Soluble Spike DNA Vaccine Provides Long-Term Protective Immunity against SARS-CoV-2 in Mice and Nonhuman Primates

Immunogenicity and protection efficacy of a COVID-19 DNA vaccine encoding spike protein with D614G mutation and optimization of large-scale DNA vaccine production

Severe acute respiratory syndrome coronavirus 2 had devastating consequences for human health. Despite the introduction of several vaccines, COVID-19 continues to pose a serious health risk due to emerging variants of concern. DNA vaccines gained importance during the pandemic due to their advantages such as induction of both arms of immune response, rapid development, stability, and safety profiles. Here, we report the immunogenicity and protective efficacy of a DNA vaccine encoding spike protein with D614G mutation (named pcoSpikeD614G) and define a large-scale production process. According to the in vitro studies, pcoSpikeD614G expressed abundant spike protein in HEK293T cells. After the administration of pcoSpikeD614G to BALB/c mice through intramuscular (IM) route and intradermal route using an electroporation device (ID + EP), it induced high level of anti-S1 IgG and neutralizing antibodies (P < 0.0001), strong Th1-biased immune response as shown by IgG2a polarization (P < 0.01), increase in IFN-γ levels (P < 0.01), and increment in the ratio of IFN-γ secreting CD4+ (3.78-10.19%) and CD8+ (5.24-12.51%) T cells. Challenging K18-hACE2 transgenic mice showed that pcoSpikeD614G administered through IM and ID + EP routes conferred 90-100% protection and there was no sign of pneumonia. Subsequently, pcoSpikeD614G was evaluated as a promising DNA vaccine candidate and scale-up studies were performed. Accordingly, a large-scale production process was described, including a 36 h fermentation process of E. coli DH5α cells containing pcoSpikeD614G resulting in a wet cell weight of 242 g/L and a three-step chromatography for purification of the pcoSpikeD614G DNA vaccine.

COVID-19 Vaccines: Where Did We Stand at the End of 2023?

Vaccine development against SARS-CoV-2 has been highly successful in slowing down the COVID-19 pandemic. A wide spectrum of approaches including vaccines based on whole viruses, protein subunits and peptides, viral vectors, and nucleic acids has been developed in parallel. For all types of COVID-19 vaccines, good safety and efficacy have been obtained in both preclinical animal studies and in clinical trials in humans. Moreover, emergency use authorization has been granted for the major types of COVID-19 vaccines. Although high safety has been demonstrated, rare cases of severe adverse events have been detected after global mass vaccinations. Emerging SARS-CoV-2 variants possessing enhanced infectivity have affected vaccine protection efficacy requiring re-design and re-engineering of novel COVID-19 vaccine candidates. Furthermore, insight is given into preparedness against emerging SARS-CoV-2 variants.

Nanovaccines: A game changing approach in the fight against infectious diseases

The field of nanotechnology has revolutionised global attempts to prevent, treat, and eradicate infectious diseases in the foreseen future. Nanovaccines have proven to be a valuable pawn in this novel technology. Nanovaccines are made up of nanoparticles that are associated with or prepared with components that can stimulate the host's immune system. In addition to their delivery capabilities, the nanocarriers have been demonstrated to possess intrinsic adjuvant properties, working as immune cell stimulators. Thus, nanovaccines have the potential to promote rapid as well as long-lasting humoral and cellular immunity. The nanovaccines have several possible benefits, including site-specific antigen delivery, increased antigen bioavailability, and a diminished adverse effect profile. To avail these benefits, several nanoparticle-based vaccines are being developed, including virus-like particles, liposomes, polymeric nanoparticles, nanogels, lipid nanoparticles, emulsion vaccines, exomes, and inorganic nanoparticles. Inspired by their distinctive properties, researchers are working on the development of nanovaccines for a variety of applications, such as cancer immunotherapy and infectious diseases. Although a few challenges still need to be overcome, such as modulation of the nanoparticle pharmacokinetics to avoid rapid elimination from the bloodstream by the reticuloendothelial system, The future prospects of this technology are also assuring, with multiple options such as personalised vaccines, needle-free formulations, and combination nanovaccines with several promising candidates.

