Rescue of rinderpest virus from cloned cDNA

Reverse Genetics Systems for the De Novo Rescue of Diverse Members of Paramyxoviridae

Paramyxoviruses place significant burdens on both human and wildlife health; while some paramyxoviruses are established within human populations, others circulate within diverse animal reservoirs. Concerningly, bat-borne paramyxoviruses have spilled over into humans with increasing frequency in recent years, resulting in severe disease. The risk of future zoonotic outbreaks, as well as the persistence of paramyxoviruses that currently circulate within humans, highlights the need for efficient tools through which to interrogate paramyxovirus biology. Reverse genetics systems provide scientists with the ability to rescue paramyxoviruses de novo, offering versatile tools for implementation in both research and public health settings. Reverse genetics systems have greatly improved over the past 30 years, with several key innovations optimizing the success of paramyxovirus rescue. Here, we describe the significance of such advances and provide a generally applicable guide for the development and use of reverse genetics systems for the rescue of diverse members of Paramyxoviridae.

Development and application of reverse genetic technology for the influenza virus

Influenza virus is a common virus in people's daily lives, and it has certain infectivity in humans and animals. Influenza viruses have the characteristics of a high mutation rate and wide distribution. Reverse genetic technology is primarily used to modify viruses at the DNA level through targeted modification of the virus cDNA. Genetically modified influenza viruses have a unique advantage when researching the transmission and pathogenicity of influenza. With the continuous development of oncolytic viruses in recent years, studies have found that influenza viruses also have certain oncolytic activity. Influenza viruses can specifically recognize tumor cells; activate cytotoxic T cells, NK cells, dendritic cells, etc.; and stimulate the body to produce an immune response, thereby killing tumor cells. This article will review the development and application of influenza virus reverse genetic technology.

Measles virus and rinderpest virus divergence dated to the sixth century BCE

Many infectious diseases are thought to have emerged in humans after the Neolithic revolution. Although it is broadly accepted that this also applies to measles, the exact date of emergence for this disease is controversial. We sequenced the genome of a 1912 measles virus and used selection-aware molecular clock modeling to determine the divergence date of measles virus and rinderpest virus. This divergence date represents the earliest possible date for the establishment of measles in human populations. Our analyses show that the measles virus potentially arose as early as the sixth century BCE, possibly coinciding with the rise of large cities.

A ligation and restriction enzyme independent cloning technique: an alternative to conventional methods for cloning hard-to-clone gene segments in the influenza reverse genetics system

BACKGROUND

Reverse genetics is used in many laboratories around the world and enables the creation of tailor-made influenza viruses with a desired genotype or phenotype. However, the process is not flawless, and difficulties remain during cloning of influenza gene segments into reverse genetics vectors (pHW2000, pHH21, pCAGGS). Reverse genetics begins with making cDNA copies of influenza gene segments and cloning them into bi-directional (pHW2000) or uni-directional plasmids (pHH21, pCAGGS) followed by transfection of the recombinant plasmid(s) to HEK-293 T or any other suitable cells which are permissive to transfection. However, the presence of internal restriction sites in the gene segments of many field isolates of avian influenza viruses makes the cloning process difficult, if employing conventional methods. Further, the genetic instability of influenza gene-containing plasmids in bacteria (especially Polymerase Basic 2 and Polymerase Basic 1 genes; PB2 and PB1) also leads to erroneous incorporation of bacterial genomic sequences into the influenza gene of interest.

METHODS

Herein, we report an easy and efficient ligation and restriction enzyme independent (LREI) cloning method for cloning influenza gene segments into pHW2000 vector. The method involves amplification of megaprimers followed by PCR amplification of megaprimers using a bait plasmid, DpnI digestion and transformation.

RESULTS

Hard-to-clone genes: PB2 of A/chicken/Bangladesh/23527/2014 (H9N2) and PB1 of A/chicken/Bangladesh/23527/2014 (H9N2), A/chicken/Jiangxi/02.05YGYXG023-P/2015 (H5N6) and A/Chicken/Vietnam/H7F-14-BN4-315/2014 (H9N2) were cloned into pHW2000 using our LREI method and recombinant viruses were subsequently rescued.

CONCLUSION

The LREI cloning procedure represents an alternative strategy for cloning influenza gene segments which have internal restriction sites for the enzymes used in reverse genetics. Further, the problem of genetic instability in bacteria can be alleviated by growing recombinant bacterial cultures at a lower temperature. This technique can be applied to clone any influenza gene segment using universal primers, which would help in rapid generation of influenza viruses and facilitate influenza research and vaccine development.

Full genome sequencing of archived wild type and vaccine rinderpest virus isolates prior to their destruction

When rinderpest virus (RPV) was declared eradicated in 2011, the only remaining samples of this once much-feared livestock virus were those held in various laboratories. In order to allow the destruction of our institute's stocks of RPV while maintaining the ability to recover the various viruses if ever required, we have determined the full genome sequence of all our distinct samples of RPV, including 51 wild type viruses and examples of three different types of vaccine strain. Examination of the sequences of these virus isolates has shown that the African isolates form a single disparate clade, rather than two separate clades, which is more in accord with the known history of the virus in Africa. We have also identified two groups of goat-passaged viruses which have acquired an extra 6 bases in the long untranslated region between the M and F protein coding sequences, and shown that, for more than half the genomes sequenced, translation of the F protein requires translational frameshift or non-standard translation initiation. Curiously, the clade containing the lapinised vaccine viruses that were developed originally in Korea appears to be more similar to the known African viruses than to any other Asian viruses.

