation by Codon Deoptimization of the A24R Gene for Vaccine Development

Poxviruses have large DNA genomes, and they are able to infect multiple vertebrate and invertebrate animals, including humans. Despite the eradication of smallpox, poxvirus infections still remain a significant public health concern. Vaccinia virus (VV) is the prototypic member in the poxviridae family and it has been used extensively for different prophylactic applications, including the generation of vaccines against multiple infectious diseases and/or for oncolytic treatment. Many attempts have been pursued to develop novel attenuated forms of VV with improved safety profiles for their implementation as vaccines and/or vaccines vectors. We and others have previously demonstrated how RNA viruses encoding codon-deoptimized viral genes are attenuated, immunogenic and able to protect, upon a single administration, against challenge with parental viruses. In this study, we employed the same experimental approach based on the use of misrepresented codons for the generation of a recombinant (r)VV encoding a codon-deoptimized A24R gene, which is a key component of the viral RNA polymerase. Similar to our previous studies with RNA viruses, the A24R codon-deoptimized rVV (v-A24cd) was highly attenuated in vivo but able to protect, after a single intranasal dose administration, against an otherwise lethal challenge with parental VV. These results indicate that poxviruses can be effectively attenuated by synonymous codon deoptimization and open the possibility of using this methodology alone or in combination with other experimental approaches for the development of attenuated vaccines for the treatment of poxvirus infection, or to generate improved VV-based vectors. Moreover, this approach could be applied to other DNA viruses. IMPORTANCE The family poxviridae includes multiple viruses of medical and veterinary relevance, being vaccinia virus (VV) the prototypic member in the family. VV was used during the smallpox vaccination campaign to eradicate variola virus (VARV), which is considered a credible bioterrorism threat. Because of novel innovations in genetic engineering and vaccine technology, VV has gained popularity as a viral vector for the development of vaccines against several infectious diseases. Several approaches have been used to generate attenuated VV for its implementation as vaccine and/or vaccine vector. Here, we generated a rVV containing a codon-deoptimized A24R gene (v-A24cd), which encodes a key component of the viral RNA polymerase. v-A24cd was stable in culture cells and highly attenuated in vivo but able to protect against a subsequent lethal challenge with parental VV. Our findings support the use of this approach for the development of safe, stable, and protective live-attenuated VV and/or vaccine vectors.

Mucosal Vaccination: A Promising Alternative Against Flaviviruses

The Flaviviridae are a family of positive-sense, single-stranded RNA enveloped viruses, and their members belong to a single genus, Flavivirus. Flaviviruses are found in mosquitoes and ticks; they are etiological agents of: dengue fever, Japanese encephalitis, West Nile virus infection, Zika virus infection, tick-borne encephalitis, and yellow fever, among others. Only a few flavivirus vaccines have been licensed for use in humans: yellow fever, dengue fever, Japanese encephalitis, tick-borne encephalitis, and Kyasanur forest disease. However, improvement is necessary in vaccination strategies and in understanding of the immunological mechanisms involved either in the infection or after vaccination. This is especially important in dengue, due to the immunological complexity of its four serotypes, cross-reactive responses, antibody-dependent enhancement, and immunological interference. In this context, mucosal vaccines represent a promising alternative against flaviviruses. Mucosal vaccination has several advantages, as inducing long-term protective immunity in both mucosal and parenteral tissues. It constitutes a friendly route of antigen administration because it is needle-free and allows for a variety of antigen delivery systems. This has promoted the development of several ways to stimulate immunity through the direct administration of antigens (e.g., inactivated virus, attenuated virus, subunits, and DNA), non-replicating vectors (e.g., nanoparticles, liposomes, bacterial ghosts, and defective-replication viral vectors), and replicating vectors (e.g., Salmonella enterica, Lactococcus lactis, Saccharomyces cerevisiae, and viral vectors). Because of these characteristics, mucosal vaccination has been explored for immunoprophylaxis against pathogens that enter the host through mucosae or parenteral areas. It is suitable against flaviviruses because this type of immunization can stimulate the parenteral responses required after bites from flavivirus-infected insects. This review focuses on the advantages of mucosal vaccine candidates against the most relevant flaviviruses in either humans or animals, providing supporting data on the feasibility of this administration route for future clinical trials.

