Nonsegmented negative-strand viruses as vaccine vectors

Current Status of Poultry Recombinant Virus Vector Vaccine Development

Inactivated and live attenuated vaccines are the mainstays of preventing viral poultry diseases. However, the development of recombinant DNA technology in recent years has enabled the generation of recombinant virus vector vaccines, which have the advantages of preventing multiple diseases simultaneously and simplifying the vaccination schedule. More importantly, some can induce a protective immune response in the presence of maternal antibodies and offer long-term immune protection. These advantages compensate for the shortcomings of traditional vaccines. This review describes the construction and characterization of primarily poultry vaccine vectors, including fowl poxvirus (FPV), fowl adenovirus (FAdV), Newcastle disease virus (NDV), Marek's disease virus (MDV), and herpesvirus of turkey (HVT). In addition, the pathogens targeted and the immunoprotective effect of different poultry recombinant virus vector vaccines are also presented. Finally, this review discusses the challenges in developing vector vaccines and proposes strategies for improving immune efficacy.

An engineered ligand-responsive Csy4 endoribonuclease controls transgene expression from Sendai virus vectors

BACKGROUND

Viral vectors are attractive gene delivery vehicles because of their broad tropism, high transduction efficiency, and durable expression. With no risk of integration into the host genome, the vectors developed from RNA viruses such as Sendai virus (SeV) are especially promising. However, RNA-based vectors have limited applicability because they lack a convenient method to control transgene expression by an external inducer.

RESULTS

We engineered a Csy4 switch in Sendai virus-based vectors by combining Csy4 endoribonuclease with mutant FKBP12 (DD: destabilizing domain) that becomes stabilized when a small chemical Shield1 is supplied. In this Shield1-responsive Csy4 (SrC) switch, Shield1 increases Csy4 fused with DD (DD-Csy4), which then cleaves and downregulates the transgene mRNA containing the Csy4 recognition sequence (Csy4RS). Moreover, when Csy4RS is inserted in the viral L gene, the SrC switch suppresses replication and transcription of the SeV vector in infected cells in a Shield1-dependent manner, thus enabling complete elimination of the vector from the cells. By temporally controlling BRN4 expression, a BRN4-expressing SeV vector equipped with the SrC switch achieves efficient, stepwise differentiation of embryonic stem cells into neural stem cells, and then into astrocytes.

CONCLUSION

SeV-based vectors with the SrC switch should find wide applications in stem cell research, regenerative medicine, and gene therapy, especially when precise control of reprogramming factor expression is desirable.

Engineering Non-Human RNA Viruses for Cancer Therapy

Alongside the development and progress in cancer immunotherapy, research in oncolytic viruses (OVs) continues advancing novel treatment strategies to the clinic. With almost 50 clinical trials carried out over the last decade, the opportunities for intervention using OVs are expanding beyond the old-fashioned concept of "lytic killers", with promising breakthrough therapeutic strategies focused on leveraging the immunostimulatory potential of different viral platforms. This review presents an overview of non-human-adapted RNA viruses engineered for cancer therapy. Moreover, we describe the diverse strategies employed to manipulate the genomes of these viruses to optimize their therapeutic capabilities. By focusing on different aspects of this particular group of viruses, we describe the insights into the promising advancements in the field of virotherapy and its potential to revolutionize cancer treatment.

Recent Advancements in Mosquito-Borne Flavivirus Vaccine Development

Lately, the global incidence of flavivirus infection has been increasing dramatically and presents formidable challenges for public health systems around the world. Most clinically significant flaviviruses are mosquito-borne, such as the four serotypes of dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus and yellow fever virus. Until now, no effective antiflaviviral drugs are available to fight flaviviral infection; thus, a highly immunogenic vaccine would be the most effective weapon to control the diseases. In recent years, flavivirus vaccine research has made major breakthroughs with several vaccine candidates showing encouraging results in preclinical and clinical trials. This review summarizes the current advancement, safety, efficacy, advantages and disadvantages of vaccines against mosquito-borne flaviviruses posing significant threats to human health.

Transgene-Free Genome Editing in Nicotiana benthamiana with CRISPR/Cas9 Delivered by a Rhabdovirus Vector

The clustered regularly interspersed short palindromic repeats (CRISPR)/Cas systems have become the most widely adopted genome editing platform owing to their unprecedented simplicity, efficiency, and versatility. Typically, the genome editing enzyme is expressed in plant cells from an integrated transgene delivered by either Agrobacterium-mediated or biolistic transformation. Recently, plant virus vectors have emerged as promising tools for the in planta delivery of CRISPR/Cas reagent. Here, we provide a protocol for CRISPR/Cas9-mediated genome editing in the model tobacco plant Nicotiana benthamiana using a recombinant negative-stranded RNA rhabdovirus vector. The method is based on infection of N. benthamiana with a Sonchus yellow net virus (SYNV)-based vector that carries the Cas9 and guide RNA expression cassettes to target specific genome loci for mutagenesis. With this method, mutant plants free of foreign DNA can be obtained within 4-5 months.

An intranasal recombinant NDV-BRSV Fopt vaccine is safe and reduces lesion severity in a colostrum-deprived calf model of RSV infection

Human respiratory syncytial virus (HRSV) is a major cause of severe lower respiratory tract disease in infants and the elderly, yet no safe, effective vaccine is commercially available. Closely related bovine RSV (BRSV) causes respiratory disease in young calves, with many similar features to those seen in HRSV. We previously showed that a Newcastle disease virus (NDV)-vectored vaccine expressing the F glycoprotein of HRSV reduced viral loads in lungs of mice and cotton rats and protected from HRSV. However, clinical signs and pathogenesis of disease in laboratory animals following HRSV infection differs from that observed in human infants. Thus, we examined whether a similar vaccine would protect neonatal calves from BRSV infection. Codon-optimized rNDV vaccine (rNDV-BRSV F_opt) was constructed and administered to colostrum-deprived calves. The rNDV-BRSV F_opt vaccine was well-tolerated and there was no evidence of vaccine-enhanced disease in the upper airways or lungs of these calves compared to the non-vaccinated calves. We found two intranasal doses reduces severity of gross and microscopic lesions and decreases viral load in the lungs. Furthermore, serum neutralizing antibodies were generated in vaccinated calves. Finally, reduced lung CXC chemokine levels were observed in vaccinated calves after BRSV challenge. In summary, we have shown that rNDV-BRSV F_opt vaccine is safe in colostrum-deprived calves, and is effective in reducing lung lesions, and decreasing viral load in upper respiratory tract and lungs after challenge.

Encoding of a transgene in-frame with a Newcastle disease virus protein increases transgene expression and stability

Newcastle disease virus (NDV) has been extensively explored as a vector for vaccine and oncolytic therapeutic development. In conventional NDV-based vectors, the transgene is arranged as a separate transcription unit in the NDV genome. Here, we expressed haemagglutinin protein (HA) of an avian influenza virus using an NDV vector design in which the transgene ORF is encoded in-frame with the ORF of an NDV gene. This arrangement does not increase the number of transcription units in the NDV genome, and imposes a selection pressure against mutations interrupting the transgene ORF. We placed the HA ORF upstream or downstream of N, M, F and HN ORFs of NDV so that both proteins are encoded in-frame and are separated by either a self-cleaving 2A peptide, furin cleavage site or both. Only constructs in which HA was placed downstream of the NDV HN were viable. These constructs expressed the transgene at a higher level compared to the vector encoding the same transgene in the same position in the NDV genome but as a separate transcription unit. Furthermore, the transgene expressed in one ORF with the NDV protein proved to be more stable over multiple passages. Thus, this design may be useful for applications where the stability of the transgene expression is highly important for a recombinant NDV vector.