Peste des petits ruminants in China since its first outbreak in 2007: A 10-year review

Peste des petits ruminants (PPR) is a highly infectious disease of small ruminants and caused by small ruminant morbillivirus (SRMV), formerly called peste-des-petits-ruminants virus (PPRV). This disease is circulating in Africa (except most countries in southern Africa), the Arabian Peninsula, the Middle East, and Central, East and South-East Asia. Peste des petits ruminants is still regarded as an exotic disease in China, where its first outbreak was reported in the Ngari region of Tibet in 2007, but effectively controlled by slaughter, vaccination and animal movement restriction in PPR-infected areas. However, PPR re-emerged in Xinjiang of China in December 2013, rapidly spread into much of China in the first half of 2014, but since then was substantially inhibited countrywide. Phylogenetic analysis shows that SRMVs from China share the highest homology with others from its neighbouring countries, possibly indicating the transboundary transmission of SRMVs. In 2015, a national eradication program for PPR was issued and has been being implemented in China, expecting to achieve a PPR-eradicating aim countrywide by 2020. Here, we reviewed a 10-year history (2007-2017) of PPR in China, including two major outbreaks, its infection in wild species, development of diagnostics and vaccines, and implementation of the national eradication program.

Efficient and Robust Paramyxoviridae Reverse Genetics Systems

The ability to manipulate the genome of paramyxoviruses and evaluate the effects of these changes at the phenotypic level is a powerful tool for the investigation of specific aspects of the viral life cycle and viral pathogenesis. However, reverse genetics systems for paramyxoviruses are notoriously inefficient, when successful. The ability to efficiently and robustly rescue paramyxovirus reverse genetics systems can be used to answer basic questions about the biology of paramyxoviruses, as well as to facilitate the considerable translational efforts being devoted to developing live attenuated paramyxovirus vaccine vectors.

The notoriously low efficiency of Paramyxoviridae reverse genetics systems has posed a limiting barrier to the study of viruses in this family. Previous approaches to reverse genetics have utilized a wide variety of techniques to overcome the technical hurdles. Although robustness (i.e., the number of attempts that result in successful rescue) has been improved in some systems with the use of stable cell lines, the efficiency of rescue (i.e., the proportion of transfected cells that yield at least one successful rescue event) has remained low. We have substantially increased rescue efficiency for representative viruses from all five major Paramyxoviridae genera (from ~1 in 10⁶-10⁷ to ~1 in 10²-10³ transfected cells) by the addition of a self-cleaving hammerhead ribozyme (Hh-Rbz) sequence immediately preceding the start of the recombinant viral antigenome and the use of a codon-optimized T7 polymerase (T7opt) gene to drive paramyxovirus rescue. Here, we report a strategy for robust, reliable, and high-efficiency rescue of paramyxovirus reverse genetics systems, featuring several major improvements: (i) a vaccinia virus-free method, (ii) freedom to use any transfectable cell type for viral rescue, (iii) a single-step transfection protocol, and (iv) use of the optimal T7 promoter sequence for high transcription levels from the antigenomic plasmid without incorporation of nontemplated G residues. The robustness of our T7opt-HhRbz system also allows for greater latitude in the ratios of transfected accessory plasmids used that result in successful rescue. Thus, our system may facilitate the rescue and interrogation of the increasing number of emerging paramyxoviruses.

IMPORTANCE The ability to manipulate the genome of paramyxoviruses and evaluate the effects of these changes at the phenotypic level is a powerful tool for the investigation of specific aspects of the viral life cycle and viral pathogenesis. However, reverse genetics systems for paramyxoviruses are notoriously inefficient, when successful. The ability to efficiently and robustly rescue paramyxovirus reverse genetics systems can be used to answer basic questions about the biology of paramyxoviruses, as well as to facilitate the considerable translational efforts being devoted to developing live attenuated paramyxovirus vaccine vectors.

Advances in peste des petits ruminants vaccines

Peste des petits ruminants (PPR) is a highly contagious disease of small ruminants that leads to high morbidity and mortality thereby results in devastating economic consequences to the livestock industry. PPR is currently endemic across most parts of Asia and Africa, the two regions with the highest concentration of poor people in the world. Sheep and goats in particularly contribute significantly towards the upliftment of livelihood of the poor and marginal farmers in these regions. In this context, PPR directly affecting the viability of sheep and goat husbandry has emerged as a major hurdle in the development of these regions. The control of PPR in these regions could significantly contribute to poverty alleviation, therefore, the Office International des Epizooties (OIE) and Food and Agricultural Organization (FAO) have targeted the control and eradication of PPR by 2030 a priority. In order to achieve this goal, a potent, safe and efficacious live-attenuated PPR vaccine with long-lasting immunity is available for immunoprophylaxis. However, the live-attenuated PPR vaccine is thermolabile and needs maintenance of an effective cold chain to deliver into the field. In addition, the infected animals cannot be differentiated from vaccinated animals. To overcome these limitations, some recombinant vaccines have been developed. This review comprehensively describes about the latest developments in PPR vaccines.