mRNA Vaccines: Past, Present, Future

mRNA vaccines have emerged as promising alternative platforms to conventional vaccines. Their ease of production, low cost, safety profile and high potency render them ideal candidates for prevention and treatment of infectious diseases, especially in the midst of pandemics. The challenges that face in vitro transcribed RNA were partially amended by addition of tethered adjuvants or co-delivery of naked mRNA with an adjuvant-tethered RNA. However, it wasn't until recently that the progress made in nanotechnology helped enhance mRNA stability and delivery by entrapment in novel delivery systems of which, lipid nanoparticles. The continuous advancement in the fields of nanotechnology and tissue engineering provided novel carriers for mRNA vaccines such as polymeric nanoparticles and scaffolds. Various studies have shown the advantages of adopting mRNA vaccines for viral diseases and cancer in animal and human studies. Self-amplifying mRNA is considered today the next generation of mRNA vaccines and current studies reveal promising outcomes. This review provides a comprehensive overview of mRNA vaccines used in past and present studies, and discusses future directions and challenges in advancing this vaccine platform to widespread clinical use.

Thrombotic Complications after COVID-19 Vaccination: Diagnosis and Treatment Options

Coronavirus disease 2019 (COVID-19) vaccines were developed a few months after the emergence of the pandemic. The first cases of vaccine-induced thrombotic complications after the use of adenoviral vector vaccines ChAdOx1 nCoV-19 by AstraZeneca, and Ad26.COV2.S by Johnson & Johnson/Janssen, were announced shortly after the initiation of a global vaccination program. In these cases, the occurrence of thrombotic events at unusual sites—predominantly located in the venous vascular system—in association with concomitant thrombocytopenia were observed. Since this new entity termed vaccine-induced thrombotic thrombocytopenia (VITT) shows similar pathophysiologic mechanisms as heparin-induced thrombocytopenia (HIT), including the presence of antibodies against heparin/platelet factor 4 (PF4), standard routine treatment for thrombotic events—arterial or venous—are not appropriate and may also cause severe harm in affected patients. Thrombotic complications were also rarely documented after vaccination with mRNA vaccines, but a typical VITT phenomenon has, to date, not been established for these vaccines. The aim of this review is to give a concise and feasible overview of diagnostic and therapeutic strategies in COVID-19 vaccine-induced thrombotic complications.

Quantification methods for viruses and virus-like particles applied in biopharmaceutical production processes

INTRODUCTION

Effective cell-based production processes of virus particles are the foundation for the global availability of classical vaccines, gene therapeutic vectors, and viral oncolytic treatments. Their production is subject to regulatory standards ensuring the safety and efficacy of the pharmaceutical product. Process analytics must be fast and reliable to provide an efficient process development and a robust process control during production. Additionally, for the product release, the drug compound and the contaminants must be quantified by assays specified by regulatory authorities.

AREAS COVERED

This review summarizes analytical methods suitable for the quantification of viruses or virus-like particles. The different techniques are grouped by the analytical question that may be addressed. Accordingly, methods focus on the infectivity of the drug component on the one hand, and on particle counting and the quantification of viral elements on the other hand. The different techniques are compared regarding their advantages, drawbacks, required assay time, and sample throughput.

EXPERT OPINION

Among the technologies summarized, a tendency toward fast methods, allowing a high throughput and a wide applicability, can be foreseen. Driving forces for this progress are miniaturization and automation, and the continuous enhancement of process-relevant databases for a successful future process control.

Therapeutic potentials of CRISPR-Cas genome editing technology in human viral infections

Viral infections are a common cause of morbidity worldwide. The emergence of Coronavirus Disease 2019 (COVID-19) has led to more attention to viral infections and finding novel therapeutics. The CRISPR-Cas9 system has been recently proposed as a potential therapeutic tool for the treatment of viral diseases. Here, we review the research progress in the use of CRISPR-Cas technology for treating viral infections, as well as the strategies for improving the delivery of this gene-editing tool in vivo. Key challenges that hinder the widespread clinical application of CRISPR-Cas9 technology are also discussed, and several possible directions for future research are proposed.

mRNA- and Adenovirus-Based Vaccines against SARS-CoV-2 in HIV-Positive People

About two years have passed since the identification of SARS-CoV-2 in China. The rapid spread of this virus all over the world and its high transmissibility and pathogenicity in humans have resulted in a global pandemic. The negative impact of COVID-19 on health, society and the economy at the global level has pushed researchers and pharmaceutical companies to develop effective vaccines to fight SARS-CoV-2. Thanks to this collaborative effort, the first COVID-19 vaccine was developed in less than a year. Since then, several COVID-19 vaccines have been validated for use by the World Health Organization. Among these, mRNA- (BNT162b2 and mRNA1273) and adenovirus-based (ChAdOx1) vaccines were developed through the use of novel technologies. While all three of these vaccines have shown effectiveness against the COVID-19 disease and their immunogenicity was characterized in clinical trials in the general population, data on their efficacy and immunogenicity in people living with HIV (PLWH) are limited. In this review, we provide a description of the characteristics of mRNA- and adenovirus-based vaccines and of the immune response elicited in the general population by vaccination. Then we describe the use of these vaccines and their efficacy and immunogenicity in people living with HIV and we conclude with a discussion regarding some open questions concerning the use of mRNA- and adenovirus-based COVID-19 vaccines in PLWH.