A single intranasal dose of human parainfluenza virus type 3-vectored vaccine induces effective antibody and memory T cell response in the lungs and protects hamsters against SARS-CoV-2

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.

Current view on novel vaccine technologies to combat human infectious diseases

Inactivated and live attenuated vaccines have improved human life and significantly reduced morbidity and mortality of several human infectious diseases. However, these vaccines have faults, such as reactivity or suboptimal efficacy and expensive and time-consuming development and production. Additionally, despite the enormous efforts to develop vaccines against some infectious diseases, the traditional technologies have not been successful in achieving this. At the same time, the concerns about emerging and re-emerging diseases urge the need to develop technologies that can be rapidly applied to combat the new challenges. Within the last two decades, the research of vaccine technologies has taken several directions to achieve safe, efficient, and economic platforms or technologies for novel vaccines. This review will give a brief overview of the current state of the novel vaccine technologies, new vaccine candidates in clinical trial phases 1-3 (listed by European Medicines Agency (EMA) and Food and Drug Administration (FDA)), and vaccines based on the novel technologies which have already been commercially available (approved by EMA and FDA) with the special reference to pandemic COVID-19 vaccines. KEY POINTS: • Vaccines of the new generation follow the minimalist strategy. • Some infectious diseases remain a challenge for the vaccine development. • The number of new vaccine candidates in the late phase clinical trials remains low.

Avian Paramyxoviruses as Vectors for Vaccine Development

Avian paramyxoviruses (APMVs) have gained a great attention to be developed as vaccine vectors against human and veterinary pathogens. Avirulent APMVs are highly safe to be used as vaccine vectors for avian and non-avian species. APMV vectored vaccines induce robust cellular and humoral immune responses in a broad range of hosts. APMV vectors can be a good platform by facilitating rapid generation of vaccines against emerging pathogens. In this chapter, we discuss application of reverse genetics of APMVs for vaccine development, design of APMV vectored vaccines, cloning of protective antigen(s) into a vector, recovery of vectored vaccines and characterization of generated vaccine viruses.

Ebolavirus: Infection, Vaccination and Control

Members of the genus Ebolavirus (family Filoviridae) are among the deadliest viral pathogens spread throughout the world with severe rate of mortality, at least 90% in some outbreaks. Their virions are filamentous and enveloped with enclosed negative-sense single-stranded RNA genome. The genome potentially expresses seven structural and nonstructural proteins. The replication cycle is complex consisting of multiple molecular processes and interactions with human-host factors and proteins. Due to high mortality rate of infection, the studies regarding cure is still infancy. This review covers the current understanding of the virus replication cycle and vaccine development, and herbal treatments to control Ebola covering the available literature on the subject.

A Methyltransferase-Defective Vesicular Stomatitis Virus-Based SARS-CoV-2 Vaccine Candidate Provides Complete Protection against SARS-CoV-2 Infection in Hamsters

The current pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to dramatic economic and health burdens. Although the worldwide SARS-CoV-2 vaccination campaign has begun, exploration of other vaccine candidates is needed due to uncertainties with the current approved vaccines, such as durability of protection, cross-protection against variant strains, and costs of long-term production and storage. In this study, we developed a methyltransferase-defective recombinant vesicular stomatitis virus (mtdVSV)-based SARS-CoV-2 vaccine candidate. We generated mtdVSVs expressing SARS-CoV-2 full-length spike (S) protein, S1, or its receptor-binding domain (RBD). All of these recombinant viruses grew to high titers in mammalian cells despite high attenuation in cell culture. The SARS-CoV-2 S protein and its truncations were highly expressed by the mtdVSV vector. These mtdVSV-based vaccine candidates were completely attenuated in both immunocompetent and immunocompromised mice. Among these constructs, mtdVSV-S induced high levels of SARS-CoV-2-specific neutralizing antibodies (NAbs) and Th1-biased T-cell immune responses in mice. In Syrian golden hamsters, the serum levels of SARS-CoV-2-specific NAbs triggered by mtdVSV-S were higher than the levels of NAbs in convalescent plasma from recovered COVID-19 patients. In addition, hamsters immunized with mtdVSV-S were completely protected against SARS-CoV-2 replication in lung and nasal turbinate tissues, cytokine storm, and lung pathology. Collectively, our data demonstrate that mtdVSV expressing SARS-CoV-2 S protein is a safe and highly efficacious vaccine candidate against SARS-CoV-2 infection. IMPORTANCE Viral mRNA cap methyltransferase (MTase) is essential for mRNA stability, protein translation, and innate immune evasion. Thus, viral mRNA cap MTase activity is an excellent target for development of live attenuated or live vectored vaccine candidates. Here, we developed a panel of MTase-defective recombinant vesicular stomatitis virus (mtdVSV)-based SARS-CoV-2 vaccine candidates expressing full-length S, S1, or several versions of the RBD. These mtdVSV-based vaccine candidates grew to high titers in cell culture and were completely attenuated in both immunocompetent and immunocompromised mice. Among these vaccine candidates, mtdVSV-S induces high levels of SARS-CoV-2-specific neutralizing antibodies (Nabs) and Th1-biased immune responses in mice. Syrian golden hamsters immunized with mtdVSV-S triggered SARS-CoV-2-specific NAbs at higher levels than those in convalescent plasma from recovered COVID-19 patients. Furthermore, hamsters immunized with mtdVSV-S were completely protected against SARS-CoV-2 challenge. Thus, mtdVSV is a safe and highly effective vector to deliver SARS-CoV-2 vaccine.

A single dose of replication-competent VSV-vectored vaccine expressing SARS-CoV-2 S1 protects against virus replication in a hamster model of severe COVID-19

The development of effective countermeasures against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the agent responsible for the COVID-19 pandemic, is a priority. We designed and produced ConVac, a replication-competent vesicular stomatitis virus (VSV) vaccine vector that expresses the S1 subunit of SARS-CoV-2 spike protein. We used golden Syrian hamsters as animal models of severe COVID-19 to test the efficacy of the ConVac vaccine. A single vaccine dose elicited high levels of SARS-CoV-2 specific binding and neutralizing antibodies; following intranasal challenge with SARS-CoV-2, animals were protected from weight loss and viral replication in the lungs. No enhanced pathology was observed in vaccinated animals upon challenge, but some inflammation was still detected. The data indicate rapid control of SARS-CoV-2 replication by the S1-based VSV-vectored SARS-CoV-2 ConVac vaccine.

