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A universal design of betacoronavirus vaccines against COVID-19, MERS and SARS

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A universal design of betacoronavirus vaccines against COVID-19, MERS and SARS

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Abstract

Vaccines are urgently needed to control the ongoing pandemic COVID-19 and previously-emerging MERS/SARS caused by coronavirus (CoV) infections. The CoV spike receptor-binding domain (RBD) is an attractive vaccine target but is undermined by limited immunogenicity. We describe a dimeric form of MERS-CoV RBD that overcomes this limitation. The RBD-dimer significantly increased neutralizing antibody (NAb) titers compared to conventional monomeric form and protected mice against MERS-CoV infection. Crystal structure showed RBD-dimer fully exposed dual receptor-binding motifs, the major target for NAbs. Structure-guided design further yielded a stable version of RBD-dimer as a tandem repeat single-chain (RBD-sc-dimer) which retained the vaccine potency. We generalized this strategy to design vaccines against COVID-19 and SARS, achieving 10-100-fold enhancement of NAb titers. RBD-sc-dimers in pilot scale production yielded high yields, supporting their scalability for further clinical development. The framework of immunogen design can be universally applied to other beta-CoV vaccines to counter emerging threats.

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... RBD is the major target for neutralizing antibodies (NAbs) and a favorable antigen for vaccine development because of its immunodominance . We previously designed novel vaccines against Beta coronavirus using tandem repeat dimeric RBD as antigens, which substantially enhanced immunogenicity in animal model (Dai et al., 2020). Based on this strategy, we developed protein subunit vaccine, ZF2001, against coronavirus diseases 2019 (COVID-19) , which has received conditional marketing authorization in China and emergency use authorization in Uzbekistan, Indonesia, and Columbia. ...
... The rebuilt models showed their overall conformations. Like MERS-CoV RBD-dimer structure as we reported earlier (PDB: 7C02) (Dai et al., 2020), both prototype and prototype-Beta chimeric SARS-CoV-2 RBD-dimers arranged as ''bilateral lung''-like structures with axial symmetry ( Figures 1E, 1F, S4D, and S4E). Two RBD subunits stack together via core domains of each other with their external domains exposed. ...
... Detailed methods are provided in the online version of this paper and include the following: Recombinant prototype SARS-CoV-2-S protein RBD-dimer, spike residues 319-537, two copies in tandem, GenBank: YP_009724390 Dai et al., 2020 N/A Recombinant Beta variant SARS-CoV-2-S protein RBD-dimer, spike residues 319-537, two copies in tandem, GISAID: EPI_ISL_736940 The monomeric Omicron (BA.1) variant RBD (S protein 316-534, GISAID: EPI_ISL_6795848) was purchased from ACROBiosystems, which was expressed from HEK293 cells. ...
Article
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Breakthrough infections by SARS-CoV-2 variants become the global challenge for pandemic control. Previously, we developed the protein subunit vaccine ZF2001 based on dimeric receptor-binding domain (RBD) of prototype SARS-CoV-2. Here, we developed a chimeric RBD-dimer vaccine approach to adapt SARS-CoV-2 variants. A prototype-Beta chimeric RBD-dimer was first designed to adapt the resistant Beta variant. Compared with its homotypic forms, the chimeric vaccine elicited broader sera neutralization of variants and conferred better protection in mice. The protection of the chimeric vaccine was further verified in macaques. This approach was generalized to develop Delta-Omicron chimeric RBD-dimer to adapt the currently prevalent variants. Again, the chimeric vaccine elicited broader sera neutralization of SARS-CoV-2 variants, and conferred better protection against challenge by either Delta or Omicron SARS-CoV-2 in mice. The chimeric approach is applicable for rapid updating of immunogens, and our data supported the use of variant-adapted multivalent vaccine against circulating and emerging variants.
... We and others have already shown that the spike RBD of SARS-CoV-2 represents a feasible immunogen for subunit vaccine development [18][19][20][21] . To further improve the antigenicity, multiple strategies for antigen multimerization targeting RBD, either by using a multimerization tag or by displaying on a proteinseneous nanoparticle, have been intensively investigated [21][22][23][24][25] , results from which indeed showed enhanced immunogenicity and improved protection. ...
... Previous studies have shown that RBD is able to induce high neutralizing antibodies as a protein vaccine with minimal side effects, and it could be manufactured at a low cost 18,19,21 . Several studies have proved that modified spike or RBD proteins, such as S trimer or RBD dimer, could generate more neutralizing antibodies, indicating that the polymeric protein vaccines might induce stronger humoral and cellular immune responses than monomeric antigens 19,22,24,41 . ...
... Previous studies have shown that RBD is able to induce high neutralizing antibodies as a protein vaccine with minimal side effects, and it could be manufactured at a low cost 18,19,21 . Several studies have proved that modified spike or RBD proteins, such as S trimer or RBD dimer, could generate more neutralizing antibodies, indicating that the polymeric protein vaccines might induce stronger humoral and cellular immune responses than monomeric antigens 19,22,24,41 . Multiple studies have reported the successful enhancement of RBD immunogenicity by using a multimerization tag or by cross-linking RBD monomer to a nanoparticle [21][22][23][24][25] . ...
Article
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The recently emerged Omicron (B.1.1.529) variant has rapidly surpassed Delta to become the predominant circulating SARS-CoV-2 variant, given the higher transmissibility rate and immune escape ability, resulting in breakthrough infections in vaccinated individuals. A new generation of SARS-CoV-2 vaccines targeting the Omicron variant are urgently needed. Here, we developed a subunit vaccine named RBD-HR/trimer by directly linking the sequence of RBD derived from the Delta variant (containing L452R and T478K) and HR1 and HR2 in SARS-CoV-2 S2 subunit in a tandem manner, which can self-assemble into a trimer. In multiple animal models, vaccination of RBD-HR/trimer formulated with MF59-like oil-in-water adjuvant elicited sustained humoral immune response with high levels of broad-spectrum neutralizing antibodies against Omicron variants, also inducing a strong T cell immune response in vivo. In addition, our RBD-HR/trimer vaccine showed a strong boosting effect against Omicron variants after two doses of mRNA vaccines, featuring its capacity to be used in a prime-boost regimen. In mice and non-human primates, RBD-HR/trimer vaccination could confer a complete protection against live virus challenge of Omicron and Delta variants. The results qualified RBD-HR/trimer vaccine as a promising next-generation vaccine candidate for prevention of SARS-CoV-2, which deserved further evaluation in clinical trials. The SARS-CoV-2 Omicron variant has quickly become the predominant circulating variant, due to the high transmissibility and immune escape. Here, the authors develop a trimeric protein vaccine candidate and show a sustained humoral immune response, and protection from challenge (Omicron and Delta) in various animal models.
... This has severely limited the application of the E. coli expression system to vaccine development. In addition, RBD exists in trimeric form in live SARS-CoV-2 [18], and it has been proven that RBD has better effects in multimeric form than in monomeric form [19,20]. If the expression of the properly folded and polymerized RBD in E. coli for vaccine production can be optimized, the production cost of the SARS-CoV-2 vaccine will be greatly reduced. ...
... After the reaction was terminated with H 2 SO 4 , a microplate reader (Thermo) was used to measure the OD450. The endpoint titer was defined as the highest reciprocal dilution of serum to give an absorbance greater than 2.1-fold of the background values [20]. ...
... The host immune response caused by this trimeric structure may not be identical to the host immune response caused by the monomeric structure. RBD dimers [20] and multimers [12,19] have better immunoprotective ability than RBD monomer. Therefore, multimerization of RBD may be a key step in the design of SARS-CoV-2 vaccines. ...
Article
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Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), seriously threatens human life and health. The correct folding and polymerization of the receptor-binding domain (RBD) protein of coronavirus in Escherichia coli may reduce the cost of SARS-CoV-2 vaccines. In this study, we constructed this nanopore by using the principle of ClyA porin polymerization triggered by the cell membrane. We used surfactants to "pick" the ClyA-RBD nanopore from the bacterial outer membrane. More importantly, the polymerized RBD displayed on the ClyA-RBD polymerized porin (RBD-PP) already displays some correct spatial conformational epitopes that can induce neutralizing antibodies. The nanostructures of RBD-PP can target lymph nodes and promote antigen uptake and processing by dendritic cells, thereby effectively eliciting the production of anti-SARS-CoV-2 neutralizing antibodies, systemic cellular immune responses, and memory T cells. We applied this PP-based vaccine platform to fabricate an RBD-based subunit vaccine against SARS-CoV-2, which will provide a foundation for the development of inexpensive coronavirus vaccines. The development of a novel vaccine delivery system is an important part of innovative drug research. This novel PP-based vaccine platform is likely to have additional applications, including other viral vaccines, bacterial vaccines, tumor vaccines, drug delivery, and disease diagnosis. Graphical Abstract
... For example, the mRNA-1273 (Moderna, USA)needs to be stored at -80 ℃ 6 . The majarity of marketed vaccines require 2 or 3 doses of vaccinations and the immune responses were generally weak after the first dose [7][8][9][10][11] . Additionally, ChAdOx1 nCoV-19 (AstraZeneca, UK) has been reported to cause thrombocytopenia and thromboembolic events. ...
... We found that one-dose S663V-RBD vaccine could generate the best immune effect among all groups in our study, and a single dose of S663V-RBD or WT-RBD could induce a more rapid, robust and lasting RBD-specific immune response than BBIBP-CorV (Figs. [3][4][5]. Especially, the RBD-specific IgG titer induced by S663V-RBD was significantly higher than that of some commercially available mRNA and subunit vaccines 14 days after first vaccination 7,8,10 , which indicates S663V-RBD can provide protective immunity more quickly than these licensed vaccines. Overall, WT-RBD showed slightly better immunogenicity than BBIBP-CorV and maintained a stable high level of the RBD-specific binding antibody and PNAb, suggesting that the AAV6 vector has the potential to be developed as a vaccine and provide long-lasting protection by only modifying the expression cassette. ...
Article
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Due to the insufficient long-term protection and significant efficacy reduction to new variants of current COVID-19 vaccines, the epidemic prevention and control are still challenging. Here, we employ a capsid and antigen structure engineering (CASE) strategy to manufacture an adeno-associated viral serotype 6-based vaccine (S663V-RBD), which expresses trimeric receptor binding domain (RBD) of spike protein fused with a biological adjuvant RS09. Impressively, the engineered S663V-RBD could rapidly induce a satisfactory RBD-specific IgG titer within 2 weeks and maintain the titer for more than 4 months. Compared to the licensed BBIBP-CorV (Sinopharm, China), a single-dose S663V-RBD induced more endurable and robust immune responses in mice and elicited superior neutralizing antibodies against three typical SARS-CoV-2 pseudoviruses including wild type, C.37 (Lambda) and B.1.617.2 (Delta). More interestingly, the intramuscular injection of S663V-RBD could overcome pre-existing immunity against the capsid. Given its effectiveness, the CASE-based S663V-RBD may provide a new solution for the current and next pandemic.
... Moreover, RBD is immunodominant among spike subunits as previously reported [8][9] . Such tailorable RBD-functionalized virus-like particle could also facilitate study of the immune activation caused by various numbers and distribution patterns of RBD.Recent SARS-CoV-2 vaccine studies have mainly focused on study of excellent immunodominance (i.e., enhanced B-cell response and promising longer-lasting protective immunity) initiated by homologous or heterologous polyvalent RBD vaccines compared to monomeric RBD immunogens [8][9][10][11][12][13][14] . ...
... Moreover, RBD is immunodominant among spike subunits as previously reported [8][9] . Such tailorable RBD-functionalized virus-like particle could also facilitate study of the immune activation caused by various numbers and distribution patterns of RBD.Recent SARS-CoV-2 vaccine studies have mainly focused on study of excellent immunodominance (i.e., enhanced B-cell response and promising longer-lasting protective immunity) initiated by homologous or heterologous polyvalent RBD vaccines compared to monomeric RBD immunogens [8][9][10][11][12][13][14] . However, few studies have investigated the virus-cell interaction based on viral immunogens with specific arranged patterns, which might facilitate the understanding of viral infection and immune responses 15 . ...
