Application of the ligation-independent cloning (LIC) method for rapid construction of a minigenome rescue system for Newcastle disease virus VG/GA strain

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.

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.

Engineered protein cages with enhanced extracellular drug release for elevated antitumor efficacy

Human heavy chain ferritin (HFn) protein cage has been explored as a nanocarrier for targeted anticancer drug delivery. Here, we introduced a matrix metalloproteinases (MMPs)-cleavable sequence into the DE loop of HFn, creating an MMP-responsive variant, MR-HFn, for localized and extracellular drug release. The crystal structure of MR-HFn revealed that the addition of the MMPs recognition sequence did not affect the self-assembly of HFn but presented a surface-exposed loop susceptible to MMPs cleavage. Biochemical analysis indicated that this engineered protein cage is responsive to MMPs, enabling the targeted release of encapsulated drugs. To evaluate the therapeutic potential of this engineered protein cage, monosubstituted β-carboxy phthalocyanine zinc (CPZ), a type of photosensitizer, was loaded inside this protein cage. The prepared CPZ@MR-HFn showed higher uptake and stronger phototoxicity in MMPs overexpressed tumor cells, as well as enhanced penetration into multicellular tumor spheroids compared with its counterpart CPZ@HFn in vitro. In vivo, CPZ@MR-HFn displayed a higher tumor inhibitory rate than CPZ@HFn under illumination. These results indicated that MR-HFn is a promising nanocarrier for anticancer drug delivery and the MMP-responsive strategy here can also be adapted for other stimuli.

Rapid construction of infectious clones for distinct Newcastle disease virus genotypes

The reverse genetics system of the Newcastle disease virus (NDV) has provided investigators with a powerful approach to understand viral molecular biology and vaccine development. It has been impressively improved with modified strategies since its first report, but it still poses some challenges. Most noteworthy, the genome complexity and length made full-length error-free cDNA assembly the most challenging and time-consuming step of NDV rescue. In the present study, we report a rapid full-length NDV genome construction with only a two-step ligation-independent cloning (LIC) strategy, which could be applied to distinct genotypes. In this approach, the genome of NDV was divided into two segments, and the cDNA clones were generated by RT-PCR followed by LIC. Subsequently, the infectious NDVs were rescued by co-transfection of the full-length cDNA clones and supporting plasmids expressing the NP, P, and L proteins of NDV in BHK-21 cells. Compared with the conventional cloning approaches, the two-step cloning method drastically reduced the number of cloning steps and saved researchers a substantial amount of time for constructing NDV infectious clones, thus enabling a rapid rescue of different genotypes of NDVs in a matter of weeks. Therefore, this two-step LIC cloning strategy may have an application to the rapid development of NDV-vectored vaccines against emerging animal diseases and the generation of different genotypes of recombinant NDVs for cancer therapy.

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.

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.

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

Within paramyxoviruses, conventional reverse genetics require the transfection of a minimum of four plasmids: three to reconstruct the viral polymerase complex that replicates and expresses the virus genome delivered by a fourth plasmid. The successful transfection of four or more plasmids of different sizes into one cell and the subsequent generation of at least one viable and replicable viral particle is a rare event, which explains the low rescue efficiency, especially of low virulent viruses with reduced replication efficiency in cell lines. In this study, we report on an improved reverse genetics system developed for an avian paramyxovirus, Newcastle Disease Virus (NDV), in which the number of plasmids was reduced from four to two. Compared to the conventional method, the 2-plasmid system enables earlier and increased production of rescued viruses and, in addition, makes it possible to rescue viruses that it was not possible to rescue using the 4-plasmid system.

Rescue of recombinant Newcastle disease virus: current cloning strategies and RNA polymerase provision systems

Since the first rescue of a recombinant Newcastle disease virus (rNDV) in the late 1990s, many more rNDVs have been rescued by researchers around the world. Regardless of methodology, the main principle behind rescue of the virus has remained the same, i.e., the formation of a functional replication complex by simultaneously providing the full-length viral RNA and the viral NP, P and L proteins. However, different strategies have been reported for the insertion of the full-length genome into a suitable transcription vector, which remains the most challenging step of the rescue. Moreover, several systems have been published for provision of the DNA-dependent RNA polymerase, which is needed for transcription of viral RNA (vRNA) from the transfected plasmid DNA. The aim of this article is to consolidate all of the current cDNA assembly strategies and transcription systems used in rescue of rNDV in order to attain a better understanding of the advantages and disadvantages of each approach.