Immunogenicity of a receptor-binding domain of SARS coronavirus spike protein in mice: implications for a subunit vaccine

Design and Assessment of a Novel In Silico Approach for Developing a Next-Generation Multi-Epitope Universal Vaccine Targeting Coronaviruses

In the past two decades, there have been three coronavirus outbreaks that have caused significant economic and health crises. Biologists predict that more coronaviruses may emerge in the near future. Therefore, it is crucial to develop preventive vaccines that can effectively combat multiple coronaviruses. In this study, we employed computational approaches to analyze genetically related coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants, focusing on the spike glycoprotein as a potential vaccine candidate. By predicting common epitopes, we identified the top epitopes and combined them to create a multi-epitope candidate vaccine. The overall quality of the candidate vaccine was validated through in silico analyses, confirming its antigenicity, immunogenicity, and stability. In silico docking and simulation studies suggested a stable interaction between the multi-epitope candidate vaccine and human toll-like receptor 2 (TLR2). In silico codon optimization and cloning were used to further explore the successful expression of the designed candidate vaccine in a prokaryotic expression system. Based on computational analysis, the designed candidate vaccine was found to be stable and non-allergenic in the human body. The efficiency of the multi-epitope vaccine in triggering effective cellular and humoral immune responses was assessed through immune stimulation, demonstrating that the designed candidate vaccine can elicit specific immune responses against multiple coronaviruses. Therefore, it holds promise as a potential candidate vaccine against existing and future coronaviruses.

A tool for the cheap and rapid screening of SARS-CoV-2 variants of concern (VoCs) by Sanger sequencing

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emerging virus that, since March 2020, has been responsible for a global and ongoing pandemic. Its rapid spread over the past nearly 3 years has caused novel variants to arise. To monitor the circulation and emergence of SARS-CoV-2 variants, surveillance systems based on nucleotide mutations are required. In this regard, we searched in the spike, ORF8, and nucleocapsid genes to detect variable sites among SARS-CoV-2 variants. We describe polymorphic genetic regions that enable us to differentiate between the Alpha, Beta, Gamma, Delta, and Omicron variants of concern (VoCs). We found 21 relevant mutations, 13 of which are unique for Omicron lineages BA.1/BA.1.1, BA.2, BA.3, BA.4, and BA.5. This genetic profile enables the discrimination between VoCs using only four reverse transcription PCR fragments and Sanger sequencing, offering a cheaper and faster alternative to whole-genome sequencing for SARS-CoV-2 surveillance. IMPORTANCE Our work describes a new (Sanger sequencing-based) screening methodology for SARS-CoV-2, performing PCR amplifications of a few target regions to detect diagnostic mutations between virus variants. Using the methodology developed in this work, we were able to discriminate between the following VoCs: Alpha, Beta, Gamma, Delta, and Omicron (BA.1/BA.1.1, BA.2, BA.3, BA.4, and BA.5). This becomes important, especially in low-income countries where current methodologies like next-generation sequencing have prohibitive costs. Furthermore, rapid detection would allow sanitary authorities to take rapid measures to limit the spread of the virus and therefore reduce the probability of new virus dispersion. With this methodological approach, 13 previously unreported diagnostic mutations among several Omicron lineages were found.

Future prospects in mRNA vaccine development

The recent advancements in messenger ribonucleic acid (mRNA) vaccine development have vastly enhanced their use as alternatives to conventional vaccines in the prevention of various infectious diseases and treatment of several types of cancers. This is mainly due to their remarkable ability to stimulate specific immune responses with minimal clinical side effects. This review gives a detailed overview of mRNA vaccines currently in use or at various stages of development, the recent advancements in mRNA vaccine development, and the challenges encountered in their development. Future perspectives on this technology are also discussed.

CHO-produced RBD-Fc subunit vaccines with alternative adjuvants generate immune responses against SARS-CoV-2

Subunit vaccines feature critical advantages over other vaccine platforms such as stability, price, and minimal adverse effects. To maximize immunological protection of subunit vaccines, adjuvants are considered as main components that are formulated within the subunit vaccine. They can modulate adverse effects and enhance immune outcomes. However, the most suitable formulation providing the best immunological outcomes and safety are still under investigation. In this report, we combined recombinant RBD with human IgG1 Fc to create an RBD dimer. This fusion protein was expressed in CHO and formulated with alternative adjuvants with different immune activation including Montanide ISA51, Poly (I:C), and MPLA/Quil-A® as potential vaccine candidate formulations. Using the murine model, a potent induction of anti-RBD IgG antibodies in immunized mice sera were observed. IgG subclass analyses (IgG1/IgG2a) illustrated that all adjuvanted formulations could stimulate both Th1 and Th2-type immune responses in particular Poly (I:C) and MPLA/Quil-A®, eliciting greater balance. In addition, Montanide ISA51-formulated RBD-Fc vaccination provided a promising level of neutralizing antibodies against live wild-type SARS-CoV-2 in vitro followed by Poly (I:C) and MPLA/Quil-A®, respectively. Also, mice sera from adjuvanted formulations could strongly inhibit RBD:ACE2 interaction. This study offers immunogenicity profiles, forecasted safety based on Vaccine-associated enhanced disease (VAED) caused by Th1-skewed immunity, and neutralizing antibody analysis of candidates of RBD-Fc-based subunit vaccine formulations to obtain an alternative subunit vaccine formulation against SARS-CoV-2.

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

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

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

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

Structural basis for mouse receptor recognition by SARS-CoV-2 omicron variant

The sudden emergence and rapid spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant has raised questions about its animal reservoir. Here, we investigated receptor recognition of the omicron's receptor-binding domain (RBD), focusing on four of its mutations (Q493R, Q498R, N501Y, and Y505H) surrounding two mutational hotspots. These mutations have variable effects on the RBD's affinity for human angiotensin-converting enzyme 2 (ACE2), but they all enhance the RBD's affinity for mouse ACE2. We further determined the crystal structure of omicron RBD complexed with mouse ACE2. The structure showed that all four mutations are viral adaptations to mouse ACE2: three of them (Q493R, Q498R, and Y505H) are uniquely adapted to mouse ACE2, whereas the other one (N501Y) is adapted to both human ACE2 and mouse ACE2. These data reveal that the omicron RBD was well adapted to mouse ACE2 before omicron started to infect humans, providing insight into the potential evolutionary origin of the omicron variant.