Preprint
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Elevated understanding of the viral infection process contributes to development of neutralizing agents and vaccine to combat infectious diseases. Although crystal structure of single SARS-CoV-2 spike/RBD and host receptor ACE2 is known, the viral attachment and immune response initiated by numbers and distribution patterns of natural spikes on SARS-CoV-2 are still obscure. Leveraging a ~74 nm DNA soccer-ball framework (DSF), we developed an aptamer-guided SARS-CoV-2 RBD precisely assembly strategy, thereby exploring the viral infection and immune response in specific numbers and distributions of RBDs. Thirty evenly distributed RBDs on DSF could achieve sufficient binding affinity against host cell (Kd of 122.2 pM), whereas 60 evenly distributed RBDs on DSF could bind to host cell rapidly (Ka of 0.845 min-1). While RBDs in centralized manner compared to evenly distribution facilitated higher and faster binding to host. Moreover, evenly distributed 20 RBDs on DSF achieved up to 88% immunity elicitation of macrophage cells. Overall, this strategy provides a prospective direction for the assembly of virus-like particles based on DNA origami, thereby facilitating understanding of viral infection and efficient vaccine design.
... Since the emergence of SARS-CoV-2 (SARS-2), multiple vaccine candidates have been developed (1,2). Several candidates use the full SARS-2 spike in various modalities (e.g., mRNA, adenoviral vectors, recombinant protein) have received WHO and country-level regulatory approval; other vaccine candidates include only the SARS-2 receptor binding domain (RBD) (3)(4)(5)(6)(7)(8)(9)(10)(11). Several RBD-based vaccine candidates are advancing as potential pan-sarbecovirus vaccines and may eventually be used clinically (4)(5)(6)(12)(13)(14). ...
... While this study does not characterize the relative protection resulting from each boosting regimen, significant evidence already exists that both spike-based and RBD-based protein immunizations provide protection (3,26,42,47,(50)(51)(52)(53). In combination with the findings of this study, these data support Sarbecovirus neutralization. ...
Article
Full-text available
Since the emergence of SARS-CoV-2 (SARS-2), multiple vaccine candidates were developed and studied both preclinically and clinically. Nearly all are based on the SARS-2 spike glycoprotein or its receptor binding domain (RBD). Studies of these vaccine candidates have largely been in a SARS-2 naïve context. However, pre-existing immunity to SARS-2 acquired through infection or vaccination continues to increase. Evaluating future vaccine candidates in context of this pre-existing immunity is necessary to understand how immune responses are subsequently influenced. Here, we evaluated the serum and IgG ⁺ B cell responses to the SARS-2 RBD in context of pre-existing immunity elicited by the full SARS-2 spike, and we compared this to boosting with the full SARS-2 spike. Boosting with the SARS-2 RBD resulted in increased reactivity to RBD epitopes, but both immunization regimens resulted in similarly broad neutralization across diverse sarbecoviruses. These findings may inform comparison among SARS-2 RBD-based vaccine candidates to currently approved spike-based candidates.
... COVID-19 is a worldwide pandemic caused by SARS-CoV-2. Although multiple measures have been adopted, COVID-19 is still rife amid the world and poses a threat to social, mental, and economic wellbeing (1,2). The newly evolved Omicron mutant spread quickly within highly vaccinated populations. ...
... (GenBank: PRJNA784547) was used for prokaryotic expression. The Omicron RBD dimer was synthesized in a tandem repeat form of the RBD monomer separated by their own flexible terminal residues (2). The corresponding sequence of the Omicron spike RBD monomer was amplified with the synthetic dimer sequence as the template. ...
Article
Full-text available
Coronavirus disease 2019 (COVID-19) vaccination regimens contribute to limiting the spread of severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). However, the emergence and rapid transmission of the SARS-CoV-2 variant Omicron raise a concern about the efficacy of the current vaccination strategy. Here, we expressed monomeric and dimeric receptor-binding domains (RBDs) of the spike protein of prototype SARS-CoV-2 and Omicron variant in E. coli and investigated the reactivity of anti-sera from Chinese subjects immunized with SARS-CoV-2 vaccines to these recombinant RBDs. In 106 human blood samples collected from 91 participants from Jiangxi, China, 26 sera were identified to be positive for SARS-CoV-2 spike protein antibodies by lateral flow dipstick (LFD) assays, which were enriched in the ones collected from day 7 to 1 month post-boost (87.0%) compared to those harvested within 1 week post-boost (23.8%) ( P < 0.0001). A higher positive ratio was observed in the child group (40.8%) than adults (13.6%) ( P = 0.0073). ELISA results showed that the binding activity of anti-SARS-CoV-2 antibody-positive sera to Omicron RBDs dropped by 1.48- to 2.07-fold compared to its homogeneous recombinant RBDs. Thus, our data indicate that current SARS-CoV-2 vaccines provide restricted humoral protection against the Omicron variant.
... Accordingly, several companies are working on developing safe and effective vaccines [70]. Generally, COVID-19 candidate vaccines can be classified based on the vaccine composition: (i) inactivated virus, which is not capable of replication but still can trigger an immune response [71][72][73]; (ii) live-attenuated virus, which has weak pathogenicity or none at all, while maintaining its capacity to trigger the immune system [74]; (iii) protein subunits, consisting only of the major viral proteins, the class into which most COVID-19 vaccines fall [74][75][76][77]; (iv) virus-vectored, where immunogenic antigens are produced by cloning their genes into virus vectors [71,78,79]; and (v) DNA and (vi) mRNA vaccines, in which viral antigens encoded by recombinant DNA [80] or mRNA are produced by protein translation in the host cell [81][82][83]. ...
... Accordingly, several companies are working on developing safe and effective vaccines [70]. Generally, COVID-19 candidate vaccines can be classified based on the vaccine composition: (i) inactivated virus, which is not capable of replication but still can trigger an immune response [71][72][73]; (ii) live-attenuated virus, which has weak pathogenicity or none at all, while maintaining its capacity to trigger the immune system [74]; (iii) protein subunits, consisting only of the major viral proteins, the class into which most COVID-19 vaccines fall [74][75][76][77]; (iv) virus-vectored, where immunogenic antigens are produced by cloning their genes into virus vectors [71,78,79]; and (v) DNA and (vi) mRNA vaccines, in which viral antigens encoded by recombinant DNA [80] or mRNA are produced by protein translation in the host cell [81][82][83]. ...
Article
Full-text available
Currently, health authorities around the world are struggling to limit the spread of COVID-19. Since the beginning of the pandemic, social distancing has been the most important strategy used by most countries to control disease spread by flattening and elongating the epidemic curve. Another strategy, herd immunity, was also applied by some countries through relaxed control measures that allow the free spread of natural infection to build up solid immunity within the population. In 2021, COVID-19 vaccination was introduced with tremendous effort as a promising strategy for limiting the spread of disease. Therefore, in this review, we present the current knowledge about social distancing, herd immunity strategies, and aspects of their implementation to control the COVID-19 pandemic in the presence of the newly developed vaccines. Finally, we suggest a short-term option for controlling the pandemic during vaccine application.
... ZF2001, a recombinant dimeric RBD protein vaccine, induces RBD-directed neutralizing response, and is undergoing phase 3 clinical trials [48][49][50]. All the serum samples of ZF2001 recipients displayed positive neutralization response against wild-type virus and ZF2001 also preserved the neutralizing activity against the Delta variant [51]. ...
Article
The coronavirus disease 19 (COVID-19) has been rampant since 2019, severely affecting global public health, and causing 5.75 million deaths worldwide. So far, many vaccines have been developed to prevent the infection of SARS-CoV-2 virus. However, the emergence of new variants may threat vaccine recipients as they might evade immunological surveillance that depends on the using of anti-SARS-CoV-2 antibody to neutralize the viral particles. Recent studies have found that recipients who received two doses of vaccination plus an additional booster shoot were able to quickly elevate neutralization response and immune response against wild-type SARS-CoV-2 virus and some initially appeared viral variants. In this review, we assessed the real-world effectiveness of different COVID-19 vaccines by population studies and neutralization assays and compared neutralization responses of booster vaccines in vitro. Finally, as the efficacy of COVID-19 vaccine is expected to decline over time, continued vaccination should be considered to achieve a long-term immune protection against coronavirus.
... The RBD-Dimer model was created using clinical-grade Chinese hamster ovary (CHO) cell lines, and then combined with aluminum hydroxide as an adjuvant to make the final vaccine (Pourmalek et al., 2021). Dai et al. (2020) described the structure-guided design of a coronavirus immunogen composed of two protein subunits containing the virus spike RBD. They joined together through a disulfide bond or tandem repeat. ...
Article
Full-text available
Two years after severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), in December 2019, the first infections were identified in Wuhan city of China. SARS-CoV-2 infection caused a global pandemic and accordingly, 5.41 million deaths worldwide. Hence, developing a safe and efficient vaccine for coronavirus disease 2019 (COVID-19) seems to be an urgent need. Attempts to produce efficient vaccines inexhaustibly are ongoing. At present time, according to the COVID-19 vaccine tracker and landscape provided by World Health Organization (WHO), there are 161 vaccine candidates in different clinical phases all over the world. In between, protein subunit vaccines are types of vaccines that contain a viral protein like spike protein or its segment as the antigen assumed to elicit humoral and cellular immunity and good protective effects. Previously, this technology of vaccine manufacturing was used in a recombinant influenza vaccine (RIV4). In the present work, we review protein subunit vaccines passing their phase 3 and 4 clinical trials, population participated in these trials, vaccines manufactures, vaccines efficiency and their side effects, and other features of these vaccines.
... To suppress and mitigate the COVID-19 pandemic, a series of stringent non-pharmacological interventions were implemented [2][3][4][5]. Moreover, with the rapid development of COVID-19 vaccines [6,7], the mass rollout of vaccination was deployed in many countries. A total of 7.98 billion doses of vaccines have been administered globally, and 54.4 % of the world population has received at least one-dose of the vaccine by 30 November 2021 (https://ourworldindata.org/covid-vaccinations). ...
Article
Full-text available
A series of stringent non-pharmacological and pharmacological interventions were implemented to contain the pandemic but the pandemic continues. Moreover, vaccination breakthrough infection and reinfection in convalescent COVID-19 cases have been reported. Further, SARS-CoV-2 variants emerged with mutations in spike (S) gene, the target of most current vaccines. Importantly, the mutations exhibit a trend of immune escape from the vaccination. Herein the scientific question that if the vaccination drives genetic or antigenic drifts of SARS-CoV-2 remains elusive. We performed correlation analyses to uncover the impact of wide vaccination on epidemiological characteristics of COVID-19. In addition, we investigated the evolutionary dynamics and genetic diversity of SARS-CoV-2 under immune pressure by utilizing the Bayesian phylodynamic inferences and the lineage entropy calculation respectively. We found that vaccination coverage was negatively related to the infections, severe cases, and deaths of COVID-19 respectively. With the increasing vaccination coverage, the lineage diversity of SARS-CoV-2 dampened, but the rapid mutation rates of the S gene were identified, and the vaccination could be one of the explanations for driving mutations in S gene. Moreover, new epidemics resurged in several countries with high vaccination coverage, questioning their current pandemic control strategies. Hence, integrated vaccination and non-pharmacological interventions are critical to controlling the pandemic. Furthermore, novel vaccine preparation should enhance its capabilities to curb both disease severity and infection possibility.
... The non-SARS-CoV-2 protein produced in BEV for a vaccine development study is human angiotensin converting enzyme 2 (hACE2) [64]. It was synthesized to investigate its binding to the SARS-CoV-2 RBD-dimer produced in mammalian cells. ...