Infectious Progression of Canine Distemper Virus from Circulating Cerebrospinal Fluid into the Central Nervous System

In the current study, we generated recombinant chimeric canine distemper viruses (CDVs) by replacing the hemagglutinin (H) and/or phosphoprotein (P) gene in an avirulent strain expressing enhanced green fluorescent protein (EGFP) with those of a mouse-adapted neurovirulent strain. An in vitro experimental infection indicated that the chimeric CDVs possessing the H gene derived from the mouse-adapted CDV acquired infectivity for neural cells. These cells lack the CDV receptors that have been identified to date (SLAM and nectin-4), indicating that the H protein defines infectivity in various cell lines. The recombinant viruses were administered intracerebrally to 1-week-old mice. Fatal neurological signs of disease were observed only with a recombinant CDV that possessed both the H and P genes of the mouse-adapted strain, similar to the parental mouse-adapted strain, suggesting that both genes are important to drive virulence of CDV in mice. Using this recombinant CDV, we traced the intracerebral propagation of CDV by detecting EGFP. Widespread infection was observed in the cerebral hemispheres and brainstems of the infected mice. In addition, EGFP fluorescence in the brain slices demonstrated a sequential infectious progression in the central nervous system: CDV primarily infected the neuroependymal cells lining the ventricular wall and the neurons of the hippocampus and cortex adjacent to the ventricle, and it then progressed to an extensive infection of the brain surface, followed by the parenchyma and cortex. In the hippocampal formation, CDV spread in a unidirectional retrograde pattern along neuronal processes in the hippocampal formation from the CA1 region to the CA3 region and the dentate gyrus. Our mouse model demonstrated that the main target cells of CDV are neurons in the acute phase and that the virus spreads via neuronal transmission pathways in the hippocampal formation.

IMPORTANCE

CDV is the etiological agent of distemper in dogs and other carnivores, and in many respects, the pathogenesis of CDV infection in animals resembles that of measles virus infection in humans. We successfully generated a recombinant CDV containing the H and P genes from a mouse-adapted neurovirulent strain and expressing EGFP. The recombinant CDV exhibited severe neurovirulence with high mortality, comparable to the parental mouse-adapted strain. The mouse-infectious model could become a useful tool for analyzing CDV infection of the central nervous system subsequent to passing through the blood-cerebrospinal fluid barrier and infectious progression in the target cells in acute disease.

Protection of Cattle against Rinderpest by Vaccination with Wild-Type but Not Attenuated Strains of Peste des Petits Ruminants Virus

Although rinderpest virus (RPV) has been eradicated in the wild, efforts are still continuing to restrict the extent to which live virus is distributed in facilities around the world and to prepare for any reappearance of the disease, whether through deliberate or accidental release. In an effort to find an alternative vaccine which could be used in place of the traditional live attenuated RPV strains, we have determined whether cattle can be protected from rinderpest by inoculation with vaccine strains of the related morbillivirus, peste des petits ruminants virus (PPRV). Cattle were vaccinated with wild-type PPRV or either of two established PPRV vaccine strains, Nigeria/75/1 or Sungri/96. All animals developed antibody and T cell immune responses to the inoculated PPRV. However, only the animals given wild-type PPRV were protected from RPV challenge. Animals given PPRV/Sungri/96 were only partially protected, and animals given PPRV/Nigeria/75/1 showed no protection against RPV challenge. While sera from animals vaccinated with the vaccine strain of RPV showed cross-neutralizing ability against PPRV, none of the sera from animals vaccinated with any strain of PPRV was able to neutralize RPV although sera from animals inoculated with wild-type PPRV were able to neutralize RPV-pseudotyped vesicular stomatitis virus.

IMPORTANCE

Rinderpest virus has been eradicated, and it is only the second virus for which this is so. Significant efforts are still required to ensure preparedness for a possible escape of RPV from a laboratory or its deliberate release. Since RPV vaccine protects sheep and goats from PPRV, it is important to determine if the reverse is true as this would provide a non-RPV vaccine for dealing with suspected RPV outbreaks. This is probably the last in vivo study with live RPV that will be approved.

Development of a helper cell-dependent form of peste des petits ruminants virus: a system for making biosafe antigen

Peste des petits ruminants (PPR) is a viral disease of sheep and goats that is spreading through many countries in the developing world. Work on the virus is often restricted to studies of attenuated vaccine strains or to work in laboratories that have high containment facilities. We have created a helper cell dependent form of PPR virus by removing the entire RNA polymerase gene and complementing it with polymerase made constitutively in a cell line. The resultant L-deleted virus grows efficiently in the L-expressing cell line but not in other cells. Virus made with this system is indistinguishable from normal virus when used in diagnostic assays, and can be grown in normal facilities without the need for high level biocontainment. The L-deleted virus will thus make a positive contribution to the control and study of this important disease.

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.

Recombinant DNA technology for producing new rinderpest virus vaccines

With few exceptions, vaccination aims to control rather than eliminate or eradicate disease. The eradication of smallpox in the 1970s led to two other human diseases, polio and measles, being targeted for eradication by the World Health Organization. In general, animal diseases are ignored by the public, however, recent targeting of the rinderpest virus, the agent of cattle plague, has put this virus on the verge of global extinction. For centuries, this virus was responsible for major cattle plagues in Europe, Asia and Africa. The success of the Global Rinderpest Eradication Program is an illustration of the power of vaccines to alter people's lives economically and socially when used in an internationally coordinated way. In this review, the history of the development of rinderpest vaccines and the new research being undertaken to produce marker vaccines, using recombinant DNA technology and reverse genetics, are described. In addition, the valuable contribution that marker vaccines can make in the final stages of the rinderpest eradication program is outlined.

Rapid Recovery of Classical Swine Fever Virus Directly from Cloned cDNA

The reverse genetics for classical swine fever virus (CSFV) is currently based on the transfection of in vitro transcribed RNA from a viral genomic cDNA clone, which is inefficient and time-consuming. This study was aimed to develop an improved method for rapid recovery of CSFV directly from cloned cDNA. Full-length genomic cDNA from the CSFV Shimen strain, which was flanked by a T7 promoter, the hepatitis delta virus ribozyme and T7 terminator sequences, was cloned into the low-copy vector pOK12, producing pOKShimen-RzTΦ. Direct transfection of pOKShimen-RzTΦ into PK/T7 cells, a PK-15-derived cell line stably expressing bacteriophage T7 RNA polymerase, allowed CSFV to be rescued rapidly and efficiently, i.e., at least 12 h faster and 31.6-fold greater viral titer when compared with the in vitro transcription-based rescue system. Furthermore, the progeny virus rescued from PK/T7 cells was indistinguishable, both in vitro and in vivo, from its parent virus and the virus rescued from classical reverse genetics. The reverse genetics based on intracellular transcription is efficient, convenient and cost-effective. The PK/T7 cell line can be used to rescue CSFV directly from cloned cDNA and it can also be used as an intracellular transcription and expression system for studying the structure and function of viral genes.