Safety and Efficacy of the Common Vaccines against COVID-19

The worldwide pandemic of coronavirus disease 2019 (COVID-19) has imposed a challenge on human health worldwide, and vaccination represents a vital strategy to control the pandemic. To date, multiple COVID-19 vaccines have been granted emergency use authorization, including inactivated vaccines, adenovirus-vectored vaccines, and nucleic acid vaccines. These vaccines have different technical principles, which will necessarily lead to differences in safety and efficacy. Therefore, we aim to implement a systematic review by synthesizing clinical experimental data combined with mass vaccination data and conducting a synthesis to evaluate the safety and efficacy of COVID-19 vaccines. Compared with other vaccines, adverse reactions after vaccination with inactivated vaccines are relatively low. The efficacy of inactivated vaccines is approximately 60%, adenovirus-vectored vaccines are 65%, and mRNA vaccines are 90%, which are always efficient against asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, symptomatic COVID-19, COVID-19 hospitalization, severe or critical hospitalization, and death. RNA-based vaccines have a number of advantages and are one of the most promising vaccines identified to date and are particularly important during a pandemic. However, further improvements are required. In time, all the antibody levels weaken gradually, so a booster dose is needed to maintain immunity. Compared with homologous prime-boost immunization, heterologous prime-boost immunization prompts more robust humoral and cellular immune responses.

Selection of Analytical Technology and Development of Analytical Procedures Using the Analytical Target Profile

A structured approach to method development can help to ensure an analytical procedure is robust across the lifecycle of its use. The analytical target profile (ATP), which describes the required quality of the reportable value to be produced by the analytical procedure, enables the analytical scientist to select the best analytical technology on which to develop their procedure(s). Once the technology has been identified, screening of potentially fit for purpose analytical procedures should take place. Analytical procedures that have been demonstrated to meet the ATP should be evaluated against business drivers (e.g., operational constraints) to determine the most suitable analytical procedure. Three case studies are covered from across small molecules, vaccines, and biotherapeutics. The case studies cover different aspects of the analytical procedure selection process, such as the use of platform method development processes and procedures, the development of multiattribute analytical procedures, and the use of analytical technologies to provide product characterization knowledge in order to define or redefine the ATP. Challenges associated with method selection are discussed such as where existing pharmacopoeial monographs link acceptance criteria to specific types of analytical technology.

Vaccine Technologies and Platforms for Infectious Diseases: Current Progress, Challenges, and Opportunities

Vaccination is a key component of public health policy with demonstrated cost-effective benefits in protecting both human and animal populations. Vaccines can be manufactured under multiple forms including, inactivated (killed), toxoid, live attenuated, Virus-like Particles, synthetic peptide, polysaccharide, polysaccharide conjugate (glycoconjugate), viral vectored (vector-based), nucleic acids (DNA and mRNA) and bacterial vector/synthetic antigen presenting cells. Several processes are used in the manufacturing of vaccines and recent developments in medical/biomedical engineering, biology, immunology, and vaccinology have led to the emergence of innovative nucleic acid vaccines, a novel category added to conventional and subunit vaccines. In this review, we have summarized recent advances in vaccine technologies and platforms focusing on their mechanisms of action, advantages, and possible drawbacks.

Innovative vaccine platforms against infectious diseases: Under the scope of the COVID-19 pandemic

While classic vaccines have proved greatly efficacious in eliminating serious infectious diseases, innovative vaccine platforms open a new pathway to overcome dangerous pandemics via the development of safe and effective formulations. Such platforms play a key role either as antigen delivery systems or as immune-stimulators that induce both innate and adaptive immune responses. Liposomes or lipid nanoparticles, virus-like particles, nanoemulsions, polymeric or inorganic nanoparticles, as well as viral vectors, all belong to the nanoscale and are the main categories of innovative vaccines that are currently on the market or in clinical and preclinical phases. In this paper, we review the above formulations used in vaccinology and we discuss their connection with the development of safe and effective prophylactic vaccines against SARS-CoV-2.