Infections associated with SARS-CoV-2 exploited via nanoformulated photodynamic therapy

Background and purpose

The pandemic of COVID-19 has highlighted the need for managing infectious diseases, which spreads by airborne transmission leading to serious health, social, and economic issues. SARS-CoV-2 is an enveloped virus with a 60-140 nm diameter and particle-like features, which majorly accounts for this disease. Expanding diagnostic capabilities, developing safe vaccinations with long-lasting immunity, and formulating effective medications are the strategies to be investigated.

Experimental approach

For the literature search, electronic databases such as Scopus, Google Scholar, MEDLINE, Embase, PubMed, and Web of Science were used as the source. Search terms like 'Nano-mediated PDT,' 'PDT for SARS-CoV-2', and 'Nanotechnology in treatment for SARS-CoV-2' were used. Out of 275 initially selected articles, 198 were chosen after the abstract screening. During the full-text screening, 80 papers were excluded, and 18 were eliminated during data extraction. Preference was given to articles published from 2018 onwards, but a few older references were cited for their valuable information.

Key results

Synthetic nanoparticles (NPs) have a close structural resemblance to viruses and interact greatly with their proteins due to their similarities in the configurations. NPs had previously been reported to be effective against a variety of viruses. In this way, with nanoparticles, photodynamic therapy (PDT) can be a viable alternative to antibiotics in fighting against microbial infections. The protocol of PDT includes the activation of photosensitizers using specific light to destroy microorganisms in the presence of oxygen, treating several respiratory diseases.

Conclusion

The use of PDT in treating COVID-19 requires intensive investigations, which has been reviewed in this manuscript, including a computational approach to formulating effective photosensitizers.

Potentiating the Cross-Reactive IFN-γ T Cell and Polyfunctional T Cell Responses by Heterologous GX-19N DNA Booster in Mice Primed with Either a COVID-19 mRNA Vaccine or Inactivated Vaccine

Waning vaccine-induced immunity, coupled with the emergence of SARS-CoV-2 variants, has inspired the widespread implementation of COVID-19 booster vaccinations. Here, we evaluated the potential of the GX-19N DNA vaccine as a heterologous booster to enhance the protective immune response to SARS-CoV-2 in mice primed with either an inactivated virus particle (VP) or an mRNA vaccine. We found that in the VP-primed condition, GX-19N enhanced the response of both vaccine-specific antibodies and cross-reactive T Cells to the SARS-CoV-2 variant of concern (VOC), compared to the homologous VP vaccine prime-boost. Under the mRNA-primed condition, GX-19N induced higher vaccine-induced T Cell responses but lower antibody responses than the homologous mRNA vaccine prime-boost. Furthermore, the heterologous GX-19N boost induced higher S-specific polyfunctional CD4⁺ and CD8⁺ T cell responses than the homologous VP or mRNA prime-boost vaccinations. Our results provide new insights into booster vaccination strategies for the management of novel COVID-19 variants.

Progress and prospects on vaccine development against Monkeypox Infection

The monkeypox virus (MPOX) is an uncommon zoonotic illness brought on by an orthopoxvirus (OPXV). MPOX can occur with symptoms similar to smallpox. Since April 25, 2023, 110 nations have reported 87,113 confirmed cases and 111 fatalities. Moreover, the outspread prevalence of MPOX in Africa and a current outbreak of MPOX in the U.S. have made it clear that naturally occurring zoonotic OPXV infections remain a public health concern. Existing vaccines, though they provide cross-protection to MPOX, are not specific for the causative virus, and their effectiveness in the light of the current multi-country outbreak is still to be verified. Furthermore, as a sequel of the eradication and cessation of smallpox vaccination for four decades, MPOX found a possibility to re-emerge, but with distinct characteristics. The World Health Organization (WHO) suggested that nations use affordable MPOX vaccines within a framework of coordinated clinical effectiveness and safety evaluations. Vaccines administered in the smallpox control program and conferred immunity against MPOX. Currently, vaccines approved by WHO for use against MPOX are replicating (ACAM2000), low replicating (LC16m8), and non-replicating (MVA-BN). Although vaccines are accessible, investigations have demonstrated that smallpox vaccination is approximately 85% efficient in inhibiting MPOX. In addition, developing new vaccine methods against MPOX can help prevent this infection. To recognize the most efficient vaccine, it is essential to assess effects, including reactogenicity, safety, cytotoxicity effect, and vaccine-associated side effects, especially for high-risk and vulnerable people. Recently, several orthopoxvirus vaccines have been produced and are being evaluated. Hence, this review aims to provide an overview of the efforts dedicated to several types of vaccine candidates with different strategies for MPOX, including inactivated, live-attenuated, virus-like particles (VLPs), recombinant protein, nucleic acid, and nanoparticle-based vaccines, which are being developed and launched.