Creation of a completely helper cell-dependent recombinant morbillivirus

We have created a completely helper cell-dependent morbillivirus by modifying the genome to remove the coding sequence of the phosphoprotein (P) and recovering the recombinant virus in a cell line constitutively expressing the P protein. The P protein-deleted virus (P⁻) grew very inefficiently unless both of the viral accessory proteins (V and C) were also expressed. Growth of the virus was restricted to the P-expressing cell line. The P⁻ virus grew more slowly than the parental virus and expressed much less viral protein in infected cells. The technique could be used to create virus-like particles for use as a vaccine or as antigen in immunological or serological assays.

Reverse Genetics of Mononegavirales: The Rabies Virus Paradigm

The neurotropic rabies virus (RABV) is a prototype member of the Mononegavirales order of viruses and is the most significant human pathogen of the Rhabdoviridae family. A reverse genetics system for RABV was established almost 20 years ago, providing a paradigm for other Mononegavirales members as well. The availability of engineered recombinant viruses opened a new era to study common aspects of Mononegavirales biology and specific aspects of the unique lifestyle and pathogenesis of individual members. Above all, the knowledge gained has allowed engineering of beneficial biomedical tools such as viral vectors, vaccines, and tracers. In this chapter, the development of the classical rabies virus reverse genetics approach is described, and some of the most exciting biomedical applications for recombinant RABV and other Mononegavirales are briefly addressed.

Phosphorylation of measles virus phosphoprotein at S86 and/or S151 downregulates viral transcriptional activity

Measles virus phosphoprotein (P protein) is a cofactor of the viral RNA polymerase (L protein) that associates with the nucleoprotein-RNA complex to support viral transcription and replication. Here, we report a significant inverse correlation between the phosphorylation level of MV-P protein and viral transcriptional activity. Upregulation of P protein phosphorylation resulted in reduction of viral transcription. Additionally, we found that strong phosphorylation at S86 and S151 of P protein, which may be generally prevented by association with nucleoprotein, downregulates the viral transcriptional activity. These findings suggest that P protein is involved in regulation of viral transcription through changes in its phosphorylation status.

Rescue of recombinant peste des petits ruminants virus: creation of a GFP-expressing virus and application in rapid virus neutralization test

Peste des petits ruminants virus (PPRV) causes high mortality in goats and sheep and the disease has shown a greatly increased geographic distribution over the last 15 years. It is responsible for serious socioeconomic problems in some of the poorest developing countries. The ability to create recombinant PPRV would provide a useful tool for investigating the biology of the virus and the pathology of disease, as well as for developing new vaccines and diagnostic methods. Here we report the first successful rescue of recombinant PPRV from a full-length cDNA clone of the virus genome. Successful recovery of PPRV was achieved by using a RNA polymerase II promoter to drive transcription of the full-length virus antigenome. We have used this technique to construct a virus expressing a tracer protein (green fluorescent protein, GFP). The recombinant virus replicated as well as the parental virus and could stably express GFP during at least 10 passages. The newly established reverse genetics system for PPRV provides a novel method for constructing a vaccine using PPRV as a vector, and will also prove valuable for fundamental research on the biology of the virus. We found that our recombinant virus allowed more rapid and higher throughput assessment of PPRV neutralization antibody titer via the virus neutralization test (VNT) compared with the traditional method.

Multigene expression in vivo: supremacy of large versus small terminators for T7 RNA polymerase

Designing and building multigene constructs is commonplace in synthetic biology. Yet functional successes at first attempts are rare because the genetic parts are not fully modular. In order to improve the modularity of transcription, we previously showed that transcription termination in vitro by bacteriophage T7 RNA polymerase could be made more efficient by substituting the standard, single, TΦ large (class I) terminator with adjacent copies of the vesicular stomatitis virus (VSV) small (class II) terminator. However, in vitro termination at the downstream VSV terminator was less efficient than at the upstream VSV terminator, and multigene overexpression in vivo was complicated by unexpectedly inefficient VSV termination within Escherichia coli cells. Here, we address hypotheses raised in that study by showing that VSV or preproparathyroid hormone (PTH) small terminators spaced further apart can work independently (i.e., more efficiently) in vitro, and that VSV and PTH terminations are severely inhibited in vivo. Surprisingly, the difference between class II terminator function in vivo versus in vitro is not due to differences in plasmid supercoiling, as supercoiling had a minimal effect on termination in vitro. We therefore turned to TΦ terminators for "BioBrick" synthesis of a pentameric gene construct suitable for overexpression in vivo. This indeed enabled coordinated overexpression and copurification of five His-tagged proteins using the first construct attempted, indicating that this strategy is more modular than other strategies. An application of this multigene overexpression and protein copurification method is demonstrated by supplying five of the six E. coli translation factors required for reconstitution of translation from a single cell line via copurification, greatly simplifying the reconstitution.