Nanovaccine Delivery Approaches and Advanced Delivery Systems for the Prevention of Viral Infections: From Development to Clinical Application

Viral infections causing pandemics and chronic diseases are the main culprits implicated in devastating global clinical and socioeconomic impacts, as clearly manifested during the current COVID-19 pandemic. Immunoprophylaxis via mass immunisation with vaccines has been shown to be an efficient strategy to control such viral infections, with the successful and recently accelerated development of different types of vaccines, thanks to the advanced biotechnological techniques involved in the upstream and downstream processing of these products. However, there is still much work to be done for the improvement of efficacy and safety when it comes to the choice of delivery systems, formulations, dosage form and route of administration, which are not only crucial for immunisation effectiveness, but also for vaccine stability, dose frequency, patient convenience and logistics for mass immunisation. In this review, we discuss the main vaccine delivery systems and associated challenges, as well as the recent success in developing nanomaterials-based and advanced delivery systems to tackle these challenges. Manufacturing and regulatory requirements for the development of these systems for successful clinical and marketing authorisation were also considered. Here, we comprehensively review nanovaccines from development to clinical application, which will be relevant to vaccine developers, regulators, and clinicians.

Sterilizing Immunity against COVID-19: Developing Helper T cells I and II activating vaccines is imperative

Six months after the publication of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) sequence, a record number of vaccine candidates were listed, and quite a number of them have since been approved for emergency use against the novel coronavirus disease 2019 (COVID-19). This unprecedented pharmaceutical feat did not only show commitment, creativity and collaboration of the scientific community, but also provided a swift solution that prevented global healthcare system breakdown. Notwithstanding, the available data show that most of the approved COVID-19 vaccines protect only a proportion of recipients against severe disease but do not prevent clinical manifestation of COVID-19. There is therefore the need to probe further to establish whether these vaccines can induce sterilizing immunity, otherwise, COVID-19 vaccination would have to become a regular phenomenon. The emergence of SARS-CoV-2 variants could further affect the capability of the available COVID-19 vaccines to prevent infection and protect recipients from a severe form of the disease. These notwithstanding, data about which vaccine(s), if any, can confer sterilizing immunity are unavailable. Here, we discuss the immune responses to viral infection with emphasis on COVID-19, and the specific adaptive immune response to SARS-CoV-2 and how it can be harnessed to develop COVID-19 vaccines capable of conferring sterilizing immunity. We further propose factors that could be considered in the development of COVID-19 vaccines capable of stimulating sterilizing immunity. Also, an old, but effective vaccine development technology that can be applied in the development of COVID-19 vaccines with sterilizing immunity potential is reviewed.

An immunologist's perspective on anti-COVID-19 vaccines

PURPOSE OF REVIEW

Antisevere acute respiratory syndrome-corona virus 2 (SARS-CoV-2) vaccines may provide prompt, effective, and safe solution for the COVID-19 pandemic. Several vaccine candidates have been evaluated in randomized clinical trials (RCTs). Furthermore, data from observational studies mimicking real-life practice and studies on specific groups, such as pregnant women or immunocompromised patients who were excluded from RCTs, are currently available. The main aim of the review is to summarize and provide an immunologist's view on mechanism of action, efficacy and safety, and future challenges in vaccination against SARS-CoV-2.

RECENT FINDINGS

mRNA and recombinant viral vector-based vaccines have been approved for conditional use in Europe and the USA. They show robust humoral and cellular responses, high with efficacy in prevention of COVID-19 infection (66.9 95%) and favorable safety profile in RCTs. High efficacy of 80-92% was observed in real-life practice. A pilot study also confirmed good safety profile of the mRNA vaccines in pregnant women. Unlike in those with secondary immunodeficiencies where postvaccination responses did not occur, encouraging results were obtained in patients with inborn errors of immunity.

SUMMARY

Although both RCTs and observational studies suggest good efficacy and safety profiles of the vaccines, their long-term efficacy and safety are still being discussed. Despite the promising results, clinical evidence for specific groups such as children, pregnant and breastfeeding women, and immunocompromised patients, and for novel virus variants are lacking.

VIDEO ABSTRACT

http://links.lww.com/COAI/A21.

