Two-plasmid system to increase the rescue efficiency of paramyxoviruses by reverse genetics: The example of rescuing Newcastle Disease Virus

Rescuing Newcastle disease virus with tag for screening viral-host interacting proteins based on highly efficient reverse genetics

The interaction between viral proteins and host proteins plays a crucial role in the process of virus infecting cells. Tags such as HA, His, and Flag do not interfere with the function of fusion proteins and are commonly used to study protein-protein interactions. Adding these tags to viral proteins will address the challenge of the lack of antibodies for screening host proteins that interact with viral proteins during infection. Obtaining viruses with tagged fusion proteins is crucial. This study established a new reverse genetic system with T7 promoter and three plasmids, which efficiently rescued Newcastle disease virus (NDV) regardless of its ability to replicate in cells. Subsequently, using this system, NDV containing a HA-tagged structural protein and NDV carrying a unique tag on each structural protein were successfully rescued. These tagged viruses replicated normally and exhibited genetic stability. Based on tag antibodies, every NDV structural protein was readily detected and showed correct subcellular localization in infected cells. After infecting cells with NDV carrying HA-tagged M protein, several proteins interacting with the M protein during the infection process were screened using HA tag antibodies. The establishment of this system laid the foundation for comprehensive exploration of the interaction between NDV proteins and host proteins.

Generation of rescued Japanese encephalitis virus genotype 1 from infectious full-size clone using reverse genetics

Japanese encephalitis virus (JEV) is a pathogen responsible for high mortality and morbidity rates among children with encephalitis. Since JEV genotype 1 (GI) is the most prevalent strain in South Korea these days, corresponding research and vaccine development is urgently required. Molecular genetic studies on JEV vaccines can be boosted by obtaining genetically stable full-length infectious JEV complementary DNA (cDNA) clones. Furthermore, the significance of the reverse genetics system in facilitating molecular biological analyses of JEV properties has been demonstrated. This study constructed a recombinant JEV-GI strain using a reverse genetics system based on a Korean wild-type GI isolate (K05GS). RNA extracted from JEV-GI was used to synthesize cDNA, a recombinant full-length JEV clone, pTRE-JEVGI, was generated from the DNA fragment, and the virus was rescued. We performed in vitro and in vivo experiments to analyze the rescued JEV-GI virus. The rescued JEV-GI exhibited similar characteristics to wild-type JEV. These results suggest that our reverse genetics system can generate full-length infectious clones that can be used to analyze molecular biological factors that influence viral properties and immunogenicity. Additionally, it may be useful as a heterologous gene expression vector and help develop new strains for JEV vaccines.

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 improved system to generate recombinant canine distemper virus

BACKGROUND

Canine distemper virus (CDV) is a pathogen with the capability of cross-species transmission. It has crossed the species barrier to infect many other species, and its host range is expanding. The reverse genetic platform, a useful tool for scientific research, allows the generation of recombinant viruses from genomic cDNA clones in vitro.

METHODS

To improve the reverse genetic system of CDV, a plasmid containing three independent expression cassettes was constructed for co-expression of the N, P, and L genes and then transfected with a full-length cDNA clone of CDV into Vero cells.

RESULTS

The results indicated that the established rescue system has the advantages of being more convenient, easy to control the transfection ratio, and high rescue efficiency compared with the conventional reverse genetics system.

CONCLUSION

This method not only reduces the number of transfection plasmids, but also improves the rescue efficiency of CDV, which could provide a reference for the recovery of other morbilliviruses.

Negative-Strand RNA Virus-Vectored Vaccines

Vectored RNA vaccines offer a variety of possibilities to engineer targeted vaccines. They are cost-effective and safe, but replication competent, activating the humoral as well as the cellular immune system.This chapter focuses on RNA vaccines derived from negative-strand RNA viruses from the order Mononegavirales with special attention to Newcastle disease virus-based vaccines and their generation. It shall provide an overview on the advantages and disadvantages of certain vector platforms as well as their scopes of application, including an additional section on experimental COVID-19 vaccines.