A critical role for MSR1 in vesicular stomatitis virus infection of the central nervous system

Macrophage scavenger receptor 1 (MSR1) plays an important role in host defense to bacterial infections, M2 macrophage polarization, and lipid homeostasis. However, its physiological function in viral pathogenesis remains poorly defined. Herein, we report that MSR1 facilitates vesicular stomatitis virus (VSV) infection in the central nervous system. Msr1-deficient (Msr1^−/−) mice presented reduced morbidity, mortality, and viral loads in the spinal cord following lethal VSV infection, along with normal viremia and innate immune responses, compared to Msr1^+/− littermates and wild-type mice. Msr1 expression was most significantly upregulated in the spinal cord, the predominant target of VSV. Mechanistically, through its extracellular domains, MSR1 interacted with VSV surface glycoprotein and facilitated its cellular entry in a low-density lipoprotein receptor-dependent manner. In conclusion, our results demonstrate that MSR1 serves as a cofactor for VSV cellular entry and facilitates its infection preferentially in the spinal cord.

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MSR1 contributes to VSV pathogenesis in mice

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MSR1 is highly upregulated and facilitates VSV infection in the central nervous system

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MSR1 facilitates cellular entry of VSV in an LDLR family-dependent manner

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MSR1 interacts with VSV glycoprotein G via its extracellular domains

Vesicular Stomatitis Virus and DNA Vaccines Expressing Zika Virus Nonstructural Protein 1 Induce Substantial but Not Sterilizing Protection against Zika Virus Infection

The nonstructural protein 1 (NS1) of several flaviviruses, including West Nile, dengue, and yellow fever viruses, is capable of inducing variable degrees of protection against flavivirus infection in animal models. However, the immunogenicity of NS1 protein of Zika virus (ZIKV) is less understood. Here, we determined the efficacy of ZIKV NS1-based vaccine candidates using two delivery platforms, methyltransferase-defective recombinant vesicular stomatitis virus (mtdVSV) and a DNA vaccine. We first show that expression of ZIKV NS1 could be significantly enhanced by optimizing the signal peptide. A single dose of mtdVSV-NS1-based vaccine or two doses of DNA vaccine induced high levels of NS1-specfic antibody and T cell immune responses but provided only partial protection against ZIKV viremia in BALB/c mice. In Ifnar1^-/- mice, neither NS1-based vaccine provided protection against a lethal high dose (10⁵ PFU) ZIKV challenge, but mtdVSV-NS1-based vaccine prevented deaths from a low dose (10³ PFU) challenge, though they experienced viremia and body weight loss. We conclude that ZIKV NS1 alone conferred substantial, but not complete, protection against ZIKV infection. Nevertheless, these results highlight the value of ZIKV NS1 for vaccine development.IMPORTANCE Most Zika virus (ZIKV) vaccine research has focused on the E or prM-E proteins and the induction of high levels of neutralizing antibodies. However, these ZIKV neutralizing antibodies cross-react with other flaviviruses, which may aggravate the disease via an antibody-dependent enhancement (ADE) mechanism. ZIKV NS1 protein may be an alternative antigen for vaccine development, since antibodies to NS1 do not bind to the virion, thereby eliminating the risk of ADE. Here, we show that recombinant VSV and DNA vaccines expressing NS1, alone, confer partial protection against ZIKV infection in both immunocompetent and immunodeficient mice, highlighting the value of NS1 as a potential vaccine candidate.

Highly efficient DNA-free plant genome editing using virally delivered CRISPR-Cas9

Genome-editing technologies using CRISPR-Cas nucleases have revolutionized plant science and hold enormous promise in crop improvement. Conventional transgene-mediated CRISPR-Cas reagent delivery methods may be associated with unanticipated genome changes or damage1,2, with prolonged breeding cycles involving foreign DNA segregation and with regulatory restrictions regarding transgenesis3. Therefore, DNA-free delivery has been developed by transfecting preassembled CRISPR-Cas9 ribonucleoproteins into protoplasts4 or in vitro fertilized zygotes5. However, technical difficulties in regeneration from these wall-less cells make impractical a general adaption of these approaches to most crop species. Alternatively, CRISPR-Cas ribonucleoproteins or RNA transcripts have been biolistically bombarded into immature embryo cells or calli to yield highly specific genome editing, albeit at low frequency6-9. Here we report the engineering of a plant negative-strand RNA virus-based vector for DNA-free in planta delivery of the entire CRISPR-Cas9 cassette to achieve single, multiplex mutagenesis and chromosome deletions at high frequency in a model allotetraploid tobacco host. Over 90% of plants regenerated from virus-infected tissues without selection contained targeted mutations, among which up to 57% carried tetra-allelic, inheritable mutations. The viral vector remained stable even after mechanical transmission, and can readily be eliminated from mutated plants during regeneration or after seed setting. Despite high on-target activities, off-target effects, if any, are minimal. Our study provides a convenient, highly efficient and cost-effective approach for CRISPR-Cas9 gene editing in plants through virus infection.

Engineering of Live Chimeric Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is an important human pathogen that, along with respiratory syncytial virus (RSV), is a major cause of respiratory tract infections in young infants. Development of an effective vaccine against Pneumoviruses has proven to be particularly difficult; despite over 50 years of research in this field, no vaccine against HMPV or RSV is currently available. Recombinant chimeric viruses expressing antigens of other viruses can be generated by reverse genetics and used for simultaneous immunization against more than one pathogen. This approach can result in the development of promising vaccine candidates against HMPV, and several studies have indeed validated viral vectors expressing HMPV antigens. In this review, we summarize current efforts in generating recombinant chimeric vaccines against HMPV, and we discuss their potential optimization based on the correspondence with RSV studies.

A recombinant avian paramyxovirus serotype 3 expressing the hemagglutinin protein protects chickens against H5N1 highly pathogenic avian influenza virus challenge

Highly pathogenic avian influenza (HPAI) is a devastating disease of poultry and a serious threat to public health. Vaccination with inactivated virus vaccines has been applied for several years as one of the major policies to control highly pathogenic avian influenza virus (HPAIV) infections in chickens. Viral-vectored HA protein vaccines are a desirable alternative for inactivated vaccines. However, each viral vector possesses its own advantages and disadvantages for the development of a HA-based vaccine against HPAIV. Recombinant Newcastle disease virus (rNDV) strain LaSota expressing HA protein vaccine has shown promising results against HPAIV; however, its replication is restricted only to the respiratory tract. Therefore, we thought to evaluate avian paramyxovirus serotype 3 (APMV-3) strain Netherlands as a safe vaccine vector against HPAIV, which has high efficiency replication in a greater range of host organs. In this study, we generated rAPMV-3 expressing the HA protein of H5N1 HPAIV using reverse genetics and evaluated the induction of neutralizing antibodies and protection by rAPMV3 and rNDV expressing the HA protein against HPAIV challenge in chickens. Our results showed that immunization of chickens with rAPMV-3 or rNDV expressing HA protein provided complete protection against HPAIV challenge. However, immunization of chickens with rAPMV-3 expressing HA protein induced higher level of neutralizing antibodies compared to that of rNDV expressing HA protein. These results suggest that a rAPMV-3 expressing HA protein might be a better vaccine for mass-vaccination of commercial chickens in field conditions.

