Attenuation and immunogenicity of host-range extended modified vaccinia virus Ankara recombinants

Safety and immunogenicity of orally administered poxvirus vectored constructs in the white-footed mouse (Peromyscus leucopus)

Globally, zoonotic spillover is becoming more frequent and represents a growing public health concern. Reservoir-targeted vaccination offers an intriguing alternative to traditional vaccine practices by establishing protection in wild populations that maintain the natural pathogen cycle. As an important pathogen reservoir, Peromyscus leucopus Rafinesque or the white-footed mouse has been the target of several experimental vaccines. However, strategies are limited by the method of administration, need for repeated dosing, or safety of constructs in the field. To address these concerns, we evaluated two highly attenuated poxviruses, raccoonpox virus (RCN) and modified vaccinia Ankara (MVA) virus as potential oral vaccine vectors in white-footed mice. Following oral administration, P. leucopus showed no adverse signs. A single oral dose elicited robust immune responses in mice to the foreign influenza hemagglutinin protein expressed by poxvirus vaccine vectors. Serum hemagglutinin inhibition antibody titers were detected by day 7 post immunization and persisted until study termination (77 days post immunization). This study establishes the safety and immunogenicity of recombinant MVA and RCN poxviruses in P. leucopus and demonstrates the suitability of these vectors as part of a reservoir-targeted vaccine strategy for white-footed mice.

Advances in vaccinia virus-based vaccine vectors, with applications in flavivirus vaccine development

Historically, virulent variola virus infection caused hundreds of millions of deaths. The smallpox pandemic in human beings has spread for centuries until the advent of the attenuated vaccinia virus (VV) vaccine, which played a crucial role in eradicating the deadly contagious disease. Decades of exploration and utilization have validated the attenuated VV as a promising vaccine vehicle against various lethal viruses. In this review, we focus on the advances in VV-based vaccine vector studies, including construction approaches of recombinant VV, the impact of VV-specific pre-existing immunity on subsequent VV-based vaccines, and antigen-specific immune responses. More specifically, the recombinant VV-based flaviviruses are intensively discussed. Based on the publication data, this review aims to provide valuable insights and guidance for future VV-based vaccine development.

Identification of Vaccinia Virus Inhibitors and Cellular Functions Necessary for Efficient Viral Replication by Screening Bioactives and FDA-Approved Drugs

Four decades after the eradication of smallpox, poxviruses continue to threaten the health of humans and other animals. Vaccinia virus (VACV) was used as the vaccine that successfully eradicated smallpox and is a prototypic member of the poxvirus family. Many cellular pathways play critical roles in productive poxvirus replication. These pathways provide opportunities to expand the arsenal of poxvirus antiviral development by targeting the cellular functions required for efficient poxvirus replication. In this study, we developed and optimized a secreted Gaussia luciferase-based, simplified assay procedure suitable for high throughput screening. Using this procedure, we screened a customized compound library that contained over 3200 bioactives and FDA (Food and Drug Administration)-approved chemicals, most having known cellular targets, for their inhibitory effects on VACV replication. We identified over 140 compounds that suppressed VACV replication. Many of these hits target cellular pathways previously reported to be required for efficient VACV replication, validating the effectiveness of our screening. Importantly, we also identified hits that target cellular functions with previously unknown roles in the VACV replication cycle. Among those in the latter category, we verified the antiviral role of several compounds targeting the janus kinase/signal transducer and activator of transcription-3 (JAK/STAT3) signaling pathway by showing that STAT3 inhibitors reduced VACV replication. Our findings identify pathways that are candidates for use in the prevention and treatment of poxvirus infections and additionally provide a foundation to investigate diverse cellular pathways for their roles in poxvirus replications.

SPI-1 is a missing host-range factor required for replication of the attenuated modified vaccinia Ankara (MVA) vaccine vector in human cells

Modified vaccinia virus Ankara (MVA) is the leading poxvirus vector for development of vaccines against diverse infectious diseases. This distinction is based on high expression of proteins and good immunogenicity despite an inability to assemble infectious progeny in human cells, which together promote efficacy and safety. Nevertheless, the basis for the host-range restriction is unknown despite past systematic attempts to identify the relevant missing viral gene(s). The search for host-range factors is exacerbated by the large number of deletions, truncations and mutations that occurred during the long passage history of MVA in chicken embryo fibroblasts. By whole genome sequencing of a panel of recombinant host-range extended (HRE) MVAs generated by marker rescue with 40 kbp segments of vaccinia virus DNA, we identified serine protease inhibitor 1 (SPI-1) as one of several candidate host-range factors present in those viruses that gained the ability to replicate in human cells. Electron microscopy revealed that the interruption of morphogenesis in human cells infected with MVA occurred at a similar stage as that of a vaccinia virus strain WR SPI-1 deletion mutant. Moreover, the introduction of the SPI-1 gene into the MVA genome led to more than a 2-log enhancement of virus spread in human diploid MRC-5 cells, whereas deletion of the gene diminished the spread of HRE viruses by similar extents. Furthermore, MRC-5 cells stably expressing SPI-1 also enhanced replication of MVA. A role for additional host range genes was suggested by the restoration of MVA replication to a lower level relative to HRE viruses, particularly in other human cell lines. Although multiple sequence alignments revealed genetic changes in addition to SPI-1 common to the HRE MVAs, no evidence for their host-range function was found by analysis thus far. Our finding that SPI-1 is host range factor for MVA should simplify use of high throughput RNAi or CRISPR/Cas single gene methods to identify additional viral and human restriction elements.