Article
Full-text available
Background The baculovirus expression vector system has been developed for expressing a wide range of proteins, including enzymes, glycoproteins, recombinant viruses, and vaccines. The availability of the SARS-CoV-2 genome sequence has enabled the synthesis of SARS-CoV2 proteins in a baculovirus-insect cell platform for various applications. Main body of the abstract The most cloned SARS-CoV-2 protein is the spike protein, which plays a critical role in SARS-CoV-2 infection. It is available in its whole length or as subunits like S1 or the receptor-binding domain (RBD). Non-structural proteins (Nsps), another recombinant SARS-CoV-2 protein generated by the baculovirus expression vector system (BEV), are used in the identification of new medications or the repurposing of existing therapies for the treatment of COVID-19. Non-SARS-CoV-2 proteins generated by BEV for SARS-CoV-2 diagnosis or treatment include moloney murine leukemia virus reverse transcriptase (MMLVRT), angiotensin converting enzyme 2 (ACE2), therapeutic proteins, and recombinant antibodies. The recombinant proteins were modified to boost the yield or to stabilize the protein. Conclusion This review covers the wide application of the recombinant protein produced using the baculovirus expression technology for COVID-19 research. A lot of improvements have been made to produce functional proteins with high yields. However, there is still room for improvement and there are parts of this field of research that have not been investigated yet.
... ZF2001 (ZIFIVAX) is a protein subunit vaccine jointly developed by us and Anhui Zhifei Longcom Biopharmaceutical Co., Ltd. ZF2001 contains the SARS-CoV-2 tandem-repeat dimeric RBD protein, which showed higher immunogenicity than monomeric RBD protein, and the aluminum hydroxide adjuvant (77). In the Phase 1 and 2 clinical trials, we demonstrated that ZF2001 induced robust humoral immune responses and balanced cellular immune responses in humans, with low reactogenicity (78). ...
Article
The unprecedented coronavirus disease 2019 (COVID-19) pandemic has caused a disaster for public health in the last 2 years, without any sign of an ending. Various vaccines were developed rapidly as soon as the outbreak occurred. Clinical trials demonstrated the reactogenicity, immunogenicity and protection efficacy in humans, and some of the vaccines have been approved for clinical use. However, waves of infections such as the recently circulating Omicron variant still occur. Newly emerging variants, especially the variants of concern, and waning humoral responses pose serious challenges to the control of the COVID-19 pandemic. Previously, we summarized the humoral and cellular immunity, safety profiles and protection efficacy of COVID-19 vaccines with clinical data published by 21 May 2021. In this review, we summarize and update the published clinical data of COVID-19 vaccines and candidates up to December 31, 2021.
... However, membraneanchored form of the S1 subunit expressed by a replicationcompetent vesicular stomatitis virus (VSV) 42 or inactivated rabies virus vectored vaccine 43 induced virus-neutralizing antibody response and protected animals from SARS-CoV-2 challenge. Furthermore, the transmembrane RBD presented as a chimeric minispike in VSV replicon 44 , virus spike RBD fused together as a tandem repeat 45 , or RBD trimerized via fusion to the trimerization domain of T4 46 were also shown to elicit neutralizing antibodies in BALB/c mice. Thus, the membrane anchored or oligomerized forms of RBD displayed by these vaccines could have better preserved the conformation of B cell epitopes and thereby immunogenicity against S1 or RBD, compared to the S1 and RBD constructs in this study. ...
Article
Full-text available
Respiratory tract vaccination has an advantage of needle-free delivery and induction of mucosal immune response in the portal of SARS-CoV-2 entry. We utilized human parainfluenza virus type 3 vector to generate constructs expressing the full spike (S) protein of SARS-CoV-2, its S1 subunit, or the receptor-binding domain, and tested them in hamsters as single-dose intranasal vaccines. The construct bearing full-length S induced high titers of neutralizing antibodies specific to S protein domains critical to the protein functions. Robust memory T cell responses in the lungs were also induced, which represent an additional barrier to infection and should be less sensitive than the antibody responses to mutations present in SARS-CoV-2 variants. Following SARS-CoV-2 challenge, animals were protected from the disease and detectable viral replication. Vaccination prevented induction of gene pathways associated with inflammation. These results indicate advantages of respiratory vaccination against COVID-19 and inform the design of mucosal SARS-CoV-2 vaccines.
... To control COVID-19 pandemic, a number of kinds of SARS-CoV-2 vaccines have been and are being developed and some have been approved or authorized for emergency use, mainly including inactivated whole-virus (12), adenovirus vector, recombinant subunit protein (13), and mRNA vaccines (14,15). Particularly, mRNA vaccines have advantages over traditional vaccines, such as ease of design, rapid production, cell free, and the induction of robust neutralizing antibody and T cell response (15)(16)(17), leading to mRNA vaccines being the first licensed vaccines against SARS-CoV-2 infections. ...
Article
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The newly emerged Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contains more than 30 mutations on the spike protein, 15 of which are located within the receptor binding domain (RBD). Consequently, Omicron is able to extensively escape existing neutralizing antibodies and may therefore compromise the efficacy of current vaccines based on the original strain, highlighting the importance and urgency of developing effective vaccines against Omicron. Here we report the rapid generation and evaluation of an mRNA vaccine candidate specific to Omicron, and explore the feasibility of heterologous immunization with WT and Omicron RBD vaccines. This mRNA vaccine encodes the RBD of Omicron (designated as RBD-O) and is formulated with lipid nanoparticle. Two doses of the RBD-O mRNA vaccine efficiently induce neutralizing antibodies in mice; however, the antisera are effective only on the Omicron variant but not on the wildtype and Delta strains, indicating a narrow neutralization spectrum. It is noted that the neutralization profile of the RBD-O mRNA vaccine is opposite to that observed for the mRNA vaccine expressing the wildtype RBD (RBD-WT). Importantly, booster with RBD-O mRNA vaccine after two doses of RBD-WT mRNA vaccine can significantly increase neutralization titers against Omicron. Additionally, an obvious increase in IFN-g, IL-2, and TNF-a-expressing RBD-specific CD4 + T cell responses was observed after immunization with the RBD-WT and/or RBD-O mRNA vaccine. Together, our work demonstrates the feasibility and potency of an RBD-based mRNA vaccine specific to Omicron, providing important information for further development of heterologous immunization program or bivalent/multivalent SARS-CoV-2 vaccines with broad-spectrum efficacy.
... Neutralizing antibodies of more than 90% were seen among vaccinated groups. The adverse events include pain and itching in the injection site, cough, headache, swelling, redness, and rhabdomyolysis [106]. ...
Article
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Coronavirus Disease 2019 (COVID-19) not only jeopardized the health condition of humankind but also bruised the economy. Researchers found several dominant and predominant strains of the coronavirus and variants, in which B.1.1.7, B.1.351, and P.1 being the most prevalent. In all the variants of severe acute respiratory syndrome coronavirus 2, modifications occur in the spike protein deciphering variants that differ based on characteristics and properties such as the extent of virulence, severity of the disease, or probability of reinfection. The development of a vaccine against the pandemic causing COVID-19 is considered a major milestone in the history of vaccines due to the speed at which the vaccine was made. The vaccine against COVID-19 vaccines are classified under nucleic acid vaccines, protein-based vaccines, viral vector vaccines, and whole virus vaccines. At present, there are 22 vaccines approved under the category of emergency use authorization. COVID-19 prevention has been the main principle behind early vaccine availability, although none of the approved vaccine candidates have completed large scale clinical trials to evaluate the efficacy. This review presents a brief idea on types of COVID-19 vaccines, approved vaccines, and vaccine candidates under development.
... Remarkably, the receptor-binding domain (RBD) induces a more focused immune response and antibodies that may elicit better neutralization, which reduces the risk of antibody-dependent enhancement (ADE) of infection compared with the S-protein [6,7]. Furthermore, a number of studies also showed that the use of RBD produced high titers of neutralizing antibodies against SARS-CoV-2 infection in the absence of ADE [8][9][10][11]. ...
Article
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Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is undoubtedly the most challenging pandemic in the current century and remains a global health emergency. As the number of COVID-19 cases in the world is on the rise and variants continue to emerge, there is an urgent need for vaccines. Among all immunization approaches, mRNA vaccines have demonstrated more promising results in response to this challenge. Herein, we designed an mRNA-based vaccine encoding the receptor-binding domain (RBD) of SARS-CoV-2 encapsulated in lipid nanoparticles (LNPs). Intramuscular (i.m.) administration of the mRNA-RBD vaccine elicited broad-spectrum neutralizing antibodies and cellular responses against not only the wild-type SARS-CoV-2 virus but also Delta and Omicron variants. These results indicated that two doses of mRNA-RBD immunization conferred a strong immune response in mice against the wild-type SARS-CoV-2, while the booster dose provided a sufficient immunity against SARS-CoV-2 and its variants. Taken together, the three-dose regimen strategy of the mRNA-RBD vaccine proposed in the present study appears to be a promising reference for the development of mRNA vaccines targeting SARS-CoV-2 variants.
... Several eukaryotic expression systems, including mammalian cells, baculovirus-insect cells and yeast, have been used to express the recombinant RBD protein Dai et al., 2020;Yang et al., 2020;Sinegubova et al., 2021). Yet, the E. coli expression system has otherwise advantages for the expression of exogenous proteins, including efficiency, time-cost saving and yield. ...
Article
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The Coronavirus disease 2019 (COVID-19) pandemic presents an unprecedented public health crisis worldwide. Although several vaccines are available, the global supply of vaccines, particularly within developing countries, is inadequate, and this necessitates a need for the development of less expensive, accessible vaccine options. To this end, here, we used the Escherichia coli expression system to produce a recombinant fusion protein comprising the receptor binding domain (RBD) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; residues 319-541) and the fragment A domain of Cross-Reacting Material 197 (CRM197); hereafter, CRMA-RBD. We show that this CRMA-RBD fusion protein has excellent physicochemical properties and strong reactivity with COVID-19 convalescent sera and representative neutralizing antibodies (nAbs). Furthermore, compared with the use of a traditional aluminum adjuvant, we find that combining the CRMA-RBD protein with a nitrogen bisphosphonate-modified zinc-aluminum hybrid adjuvant (FH-002C-Ac) leads to stronger humoral immune responses in mice, with 4-log neutralizing antibody titers. Overall, our study highlights the value of this E. coli-expressed fusion protein as an alternative vaccine candidate strategy against COVID-19.
... 15 We developed a protein subunit Covid-19 vaccine, ZF2001, using the tandem-repeat dimeric RBD of the SARS-CoV-2 spike protein (from the original Wuhan-Hu-1 strain) as the antigen. 19 The antigen protein is produced in Chinese hamster ovary cells and then adjuvanted with aluminum hydroxide to produce the vaccine. ZF2001 requires less stringent cold-chain transport and storage, a factor that facilitates its availability in the global supply. ...
Article
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Background: The ZF2001 vaccine, which contains a dimeric form of the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 and aluminum hydroxide as an adjuvant, was shown to be safe, with an acceptable side-effect profile, and immunogenic in adults in phase 1 and 2 clinical trials. Methods: We conducted a randomized, double-blind, placebo-controlled, phase 3 trial to investigate the efficacy and confirm the safety of ZF2001. The trial was performed at 31 clinical centers across Uzbekistan, Indonesia, Pakistan, and Ecuador; an additional center in China was included in the safety analysis only. Adult participants (≥18 years of age) were randomly assigned in a 1:1 ratio to receive a total of three 25-μg doses (30 days apart) of ZF2001 or placebo. The primary end point was the occurrence of symptomatic coronavirus disease 2019 (Covid-19), as confirmed on polymerase-chain-reaction assay, at least 7 days after receipt of the third dose. A key secondary efficacy end point was the occurrence of severe-to-critical Covid-19 (including Covid-19-related death) at least 7 days after receipt of the third dose. Results: Between December 12, 2020, and December 15, 2021, a total of 28,873 participants received at least one dose of ZF2001 or placebo and were included in the safety analysis; 25,193 participants who had completed the three-dose regimen, for whom there were approximately 6 months of follow-up data, were included in the updated primary efficacy analysis that was conducted at the second data cutoff date of December 15, 2021. In the updated analysis, primary end-point cases were reported in 158 of 12,625 participants in the ZF2001 group and in 580 of 12,568 participants in the placebo group, for a vaccine efficacy of 75.7% (95% confidence interval [CI], 71.0 to 79.8). Severe-to-critical Covid-19 occurred in 6 participants in the ZF2001 group and in 43 in the placebo group, for a vaccine efficacy of 87.6% (95% CI, 70.6 to 95.7); Covid-19-related death occurred in 2 and 12 participants, respectively, for a vaccine efficacy of 86.5% (95% CI, 38.9 to 98.5). The incidence of adverse events and serious adverse events was balanced in the two groups, and there were no vaccine-related deaths. Most adverse reactions (98.5%) were of grade 1 or 2. Conclusions: In a large cohort of adults, the ZF2001 vaccine was shown to be safe and effective against symptomatic and severe-to-critical Covid-19 for at least 6 months after full vaccination. (Funded by the National Science and Technology Major Project and others; ClinicalTrials.gov number, NCT04646590.).
