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Lorenzo MM, Marín-López A, Chiem K, Jimenez-Cabello L, Ullah I, Utrilla-Trigo S, Calvo-Pinilla E, Lorenzo G, Moreno S, Ye C, Park JG, Matía A, Brun A, Sánchez-Puig JM, Nogales A, Mothes W, Uchil PD, Kumar P, Ortego J, Fikrig E, Martinez-Sobrido L, Blasco R. Vaccinia Virus Strain MVA Expressing a Prefusion-Stabilized SARS-CoV-2 Spike Glycoprotein Induces Robust Protection and Prevents Brain Infection in Mouse and Hamster Models. Vaccines (Basel) 2023; 11:1006. [PMID: 37243110 PMCID: PMC10220993 DOI: 10.3390/vaccines11051006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 05/11/2023] [Accepted: 05/15/2023] [Indexed: 05/28/2023] Open
Abstract
The COVID-19 pandemic has underscored the importance of swift responses and the necessity of dependable technologies for vaccine development. Our team previously developed a fast cloning system for the modified vaccinia virus Ankara (MVA) vaccine platform. In this study, we reported on the construction and preclinical testing of a recombinant MVA vaccine obtained using this system. We obtained recombinant MVA expressing the unmodified full-length SARS-CoV-2 spike (S) protein containing the D614G amino-acid substitution (MVA-Sdg) and a version expressing a modified S protein containing amino-acid substitutions designed to stabilize the protein a in a pre-fusion conformation (MVA-Spf). S protein expressed by MVA-Sdg was found to be expressed and was correctly processed and transported to the cell surface, where it efficiently produced cell-cell fusion. Version Spf, however, was not proteolytically processed, and despite being transported to the plasma membrane, it failed to induce cell-cell fusion. We assessed both vaccine candidates in prime-boost regimens in the susceptible transgenic K18-human angiotensin-converting enzyme 2 (K18-hACE2) in mice and in golden Syrian hamsters. Robust immunity and protection from disease was induced with either vaccine in both animal models. Remarkably, the MVA-Spf vaccine candidate produced higher levels of antibodies, a stronger T cell response, and a higher degree of protection from challenge. In addition, the level of SARS-CoV-2 in the brain of MVA-Spf inoculated mice was decreased to undetectable levels. Those results add to our current experience and range of vaccine vectors and technologies for developing a safe and effective COVID-19 vaccine.
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Affiliation(s)
- María M. Lorenzo
- Departamento de Biotecnología, INIA CSIC, Carretera La Coruña km 7.5, E-28040 Madrid, Spain; (M.M.L.); (S.M.); (A.M.); (J.M.S.-P.)
| | - Alejandro Marín-López
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT 06519, USA; (A.M.-L.); (I.U.); (E.F.)
| | - Kevin Chiem
- Texas Biomedical Research Institute, San Antonio, TX 78227, USA; (K.C.); (C.Y.); (J.-G.P.); (P.K.)
| | - Luis Jimenez-Cabello
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Irfan Ullah
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT 06519, USA; (A.M.-L.); (I.U.); (E.F.)
| | - Sergio Utrilla-Trigo
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Eva Calvo-Pinilla
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Gema Lorenzo
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Sandra Moreno
- Departamento de Biotecnología, INIA CSIC, Carretera La Coruña km 7.5, E-28040 Madrid, Spain; (M.M.L.); (S.M.); (A.M.); (J.M.S.-P.)
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Chengjin Ye
- Texas Biomedical Research Institute, San Antonio, TX 78227, USA; (K.C.); (C.Y.); (J.-G.P.); (P.K.)
| | - Jun-Gyu Park
- Texas Biomedical Research Institute, San Antonio, TX 78227, USA; (K.C.); (C.Y.); (J.-G.P.); (P.K.)
| | - Alejandro Matía
- Departamento de Biotecnología, INIA CSIC, Carretera La Coruña km 7.5, E-28040 Madrid, Spain; (M.M.L.); (S.M.); (A.M.); (J.M.S.-P.)
| | - Alejandro Brun
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Juana M. Sánchez-Puig
- Departamento de Biotecnología, INIA CSIC, Carretera La Coruña km 7.5, E-28040 Madrid, Spain; (M.M.L.); (S.M.); (A.M.); (J.M.S.-P.)
| | - Aitor Nogales
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Walther Mothes
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510, USA; (W.M.); (P.D.U.)
| | - Pradeep D. Uchil
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510, USA; (W.M.); (P.D.U.)
| | - Priti Kumar
- Texas Biomedical Research Institute, San Antonio, TX 78227, USA; (K.C.); (C.Y.); (J.-G.P.); (P.K.)