Small GTPase-a Key Role in Host Cell for Coronavirus Infection and a Potential Target for Coronavirus Vaccine Adjuvant Discovery

Small GTPases are signaling molecules in regulating key cellular processes (e.g., cell differentiation, proliferation, and motility) as well as subcellular events (e.g., vesicle trafficking), making them key participants, especially in a great array of coronavirus infection processes. In this review, we discuss the role of small GTPases in the coronavirus life cycle, especially pre-entry, endocytosis, intracellular traffic, replication, and egress from the host cell. Furthermore, we also suggest the molecules that have potent adjuvant activity by targeting small GTPases. These studies provide deep insights and references to understand the pathogenesis of coronavirus as well as to propose the potential of small GTPases as targets for adjuvant development.

The chimera of S1 and N proteins of SARS-CoV-2: can it be a potential vaccine candidate for COVID-19?

INTRODUCTION

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emerged as one of the biggest global health issues. Spike protein (S) and nucleoprotein (N), the major immunogenic components of SARS-CoV-2, have been shown to be involved in the attachment and replication of the virus inside the host cell.

AREAS COVERED

Several investigations have shown that the SARS-CoV-2 nucleoprotein can elicit a cell-mediated immune response capable of regulating viral replication and lowering viral burden. However, the development of an effective vaccine that can stop the transmission of SARS-CoV-2 remains a matter of concern. Literature was retrieved using the keywords COVID-19 vaccine, role of nucleoprotein as vaccine candidate, spike protein, nucleoprotein immune responses against SARS-CoV-2, and chimera vaccine in PubMed, Google Scholar, and Google.

EXPERT OPINION

We have focussed on the use of chimera protein, consisting of N and S-1 protein components of SARS-CoV-2, as a potential vaccine candidate. This may act as a polyvalent mixed recombinant protein vaccine to elicit a strong T and B cell immune response, which will be capable of neutralizing the wild and mutated variants of SARS-CoV-2, and also restricting its attachment, replication, and budding in the host cell.

Monoclonal antibody designed for SARS-nCoV-2 spike protein of receptor binding domain on antigenic targeted epitopes for inhibition to prevent viral entry

SARS, or severe acute respiratory syndrome, is caused by a novel coronavirus (COVID-19). This situation has compelled many pharmaceutical R&D companies and public health research sectors to focus their efforts on developing effective therapeutics. SARS-nCoV-2 was chosen as a protein spike to targeted monoclonal antibodies and therapeutics for prevention and treatment. Deep mutational scanning created a monoclonal antibody to characterize the effects of mutations in a variable antibody fragment based on its expression levels, specificity, stability, and affinity for specific antigenic conserved epitopes to the Spike-S-Receptor Binding Domain (RBD). Improved contacts between Fv light and heavy chains and the targeted antigens of RBD could result in a highly potent neutralizing antibody (NAbs) response as well as cross-protection against other SARS-nCoV-2 strains. It undergoes multipoint core mutations that combine enhancing mutations, resulting in increased binding affinity and significantly increased stability between RBD and antibody. In addition, we improved. Structures of variable fragment (Fv) complexed with the RBD of Spike protein were subjected to our established in-silico antibody-engineering platform to obtain enhanced binding affinity to SARS-nCoV-2 and develop ability profiling. We found that the size and three-dimensional shape of epitopes significantly impacted the activity of antibodies produced against the RBD of Spike protein. Overall, because of the conformational changes between RBD and hACE2, it prevents viral entry. As a result of this in-silico study, the designed antibody can be used as a promising therapeutic strategy to treat COVID-19.

SARS-CoV-2 and Influenza Viruses: Strategies to Cope with Co-infection and Bioinformatics Perspective

Almost a century after the devastating pandemic of the Spanish flu, humankind is facing the relatively comparable global outbreak of COVID‐19. COVID‐19 is an infectious disease caused by SARS‐CoV‐2 with an unprecedented transmission pattern. In the face of the recent repercussions of COVID‐19, many have argued that the clinical experience with influenza through the last century may have tremendous implications in the containment of this newly emerged viral disease. During the last 2 years, from the emergence of COVID‐19, tremendous advances have been made in diagnosing and treating coinfections. Several approved vaccines are available now for the primary prevention of COVID‐19 and specific treatments exist to alleviate symptoms. The present review article aims to discuss the pathophysiology, diagnosis, and treatment of SARS‐CoV‐2 and influenza A virus coinfection while delivering a bioinformatics‐based insight into this subject matter.

SARS-CoV-2 E484K Mutation Narrative Review: Epidemiology, Immune Escape, Clinical Implications, and Future Considerations

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread rapidly over the world and claimed million lives. The virus evolves constantly, and a swarm of mutants is a now major concern globally. Distinct variants could have independently converged on same mutation, despite being detected in different geographic regions, which suggested it could confer an evolutionary advantage. E484K has rapidly emerged and has frequently been detected in several SARS-CoV-2 variants of concern. In this study, we review the epidemiology and impact of E484K, its effects on neutralizing effect of several monoclonal antibodies, convalescent plasma, and post-vaccine sera.

Design and Immunological Properties of the Novel Subunit Virus-like Vaccine against SARS-CoV-2

The COVID-19 pandemic is ongoing, and the need for safe and effective vaccines to prevent infection and to control spread of the virus remains urgent. Here, we report the development of a SARS-CoV-2 subunit vaccine candidate (Betuvax-CoV-2) based on RBD and SD1 domains of the spike (S) protein fused to a human IgG1 Fc fragment. The antigen is adsorbed on betulin adjuvant, forming spherical particles with a size of 100-180 nm, mimicking the size of viral particles. Here we confirm the potent immunostimulatory activity of betulin adjuvant, and demonstrate that two immunizations of mice with Betuvax-CoV-2 elicited high titers of RBD-specific antibodies. The candidate vaccine was also effective in stimulating a neutralizing antibody response and T cell immunity. The results indicate that Betuvax-CoV-2 has good potential for further development as an effective vaccine against SARS-CoV-2.

