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1.
Int J Mol Sci ; 22(21)2021 Oct 28.
Article in English | MEDLINE | ID: covidwho-1518611

ABSTRACT

Inhaled nebulized interferon (IFN)-α and IFN-ß have been shown to be effective in the management of coronavirus disease 2019 (COVID-19). We aimed to construct a virus-free rapid detection system for high-throughput screening of IFN-like compounds that induce viral RNA degradation and suppress the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We prepared a SARS-CoV-2 subreplicon RNA expression vector which contained the SARS-CoV-2 5'-UTR, the partial sequence of ORF1a, luciferase, nucleocapsid, ORF10, and 3'-UTR under the control of the cytomegalovirus promoter. The expression vector was transfected into Calu-3 cells and treated with IFN-α and the IFNAR2 agonist CDM-3008 (RO8191) for 3 days. SARS-CoV-2 subreplicon RNA degradation was subsequently evaluated based on luciferase levels. IFN-α and CDM-3008 suppressed SARS-CoV-2 subreplicon RNA in a dose-dependent manner, with IC50 values of 193 IU/mL and 2.54 µM, respectively. HeLa cells stably expressing SARS-CoV-2 subreplicon RNA were prepared and treated with the IFN-α and pan-JAK inhibitor Pyridone 6 or siRNA-targeting ISG20. IFN-α activity was canceled with Pyridone 6. The knockdown of ISG20 partially canceled IFN-α activity. Collectively, we constructed a virus-free rapid detection system to measure SARS-CoV-2 RNA suppression. Our data suggest that the SARS-CoV-2 subreplicon RNA was degraded by IFN-α-induced ISG20 exonuclease activity.


Subject(s)
Antiviral Agents/pharmacology , Drug Evaluation, Preclinical/methods , Interferon-alpha/pharmacology , RNA, Viral/metabolism , SARS-CoV-2/genetics , Cell Line, Tumor , Dose-Response Relationship, Drug , Exoribonucleases/genetics , Genetic Vectors , HeLa Cells , Humans , Interferon-alpha/administration & dosage , Luciferases/genetics , Luciferases/metabolism , Naphthyridines/administration & dosage , Naphthyridines/pharmacology , Oxadiazoles/administration & dosage , Oxadiazoles/pharmacology , RNA, Viral/drug effects , Replicon
2.
Proc Natl Acad Sci U S A ; 118(43)2021 10 26.
Article in English | MEDLINE | ID: covidwho-1481965

ABSTRACT

Self-amplifying RNA replicons are promising platforms for vaccine generation. Their defects in one or more essential functions for viral replication, particle assembly, or dissemination make them highly safe as vaccines. We previously showed that the deletion of the envelope (E) gene from the Middle East respiratory syndrome coronavirus (MERS-CoV) produces a replication-competent propagation-defective RNA replicon (MERS-CoV-ΔE). Evaluation of this replicon in mice expressing human dipeptidyl peptidase 4, the virus receptor, showed that the single deletion of the E gene generated an attenuated mutant. The combined deletion of the E gene with accessory open reading frames (ORFs) 3, 4a, 4b, and 5 resulted in a highly attenuated propagation-defective RNA replicon (MERS-CoV-Δ[3,4a,4b,5,E]). This RNA replicon induced sterilizing immunity in mice after challenge with a lethal dose of a virulent MERS-CoV, as no histopathological damage or infectious virus was detected in the lungs of challenged mice. The four mutants lacking the E gene were genetically stable, did not recombine with the E gene provided in trans during their passage in cell culture, and showed a propagation-defective phenotype in vivo. In addition, immunization with MERS-CoV-Δ[3,4a,4b,5,E] induced significant levels of neutralizing antibodies, indicating that MERS-CoV RNA replicons are highly safe and promising vaccine candidates.


