Optimized conditions for preserving stability and integrity of porcine circovirus type2 virus-like particles during long-term storage

Using the Sleeping Beauty (SB) Transposon to Generate Stable Cells Producing Enveloped Virus-Like Particles (eVLPs) Pseudotyped with SARS-CoV-2 Proteins for Vaccination

The Sleeping Beauty (SB) transposon system is an efficient non-viral tool for gene transfer into a variety of cells, including human cells. Through a cut-and-paste mechanism, your favorite gene (YFG) is integrated into AT-rich regions within the genome, providing stable long-term expression of the transfected gene. The SB system is evolving and has become a powerful tool for gene therapy. There are no safety concerns using this system, the handling is easy, and the time required to obtain a stable cell line is significantly reduced compared to other systems currently available. Here, we present a novel application of this system to generate, within 8 days, a stable producer HEK293T cell line capable of constitutively delivering enveloped virus-like particles (eVLPs) for vaccination. We provide step-by-step protocols for generation of the SB transposon constructs, transfection procedures, and validation of the produced eVLPs. We next describe a method to pseudotype the constitutively produced eVLPs using the Spike protein derived from the SARS-CoV-2 virus (by coating the eVLP capsid with the heterologous antigen). We also describe optimization methods to scale up the production of pseudotyped eVLPs in a laboratory setting (from 100 µg to 5 mg). © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Generation of the SB plasmids Basic Protocol 2: Generation of a stable HEK293T cell line constitutively secreting MLV-based eVLPs Basic Protocol 3: Evaluation of the SB constructs by immunofluorescence assay Basic Protocol 4: Validation of eVLPs by denaturing PAGE and western blot Alternate Protocol 1: Analysis of SARS-CoV-2 Spike protein oligomerization using blue native gel electrophoresis and western blot Alternate Protocol 2: Evaluation of eVLP quality by electron microscopy (negative staining) Basic Protocol 5: Small-scale production of eVLPs Alternate Protocol 3: Large-scale production of eVLPs (up to about 1 to 3 mg VLPs) Alternate Protocol 4: Large-scale production of eVLPs (up to about 3 to 5 mg VLPs) Support Protocol: Quantification of total protein concentration by Bradford assay.

Targeted Delivery of Nanovaccine to Dendritic Cells via DC-Binding Peptides Induces Potent Antiviral Immunity in vivo

Background

Methods

Results

Conclusion

Self-Assembling Nanovaccine Enhances Protective Efficacy Against CSFV in Pigs

Classical swine fever virus (CSFV) is a highly contagious pathogen, which pose continuous threat to the swine industry. Though most attenuated vaccines are effective, they fail to serologically distinguish between infected and vaccinated animals, hindering CSFV eradication. Beneficially, nanoparticles (NPs)-based vaccines resemble natural viruses in size and antigen structure, and offer an alternative tool to circumvent these limitations. Using self-assembling NPs as multimerization platforms provides a safe and immunogenic tool against infectious diseases. This study presented a novel strategy to display CSFV E2 glycoprotein on the surface of genetically engineered self-assembling NPs. Eukaryotic E2-fused protein (SP-E2-mi3) could self-assemble into uniform NPs as indicated in transmission electron microscope (TEM) and dynamic light scattering (DLS). SP-E2-mi3 NPs showed high stability at room temperature. This NP-based immunization resulted in enhanced antigen uptake and up-regulated production of immunostimulatory cytokines in antigen presenting cells (APCs). Moreover, the protective efficacy of SP-E2-mi3 NPs was evaluated in pigs. SP-E2-mi3 NPs significantly improved both humoral and cellular immunity, especially as indicated by the elevated CSFV-specific IFN-γ cellular immunity and >10-fold neutralizing antibodies as compared to monomeric E2. These observations were consistent to in vivo protection against CSFV lethal virus challenge in prime-boost immunization schedule. Further results revealed single dose of 10 μg of SP-E2-mi3 NPs provided considerable clinical protection against lethal virus challenge. In conclusion, these findings demonstrated that this NP-based technology has potential to enhance the potency of subunit vaccine, paving ways for nanovaccine development.