Antigenic variation in hemagglutinin-neuraminidase of Newcastle disease virus isolated from Tibet, China

Vaccines are widely used to prevent Newcastle disease virus (NDV). Under the pressure of immunization, NDVs with mutations among epitopes of F and HN protein were isolated, which indicates that the efficiency of vaccine may decrease in terms of preventing emerged NDV. However, the lack of evidences to support whether these mutations contribute to antigenic mutation and immune escape in NDV leading to the controversy that the matched vaccine is more effective than the mismatched vaccine. In this study, a genotype VII velogenic NDV strain (C22) was isolated from a vaccinated farm in Tibet, China. We found that this strain was close to NDV from east China, but it had a specific mutation (K138R) in one epitope (131DYIGGIGKE139) of HN protein. This mutation might change the interaction between amino acids in stalk-head link region of HN protein and then induce the specific antibody to worse recognize the C22 strain, but it did not alter viral virulence and growth ability. Then, the C22 strain was attenuated via modification of the F protein cleavage site to generate a matched vaccine. Comparing to a mismatched vaccine (LaSota), this matched vaccine showed advantages in inhibiting viral shedding and tissue damage. However, both vaccines induced chicken to generate similar level of neutralizing antibodies against C22, C22mut (R138K) and LaSota. These results suggest that the epitope mutation is insufficient to help NDV escaping neutralizing antibodies of vaccinated chicken, supporting that the merits of NDV matched vaccine are not totally related to humoral immunity.

Concentrating all helper protein functions on a single entity allows rescue of recombinant measles virus by transfection of just two plasmids

The generation of recombinant measles virus (MeV) from manipulated genomes on plasmid DNA is quite a complex and inefficient process. As a member of the order Mononegavirales its single-stranded ssRNA genome in negative sense orientation is not infectious, but requires co-availability of the viral RNA-dependent RNA polymerase L, the polymerase co-factor phosphoprotein P, and the nucleocapsid protein N in defined relative amounts to establish infectious centres in transfected cell cultures that release replication-competent recombinant MeV particles. For this so-called rescue, different rescue systems were developed that rely on at least four different components. In this work, we establish a functional MeV rescue system just being composed of two components: the plasmid encoding the (modified) viral genome, and a one-helper-plasmid bundling all helper functions. In contrast to a rescue-system for Newcastle Disease Virus, another paramyxovirus, co-expression of all helper proteins by the same promoter failed. Instead, adaptation of the strength of the respective promoters to drive each helper gene´s expression to the relative expression found in MeV-infected cells or other rescue systems, which indeed adjusted respective mRNA and protein expression, yielded success, albeit not yet to the same efficacy as the four-component system. Thereby, our study paves the way for the development of easier and, after further optimization, more efficient rescue systems to generate recombinant MeV for e.g. the application as a vaccine platform or oncolytic virus, for example.

Chicken ISG12(2) attenuates Newcastle disease virus and enhances the efficiency of Newcastle disease vaccine via activating immune pathways

Low virulence and strong immunogenicity are quite important for Newcastle disease virus (NDV) producing Newcastle disease (ND) living-attenuated vaccine. However, immunogenicity of NDV positively correlates to its virulence. Usually, the velogenic NDV induces stronger immune responses of poultry than the lentogenic strain, but virulent NDV poses a risk for chicken. In this study, we identified the chicken interferon (IFN)-stimulated gene 12-2 (ISG12(2)) not only attenuated NDV, but also increased immunogenicity of ND vaccine strain. Firstly, we found that NDV infection or IFNs stimulation induced expression of chicken ISG12(2) that reinforced expression of IFNs. Overexpression or knockdown proved that chicken ISG12(2) inhibited NDV replication. Then, recombinant NDV LaSota strains (rLaSota/Fmut/ISG12(2) and rLaSota/ISG12(2)), expressing ISG12(2), were rescued. Pathogenicity tests showed that ISG12(2) expression attenuated NDV. RNA-seq or RT-qPCR demonstrated that, comparing to rLaSota/Fmut and rLaSota, rLaSota/Fmut/ISG12(2) and rLaSota/ISG12(2) induced hosts to produce cytokines enriching in innate and adaptive immune pathways in vitro and in vivo. Finally, we showed that rLaSota/ISG12(2) vaccination improved immune condition of chicken to quickly response NDV infection and then enhance protection. These results suggest that chicken ISG12(2) is a potential novel molecular adjuvant to regulate immune responses, which decrease virulence and increase immunogenicity of NDV. The chicken ISG12(2) may contribute to development of high efficient poultry vaccine. This article is protected by copyright. All rights reserved.