Needle-free injection system delivery of ZyCoV-D DNA vaccine demonstrated improved immunogenicity and protective efficacy in rhesus macaques against SARS-CoV-2

The apprehension of needles related to injection site pain, risk of transmitting bloodborne pathogens, and effective mass immunization have led to the development of a needle-free injection system (NFIS). Here, we evaluated the efficacy of the NFIS and needle injection system (NIS) for the delivery and immunogenicity of DNA vaccine candidate ZyCoV-D in rhesus macaques against SARS-CoV-2 infection. Briefly, 20 rhesus macaques were divided into 5 groups (4 animals each), that is, I (1 mg dose by NIS), II (2 mg dose by NIS), III (1 mg dose by NFIS), IV (2 mg dose by NFIS) and V (phosphate-buffer saline [PBS]). The macaques were immunized with the vaccine candidates/PBS intradermally on Days 0, 28, and 56. Subsequently, the animals were challenged with live SARS-CoV-2 after 15 weeks of the first immunization. Blood, nasal swab, throat swab, and bronchoalveolar lavage fluid specimens were collected on 0, 1, 3, 5, and 7 days post infection from each animal to determine immune response and viral clearance. Among all the five groups, 2 mg dose by NFIS elicited significant titers of IgG and neutralizing antibody after immunization with enhancement in their titers postvirus challenge. Besides this, it also induced increased lymphocyte proliferation and cytokine response. The minimal viral load post-SARS-CoV-2 challenge and significant immune response in the immunized animals demonstrated the efficiency of NFIS in delivering 2 mg ZyCoV-D vaccine candidate.

Towards novel nano-based vaccine platforms for SARS-CoV-2 and its variants of concern: Advances, challenges and limitations

Vaccination is the most effective tool available for fighting the spread of COVID-19. Recently, emerging variants of SARS-CoV-2 have led to growing concerns about increased transmissibility and decreased vaccine effectiveness. Currently, many vaccines are approved for emergency use and more are under development. This review highlights the ongoing advances in the design and development of different nano-based vaccine platforms. The challenges, limitations, and ethical consideration imposed by these nanocarriers are also discussed. Further, the effectiveness of the leading vaccine candidates against all SARS-CoV-2 variants of concern are highlighted. The review also focuses on the possibility of using an alternative non-invasive routes of vaccine administration using micro and nanotechnologies to enhance vaccination compliance and coverage.

Cynomolgus Macaque Model for COVID-19 Delta Variant

With the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, which are randomly mutated, the dominant strains in regions are changing globally. The development of preclinical animal models is imperative to validate vaccines and therapeutics against SARS-CoV-2 variants. The objective of this study was to develop a non-human primate (NHP) model for SARS-CoV-2 Delta variant infection. Cynomolgus macaques infected with Delta variants showed infectious viruses and viral RNA in the upper (nasal and throat) and lower respiratory (lung) tracts during the acute phase of infection. After 3 days of infection, lesions consistent with diffuse alveolar damage were observed in the lungs. For cellular immune responses, all macaques displayed transient lymphopenia and neutrophilia in the early stages of infection. SARS-CoV-2 Delta variant spike protein-specific IgM, IgG, and IgA levels were significantly increased in the plasma of these animals 14 days after infection. This new NHP Delta variant infection model can be used for comparative analysis of the difference in severity between SARS-CoV-2 variants of concern and may be useful in the efficacy evaluation of vaccines and universal therapeutic drugs for mutations.