Characterization of the nuclear localization sequence of beak and feather disease virus capsid proteins and their assembly into virus-like particles

Beak and feather disease virus (BFDV) is a single-stranded circular DNA icosahedral virus that belongs to the Circoviridae family. This virus is the causative pathogen of beak and feather disease, which leads to feather loss, malformed claws, and immunosuppression of psittacine birds. Our study produced BFDV virus-like particles (VLPs) including capsid proteins, mutant Cap proteins (Cap ΔNLS₅₄, Cap ΔNLS₆₂, Cap C₂₂₈S, and Cap ΔNES) and chimeric Cap proteins carrying the epitope (amino acid residues 64-70) of the replication-associated protein (R-Cap, Cap-R, R-Cap ΔNLS₅₄, and Cap ΔNLS₅₄-R). All of the aforementioned VLPs were observed via transmission electron microscopy and verified through immunogold labeling. The nuclear localization sequence (NLS) of the Cap protein was identified between amino acid residues 55-62. Nuclear export of the Cap protein depended on the nuclear export sequence (NES). All VLPs except Cap ΔNLS₆₂ and Cap ΔNES entered the cells 2 h post-infection (hpi) and were shuttled into the nucleus at 8 hpi. Wheat germ agglutinin (WGA) blocked the nuclear entry of Cap proteins at 8 hpi and the nuclear export of Cap proteins at 16 hpi was inhibited by leptomycin B. The nuclear entry of Cap protein was inhibited by importin α and importin β inhibitors, as well as NLS peptides. Moreover, the interactions of Cap proteins and Cap VLPs with both importin α and importin β were characterized via the GST pull-down and immunofluorescence assays. These interactions were blocked by the presence of importin α and importin β inhibitors, as well as NLS peptides. Therefore, our study is the first to describe the precise position of the NLS of the BFDV Cap protein and the interaction of Cap protein with importin α and importin β in vitro.

Incorporation of a truncated form of flagellin (TFlg) into porcine circovirus type 2 virus-like particles enhances immune responses in mice

Background

Porcine circovirus type 2 (PCV2) is an economically important pathogen in the swine industry worldwide. Vaccination remains the principal tool to control PCV2-associated diseases (PCVADs). Current vaccines do not eliminate viral shedding in the environment. To enhance the efficacy of PCV2 vaccines, recombinant virus-like particles (VLPs) of PCV2 were generated by fusing a truncated form of flagellin FliC (TFlg: 85-111aa) with the PCV2 capsid protein (Cap).

Results

The recombinant proteins were expressed in Escherichia coli and detected using Western blotting. The abilities of the recombinant proteins to assemble into VLPs were observed under transmission electron microscopy (TEM). The protective immune responses of recombinant VLPs were further evaluated by immunization of mice. The results showed that insertion of TFlg into C terminal of the Cap protein did not affect the formation of VLPs and boosted both humoral and cellular immune responses in mice. After a challenge with PCV2, in the Cap-TFlg vaccinated group, viremia was milder and viral loads were lower as compared with those in the Cap vaccinated group.

Conclusion

These results suggest that recombinant VLPs of PCV2 containing a TFlg adjuvant can be used as a promising PCV2 vaccine candidate.

Trehalose significantly enhances the recovery of serum and serum exosomal miRNA from a paper-based matrix

The preservation of nucleic acids from clinical samples is critical to facilitate accurate molecular diagnosis. The use of a paper matrix, Flinders Technology Associates (FTA) Elute cards, to archive DNA and viral RNA is well-documented. However, the feasibility of FTA Elute cards for archiving serum and serum exosomal microRNAs (miRNAs) remains unclear. Here, we performed a comprehensive evaluation of FTA Elute cards for miRNA storage and recovery in different pre-analytical conditions. The recovery of serum miRNA dry-spotted on FTA Elute cards by direct elution with water at high temperature was poor. However, serum miRNAs dry-spotted on the cards were isolated with about 40% yield when using QIAzol lysis reagent and recovery was improved remarkably (>80%) upon extraction from cards pre-treated with trehalose. miRNAs stored on the cards remained stable at room temperature and can be kept for prolonged periods. Furthermore, miRNAs could be similarly recovered from serum exosomes dry-spotted on the cards. Importantly, when using sera from gastric cancer (GC) patients, the miRNAs were efficiently recovered from trehalose pre-treated cards without affecting their representation. Collectively, we have demonstrated the potential of FTA Elute cards to archive serum and serum exosomal miRNAs, making it useful for biomarker discovery and diagnostics.