Murine monoclonal antibodies against RBD of the SARS-CoV-2 spike protein as useful analytical tools for subunit vaccine development and clinical trials

COVID-19 pandemic poses a serious threat to human health; it has completely disrupted global stability, making vaccine development an important goal to achieve. Monoclonal antibodies play an important role in subunit vaccines strategies. In this work, nine murine MAbs against the RBD of the SARS-CoV-2 spike protein were obtained by hybridoma technology. Characterization of purified antibodies demonstrated that five of them have affinities in the order of 10⁸ L/mol. Six MAbs showed specific recognition of different recombinant RBD-S antigens in solution. Studies of the additivity index of anti-RBD antibodies, by using a novel procedure to determine the additivity cut point, showed recognition of at least five different epitopes. The MAbs CBSSRBD-S.11 and CBSSRBD-S.8 revealed significant neutralizing capacity against SARS-CoV-2 in an ACE2-RBD binding inhibition assay (IC₅₀ = 85.5pM and IC₅₀ = 122.7pM, respectively) and in a virus neutralizing test with intact SARS-CoV-2 (VN₅₀ = 0.552 nM and VN₅₀ = 4.854 nM, respectively) when D614G strain was used to infect Vero cells. Also CBSSRBD-S.11 neutralized the SARS-CoV-2 strains Alpha and Beta: VN₅₀ = 0.707 nM and VN₅₀ = 0.132 nM, respectively. The high affinity CBSSRBD-S.8 and CBSSRBD-S.7 recognized different epitopes, so they are suitable for the development of a sandwich ELISA to quantitate RBD-S recombinant antigens in biomanufacturing processes, as well as in pharmacokinetic studies in clinical and preclinical trials.

Emerging importance of nanotechnology-based approaches to control the COVID-19 pandemic; focus on nanomedicine iterance in diagnosis and treatment of COVID-19 patients

The ongoing outbreak of the newly emerged coronavirus disease 2019, which has tremendously concerned global health safety, is the result of infection with severe acute respiratory syndrome of coronavirus 2 with high morbidity and mortality. Because of the coronavirus has no specific treatment, so it is necessary to early detection and produce antiviral agents and efficacious vaccines in order to prevent the contagion of coronavirus. Due to the unique properties of nanomaterials, nanotechnology appears to be a highly relevant discipline in this global emergency, providing expansive chemical functionalization to develop advanced biomedical tools. Fascinatingly, nanomedicine as a hopeful approach for the treatment and diagnosis of diseases, could efficiently help success the fight among coronavirus and host cells. In this review, we will critically discuss how nanomedicine can play an indispensable role in creating useful treatments and diagnostics for coronavirus.

[Vaccine against COVID-19]

The COVID-19 pandemic has produced a huge health, economic and psychological collapse in our society. Health workers have had to face one of the greatest challenges in history, trying to show the population how to deal with this disease. We have learned that vaccines are the great instrument for the fight against infectious diseases and a large number of them began to appear, not as a product of chance but as a product of the enormous progress experienced in recent years with vaccines against new infectious diseases, against other diseases such as Alzheimer's and especially against cancer. All this knowledge has been applied to this disease. Practitioners lamented the little information available to them when asked questions from patients. This document wanted to be a response to these concerns, with a scientific desire, with evidence that put aside unverified data and hoaxes. Faced with an avalanche of information, most of it without the appropriate "peer review" as indicated in the introduction, any publication becomes obsolete at the time of publication, and we opted for an "online" publication, with the incorporation of versions. This online publication has been published in the documents of Spanish Society of Chemotherapy, at https://seq.es/vacunacion-covid-19.

SARS-CoV-2 spike protein: Site-specific breakpoints for the development of COVID-19 vaccines

SARS-CoV2 is a member of human coronaviruses and is the causative agent of the present pandemic COVID-19 virus. In order to control COVID-19, studies on viral structure and mechanism of infectivity and pathogenicity are sorely needed. The spike (S) protein is comprised of S1 & S2 subunits. These spike protein subunits enable viral attachment by binding to the host cell via ACE-2 (angiotensin converting enzyme-2) receptor, thus facilitating the infection. During viral entry, one of the key steps is the cleavage of the S1-S2 spike protein subunits via surface TMPRSS2 (transmembrane protease serine 2) and results in viral infection. Hence, the S-protein is critical for the viral attachment and penetration into the host. The rapid advancement of our knowledge on the structural and functional aspects of the spike protein could lead to development of numerous candidate vaccines against SARS-CoV2. Here the authors discuss about the structure of spike protein and explore its related functions. Our aim is to provide a better understanding that may aid in fighting against CoVID-19 and its treatment.

Development of recombinant COVID-19 vaccine based on CHO-produced, prefusion spike trimer and alum/CpG adjuvants

COVID-19 pandemic has severely impacted the public health and social economy worldwide. A safe, effective, and affordable vaccine against SARS-CoV-2 infections/diseases is urgently needed. We have been developing a recombinant vaccine based on a prefusion-stabilized spike trimer of SARS-CoV-2 and formulated with aluminium hydroxide and CpG 7909. The spike protein was expressed in Chinese hamster ovary (CHO) cells, purified, and prepared as a stable formulation with the dual adjuvant. Immunogenicity studies showed that candidate vaccines elicited robust neutralizing antibody responses and substantial CD4⁺ T cell responses in both mice and non-human primates. And vaccine-induced neutralizing antibodies persisted at high level for at least 6 months. Challenge studies demonstrated that candidate vaccine reduced the viral loads and inflammation in the lungs of SARS-CoV-2 infected golden Syrian hamsters significantly. In addition, the vaccine-induced antibodies showed cross-neutralization activity against B.1.1.7 and B.1.351 variants. These data suggest candidate vaccine is efficacious in preventing SARS-CoV-2 infections and associated pneumonia, thereby justifying ongoing phase I/II clinical studies in China (NCT04982068 and NCT04990544).

COVID-19 Animal Models and Vaccines: Current Landscape and Future Prospects

The worldwide pandemic of coronavirus disease 2019 (COVID-19) has become an unprecedented challenge to global public health. With the intensification of the COVID-19 epidemic, the development of vaccines and therapeutic drugs against the etiological agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is also widespread. To prove the effectiveness and safety of these preventive vaccines and therapeutic drugs, available animal models that faithfully recapitulate clinical hallmarks of COVID-19 are urgently needed. Currently, animal models including mice, golden hamsters, ferrets, nonhuman primates, and other susceptible animals have been involved in the study of COVID-19. Moreover, 117 vaccine candidates have entered clinical trials after the primary evaluation in animal models, of which inactivated vaccines, subunit vaccines, virus-vectored vaccines, and messenger ribonucleic acid (mRNA) vaccines are promising vaccine candidates. In this review, we summarize the landscape of animal models for COVID-19 vaccine evaluation and advanced vaccines with an efficacy range from about 50% to more than 95%. In addition, we point out future directions for COVID-19 animal models and vaccine development, aiming at providing valuable information and accelerating the breakthroughs confronting SARS-CoV-2.