Counting on COVID-19 Vaccine: Insights into the Current Strategies, Progress and Future Challenges

The emergence of a novel coronavirus viz., severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 and its subsequent substantial spread produced the coronavirus disease 2019 (COVID-19) pandemic worldwide. Given its unprecedented infectivity and pathogenicity, the COVID-19 pandemic had a devastating impact on human health, and its clinical management has been a great challenge, which has led to the development and speedy trials of several vaccine candidates against SARS-CoV-2 at an exceptional pace. As a result, several COVID-19 vaccines were made commercially available in the first half of 2021. Although several COVID-19 vaccines showed promising results, crucial insights into their epidemiology, protective mechanisms, and the propensities of reinfection are not largely reviewed. In the present report, we provided insights into the prospects of vaccination against COVID-19 and assessed diverse vaccination strategies including DNA, mRNA, protein subunits, vector-based, live attenuated, and inactivated whole/viral particle-based vaccines. Next, we reviewed major aspects of various available vaccines approved by the World Health Organization and by the local administrations to use against COVID-19. Moreover, we comprehensively assessed the success of these approved vaccines and also their untoward effects, including the possibility of reinfection. We also provided an update on the vaccines that are under development and could be promising candidates in the future. Conclusively, we provided insights into the COVID-19 vaccine epidemiology, their potency, and propensity for SARS-CoV-2 reinfection, while a careful review of their current status, strategies, success, and future challenges was also presented.

The Rise of Vectored Vaccines: A Legacy of the COVID-19 Global Crisis

The COVID-19 pandemic represents a milestone in vaccine research and development in a global context. A worldwide effort, as never seen before, involved scientists from all over the world in favor of the fast, accurate and precise construction and testing of immunogens against the new coronavirus, SARS-CoV-2. Among all the vaccine strategies put into play for study and validation, those based on recombinant viral vectors gained special attention due to their effectiveness, ease of production and the amplitude of the triggered immune responses. Some of these new vaccines have already been approved for emergency/full use, while others are still in pre- and clinical trials. In this article we will highlight what is behind adeno-associated vectors, such as those presented by the immunogens ChaAdOx1, Sputnik, Convidecia (CanSino, Tianjin, China), and Janssen (Johnson & Johnson, New Jersey, EUA), in addition to other promising platforms such as Vaccinia virus MVA, influenza virus, and measles virus, among others.

Application of Non-Viral Vectors in Drug Delivery and Gene Therapy

Vectors and carriers play an indispensable role in gene therapy and drug delivery. Non-viral vectors are widely developed and applied in clinical practice due to their low immunogenicity, good biocompatibility, easy synthesis and modification, and low cost of production. This review summarized a variety of non-viral vectors and carriers including polymers, liposomes, gold nanoparticles, mesoporous silica nanoparticles and carbon nanotubes from the aspects of physicochemical characteristics, synthesis methods, functional modifications, and research applications. Notably, non-viral vectors can enhance the absorption of cargos, prolong the circulation time, improve therapeutic effects, and provide targeted delivery. Additional studies focused on recent innovation of novel synthesis techniques for vector materials. We also elaborated on the problems and future research directions in the development of non-viral vectors, which provided a theoretical basis for their broad applications.

Promising Technologies in the Field of Helminth Vaccines

Helminths contribute a larger global burden of disease than both malaria and tuberculosis. These eukaryotes have caused human infections since before our earliest recorded history (i.e.: earlier than 1200 B.C. for Schistosoma spp.). Despite the prevalence and importance of these infections, helminths are considered a neglected tropical disease for which there are no vaccines approved for human use. Similar to other parasites, helminths are complex organisms which employ a plethora of features such as: complex life cycles, chronic infections, and antigenic mimicry to name a few, making them difficult to target by conventional vaccine strategies. With novel vaccine strategies such as viral vectors and genetic elements, numerous constructs are being defined for a wide range of helminth parasites; however, it has yet to be discussed which of these approaches may be the most effective. With human trials being conducted, and a pipeline of potential anti-helminthic antigens, greater understanding of helminth vaccine-induced immunity is necessary for the development of potent vaccine platforms and their optimal design. This review outlines the conventional and the most promising approaches in clinical and preclinical helminth vaccinology.

Intranasal immunization with O-2'-Hydroxypropyl trimethyl ammonium chloride chitosan nanoparticles loaded with Newcastle disease virus DNA vaccine enhances mucosal immune response in chickens

Background

There has been a great interest in developing strategies for enhancing antigen delivery to the mucosal immune system as well as identifying mucosal active immunostimulating agents. To elevate the potential of O-2ʹ-Hydroxypropyl trimethyl ammonium chloride chitosan (O-2ʹ-HACC) as an adjuvant and mucosal immune delivery carrier for DNA vaccine, we prepared the O-2ʹ-HACC loaded with Newcastle disease virus (NDV) F gene plasmid DNA and C3d6 molecular adjuvant (O-2ʹ-HACC/pFDNA microparticles).