Rapid Generation of a Recombinant Genotype VIII Newcastle Disease Virus (NDV) Using Full-Length Synthetic cDNA

Rescue of (-)ssRNA viruses involves the sequential assembly and cloning of the full-length cDNA, which is often a challenging and time-consuming process. The objective of this study was to develop a novel method to rapidly clone the full-length cDNA of a very virulent NDV by only one assembly step. A completely synthetic 15 kb cDNA of a Malaysian genotype VIII NDV known as strain AF2240-I with additional flanking BsmBI sites was synthesised. However, to completely follow the rule-of-six, the additional G residues that are traditionally added after the T7 promoter transcription initiation site were not synthesised. The synthetic fragment was then cloned into low-copy number transcription vector pOLTV5-phiX between the T7 promoter and HDV Rz sequences through digestion with BbsI. The construct was co-transfected with helper plasmids into BSRT7/5 cells. A recombinant NDV called rAF was successfully rescued using transfection supernatant harvested as early as 16 h post-transfection. Virus from each passage showed an intracerebral pathogenicity index (ICPI) and a mean death time (MDT) similar to the parent strain AF2240-I. Moreover, rAF possessed an introduced mutation which was maintained for several passages. The entire rescue using the one-step assembly procedure was completed within a few weeks, which is extremely fast compared to previously used methods.

Exploring the Prospects of Engineered Newcastle Disease Virus in Modern Vaccinology

Many traditional vaccines have proven to be incapable of controlling newly emerging infectious diseases. They have also achieved limited success in the fight against a variety of human cancers. Thus, innovative vaccine strategies are highly needed to overcome the global burden of these diseases. Advances in molecular biology and reverse genetics have completely restructured the concept of vaccinology, leading to the emergence of state-of-the-art technologies for vaccine design, development and delivery. Among these modern vaccine technologies are the recombinant viral vectored vaccines, which are known for their incredible specificity in antigen delivery as well as the induction of robust immune responses in the vaccinated hosts. Although a number of viruses have been used as vaccine vectors, genetically engineered Newcastle disease virus (NDV) possesses some useful attributes that make it a preferable candidate for vectoring vaccine antigens. Here, we review the molecular biology of NDV and discuss the reverse genetics approaches used to engineer the virus into an efficient vaccine vector. We then discuss the prospects of the engineered virus as an efficient vehicle of vaccines against cancer and several infectious diseases of man and animals.

An improved method for the rescue of recombinant Newcastle disease virus

Reverse genetics has been used to generate recombinant Newcastle disease virus with enhanced immunogenic properties for vaccine development. The system, which involves co-transfecting the viral antigenomic plasmid with three helper plasmids into a T7 RNA polymerase-expressing cell to produce viral progenies, poses a great challenge. We have modified the standard transfection method to improve the transfection efficiency of the plasmids, resulting in a higher titer of virus progeny production. Two transfection reagents (i.e., lipofectamine and polyethylenimine) were used to compare the transfection efficiency of the four plasmids. The virus progenies produced were quantitated with flow cytometry analysis of the infectious virus unit. The modified transfection method increased the titer of virus progenies compared with that of the standard transfection method.

Host CARD11 Inhibits Newcastle Disease Virus Replication by Suppressing Viral Polymerase Activity in Neurons