COVID-19 and Diabetes Mellitus: A Complex Interplay

COVID-19 pandemic, which caused by the newly emerged severe acute respiratory syndrome coronavirus-2 (SARS- CoV-2), puts the entire world in an unprecedented crisis, leaving behind huge human losses and serious socio-economical damages. The clinical spectrum of COVID-19 varies from asymptomatic to multi-organ manifestations. Diabetes mellitus (DM) is a chronic inflammatory condition, which associated with metabolic and vascular abnormalities, increases the risk for SARS-CoV-2 infection, severity and mortality. Due to global prevalence, DM effect on COVID-19 outcomes as well as the potential mechanisms by which DM modulates the host-viral interactions and host-immune responses are discussed in this review. This review also highlights the effects of anti-diabetic drugs on treatment of SARS-CoV-2 infection and vice versa.

Current Update on Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine Development with a Special Emphasis on Gene Therapy Viral Vector Design and Construction for Vaccination

Severe acute respiratory syndrome (SARS) is a newly emerging infectious disease (COVID-19) caused by the novel coronavirus SARS-coronavirus 2 (CoV-2). To combat the devastating spread of SARS-CoV-2, extraordinary efforts from numerous laboratories have focused on the development of effective and safe vaccines. Traditional live-attenuated or inactivated viral vaccines are not recommended for immunocompromised patients as the attenuated virus can still cause disease via phenotypic or genotypic reversion. Subunit vaccines require repeated dosing and adjuvant use to be effective, and DNA vaccines exhibit lower immune responses. mRNA vaccines can be highly unstable under physiological conditions. On the contrary, naturally antigenic viral vectors with well-characterized structure and safety profile serve as among the most effective gene carriers to provoke immune response via heterologous gene transfer. Viral vector-based vaccines induce both an effective cellular immune response and a humoral immune response owing to their natural adjuvant properties via transduction of immune cells. Consequently, viral vectored vaccines carrying the SARS-CoV-2 spike protein have recently been generated and successfully used to activate cytotoxic T cells and develop a neutralizing antibody response. Recent progress in SARS-CoV-2 vaccines, with an emphasis on gene therapy viral vector-based vaccine development, is discussed in this review.

Comparative Immunomodulatory Evaluation of the Receptor Binding Domain of the SARS-CoV-2 Spike Protein; a Potential Vaccine Candidate Which Imparts Potent Humoral and Th1 Type Immune Response in a Mouse Model

The newly emerged novel coronavirus, SARS-CoV-2, the causative agent of COVID-19 has proven to be a threat to the human race globally, thus, vaccine development against SARS-CoV-2 is an unmet need driving mass vaccination efforts. The receptor binding domain of the spike protein of this coronavirus has multiple neutralizing epitopes and is associated with viral entry. Here we have designed and characterized the SARS-CoV-2 spike protein fragment 330-526 as receptor binding domain 330-526 (RBD330-526) with two native glycosylation sites (N331 and N343); as a potential subunit vaccine candidate. We initially characterized RBD330-526 biochemically and investigated its thermal stability, humoral and T cell immune response of various RBD protein formulations (with or without adjuvant) to evaluate the inherent immunogenicity and immunomodulatory effect. Our result showed that the purified RBD immunogen is stable up to 72 h, without any apparent loss in affinity or specificity of interaction with the ACE2 receptor. Upon immunization in mice, RBD generates a high titer humoral response, elevated IFN-γ producing CD4+ cells, cytotoxic T cells, and robust neutralizing antibodies against live SARS-CoV-2 virus. Our results collectively support the potential of RBD330-526 as a promising vaccine candidate against SARS-CoV-2.

Methodical Design of Viral Vaccines Based on Avant-Garde Nanocarriers: A Multi-Domain Narrative Review

The current health crisis caused by coronavirus 2019 (COVID-19) and associated pathogens emphasize the urgent need for vaccine systems that can generate protective and long-lasting immune responses. Vaccination, employing peptides, nucleic acids, and other molecules, or using pathogen-based strategies, in fact, is one of the most potent approaches in the management of viral diseases. However, the vaccine candidate requires protection from degradation and precise delivery to the target cells. This can be achieved by employing different types of drug and vaccine delivery strategies, among which, nanotechnology-based systems seem to be more promising. This entry aims to provide insight into major aspects of vaccine design and formulation to address different diseases, including the recent outbreak of SARS-CoV-2. Special emphasis of this review is on the technical and practical aspects of vaccine construction and theranostic approaches to precisely target and localize the active compounds.

Promising role of defensins peptides as therapeutics to combat against viral infection

Antimicrobial peptides (AMPs) are ubiquitously present small peptides, which play a critical function in the innate immune system. The defensin class of AMPs represented an evolutionarily ancient family containing cationic cysteine residue and frequently expressed in epithelial or neutrophils cells. It plays myriad functions in host innate immune responses against various infection. Defensin has a broad spectrum of antimicrobial activities, including anti-bacteria, anti-viruses (AVPs), anti-fungi, anti-cancers, and also overcoming bacterial drug resistance. In this review, we compiled the progress on defensin, particularly incorporating the mechanism of action, their application as an antiviral agent, prospects in different areas, and limitations to be solved as an antiviral peptide. Defensins were explored, in particular, their capacity to stimulate innate and adaptive immunity by trigging as anti-coronavirus (COVID-19) peptides. The present review summarised its immunomodulatory and immunoenhancing properties and predominantly focused on its promising therapeutic adjuvant choices for combat against viral infection.

Nanocarrier vaccines for SARS-CoV-2

The SARS-CoV-2 global pandemic has seen rapid spread, disease morbidities and death associated with substantive social, economic and societal impacts. Treatments rely on re-purposed antivirals and immune modulatory agents focusing on attenuating the acute respiratory distress syndrome. No curative therapies exist. Vaccines remain the best hope for disease control and the principal global effort to end the pandemic. Herein, we summarize those developments with a focus on the role played by nanocarrier delivery.