A Versatile Plant Rhabdovirus-Based Vector for Gene Silencing, miRNA Expression and Depletion, and Antibody Production

Plant virus vectors are ideal tools for delivery of genetic cargo into host cells for functional genomics studies and protein overexpression. Although a vast number of plant virus vectors have been developed for different purposes, the utility of a particular virus vector is generally limited. Here, we report a multipurpose plant rhabdovirus-based vector system suitable for a wide range of applications in Nicotiana benthamiana. We engineered sonchus yellow net rhabdovirus (SYNV)-based gene silencing vectors through expressing a sense, antisense, or double-stranded RNAs of target genes. Robust target gene silencing was also achieved with an SYNV vector expressing a designed artificial microRNA. In addition, ectopic expression of a short tandem target mimic RNA using the SYNV vector led to a significant depletion of the target miR165/166 and caused abnormal leaf development. More importantly, SYNV was able to harbor two expression cassettes that permitted simultaneous RNA silencing and overexpression of large reporter gene. This dual capacity vector also enabled systemic expression of a whole-molecule monoclonal antibody consisting of light and heavy chains. These results highlight the utility of the SYNV vector system in gene function studies and agricultural biotechnology and provide a technical template for developing similar vectors of other economically important plant rhabdoviruses.

Genetically Modified Rabies Virus Vector-Based Rift Valley Fever Virus Vaccine is Safe and Induces Efficacious Immune Responses in Mice

Rift Valley fever virus (RVFV), which causes Rift Valley fever (RVF), is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. RVF is a World Health Organization (WHO) priority disease and, together with rabies, is a major health burden in Africa. Here, we present the development and characterization of an inactivated recombinant RVFV and rabies virus (RABV) vaccine candidate (rSRV9-eGn). Immunization with rSRV9-eGn stimulated the production of RVFV-specific IgG antibodies and induced humoral and cellular immunity in mice but did not induce the production of neutralizing antibodies. IgG1 and IgG2a were the main isotypes observed by IgG subtype detection, and IgG3 antibodies were not detected. The ratios of IgG1/IgG2a > 1 indicated a Type 2 humoral immune response. An effective vaccine is intended to establish a long-lived population of memory T cells, and mice generated memory cells among the proliferating T cell population after immunization with rSRV9-eGn, with effector memory T cells (T_EM) as the major population. Due to the lack of prophylactic treatment experiments, it is impossible to predict whether this vaccine can protect animals from RVFV infection with only high titres of anti-RVFV IgG antibodies and no neutralizing antibodies induced, and thus, protection confirmation needs further verification. However, this RVFV vaccine designed with RABV as the vector provides ideas for the development of vaccines that prevent RVFV and RABV infections.

On the stability of sequences inserted into viral genomes

Viruses are widely used as vectors for heterologous gene expression in cultured cells or natural hosts, and therefore a large number of viruses with exogenous sequences inserted into their genomes have been engineered. Many of these engineered viruses are viable and express heterologous proteins at high levels, but the inserted sequences often prove to be unstable over time and are rapidly lost, limiting heterologous protein expression. Although virologists are aware that inserted sequences can be unstable, processes leading to insert instability are rarely considered from an evolutionary perspective. Here, we review experimental work on the stability of inserted sequences over a broad range of viruses, and we present some theoretical considerations concerning insert stability. Different virus genome organizations strongly impact insert stability, and factors such as the position of insertion can have a strong effect. In addition, we argue that insert stability not only depends on the characteristics of a particular genome, but that it will also depend on the host environment and the demography of a virus population. The interplay between all factors affecting stability is complex, which makes it challenging to develop a general model to predict the stability of genomic insertions. We highlight key questions and future directions, finding that insert stability is a surprisingly complex problem and that there is need for mechanism-based, predictive models. Combining theoretical models with experimental tests for stability under varying conditions can lead to improved engineering of viral modified genomes, which is a valuable tool for understanding genome evolution as well as for biotechnological applications, such as gene therapy.

Innovation in Newcastle Disease Virus Vectored Avian Influenza Vaccines

Highly pathogenic avian influenza (HPAI) and Newcastle disease are economically important avian diseases worldwide. Effective vaccination is critical to control these diseases in poultry. Live attenuated Newcastle disease virus (NDV) vectored vaccines have been developed for bivalent vaccination against HPAI viruses and NDV. These vaccines have been generated by inserting the hemagglutinin (HA) gene of avian influenza virus into NDV genomes. In laboratory settings, several experimental NDV-vectored vaccines have protected specific pathogen-free chickens from mortality, clinical signs, and virus shedding against H5 and H7 HPAI viruses and NDV challenges. NDV-vectored H5 vaccines have been licensed for poultry vaccination in China and Mexico. Recently, an antigenically chimeric NDV vector has been generated to overcome pre-existing immunity to NDV in poultry and to provide early protection of poultry in the field. Prime immunization of one-day-old poults with a chimeric NDV vector followed by boosting with a conventional NDV vector has shown to protect broiler chickens against H5 HPAI viruses and a highly virulent NDV. This novel vaccination approach can provide efficient control of HPAI viruses in the field and facilitate poultry vaccination.

A Recombinant Rabies Virus Expressing the Marburg Virus Glycoprotein Is Dependent upon Antibody-Mediated Cellular Cytotoxicity for Protection against Marburg Virus Disease in a Murine Model

Marburg virus (MARV) is a filovirus related to Ebola virus (EBOV) associated with human hemorrhagic disease. Outbreaks are sporadic and severe, with a reported case mortality rate of upward of 88%. There is currently no antiviral or vaccine available. Given the sporadic nature of outbreaks, vaccines provide the best approach for long-term control of MARV in regions of endemicity. We have developed an inactivated rabies virus-vectored MARV vaccine (FILORAB3) to protect against Marburg virus disease. Immunogenicity studies in our labs have shown that a Th1-biased seroconversion to both rabies virus and MARV glycoproteins (GPs) is beneficial for protection in a preclinical murine model. As such, we adjuvanted FILORAB3 with glucopyranosyl lipid adjuvant (GLA), a Toll-like receptor 4 agonist, in a squalene-in-water emulsion. Across two different BALB/c mouse challenge models, we achieved 92% protection against murine-adapted Marburg virus (ma-MARV). Although our vaccine elicited strong MARV GP antibodies, it did not strongly induce neutralizing antibodies. Through both in vitro and in vivo approaches, we elucidated a critical role for NK cell-dependent antibody-mediated cellular cytotoxicity (ADCC) in vaccine-induced protection. Overall, these findings demonstrate that FILORAB3 is a promising vaccine candidate for Marburg virus disease.IMPORTANCE Marburg virus (MARV) is a virus similar to Ebola virus and also causes a hemorrhagic disease which is highly lethal. In contrast to EBOV, only a few vaccines have been developed against MARV, and researchers do not understand what kind of immune responses are required to protect from MARV. Here we show that antibodies directed against MARV after application of our vaccine protect in an animal system but fail to neutralize the virus in a widely used virus neutralization assay against MARV. This newly discovered activity needs to be considered more when analyzing MARV vaccines or infections.

Immunogenicity of the Multi-Epitopic Recombinant Glycoproteins of Newcastle Disease Virus: Implications for the Serodiagnosis Applications

Background

Newcastle disease virus (NDV) is a dangerous viral disease, infecting a broad range of birds, and has a fatal effect on the poultry industries. The attachment and consequently fusion of the virus to the host cell membrane is directed by the two superficial glycoproteins, the hemagglutinin-neuraminidase (HN) and the fusion (F) which is considered as the important targets for the poultry immune response.

Objectives

The principal goal of this investigation was to realize the potential efficacy of the E. coli expression system for the production of the multi-epitopic HN, and F proteins with respect to the ability for the stimulation of the immune system and production of the cross-reactive antibodies in mice.