Host factors play multiple essential roles in the replication and pathogenesis of mammalian neurotropic viruses. However, the cellular proteins of the central nervous system (CNS) involved in avian neurotropic virus infection have not been completely elucidated. Here, we employed a gene microarray to identify caspase recruitment domain-containing protein 11 (CARD11), a lymphoma-associated scaffold protein presenting brain-specific upregulated expression in a virulent neurotropic Newcastle disease virus (NDV)-infected natural host. Chicken primary neuronal cells infected with NDV appeared slightly syncytial and died quickly. CARD11 overexpression inhibited viral replication and delayed cytopathic effects; conversely, depletion of CARD11 enhanced viral replication and cytopathic effects in chicken primary neuronal cells. The inhibition of viral replication by CARD11 could not be blocked with CARD11-Bcl10-MALT1 (CBM) signalosome and NF-κB signaling inhibitors. CARD11 was found to interact directly with the viral phosphoprotein (P) through its CC1 domain and the X domain of P; this X domain also mediated the interaction between P and the viral large polymerase protein (L). The CARD11 CC1 domain and L competitively bound to P via the X domain that hindered the P-L interaction of the viral ribonucleoprotein (RNP) complex, resulting in a reduction of viral polymerase activity in a minigenome assay and inhibition of viral replication. Animal experiments further revealed that CARD11 contributed to viral replication inhibition and neuropathology in infected chicken brains. Taken together, our findings identify CARD11 as a brain-specific antiviral factor of NDV infection in avian species.IMPORTANCE Newcastle disease virus (NDV) substantially impacts the poultry industry worldwide and causes viral encephalitis and neurological disorders leading to brain damage, paralysis, and death. The mechanism of interaction between this neurotropic virus and the avian central nervous system (CNS) is largely unknown. Here, we report that host protein CARD11 presented brain-specific upregulated expression that inhibited NDV replication, which was not due to CARD11-Bcl10-MALT1 (CBM) complex-triggered activation of its downstream signaling pathways. The inhibitory mechanism of viral replication is through the CARD11 CC1 domain, and the viral large polymerase protein (L) competitively interacts with the X domain of the viral phosphoprotein (P), which hampers the P-L interaction, suppressing the viral polymerase activity and viral replication. An in vivo study indicated that CARD11 alleviated neuropathological lesions and reduced viral replication in chicken brains. These results provide insight into the interaction between NDV infection and the host defense in the CNS and a potential antiviral target for viral neural diseases.

Rescue of recombinant Newcastle disease virus: a promising vector with two decades of intensive vaccine research

Two decades have passed since the first reverse genetics system for the rescue of recombinant Newcastle disease virus was developed. Since then, the recombinant Newcastle disease virus vector has shown promising results as a safe and potent vector for development of many vaccines for both avian and human use. Herein, we review several technical topics that would be useful to further understanding of this technology. First, the effect of using helper plasmids encoding proteins belonging to strains other than the full-length cDNA and the possible incorporation of these expressed proteins into progeny virus will be discussed. Then, we will discuss the effect of removal of additional G residues from the T7 initiation sequence and finally, we will review different ways to improve rescue efficiency.

Reverse Genetics for Peste des Petits Ruminants Virus: Current Status and Lessons to Learn from Other Non-segmented Negative-Sense RNA Viruses

Peste des petits ruminants (PPR) is a highly contagious transboundary animal disease with a severe socio-economic impact on the livestock industry, particularly in poor countries where it is endemic. Full understanding of PPR virus (PPRV) pathobiology and molecular biology is critical for effective control and eradication of the disease. To achieve these goals, establishment of stable reverse genetics systems for PPRV would play a key role. Unfortunately, this powerful technology remains less accessible and poorly documented for PPRV. In this review, we discussed the current status of PPRV reverse genetics as well as the recent innovations and advances in the reverse genetics of other non-segmented negative-sense RNA viruses that could be applicable to PPRV. These strategies may contribute to the improvement of existing techniques and/or the development of new reverse genetics systems for PPRV.

Can genotype mismatch really affect the level of protection conferred by Newcastle disease vaccines against heterologous virulent strains?

Newcastle disease (ND), caused by virulent class II avian paramyxovirus 1 (Newcastle disease virus, NDV), occurs sporadically in poultry despite their having been immunized with commercial vaccines. These vaccines were all derived from NDV strains isolated around 70 years ago. Since then, class II NDV strains have evolved into 18 genotypes. Whether the vaccination failure results from genotype mismatches between the currently used vaccine strains and field-circulating velogenic strains or from an impaired immune response in the vaccination remains unclear. To test the first hypothesis, we performed a heterologous genotype II vaccine/genotype XI challenge in one-day old specific pathogen free (SPF) chicks and reproduced viral shedding. We then produced two attenuated strains of genotype II and XI by reverse genetics and used them to immunize two-week old SPF chickens that were subsequently challenged with velogenic strains of genotypes II, VII and XI. We found that both vaccines could induce antibodies with hemagglutination inhibition titers higher than 6.5 log₂. Vaccination also completely prevented disease, viral shedding in swabs, and blocked viral replication in tissues from different genotypes in contrast to unvaccinated chickens that died shortly after challenge. Taken together, our results support the hypothesis that, in immunocompetent poultry, genotype mismatch is not the main reason for vaccination failure.