Evaluation of the human host range of bovine and porcine viruses that may contaminate bovine serum and porcine trypsin used in the manufacture of biological products

Current U.S. requirements for testing cell substrates used in production of human biological products for contamination with bovine and porcine viruses are U.S. Department of Agriculture (USDA) 9CFR tests for bovine serum or porcine trypsin. 9CFR requires testing of bovine serum for seven specific viruses in six families (immunofluorescence) and at least 2 additional families non-specifically (cytopathicity and hemadsorption). 9CFR testing of porcine trypsin is for porcine parvovirus. Recent contaminations suggest these tests may not be sufficient. Assay sensitivity was not the issue for these contaminations that were caused by viruses/virus families not represented in the 9CFR screen. A detailed literature search was undertaken to determine which viruses that infect cattle or swine or bovine or porcine cells in culture also have human host range [ability to infect humans or human cells in culture] and to predict their detection by the currently used 9CFR procedures. There are more viruses of potential risk to biological products manufactured using bovine or porcine raw materials than are likely to be detected by 9CFR testing procedures; even within families, not all members would necessarily be detected. Testing gaps and alternative methodologies should be evaluated to continue to ensure safe, high quality human biologicals.

Determination of a phosphorylation site in Nipah virus nucleoprotein and its involvement in virus transcription

Many viruses use their host’s cellular machinery to regulate the functions of viral proteins. The phosphorylation of viral proteins is known to play a role in genome transcription and replication in paramyxoviruses. The paramyxovirus nucleoprotein (N), the most abundant protein in infected cells, is a component of the N–RNA complex and supports the transcription and replication of virus mRNA and genomic RNA. Recently, we reported that the phosphorylation of measles virus N is involved in the regulation of viral RNA synthesis. In this study, we report a rapid turnover of phosphorylation in the Nipah virus N (NiV-N). The phosphorylated NiV-N was hardly detectable in steady-state cells, but was detected after inhibition of cellular protein phosphatases. We identified a phosphorylated serine residue at Ser451 of NiV-N by peptide mass fingerprinting by electrospray ionization–quadrupole time-of-flight mass spectrometry. In the NiV minigenome assay, using luciferase as a reporter gene, the substitution of Ser451 for alanine in NiV-N resulted in a reduction in luciferase activity of approximately 45 % compared with the wild-type protein. Furthermore, the substitution of Ser451 for glutamic acid, which mimics a phosphoserine, led to a more significant decrease in luciferase activity – approximately 81 %. Northern blot analysis showed that both virus transcription and replication were reduced by these mutations. These results suggest that a rapid turnover of the phosphorylation of NiV-N plays an important role in virus transcription and replication.

Novel phosphoprotein-interacting region in Nipah virus nucleocapsid protein and its involvement in viral replication

The interaction of Nipah virus (NiV) nucleocapsid (N) protein with phosphoprotein (P) during nucleocapsid assembly is the essential process in the viral life cycle, since only the encapsidated RNA genome can be used for replication. To identify the region responsible for N-P interaction, we utilized fluorescent protein tags to visualize NiV N and P proteins in live cells and analyzed their cellular localization. N protein fused to monomeric enhanced cyan fluorescence protein (N-ECFP) exhibited a dotted pattern in transfected cells, while P protein fused to monomeric red fluorescent protein (P-mRFP) showed diffuse distribution. When the two proteins were coexpressed, P-mRFP colocalized with N-ECFP dots. N-ECFP mutants with serial amino acid deletions were generated to search for the region(s) responsible for this N-P colocalization. We found that, in addition to the 467- to 496-amino-acid (aa) region reported previously, aa 135 to 146 were responsible for the N-P colocalization. The residues crucial for N-P interaction were further investigated by introducing alanine substitutions into the untagged N protein. Alanine scanning in the region of aa 135 to 146 has revealed that there are distinct regions essential for the interaction of N-P and the function of N. This is the first study to visualize Nipah viral proteins in live cells and to assess the essential domain of N protein for the interaction with P protein.

Engineering multigene expression in vitro and in vivo with small terminators for T7 RNA polymerase

Engineering protein expression in vitro or in vivo is usually straightforward for single genes, but remains challenging for multiple genes because of the requirement of coordinated control. RNA and protein overexpression strategies often exploit T7 RNA polymerase and its natural TPhi Class I terminator. However, this terminator's inefficiency and large size (100 bp) are problematic for multigene construction and expression. Here, we measure the effects of tandem copies of a small (18 bp) Class II T7 terminator from vesicular stomatitis virus on transcription in vitro and on translation in vitro and in vivo. We first test monomeric and dimeric gene constructs, then attempt extension to pentameric gene constructs. "BioBrick" versions of a pET vector and translation factor genes were constructed to facilitate cloning, and His-tags were incorporated to allow copurification of all protein products for relatively unbiased analysis and easy purification. Several results were surprising, including imbalanced expression of the pentameric constructs in vivo, illustrating the value of synthetic biology for investigating gene expression. However, these problems were solved rationally by changing the orders of the genes and by adding extra promoters to the upstream gene or by moving to a more predictable in vitro translation system. These successes were significant, given our initial unexpected results and that we are unaware of another example of coordinated overexpression of five proteins. Our modular, flexible, rational method should further empower synthetic biologists wishing to overexpress multiple proteins simultaneously.

Comparative and mutational analyses of promoter regions of rinderpest virus

Comparative and mutational analysis of promoter regions of rinderpest virus was conducted. Minigenomic RNAs harboring the genomic and antigenomic promoter of the lapinized virulent strain (Lv) or an attenuated vaccine strain (RBOK) were constructed, and the expression of the reporter gene was examined. The activities of the antigenomic promoters of these strains were similar, whereas the activity of the genomic promoter (GP) of the RBOK strain was significantly higher than that of the Lv strain, regardless of cell type and the source of the N, P and L proteins. Increased replication (and/or encapsidation) activities were observed in the minigenomes that contained RBOK GP. Mutational analysis revealed that the nucleotides specific to the RBOK strain are responsible for the strong GP activity of the strain. It was also demonstrated that other virulent strains of RPV (Kabete O, Saudi/81 and Kuwait 82/1) have weaker GPs than that of the RBOK strain.