Poxvirus vectors have outstanding properties for development of vaccines against a myriad of infectious agents due to their ability to retain long segments of foreign DNA and high-level gene expression. Safety concerns led to a preference for attenuated poxviruses that lost the ability to produce infectious progeny in human cells. The most widely used poxvirus vector is modified vaccinia virus Ankara (MVA), which exhibits an extreme host-range restriction in most mammalian cells. MVA was attenuated by passaging more than 500 times in chicken embryo fibroblasts during which large deletions and numerous additional genetic changes occurred. Despite ongoing clinical testing of MVA-vectored vaccines, the basis for its host-range restriction remained unknown. Here we show that re-introduction of the SPI-1 gene into MVA or host cells increased virus spread by more than 100-fold in a human diploid cell line, providing an important insight into the mechanism responsible for the host-range restriction. This information could help design improved vectors and develop non-avian cell lines for propagation of candidate MVA vaccines.

Construction of an attenuated Tian Tan vaccinia virus strain by deletion of TA35R and TJ2R genes

rVTT-TA35-TJ, an attenuated vaccinia virus Tian Tan strain (VTT), was constructed by knocking out two non-essential gene fragments (TA35R and TJ2R) related to virulence, immunomodulation, and host range; and by combining double marker screening with exogenous and endogenous selectable marker knock-out techniques. Here, the shuttle plasmids pSK-TA35 and pSK-TJ were constructed, containing two pairs of recombinant arms: early and late strong promoter pE/L and EGFP as an exogenous selectable marker. The recombinant vaccinia virus rVTT-TA35-TJ without exogenous selection markers was then obtained through homologous recombination technology and the Cre/loxP system. Knocking out the two gene fragments does not affect the replication ability of the virus and displays a good genetic stability. Furthermore, a series of in vivo and in vitro experiments demonstrate that although virulence of rVTT-TA35-TJ is attenuated significantly, high immunogenicity was maintained. These results support the potential development of rVTT-TA35-TJ as a safe viral vector or vaccine.

Characterizing the effects of insertion of a 5.2 kb region of a VACV genome, which contains known immune evasion genes, on MVA immunogenicity

Modified Vaccinia virus Ankara (MVA) is an attenuated Vaccinia virus (VACV) that is a popular vaccine vector candidate against many different pathogens. Its replication-restricted nature makes it a safe vaccine. However, higher doses or multiple boosts of MVA are necessary to elicit an immune response similar to wild-type VACV. Multiple strategies have been used to create modified MVA viruses that remain safe, but have increased immunogenicity. For example, one common strategy is to delete MVA immunomodulatory proteins in hopes of increasing the host immune response. Here, we take the opposite approach and examine, for the first time, how re-introduction of a 5.2 kb region of VACV DNA (that codes for multiple immunomodulatory proteins) into MVA alters viral immunogenicity. Since antigen presenting cells (APCs) are critical connectors between the innate and adaptive immune system, we examined the effect of MVA/5.2 kb infection in these cells in vitro. MVA/5.2 kb infection decreased virus-induced apoptosis and virus-induced NF-κB activation. MVA.5.2 kb infection decreased TNF production. However, MVA/5.2 kb infection did not alter APC maturation or IL-6 and IL-8 production in vitro. We further explored MVA/5.2 kb immunogenicity in vivo. VACV-specific CD8⁺ T cells were decreased after in vivo infection with MVA/5.2 kb versus MVA, suggesting that the MVA/5.2 kb construct is less immunogenic than MVA. These results demonstrate the limitations of in vitro studies for predicting the effects of genetic manipulation of MVA on immunogenicity. Although MVA/5.2 kb did not enhance MVA's immunogenicity, this study examined an unexplored strategy for optimizing MVA, and the insight gained from these results can help direct how to modify MVA in the future.