... The ∼30 and ∼60 kDa peaks corresponded to the monomer and dimer of RBD protein as observed before. 61 Synthesis of CLIO NWs-NH 2 . CLIO NWs were prepared by the previously described method 23,63 with modifications. ...
Article
Many aspects of innate immune responses to SARS viruses remain unclear. Of particular interest is the role of emerging neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in complement activation and opsonization. To overcome challenges with purified virions, here we introduce "pseudovirus-like" nanoparticles with ∼70 copies of functional recombinant RBD to map complement responses. Nanoparticles fix complement in an RBD-dependent manner in sera of all vaccinated, convalescent, and naı̈ve donors, but vaccinated and convalescent donors with the highest levels of anti-RBD antibodies show significantly higher IgG binding and higher deposition of the third complement protein (C3). The opsonization via anti-RBD antibodies is not an efficient process: on average, each bound antibody promotes binding of less than one C3 molecule. C3 deposition is exclusively through the alternative pathway. C3 molecules bind to protein deposits, but not IgG, on the nanoparticle surface. Lastly, "pseudovirus-like" nanoparticles promote complement-dependent uptake by granulocytes and monocytes in the blood of vaccinated donors with high anti-RBD titers. Using nanoparticles displaying SARS-CoV-2 proteins, we demonstrate subject-dependent differences in complement opsonization and immune recognition.
... Participants received one injection every day, and the results showed that the vaccine was well-tolerated, and no adverse events being reported under all treatment conditions (43). The ZF2001 vaccine is based on the previous MERS coronavirus spike protein (S) receptor-binding domain (RBD) (44). ...
Article
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The outbreak of COVID-19 (caused by SARS-CoV-2) has posed a significant threat to global public health security because of its high pathogenicity and infectivity. To date, the pathogenic mechanism of this novel coronavirus (SARS-CoV-2) is still unclear, and there is no effective treatment. As one of the most effective strategies to prevent viral infection, vaccines have become a research hotspot. Based on the current understanding of SARS-CoV-2, the research and development of its vaccines cover almost all forms of current vaccine research, including inactivated vaccines, recombinant protein vaccines, viral vector vaccines, and nucleic acid vaccines. Moreover, with the spread of the new mutant virus, it is necessary to evaluate the protection rate of previous administered vaccines. This article reviews the candidate targets, vaccine types, research and development status, progress of SARS-CoV-2 vaccines, and the effectiveness of neutralizing antibodies against SARS-CoV-2 mutants (B.1.1.7, B.1.351, P.1, B.1.617.2, and B.1.1.529) induced by these vaccines, to provide a reference for follow-up research and prevention.
... However, either the detection of nAbs in the serum and milk of vaccinated household farm animals using EUA human vaccines, or the effect of pasteurization of such immune milk on the SARS-CoV-2 virus-neutralizing activity, has not yet been experimentally validated. To address these important open questions, we performed a series of pilot experiments in 60 milk and serum samples of cows and goats vaccinated with the ZF-UZ-VAC2001 recombinant SARS-CoV-2 human vaccine, containing a dimeric form of the receptor-binding domain (RBD) as the antigen (9). We used this particular vaccine because it had successfully passed a third phase clinical trial in Uzbekistan and was approved for the massive vaccination of the population (10). ...
Article
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Here, we present the first experimental validation of the possibility for obtaining immune milk with neutralizing antibodies against SARS-CoV-2 from vaccinated cows and goat using approved recombinant protein human coronavirus vaccine, ZF-UZ-VAC2001, in the Republic of Uzbekistan. In the period of 2 weeks after first vaccination, we detected the neutralizing antibodies against coronavirus in the blood serum of vaccinated animals. The neutralizing activity, in its peak on the 21st day after receiving the third dose (77th day from first dose), was effective in neutralization test using a live SARS-CoV-2 in Vero E6 cells, even after 120-fold serum titration. In cows receiving three dose of human vaccine, the MAGLUMI® SARS-CoV-2 neutralizing antibody competitive chemiluminescence immunoassay revealed that colostrum of the first day after calving had a greater activity to neutralize the SARS-CoV-2 compared to colostrum of subsequent three days (4.080 μg/ml vs 2.106, 1.960 and 1.126 μg/ml). In comparison, the neutralizing activity for goat and cow milk was 1.486 μg/ml and 0.222 μg/ml, respectively. We observed a positive correlation of receptor-binding domain (RBD)-specific IgG antibodies between the serum of actively immunized cow and milk-feeding calf during the entire course of vaccination (r = 0.95, p = 0.05). We showed an optimal regime for immune milk pasteurization at 62.5°C for 30 min, which retained specific neutralizing activity to SARS-CoV-2, potentially useful for passive immunization against coronavirus infection threats as an additive approach to the vaccination. This strategy, as a supportive approach to the vaccination, could also be applicable for directly reducing the effect of COVID-19 infection in gastrointestinal tract, supporting mucosal immunity.
... Considering the complex structure of S proteins, total expression with the help of T3SS may lead to structural interference, as well as difficulties in secretion (Van Engelenburg & Palmer, 2010). In addition, the non-RBD domains included in the S protein, such as NTD and S2, can all induce neutralizing antibodies (Wang et al., 2019), while some other regions of the protein may induce the production of nonneutralizing antibodies, leading to antibody-dependent enhancement effects, which not only fail to destroy the virus but may also enhance its ability to invade the cells (Dai et al., 2020). Therefore, we tried to use different strains to express different regions of the S protein and mix them proportionally, which effectively avoided these problems. ...
Article
Aims: This study aimed to provide a safe, stable and efficient SARS-CoV-2 oral vaccine development strategy based on the type III secretion system of attenuated Salmonella and a reference for the development of a SARS-CoV-2 vaccine. Methods and results: The attenuated Salmonella mutant ΔhtrA-VNP was used as a vector to secrete the antigen SARS-CoV-2 based on the type III secretion system (T3SS). The Salmonella pathogenicity island 2 (SPI-2)-encoded T3SS promoter (sifB) was screened to express heterologous antigens (RBD, NTD, S2), and the SPI-2-encoded secretion system (sseJ) was employed to secrete this molecule (psifB-sseJ-antigen, abbreviated BJ-antigen). Both immunoblotting and fluorescence microscopy revealed effective expression and secretion of the antigen into the cytosol of macrophages in vitro. The mixture of the three strains (BJ-RBD/NTD/S2, named AisVax) elicited a marked increase in the induction of IgA or IgG S-protein Abs after oral gavage, intraperitoneal and subcutaneous administration. Flow cytometric analysis proved that AisVax caused T-cell activation, as shown by a significant increase in CD44 and CD69 expression. Significant production of IgA or IgG N-protein Abs was also detected by using psifB-sseJ-N(FL), indicating the universality of this strategy. Conclusions: Delivery of multiple SARS-CoV-2 antigens using the type III secretion system of attenuated Salmonella ΔhtrA-VNP is a potential COVID-19 vaccine strategy. Significance and impact of the study: 1) The attenuated Salmonella strain ΔhtrA-VNP showed excellent performance as a vaccine vector. 2) The Salmonella SPI-2-encoded T3SS showed highly efficient delivery of SARS-COV-2 antigens. 3) Anti-loss elements integrated into the plasmid stabilized the phenotype of the vaccine strain. 4) Mixed administration of antigen-expressing strains improved antibody induction.
... Coronavirus pandemic preparedness mainly involves effective respond towards the viruses as soon as it appears leading its containment or minimizing their spread. Alternatively, discovery of neutralizing antibodies (nAbs) against coronaviruses, and by utilizing the molecular knowledge of their epitopes leads towards rational designing of pan-coronavirus vaccines (Dai et al. 2020). Receptor Binding Domain (RBD) is a highly immunogenic component of spike protein which is recognized by the majority of nAbs and is, therefore, a major target of current nAb-based vaccine design efforts (Cao et al. 2020, p. 2;Robbiani et al. 2020;Bertoglio et al. 2021). ...
Article
We used human semi-synthetic phage antibody gene libraries to select anti-SARS-CoV-2 RBD scFv antibody fragment and subsequent characterization of this novel tetravalent monoclonal antibody targeting conformational epitopes in the receptor binding domain of SARS-CoV-2. Binding studies suggest that II62 tetravalent antibody cross-reacts with RBD protein of SARS-CoV2 and its different variants of concerns. The epitope mapping data reveals that II62 tetravalent antibody targets an epitope that does not directly interferes with RBD: ACE2 interaction. Neutralization studies with live authentic SARS-CoV2 virus suggests that increase in valency of II62 mAb from monovalent to tetravalent doesn't perturbate virus interactions with the ACE2 expressing host cells in cytopathic effect-based (CPE) assay. Supplementary information: The online version contains supplementary material available at 10.1007/s13205-022-03272-6.
... accessed on 7 September 2022), with numbers continuing to rise. The biomedical research community has made huge efforts to rapidly respond to this challenge, most notably the development of vaccines that are safe and effective against early SARS-CoV-2 strains [9][10][11]. However, the constantly emerging viral variants, including the most recently emerged Omicron sub-lineages BA.4 and BA.5, have compromised vaccine effectiveness [12][13][14][15]. ...
Article
The ongoing spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused hundreds of millions of cases and millions of victims worldwide with serious consequences to global health and economies. Although many vaccines protecting against SARS-CoV-2 are currently available, constantly emerging new variants necessitate the development of alternative strategies for prevention and treatment of COVID-19. Inhibitors that target the main protease (Mpro) of SARS-CoV-2, an essential enzyme that promotes viral maturation, represent a key class of antivirals. Here, we showed that a peptidomimetic compound with benzothiazolyl ketone as warhead, YH-53, is an effective inhibitor of SARS-CoV-2, SARS-CoV, and MERS-CoV Mpros. Crystal structures of Mpros from SARS-CoV-2, SARS-CoV, and MERS-CoV bound to the inhibitor YH-53 revealed a unique ligand-binding site, which provides new insights into the mechanism of inhibition of viral replication. A detailed analysis of these crystal structures defined the key molecular determinants required for inhibition and illustrate the binding mode of Mpros from other coronaviruses. In consideration of the important role of Mpro in developing antivirals against coronaviruses, insights derived from this study should add to the design of pan-coronaviral Mpro inhibitors that are safer and more effective.
... In addition to mRNA and viral-based vaccine platforms, protein-based adjuvanted vaccines (Novavax) that broaden the current immune responses are also a valuable approach to contain Wuhan and future Omicron subvariants [40]. Furthermore, RBD-dimeric vaccines, mosaic RBD nanoparticle vaccines, and conservative S2-targeting vaccines have shown their potential for pan-beta-coronaviruses, including SARS-CoV-2 and the SARS-like sarbecoviruses, as well as human endemic coronavirus protections by inducing broadly neutralizing antibodies [41][42][43]. These active and passive vaccination efforts collectively contribute to our long-term path to pan-beta-coronavirus, or pan-coronavirus, protection. ...
Article
Since the SARS-CoV-2 Omicron variant (B.1.1.529) was declared a variant of concern (VOC) by the WHO on 24 November 2021, it has caused another global surge of cases. With extensive mutations in its spike glycoprotein, Omicron gained substantial capabilities to evade the antiviral immunity provided by vaccination, hybrid immunity, or monoclonal antibodies. The Omicron subvariants BA.1, BA.2, BA.2.12.1, BA.4 and BA.5 extended this immune evasion capability by having additional unique mutations in their respective spike proteins. The ongoing Omicron wave and emergence of new Omicron subvariants leads to additional concerns regarding the efficacy of the current antiviral measurements. To have a better understanding of the Omicron subvariants, this review summarizes reports of the immune evasion of subvariants BA.1, BA.2, BA.2.12.1, BA.4, and BA.5 as well as the molecular basis of immune evasion.