Materials and Methods

The recombinant HN and F (rHN, rF) have accumulated almost 40% of the total bacterial proteins. The presence of rHN and rF proteins recognized by the Western blotting with specific anti-HN, anti-F, anti-Newcastle B1, and anti-poly 6x His-tag antibodies. Furthermore, both rHN and rF have shown the specific reactivity against the Newcastle B1 antiserum as a standard strain.

Results

The ELISA analysis showed that the higher dilutions of the antibody against Newcastle B1 could react with the as least quantity as 100 ng of the purified rHN, and rF. Cross-reactivity analysis of the sera from the mice immunized with Newcastle B1 in two time points indicated that the raise of anti-Newcastle B1, anti-HN and anti-F antibodies peaked at 28 days post immunization (dpi). Moreover, temporal variation in IgG titration between both time points was significant at 5% probability level.

Conclusion

The results provided valuable information about the cross-reactivity patterns and biological activity of the multi-epitopic proteins compared to the NDV standard strain which was determined by the Western blotting and ELISA.

Co-expression of the Hemagglutinin and Neuraminidase by Heterologous Newcastle Disease Virus Vectors Protected Chickens against H5 Clade 2.3.4.4 HPAI Viruses

Avian influenza remains an important zoonotic disease with a significant global impact. The spread of H5 highly pathogenic avian influenza (HPAI) viruses (clade 2.3.4.4) by migratory birds has caused outbreaks in wide geographic regions (Asia, Europe, and North America) with great economic losses during 2014-2015. Efficient vaccines and vaccination approaches are needed to enhance protective immunity against HPAI viruses. Although several vaccination strategies have been developed, none has been satisfactory. Our strategy has been to use avirulent vaccine strain of Newcastle disease virus (NDV) as a vaccine vector for HPAI viruses. For poultry vaccination, we previously generated a new platform of chimeric NDV vector to overcome preexisting maternal antibodies to NDV in poultry. In this study, we have generated vaccine candidates targeting H5 clade 2.3.4.4 HPAI viruses by using our chimeric NDV and conventional NDV strain LaSota vectors for a heterologous prime-boost immunization approach. Co-expression of the HA and NA proteins by our vaccine vectors induced enhanced HPAI virus specific immune responses in specific-pathogen free and broiler chickens prior to challenge. Further, these vaccine candidates efficiently protected broiler chickens from mortality, clinical signs, and shedding of homologous and heterologous H5 HPAI viruses and highly virulent NDV, thus providing a dual vaccination approach in the field.

A Zika virus vaccine expressing premembrane-envelope-NS1 polyprotein

Current efforts to develop Zika virus (ZIKV) subunit vaccines have been focused on pre-membrane (prM) and envelope (E) proteins, but the role of NS1 in ZIKV-specific immune response and protection is poorly understood. Here, we develop an attenuated recombinant vesicular stomatitis virus (rVSV)-based vaccine expressing ZIKV prM-E-NS1 as a polyprotein. This vectored vaccine candidate is attenuated in mice, where a single immunization induces ZIKV-specific antibody and T cell immune responses that provide protection against ZIKV challenge. Co-expression of prM, E, and NS1 induces significantly higher levels of Th2 and Th17 cytokine responses than prM-E. In addition, NS1 alone is capable of conferring partial protection against ZIKV infection in mice even though it does not induce neutralizing antibodies. These results demonstrate that attenuated rVSV co-expressing prM, E, and NS1 is a promising vaccine candidate for protection against ZIKV infection and highlights an important role for NS1 in ZIKV-specific cellular immune responses.

Chimeric rabies glycoprotein with a transmembrane domain and cytoplasmic tail from Newcastle disease virus fusion protein incorporates into the Newcastle disease virion at reduced levels

Rabies remains an important worldwide health problem. Newcastle disease virus (NDV) was developed as a vaccine vector in animals by using a reverse genetics approach. Previously, our group generated a recombinant NDV (LaSota strain) expressing the complete rabies virus G protein (RVG), named rL-RVG. In this study, we constructed the variant rL-RVGTM, which expresses a chimeric rabies virus G protein (RVGTM) containing the ectodomain of RVG and the transmembrane domain (TM) and a cytoplasmic tail (CT) from the NDV fusion glycoprotein to study the function of RVG's TM and CT. The RVGTM did not detectably incorporate into NDV virions, though it was abundantly expressed at the surface of infected BHK-21 cells. Both rL-RVG and rL-RVGTM induced similar levels of NDV virus-neutralizing antibody (VNA) after initial and secondary vaccination in mice, whereas rabies VNA induction by rL-RVGTM was markedly lower than that induced by rL-RVG. Though rL-RVG could spread from cell to cell like that in rabies virus, rL-RVGTM lost this ability and spread in a manner similar to the parental NDV. Our data suggest that the TM and CT of RVG are essential for its incorporation into NDV virions and for spreading of the recombinant virus from the initially infected cells to surrounding cells.

Oncolytic Recombinant Vesicular Stomatitis Virus (VSV) Is Nonpathogenic and Nontransmissible in Pigs, a Natural Host of VSV

Vesicular stomatitis virus (VSV) is a negative-stranded RNA virus that naturally causes disease in livestock including horses, cattle and pigs. The two main identified VSV serotypes are New Jersey (VSNJV) and Indiana (VSIV). VSV is a rapidly replicating, potently immunogenic virus that has been engineered to develop novel oncolytic therapies for cancer treatment. Swine are a natural host for VSV and provide a relevant and well-established model, amenable to biological sampling to monitor virus shedding and neutralizing antibodies. Previous reports have documented the pathogenicity and transmissibility of wild-type isolates and recombinant strains of VSIV and VSNJV using the swine model. Oncolytic VSV engineered to express interferon-beta (IFNβ) and the sodium iodide symporter (NIS), VSV-IFNβ-NIS, has been shown to be a potent new therapeutic agent inducing rapid and durable tumor remission following systemic therapy in preclinical mouse models. VSV-IFNβ-NIS is currently undergoing clinical evaluation for the treatment of advanced cancer in human and canine patients. To support clinical studies and comprehensively assess the risk of transmission to susceptible species, we tested the pathogenicity and transmissibility of oncolytic VSV-IFNβ-NIS using the swine model. Following previously established protocols to evaluate VSV pathogenicity, intradermal inoculation with 10⁷ TCID₅₀ VSV-IFNβ-NIS caused no observable symptoms in pigs. There was no detectable shedding of infectious virus in VSV-IFNβ-NIS in biological excreta of inoculated pigs or exposed naive pigs kept in direct contact throughout the experiment. VSV-IFNβ-NIS inoculated pigs became seropositive for VSV antibodies, while contact pigs displayed no symptoms of VSV infection, and importantly did not seroconvert. These data indicate that oncolytic VSV is both nonpathogenic and not transmissible in pigs, a natural host. These findings support further clinical development of oncolytic VSV-IFNβ-NIS as a safe therapeutic for human and canine cancer.