COVID-19 vaccines: The status and perspectives in delivery points of view

Due to the high prevalence and long incubation periods often without symptoms, the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has infected millions of individuals globally, causing the coronavirus disease 2019 (COVID-19) pandemic. Even with the recent approval of the anti-viral drug, remdesivir, and Emergency Use Authorization of monoclonal antibodies against S protein, bamlanivimab and casirimab/imdevimab, efficient and safe COVID-19 vaccines are still desperately demanded not only to prevent its spread but also to restore social and economic activities via generating mass immunization. Recent Emergency Use Authorization of Pfizer and BioNTech's mRNA vaccine may provide a pathway forward, but monitoring of long-term immunity is still required, and diverse candidates are still under development. As the knowledge of SARS-CoV-2 pathogenesis and interactions with the immune system continues to evolve, a variety of drug candidates are under investigation and in clinical trials. Potential vaccines and therapeutics against COVID-19 include repurposed drugs, monoclonal antibodies, antiviral and antigenic proteins, peptides, and genetically engineered viruses. This paper reviews the virology and immunology of SARS-CoV-2, alternative therapies for COVID-19 to vaccination, principles and design considerations in COVID-19 vaccine development, and the promises and roles of vaccine carriers in addressing the unique immunopathological challenges presented by the disease.

A comparative study of human betacoronavirus spike proteins: structure, function and therapeutics

Coronaviruses are the paradigm of emerging 21st century zoonotic viruses, triggering numerous outbreaks and a severe global health crisis. The current COVID-19 pandemic caused by SARS-CoV-2 has affected more than 51 million people across the globe as of 12 November 2020. The crown-like spikes on the surface of the virion are the unique structural feature of viruses in the family Coronaviridae. The spike (S) protein adopts distinct conformations while mediating entry of the virus into the host. This multifunctional protein mediates the entry process by recognizing its receptor on the host cell, followed by the fusion of the viral membrane with the host cell membrane. This review article focuses on the structural and functional comparison of S proteins of the human betacoronaviruses, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we review the current state of knowledge about receptor recognition, the membrane fusion mechanism, structural epitopes, and glycosylation sites of the S proteins of these viruses. We further discuss various vaccines and other therapeutics such as monoclonal antibodies, peptides, and small molecules based on the S protein of these three viruses.

Domains and Functions of Spike Protein in Sars-Cov-2 in the Context of Vaccine Design

The spike protein in SARS-CoV-2 (SARS-2-S) interacts with the human ACE2 receptor to gain entry into a cell to initiate infection. Both Pfizer/BioNTech's BNT162b2 and Moderna's mRNA-1273 vaccine candidates are based on stabilized mRNA encoding prefusion SARS-2-S that can be produced after the mRNA is delivered into the human cell and translated. SARS-2-S is cleaved into S1 and S2 subunits, with S1 serving the function of receptor-binding and S2 serving the function of membrane fusion. Here, I dissect in detail the various domains of SARS-2-S and their functions discovered through a variety of different experimental and theoretical approaches to build a foundation for a comprehensive mechanistic understanding of how SARS-2-S works to achieve its function of mediating cell entry and subsequent cell-to-cell transmission. The integration of structure and function of SARS-2-S in this review should enhance our understanding of the dynamic processes involving receptor binding, multiple cleavage events, membrane fusion, viral entry, as well as the emergence of new viral variants. I highlighted the relevance of structural domains and dynamics to vaccine development, and discussed reasons for the spike protein to be frequently featured in the conspiracy theory claiming that SARS-CoV-2 is artificially created.

COVID-19 vaccine: where are we now and where should we go?

INTRODUCTION

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has currently caused the pandemic with a high progressive speed and has been considered as the global public health crisis in 2020. This new member of the coronavirus family has created a potentially fatal disease, called coronavirus disease-2019 (COVID-19). Despite the continuous efforts of researchers to find effective vaccines and drugs for COVID-19, there is still no success in this matter.

AREAS COVERED

Here, the literature regarding the COVID-19 vaccine candidates currently in the clinical trials, as well as main candidates in pre-clinical stages for development and research, were reviewed. These candidates have been developed under five different major platforms, including live-attenuated vaccine, mRNA-based vaccine, DNA vaccines, inactivated virus, and viral-vector-based vaccine.

EXPERT OPINION

There are several limitations in the field of the rapid vaccine development against SARS-CoV-2, and other members of the coronavirus family such as SARS-CoV and MERS-CoV. The key challenges of designing an effective vaccine within a short time include finding the virulence ability of an emerging virus and potential antigen, choosing suitable experimental models and efficient route of administration, the immune-response study, designing the clinical trials, and determining the safety, as well as efficacy.

Current advances in the development of SARS-CoV-2 vaccines

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is now a global pandemic that has wreaked havoc globally, which has put a heavy toll on public health, lives, and the world economy. Vaccination is considered as one of the greatest successes in medical history. Based on prior experience with the development of SARS-CoV vaccines, all COVID-19 vaccines must be subjected to the tests for protective effects and harmful risks derived from antibody-dependent enhancement that may contribute to augmented infectivity and/or eosinophilic infiltration. The SARS-CoV-2 vaccine is now being developed urgently in several different ways. China is regarded as one of the world's leading countries in SARS-CoV-2 vaccine development, up to date the last inactivated vaccine international clinical (Phase III) trial was launched in the United Arab Emirates by Sinopharm China National Biotec Group (CNBG). In this review, we outline the current status of vaccine development against clinically relevant SARS-CoV-2 strains, anticipating that such attempts would help create efficacious and sage SARS-CoV-2 vaccines.

Platforms Exploited for SARS-CoV-2 Vaccine Development

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the only zoonotic-origin coronavirus (CoV) that has reached the pandemic stage. The virus uses its spike (S) glycoprotein to attach to the host cells and initiate a cascade of events that leads to infection. It has sternly affected public health, economy, education, and social behavior around the world. Several scientific and medical communities have mounted concerted efforts to limit this pandemic and the subsequent wave of viral spread by developing preventative and potential vaccines. So far, no medicine or vaccine has been approved to prevent or treat coronavirus disease 2019 (COVID-19). This review describes the latest advances in the development of SARS-CoV-2 vaccines for humans, mainly focusing on the lead candidates in clinical trials. Moreover, we seek to provide both the advantages and the disadvantages of the leading platforms used in current vaccine development, based on past vaccine delivery efforts for non-SARS CoV-2 infections. We also highlight the population groups who should receive a vaccine against COVID-19 in a timely manner to eradicate the pandemic rapidly.

