Development of HiBiT-Tagged Recombinant Infectious Bronchitis Coronavirus for Efficient in vitro and in vivo Viral Quantification

Highly sensitive and quantitative HiBiT-tagged Nipah virus-like particles: A platform for rapid antibody neutralization studies

Biocontainment regulations restrict the research on NiV to BSL-4 laboratories, thus limiting the mechanistic studies related to viral entry and allied pathogenesis. Understanding the precise process of viral-particle production and host cell entry is critical for designing targeted therapies or particle-based vaccines. In this study, we have synthesized HiBiT-tagged-NiV-VLPs to ease in-vitro BSL-2 particle handling. We propose a simple yet effective approach of generating substantial amount of HiBiT-tagged NiV-VLPs in vitro by co-expressing viral structural proteins in HEK293T cells. Though homologous to parent virus, the incapacitated replication potential facilitates a BSL-2 handling of these particles. The inclusion of a highly sensitive HiBiT tag on these VLPs allows for a quick detection of viral binding and entry, as well as in assessing the efficiency of neutralizing antibodies in vitro using the NanoBiT technology. The HiBiT-tag binds in high affinity with LgBiT (Large BiT an 18 kDa fusion protein and complementary subunit of HiBiT peptide), and the resultant complex elicits high intensity luminescence in the presence of substrate. The VLPs produced were morphologically and functionally identical to the native virus, and the HiBiT-tag permitted their quick application in viral binding, entry, and antibody neutralization assays. "Thus, we report a simple setting for generating HiBiT-NiV VLPs which can be utilized in a BSL-2 laboratory, to concurrently quantify features of NiV assembly, binding and entry. This also offers an alternate-safe and effective platform for viral based antibody neutralization assays in vitro".

Integration of HiBiT into enteroviruses: A universal tool for advancing enterovirus virology research

The utilization of enteroviruses engineered with reporter genes serves as a valuable tool for advancing our understanding of enterovirus biology and its applications, enabling the development of effective therapeutic and preventive strategies. In this study, our initial attempts to introduce a NanoLuc luciferase (NLuc) reporter gene into recombinant enteroviruses were unsuccessful in rescuing viable progenies. We hypothesized that the size of the inserted tag might be a determining factor in the rescue of the virus. Therefore, we inserted the 11-amino-acid HiBiT tag into the genomes of enterovirus A71 (EV-A71), coxsackievirus A10 (CVA10), coxsackievirus A7 (CVA7), coxsackievirus A16 (CVA16), namely EV-A71-HiBiT, CVA16-HiBiT, CVA10-HiBiT, CVA7-HiBiT, and observed that the HiBiT-tagged viruses exhibited remarkably high rescue efficiency. Notably, the HiBiT-tagged enteroviruses displayed comparable characteristics to the wild-type viruses. A direct comparison between CVA16-NLuc and CVA16-HiBiT recombinant viruses revealed that the tiny HiBiT insertion had minimal impact on virus infectivity and replication kinetics. Moreover, these HiBiT-tagged enteroviruses demonstrated high genetic stability in different cell lines over multiple passages. In addition, the HiBiT-tagged viruses were successfully tested in antiviral drug assays, and the sensitivity of the viruses to drugs was not affected by the HiBiT tag. Ultimately, our findings provide definitive evidence that the integration of HiBiT into enteroviruses presents a universal, convenient, and invaluable method for advancing research in the realm of enterovirus virology. Furthermore, HiBiT-tagged enteroviruses exhibit great potential for diverse applications, including the development of antivirals and the elucidation of viral infection mechanisms.

A New Derivative of Retro-2 Displays Antiviral Activity against Respiratory Syncytial Virus

Human respiratory syncytial virus (hRSV) is the most common cause of bronchiolitis and pneumonia in newborns, with all children being infected before the age of two. Reinfections are very common throughout life and can cause severe respiratory infections in the elderly and immunocompromised adults. Although vaccines and preventive antibodies have recently been licensed for use in specific subpopulations of patients, there is still no therapeutic treatment commonly available for these infections. Here, we investigated the potential antiviral activity of Retro-2.2, a derivative of the cellular retrograde transport inhibitor Retro-2, against hRSV. We show that Retro-2.2 inhibits hRSV replication in cell culture and impairs the ability of hRSV to form syncytia. Our results suggest that Retro-2.2 treatment affects virus spread by disrupting the trafficking of the viral de novo synthetized F and G glycoproteins to the plasma membrane, leading to a defect in virion morphogenesis. Taken together, our data show that targeting intracellular transport may be an effective strategy against hRSV infection.