Newcastle disease virus-based MERS-CoV candidate vaccine elicits high-level and lasting neutralizing antibodies in Bactrian camels

Middle East respiratory syndrome coronavirus (MERS-CoV), a member of the Coronaviridae family, is the causative pathogen for MERS that is characterized by high fever, pneumonia, acute respiratory distress syndrome (ARDS), as well as extrapulmonary manifestations. Currently, there are no approved treatment regimens or vaccines for MERS. Here, we generated recombinant nonvirulent Newcastle disease virus (NDV) LaSota strain expressing MERS-CoV S protein (designated as rLa-MERS-S), and evaluated its immunogenicity in mice and Bactrian camels. The results revealed that rLa-MERS-S showed similar growth properties to those of LaSota in embryonated chicken eggs, while animal immunization studies showed that rLa-MERS-S induced MERS-CoV neutralizing antibodies in mice and camels. Our findings suggest that recombinant rLa-MERS-S may be a potential MERS-CoV veterinary vaccine candidate for camels and other animals affected by MERS.

Permissiveness of human hepatocellular carcinoma cell lines for hepatitis C virus entry and replication

Hepatitis C virus (HCV) is a globally prevalent pathogen and is associated with high death rates and morbidity. Since its discovery in 1989, HCV research has been impeded by the lack of a robust infectious cell culture system and thus in vitro studies on diverse genetic backgrounds are hampered because of the limited number of hepatoma cell lines which are able to support different aspects of the HCV life cycle. In the current study, we sought to expand the limited number of permissive cells capable of supporting the diverse phases of the HCV life cycle. Initially, we screened a panel of new hepatoma-derived cell lines, designated BCLC-1, -2, -3, -4, -5, -6, -9 and -10 cells, for their ability to express essential HCV receptors and subsequently to support HCV entry by using the well-characterized HCV pseudoparticle system (HCVpp). Apart from BCLC-9, all BCLC cell lines were permissive for HCVpp infection. Next, BCLC cells were subjected to short- and long-term HCV RNA replication studies using HCV subgenomic replicons. Interestingly, only BCLC-1, -5 and -9 cells, supported short-term HCV RNA replication, but the latter were excluded from further studies since they were refractory for HCV entry. BCLC-1, -5 were able to support long-term HCV replication too; yet BCLC-5 cells supported the highest long-term HCV RNA replication levels. Furthermore, cured BCLC-5 clones from HCV subgenomic replicon, showed increased permissiveness for HCV RNA replication. Strikingly, we were unable to detect endogenous BCLC-5 miR122 expression - an important HCV host factor- and as expected, the exogenous expression of miR122 in BCLC-5 cells increased their permissiveness for HCV RNA replication. However, this cell line was unable to produce HCV infectious particles despite ectopic expression of apolipoprotein E, which in other hepatoma cell lines has been shown to be sufficient to enable the HCV secretion process, suggesting a lack of other host cellular factor(s) and/or the presence of inhibitory factor(s). In conclusion, the establishment of these new permissive cell lines for HCV entry and replication, which possess a different genetic background compared to the well-established models, expands the current repertoire of hepatoma cell lines susceptible to the study of the HCV life cycle and also will aid to further elucidate the cellular determinants that modulate HCV replication, assembly and egress.

Heterologous prime-boost immunization of Newcastle disease virus vectored vaccines protected broiler chickens against highly pathogenic avian influenza and Newcastle disease viruses

Avian Influenza virus (AIV) is an important pathogen for both human and animal health. There is a great need to develop a safe and effective vaccine for AI infections in the field. Live-attenuated Newcastle disease virus (NDV) vectored AI vaccines have shown to be effective, but preexisting antibodies to the vaccine vector can affect the protective efficacy of the vaccine in the field. To improve the efficacy of AI vaccine, we generated a novel vectored vaccine by using a chimeric NDV vector that is serologically distant from NDV. In this study, the protective efficacy of our vaccines was evaluated by using H5N1 highly pathogenic avian influenza virus (HPAIV) strain A/Vietnam/1203/2004, a prototype strain for vaccine development. The vaccine viruses were three chimeric NDVs expressing the hemagglutinin (HA) protein in combination with the neuraminidase (NA) protein, matrix 1 protein, or nonstructural 1 protein. Comparison of their protective efficacy between a single and prime-boost immunizations indicated that prime immunization of 1-day-old SPF chicks with our vaccine viruses followed by boosting with the conventional NDV vector strain LaSota expressing the HA protein provided complete protection of chickens against mortality, clinical signs and virus shedding. Further verification of our heterologous prime-boost immunization using commercial broiler chickens suggested that a sequential immunization of chickens with chimeric NDV vector expressing the HA and NA proteins following the boost with NDV vector expressing the HA protein can be a promising strategy for the field vaccination against HPAIVs and against highly virulent NDVs.

Ebola Vaccine: How Far are we?

Ebola viruses have been identified as an emerging threat as it causes severe haemorrhagic fever in human with mortality rates ranging from 50 to 90%. In addition to being a global health concern, the virus also is considered a potential biological threat agent. As for now, no licensed vaccine is available for pre or post exposure treatment. Recent epidemic of this disease in South Africa has led to concern towards development of an effective vaccine on a priority basis. This review is an attempt to look upon current progress in the development of Ebola virus vaccines and highlights strategies that have the greatest potential for commercial development.

Multivalent and Multipathogen Viral Vector Vaccines

The presentation and delivery of antigens are crucial for inducing immunity and, desirably, lifelong protection. Recombinant viral vectors-proven safe and successful in veterinary vaccine applications-are ideal shuttles to deliver foreign proteins to induce an immune response with protective antibody levels by mimicking natural infection. Some examples of viral vectors are adenoviruses, measles virus, or poxviruses. The required attributes to qualify as a vaccine vector are as follows: stable insertion of coding sequences into the genome, induction of a protective immune response, a proven safety record, and the potential for large-scale production. The need to develop new vaccines for infectious diseases, increase vaccine accessibility, reduce health costs, and simplify overloaded immunization schedules has driven the idea to combine antigens from the same or various pathogens. To protect effectively, some vaccines require multiple antigens of one pathogen or different pathogen serotypes/serogroups in combination (multivalent or polyvalent vaccines). Future multivalent vaccine candidates are likely to be required for complex diseases like malaria and HIV. Other novel strategies propose an antigen combination of different pathogens to protect against several diseases at once (multidisease or multipathogen vaccines).

Veterinary Replicon Vaccines

Vaccination is essential in livestock farming and in companion animal ownership. Nucleic acid vaccines based on DNA or RNA provide an elegant alternative to those classical veterinary vaccines that have performed suboptimally. Recent advances in terms of rational design, safety, and efficacy have strengthened the position of nucleic acid vaccines in veterinary vaccinology. The present review focuses on replicon vaccines designed for veterinary use. Replicon vaccines are self-amplifying viral RNA sequences that, in addition to the sequence encoding the antigen of interest, contain all elements necessary for RNA replication. Vaccination results in high levels of in situ antigen expression and induction of potent immune responses. Both positive- and negative-stranded viruses have been used to construct replicons, and they can be delivered as RNA, DNA, or viral replicon particles. An introduction to the biology and the construction of different viral replicon vectors is given, and examples of veterinary replicon vaccine applications are discussed.