COVID-19: Coronavirus Vaccine Development Updates

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

Adjuvants for Coronavirus Vaccines

Vaccine development utilizing various platforms is one of the strategies that has been proposed to address the coronavirus disease 2019 (COVID-19) pandemic. Adjuvants are critical components of both subunit and certain inactivated vaccines because they induce specific immune responses that are more robust and long-lasting. A review of the history of coronavirus vaccine development demonstrates that only a few adjuvants, including aluminum salts, emulsions, and TLR agonists, have been formulated for the severe acute respiratory syndrome-associated coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), and currently the SARS-CoV-2 vaccines in experimental and pre-clinical studies. However, there is still a lack of evidence regarding the effects of the adjuvants tested in coronavirus vaccines. This paper presents an overview of adjuvants that have been formulated in reported coronavirus vaccine studies, which should assist with the design and selection of adjuvants with optimal efficacy and safety profiles for COVID-19 vaccines.

Structural Basis of SARS-CoV-2 and SARS-CoV Antibody Interactions

The 2019 coronavirus pandemic remains a major public health concern. Neutralizing antibodies (nAbs) represent a cutting-edge antiviral strategy. We focus here on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and SARS-CoV, and discuss current progress in antibody research against rampant SARS-CoV-2 infections. We provide a perspective on the mechanisms of SARS-CoV-2-derived nAbs, comparing these with existing SARS-CoV-derived antibodies. We offer insight into how these antibodies cross-react and cross-neutralize by analyzing available structures of spike (S) glycoprotein-antibody complexes. We also propose ways of adopting antibody-based strategies - such as cocktail antibody therapeutics against SARS-CoV-2 - to overcome the possible resistance of currently identified mutants and mitigate possible antibody-dependent enhancement (ADE) pathologies. This review provides a platform for the progression of antibody and vaccine design against SARS-CoV-2, and possibly against future coronavirus pandemics.

Sequence analysis of SARS-CoV-2 genome reveals features important for vaccine design

As the SARS-CoV-2 pandemic is rapidly progressing, the need for the development of an effective vaccine is critical. A promising approach for vaccine development is to generate, through codon pair deoptimization, an attenuated virus. This approach carries the advantage that it only requires limited knowledge specific to the virus in question, other than its genome sequence. Therefore, it is well suited for emerging viruses, for which we may not have extensive data. We performed comprehensive in silico analyses of several features of SARS-CoV-2 genomic sequence (e.g., codon usage, codon pair usage, dinucleotide/junction dinucleotide usage, RNA structure around the frameshift region) in comparison with other members of the coronaviridae family of viruses, the overall human genome, and the transcriptome of specific human tissues such as lung, which are primarily targeted by the virus. Our analysis identified the spike (S) and nucleocapsid (N) proteins as promising targets for deoptimization and suggests a roadmap for SARS-CoV-2 vaccine development, which can be generalizable to other viruses.

A Putative Prophylactic Solution for COVID-19: Development of Novel Multiepitope Vaccine Candidate against SARS-COV-2 by Comprehensive Immunoinformatic and Molecular Modelling Approach

The outbreak of 2019-novel coronavirus (SARS-CoV-2) that causes severe respiratory infection (COVID-19) has spread in China, and the World Health Organization has declared it a pandemic. However, no approved drug or vaccines are available, and treatment is mainly supportive and through a few repurposed drugs. The urgency of the situation requires the development of SARS-CoV-2-based vaccines. Immunoinformatic and molecular modelling are time-efficient methods that are generally used to accelerate the discovery and design of the candidate peptides for vaccine development. In recent years, the use of multiepitope vaccines has proved to be a promising immunization strategy against viruses and pathogens, thus inducing more comprehensive protective immunity. The current study demonstrated a comprehensive in silico strategy to design stable multiepitope vaccine construct (MVC) from B-cell and T-cell epitopes of essential SARS-CoV-2 proteins with the help of adjuvants and linkers. The integrated molecular dynamics simulations analysis revealed the stability of MVC and its interaction with human Toll-like receptors (TLRs), which trigger an innate and adaptive immune response. Later, the in silico cloning in a known pET28a vector system also estimated the possibility of MVC expression in Escherichia coli. Despite that this study lacks validation of this vaccine construct in terms of its efficacy, the current integrated strategy encompasses the initial multiple epitope vaccine design concepts. After validation, this MVC can be present as a better prophylactic solution against COVID-19.

Vaccine development against coronavirus (2003 to present): An overview, recent advances, current scenario, opportunities and challenges

BACKGROUND AND AIM

The pandemic COVID-19 occurring due to novel emerging coronavirus-2019 (SARS-CoV-2) is severely affecting the worldwide public health, culture, economy and human social behaviour. Till date, there is no approved medicine/treatment to cure COVID-19, whereas, vaccine development efforts are going on high priority. This review aimed to provide an overview of prior art, recent advances, vaccine designing strategies, current scenario, opportunities and challenges related to development of coronavirus vaccine.

METHOD

A literature survey was conducted using Scopus, PubMed and Google Scholar with the search key as: coronavirus vaccine, SARS vaccine, MERS vaccine and COVID-19 vaccine. Articles related to above search query were retrieved, sorted, analyzed and developed into an easy-to-understand review.

RESULTS

The genome phylogenetic analysis suggested that genomic sequence of SARS-CoV-2 is almost 80% similar to that of SARS-CoV, further both these viruses bind to same host cell receptor ACE-2. Hence it is expected that, previously available literature data about coronavirus vaccine designing may play crucial role in development of rapid vaccine against COVID-19. In view of this, the present review discuss (i) existing information (from 2003 to present) about the type of vaccine, antigen, immunogenic response, animal model, route of administration, adjuvants and current scenario for designing of coronavirus vaccine (ii) potential factors and challenges related to rapid development of COVID-19 vaccine.

CONCLUSION

In conclusion, we discuss possible clues/ target sites for designing of vaccine against SARS-CoV-2 virus based on prior-art.