Results

The O-2ʹ-HACC/pFDNA exhibited a regular spherical morphology with a particle size of 202.3 ± 0.52 nm, a zeta potential of 50.8 ± 8.21 mV, encapsulation efficiency of 90.74 ± 1.10%, and a loading capacity of 49.84 ± 1.20%. The plasmid DNA could be sustainably released from the O-2ʹ-HACC/pFDNA after an initial burst release. Intranasal vaccination of chickens immunized with O-2ʹ-HACC/pFDNA not only induced higher anti-NDV IgG and sIgA antibody titers but also significantly promoted lymphocyte proliferation and produced higher levels of IL-2, IL-4, IFN-γ, CD4+, and CD8 + T lymphocytes compared with the NDV commercial live attenuated vaccine. Intranasal delivery of the O-2ʹ-HACC/pFDNA enhanced humoral, cellular, and mucosal immune responses and protected chickens from the infection of highly virulent NDV compared with the intramuscular delivery.

Conclusions

Collectively, our findings indicated that the O-2ʹ-HACC could be used as a vaccine adjuvant and delivery system for mucosal immunity and have an immense application promise.

Graphic Abstract

Intracellular controlled release prolongs the time period of siRNA-based gene suppression

RNA interference (RNAi) is a gene silencing process by inhibiting a target messenger RNA (mRNA) in the sequence-specific manner in the cell cytoplasm. Small interfering RNA (siRNA) cleaves the target mRNA. However, siRNA is not generally internalized into cells in the native state. The objective of this study is to prepare cationized gelatin nanospheres (cGNS) incorporating small interfering RNA (siRNA) and to prolong the time period of gene expression suppression. The cGNS with different degradabilities were prepared to evaluate the effect on the suppression of gene expression. There was no difference in the apparent size and zeta potential of cGNS among the amounts of glutaraldehyde (GA) added for crosslinking. The degradation of cGNS tended to become slowly with an increase of GA amounts used in preparation. After MC3T3-E1 cells were incubated with cGNS incorporating siRNA, the gene expression of cells was evaluated by real-time polymerase chain reaction (PCR). The time period of gene suppression increased with an increased amount of siRNA incorporated in cGNS. Moreover, the significant gene suppression was extended over 4 days. It is concluded that the intracellular controlled release with the cGNS enabled siRNA to prolong the time period of gene expression suppression.

Administration of COVID-19 vaccines in immunocompromised patients

Since the beginning of vaccination programs against COVID-19 in different countries, several populations such as patients with specific immunological conditions have been considered as the priorities for immunization. In this regard, patients with autoimmune diseases or those receiving immunosuppressive agents and anti-cancer therapies, need special attention. However, no confirmed data is presently available regarding COVID-19 vaccines in these populations due to exclusion from the conducted clinical trials. Given the probable suppression or over-activation of the immune system in such patients, reaching a consensus for their vaccination is critical, besides gathering data and conducting trials, which could probably clarify this matter in the future. In this review, besides a brief on the available COVID-19 vaccines, considerations and available knowledge about administering similar vaccines in patients with cancer, hematopoietic stem cell transplantation, solid organ transplantation, multiple sclerosis (MS), inflammatory bowel disease (IBD), and rheumatologic and dermatologic autoimmune disorders are summarized to help in decision making. As discussed, live-attenuated viruses, which should be avoided in these groups, are not employed in the present COVID-19 vaccines. Thus, the main concern regarding efficacy could be met using a potent COVID-19 vaccine. Moreover, the vaccination timing for maximum efficacy could be decided according to the patient’s condition, indicated medications, and the guides provided here. Post-vaccination monitoring is also advised to ensure an adequate immune response. Further studies in this area are urgently warranted.