Development of a HiBiT-tagged reporter hepatitis E virus and its utility as an antiviral drug screening platform

Previously, we developed an infectious hepatitis E virus (HEV) harboring the nanoKAZ gene in the hypervariable region of the open reading frame 1 (ORF1) of the HEV3b (JE03-1760F/P10) genome and demonstrated the usefulness for screening anti-HEV drugs that inhibit the early infection process. In the present study, we constructed another reporter HEV (HEV3b-HiBiT) by placing a minimized HiBiT tag derived from NanoLuc luciferase at the 3'-end of the viral capsid (ORF2) coding sequence. It replicated efficiently in PLC/PRF/5 cells, produced membrane-associated particles identical to those of the parental virus, and was genetically stable and infectious. The HiBiT tag was fused to both secreted ORF2s (ORF2s-HiBiT) and ORF2c capsid protein (ORF2c-HiBiT). The ORF2c-HiBiT formed membrane-associated HEV particles (eHEV3b-HiBiT). By treating these particles with digitonin, we demonstrated that the HiBiT tag was expressed on the surface of capsid and was present inside the lipid membrane. To simplify the measurement of luciferase activity and provide a more convenient screening platform, we constructed an ORF2s-defective mutant (HEV3b-HiBiT/ΔORF2s) in which the secreted ORF2s are suppressed. We used this system to evaluate the effects of introducing small interfering RNAs and treatment with an inhibitor or accelerator of exosomal release on HEV egress and demonstrated that the effects on virus release can readily be analyzed. Therefore, HEV3b-HiBiT and HEV3b-HiBiT/ΔORF2s reporters may be useful for investigating the virus life cycle and can serve as a more convenient screening platform to search for candidate drugs targeting the late stage of HEV infection such as particle formation and release. IMPORTANCE The construction of recombinant infectious viruses harboring a stable luminescence reporter gene is essential for investigations of the viral life cycle, such as viral replication and pathogenesis, and the development of novel antiviral drugs. However, it is difficult to maintain the stability of a large foreign gene inserted into the viral genome. In the present study, we successfully generated a recombinant HEV harboring the 11-amino acid HiBiT tag in the ORF2 coding region and demonstrated the infectivity, efficient virus growth, particle morphology, and genetic stability, suggesting that this recombinant HEV is useful for in vitro assays. Furthermore, this system can serve as a more convenient screening platform for anti-HEV drugs. Thus, an infectious recombinant HEV is a powerful approach not only for elucidating the molecular mechanisms of the viral life cycle but also for the screening and development of novel antiviral agents.

Surface decorated reporter-tagged chikungunya virus-like particles for clinical diagnostics and identification of virus entry inhibitors

The ever-evolving and versatile VLP technology is becoming an increasingly popular area of science. This study presents surface decorated reporter-tagged VLPs of CHIKV, an enveloped RNA virus of the genus alphavirus and its applications. Western blot, IFA and live-cell imaging confirm the expression of reporter-tagged CHIK-VLPs from transfected HEK293Ts. CryoEM micrographs reveal particle diameter as ∼67nm and 56-70 nm, respectively, for NLuc CHIK-VLPs and mCherry CHIK-VLPs. Our study demonstrates that by exploiting NLuc CHIK-VLPs as a detector probe, robust ratiometric luminescence signal in CHIKV-positive sera compared to healthy controls can be achieved swiftly. Moreover, the potential activity of the Suramin drug as a CHIKV entry inhibitor has been validated through the reporter-tagged CHIK-VLPs. The results reported in this study open new avenues in the eVLPs domain and offer potential for large-scale screening of clinical samples and antiviral agents targeting entry of CHIKV and other alphaviruses.