Infection of bovine dendritic cells by rinderpest or measles viruses induces different changes in host transcription

The morbilliviruses are a closely related genus which are very similar in their sequences and share a common receptor, but nevertheless show significant restriction in the host species in which they cause disease. One contribution to this restriction might be the nature of the hosts' responses to infection. We have used microarrays to study the changes in the transcriptome of bovine dendritic cells after infection with wild-type (pathogenic) and vaccine (apathogenic) strains of rinderpest virus (RPV), a bovine pathogen, and a wild-type isolate of measles virus (MV), a morbillivirus that causes disease only in humans and some other primates. We found that, as previously observed in human cells, MV induces a rapid interferon response, while that induced by RPV was delayed and much reduced in magnitude. Pathogenic and apathogenic RPV also showed significant differences, with the latter inducing a slightly higher interferon response as well as significant effects on transcription of genes involved in cell cycle regulation.

Reverse genetics of measles virus and resulting multivalent recombinant vaccines: applications of recombinant measles viruses

An overview is given on the development of technologies to allow reverse genetics of RNA viruses, i.e., the rescue of viruses from cDNA, with emphasis on nonsegmented negative-strand RNA viruses ( Mononegavirales ), as exemplified for measles virus (MV). Primarily, these technologies allowed site-directed mutagenesis, enabling important insights into a variety of aspects of the biology of these viruses. Concomitantly, foreign coding sequences were inserted to (a) allow localization of virus replication in vivo through marker gene expression, (b) develop candidate multivalent vaccines against measles and other pathogens, and (c) create candidate oncolytic viruses. The vector use of these viruses was experimentally encouraged by the pronounced genetic stability of the recombinants unexpected for RNA viruses, and by the high load of insertable genetic material, in excess of 6 kb. The known assets, such as the small genome size of the vector in comparison to DNA viruses proposed as vectors, the extensive clinical experience of attenuated MV as vaccine with a proven record of high safety and efficacy, and the low production cost per vaccination dose are thus favorably complemented.

Defense Against Biological Weapons (Biodefense)

Biological warfare (germ warfare) is defined as the use of any disease-causing organism or toxin(s) found in nature as weapons of war with the intent to destroy an adversary. Though rare, the use of biological weapons has occurred throughout the centuries.

The rinderpest virus non-structural C protein blocks the induction of type 1 interferon

The innate immune response, in particular the production of type 1 interferons, is an essential part of the mammalian host response to viral infection. We have previously shown that rinderpest virus, a morbillivirus closely related to the human pathogen measles virus, blocks the actions of type 1 and type 2 interferons. We show here that this virus can also block the induction of type 1 interferon. The viral non-structural C protein appears to be the active agent, since expressing this protein in cells makes them resistant to activation of the interferon-beta promoter while recombinant virus that does not express the C protein activates this promoter much more than virus expressing the C protein. In addition, differences in activation of the interferon-beta promoter by different strains of rinderpest virus are reflected in differing abilities of their respective C proteins to block activation of the promoter by dsRNA. The C protein blocks the activation of this promoter induced by either cytoplasmic dsRNA or by Newcastle disease virus (NDV) infection, as well as activation induced by overexpression of several elements of the signalling pathway, including mda-5, RIG-I and IRF-3. The RPV C protein also blocks transcription from promoters responsive individually to the three transcription factors that make up the interferon-beta promoter enhanceosome, although it does not appear to block the activation of IRF-3.

Identification of functional domains of phosphoproteins of two morbilliviruses using chimeric proteins

The paramyxovirus P protein is an essential component of the transcriptase and replicase complex along with L protein. In this article, we have examined the functional roles of different domains of P proteins of two closely related morbilliviruses, Rinderpest virus (RPV) and Peste des petits ruminants virus (PPRV). The PPRV P protein physically interacts with RPV L as well as RPV N protein when expressed in transfected cells, as shown by co-immunoprecipitation. The heterologous L-P complex is biologically active when tested in a RPV minigenome replication/transcription system, only when used with PPRV N protein but not with RPV N protein. Employing chimeric PPRV/RPV cDNAs having different coding regions of P protein in the minigenome replication/transcription system, we identified a region between 290 and 346 aa in RPV P protein necessary for transcription of the minigenome.

Scalable culture systems using different cell lines for the production of Peste des Petits ruminants vaccine

Peste des Petits ruminants (PPR) is considered as one of the major constraints to the productivity of small ruminants in Africa and Asian countries. Currently PPR control is done by vaccination with an attenuated PPR strain (Nigeria 75/1) produced in monolayers of Vero cells grown in roller bottles or static flasks. This work focuses on the production of a PPR vaccine strain using stirred conditions as an advanced option for process scale-up. Non-porous microcarriers (Cytodex-1) were used to support Vero cell growth in suspension cultures. The use of Ex-Cell medium could improve cell specific productivities obtained with standard serum containing medium, independently of the type of system used, i.e. static as well as suspension stirred cultures. As an alternative, several cell lines adapted to grow as single cells in suspension (CHO-K1, BHK-21A and 293) and another anchorage-dependent (MRC-5) were evaluated in their capacity to produce a PPR vaccine. BHK-21A and 293 cells grown as single-cell suspension in serum free medium were both suited to produce PPR vaccine with productivities similar to Vero cells, namely 10(6)TCID(50)/mL. However, for the 293 cells, these results were only obtained 2-3 days later. CHO-K1 and MRC-5 cells have shown not to be suitable to adequately produce this virus. These results provide further insights into the feasibility of applying microcarrier cell culture technology to produce PPR vaccine in Vero cells as well as in the alternative use of single-cell suspension cultures of BHK-21A, significantly simplifying the existing production process.