Two DNA vaccines protect against severe disease and pathology due to SARS-CoV-2 in Syrian hamsters

The SARS-CoV-2 pandemic is an ongoing threat to global health, and wide-scale vaccination is an efficient method to reduce morbidity and mortality. We designed and evaluated two DNA plasmid vaccines, based on the pIDV-II system, expressing the SARS-CoV-2 spike gene, with or without an immunogenic peptide, in mice, and in a Syrian hamster model of infection. Both vaccines demonstrated robust immunogenicity in BALB/c and C57BL/6 mice. Additionally, the shedding of infectious virus and the viral burden in the lungs was reduced in immunized hamsters. Moreover, high-titers of neutralizing antibodies with activity against multiple SARS-CoV-2 variants were generated in immunized animals. Vaccination also protected animals from weight loss during infection. Additionally, both vaccines were effective at reducing both pulmonary and extrapulmonary pathology in vaccinated animals. These data show the potential of a DNA vaccine for SARS-CoV-2 and suggest further investigation in large animal and human studies could be pursued.

Safety and immunogenicity of two recombinant DNA COVID-19 vaccines containing the coding regions of the spike or spike and nucleocapsid proteins: an interim analysis of two open-label, non-randomised, phase 1 trials in healthy adults

Background

We assessed the safety and immunogenicity of two recombinant DNA vaccines for COVID-19: GX-19 containing plasmid DNA encoding the SARS-CoV-2 spike protein, and GX-19N containing plasmid DNA encoding the SARS-CoV-2 receptor-binding domain (RBD) foldon, nucleocapsid protein, and plasmid DNA encoding the spike protein.

Methods

Two open-label non-randomised phase 1 trials, one of GX-19 and the other of GX-19N were done at two hospitals in South Korea. We enrolled healthy adults aged 19–49 years for the GX-19 trial and healthy adults aged 19–54 years for the GX-19N trial. Participants who tested positive by serological testing for SARS-CoV-2 were excluded. At 4-week intervals, the GX-19 trial participants received two vaccine doses (either 1·5 mg or 3·0 mg), and the GX-19N trial participants received two 3·0 mg doses. The vaccines were delivered intramuscularly using an electroporator. The participants were followed up for 52 weeks after first vaccination. Data collected up to day 57 after first vaccination were analysed in this interim analysis. The primary outcome was safety within 28 days after each vaccination measured in the intention-to-treat population. The secondary outcome was vaccine immunogenicity using blood samples collected on day 43 or 57 after first vaccination measured in the intention-to-treat population. The GX-19 (NCT044445389) and GX-19N (NCT04715997) trials are registered with ClinicalTrials.gov.

Findings

Between June 17 and July 30, 2020, we screened 97 individuals, of whom 40 (41%) participants were enrolled in the GX-19 trial (20 [50%] in the 1·5 mg group and 20 [50%] in the 3·0 mg group). Between Dec 28 and 31, 2020, we screened 23 participants, of whom 21 (91%) participants were enrolled on the GX-19N trial. 32 (52%) of 61 participants reported 80 treatment-emergent adverse events after vaccination. All solicited adverse events were mild except one (2%) case of moderate fatigue in the 1·5 mg GX-19 group; no serious vaccine-related adverse events were detected. Binding antibody responses increased after second dose of vaccination in all groups (p=0·0002 in the 1·5 mg GX-19 group; p<0·0001 in the 3·0 mg GX-19; and p=0·0004 for the spike protein and p=0·0001 for the RBD in the 3·0 mg GX-19N group).

Interpretation

GX-19 and GX-19N are safe and well tolerated. GX-19N induces humoral and broad SARS-CoV-2-specific T-cell responses. GX-19N shows lower neutralising antibody responses and needs improvement to enhance immunogenicity.