From COVID-19 to Cancer mRNA Vaccines: Moving From Bench to Clinic in the Vaccine Landscape

Recently, mRNA vaccines have become a significant type of therapeutic and have created new fields in the biopharmaceutical industry. mRNA vaccines are promising next-generation vaccines that have introduced a new age in vaccinology. The recent approval of two COVID-19 mRNA vaccines (mRNA-1273 and BNT162b2) has accelerated mRNA vaccine technology and boosted the pharmaceutical and biotechnology industry. These mRNA vaccines will help to tackle COVID-19 pandemic through immunization, offering considerable hope for future mRNA vaccines. Human trials with data both from mRNA cancer vaccines and mRNA infectious disease vaccines have provided encouraging results, inspiring the pharmaceutical and biotechnology industries to focus on this area of research. In this article, we discuss current mRNA vaccines broadly in two parts. In the first part, mRNA vaccines in general and COVID-19 mRNA vaccines are discussed. We presented the mRNA vaccine structure in general, the different delivery systems, the immune response, and the recent clinical trials for mRNA vaccines (both for cancer mRNA vaccines and different infectious diseases mRNA vaccines). In the second part, different COVID-19 mRNA vaccines are explained. Finally, we illustrated a snapshot of the different leading mRNA vaccine developers, challenges, and future prospects of mRNA vaccines.

Updates on the coronavirus disease 2019 vaccine and consideration in children

Humanity has been suffering from the global severe acute respiratory syndrome coronavirus 2 pandemic that began late in 2019. In 2020, for the first time in history, new vaccine platforms-including mRNA vaccines and viral vector-based DNA vaccines-have been given emergency use authorization, leading to mass vaccinations. The purpose of this article is to review the currently most widely used coronavirus disease 2019 vaccines, investigate their immunogenicity and efficacy data, and analyze the vaccine safety profiles that have been published, to date.

Evolving pharmacovigilance requirements with novel vaccines and vaccine components

This paper explores the pipeline of new and upcoming vaccines as it relates to monitoring their safety. Compared with most currently available vaccines, that are constituted of live attenuated organisms or inactive products, future vaccines will also be based on new technologies. Several products that include such technologies are either already licensed or at an advanced stage of clinical development. Those include viral vectors, genetically attenuated live organisms, nucleic acid vaccines, novel adjuvants, increased number of antigens present in a single vaccine, novel mode of vaccine administration and thermostabilisation. The Global Advisory Committee on Vaccine Safety (GACVS) monitors novel vaccines, from the time they become available for large scale use. GACVS maintains their safety profile as evidence emerges from post-licensure surveillance and observational studies. Vaccines and vaccine formulations produced with novel technologies will have different safety profiles that will require adapting pharmacovigilance approaches. For example, GACVS now considers viral vector templates developed on the model proposed by Brighton Collaboration. The characteristics of those novel products will also have implications for the risk management plans (RMPs). Questions related to the duration of active monitoring for genetic material, presence of adventitious agents more easily detected with enhanced biological screening, or physiological mechanisms of novel adjuvants are all considerations that will belong to the preparation of RMPs. In addition to assessing those novel products and advising experts, GACVS will also consider how to more broadly communicate about risk assessment, so vaccine users can also benefit from the committee’s advice.

Mutations of SARS-CoV-2 spike protein: Implications on immune evasion and vaccine-induced immunity

Responsible for more than 4.9 million deaths so far, COVID-19, caused by SARS-CoV-2, is instigating devastating effects on the global health care system whose impacts could be longer for the years to come. Acquiring a comprehensive knowledge of host-virus interaction is critical for designing effective vaccines and/or drugs. Understanding the evolution of the virus and the impact of genetic variability on host immune evasion and vaccine efficacy is helpful to design novel strategies to minimize the effects of the emerging variants of concern (VOC). Most vaccines under development and/or in current use target the spike protein owning to its unique function of host receptor binding, relatively conserved nature, potent immunogenicity in inducing neutralizing antibodies, and being a good target of T cell responses. However, emerging SARS-CoV-2 strains are exhibiting variability on the spike protein which could affect the efficacy of vaccines and antibody-based therapies in addition to enhancing viral immune evasion mechanisms. Currently, the degree to which mutations on the spike protein affect immunity and vaccination, and the ability of the current vaccines to confer protection against the emerging variants attracts much attention. This review discusses the implications of SARS-CoV-2 spike protein mutations on immune evasion and vaccine-induced immunity and forward directions which could contribute to future studies focusing on designing effective vaccines and/or immunotherapies to consider viral evolution. Combining vaccines derived from different regions of the spike protein that boost both the humoral and cellular wings of adaptive immunity could be the best options to cope with the emerging VOC.