Subject(s)
Coronavirus Infections/prevention & control , Middle East Respiratory Syndrome Coronavirus/genetics , Middle East Respiratory Syndrome Coronavirus/immunology , RNA, Viral/administration & dosage , Replicon , Viral Vaccines/administration & dosage , Animals , Antibodies, Neutralizing/biosynthesis , Antibodies, Viral/biosynthesis , Coronavirus Infections/genetics , Coronavirus Infections/immunology , Coronavirus Infections/virology , Defective Viruses/genetics , Defective Viruses/immunology , Female , Gene Deletion , Genes, env , Humans , Mice , Mice, Inbred C57BL , Mice, Transgenic , Middle East Respiratory Syndrome Coronavirus/pathogenicity , RNA, Viral/genetics , RNA, Viral/immunology , Vaccines, DNA , Vaccines, Virus-Like Particle/administration & dosage , Vaccines, Virus-Like Particle/genetics , Vaccines, Virus-Like Particle/immunology , Viral Vaccines/genetics , Viral Vaccines/immunology , Virulence/genetics , Virulence/immunology
3.
Int J Mol Sci ; 22(21)2021 Oct 28.
Article in English | MEDLINE | ID: covidwho-1488612

ABSTRACT

Inhaled nebulized interferon (IFN)-α and IFN-ß have been shown to be effective in the management of coronavirus disease 2019 (COVID-19). We aimed to construct a virus-free rapid detection system for high-throughput screening of IFN-like compounds that induce viral RNA degradation and suppress the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We prepared a SARS-CoV-2 subreplicon RNA expression vector which contained the SARS-CoV-2 5'-UTR, the partial sequence of ORF1a, luciferase, nucleocapsid, ORF10, and 3'-UTR under the control of the cytomegalovirus promoter. The expression vector was transfected into Calu-3 cells and treated with IFN-α and the IFNAR2 agonist CDM-3008 (RO8191) for 3 days. SARS-CoV-2 subreplicon RNA degradation was subsequently evaluated based on luciferase levels. IFN-α and CDM-3008 suppressed SARS-CoV-2 subreplicon RNA in a dose-dependent manner, with IC50 values of 193 IU/mL and 2.54 µM, respectively. HeLa cells stably expressing SARS-CoV-2 subreplicon RNA were prepared and treated with the IFN-α and pan-JAK inhibitor Pyridone 6 or siRNA-targeting ISG20. IFN-α activity was canceled with Pyridone 6. The knockdown of ISG20 partially canceled IFN-α activity. Collectively, we constructed a virus-free rapid detection system to measure SARS-CoV-2 RNA suppression. Our data suggest that the SARS-CoV-2 subreplicon RNA was degraded by IFN-α-induced ISG20 exonuclease activity.


Subject(s)
Antiviral Agents/pharmacology , Drug Evaluation, Preclinical/methods , Interferon-alpha/pharmacology , RNA, Viral/metabolism , SARS-CoV-2/genetics , Cell Line, Tumor , Dose-Response Relationship, Drug , Exoribonucleases/genetics , Genetic Vectors , HeLa Cells , Humans , Interferon-alpha/administration & dosage , Luciferases/genetics , Luciferases/metabolism , Naphthyridines/administration & dosage , Naphthyridines/pharmacology , Oxadiazoles/administration & dosage , Oxadiazoles/pharmacology , RNA, Viral/drug effects , Replicon
4.
Signal Transduct Target Ther ; 6(1): 369, 2021 10 25.
Article in English | MEDLINE | ID: covidwho-1483125