Recovery of genetically defined murine norovirus in tissue culture by using a fowlpox virus expressing T7 RNA polymerase

Despite the significant disease burden caused by human norovirus infection, an efficient tissue-culture system for these viruses remains elusive. Murine norovirus (MNV) is an ideal surrogate for the study of norovirus biology, as the virus replicates efficiently in tissue culture and a low-cost animal model is readily available. In this report, a reverse-genetics system for MNV is described, using a fowlpox virus (FWPV) recombinant expressing T7 RNA polymerase to recover genetically defined MNV in tissue culture for the first time. These studies demonstrated that approaches that have proved successful for other members of the family Caliciviridae failed to lead to recovery of MNV. This was due to our observation that vaccinia virus infection had a negative effect on MNV replication. In contrast, FWPV infection had no deleterious effect and allowed the recovery of infectious MNV from cells previously transfected with MNV cDNA constructs. These studies also indicated that the nature of the 3′-terminal nucleotide is critical for efficient virus recovery and that inclusion of a hepatitis delta virus ribozyme at the 3′ end can increase the efficiency with which virus is recovered. This system now allows the recovery of genetically defined noroviruses and will facilitate the analysis of the effects of genetic variation on norovirus pathogenesis.

Reverse genetics for peste-des-petits-ruminants virus (PPRV): Promoter and protein specificities

Peste-des-petits-ruminants virus (PPRV) (family Paramyxoviridae, genus Morbillivirus) causes an acute febrile illness in sheep and goats resulting in significant morbidity and mortality in infected herds. The paramyxoviruses all have negative sense, non-segmented RNA genomes and their host range and pathogenic determinants have been extensively studied using reverse genetics. This technology also enables a more rational approach to be taken with respect to vaccine design. In order to initiate this type of work for PPRV we constructed a PPRV minigenome and studied its expression in transfected cells. As for other morbilliviruses, the minimum requirements for minigenome rescue were shown to be the cis-acting elements of the genome (GP) and antigenome (AGP) promoters as well as the three trans-acting helper proteins N (nucleocapsid), P (phosphoprotein) and L (large polymerase). Homologous PPRV helper proteins were compared to their heterologous analogues from the closely related rinderpest virus (RPV) and heterologous minigenome rescue was found to be a much less efficient process. By engineering two GP/AGP chimeric minigenomes we also identified differences between the two viruses in the specific interactions between the promoters and the transcriptase/replicase complexes. The PPRV minigenome was also shown not to strictly comply with the "rule of six"in vitro.

Host range and receptor utilization of canine distemper virus analyzed by recombinant viruses: Involvement of heparin-like molecule in CDV infection

We constructed recombinant viruses expressing enhanced green fluorescent protein (EGFP) or firefly luciferase from cDNA clones of the canine distemper virus (CDV) (a Japanese field isolate, Yanaka strain). Using these viruses, we examined susceptibilities of different cell lines to CDV infection. The results revealed that the recombinant CDVs can infect a broad range of cell lines. Infectivity inhibition assay using a monoclonal antibody specific to the human SLAM molecule indicated that the infection of B95a cells with these recombinant CDVs is mainly mediated by SLAM but the infection of 293 cell lines with CDV is not, implying the presence of one or more alternative receptors for CDV in non-lymphoid tissue. Infection of 293 cells with the recombinant CDV was inhibited by soluble heparin, and the recombinant virus bound to immobilized heparin. Both F and H proteins of CDV could bind to immobilized heparin. These results suggest that heparin-like molecules are involved in CDV infection.

Rinderpest virus blocks type I and type II interferon action: role of structural and nonstructural proteins

Rinderpest virus (RPV) is a paramyxovirus closely related to the human pathogen Measles virus. It causes severe disease in cattle, buffalo, and some wild animals; although it can infect humans, it does not cause disease. Here, we demonstrate that RPV blocks the action of both type I (alpha) and type II (gamma) interferons (IFNs) by blocking the phosphorylation and nuclear translocation of STAT1 and STAT2 and that this block is not related to species specificity. In addition, both wild-type virulent and vaccine strains of the virus blocked IFN action. Unlike the case with some other paramyxoviruses, neither STAT1 nor STAT2 is degraded upon virus infection. STAT1 is bound by both the viral structural protein P, and thereby recruited to concentrations of viral protein in the cell, and the nonstructural protein V. Although both P and V proteins bind to STAT1 and can block IFN action when expressed in transfected cells, the IFN antagonist activity of the P protein is weaker than that of the V protein. The viral C protein also seems to weakly block IFN-induced activation of STAT1 in transfection experiments. However, studies with knockout viruses showed that the viral V protein appears to be the dominant inhibitor of IFN signaling in the context of virus infection, since prevention of viral V expression restored the IFN sensitivity of infected cells. Although a change in the distribution pattern of STAT2 was observed in virus-infected cells, STAT2 was not bound by any viral protein.