Cleavage site of Newcastle disease virus determines viral fitness in persistent infection cells

Newcastle disease, caused by infection with virulent strains of Newcastle disease virus (NDV), poses a risk for the poultry industry. The virulence of NDV is mainly determined by the cleavage site of F protein. Lentogenic NDV can become velogenic after passages in SPF chicken brain and air sac based on some strains isolated from water birds, because the proportion of virulent-related strains gradually increases. In contrast, this proportion remains unchanged if NDV is passaged via 10-day-old SPF chicken embryos. This information suggests that environmental conditions rather than mutation affect NDV fitness in quasispecies. However, it is unknown how the environment selects virulent-related strains from a viral population. In this study, velogenic and lentogenic NDV marked by green or red fluorescence were used to establish persistent infection (PI) in BHK-21 cells. Monitoring viruses by different methods, we found that, without competition, persistently infected cells harbored lentogenic and velogenic NDV strains similarly in terms of viral release, viral spread and the period of persistent viral infection. In contrast, under competitive co-infection, velogenic NDV became dominant in quasispecies from the fifth passage of PI cells, which resulted in the progressive disappearance of the lentogenic NDV strain. This domination was concomitant with a short-term reduction in the superinfection exclusion and supernatant interference in PI cells resulting in a velogenic virus rebound. We concluded that virulent-related F protein cleavage site facilitates the spread and replication of NDV in conditions under which cells do not secret trypsin-like proteases and do not inhibit free virus infection, resulting in a gradual increase in virulent strains in quasispecies with the number of passages.

Rapid Construction of Complex Plant RNA Virus Infectious cDNA Clones for Agroinfection Using a Yeast-E. coli-Agrobacterium Shuttle Vector

The availability of infectious full-length clone is indispensable for reverse genetics studies of virus biology, pathology and construction of viral vectors. However, for RNA viruses with large genome sizes or those exhibiting inherent cloning difficulties, procedure to generate biologically active complementary DNA (cDNA) clones can be time-consuming or technically challenging. Here we have constructed a yeast-Escherichia coli-Agrobacterium shuttle vector that enables highly efficient homologous recombination in yeast for assembly of Agrobacterium compatible plant virus clones. Using this vector, we show that infectious cDNA clones of a plant negative-stranded RNA virus, sonchus yellow net rhabdovirus, can be rapidly assembled. In addition, one-step assembly of infectious clones of potato virus Y in yeast, either with or without intron, was readily achieved from as many as eight overlapping DNA fragments. More importantly, the recovered yeast plasmids can be transformed directly into Agrobacterium for inoculation, thereby obviating the E. coli cloning steps and associated toxicity issues. This method is rapid, highly efficient and cost-effective and should be readily applicable to a broad range of plant viruses.

Comparison of the efficiency of different newcastle disease virus reverse genetics systems

Rescue of negative-sense single-stranded RNA viruses ((-)ssRNA virus), generally requires the handling of a large number of plasmids to provide the virus genome and essential components for gene expression and genome replication. This constraint probably renders reverse genetics of (-)ssRNA virus more complex and less efficient. Some authors have shown that the fewer the plasmids, the more efficient reverse genetics is for segmented RNA virus. However, it is not clear if the same applies for (-)ssRNA, such as Newcastle disease virus (NDV). To address this issue, six variants of NDV reverse genetic systems were established by cloning combinations of NP, P and L genes, mini-genome or full-genome in 4, 3, 2 and 1 plasmid. In terms of mini-genome and full-genome rescue, we showed that only the 2-plasmid system, assembling three support plasmids together, was able to improve the rescue efficiency over that of the conventional 4-plasmid system. These results may help establish and/or improve reverse genetics for other mononegaviruses.