ABSTRACT

The lung is the prophylaxis target against SARS-CoV-2 infection, and neutralizing antibodies are a leading class of biological products against various infectious viral pathogen. In this study, we develop a safe and cost-effective platform to express neutralizing antibody in the lung with replicating mRNA basing on alphavirus replicon particle (VRP) delivery system, to prevent SARS-CoV-2 infections. First, a modified VEEV replicon with two subgenomic (sg) promoters was engineered to translate the light and heavy chains of antibody simultaneously, for expression and assembly of neutralizing anti-SARS-CoV-2 antibody CB6. Second, the feasibility and protective efficacy of replicating mRNA against SARS-CoV-2 infection were demonstrated through both in vitro and in vivo assays. The lung target delivery with the help of VRP system resulted in efficiently block SARS-CoV-2 infection with reducing viral titer and less tissue damage in the lung of mice. Overall, our data suggests that expressing neutralizing antibodies in the lungs with the help of self-replicating mRNA could potentially be a promising prophylaxis approach against SARS-CoV-2 infection.


Subject(s)
Alphavirus , Antibodies, Neutralizing , Antibodies, Viral , COVID-19/therapy , Replicon , SARS-CoV-2/metabolism , Animals , Antibodies, Neutralizing/biosynthesis , Antibodies, Neutralizing/genetics , Antibodies, Viral/biosynthesis , Antibodies, Viral/genetics , COVID-19/genetics , COVID-19/metabolism , Chlorocebus aethiops , Cricetinae , Female , Mice , Mice, Inbred BALB C , RNA, Messenger/genetics , RNA, Messenger/metabolism , SARS-CoV-2/genetics , Vero Cells
5.
Mol Ther ; 29(6): 1970-1983, 2021 06 02.
Article in English | MEDLINE | ID: covidwho-1386766

ABSTRACT

A self-transcribing and replicating RNA (STARR)-based vaccine (LUNAR-COV19) has been developed to prevent SARS-CoV-2 infection. The vaccine encodes an alphavirus-based replicon and the SARS-CoV-2 full-length spike glycoprotein. Translation of the replicon produces a replicase complex that amplifies and prolongs SARS-CoV-2 spike glycoprotein expression. A single prime vaccination in mice led to robust antibody responses, with neutralizing antibody titers increasing up to day 60. Activation of cell-mediated immunity produced a strong viral antigen-specific CD8+ T lymphocyte response. Assaying for intracellular cytokine staining for interferon (IFN)γ and interleukin-4 (IL-4)-positive CD4+ T helper (Th) lymphocytes as well as anti-spike glycoprotein immunoglobulin G (IgG)2a/IgG1 ratios supported a strong Th1-dominant immune response. Finally, single LUNAR-COV19 vaccination at both 2 µg and 10 µg doses completely protected human ACE2 transgenic mice from both mortality and even measurable infection following wild-type SARS-CoV-2 challenge. Our findings collectively suggest the potential of LUNAR-COV19 as a single-dose vaccine.


Subject(s)
Antibodies, Neutralizing/biosynthesis , Antibodies, Viral/biosynthesis , COVID-19 Vaccines/administration & dosage , COVID-19/prevention & control , SARS-CoV-2/drug effects , Spike Glycoprotein, Coronavirus/immunology , Vaccines, Synthetic/administration & dosage , Alphavirus/genetics , Alphavirus/immunology , Angiotensin-Converting Enzyme 2/genetics , Angiotensin-Converting Enzyme 2/immunology , Animals , CD8-Positive T-Lymphocytes/drug effects , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/virology , COVID-19/immunology , COVID-19/pathology , COVID-19/virology , COVID-19 Vaccines/biosynthesis , COVID-19 Vaccines/genetics , COVID-19 Vaccines/immunology , Female , Gene Expression , Humans , Immunity, Cellular/drug effects , Immunity, Humoral/drug effects , Interferon-gamma/genetics , Interferon-gamma/immunology , Interleukin-4/genetics , Interleukin-4/immunology , Mice , Mice, Transgenic , Replicon/immunology , SARS-CoV-2/immunology , SARS-CoV-2/pathogenicity , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/genetics , Th1 Cells/drug effects , Th1 Cells/immunology , Th1 Cells/virology , Transgenes , Treatment Outcome , Vaccination/methods , Vaccines, Synthetic/biosynthesis , Vaccines, Synthetic/genetics , Vaccines, Synthetic/immunology
6.
Viruses ; 12(6)2020 05 30.
Article in English | MEDLINE | ID: covidwho-1389514