Importance of the extracellular and cytoplasmic/transmembrane domains of the haemagglutinin protein of rinderpest virus for recovery of viable virus from cDNA copies

A specific interaction between the F and H proteins is required to enable fusion of the virus and host cell membranes and in some cases these proteins are not interchangeable between related viruses of the family Paramyxoviridae. For example, the F and H proteins of two ruminant morbilliviruses, rinderpest virus (RPV) and Peste-des-petits-ruminants virus (PPRV), are not interchangeable since viable virus could not be rescued from cDNA constructs where an individual glycoprotein gene of RPV was replaced with that from PPRV. To investigate which domain of the H protein, extracellular or cytoplasmic/transmembrane, was most important for preventing this interaction, two chimeric H gene constructs were made where the normal H gene of RPV was substituted with variant H genes where the transmembrane/cytoplasmic tail region (pRPV2C-PPRTm) or the whole ectodomain (pRPV2C-PPRExt) were derived from PPRV. Chimeric viruses were rescued from both the constructs and, while RPV2C-PPRTm virus grew to as high titres as the parent virus, RPV2C-PPRExt virus was extremely debilitated with respect to growth in tissue culture. Thus the ectodomain of H is the most important region required for effective interactions of the two glycoproteins for the recovery of viable virus. Nevertheless, the transmembrane/cytoplasmic domain of RPV alone can allow a chimeric virus to be rescued, which was not possible when the complete H gene was derived from PPRV. Both versions of the H protein and also the F protein were found to be incorporated into the envelope of the budded virions.

Rational attenuation of a morbillivirus by modulating the activity of the RNA-dependent RNA polymerase

Negative-strand RNA viruses encode a single RNA-dependent RNA polymerase (RdRp) which transcribes and replicates the genome. The open reading frame encoding the RdRp from a virulent wild-type strain of rinderpest virus (RPV) was inserted into an expression plasmid. Sequences encoding enhanced green fluorescent protein (EGFP) were inserted into a variable hinge of the RdRp. The resulting polymerase was autofluorescent, and its activity in the replication/transcription of a synthetic minigenome was reduced. We investigated the potential of using this approach to rationally attenuate a virus by inserting the DNA sequences encoding the modified RdRp into a full-length anti-genome plasmid from which a virulent virus (rRPV(KO)) can be rescued. A recombinant virus, rRPV(KO)L-RRegfpR, which grew at an indistinguishable rate and to an identical titer as rRPV(KO) in vitro, was rescued. Fluorescently tagged polymerase was visible in large cytoplasmic inclusions and beneath the cell membrane. Subcutaneous injection of 10(4) TCID(50) of the rRPV(KO) parental recombinant virus into cattle leads to severe disease symptoms (leukopenia/diarrhea and pyrexia) and death by 9 days postinfection. Animals infected with rRPV(KO)L-RRegfpR exhibited transient leukopenia and mild pyrexia, and the only noticeable clinical signs were moderate reddening of one eye and a slight ocular-nasal discharge. Viruses that expressed the modified polymerase were isolated from peripheral blood lymphocytes and eye swabs. This demonstrates that a virulent morbillivirus can be attenuated in a single step solely by modulating RdRp activity and that there is not necessarily a correlation between virus growth in vitro and in vivo.

Efficient rescue of measles virus from cloned cDNA using SLAM-expressing Chinese hamster ovary cells

We here report a highly efficient reverse genetics system for measles virus (MeV), using Chinese hamster ovary cells constitutively expressing a MeV receptor human signaling lymphocyte activation molecule (CHO/hSLAM cells). The recombinant vaccinia virus vTF7-3 that encodes the T7 RNA polymerase under the control of the early/late promoter was used in the system. Replication of vTF7-3 was highly restricted in CHO/hSLAM cells, but the virus could still drive the T7 promoter, allowing us to recover MeV from the transfected cDNA efficiently. With this system the number of infectious centers, in which MeV replication cycles are initiated from transfected cDNAs, was approximately 100 times higher than that with the previous system (. J. Virol. 74, 6643-6647), and the recovery rate was 100%. The wild-type MeV that encodes the lac-Z gene of approximately 3.2kb in length, was easily generated with this CHO/hSLAM system, while such virus could not be recovered with the previous system. Since SLAM acts as a cellular receptor for both MeV vaccine and wild-type strains, the Edmonston vaccine strain was also recovered with this system more efficiently than with any other systems reported previously. Thus, the CHO/hSLAM-based system would expand applications of the MeV reverse genetics by allowing productions of mutant MeVs that have been difficult to generate with less efficient systems.

Wild-type Rinderpest virus uses SLAM (CD150) as its receptor

Rinderpest virus (RPV) is a morbillivirus, related closely to the human pathogen Measles virus (MV). Although cell culture-adapted strains of RPV can infect many kinds of cell from different hosts, one such strain has previously been shown to have a detectable preference for cells expressing the MV receptor CD150 (SLAM), a protein found only on certain types of activated T cells, B cells and dendritic cells. Here, it is shown that the wild-type, virulent parent of the most common vaccine strain of RPV requires CD150 as a receptor, whilst the cell culture-adapted vaccine strain has acquired the ability to use heparan sulphate as an alternative receptor.

'Rescue' of mini-genomic constructs and viruses by combinations of morbillivirus N, P and L proteins

Chloramphenicol acetyltransferase (CAT)-expressing negative-sense mini-genomic constructs of measles virus (MV) and rinderpest virus (RPV) were rescued by standard technology with helper plasmids expressing the nucleocapsid (N), phospho- (P) and large (L) proteins of MV, canine distemper virus (CDV) or RPV in order to determine whether the proteins of different viruses can function together. Homogeneous sets consisting of N, P and L plasmids derived from one virus were able to generate reporter gene expression from either mini-genomic construct. Heterogeneous sets of proteins from different viruses were not functional, with the exception that a low level of activity was obtained when MV N and P protein were combined with RPV L protein in the rescue of the MV mini-genomic construct, or CDV N was combined with RPV P and L in the rescue of the RPV mini-genome. However, only homogeneous sets of plasmids were able to rescue infectious virus from full-length anti-genome-expressing plasmids.