Optimal CD8+ T-cell memory formation following subcutaneous cytomegalovirus infection requires virus replication but not early dendritic cell responses

Cytomegalovirus (CMV) induction of large frequencies of highly functional memory T cells has attracted much interest in the utility of CMV‐based vaccine vectors, with exciting preclinical data obtained in models of infectious diseases and cancer. However, pathogenesis of human CMV (HCMV) remains a concern. Attenuated CMV‐based vectors, such as replication‐ or spread‐deficient viruses, potentially offer an alternative to fully replicating vectors. However, it is not well understood how CMV attenuation impacts vector immunogenicity, particularly when administered via relevant routes of immunization such as the skin. Herein, we used the murine cytomegalovirus (MCMV) model to investigate the impact of vector attenuation on T‐cell memory formation following subcutaneous administration. We found that the spread‐deficient virus (ΔgL‐MCMV) was impaired in its ability to induce memory CD8⁺ T cells reactive to some (M38, IE1) but not all (IE3) viral antigens. Impaired‐memory T‐cell development was associated with a preferential and pronounced loss of polyfunctional (IFN‐γ⁺ TNF‐α⁺) T cells and also reduced accumulation of TCF1⁺ T cells, and was not rescued by increasing the dose of replication‐defective MCMV. Finally, whilst vector attenuation reduced dendritic cell (DC) recruitment to skin‐draining lymph nodes, systematic depletion of multiple DC subsets during acute subcutaneous MCMV infection had a negligible impact on T‐cell memory formation, implying that attenuated responses induced by replication‐deficient vectors were likely not a consequence of impaired initial DC activation. Thus, overall, these data imply that the choice of antigen and/or cloning strategy of exogenous antigen in combination with the route of immunization may influence the ability of attenuated CMV vectors to induce robust functional T‐cell memory.

Older adults: panoramic view on the COVID-19 vaccination

In December 2020, COVID-19 vaccination started in many countries, with which the world community hopes to stop the further spread of the current pandemic. More than 90% of sick and deceased patients belong to the category of older adults (65 years and older). This category of the population is most vulnerable to infectious diseases, so vaccination is the most effective preventive strategy, the need for which for older adults is indisputable. Here we briefly summarize information about age-related changes in the immune system and present current data on their impact on the formation of the immune response to vaccination. Older age is accompanied by the process of biological aging accompanied by involution of the immune system with increased susceptibility to infections and a decrease in the effect of immunization. Therefore, in the ongoing mass COVID-19 vaccination, the older adults are a growing public health concern. The authors provide an overview of the various types of COVID-19 vaccines approved for mass immunization of the population by the end of 2020, including older adults, as well as an overview of strategies and platforms to improve the effectiveness of vaccination of this population. In the final part, the authors propose for discussion a system for assessing the safety and monitoring the effectiveness of COVID-19 vaccines for the older adults.

An Updated Review of SARS-CoV-2 Vaccines and the Importance of Effective Vaccination Programs in Pandemic Times

Since the worldwide COVID-19 pandemic was declared a year ago, the search for vaccines has become the top priority in order to restore normalcy after 2.5 million deaths worldwide, overloaded sanitary systems, and a huge economic burden. Vaccine development has represented a step towards the desired herd immunity in a short period of time, owing to a high level of investment, the focus of researchers, and the urge for the authorization of the faster administration of vaccines. Nevertheless, this objective may only be achieved by pursuing effective strategies and policies in various countries worldwide. In the present review, some aspects involved in accomplishing a successful vaccination program are addressed, in addition to the importance of vaccination in a pandemic in the face of unwillingness, conspiracy theories, or a lack of information among the public. Moreover, we provide some updated points related to the landscape of the clinical development of vaccine candidates, specifically, the top five vaccines that are already being assessed in Phase IV clinical trials (BNT162b2, mRNA-1273, AZD1222, Ad26.COV2.S, and CoronaVac).

Essential considerations during vaccine design against COVID-19 and review of pioneering vaccine candidate platforms

The calamity of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), COVID-19, is still a global human tragedy. To date, no specific antiviral drug or therapy has been able to break the widespread of SARS-CoV2. It has been generally believed that stimulating protective immunity via universal vaccination is the individual strategy to manage this pandemic. Achieving an effective COVID-19 vaccine requires attention to the immunological and non-immunological standpoints mentioned in this article. Here, we try to introduce the considerable immunological aspects, potential antigen targets, appropriate adjuvants as well as key points in the various stages of COVID-19 vaccine development. Also, the principal features of the preclinical and clinical studies of pioneering COVID-19 vaccine candidates were pointed out by reviewing the available information. Finally, we discuss the key challenges in the successful design of the COVID-19 vaccine and address the most fundamental strengths and weaknesses of common vaccine platforms.