ABSTRACT

Single-stranded positive RNA ((+) ssRNA) viruses include several important human pathogens. Some members are responsible for large outbreaks, such as Zika virus, West Nile virus, SARS-CoV, and SARS-CoV-2, while others are endemic, causing an enormous global health burden. Since vaccines or specific treatments are not available for most viral infections, the discovery of direct-acting antivirals (DAA) is an urgent need. Still, the low-throughput nature of and biosafety concerns related to traditional antiviral assays hinders the discovery of new inhibitors. With the advances of reverse genetics, reporter replicon systems have become an alternative tool for the screening of DAAs. Herein, we review decades of the use of (+) ssRNA viruses replicon systems for the discovery of antiviral agents. We summarize different strategies used to develop those systems, as well as highlight some of the most promising inhibitors identified by the method. Despite the genetic alterations introduced, reporter replicons have been shown to be reliable systems for screening and identification of viral replication inhibitors and, therefore, an important tool for the discovery of new DAAs.


Subject(s)
Antiviral Agents/pharmacology , Drug Discovery/methods , Genes, Reporter/physiology , RNA Viruses/drug effects , Replicon/physiology , Animals , Antiviral Agents/chemistry , Cell Line , Chlorocebus aethiops , Cricetinae , Humans , RNA Viruses/genetics , Transfection , Vero Cells
7.
J Virol ; 95(18): e0068721, 2021 08 25.
Article in English | MEDLINE | ID: covidwho-1373942

ABSTRACT

The emerging coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread worldwide, resulting in global public health emergencies and economic crises. In the present study, a noninfectious and biosafety level 2 (BSL2)-compatible SARS-CoV-2 replicon expressing a nano luciferase (nLuc) reporter was constructed in a bacterial artificial chromosomal (BAC) vector by reverse genetics. The nLuc reporter is highly sensitive, easily quantifiable, and high throughput adaptable. Upon transfecting the SARS-CoV-2 replicon BAC plasmid DNA into Vero E6 cells, we could detect high levels of nLuc reporter activity and viral RNA transcript, suggesting the replication of the replicon. The replicon replication was further demonstrated by the findings that deleting nonstructural protein 15 or mutating its catalytic sites significantly reduced replicon replication, whereas providing the nucleocapsid protein in trans enhanced replicon replication in a dose-dependent manner. Finally, we showed that remdesivir, a U.S. Food and Drug Administration-approved antiviral drug, significantly inhibited the replication of the replicon, providing proof of principle for the application of our replicon as a useful tool for developing antivirals. Taken together, this study established a sensitive and BSL2-compatible reporter system in a single BAC plasmid for investigating the functions of SARS-CoV-2 proteins in viral replication and evaluating antiviral compounds. This should contribute to the global effort to combat this deadly viral pathogen. IMPORTANCE The COVID-19 pandemic caused by SARS-CoV-2 is having a catastrophic impact on human lives. Combatting the pandemic requires effective vaccines and antiviral drugs. In the present study, we developed a SARS-CoV-2 replicon system with a sensitive and easily quantifiable reporter. Unlike studies involving infectious SARS-CoV-2 virus that must be performed in a biosafety level 3 (BSL3) facility, the replicon is noninfectious and thus can be safely used in BSL2 laboratories. The replicon will provide a valuable tool for testing antiviral drugs and studying SARS-CoV-2 biology.