Generation of an Attenuated Tiantan Vaccinia Virus Strain by Deletion of Multiple Genes

An attenuated vaccinia virus-MVTT_EAB-was constructed by deletion of non-essential gene segments related to the immunomodulatory and virulence functions of the vaccinia virus Tiantan strain (VVTT). The shuttle plasmids pTC-EGFP, pTE-EGFP, pTA35-EGFP, pTB-EGFP, and pTA66-EGFP were constructed and combined with the early and late strong promoter pE/L and EGFP as an exogenous selectable marker. Then, through the homologous recombination technology and Cre/loxP system, the following gene fragments were gradually knocked out one by one: TC7L-TK2L, TE3L, TA35R, TB13R, and TA66R. Ultimately, the five-segment-deleted attenuated strain MVTT_EAB was obtained. Knockout of these segments and genetic stability of MVTT_EAB were confirmed, and it was also shown that knockout of these segments did not affect the replication ability of the virus. Further, a series of in vivo and in vitro experiments demonstrated that the virulence of MVTT_EAB was attenuated significantly, but at same time, high immunogenicity was maintained. These results indicate that MVTT_EAB has potential for clinical use as a safe viral vector or vaccine with good attenuation and immunogenicity.

Generation of Recombinant Modified Vaccinia Virus Ankara Encoding VP2, NS1, and VP7 Proteins of Bluetongue Virus

Modified Vaccinia Virus Ankara (MVA) is employed widely as an experimental vaccine vector for its lack of replication in mammalian cells and high expression level of foreign/heterologous genes. Recombinant MVAs (rMVAs) are used as platforms for protein production as well as vectors to generate vaccines against a high number of infectious diseases and other pathologies. The portrait of the virus combines desirable elements such as high-level biological safety, the ability to activate appropriate innate immune mediators upon vaccination, and the capacity to deliver substantial amounts of heterologous antigens. Recombinant MVAs encoding proteins of bluetongue virus (BTV), an Orbivirus that infects domestic and wild ruminants transmitted by biting midges of the Culicoides species, are excellent vaccine candidates against this virus. In this chapter we describe the methods for the generation of rMVAs encoding VP2, NS1, and VP7 proteins of bluetongue virus as a model example for orbiviruses. The protocols included cover the cloning of VP2, NS1, and VP7 BTV-4 genes in a transfer plasmid, the construction of recombinant MVAs, the titration of virus working stocks and the protein expression analysis by immunofluorescence and radiolabeling of rMVA infected cells as well as virus purification.

Percutaneous Vaccination as an Effective Method of Delivery of MVA and MVA-Vectored Vaccines

The robustness of immune responses to an antigen could be dictated by the route of vaccine inoculation. Traditional smallpox vaccines, essentially vaccinia virus strains, that were used in the eradication of smallpox were administered by percutaneous inoculation (skin scarification). The modified vaccinia virus Ankara is licensed as a smallpox vaccine in Europe and Canada and currently undergoing clinical development in the United States. MVA is also being investigated as a vector for the delivery of heterologous genes for prophylactic or therapeutic immunization. Since MVA is replication-deficient, MVA and MVA-vectored vaccines are often inoculated through the intramuscular, intradermal or subcutaneous routes. Vaccine inoculation via the intramuscular, intradermal or subcutaneous routes requires the use of injection needles, and an estimated 10 to 20% of the population of the United States has needle phobia. Following an observation in our laboratory that a replication-deficient recombinant vaccinia virus derived from the New York City Board of Health strain elicited protective immune responses in a mouse model upon inoculation by tail scarification, we investigated whether MVA and MVA recombinants can elicit protective responses following percutaneous administration in mouse models. Our data suggest that MVA administered by percutaneous inoculation, elicited vaccinia-specific antibody responses, and protected mice from lethal vaccinia virus challenge, at levels comparable to or better than subcutaneous or intramuscular inoculation. High titers of specific neutralizing antibodies were elicited in mice inoculated with a recombinant MVA expressing the herpes simplex type 2 glycoprotein D after scarification. Similarly, a recombinant MVA expressing the hemagglutinin of attenuated influenza virus rgA/Viet Nam/1203/2004 (H5N1) elicited protective immune responses when administered at low doses by scarification. Taken together, our data suggest that MVA and MVA-vectored vaccines inoculated by scarification can elicit protective immune responses that are comparable to subcutaneous vaccination, and may allow for antigen sparing when vaccine supply is limited.