| | - Javier Ortego
- Centro de Investigación en Sanidad Animal, INIA CSIC, Carretera Valdeolmos a El Casar, Valdeolmos, E-28130 Madrid, Spain; (L.J.-C.); (S.U.-T.); (E.C.-P.); (G.L.); (A.B.); (A.N.); (J.O.)
| | - Erol Fikrig
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT 06519, USA; (A.M.-L.); (I.U.); (E.F.)
| | - Luis Martinez-Sobrido
- Texas Biomedical Research Institute, San Antonio, TX 78227, USA; (K.C.); (C.Y.); (J.-G.P.); (P.K.)
| | - Rafael Blasco
- Departamento de Biotecnología, INIA CSIC, Carretera La Coruña km 7.5, E-28040 Madrid, Spain; (M.M.L.); (S.M.); (A.M.); (J.M.S.-P.)
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Lorenzo MM, Nogales A, Chiem K, Blasco R, Martínez-Sobrido L. Vaccinia Virus Attenuation by Codon Deoptimization of the A24R Gene for Vaccine Development. Microbiol Spectr 2022; 10:e0027222. [PMID: 35583360 PMCID: PMC9241885 DOI: 10.1128/spectrum.00272-22] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 04/20/2022] [Indexed: 11/20/2022] Open
Abstract
Poxviruses have large DNA genomes, and they are able to infect multiple vertebrate and invertebrate animals, including humans. Despite the eradication of smallpox, poxvirus infections still remain a significant public health concern. Vaccinia virus (VV) is the prototypic member in the poxviridae family and it has been used extensively for different prophylactic applications, including the generation of vaccines against multiple infectious diseases and/or for oncolytic treatment. Many attempts have been pursued to develop novel attenuated forms of VV with improved safety profiles for their implementation as vaccines and/or vaccines vectors. We and others have previously demonstrated how RNA viruses encoding codon-deoptimized viral genes are attenuated, immunogenic and able to protect, upon a single administration, against challenge with parental viruses. In this study, we employed the same experimental approach based on the use of misrepresented codons for the generation of a recombinant (r)VV encoding a codon-deoptimized A24R gene, which is a key component of the viral RNA polymerase. Similar to our previous studies with RNA viruses, the A24R codon-deoptimized rVV (v-A24cd) was highly attenuated in vivo but able to protect, after a single intranasal dose administration, against an otherwise lethal challenge with parental VV. These results indicate that poxviruses can be effectively attenuated by synonymous codon deoptimization and open the possibility of using this methodology alone or in combination with other experimental approaches for the development of attenuated vaccines for the treatment of poxvirus infection, or to generate improved VV-based vectors. Moreover, this approach could be applied to other DNA viruses. IMPORTANCE The family poxviridae includes multiple viruses of medical and veterinary relevance, being vaccinia virus (VV) the prototypic member in the family. VV was used during the smallpox vaccination campaign to eradicate variola virus (VARV), which is considered a credible bioterrorism threat. Because of novel innovations in genetic engineering and vaccine technology, VV has gained popularity as a viral vector for the development of vaccines against several infectious diseases. Several approaches have been used to generate attenuated VV for its implementation as vaccine and/or vaccine vector. Here, we generated a rVV containing a codon-deoptimized A24R gene (v-A24cd), which encodes a key component of the viral RNA polymerase. v-A24cd was stable in culture cells and highly attenuated in vivo but able to protect against a subsequent lethal challenge with parental VV. Our findings support the use of this approach for the development of safe, stable, and protective live-attenuated VV and/or vaccine vectors.
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Affiliation(s)
- María M. Lorenzo
- Departamento de Biotecnología, Centro Nacional INIA, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Aitor Nogales
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA
- Animal Health Research Centre (CISA), National Institute for Agriculture and Food Research and Technology (INIA-CSIC), Valdeolmos, Madrid, Spain
| | - Kevin Chiem
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA
- Texas Biomedical Research Institute, San Antonio, Texas, USA
| | - Rafael Blasco
- Departamento de Biotecnología, Centro Nacional INIA, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Luis Martínez-Sobrido
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA
- Texas Biomedical Research Institute, San Antonio, Texas, USA
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Comparison of Recombinant MVA Selection Methods Based on F13L, D4R and K1L Genes. Viruses 2022; 14:v14030528. [PMID: 35336935 PMCID: PMC8954814 DOI: 10.3390/v14030528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/13/2022] [Accepted: 03/01/2022] [Indexed: 02/04/2023] Open
Abstract
Modified vaccinia Ankara (MVA) is a promising vaccine vector due to its highly attenuated phenotype and good immunogenicity. However, obtaining a new recombinant MVA remains a tedious and laborious procedure involving many rounds of plaque purification. Recombinant MVA generation can be greatly improved and facilitated by different selection techniques. Here, we describe a comparison between techniques based on K1L, F13L and D4R genes.