Subject(s)
Antiviral Agents/pharmacology , COVID-19/drug therapy , Drug Evaluation, Preclinical , Green Fluorescent Proteins/metabolism , Replicon , SARS-CoV-2/drug effects , Virus Replication/drug effects , Animals , COVID-19/virology , Chlorocebus aethiops , Green Fluorescent Proteins/genetics , HEK293 Cells , High-Throughput Screening Assays , Humans
8.
Virol Sin ; 36(5): 913-923, 2021 Oct.
Article in English | MEDLINE | ID: covidwho-1230296

ABSTRACT

SARS-CoV-2 causes the pandemic of COVID-19 and no effective drugs for this disease are available thus far. Due to the high infectivity and pathogenicity of this virus, all studies on the live virus are strictly confined in the biosafety level 3 (BSL3) laboratory but this would hinder the basic research and antiviral drug development of SARS-CoV-2 because the BSL3 facility is not commonly available and the work in the containment is costly and laborious. In this study, we constructed a reverse genetics system of SARS-CoV-2 by assembling the viral cDNA in a bacterial artificial chromosome (BAC) vector with deletion of the spike (S) gene. Transfection of the cDNA into cells results in the production of an RNA replicon that keeps the capability of genome or subgenome replication but is deficient in virion assembly and infection due to the absence of S protein. Therefore, such a replicon system is not infectious and can be used in ordinary biological laboratories. We confirmed the efficient replication of the replicon by demonstrating the expression of the subgenomic RNAs which have similar profiles to the wild-type virus. By mutational analysis of nsp12 and nsp14, we showed that the RNA polymerase, exonuclease, and cap N7 methyltransferase play essential roles in genome replication and sgRNA production. We also created a SARS-CoV-2 replicon carrying a luciferase reporter gene and this system was validated by the inhibition assays with known anti-SARS-CoV-2 inhibitors. Thus, such a one-plasmid system is biosafe and convenient to use, which will benefit both fundamental research and development of antiviral drugs.


Subject(s)
Antiviral Agents , COVID-19 , Antiviral Agents/pharmacology , Containment of Biohazards , Humans , Replicon , SARS-CoV-2 , Virus Replication
9.
J Gen Virol ; 102(5)2021 05.
Article in English | MEDLINE | ID: covidwho-1218063

ABSTRACT

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus, which is highly pathogenic and classified as a biosafety level 3 (BSL-3) agent, has greatly threatened global health and efficacious antivirals are urgently needed. The high requirement of facilities to manipulate the live virus has limited the development of antiviral study. Here, we constructed a reporter replicon of SARS-CoV-2, which can be handled in a BSL-2 laboratory. The Renilla luciferase activity effectively reflected the transcription and replication levels of the replicon genome. We identified the suitability of the replicon in antiviral screening using the known inhibitors, and thus established the replicon-based high-throughput screening (HTS) assay for SARS-CoV-2. The application of the HTS assay was further validated using a few hit natural compounds, which were screened out in a SARS-CoV-2 induced cytopathic-effect-based HTS assay in our previous study. This replicon-based HTS assay will be a safe platform for SARS-CoV-2 antiviral screening in a BSL-2 laboratory without the live virus.


Subject(s)
Antiviral Agents/pharmacology , Drug Evaluation, Preclinical/methods , Replicon/drug effects , SARS-CoV-2/drug effects , Animals , COVID-19/drug therapy , Chlorocebus aethiops , Drug Discovery , High-Throughput Screening Assays/methods , Humans , Replicon/genetics , SARS-CoV-2/genetics , Vero Cells , Virus Replication/drug effects
10.
Virol Sin ; 36(5): 890-900, 2021 Oct.
Article in English | MEDLINE | ID: covidwho-1174013