... In this study, the RBD gene and its variants were chosen for display on the S. cerevisiae surface. (41). It is necessary to enhance the immunogenicity through artificial optimization of RBD in future studies. ...
Article
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Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), represents a significant global human health threat. The most effective way to end the pandemic is through timely vaccination. In this study, the receptor-binding domains (RBDs) of Spike protein of the initial strain of SARS-CoV-2 and its variants, B.1.1.7 (Alpha), B.1.351 (Beta), and B.1.617.1 (Kappa), were successfully displayed on the surface of a Saccharomyces cerevisiae strain for development as a vaccine candidate. To rapidly express the recombinant protein and avoid the need for expensive galactose as an inducer, the gal80 gene of S. cerevisiae was knocked out, and the conventional 72-h culture period was thus successfully shortened to 24 h. Mice vaccinated against variant B.1.617.1 showed robust humoral and cellular immune responses. Moreover, the antiserum in the B.1.671.1 group had neutralizing activity against wild-type RBD and high binding titers against RBD mutants of variants B.1.351 and B.1.1.7. Double deglycosylation at N331Q and N343Q resulted in marked reduction of the affinity of RBD binding to angiotensin converting enzyme 2 (ACE2) and escaped antibody neutralization. This study demonstrates that yeast surface display technology can provide an alternative approach to rapid large-scale preparation of promising SARS-CoV-2 vaccine candidates at low cost.
... The rate of infection even in the Brazilian military is higher than in the civilian population [236], whereas the opposite is observed in the Korean military [237], thus confirming that the rate of infection may depend on many variables, including the coverage of the vaccination in the military compared with the general population. Moreover, despite the vaccine's effectiveness against severe disease, the protection against infection seems to be quite limited, in particular for some types of viral variants of concern; thus, the research is actively engaged in developing more effective vaccines, possibly a "universal" vaccine [238], such as the one that is desirable to obtain even for influenza [239]. However, despite that no documents are yet available on the vaccination coverage of the military in all the countries of the world, it may be hypothesized that in all countries, the military have been considered a category to be primarily vaccinated, such as health care workers and vulnerable patients. ...
Article
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The environmental conditions generated by war and characterized by poverty, undernutrition, stress, difficult access to safe water and food as well as lack of environmental and personal hygiene favor the spread of many infectious diseases. Epidemic typhus, plague, malaria, cholera, typhoid fever, hepatitis, tetanus, and smallpox have nearly constantly accompanied wars, frequently deeply conditioning the outcome of battles/wars more than weapons and military strategy. At the end of the nineteenth century, with the birth of bacteriology, military medical researchers in Germany, the United Kingdom, and France were active in discovering the etiological agents of some diseases and in developing preventive vaccines. Emil von Behring, Ronald Ross and Charles Laveran, who were or served as military physicians, won the first, the second, and the seventh Nobel Prize for Physiology or Medicine for discovering passive anti-diphtheria/tetanus immunotherapy and for identifying mosquito Anopheline as a malaria vector and plasmodium as its etiological agent, respectively. Meanwhile, Major Walter Reed in the United States of America discovered the mosquito vector of yellow fever, thus paving the way for its prevention by vector control. In this work, the military relevance of some vaccine-preventable and non-vaccine-preventable infectious diseases, as well as of biological weapons, and the military contributions to their control will be described. Currently, the civil–military medical collaboration is getting closer and becoming interdependent, from research and development for the prevention of infectious diseases to disasters and emergencies management, as recently demonstrated in Ebola and Zika outbreaks and the COVID-19 pandemic, even with the high biocontainment aeromedical evacuation, in a sort of global health diplomacy.
... These manufacturing and distribution benefits would be even more meaningful in the event that seasonal updates and mass vaccination campaigns are required. Last, these immunogens can be easily improved by established methods of foldon trimerization, multimerization, and/or nanoparticle display (44)(45)(46)(47)(48). ...
Article
The receptor binding domain (RBD) of the SARS-CoV-2 spike protein is the primary target of neutralizing antibodies and is a component of almost all current vaccines. Here, RBD immunogens were created with stabilizing amino acid changes that improve the neutralizing antibody response, as well as characteristics for production, storage, and distribution. A computational design and in vitro screening platform identified three improved immunogens, each with approximately nine amino acid changes relative to the native RBD sequence, and four key changes conserved between immunogens. The changes are adaptable to all vaccine platforms and compatible with mutations in emerging variants of concern. The immunogens elicit higher levels of neutralizing antibodies than native RBD, focus the immune response to structured neutralizing epitopes, and have increased production yields and thermostability. Incorporating these variant-independent amino acid changes in next-generation COVID vaccines may enhance the neutralizing antibody response and lead to longer duration and broader protection.
... It is believed that optimizing the antigen design is a feasible approach to improving the immunogenicity. For example, the receptor binding domain (RBD)-dimer, as a tandem-repeat single-chain, was subtly designed in ZF2001, a vaccine with emergency use authorization in China, to improve the immunogenicity compared with that of the monomer RBD [4,5]. Subsequently, the Delta-Omicron RBD-dimer was designed as an antigen to prepare the second-generation recombinant protein vaccine to combat the epidemics of the Delta and Omicron variants [6]. ...
Article
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The research and development (R&D) of novel adjuvants is an effective measure for improving the immunogenicity of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant protein vaccine. Toward this end, we designed a novel single-stranded RNA-based adjuvant, L2, from the SARS-CoV-2 prototype genome. L2 could initiate retinoic acid-inducible gene-I signaling pathways to effectively activate the innate immunity. ZF2001, an aluminum hydroxide (Al) adjuvanted SARS-CoV-2 recombinant receptor binding domain (RBD) subunit vaccine with emergency use authorization in China, was used for comparison. L2, with adjuvant compatibility with RBD, elevated the antibody response to a level more than that achieved with Al, CpG 7909, or poly(I:C) as adjuvants in mice. L2 plus Al with composite adjuvant compatibility with RBD markedly improved the immunogenicity of ZF2001; in particular, neutralizing antibody titers increased by about 44-fold for Omicron, and the combination also induced higher levels of antibodies than CpG 7909/poly(I:C) plus Al in mice. Moreover, L2 and L2 plus Al effectively improved the Th1 immune response, rather than the Th2 immune response. Taken together, L2, used as an adjuvant, enhanced the immune response of the SARS-CoV-2 recombinant RBD protein vaccine in mice. These findings should provide a basis for the R&D of novel RNA-based adjuvants.
... ; https://doi.org/10.1101/2022.08.02.502186 doi: bioRxiv preprint 4 higher level of neutralizing antibody titer in comparison with monomeric RBD. [25][26][27][28] However, the limited control offered by NPs does not allow for assessing the role of structural parameters related to antigen presentation (e.g., density, stoichiometry, nanoscale organization, and NP geometries) on cellular uptake and immunogenicity that could enable rational design of vaccines. 29,30 Scaffolded DNA origami nanoparticles (DNA-NPs), on the other hand, provide an ideal biocompatible platform for assessing antigen presentation parameters. ...
Preprint
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Effective and safe vaccines are invaluable tools in the arsenal to fight infectious diseases. The rapid spreading of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible of the coronavirus disease 2019 pandemic has highlighted the need to develop methods for rapid and efficient vaccine development. DNA origami nanoparticles (DNA-NPs) presenting multiple antigens in prescribed nanoscale patterns have recently emerged as a safe, efficient, and easily scalable alternative for rational design of vaccines. Here, we are leveraging the unique properties of these DNA-NPs and demonstrate that precisely patterning ten copies of a reconstituted trimer of the receptor binding domain (RBD) of SARS-CoV-2 along with CpG adjuvants on the DNA-NPs is able to elicit a robust protective immunity against SARS-CoV-2 in a mouse model. Our results demonstrate the potential of our DNA-NP-based approach for developing safe and effective nanovaccines against infectious diseases.
... In particular, the receptor-binding domain (RBD) of S1 can recognize and bind to the host cell receptor ACE2 [4]. It has been proposed that inhibition of the RBD-ACE2 interaction may be useful in the prevention of SARS-CoV-2 infection [10,11]; thus, the SARS-CoV-2 RBD region is an attractive target for the development of new subunit vaccines. ...
Article
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The coronavirus disease-19 (COVID-19) pandemic has been ongoing since December 2019, with more than 6.3 million deaths reported globally as of August 2022. Despite the success of several SARS-CoV-2 vaccines, the rise in variants, some of which are resistant to the effects of vaccination, highlights the need for a so-called pan-coronavirus (universal) vaccine. Here, we performed an immunogenicity comparison of prototype vaccines containing spike protein receptor-binding domain (RBD) residues 319–541, or spike protein regions S1, S2 and S fused to a histidine-tagged or human IgG1 Fc (hFC) fragment with either a longer (six residues) or shorter (three residues) linker. While all recombinant protein vaccines developed were effective in eliciting humoral immunity, the RBD-hFc vaccine was able to generate a potent neutralizing antibody response as well as a cellular immune response. We then compared the effects of recombinant protein length and linker size on immunogenicity in vivo. We found that a longer recombinant RBD protein (residues 319–583; RBD-Plus-hFc) containing a small alanine linker (AAA) was able to trigger long-lasting, high-titer neutralizing antibodies in mice. Finally, we evaluated cross-neutralization of wild-type and mutant RBD-Plus-hFc vaccines against wild-type, Alpha, Beta, Delta and Omicron SARS-CoV-2 variants. Significantly, at the same antigen dose, wild-type RBD-Plus-hFc immune sera induced broadly neutralizing antibodies against wild-type, Alpha, Beta, Delta and Omicron variants. Taken together, our findings provide valuable information for the continued development of recombinant protein-based SARS-CoV-2 vaccines and a basic foundation for booster vaccinations to avoid reinfection with SARS-CoV-2 variants.
Article
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, development of an effective vaccine that can stop the transmission of SARS-CoV-2 remains a matter of concern. Literature was retrieved using the key words 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 focused 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 polyvalent mixed recombinant protein vaccine to elicit 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.
Article
Effective antigen delivery and immune stimulation in nasal mucosa determine the success of mucosal immunity. Here, an oil-in-ionic liquid (o/IL) nanoemulsion formulated with choline and niacin IL ([Cho][Nic]), squalene, and Tween 80 surfactant is explored as a vaccine delivery system for intranasal mucosal immunization. Compared to the o/w emulsion counterpart without the ILs, the o/IL manoemulsion showed a reduced and more uniform size of approximately 168 nm and significantly improved stability. Studies in mice model showed that when was used as an intranasal vaccine delivery system for influenza split-virus antigens, the antigens in the o/IL nanoemulsion induced strong mucosal immune responses with secretory IgA titers 25- and 5.8-fold higher than those of naked and commercial MF59-adjuvanted antigens, respectively. The o/IL nanoemulsion system also induced stronger systemic humoral responses. The excellent mucosal adjuvant effects of the o/IL nanoemulsion mainly benefited from the prolonged retention of antigens in the nasal cavity, enhanced antigen permeation into the submucosa, and the consequently promoted proliferation of CD11b cells and CD4+ T cells in nasal mucosa-associated lymphoid tissue. Moreover, when used as an injection adjuvant, the o/IL nanoemulsion also induced stronger humoral immune responses than MF59. Thus, the [Cho][Nic]-based o/IL nanoemulsion vaccine delivery system can serve as a promising adjuvant platform.
Preprint
To address the need for multivalent vaccines against Coronaviridae that can be rapidly developed and manufactured, we compared antibody responses against SARS-CoV, SARS-CoV-2, and several variants of concern in mice immunized with mRNA-lipid nanoparticle vaccines encoding homodimers or heterodimers of SARS-CoV/SARS-CoV-2 receptor-binding domains. All vaccine constructs induced robust anti-viral antibody responses, and the heterodimeric vaccine elicited an IgG response capable of cross-neutralizing SARS-CoV, SARS-CoV-2 Wuhan-Hu-1, B.1.351 (beta), and B.1.617.2 (delta) variants.