Establishment and Cross-Protection Efficacy of a Recombinant Avian Gammacoronavirus Infectious Bronchitis Virus Harboring a Chimeric S1 Subunit

Infectious bronchitis virus (IBV) is a gammacoronavirus that causes a highly contagious disease in chickens and seriously endangers the poultry industry. A diversity of serotypes and genotypes of IBV have been identified worldwide, and the currently available vaccines do not cross-protect. In the present study, an efficient reverse genetics technology based on Beaudette-p65 has been used to construct a recombinant IBV, rIBV-Beaudette-KC(S1), by replacing the nucleotides 21,704–22,411 with the corresponding sequence from an isolate of QX-like genotype KC strain. Continuous passage of this recombinant virus in chicken embryos resulted in the accumulation of two point mutations (G21556C and C22077T) in the S1 region. Further studies showed that the T248S (G21556C) substitution may be essential for the adaptation of the recombinant virus to cell culture. Immunization of chicks with the recombinant IBV elicited strong antibody responses and showed high cross-protection against challenges with virulent M41 and a QX-like genotype IBV. This study reveals the potential of developing rIBV-Beau-KC(S1) as a cell-based vaccine with a broad protective immunity against two different genotypes of IBV.

Detecting SARS-CoV-2 neutralizing immunity: highlighting the potential of split nanoluciferase technology

The coronavirus disease 2019 (COVID-19) pandemic has progressed over 2 years since its onset causing significant health concerns all over the world and is currently curtailed by mass vaccination. Immunity acquired against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be following either infection or vaccination. However, one can never be sure whether the acquired immunity is adequate to protect the individual from subsequent infection because of three important factors: individual variations in humoral response dynamics, waning of protective antibodies over time, and the emergence of immune escape mutants. Therefore, a test that can accurately differentiate the protected from the vulnerable is the need of the hour. The plaque reduction neutralization assay is the conventional gold standard test for estimating the titers of neutralizing antibodies that confer protection. However, it has got several drawbacks, which hinder the practical application of this test for wide-scale usage. Hence, various tests have been developed to detect protective immunity against SARS-CoV-2 that directly or indirectly assess the presence of neutralizing antibodies to SARS-CoV-2 in a lower biosafety setting. In this review, the pros and cons of the currently available assays are elaborated in detail and special focus is put on the scope of the novel split nanoluciferase technology for detecting SARS-CoV-2 neutralizing antibodies.

The NanoBiT-Based Homogenous Ligand-Receptor Binding Assay

NanoLuc Binary Technology (NanoBiT) was recently developed by Promega, based on a large NanoLuc fragment (LgBiT) and two small complementation tags, the low-affinity SmBiT tag and the high-affinity HiBiT tag. In recent studies, we applied NanoBiT to ligand-binding assays of some G protein-coupled receptors via genetic fusion of a secretory LgBiT (sLgBiT) to the extracellular N-terminus of the receptors and covalent attachment of the low-affinity SmBiT tag to an appropriate position of their peptide ligands. The NanoBiT-based homogenous ligand-receptor binding assay is convenient for use and suitable for both the wild-type and mutant receptors, representing a novel tool for interaction mechanism studies of these receptors with their ligands. In the present chapter, we provide detailed protocols for setting up the NanoBiT-based homogenous binding assay using growth hormone secretagogue receptor type 1a (GHSR1a) and its endogenous agonist and antagonist as a representative model system.

Assembly and Entry of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV2): Evaluation Using Virus-Like Particles

Research on infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) is currently restricted to BSL-3 laboratories. SARS-CoV2 virus-like particles (VLPs) offer a BSL-1, replication-incompetent system that can be used to evaluate virus assembly and virus-cell entry processes in tractable cell culture conditions. Here, we describe a SARS-CoV2 VLP system that utilizes nanoluciferase (Nluc) fragment complementation to track assembly and entry. We utilized the system in two ways. Firstly, we investigated the requirements for VLP assembly. VLPs were produced by concomitant synthesis of three viral membrane proteins, spike (S), envelope (E), and matrix (M), along with the cytoplasmic nucleocapsid (N). We discovered that VLP production and secretion were highly dependent on N proteins. N proteins from related betacoronaviruses variably substituted for the homologous SARS-CoV2 N, and chimeric betacoronavirus N proteins effectively supported VLP production if they contained SARS-CoV2 N carboxy-terminal domains (CTD). This established the CTDs as critical features of virus particle assembly. Secondly, we utilized the system by investigating virus-cell entry. VLPs were produced with Nluc peptide fragments appended to E, M, or N proteins, with each subsequently inoculated into target cells expressing complementary Nluc fragments. Complementation into functional Nluc was used to assess virus-cell entry. We discovered that each of the VLPs were effective at monitoring virus-cell entry, to various extents, in ways that depended on host cell susceptibility factors. Overall, we have developed and utilized a VLP system that has proven useful in identifying SARS-CoV2 assembly and entry features.