ABSTRACT

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a devastating pandemic worldwide. Vaccines and antiviral drugs are the most promising candidates for combating this global epidemic, and scientists all over the world have made great efforts to this end. However, manipulation of the SARS-CoV-2 should be performed in the biosafety level 3 laboratory. This makes experiments complicated and time-consuming. Therefore, a safer system for working with this virus is urgently needed. Here, we report the construction of plasmid-based, non-infectious SARS-CoV-2 replicons with turbo-green fluorescent protein and/or firefly luciferase reporters by reverse genetics using transformation-associated recombination cloning in Saccharomyces cerevisiae. Replication of these replicons was achieved simply by direct transfection of cells with the replicon plasmids as evident by the expression of reporter genes. Using SARS-CoV-2 replicons, the inhibitory effects of E64-D and remdesivir on SARS-CoV-2 replication were confirmed, and the half-maximal effective concentration (EC50) value of remdesivir and E64-D was estimated by different quantification methods respectively, indicating that these SARS-CoV-2 replicons are useful tools for antiviral drug evaluation.


Subject(s)
COVID-19 , SARS-CoV-2 , Antiviral Agents/pharmacology , Drug Evaluation , Humans , Replicon , Virus Replication
11.
Proc Natl Acad Sci U S A ; 118(15)2021 04 13.
Article in English | MEDLINE | ID: covidwho-1152940

ABSTRACT

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) research and antiviral discovery are hampered by the lack of a cell-based virus replication system that can be readily adopted without biosafety level 3 (BSL-3) restrictions. Here, the construction of a noninfectious SARS-CoV-2 reporter replicon and its application in deciphering viral replication mechanisms and evaluating SARS-CoV-2 inhibitors are presented. The replicon genome is replication competent but does not produce progeny virions. Its replication can be inhibited by RdRp mutations or by known SARS-CoV-2 antiviral compounds. Using this system, a high-throughput antiviral assay has also been developed. Significant differences in potencies of several SARS-CoV-2 inhibitors in different cell lines were observed, which highlight the challenges of discovering antivirals capable of inhibiting viral replication in vivo and the importance of testing compounds in multiple cell culture models. The generation of a SARS-CoV-2 replicon provides a powerful platform to expand the global research effort to combat COVID-19.


Subject(s)
Antiviral Agents/pharmacology , COVID-19/virology , High-Throughput Screening Assays/methods , Replicon/drug effects , SARS-CoV-2/drug effects , A549 Cells , Animals , Chlorocebus aethiops , Coronavirus RNA-Dependent RNA Polymerase/genetics , HEK293 Cells , Humans , Replicon/genetics , SARS-CoV-2/genetics , Vero Cells , Virus Replication/drug effects
12.
mBio ; 12(1)2021 01 19.
Article in English | MEDLINE | ID: covidwho-1066818

ABSTRACT

The etiologic agent of COVID-19 is highly contagious and has caused a severe global pandemic. Until now, there has been no simple and reliable system available in a lower-biosafety-grade laboratory for SARS-CoV-2 virologic research and inhibitor screening. In this study, we reported a replicon system which consists of four plasmids expressing the required segments of SARS-CoV-2. Our study revealed that the features for viral RNA synthesis and responses to antivirus drugs of the replicon are similar to those of wild-type viruses. Further analysis indicated that ORF6 provided potent in trans stimulation of the viral replication. Some viral variations, such as 5'UTR-C241T and ORF8-(T28144C) L84S mutation, also exhibit their different impact upon viral replication. Besides, the screening of clinically used drugs identified that several tyrosine kinase inhibitors and DNA-Top II inhibitors potently inhibit the replicon, as well as authentic SARS-CoV-2 viruses. Collectively, this replicon system provides a biosafety-worry-free platform for studying SARS-CoV-2 virology, monitoring the functional impact of viral mutations, and developing viral inhibitors.IMPORTANCE COVID-19 has caused a severe global pandemic. Until now, there has been no simple and reliable system available in a lower-biosafety-grade laboratory for SARS-CoV-2 virologic research and inhibitor screening. We reported a replicon system which consists of four ordinary plasmids expressing the required segments of SARS-CoV-2. Using the replicon system, we developed three application scenarios: (i) to identify the effects of viral proteins on virus replication, (ii) to identify the effects of mutations on viral replication during viral epidemics, and (iii) to perform high-throughput screening of antiviral drugs. Collectively, this replicon system would be useful for virologists to study SARS-CoV-2 virology, for epidemiologists to monitor virus mutations, and for industry to develop antiviral drugs.