Nanomedicine as a promising approach for diagnosis, treatment and prophylaxis against COVID-19

The COVID-19 pandemic caused by the newly emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) puts the world in an unprecedented crisis, leaving behind huge human losses and deep socioeconomic damages. Due to the lack of specific treatment against SARS-CoV-2, effective vaccines and antiviral agents are urgently needed to properly restrain the COVID-19 pandemic. Repositioned drugs such as remdesivir have revealed a promising clinical efficacy against COVID-19. Interestingly, nanomedicine as a promising therapeutic approach could effectively help win the battle between coronaviruses (CoVs) and host cells. This review discusses the potential therapeutic approaches, in addition to the contribution of nanomedicine against CoVs in the fields of vaccination, diagnosis and therapy.

Potential adjuvants for the development of a SARS-CoV-2 vaccine based on experimental results from similar coronaviruses

The extensive efforts around the globe are being made to develop a suitable vaccine against COVID-19 (Coronavirus Disease-19) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2). An effective vaccine should be able to induce high titers of neutralizing antibodies to prevent the virus from attaching to the host cell receptors. However, to elicit the protective levels of antibodies, a vaccine may require multiple doses or assistance from other immunostimulatory molecules. Further, the vaccine should be able to induce protective levels of antibodies rapidly with the least amount of antigen used. This decreases the cost of a vaccine and makes it affordable. As the pandemic has hit most countries across the globe, there will be an overwhelming demand for the vaccine in a quick time. Incorporating a suitable adjuvant in a SARS-CoV-2 vaccine may address these requirements. This review paper will discuss the experimental results of the adjuvanted vaccine studies with similar coronaviruses (CoVs) which might be useful to select an appropriate adjuvant for a vaccine against rapidly emergingSARS-CoV-2. We also discuss the current progress in the development of adjuvanted vaccines against the disease.

Kader H, Munawar N, Abdul Rahman S, Elshaer S, Batiha GEIS, Muhammad K. Investigating Virological, Immunological, and Pathological Avenues to Identify Potential Targets for Developing COVID-19 Treatment and Prevention Strategies

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emerging coronavirus causing respiratory disease commonly known as COVID-19. This novel coronavirus transmits from human to human and has caused profound morbidity and mortality worldwide leading to the ongoing pandemic. Moreover, disease severity differs considerably from individual to individual. Investigating the virology of COVID-19 and immunological pathways underlying its clinical manifestations will enable the identification and design of effective vaccines and potential therapies. In this review, we explore COVID-19 virology, the contribution of the immune system (innate and adaptive) during infection and control of the virus. Finally, we highlight vaccine development and implications of immune system modulation for potential therapeutic interventions to design better therapeutic strategies to guide future cure.

Kader H, Munawar N, Abdul Rahman S, Elshaer S, Batiha GEIS, Muhammad K. Investigating Virological, Immunological, and Pathological Avenues to Identify Potential Targets for Developing COVID-19 Treatment and Prevention Strategies

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emerging coronavirus causing respiratory disease commonly known as COVID-19. This novel coronavirus transmits from human to human and has caused profound morbidity and mortality worldwide leading to the ongoing pandemic. Moreover, disease severity differs considerably from individual to individual. Investigating the virology of COVID-19 and immunological pathways underlying its clinical manifestations will enable the identification and design of effective vaccines and potential therapies. In this review, we explore COVID-19 virology, the contribution of the immune system (innate and adaptive) during infection and control of the virus. Finally, we highlight vaccine development and implications of immune system modulation for potential therapeutic interventions to design better therapeutic strategies to guide future cure.

Construction and immunogenic studies of a mFc fusion receptor binding domain (RBD) of spike protein as a subunit vaccine against SARS-CoV-2 infection

Herein, we report that a recombinant fusion protein, containing a 457 amino acid SARS-CoV-2 receptor binding domain (RBD, residues 319-541) and a mouse IgG1 Fc domain, could induce highly potent neutralizing antibodies and stimulate humoral and cellular immunity in mice. The antibodies also effectively suppressed SARS-CoV-2 RBD binding to soluble ACE2, indicating that RBD-mFc may be further developed as a safe and effective SARS-CoV-2 vaccine.

Highly pathogenic coronaviruses: thrusting vaccine development in the spotlight

Coronaviruses (CoVs) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) disease (COVID-19) has caused major public health crises. There have been more than 4,400,000 reported cases of COVID-2019 and more than 300,000 reported deaths to date (16/05/2020). SARS-CoV, MERS-CoV and SARS-CoV-2 have attracted widespread global attention due to their high infectivity and pathogenicity. To date, there is no specific treatment proven effective against these viral infectious diseases. Vaccination is considered one of the most effective strategies to prevent viral infections. Therefore, the development of effective vaccines against highly pathogenic coronaviruses is essential. In this review, we will briefly describe coronavirus vaccine design targets, summarize recent advances in the development of coronavirus vaccines, and highlight current adjuvants for improving the efficacy of coronavirus vaccines.

Vaccines for SARS-CoV-2: Lessons from Other Coronavirus Strains

The emergence of the strain of coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) and its impact on global health have made imperative the development of effective and safe vaccines for this lethal strain. SARS-CoV-2 now adds to the list of coronavirus diseases that have threatened global health, along with the SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome) coronaviruses that emerged in 2002/2003 and 2012, respectively. As of April 2020, no vaccine is commercially available for these coronavirus strains. Nevertheless, the knowledge obtained from the vaccine development efforts for MERS and SARS can be of high value for COVID-19 (coronavirus disease 2019). Here, we review the past and ongoing vaccine development efforts for clinically relevant coronavirus strains with the intention that this information helps in the development of effective and safe vaccines for COVID-19. In addition, information from naturally exposed individuals and animal models to coronavirus strains is described for the same purpose of helping into the development of effective vaccines against COVID-19.

Progress and Prospects on Vaccine Development against SARS-CoV-2

In December 2019, the outbreak of pneumonia caused by a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a serious pandemic in China and other countries worldwide. So far, more than 460,000 confirmed cases were diagnosed in nearly 190 countries, causing globally over 20,000 deaths. Currently, the epidemic is still spreading and there is no effective means to prevent the infection. Vaccines are proved to be the most effective and economical means to prevent and control infectious diseases. Several countries, companies, and institutions announced their programs and progress on vaccine development against the virus. While most of the vaccines are under design and preparation, there are some that have entered efficacy evaluation in animals and initial clinical trials. This review mainly focused on the progress and our prospects on field of vaccine development against SARS-CoV-2.