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Matía A, Lorenzo MM, Blasco R. Tools for the targeted genetic modification of poxvirus genomes. Curr Opin Virol 2020; 44:183-190. [PMID: 33242829 DOI: 10.1016/j.coviro.2020.10.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 10/27/2020] [Accepted: 10/27/2020] [Indexed: 12/14/2022]
Abstract
The potential of viruses as biotechnology platforms is becoming more appealing due to technological advances in synthetic biology techniques and to the increasing accessibility of means to manipulate virus genomes. Among viral systems, poxviruses, and their prototype member Vaccinia Virus, are one of the outstanding choices for different biotechnological and medical applications based on heterologous gene expression, recombinant vaccines or oncolytic viruses. The refinement of genetic engineering methods on Vaccinia Virus over the last decades have contributed to facilitate the manipulation of the genomes of poxviruses, and may aid in the improvement of virus variants designed for different goals through reverse genetic approaches. Targeted genetic changes are usually performed by homologous recombination with the viral genome. In addition to the classic approach, recent methodological advances that may assist new strategies for the mutation or edition of poxvirus genomes are reviewed.
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Affiliation(s)
- Alejandro Matía
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Ctra. La Coruña km 7.5, E-28040 Madrid, Spain
| | - María M Lorenzo
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Ctra. La Coruña km 7.5, E-28040 Madrid, Spain
| | - Rafael Blasco
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Ctra. La Coruña km 7.5, E-28040 Madrid, Spain.
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Calvo-Pinilla E, Marín-López A, Moreno S, Lorenzo G, Utrilla-Trigo S, Jiménez-Cabello L, Benavides J, Nogales A, Blasco R, Brun A, Ortego J. A protective bivalent vaccine against Rift Valley fever and bluetongue. NPJ Vaccines 2020; 5:70. [PMID: 32793399 PMCID: PMC7393076 DOI: 10.1038/s41541-020-00218-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 07/06/2020] [Indexed: 11/09/2022] Open
Abstract
Rift Valley fever (RVF) and bluetongue (BT) are two important ruminant diseases transmitted by arthropods. Both viruses have shown important geographic spread leading to endemicity of BT virus (BTV) in Africa and Europe. In this work, we report a dual vaccine that simultaneously induces protective immune responses against BTV and RVFV based on modified vaccinia Ankara virus (MVA) expressing BTV proteins VP2, NS1, or a truncated form of NS1 (NS1-Nt), and RVFV Gn and Gc glycoproteins. IFNAR(-/-) mice immunized with two doses of MVA-GnGc-VP2 developed a significant neutralizing antibody response against BTV-4 and RVFV. Furthermore, the homologous prime-boost immunization with MVA-GnGc-NS1 or MVA-GnGc-NS1-Nt triggered neutralizing antibodies against RVFV and NS1-specific cytotoxic CD8+ T cells in mice. Moreover, all mice immunized with MVA-GnGc-NS1 or MVA-GnGc-NS1-Nt remained healthy after lethal challenge with RVFV or BTV-4. The homologous prime-boost vaccination with MVA-GnGc-NS1, which was the best immunization strategy observed in mice, was assayed in sheep. Clinical signs and viremia were absent or highly reduced in vaccinated sheep after challenge with BTV-4 or RVFV. These results indicate that MVA-GnGc-NS1 vaccination elicits immune protection against RVFV and BTV in sheep.
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Affiliation(s)
- Eva Calvo-Pinilla
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Alejandro Marín-López
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain.,Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT USA
| | - Sandra Moreno
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Gema Lorenzo
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Sergio Utrilla-Trigo
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Luis Jiménez-Cabello
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Julio Benavides
- Instituto de Ganadería de Montaña (CSIC-Universidad de León), León, Spain
| | - Aitor Nogales
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Rafael Blasco
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Departamento de Biotecnología, Madrid, Spain
| | - Alejandro Brun
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
| | - Javier Ortego
- Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Centro de Investigación en Sanidad Animal (INIA-CISA), Madrid, Spain
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Lorenzo MM, Sanchez-Puig JM, Blasco R. Vaccinia virus and Cowpox virus are not susceptible to the interferon-induced antiviral protein MxA. PLoS One 2017; 12:e0181459. [PMID: 28727764 PMCID: PMC5519081 DOI: 10.1371/journal.pone.0181459] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Accepted: 06/19/2017] [Indexed: 12/16/2022] Open
Abstract
MxA protein is expressed in response to type I and type III Interferon and constitute an important antiviral factor with broad antiviral activity to diverse RNA viruses. In addition, some studies expand the range of MxA antiviral activity to include particular DNA viruses like Monkeypox virus (MPXV) and African Swine Fever virus (ASFV). However, a broad profile of activity of MxA to large DNA viruses has not been established to date. Here, we investigated if some well characterized DNA viruses belonging to the Poxviridae family are sensitive to human MxA. A cell line inducibly expressing MxA to inhibitory levels showed no anti-Vaccinia virus (VACV) virus activity, indicating either lack of susceptibility of the virus, or the existence of viral factors capable of counteracting MxA inhibition. To determine if VACV resistance to MxA was due to a virus-encoded anti-MxA activity, we performed coinfections of VACV and the MxA-sensitive Vesicular Stomatitis virus (VSV), and show that VACV does not protect VSV from MxA inhibition in trans. Those results were extended to several VACV strains and two CPXV strains, thus confirming that those Orthopoxviruses do not block MxA action. Overall, these results point to a lack of susceptibility of the Poxviridae to MxA antiviral activity.