Subject(s)
Antiviral Agents/pharmacology , COVID-19/virology , RNA, Viral/biosynthesis , Replicon/drug effects , SARS-CoV-2/drug effects , SARS-CoV-2/genetics , Drug Evaluation, Preclinical/methods , Female , Genetic Engineering , HEK293 Cells , High-Throughput Screening Assays , Humans , Inhibitory Concentration 50 , Mutation , Pandemics , RNA, Viral/genetics , Replicon/genetics , SARS-CoV-2/metabolism , Virus Replication/drug effects
13.
Antiviral Res ; 185: 104974, 2021 01.
Article in English | MEDLINE | ID: covidwho-927811

ABSTRACT

Vaccines and antiviral agents are in urgent need to stop the COVID-19 pandemic. To facilitate antiviral screening against SARS-CoV-2 without requirement for high biosafety level facility, we developed a bacterial artificial chromosome (BAC)-vectored replicon of SARS-CoV-2, nCoV-SH01 strain, in which secreted Gaussia luciferase (sGluc) was encoded in viral subgenomic mRNA as a reporter gene. The replicon was devoid of structural genes spike (S), membrane (M), and envelope (E). Upon transfection, the replicon RNA replicated in various cell lines, and was sensitive to interferon alpha (IFN-α), remdesivir, but was resistant to hepatitis C virus inhibitors daclatasvir and sofosbuvir. Replication of the replicon was also sensitive overexpression to zinc-finger antiviral protein (ZAP). We also constructed a four-plasmid in-vitro ligation system that is compatible with the BAC system, which makes it easy to introduce desired mutations into the assembly plasmids for in-vitro ligation. This replicon system would be helpful for performing antiviral screening and dissecting virus-host interactions.


Subject(s)
Antiviral Agents/pharmacology , COVID-19/virology , Chromosomes, Artificial, Bacterial , Replicon/drug effects , SARS-CoV-2/drug effects , SARS-CoV-2/genetics , Adenosine Monophosphate/analogs & derivatives , Adenosine Monophosphate/pharmacology , Alanine/analogs & derivatives , Alanine/pharmacology , Animals , COVID-19/drug therapy , Cell Line , Chlorocebus aethiops , HEK293 Cells , Hepacivirus/drug effects , Hepatitis C/drug therapy , Hepatitis C/virology , Humans , Interferon-alpha/pharmacology , RNA-Binding Proteins/biosynthesis , RNA-Binding Proteins/genetics , Sofosbuvir/pharmacology , Vero Cells , Virus Replication/drug effects
14.
J Virol ; 94(14)2020 07 01.
Article in English | MEDLINE | ID: covidwho-840682