Funding

The Korea Drug Development Fund, funded by the Ministry of Science and ICT, Ministry of Trade, Industry, and Energy, and Ministry of Health and Welfare.

DNA Based Vaccine Expressing SARS-CoV-2 Spike-CD40L Fusion Protein Confers Protection Against Challenge in a Syrian Hamster Model

SARS-CoV-2 infections present a tremendous threat to public health. Safe and efficacious vaccines are the most effective means in preventing the infections. A variety of vaccines have demonstrated excellent efficacy and safety around the globe. Yet, development of alternative forms of vaccines remains beneficial, particularly those with simpler production processes, less stringent storage conditions, and the capability of being used in heterologous prime/boost regimens which have shown improved efficacy against many diseases. Here we reported a novel DNA vaccine comprised of the SARS-CoV-2 spike protein fused with CD40 ligand (CD40L) serving as both a targeting ligand and molecular adjuvant. A single intramuscular injection in Syrian hamsters induced significant neutralizing antibodies 3-weeks after vaccination, with a boost substantially improving immune responses. Moreover, the vaccine also reduced weight loss and suppressed viral replication in the lungs and nasal turbinates of challenged animals. Finally, the incorporation of CD40L into the DNA vaccine was shown to reduce lung pathology more effectively than the DNA vaccine devoid of CD40L. These results collectively indicate that this DNA vaccine candidate could be further explored because of its efficacy and known safety profile.

Assessment of the efficacy of SARS-CoV-2 vaccines in non-human primate studies: a systematic review

Background: The outbreak of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) triggered the rapid and successful development of vaccines to help mitigate the effect of COVID-19 and circulation of the virus. Vaccine efficacy is often defined as capacity of vaccines to prevent (severe) disease. However, the efficacy to prevent transmission or infectiousness is equally important at a population level. This is not routinely assessed in clinical trials. Preclinical vaccine trials provide a wealth of information about the presence and persistence of viruses in different anatomical sites. Methods: We systematically reviewed all available preclinical SARS-CoV-2 candidate vaccine studies where non-human primates were challenged after vaccination (PROSPERO registration: CRD42021231199). We extracted the underlying data, and recalculated the reduction in viral shedding. We summarized the efficacy of  vaccines to reduce viral RNA shedding after challenge by standardizing and stratifying the results by different anatomical sites and diagnostic methods. We considered shedding of viral RNA as a proxy measure for infectiousness. Results: We found a marked heterogeneity between the studies in the experimental design and the assessment of the outcomes. The best performing vaccine candidate per study caused only low (6 out of 12 studies), or moderate (5 out of 12) reduction of viral genomic RNA, and low (5 out of 11 studies) or moderate (3 out of 11 studies) reduction of subgenomic RNA in the upper respiratory tract, as assessed with nasal samples. Conclusions: Since most of the tested vaccines only triggered a low or moderate reduction of viral RNA in the upper respiratory tract, we need to consider that most SARS-CoV-2 vaccines that protect against disease might not fully protect against infectiousness and vaccinated individuals might still contribute to SARS-CoV-2 transmission. Careful assessment of secondary attack rates from vaccinated individuals is warranted. Standardization in design and reporting of preclinical trials is necessary.

SARS-CoV-2 subunit vaccine adjuvants and their signaling pathways

INTRODUCTION

Vaccines are the agreed upon weapon against the COVID-19 pandemic. This review discusses about COVID-19 subunit vaccines adjuvants and their signaling pathways, which could provide a glimpse into the selection of appropriate adjuvants for prospective vaccine development studies.

AREAS COVERED

In the introduction, a brief background about the SARS-CoV-2 pandemic, the vaccine development race and classes of vaccine adjuvants were provided. . The antigen, trial stage, and types of adjuvants were extracted from the included articles and thun assimilated. Finally, the pattern recognition receptors (PRRs), their classes, cognate adjuvants, and potential signaling pathways were comprehended.