Seven major genomic deletions of vaccinia virus Tiantan strain are sufficient to decrease pathogenicity

Attenuated strain TTVAC7, as a multi-gene-deleted vaccinia virus Tiantan strain (VTT), was constructed by knocking out parts of non-essential genes related to virulence, host range and immunomodulation of VTT, and by combining double marker screening with exogenous selectable marker knockout techniques. In this study, shuttle vector plasmids pTC-EGFP, pTA35-EGFP, pTA66-EGFP, pTE-EGFP, pTB-EGFP, pTI-EGFP and pTJ-EGFP were constructed, which contained seven pairs of recombinant arms linked to the early and late strong promoter pE/L, as well as to enhanced green fluorescent protein (EGFP) as an exogenous selectable marker. BHK cells were co-transfected/infected successively with the above plasmids and VTT or gene-deleted VTT, and homologous recombination and fluorescence plaque screening methods were used to knock out the gene fragments (TC: TC7L ∼ TK2L; TA35: TA35L; TA66: TA66R; TE: TE3L ∼ TE4L; TB: TB13R; TI: TI4L; TJ: TJ2R). The Cre/LoxP system was then applied to knock out the exogenous selectable marker, and ultimately the gene-deleted attenuated strain TTVAC7 was obtained. A series of in vivo and in vitro experiments demonstrated that not only the host range of TTVAC7 could be narrowed and its toxicity weakened significantly, but its high immunogenicity was maintained at the same time. These results support the potential of TTVAC7 to be developed as a safe viral vector or vaccine.

Recombinant rubella vectors elicit SIV Gag-specific T cell responses with cytotoxic potential in rhesus macaques

Live-attenuated rubella vaccine strain RA27/3 has been demonstrated to be safe and immunogenic in millions of children. The vaccine strain was used to insert SIV gag sequences and the resulting rubella vectors were tested in rhesus macaques alone and together with SIV gag DNA in different vaccine prime-boost combinations. We previously reported that such rubella vectors induce robust and durable SIV-specific humoral immune responses in macaques. Here, we report that recombinant rubella vectors elicit robust de novo SIV-specific cellular immune responses detectable for >10 months even after a single vaccination. The antigen-specific responses induced by the rubella vector include central and effector memory CD4(+) and CD8(+) T cells with cytotoxic potential. Rubella vectors can be administered repeatedly even after vaccination with the rubella vaccine strain RA27/3. Vaccine regimens including rubella vector and SIV gag DNA in different prime-boost combinations resulted in robust long-lasting cellular responses with significant increase of cellular responses upon boost. Rubella vectors provide a potent platform for inducing HIV-specific immunity that can be combined with DNA in a prime-boost regimen to elicit durable cellular immunity.

The contribution of biotechnology toward progress in diagnosis, management, and treatment of allergic diseases

'Biotechnology' has been intuitively used by humans since thousands of years for the production of foods, beverages, and drugs based on the experience without any scientific background. However, the golden era of this discipline emerged only during the second half of the last century. Incredible progresses have been achieved on all fields starting from the industrialization of the production of foods to the discovery of antibiotics, the decipherment of the genetic code, and rational approaches to understand and define the status we now call 'healthy'. The extremely complex interactions between genetic background, life style, and environmental factors influencing our continuously increasing life span have become more and more evident and steadily generate new questions which are only partly answered. Here, we try to summarize the contribution of biotechnology to our understanding, control, and cure of IgE-mediated allergic diseases. We are aware that a review of such a vast topic can never cover all aspects of the progress achieved in the different fields.

Vaccinia virus F5 is required for normal plaque morphology in multiple cell lines but not replication in culture or virulence in mice

Vaccinia virus (VACV) gene F5L was recently identified as a determinant of plaque morphology that is truncated in Modified Vaccinia virus Ankara (MVA). Here we show that F5L also affects plaque morphology of the virulent VACV strain Western Reserve (WR) in some, but not all cell lines, and not via previously described mechanisms. Further, despite a reduction in plaque size for VACV WR lacking F5L there was no evidence of reduced virus replication or spread in vitro or in vivo. In vivo we examined two mouse models, each with more than one dose and measured signs of disease and virus burden. These data provide an initial characterization of VACV F5L in a virulent strain of VACV. Further they show the necessity of testing plaque phenotypes in more than one cell type and provide an example of a VACV gene required for normal plaque morphology but not replication and spread.

Truncation of gene F5L partially masks rescue of vaccinia virus strain MVA growth on mammalian cells by restricting plaque size

Modified vaccinia virus Ankara (MVA) is a candidate vaccine vector that is severely attenuated due to mutations acquired during several hundred rounds of serial passage in vitro. A previous study used marker rescue to produce a set of MVA recombinants with improved replication on mammalian cells. Here, we extended the characterization of these rescued MVA strains and identified vaccinia virus (VACV) gene F5L as a determinant of plaque morphology but not replication in vitro. F5 joins a growing group of VACV proteins that influence plaque formation more strongly than virus replication and which are disrupted in MVA. These defective genes in MVA confound the interpretation of marker rescue experiments designed to map mutations responsible for the attenuation of this important VACV strain.