ABSTRACT

Autonomously replicating subgenomic Bungowannah virus (BuPV) RNAs (BuPV replicons) with deletions of the genome regions encoding the structural proteins C, ERNS, E1, and E2 were constructed on the basis of an infectious cDNA clone of BuPV. Nanoluciferase (Nluc) insertion was used to compare the replication efficiencies of all constructs after electroporation of in vitro-transcribed RNA from the different clones. Deletion of C, E1, E2, or the complete structural protein genome region (C-ERNS-E1-E2) prevented the production of infectious progeny virus, whereas deletion of ERNS still allowed the generation of infectious particles. However, those ΔERNS viral particles were defective in virus assembly and/or egress and could not be further propagated for more than three additional passages in porcine SK-6 cells. These "defective-in-third-cycle" BuPV ΔERNS mutants were subsequently used to express the classical swine fever virus envelope protein E2, the N-terminal domain of the Schmallenberg virus Gc protein, and the receptor binding domain of the Middle East respiratory syndrome coronavirus spike protein. The constructs could be efficiently complemented and further passaged in SK-6 cells constitutively expressing the BuPV ERNS protein. Importantly, BuPVs are able to infect a wide variety of target cell lines, allowing expression in a very wide host spectrum. Therefore, we suggest that packaged BuPV ΔERNS replicon particles have potential as broad-spectrum viral vectors.IMPORTANCE The proteins NPRO and ERNS are unique for the genus Pestivirus, but only NPRO has been demonstrated to be nonessential for in vitro growth. While this was also speculated for ERNS, it has always been previously shown that pestivirus replicons with deletions of the structural proteins ERNS, E1, or E2 did not produce any infectious progeny virus in susceptible host cells. Here, we demonstrated for the first time that BuPV ERNS is dispensable for the generation of infectious virus particles but still important for efficient passaging. The ERNS-defective BuPV particles showed clearly limited growth in cell culture but were capable of several rounds of infection, expression of foreign genes, and highly efficient trans-complementation to rescue virus replicon particles (VRPs). The noncytopathic characteristics and the absence of preexisting immunity to BuPV in human populations and livestock also provide a significant benefit for a possible use, e.g., as a vector vaccine platform.


Subject(s)
Pestivirus Infections/virology , Pestivirus/physiology , RNA, Viral , Viral Envelope Proteins/metabolism , Virus Replication , Gene Deletion , Gene Expression , Genes, Reporter , Genetic Engineering , Host-Pathogen Interactions , Pestivirus Infections/immunology , Replicon , Viral Envelope Proteins/genetics , Virion , Virus Assembly
16.
Sci Transl Med ; 12(555)2020 08 05.
Article in English | MEDLINE | ID: covidwho-655207

ABSTRACT

The coronavirus disease 2019 (COVID-19) pandemic, caused by infection with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), is having a deleterious impact on health services and the global economy, highlighting the urgent need for an effective vaccine. Such a vaccine would need to rapidly confer protection after one or two doses and would need to be manufactured using components suitable for scale up. Here, we developed an Alphavirus-derived replicon RNA vaccine candidate, repRNA-CoV2S, encoding the SARS-CoV-2 spike (S) protein. The RNA replicons were formulated with lipid inorganic nanoparticles (LIONs) that were designed to enhance vaccine stability, delivery, and immunogenicity. We show that a single intramuscular injection of the LION/repRNA-CoV2S vaccine in mice elicited robust production of anti-SARS-CoV-2 S protein IgG antibody isotypes indicative of a type 1 T helper cell response. A prime/boost regimen induced potent T cell responses in mice including antigen-specific responses in the lung and spleen. Prime-only immunization of aged (17 months old) mice induced smaller immune responses compared to young mice, but this difference was abrogated by booster immunization. In nonhuman primates, prime-only immunization in one intramuscular injection site or prime/boost immunizations in five intramuscular injection sites elicited modest T cell responses and robust antibody responses. The antibody responses persisted for at least 70 days and neutralized SARS-CoV-2 at titers comparable to those in human serum samples collected from individuals convalescing from COVID-19. These data support further development of LION/repRNA-CoV2S as a vaccine candidate for prophylactic protection against SARS-CoV-2 infection.


Subject(s)
Alphavirus/genetics , Antibodies, Neutralizing/immunology , Betacoronavirus/immunology , Coronavirus Infections/immunology , Pneumonia, Viral/immunology , RNA, Viral/genetics , Replicon/genetics , T-Lymphocytes/immunology , Viral Vaccines/immunology , Animals , Antibody Formation/immunology , COVID-19 , COVID-19 Vaccines , Coronavirus Infections/prevention & control , Inorganic Chemicals/chemistry , Lipids/chemistry , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Nanoparticles/chemistry , Pandemics , Primates , SARS-CoV-2
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