Novel Strategy to Control Transgene Expression Mediated by a Sendai Virus-Based Vector Using a Nonstructural C Protein and Endogenous MicroRNAs

Tissue-specific control of gene expression is an invaluable tool for studying various biological processes and medical applications. Efficient regulatory systems have been utilized to control transgene expression in various types of DNA viral or integrating viral vectors. However, existing regulatory systems are difficult to transfer into negative-strand RNA virus vector platforms because of significant differences in their transcriptional machineries. In this study, we developed a novel strategy for regulating transgene expression mediated by a cytoplasmic RNA vector based on a replication-defective and persistent Sendai virus (SeVdp). Because of the capacity of Sendai virus (SeV) nonstructural C proteins to specifically inhibit viral RNA synthesis, overexpression of C protein significantly reduced transgene expression mediated by SeVdp vectors. We found that SeV C overexpression concomitantly reduced SeVdp mRNA levels and genomic RNA synthesis. To control C expression, target sequences for an endogenous microRNA were incorporated into the 3′ untranslated region of the C genes. Incorporation of target sequences for miR-21 into the SeVdp vector restored transgene expression in HeLa cells by decreasing C expression. Furthermore, the SeVdp vector containing target sequences for let-7a enabled cell-specific control of transgene expression in human fibroblasts and induced pluripotent stem cells. Our findings demonstrate that SeV C can be used as an effective regulator for controlling transgene expression. This strategy will contribute to efficient and less toxic SeVdp-mediated gene transfer in various biological applications.

Characterization of a recombinant Newcastle disease virus expressing the glycoprotein of bovine ephemeral fever virus

Bovine ephemeral fever (BEF) is caused by the arthropod-borne bovine ephemeral fever virus (BEFV), which is a member of the family Rhabdoviridae and the genus Ephemerovirus. BEFV causes an acute febrile infection in cattle and water buffalo. In this study, a recombinant Newcastle disease virus (NDV) expressing the glycoprotein (G) of BEFV (rL-BEFV-G) was constructed, and its biological characteristics in vitro and in vivo, pathogenicity, and immune response in mice and cattle were evaluated. BEFV G enabled NDV to spread from cell to cell. rL-BEFV-G remained nonvirulent in poultry and mice compared with vector LaSota virus. rL-BEFV-G triggered a high titer of neutralizing antibodies against BEFV in mice and cattle. These results suggest that rL-BEFV-G might be a suitable candidate vaccine against BEF.

Toward an Effective Ebola Virus Vaccine

Long-term control of viral outbreaks requires the use of vaccines to impart acquired resistance and ensuing protection. In the wake of an epidemic, established immunity against a particular disease can limit spread and significantly decrease mortality. Creation of a safe and efficacious vaccine against Ebola virus (EBOV) has proven elusive so far, but various inventive strategies are now being employed to counteract the threat of outbreaks caused by EBOV and related filoviruses. Here, we present a current overview of progress in the field of Ebola virus vaccine development.

Genetically engineered Newcastle disease virus expressing human interferon-λ1 induces apoptosis in gastric adenocarcinoma cells and modulates the Th1/Th2 immune response

Interferon-λ1 (IFN-λ1), a recently discovered cytokine of the type III IFN family, was found to be a therapeutic alternative to type I IFN in terms of tumors. Using reverse genetics technique, we generated a recombinant Newcastle disease virus (NDV) LaSota strains named as human IFN‑λ1 recombinant adenovirus (rL-hIFN-λ1) containing human IFN-λ1 gene and further evaluated the expressing of IFN-λ1 in human gastric adenocarcinoma cell line SGC-7901 after infected with rL-hIFN-λ1 by using western blot analysis, RT-PCR and immunofluorescence analyses. IFN-λl specific receptor IFNLR1 was detected on several gastric tumor cell lines including SGC-7901 and AGS and on PBMCs.The expression of the IFN-λ1 proteins reached a high level detected in the supernatant harvested 24 h after the infection of tumor cells. The proliferation changes of SGC infected with rL-hIFN-λ1 was significantly inhibited compared with NDV-infected group. Apoptosis was significantly induced by rL-hIFN-λ1 in gastric cancer cells compared with NDV virus tested by TUNEL assay, western blot analysis and Annexin V flow cytometry. Due to the high dose of IFN-λ1 expressed by the rL-hIFN-λ1-infected tumor cells, the immune study showed that rL-hIFN-λ1 increased IFN-γ production [the T helper cell subtype 1 (Th1) response] and inhibited interleukin (IL)-13 production [the T helper cell subtype 2 (Th2) response] to change the Th1/Th2 response of tumor microenvironment which inhibited tumor growth. This study aims at building recombinant NDV rL-hIFN-λ1 as an efficient antitumor agent.

Newcastle Disease Virus as a Vaccine Vector for Development of Human and Veterinary Vaccines

Viral vaccine vectors have shown to be effective in inducing a robust immune response against the vaccine antigen. Newcastle disease virus (NDV), an avian paramyxovirus, is a promising vaccine vector against human and veterinary pathogens. Avirulent NDV strains LaSota and B1 have long track records of safety and efficacy. Therefore, use of these strains as vaccine vectors is highly safe in avian and non-avian species. NDV replicates efficiently in the respiratory track of the host and induces strong local and systemic immune responses against the foreign antigen. As a vaccine vector, NDV can accommodate foreign sequences with a good degree of stability and as a RNA virus, there is limited possibility for recombination with host cell DNA. Using NDV as a vaccine vector in humans offers several advantages over other viral vaccine vectors. NDV is safe in humans due to host range restriction and there is no pre-existing antibody to NDV in the human population. NDV is antigenically distinct from common human pathogens. NDV replicates to high titer in a cell line acceptable for human vaccine development. Therefore, NDV is an attractive vaccine vector for human pathogens for which vaccines are currently not available. NDV is also an attractive vaccine vector for animal pathogens.

Newcastle disease virus-vectored West Nile fever vaccine is immunogenic in mammals and poultry

BACKGROUND

West Nile virus (WNV) is an emerging zoonotic pathogen which is harmful to human and animal health. Effective vaccination in susceptible hosts should protect against WNV infection and significantly reduce viral transmission between animals and from animals to humans. A versatile vaccine suitable for different species that can be delivered via flexible routes remains an essential unmet medical need. In this study, we developed a recombinant avirulent Newcastle disease virus (NDV) LaSota strain expressing WNV premembrane/envelope (PrM/E) proteins (designated rLa-WNV-PrM/E) and evaluated its immunogenicity in mice, horses, chickens, ducks and geese.

RESULTS

Mouse immunization experiments disclosed that rLa-WNV-PrM/E induces significant levels of WNV-neutralizing antibodies and E protein-specific CD4+ and CD8+ T-cell responses. Moreover, recombinant rLa-WNV-PrM/E elicited significant levels of WNV-specific IgG in horses upon delivery via intramuscular immunization, and in chickens, ducks and geese via intramuscular, oral or intranasal immunization.

CONCLUSIONS

Our results collectively support the utility of rLa-WNV-PrM/E as a promising WNV veterinary vaccine candidate for mammals and poultry.

Protective efficacy of a recombinant Newcastle disease virus expressing glycoprotein of vesicular stomatitis virus in mice

BACKGROUND

Vesicular stomatitis virus (VSV) causes severe losses to the animal husbandry industry. In this study, a recombinant Newcastle disease virus (NDV) expressing the glycoprotein (G) of VSV (rL-VSV-G) was constructed and its pathogenicity and immune protective efficacy in mouse were evaluated.