Article
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The adaptive immune response induced by SARS-CoV-2 plays a key role in the antiviral process and can protect the body from the threat of infection for a certain period of time. However, owing to the limitations of clinical studies, the antiviral mechanisms, protective thresholds, and persistence of the immune memory of adaptive immune responses remain unclear. This review summarizes existing research models for SARS-CoV-2 and elaborates on the advantages of animal models in simulating the clinical symptoms of COVID-19 in humans. In addition, we systematically summarize the research progress on the SARS-CoV-2 adaptive immune response and the remaining key issues, as well as the application and prospects of animal models in this field. This paper provides direction for in-depth analysis of the anti-SARS-CoV-2 mechanism of the adaptive immune response and lays the foundation for the development and application of vaccines and drugs.
Article
The devastating economic and public health consequences caused by the COVID-19 pandemic have prompted outstanding efforts from the scientific community and pharmaceutical companies to develop antibody-based therapeutics against SARS-CoV-2. Those efforts are encouraging and fruitful. An unprecedentedly large number of monoclonal antibodies (mAbs) targeting a large spectrum of epitopes on the spike protein has been developed in the last two years. The development of structural biology, especially the cryo-EM technology, provides structural insights into the molecular neutralizing mechanisms of those mAbs. Moreover, neutralizing antibodies are essential in protecting host from infection. Therefore, understanding the antibody neutralizing mechanism is critical for optimizing effective antibody-based therapeutics and developing next-generation pan-coronavirus vaccines. This review summarizes the latest understanding of antibody neutralizing mechanisms against SARS-CoV-2 at the molecular and structural levels.
Article
Adjuvants are essential components of vaccines. Invariant natural killer T (iNKT) cells are a distinct subset of T cells that function to bridge the innate and adaptive immunities and are capable of mediating strong and rapid responses to a range of diseases, including cancer and infectious disease. An increasing amount of evidence suggests that iNKT cells can help fight viral infection. In particular, iNKT-secreting IL-4 is a key mediator of humoral immunity and has a positive correlation with the levels of neutralizing antibodies. As iNKT cell agonists, αGC glycolipid (α-galactosylceramide, or KRN7000) and its analogues as vaccine adjuvants have begun to provide vaccinologists with a new toolset. Herein we found that a new iNKT-cell agonist αGC-CPOEt elicited a strong cytokine response with increased IL-4 production. Remarkably, after three immunizations, SARS-CoV-2 RBD-Fc adjuvanted by αGC-CPOEt evoked robust neutralizing antibody responses that were about 5.5-fold more than those induced by αGC/RBD-Fc and 25-fold greater than those induced by unadjuvanted RBD-Fc. These findings imply that αGC-CPOEt could be investigated further as a new COVID-19 vaccine adjuvant to prevent current and future infectious disease outbreaks.
Article
Harnessing highly conserved peptides derived from the receptor binding domain (RBD) of spike (S) protein to construct peptide-based inhibitors is one of the most effective strategies to fight against the ever-mutating coronavirus SARS-CoV-2. But how the O-glycosylation affects their inhibition abilities has not been intensively explored. Herein, an intrinsic O-glycosylated peptide P320-334 derived from RBD was screened and homogeneous O-linked glycopeptides containing Tn (GalNAcα1-O-Ser/Thr), T (Galβ1-3GalNAcα1-O-Ser/Thr), sialyl-Tn (sTn, Siaα2-6GalNAcα1-O-Ser/Thr), and sialyl-T (sT, Siaα2-3Galβ1-3GalNAcα1-O-Ser/Thr) structures were first synthesized via chemoenzymatic strategies. Compared with the unglycosylated peptide, the binding of sT-P320-334 to hACE2 was enhanced to 133% and the inhibition capacity against RBD-hACE2 binding of sTn- and sT-P320-334 was significantly increased up to 150-410%. Thus, our results suggest the sialic acid residue on the terminal of short O-glycan structures might strengthen the inhibition capacities of these peptide-based inhibitors, which might provide novel optimization directions for the inhibitor design.
Article
Rational vaccine design, especially vaccine antigen identification and optimization, is critical to successful and efficient vaccine development against various infectious diseases including coronavirus disease 2019 (COVID-19). In general, computational vaccine design includes three major stages: (i) identification and annotation of experimentally verified gold standard protective antigens through literature mining, (ii) rational vaccine design using reverse vaccinology (RV) and structural vaccinology (SV) and (iii) post-licensure vaccine success and adverse event surveillance and its usage for vaccine design. Protegen is a database of experimentally verified protective antigens, which can be used as gold standard data for rational vaccine design. RV predicts protective antigen targets primarily from genome sequence analysis. SV refines antigens through structural engineering. Recently, RV and SV approaches, with the support of various machine learning methods, have been applied to COVID-19 vaccine design. The analysis of post-licensure vaccine adverse event report data also provides valuable results in terms of vaccine safety and how vaccines should be used or paused. Ontology standardizes and incorporates heterogeneous data and knowledge in a human- and computer-interpretable manner, further supporting machine learning and vaccine design. Future directions on rational vaccine design are discussed.
Article
There is an urgent need to stop the coronavirus disease 2019 (COVID-19) pandemic through the development of efficient and safe vaccination methods. Over the short term, plasmid DNA vaccines can be developed as they are molecularly stable, thus facilitating easy transport and storage. pVAX1-SARS-CoV2-co was designed for the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) S protein. The antibodies produced led to immunoreactions against the S protein, an anti-receptor-binding-domain, and a neutralizing action of the pVAX1-SARS-CoV2-co, as previously confirmed. To promote the efficacy of the pVAX1-SARS-CoV2-co vaccine a pyro-drive jet injector (PJI) was used. An intradermally adjusted PJI demonstrated that the pVAX1-SARS-CoV2-co vaccine injection caused a high production of anti-S protein antibodies, triggered immunoreactions, and neutralized the actions against SARS-CoV-2. A high-dose pVAX1-SARS-CoV2-co intradermal injection using PJI did not cause any serious disorders in the rat model. A viral challenge confirmed that intradermally immunized mice were potently protected from COVID-19. A pVAX1-SARS-CoV2-co intradermal injection using PJI is a safe and promising vaccination method for overcoming the COVID-19 pandemic.
Article
With the global pandemic of the new coronavirus disease (COVID-19), a safe, effective, and affordable mass-produced vaccine remains the current focus of research. Herein, we designed an adjuvant-protein conjugate vaccine candidate, in which the TLR7 agonist (TLR7a) was conjugated to S1 subunit of SARS-CoV-2 spike protein, and systematically compared the effect of different numbers of built-in TLR7a on the immune activity for the first time. As the number of built-in TLR7a increased, a bell-shaped reaction was observed in three TLR7a-S1 conjugates, with TLR7a(10)-S1 (with around 10 built-in adjuvant molecules on one S1 protein) eliciting a more potent immune response than TLR7a(2)-S1 and TLR7a(18)-S1. This adjuvant-protein conjugate strategy allows the built-in adjuvant to provide cluster effects and prevents systemic toxicity and facilitates the co-delivery of adjuvant and antigen. Vaccination of mice with TLR7a(10)-S1 triggered a potent humoral and cellular immunity and a balanced Th1/Th2 immune response. Meanwhile, the vaccine induces effective neutralizing antibodies against SARS-CoV-2 and all variants of concern (B.1.1.7/alpha, B.1.351/beta, P.1/gamma, B.1.617.2/delta, and B.1.1.529/omicron). It is expected that the adjuvant-protein conjugate strategy has great potential to construct a potent recombinant protein vaccine candidate against various types of diseases.
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Since the 20th century, humans have lived through five pandemics caused by influenza A viruses (IAVs) (H1N1/1918, H2N2/1957, H3N2/1968, and H1N1/2009), and the coronavirus (CoV) SARS-CoV-2. IAVs and CoVs both have broad host ranges and share multiple hosts. Virus co-circulation and even co-infections facilitate genetic reassortment among IAVs and recombination among CoVs, further altering virus evolution dynamics and generating novel variants with increased cross-species transmission risk. Moreover, SARS-CoV-2 may maintain long-term circulation in humans as seasonal IAVs. Co-existence and co-infection of both viruses in humans could alter disease transmission patterns and aggravate disease burden. Herein, we demonstrate how virus-host ecology correlates with the co-existence and co-infection of IAVs and/or CoVs, further affecting virus evolution and disease dynamics and burden, calling for active virus surveillance and countermeasures for future public health challenges.
Article
New variants in the SARS-CoV-2 pandemic are more contagious (Alpha/Delta), evade neutralizing antibodies (Beta), or both (Omicron). This poses a challenge in vaccine development according to WHO. We designed a more universal SARS-CoV-2 DNA vaccine containing receptor-binding domain loops from the huCoV-19/WH01, the Alpha, and the Beta variants, combined with the membrane and nucleoproteins. The vaccine induced spike antibodies crossreactive between huCoV-19/WH01, Beta, and Delta spike proteins that neutralized huCoV-19/WH01, Beta, Delta, and Omicron virus in vitro. The vaccine primed nucleoprotein-specific T cells, unlike spike-specific T cells, recognized Bat-CoV sequences. The vaccine protected mice carrying the human ACE2 receptor against lethal infection with the SARS-CoV-2 Beta variant. Interestingly, priming of cross-reactive nucleoprotein-specific T cells alone was 60% protective, verifying observations from humans that T cells protect against lethal disease. This SARS-CoV vaccine induces a uniquely broad and functional immunity that adds to currently used vaccines.
Article
Background: SARS-CoV-2 pandemic is a global threat to humans and the world’s economy. Effective and safe vaccines against this virus are essential to control and eradicate the pandemic. The currently applied vaccines carry SARS-CoV-2 spike-protein mRNA/cDNA. These vaccines go through several cellular processes in the recipients for producing antigens. On the contrary, the SARS-CoV-2 RBD (receptor binding domain)-protein is an antigen. It will directly stimulate antibody production against SARS-CoV-2. Hence, we propose to produce SARS-CoV-2 RBD-protein as a fast acting, effective and safe vaccine. Methods: We propose to reconstruct a plasmid carrying three types of DNA sequences: RBD cDNA, FP (fusion peptide) DNA and sfGFP(superfolder-green-fluorescent-protein), cDNA creating the RBD-FP-sfGFP DNA within an orf (open-reading-frame). Escherichia coli, C2566H, transformed with the reconstructed plasmid will express RBD-FP-sfGFP fusion protein producing green fluorescent cfu (colony forming unit). The RBD-protein will be separated from the sfGFP using an FP specific enterokinase, and eluted by HIC ( hydrophobic-interaction-chromatography ), detected with a BioVision-Elisa-Kit, and quantified by spectrophotometry at UV280 nm and immune simulation will be carried out using C57BL mice. Results: The plasmid reconstruct will carry amp r (ampicillin-resistant) gene as a selective marker and a T7 promoter controlling the expression of RBD-FP-sfGFP fusion protein. The transformed Escherichia coli will efficiently express the RBD-FP-sfGFP fusion protein. The highly efficient sfGFP fused within the RBD-FP-sfGFP will produce green fluorescent cfu . The RBD-FP-sfGFP protein extract from the green cfu, digested by enterokinase and separated by the HIC will produce pure immunoreactive RBD protein. Conclusion: A positive BioVision-ELISA test detects <10 pg RBD protein/ml of the sample. A larger sample of the purified RBD protein can be used as a vaccine following a standard formulation and safety protocols. Once administered, the RBD protein will stimulate antibody production against the SARS-CoV-2 virus. The RBD protein has no potential to recombine with human genome.