EXPERT OPINION

Adjuvants are unsung heroes of subunit vaccines. The in silico studies are very vital in avoiding several costly trial errors and save much work times. The majority of the (pre)clinical studies are promising. It is encouraging that most of the selected adjuvants are novel. Much emphasis must be paid to the optimal paring of antigen-adjuvant-PRRs for obtaining the desired vaccine effect. A good subunit vaccine/adjuvant is one that has high efficacy, safety, dose sparing, and rapid seroconversion rate and broad spectrum of immune response. In the years to come, COVID-19 adjuvanted subunit vaccines are expected to have superior utility than any other vaccines for various reasons.

Immunogenicity and protective efficacy of a DNA vaccine inducing optimal expression of the SARS-CoV-2 S gene in hACE2 mice

The wide spread of coronavirus disease 2019 (COVID-19) has significantly threatened public health. Human herd immunity induced by vaccination is essential to fight the epidemic. Therefore, highly immunogenic and safe vaccines are necessary to control SARS-CoV-2, whose S protein is the antigenic determinant responsible for eliciting antibodies that prevent viral entry and fusion. In this study, we developed a SARS-CoV-2 DNA vaccine expressing the S protein, named pVAX-S-OP, which was optimized according to the human-origin codon preference and using polyinosinic-polycytidylic acid as an adjuvant. pVAX-S-OP induced specific antibodies and neutralizing antibodies in BALB/c and hACE2 transgenic mice. Furthermore, we observed 1.43-fold higher antibody titers in mice receiving pVAX-S-OP plus adjuvant than in those receiving pVAX-S-OP alone. Interferon gamma production in the pVAX-S-OP-immunized group was 1.58 times (CD3⁺CD4⁺IFN-gamma⁺) and 2.29 times (CD3⁺CD8⁺IFN-gamma⁺) lower than that in the pVAX-S-OP plus adjuvant group but higher than that in the control group. The pVAX-S-OP vaccine was also observed to stimulate a Th1-type immune response. When, hACE2 transgenic mice were challenged with SARS-CoV-2, qPCR detection of N and E genes showed that the viral RNA loads in pVAX-S-OP-immunized mice lung tissues were 10⁴ times and 10⁶ times lower than those of the PBS control group, which shows that the vaccine could reduce the amount of live virus in the lungs of hACE2 mice. In addition, pathological sections showed less lung damage in the pVAX-S-OP-immunized group. Taken together, our results demonstrated that pVAX-S-OP has significant immunogenicity, which provides support for developing SARS-CoV-2 DNA candidate vaccines.

Immunogenic Properties of the DNA Construct Encoding the Receptor-Binding Domain of the SARS-CoV-2 Spike Protein

The development of preventive vaccines became the first order task in the COVID-19 pandemic caused by SARS-CoV-2. This paper reports the construction of the pVAX-RBD plasmid containing the Receptor-Binding Domain (RBD) of the S protein and a unique signal sequence 176 which promotes target protein secretion into the extracellular space thereby increasing the efficiency of humoral immune response activation. A polyglucine-spermidine conjugate (PGS) was used to deliver pVAX-RBD into the cells. The comparative immunogenicity study of the naked pVAX-RBD and pVAX-RBD enclosed in the PGS envelope showed that the latter was more efficient in inducing an immune response in the immunized mice. In particular, RBD-specific antibody titers were shown in ELISA to be no higher than 1 : 1000 in the animals from the pVAX-RBD group and 1 : 42 000, in the pVAX-RBD-PGS group. The pVAX-RBD‒PGS construct effectively induced cellular immune response. Using ELISpot, it has been demonstrated that splenocytes obtained from the immunized animals effectively produced INF-γ in response to stimulation with the S protein-derived peptide pool. The results suggest that the polyglucine-spermidine conjugate-enveloped pVAX-RBD construct may be considered as a promising DNA vaccine against COVID-19.