RESULTS

In pathogenicity evaluation test, the analysis of the viral distribution in mouse organs and body weight change showed that rL-VSV-G was safe in mice. In immune protection assay, the recombinant rL-VSV-G triggered a high titer of neutralizing antibodies against VSV. After challenge, the wild-type (wt) VSV viral load in mouse organs was lower in rL-VSV-G group than that in rLaSota groups. wt VSV was not detected in the blood, liver, or kidneys of mice, whereas it was found in these tissues in control groups. The mice body weight had no significant change after challenge in the rL-VSV-G group. Additionally, suckling mice produced from female mice immunized with rL-VSV-G were partially protected from wt VSV challenge.

CONCLUSIONS

These results demonstrated that rL-VSV-G may be a suitable candidate vaccine against vesicular stomatitis (VS).

Recombinant Newcastle disease virus-vectored vaccines against human and animal infectious diseases

Recent advances in recombinant genetic engineering techniques have brought forward a leap in designing new vaccines in modern medicine. One attractive strategy is the application of reverse genetics technology to make recombinant Newcastle disease virus (rNDV) deliver protective antigens of pathogens. In recent years, numerous studies have demonstrated that rNDV-vectored vaccines can induce quicker and better humoral and mucosal immune responses than conventional vaccines and are protective against pathogen challenges. With deeper understanding of NDV molecular biology, it is feasible to develop gene-modified rNDV vaccines accompanied by good safety, high efficacy, low toxicity and better immunogenicity. This review summarizes the development of reverse genetics technology in using NDV as a promising vaccine vector to design new vaccines for human and animal use.

Immunogenic Subviral Particles Displaying Domain III of Dengue 2 Envelope Protein Vectored by Measles Virus

Vaccines against dengue virus (DV) are commercially nonexistent. A subunit vaccination strategy may be of value, especially if a safe viral vector acts as biologically active adjuvant. In this paper, we focus on an immunoglobulin-like, independently folded domain III (DIII) from DV 2 envelope protein (E), which contains epitopes that elicits highly specific neutralizing antibodies. We modified the hepatitis B small surface antigen (HBsAg, S) in order to display DV 2 DIII on a virus-like particle (VLP), thus generating the hybrid antigen DIII-S. Two varieties of measles virus (MV) vectors were developed to express DIII-S. The first expresses the hybrid antigen from an additional transcription unit (ATU) and the second additionally expresses HBsAg from a separate ATU. We found that this second MV vectoring the hybrid VLPs displaying DIII-S on an unmodified HBsAg scaffold were immunogenic in MV-susceptible mice (HuCD46Ge-IFNar^ko), eliciting robust neutralizing responses (averages) against MV (1:1280 NT₉₀), hepatitis B virus (787 mIU/mL), and DV2 (1:160 NT₅₀) in all of the tested animals. Conversely, the MV vector expressing only DIII-S induced immunity against MV alone. In summary, DV2 neutralizing responses can be generated by displaying E DIII on a scaffold of HBsAg-based VLPs, vectored by MV.

Genome rearrangement affects RNA virus adaptability on prostate cancer cells

Gene order is often highly conserved within taxonomic groups, such that organisms with rearranged genomes tend to be less fit than wild type gene orders, and suggesting natural selection favors genome architectures that maximize fitness. But it is unclear whether rearranged genomes hinder adaptability: capacity to evolutionarily improve in a new environment. Negative-sense non-segmented RNA viruses (order Mononegavirales) have specific genome architecture: 3' UTR - core protein genes - envelope protein genes - RNA-dependent RNA-polymerase gene - 5' UTR. To test how genome architecture affects RNA virus evolution, we examined vesicular stomatitis virus (VSV) variants with the nucleocapsid (N) gene moved sequentially downstream in the genome. Because RNA polymerase stuttering in VSV replication causes greater mRNA production in upstream genes, N gene translocation toward the 5' end leads to stepwise decreases in N transcription, viral replication and progeny production, and also impacts the activation of type 1 interferon mediated antiviral responses. We evolved VSV gene-order variants in two prostate cancer cell lines: LNCap cells deficient in innate immune response to viral infection, and PC-3 cells that mount an IFN stimulated anti-viral response to infection. We observed that gene order affects phenotypic adaptability (reproductive growth; viral suppression of immune function), especially on PC-3 cells that strongly select against virus infection. Overall, populations derived from the least-fit ancestor (most-altered N position architecture) adapted fastest, consistent with theory predicting populations with low initial fitness should improve faster in evolutionary time. Also, we observed correlated responses to selection, where viruses improved across both hosts, rather than suffer fitness trade-offs on unselected hosts. Whole genomics revealed multiple mutations in evolved variants, some of which were conserved across selective environments for a given gene order.

Reverse genetics of Mononegavirales: How they work, new vaccines, and new cancer therapeutics

The order Mononegavirales includes five families: Bornaviridae, Filoviridae, Nyamaviridae, Paramyxoviridae, and Rhabdoviridae. The genome of these viruses is one molecule of negative-sense single strand RNA coding for five to ten genes in a conserved order. The RNA is not infectious until packaged by the nucleocapsid protein and transcribed by the polymerase and co-factors. Reverse genetics approaches have answered fundamental questions about the biology of Mononegavirales. The lack of icosahedral symmetry and modular organization in the genome of these viruses has facilitated engineering of viruses expressing fluorescent proteins, and these fluorescent proteins have provided important insights about the molecular and cellular basis of tissue tropism and pathogenesis. Studies have assessed the relevance for virulence of different receptors and the interactions with cellular proteins governing the innate immune responses. Research has also analyzed the mechanisms of attenuation. Based on these findings, ongoing clinical trials are exploring new live attenuated vaccines and the use of viruses re-engineered as cancer therapeutics.

Development of a duplex real-time RT-qPCR assay to monitor genome replication, gene expression and gene insert stability during in vivo replication of a prototype live attenuated canine distemper virus vector encoding SIV gag

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The duplex assay monitored replication, tissue distribution, and mRNA expression.

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The duplex assay monitored insert genetic stability during in vivo replication.

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Primary site of CDV replication in ferrets was abdominal cavity lymphoid tissue.

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CDV gRNA or mRNA was undetectable in brain tissue.

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Specific primers were used in the RT step to distinguish gRNA from mRNA.

Advancement of new vaccines based on live viral vectors requires sensitive assays to analyze in vivo replication, gene expression and genetic stability. In this study, attenuated canine distemper virus (CDV) was used as a vaccine delivery vector and duplex 2-step quantitative real-time RT-PCR (RT-qPCR) assays specific for genomic RNA (gRNA) or mRNA have been developed that concurrently quantify coding sequences for the CDV nucleocapsid protein (N) and a foreign vaccine antigen (SIV Gag). These amplicons, which had detection limits of about 10 copies per PCR reaction, were used to show that abdominal cavity lymphoid tissues were a primary site of CDV vector replication in infected ferrets, and importantly, CDV gRNA or mRNA was undetectable in brain tissue. In addition, the gRNA duplex assay was adapted for monitoring foreign gene insert genetic stability during in vivo replication by analyzing the ratio of CDV N and SIV gag genomic RNA copies over the course of vector infection. This measurement was found to be a sensitive probe for assessing the in vivo genetic stability of the foreign gene insert.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.