Subunit Vaccines Against Emerging Pathogenic Human Coronaviruses

Seven coronaviruses (CoVs) have been isolated from humans so far. Among them, three emerging pathogenic CoVs, including severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and a newly identified CoV (2019-nCoV), once caused or continue to cause severe infections in humans, posing significant threats to global public health. SARS-CoV infection in humans (with about 10% case fatality rate) was first reported from China in 2002, while MERS-CoV infection in humans (with about 34.4% case fatality rate) was first reported from Saudi Arabia in June 2012. 2019-nCoV was first reported from China in December 2019, and is currently infecting more than 70000 people (with about 2.7% case fatality rate). Both SARS-CoV and MERS-CoV are zoonotic viruses, using bats as their natural reservoirs, and then transmitting through intermediate hosts, leading to human infections. Nevertheless, the intermediate host for 2019-nCoV is still under investigation and the vaccines against this new CoV have not been available. Although a variety of vaccines have been developed against infections of SARS-CoV and MERS-CoV, none of them has been approved for use in humans. In this review, we have described the structure and function of key proteins of emerging human CoVs, overviewed the current vaccine types to be developed against SARS-CoV and MERS-CoV, and summarized recent advances in subunit vaccines against these two pathogenic human CoVs. These subunit vaccines are introduced on the basis of full-length spike (S) protein, receptor-binding domain (RBD), non-RBD S protein fragments, and non-S structural proteins, and the potential factors affecting these subunit vaccines are also illustrated. Overall, this review will be helpful for rapid design and development of vaccines against the new 2019-nCoV and any future CoVs with pandemic potential. This review was written for the topic of Antivirals for Emerging Viruses: Vaccines and Therapeutics in the Virology section of Frontiers in Microbiology.

Investigations into the efficacy of multi-component cocaine vaccines

Although cocaine addiction remains a serious health and societal problem in the United States, no FDA-approved treatment has been developed. Vaccines offer an exciting strategy for the treatment of cocaine addiction; however, vaccine formulations need to be optimized to improve efficacy. Herein, we examine the effectiveness of a tricomponent cocaine vaccine, defined as having its hapten (GNE) and adjuvant (cytosine-guanine oligodeoxynucleotide 1826, CpG ODN 1826) covalently linked via the immunogenic protein ovalbumin (OVA). The tricomponent vaccine (GNE-OVA-CpG 1826) and a vaccine of analogous, individual components (GNE-OVA+CpG ODN 1826) were found to similarly induce highly specific anticocaine antibody production in mice and block cocaine's stimulant effects in hyperlocomotor testing.

Viral metagenomics, protein structure, and reverse genetics: Key strategies for investigating coronaviruses

Viral metagenomics, modeling of protein structure, and manipulation of viral genetics are key approaches that have laid the foundations of our understanding of coronavirus biology. In this review, we discuss the major advances each method has provided and discuss how future studies should leverage these strategies synergistically to answer novel questions.

Receptor-binding domain-based subunit vaccines against MERS-CoV

Development of effective vaccines, in particular, subunit-based vaccines, against emerging Middle East respiratory syndrome (MERS) caused by the MERS coronavirus (MERS-CoV) will provide the safest means of preventing the continuous spread of MERS in humans and camels. This review briefly describes the structure of the MERS-CoV spike (S) protein and its receptor-binding domain (RBD), discusses the current status of MERS vaccine development and illustrates the strategies used to develop RBD-based subunit vaccines against MERS. It also summarizes currently available animal models for MERS-CoV and proposes a future direction for MERS vaccines. Taken together, this review will assist researchers working to develop effective and safe subunit vaccines against MERS-CoV and any other emerging coronaviruses that might cause future pandemics.

Effects of human anti-spike protein receptor binding domain antibodies on severe acute respiratory syndrome coronavirus neutralization escape and fitness

The receptor binding domain (RBD) of the spike (S) glycoprotein of severe acute respiratory syndrome coronavirus (SARS-CoV) is a major target of protective immunity in vivo. Although a large number of neutralizing antibodies (nAbs) have been developed, it remains unclear if a single RBD-targeting nAb or two in combination can prevent neutralization escape and, if not, attenuate viral virulence in vivo. In this study, we used a large panel of human nAbs against an epitope that overlaps the interface between the RBD and its receptor, angiotensin-converting enzyme 2 (ACE2), to assess their cross-neutralization activities against a panel of human and zoonotic SARS-CoVs and neutralization escape mutants. We also investigated the neutralization escape profiles of these nAbs and evaluated their effects on receptor binding and virus fitness in vitro and in mice. We found that some nAbs had great potency and breadth in neutralizing multiple viral strains, including neutralization escape viruses derived from other nAbs; however, no single nAb or combination of two blocked neutralization escape. Interestingly, in mice the neutralization escape mutant viruses showed either attenuation (Urbani background) or increased virulence (GD03 background) consistent with the different binding affinities between their RBDs and the mouse ACE2. We conclude that using either single nAbs or dual nAb combinations to target a SARS-CoV RBD epitope that shows plasticity may have limitations for preventing neutralization escape during in vivo immunotherapy. However, RBD-directed nAbs may be useful for providing broad neutralization and prevention of escape variants when combined with other nAbs that target a second conserved epitope with less plasticity and more structural constraint.

IMPORTANCE

The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002 and Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 has resulted in severe human respiratory disease with high death rates. Their zoonotic origins highlight the likelihood of reemergence or further evolution into novel human coronavirus pathogens. Broadly neutralizing antibodies (nAbs) that prevent infection of related viruses represent an important immunostrategy for combating coronavirus infections; however, for this strategy to succeed, it is essential to uncover nAb-mediated escape pathways and to pioneer strategies that prevent escape. Here, we used SARS-CoV as a research model and examined the escape pathways of broad nAbs that target the receptor binding domain (RBD) of the virus. We found that neither single nAbs nor two nAbs in combination blocked escape. Our results suggest that targeting conserved regions with less plasticity and more structural constraint rather than the SARS-CoV RBD-like region(s) should have broader utility for antibody-based immunotherapy.