Article
Introduction: Vaccination continues to be the most effective method for controlling COVID-19 infectious diseases. Nonetheless, SARS-CoV-2 variants continue to evolve and emerge, resulting in significant public concerns worldwide even after more than two years since the COVID-19 pandemic. It is significant to better understand how different COVID-19 vaccine platforms work, why SARS-CoV-2 variants continue to emerge, and what options for improving COVID-19 vaccines can be considered to fight against SARS-CoV-2 variants and future pandemics. Area covered: Here, we reviewed the innate immune sensors in the recognition of SARS-CoV-2 virus, innate and adaptive immunity including neutralizing antibodies by different COVID-19 vaccines. Efficacy comparison of the several COVID-19 vaccine platforms approved to use in humans, concerns about SARS-CoV-2 variants and breakthrough infections, and the options for developing future COIVD-19 vaccines were also covered. Expert opinion: Owing to the continuous emergence of novel pathogens and the re-emergence of variants, safer and more effective new vaccines are needed. This review is also aimed to provide the knowledge basis for the development of next-generation COVID-19 and pan-coronavirus vaccines to provide cross-protection against new SARS-CoV-2 variants and future coronavirus pandemics.
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To combat the HIV epidemic and emerging threats such as SARS-CoV-2, immunization strategies are needed that elicit protection at mucosal portals of pathogen entry. Immunization directly through airway surfaces is effective in driving mucosal immunity, but poor vaccine uptake across the mucus and epithelial lining is a limitation. The major blood protein albumin is constitutively transcytosed bidirectionally across the airway epithelium through interactions with neonatal Fc receptors (FcRn). Exploiting this biology, here, we demonstrate a strategy of “albumin hitchhiking” to promote mucosal immunity using an intranasal vaccine consisting of protein immunogens modified with an amphiphilic albumin-binding polymer-lipid tail, forming amph-proteins. Amph-proteins persisted in the nasal mucosa of mice and nonhuman primates and exhibited increased uptake into the tissue in an FcRn-dependent manner, leading to enhanced germinal center responses in nasal-associated lymphoid tissue. Intranasal immunization with amph-conjugated HIV Env gp120 or SARS-CoV-2 receptor binding domain (RBD) proteins elicited 100- to 1000-fold higher antigen-specific IgG and IgA titers in the serum, upper and lower respiratory mucosa, and distal genitourinary mucosae of mice compared to unmodified protein. Amph-RBD immunization induced high titers of SARS-CoV-2–neutralizing antibodies in serum, nasal washes, and bronchoalveolar lavage. Furthermore, intranasal amph-protein immunization in rhesus macaques elicited 10-fold higher antigen-specific IgG and IgA responses in the serum and nasal mucosa compared to unmodified protein, supporting the translational potential of this approach. These results suggest that using amph-protein vaccines to deliver antigen across mucosal epithelia is a promising strategy to promote mucosal immunity against HIV, SARS-CoV-2, and other infectious diseases.
Article
The ongoing coronavirus disease-19 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has drastically changed our way of life and continues to have an unmitigated socioeconomic impact across the globe. Research into potential vaccine design and production is focused on the spike (S) protein of the virus, which is critical for virus entry into host cells. Yet, whether the degree of glycosylation in the S protein is associated with vaccine efficacy remains unclear. Here, we first optimized the expression of the S protein in mammalian cells. While we found no significant discrepancy in purity, homogeneity, or receptor binding ability among S proteins derived from 293F cells (referred to as 293F S-2P), 293S GnTI- cells (defective in N-acetylglucosaminyl transferase I enzyme; 293S S-2P), or TN-5B1-4 insect cells (Bac S-2P), there was significant variation in the glycosylation patterns and thermal stability of the proteins. Compared with the partially glycosylated 293S S-2P or Bac S-2P, the fully glycosylated 293F S-2P exhibited higher binding reactivity to convalescent sera. In addition, 293F S-2P induced higher IgG and neutralizing antibody titres than 293S or Bac S-2P in mice. Furthermore, a prime-boost-boost regimen, using a combined immunization of S-2P proteins with various degrees of glycosylation, elicited a more robust neutralizing antibody response than a single S-2P alone. Collectively, this study provides insight into ways to design a more effective SARS-CoV-2 immunogen.
Article
Background: SARS-CoV-2 pandemic is a global threat to humans and the world’s economy. Effective and safe vaccines against this virus are essential to control and eradicate the pandemic. The currently applied vaccines carry SARS-CoV-2 spike-protein mRNA/cDNA. These vaccines go through several cellular processes in the recipients for producing antigens. On the contrary, the SARS-CoV-2 RBD (receptor binding domain)-protein is an antigen. It will directly stimulate antibody production against SARS-CoV-2. Hence, we propose to produce SARS-CoV-2 RBD-protein as a fast acting, effective and safe vaccine. Methods: We propose to reconstruct a plasmid carrying three types of DNA sequences: RBD cDNA, FP (fusion peptide) DNA and sfGFP(superfolder-green-fluorescent-protein), cDNA creating the RBD-FP-sfGFP DNA within an orf (open-reading-frame). Escherichia coli, C2566H, transformed with the reconstructed plasmid will express RBD-FP-sfGFP fusion protein producing green fluorescent cfu (colony forming unit). The RBD-protein will be separated from the sfGFP using an FP specific enterokinase, and eluted by HIC ( hydrophobic-interaction-chromatography ), detected with a BioVision-Elisa-Kit, and quantified by spectrophotometry at UV280 nm and immune simulation will be carried out using C57BL mice. Results: The plasmid reconstruct will carry amp r (ampicillin-resistant) gene as a selective marker and a T7 promoter controlling the expression of RBD-FP-sfGFP fusion protein. The transformed Escherichia coli will efficiently express the RBD-FP-sfGFP fusion protein. The highly efficient sfGFP fused within the RBD-FP-sfGFP will produce green fluorescent cfu . The RBD-FP-sfGFP protein extract from the green cfu, digested by enterokinase and separated by the HIC will produce pure immunoreactive RBD protein. Conclusion: A positive BioVision-ELISA test detects <10 pg RBD protein/ml of the sample. A larger sample of the purified RBD protein can be used as a vaccine following a standard formulation and safety protocols. Once administered, the RBD protein will stimulate antibody production against the SARS-CoV-2 virus. The RBD protein has no potential to recombine with human genome.
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An outbreak of the coronavirus disease 2019 (COVID-19)1–3, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)4 spread globally. Countermeasures are needed to treat and prevent further dissemination of the virus. In this study, we report the isolation of 2 specific human monoclonal antibodies (MAbs) from a convalescent COVID-19 patient. CA1 and CB6 demonstrated potent SARS-CoV-2-specific neutralization activity in vitro against SARS-CoV-2. In addition, CB6 inhibited SARS-CoV-2 infection in rhesus monkeys at both prophylactic and treatment settings. Further structural studies revealed that CB6 recognizes an epitope that overlaps with angiotensin converting enzyme 2 (ACE2)-binding sites in SARS-CoV-2 receptor binding domain (RBD), thereby interfering with the virus/receptor interactions by both steric hindrance and direct interface-residue competition. Our results suggest CB6 deserves further clinical translation.
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An antibody defense against COVID-19 One of the responses of the immune system to invading viruses is the production of antibodies. Some of these are neutralizing, meaning that they prevent the virus from being infectious, and can thus be used to treat viral diseases. Wu et al. isolated four neutralizing antibodies from a convalescent coronavirus disease 2019 (COVID-19) patient. Two of the antibodies, B38 and H4, blocked the receptor binding domain (RBD) of the viral spike protein from binding to the cellular receptor, angiotensin-converting enzyme 2 (ACE2). The structure of the RBD bound to B38 shows that the B38-binding site overlaps with the binding site for ACE2. Although H4 also blocks RBD binding to ACE2, it binds at a different site, and thus the two antibodies can bind simultaneously. This pair of antibodies could potentially be used together in clinical applications. Science , this issue p. 1274
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Coronavirus (CoV) disease 2019 (COVID-19) caused by severe acute respiratory syndrome (SARS)-CoV-2 (also known as 2019-nCoV) is threatening global public health, social stability, and economic development. To meet this challenge, this article discusses advances in the research and development of neutralizing antibodies (nAbs) for the prevention and treatment of infection by SARS-CoV-2 and other human CoVs.
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A novel and highly pathogenic coronavirus (SARS-CoV-2) has caused an outbreak in Wuhan city, Hubei province of China since December 2019, and soon spread nationwide and spilled over to other countries around the world1–3. To better understand the initial step of infection at an atomic level, we determined the crystal structure of the SARS-CoV-2 spike receptor-binding domain (RBD) bound to the cell receptor ACE2 at 2.45 Å resolution. The overall ACE2-binding mode of the SARS-CoV-2 RBD is nearly identical to that of the SARS-CoV RBD, which also utilizes ACE2 as the cell receptor⁴. Structural analysis identified residues in the SARS-CoV-2 RBD that are critical for ACE2 binding, the majority of which either are highly conserved or share similar side chain properties with those in the SARS-CoV RBD. Such similarity in structure and sequence strongly argue for convergent evolution between the SARS-CoV-2 and SARS-CoV RBDs for improved binding to ACE2, although SARS-CoV-2 does not cluster within SARS and SARS-related coronaviruses1–3,5. The epitopes of two SARS-CoV antibodies targeting the RBD are also analysed with the SARS-CoV-2 RBD, providing insights into the future identification of cross-reactive antibodies.
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A novel SARS-like coronavirus (SARS-CoV-2) recently emerged and is rapidly spreading in humans1,2. A key to tackling this epidemic is to understand the virus’s receptor recognition mechanism, which regulates its infectivity, pathogenesis and host range. SARS-CoV-2 and SARS-CoV recognize the same receptor - human ACE2 (hACE2)3,4. Here we determined the crystal structure of the SARS-CoV-2 receptor-binding domain (RBD) (engineered to facilitate crystallization) in complex with hACE2. Compared with the SARS-CoV RBD, a hACE2-binding ridge in SARS-CoV-2 RBD takes a more compact conformation; moreover, several residue changes in SARS-CoV-2 RBD stabilize two virus-binding hotspots at the RBD/hACE2 interface. These structural features of SARS-CoV-2 RBD enhance its hACE2-binding affinity. Additionally, we show that RaTG13, a bat coronavirus closely related to SARS-CoV-2, also uses hACE2 as its receptor. The differences among SARS-CoV-2, SARS-CoV and RaTG13 in hACE2 recognition shed light on potential animal-to-human transmission of SARS-CoV-2. This study provides guidance for intervention strategies targeting receptor recognition by SARS-CoV-2.
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Pseudoviruses are useful virological tools because of their safety and versatility, especially for emerging and re-emerging viruses. Due to its high pathogenicity and infectivity and the lack of effective vaccines and therapeutics, live SARS-CoV-2 has to be handled under biosafety level 3 conditions, which has hindered the development of vaccines and therapeutics. Based on a VSV pseudovirus production system, a pseudovirus-based neutralization assay has been developed for evaluating neutralizing antibodies against SARS-CoV-2 in biosafety level 2 facilities. The key parameters for this assay were optimized, including cell types, cell numbers, virus inoculum. When tested against the SARS-CoV-2 pseudovirus, SARS-CoV-2 convalescent patient sera showed high neutralizing potency, which underscore its potential as therapeutics. The limit of detection for this assay was determined as 22.1 and 43.2 for human and mouse serum samples respectively using a panel of 120 negative samples. The cutoff values were set as 30 and 50 for human and mouse serum samples, respectively. This assay showed relatively low coefficient of variations with 15.9% and 16.2% for the intra- and inter-assay analyses respectively. Taken together, we established a robust pseudovirus-based neutralization assay for SARS-CoV-2 and are glad to share pseudoviruses and related protocols with the developers of vaccines or therapeutics to fight against this lethal virus.
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How SARS-CoV-2 binds to human cells Scientists are racing to learn the secrets of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2), which is the cause of the pandemic disease COVID-19. The first step in viral entry is the binding of the viral trimeric spike protein to the human receptor angiotensin-converting enzyme 2 (ACE2). Yan et al. present the structure of human ACE2 in complex with a membrane protein that it chaperones, B ⁰ AT1. In the context of this complex, ACE2 is a dimer. A further structure shows how the receptor binding domain of SARS-CoV-2 interacts with ACE2 and suggests that it is possible that two trimeric spike proteins bind to an ACE2 dimer. The structures provide a basis for the development of therapeutics targeting this crucial interaction. Science , this issue p. 1444
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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.