A Yellow Fever 17D Virus Replicon-Based Vaccine Platform for Emerging Coronaviruses

The tremendous global impact of the current SARS-CoV-2 pandemic, as well as other current and recent outbreaks of (re)emerging viruses, emphasize the need for fast-track development of effective vaccines. Yellow fever virus 17D (YF17D) is a live-attenuated virus vaccine with an impressive efficacy record in humans, and therefore, it is a very attractive platform for the development of novel chimeric vaccines against various pathogens. In the present study, we generated a YF17D-based replicon vaccine platform by replacing the prM and E surface proteins of YF17D with antigenic subdomains from the spike (S) proteins of three different betacoronaviruses: MERS-CoV, SARS-CoV and MHV. The prM and E proteins were provided in trans for the packaging of these RNA replicons into single-round infectious particles capable of expressing coronavirus antigens in infected cells. YF17D replicon particles expressing the S1 regions of the MERS-CoV and SARS-CoV spike proteins were immunogenic in mice and elicited (neutralizing) antibody responses against both the YF17D vector and the coronavirus inserts. Thus, YF17D replicon-based vaccines, and their potential DNA- or mRNA-based derivatives, may constitute a promising and particularly safe vaccine platform for current and future emerging coronaviruses.

DNA vaccines for SARS-CoV-2: toward third-generation vaccination era

Introduction: Coronavirus outbreak 2019 (COVID-19) has affected all the corners of the globe and created chaos to human life. In order to put some control on the pandemic, vaccines are urgently required that are safe, cost effective, easy to produce, and most importantly induce appropriate immune responses and protection against viral infection. DNA vaccines possess all these features and are promising candidates for providing protection against SARS-CoV-2.Area covered: Current understanding and advances in DNA vaccines toward COVID-19, especially those under various stages of clinical trials.Expert opinion: Through DNA vaccines, host cells are momentarily transformed into factories that produce proteins of the SARS-CoV-2. The host immune system detects these proteins to develop antibodies that neutralize and prevent the infection. This vaccine platform has additional benefits compared to traditional vaccination strategies like strong cellular immune response, higher safety margin, a simple production process as per cGMP norms, lack of any infectious agent, and a robust platform for large-scale production.

Immunological Mechanisms of Vaccine-Induced Protection against SARS-CoV-2 in Humans

The SARS-CoV-2 infection spread rapidly throughout the world and appears to involve in both humoral and cell-mediated immunity. SARS-CoV-2 is attached to host cells via binding to the viral spike (S) proteins and its cellular receptors angiotensin-converting enzyme 2 (ACE2). Consequently, the S protein is primed with serine proteases TMPRSS2 and TMPRSS4, which facilitate the fusion of viral and cellular membranes result in the entry of viral RNA into the host cell. Vaccines are urgently required to combat the coronavirus disease 2019 (COVID-19) outbreak and aid in the recovery to pre-pandemic levels of normality. The long-term protective immunity is provided by the vaccine antigen (or pathogen)-specific immune effectors and the activation of immune memory cells that can be efficiently and rapidly reactivated upon pathogen exposure. Research efforts aimed towards the design and development of vaccines for SARS-CoV-2 are increasing. Numerous coronavirus disease 2019 (COVID-19) vaccines have passed late-stage clinical investigations with promising outcomes. This review focuses on the present state and future prospects of COVID-19 vaccines research and development, with a particular emphasis on immunological mechanisms of various COVID-19vaccines such as adenoviral vector-based vaccines, mRNA vaccines, and DNA vaccines that elicits immunological responses against SARS-CoV-2 infections in humans.

SARS-CoV-2 (Covid-19) vaccines structure, mechanisms and effectiveness: A review

The world has been suffering from COVID-19 disease for more than a year, and it still has a high mortality rate. In addition to the need to minimize transmission of the virus through non-pharmacological measures such as the use of masks and social distance, many efforts are being made to develop a variety of vaccines to prevent the disease worldwide. So far, several vaccines have reached the final stages of safety and efficacy in various phases of clinical trials, and some, such as Moderna/NIAID and BioNTech/Pfizer, have reported very high safety and protection. The important point is that comparing different vaccines is not easy because there is no set standard for measuring neutralization. In this study, we have reviewed the common platforms of COVID-19 vaccines and tried to present the latest reports on the effectiveness of these vaccines.