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Affiliation(s)
- María M. Lorenzo
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
| | - Juana M. Sanchez-Puig
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
| | - Rafael Blasco
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
- * E-mail:
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Sánchez-Puig JM, Lorenzo MM, Blasco R. A vaccinia virus recombinant transcribing an alphavirus replicon and expressing alphavirus structural proteins leads to packaging of alphavirus infectious single cycle particles. PLoS One 2013; 8:e75574. [PMID: 24130722 PMCID: PMC3793997 DOI: 10.1371/journal.pone.0075574] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Accepted: 08/15/2013] [Indexed: 01/15/2023] Open
Abstract
Poxviruses and Alphaviruses constitute two promising viral vectors that have been used extensively as expression systems, or as vehicles for vaccine purposes. Poxviruses, like vaccinia virus (VV) are well-established vaccine vectors having large insertion capacity, excellent stability, and ease of administration. In turn, replicons derived from Alphaviruses like Semliki Forest virus (SFV) are potent protein expression and immunization vectors but stocks are difficult to produce and maintain. In an attempt to demonstrate the use of a Poxvirus as a means for the delivery of small vaccine vectors, we have constructed and characterized VV/SFV hybrid vectors. A SFV replicon cDNA was inserted in the VV genome and placed under the control of a VV early promoter. The replicon, transcribed from the VV genome as an early transcript, was functional, and thus capable of initiating its own replication and transcription. Further, we constructed a VV recombinant additionally expressing the SFV structural proteins under the control of a vaccinia synthetic early/late promoter. Infection with this recombinant produced concurrent transcription of the replicon and expression of SFV structural proteins, and led to the generation of replicon-containing SFV particles that were released to the medium and were able to infect additional cells. This combined VV/SFV system in a single virus allows the use of VV as a SFV delivery vehicle in vivo. The combination of two vectors, and the possibility of generating in vivo single-cycle, replicon containing alphavirus particles, may open new strategies in vaccine development or in the design of oncolytic viruses.
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Affiliation(s)
- Juana M. Sánchez-Puig
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
| | - María M. Lorenzo
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
| | - Rafael Blasco
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A.), Madrid, Spain
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Characterization of ectromelia virus deficient in EVM036, the homolog of vaccinia virus F13L, and its application for rapid generation of recombinant viruses. J Virol 2012; 86:13501-7. [PMID: 23035222 DOI: 10.1128/jvi.01732-12] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The orthopoxvirus (OPV) vaccinia virus (VACV) requires an intact F13L gene to produce enveloped virions (EV) and to form plaques in cell monolayers. Simultaneous introduction of an exogenous gene and F13L into F13L-deficient VACV results in expression of the foreign gene and restoration of plaque size. This is used as a method to rapidly generate VACV recombinants without the need for drug selection. However, whether other OPVs require the orthologs of F13L to generate EV and form plaques, whether F13L orthologs and EV are important for OPV pathogenesis in natural hosts, and whether a system based on F13L ortholog deficiency can be used to generate recombinant OPVs other than VACV have not been reported. The F13L ortholog in ectromelia virus (ECTV), the agent of mousepox, is EVM036. We show that ECTV lacking EVM036 formed small plaques and was highly attenuated in vivo but still induced strong antibody responses. Reintroduction of EVM036 in tandem with the DsRed gene resulted in a virus that expressed DsRed in infected cells but was indistinguishable from wild-type ECTV in terms of plaque size and in vivo virulence. Thus, our data show that, like F13L in VACV, EVM036 is required for ECTV plaque formation and that EVM036 and EV are important for ECTV virulence. Our experiments also suggest that OPVs deficient in F13L orthologs could serve as safer anti-OPV vaccines. Further, our results demonstrate that ECTV deficient in EVM036 can be exploited for the rapid generation of fully virulent ECTV expressing foreign genes of interest.
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