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In December 2019, a cluster of patients with pneumonia of unknown cause was linked to a seafood wholesale market in Wuhan, China. A previously unknown betacoronavirus was discovered through the use of unbiased sequencing in samples from patients with pneumonia. Human airway epithelial cells were used to isolate a novel coronavirus, named 2019-nCoV, which formed another clade within the subgenus sarbecovirus, Orthocoronavirinae subfamily. Different from both MERS-CoV and SARS-CoV, 2019-nCoV is the seventh member of the family of coronaviruses that infect humans. Enhanced surveillance and further investigation are ongoing. (Funded by the National Key Research and Development Program of China and the National Major Project for Control and Prevention of Infectious Disease in China.).
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Middle East respiratory syndrome coronavirus (MERS-CoV) emerged into the human population in 2012 and has caused substantial morbidity and mortality. Potently neutralizing antibodies targeting the receptor-binding domain (RBD) on MERS-CoV spike (S) protein have been characterized, but much less is known about antibodies targeting non-RBD epitopes. Here, we report the structural and functional characterization of G2, a neutralizing antibody targeting the MERS-CoV S1 N-terminal domain (S1-NTD). Structures of G2 alone and in complex with the MERS-CoV S1-NTD define a site of vulnerability comprising two loops, each of which contain a residue mutated in G2-escape variants. Cell-surface binding studies and in vitro competition experiments demonstrate that G2 strongly disrupts the attachment of MERS-CoV S to its receptor, dipeptidyl peptidase-4 (DPP4), with the inhibition requiring the native trimeric S conformation. These results advance our understanding of antibody-mediated neutralization of coronaviruses and should facilitate the development of immunotherapeutics and vaccines against MERS-CoV.
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Middle East respiratory syndrome coronavirus (MERS-CoV), a new coronavirus that has been causing severe and fatal acute respiratory illnesses in humans since its outbreak in 2012, has raised public fear worldwide. The development of prophylactics and therapeutics is urgently needed to prevent and control MERS-CoV infections. In this study, a bacterium (Lactococcus lactis)-like particle (BLP) vaccine displaying the MERS-CoV receptor-binding domain (RBD) was developed, and gram-positive enhancer matrix (GEM) particles were used as substrates to externally bind to the MERS-CoV RBD through a protein anchor (PA). The designs included different numbers of lysin motif (LysM) repeats in the PAs linked by linkers (RBD-linker-PA2 (RLP2), RBD-linker-PA3 (RLP3) and RBD-PA3 (RP3)), and three LysM repeats and a linker in the fusion proteins increased the binding activity to the RBD. The specific immune responses were tested by intranasally immunizing mice with RLP3-GEM with or without the adjuvant GEL01. The results showed that GEL01-adjuvanted RLP3-GEM increased the systemic humoral, cellular and local mucosal immune responses in the mouse model, especially in the intestinal tract. The above results indicate that the MERS-CoV BLP product has the potential to be developed into a promising mucosal candidate vaccine to protect against MERS-CoV infections.
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Most neutralizing antibodies against Middle East respiratory syndrome coronavirus (MERS-CoV) target the receptor-binding domain (RBD) of the spike glycoprotein and block its binding to the cellular receptor dipeptidyl peptidase 4 (DPP4). The epitopes and mechanisms of mAbs targeting non-RBD regions have not been well characterized yet. Here we report the monoclonal antibody 7D10 that binds to the N-terminal domain (NTD) of the spike glycoprotein and inhibits the cell entry of MERS-CoV with high potency. Structure determination and mutagenesis experiments reveal the epitope and critical residues on the NTD for 7D10 binding and neutralization. Further experiments indicate that the neutralization by 7D10 is not solely dependent on the inhibition of DPP4 binding, but also acts after viral cell attachment, inhibiting the pre-fusion to post-fusion conformational change of the spike. These properties give 7D10 a wide neutralization breadth and help explain its synergistic effects with several RBD-targeting antibodies.
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Bats are a unique group of mammals of the order Chiroptera. They are highly diversified and are the group of mammals with the second largest number of species. Such highly diversified cell types and receptors facilitate them to be potential hosts of a large variety of viruses. Bats are the only group of mammals capable of sustained flight, which enables them to disseminate the viruses they harbor and enhance the chance of interspecies transmission. This article aims at reviewing the various aspects of the global epidemiology of bat coronaviruses (CoVs). Before the SARS epidemic, bats were not known to be hosts for CoVs. In the last 15 years, bats have been found to be hosts of >30 CoVs with complete genomes sequenced, and many more if those without genome sequences are included. Among the four CoV genera, only alphaCoVs and betaCoVs have been found in bats. As a whole, both alphaCoVs and betaCoVs have been detected from bats in Asia, Europe, Africa, North and South America and Australasia; but alphaCoVs seem to be more widespread than betaCoVs, and their detection rate is also higher. For betaCoVs, only those from subgenera Sarbecovirus, Merbecovirus, Nobecovirus and Hibecovirus have been detected in bats. Most notably, horseshoe bats are the reservoir of SARS-CoV, and several betaCoVs from subgenus Merbecovirus are closely related to MERS-CoV. In addition to the interactions among various bat species themselves, bat–animal and bat–human interactions, such as the presence of live bats in wildlife wet markets and restaurants in Southern China, are important for interspecies transmission of CoVs and may lead to devastating global outbreaks.
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Middle East respiratory syndrome (MERS) coronavirus (MERS-CoV) is an infectious virus that was first reported in 2012. The MERS-CoV genome encodes four major structural proteins, among which the spike (S) protein has a key role in viral infection and pathogenesis. The receptor-binding domain (RBD) of the S protein contains a critical neutralizing domain and is an important target for development of MERS vaccines and therapeutics. In this review, we describe the relevant features of the MERS-CoV S-protein RBD, summarize recent advances in the development of MERS-CoV RBD-based vaccines and therapeutic antibodies, and illustrate potential challenges and strategies to further improve their efficacy.
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The major mechanism of antibody-mediated neutralization of the Middle East respiratory syndrome coronavirus (MERS-CoV) involves competition with the cellular receptor dipeptidyl peptidase 4 (DPP4) for binding to the receptor-binding domain (RBD) of the spike (S) glycoprotein. Here, we report a unique epitope and unusual neutralizing mechanism of the isolated human antibody MERS-4. Structurally, MERS-4 approached the RBD from the outside of the RBD-DPP4 binding interface. Such binding resulted in the folding of the β5-β6 loop toward a shallow groove on the RBD interface critical for accommodating DPP4. The key residues for binding are identified through site-directed mutagenesis. Structural modeling revealed that MERS-4 binds to RBD only in the "up" position in the S trimer. Furthermore, MERS-4 demonstrated synergy with several reported antibodies. These results indicate that MERS-4 neutralizes MERS-CoV by indirect rather than direct competition with DPP4. This mechanism provides a valuable addition for the combined use of antibodies against MERS-CoV infection.
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The folding of monomeric antigens and their subsequent assembly into higher ordered structures are crucial for robust and effective production of nanoparticle (NP) vaccines in a timely and reproducible manner. Despite significant advances in in silico design and structure-based assembly, most engineered NPs are refractory to soluble expression and fail to assemble as designed, presenting major challenges in the manufacturing process. The failure is due to a lack of understanding of the kinetic pathways and enabling technical platforms to ensure successful folding of the monomer antigens into regular assemblages. Capitalizing on a novel function of RNA as a molecular chaperone (chaperna: chaperone + RNA), we provide a robust protein-folding vehicle that may be implemented to NP assembly in bacterial hosts. The receptor-binding domain (RBD) of Middle East respiratory syndrome-coronavirus (MERS-CoV) was fused with the RNA-interaction domain (RID) and bacterioferritin, and expressed in Escherichia coli in a soluble form. Site-specific proteolytic removal of the RID prompted the assemblage of monomers into NPs, which was confirmed by electron microscopy and dynamic light scattering. The mutations that affected the RNA binding to RBD significantly increased the soluble aggregation into amorphous structures, reducing the overall yield of NPs of a defined size. This underscored the RNA-antigen interactions during NP assembly. The sera after mouse immunization effectively interfered with the binding of MERS-CoV RBD to the cellular receptor hDPP4. The results suggest that RNA-binding controls the overall kinetic network of the antigen folding pathway in favor of enhanced assemblage of NPs into highly regular and immunologically relevant conformations. The concentration of the ion Fe2+, salt, and fusion linker also contributed to the assembly in vitro, and the stability of the NPs. The kinetic “pace-keeping” role of chaperna in the super molecular assembly of antigen monomers holds promise for the development and delivery of NPs and virus-like particles as recombinant vaccines and for serological detection of viral infections.
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Middle East respiratory syndrome coronavirus (MERS-CoV) has caused fatal infections, some through hospital-acquired transmission, in affected regions since its emergence in 2012. Although the virus is not pandemic among humans, it poses a great threat to public health due to its zoonotic origin. Thus, both preventative and therapeutic countermeasures are urgently needed. In this study, we discovered a panel of neutralizing monoclonal antibodies (mAbs) against MERS-CoV, which mapped to a wide range of regions on the spike (S) protein of the virus. In addition to mAbs with neutralizing epitopes located on the receptor-binding domain, one mAb, 5F9, which binds to the N-terminal domain (NTD) of the MERS-CoV S1 subunit, showed efficient neutralizing activity against the wild-type MERS-CoV strain EMC/2012, with a half maximal inhibitory concentration of 0.2 μg/mL. We concluded that a novel neutralizing epitope for MERS-CoV also resides on the NTD of the S protein, indicating that the NTD might be important during the viral infection process. Our findings have significant implications for further vaccine design and for the development of prophylactic and therapeutic monoclonal immunotherapies against MERS-CoV infection.
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The newly-emerging Middle East respiratory syndrome coronavirus (MERS-CoV) can cause severe and fatal acute respiratory disease in humans. Despite global efforts, the potential for an associated pandemic in the future cannot be excluded. The development of effective counter-measures is urgent. MERS-CoV-specific anti-viral drugs or vaccines are not yet available. Using the spike receptor-binding domain of MERS-CoV (MERS-RBD) to immunize mice, we identified two neutralizing monoclonal antibodies (mAbs) 4C2 and 2E6. Both mAbs potently bind to MERS-RBD and block virus entry in vitro with high efficacy. We further investigated their mechanisms of neutralization by crystallizing the complex between the Fab fragments and the RBD, and solved the structure of the 4C2 Fab/MERS-RBD complex. The structure showed that 4C2 recognizes an epitope that partially overlaps the receptor-binding footprint in MERS-RBD, thereby interfering with the virus/receptor interactions by both steric hindrance and interface-residue competition. 2E6 also blocks receptor binding, and competes with 4C2 for binding to MERS-RBD. Based on the structure, we further humanized 4C2 by preserving only the paratope residues and substituting the remaining amino acids with the counterparts from human immunoglobulins. The humanized 4C2 (4C2h) antibody sustained similar neutralizing activity and biochemical characteristics to the parental mouse antibody. Finally, we showed that 4C2h can significantly abate the virus titers in lungs of Ad5-hCD26-transduced mice infected with MERS-CoV, therefore representing a promising agent for prophylaxis and therapy in clinical settings.Cell Research advance online publication 22 September 2015; doi:10.1038/cr.2015.113.
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ENDscript 2 is a friendly Web server for extracting and rendering a comprehensive analysis of primary to quaternary protein structure information in an automated way. This major upgrade has been fully re-engineered to enhance speed, accuracy and usability with interactive 3D visualization. It takes advantage of the new version 3 of ESPript, our well-known sequence alignment renderer, improved to handle a large number of data with reduced computation time. From a single PDB entry or file, ENDscript produces high quality figures displaying multiple sequence alignment of proteins homologous to the query, colored according to residue conservation. Furthermore, the experimental secondary structure elements and a detailed set of relevant biophysical and structural data are depicted. All this information and more are now mapped on interactive 3D PyMOL representations. Thanks to its adaptive and rigorous algorithm, beginner to expert users can modify settings to fine-tune ENDscript to their needs. ENDscript has also been upgraded as an open platform for the visualization of multiple biochemical and structural data coming from external biotool Web servers, with both 2D and 3D representations. ENDscript 2 and ESPript 3 are freely available at http://endscript.ibcp.fr and http://espript.ibcp.fr, respectively.
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