Are We Paving the Way to Dig Out of the "Pandemic Hole"? A Narrative Review on SARS-CoV-2 Vaccination: From Animal Models to Human Immunization

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a new pathogen agent causing the coronavirus infectious disease (COVID-19). This novel virus originated the most challenging pandemic in this century, causing economic and social upheaval internationally. The extreme infectiousness and high mortality rates incentivized the development of vaccines to control this pandemic to prevent further morbidity and mortality. This international scenario led academic scientists, industries, and governments to work and collaborate strongly to make a portfolio of vaccines available at an unprecedented pace. Indeed, the robust collaboration between public systems and private companies led to resolutive actions for accelerating therapeutic interventions and vaccines mechanism. These strategies contributed to rapidly identifying safe and effective vaccines as quickly and efficiently as possible. Preclinical research employed animal models to develop vaccines that induce protective and long-lived immune responses. A spectrum of vaccines is worldwide under investigation in various preclinical and clinical studies to develop both individual protection and safe development of population-level herd immunity. Companies employed and developed different technological approaches for vaccines production, including inactivated vaccines, live-attenuated, non-replicating viral vector vaccines, as well as acid nucleic-based vaccines. In this view, the present narrative review provides an overview of current vaccination strategies, taking into account both preclinical studies and clinical trials in humans. Furthermore, to better understand immunization, animal models on SARS-CoV-2 pathogenesis are also briefly discussed.

SARS-CoV-2 Vaccines Based on the Spike Glycoprotein and Implications of New Viral Variants

Coronavirus 19 Disease (COVID-19) originating in the province of Wuhan, China in 2019, is caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), whose infection in humans causes mild or severe clinical manifestations that mainly affect the respiratory system. So far, the COVID-19 has caused more than 2 million deaths worldwide. SARS-CoV-2 contains the Spike (S) glycoprotein on its surface, which is the main target for current vaccine development because antibodies directed against this protein can neutralize the infection. Companies and academic institutions have developed vaccines based on the S glycoprotein, as well as its antigenic domains and epitopes, which have been proven effective in generating neutralizing antibodies. However, the emergence of new SARS-CoV-2 variants could affect the effectiveness of vaccines. Here, we review the different types of vaccines designed and developed against SARS-CoV-2, placing emphasis on whether they are based on the complete S glycoprotein, its antigenic domains such as the receptor-binding domain (RBD) or short epitopes within the S glycoprotein. We also review and discuss the possible effectiveness of these vaccines against emerging SARS-CoV-2 variants.

Comparison of the immunogenicity & protective efficacy of various SARS-CoV-2 vaccine candidates in non-human primates

BACKGROUND & OBJECTIVES

The COVID-19 pandemic has emerged as a global public health crisis and research groups worldwide are engaged in developing vaccine candidates to curb its transmission, with a few vaccines having progressed to advanced stages of clinical trials. The aim of this systematic review was to compare immunogenicity and protective efficacy of various SARS-CoV-2 vaccine candidates tested in non-human primate (NHP) models.

METHODS

Literature on effect of SARS-CoV-2 vaccines in NHP models reported on PubMed and preprint platforms (medRxiv and bioRxiv) till October 22, 2020, was searched with the following terms: coronavirus vaccine, COVID-19 vaccine, SARS-CoV-2 vaccine, nonhuman primate, and rhesus macaque.

RESULTS

Our search yielded 19 studies, which reported immune response elicited by 18 vaccine candidates in NHP. All the vaccines induced detectable neutralizing antibody (NAb) titres in the serum of vaccinated animals, with some showing effective viral clearance from various organs. The vaccinated animals also showed nil to mild histopathological changes in their lungs compared to placebo groups in the trials that performed necropsy.

INTERPRETATION & CONCLUSIONS

Our findings highlighted onset of quick immunogenicity and protective efficacy of mRNA-1273, followed by Ad26.CoV2.S, NVX-CoV2373, BNT162b2, RBD and BBV152 vaccine candidates in preclinical trials as compared to the others. NHP data also showed correlation with clinical trial data available for a few vaccines. Preclinical trials of COVID-19 vaccine candidates in NHPs yielded promising results, with some candidates faring better than others.