Apropos of Universal Epitope Discovery for COVID-19 Vaccines: A Framework for Targeted Phage Display-Based Delivery and Integration of New Evaluation Tools

Targeted bacteriophage (phage) particles are potentially attractive yet inexpensive platforms for immunization. Herein, we describe targeted phage capsid display of an immunogenically relevant epitope of the SARS-CoV-2 Spike protein that is empirically conserved, likely due to the high mutational cost among all variants identified to date. This observation may herald an approach to developing vaccine candidates for broad-spectrum, towards universal, protection against multiple emergent variants of coronavirus that cause COVID-19.

Chimeric virus-like particles of universal antigen epitopes of coronavirus and phage Qβ coat protein trigger the production of neutralizing antibodies

Background: Virus-like particles (VLPs) are non-genetic multimeric nanoparticles synthesized through in vitro or in vivo self-assembly of one or more viral structural proteins. Immunogenicity and safety of VLPs make them ideal candidates for vaccine development and efficient nanocarriers for foreign antigens or adjuvants to activate the immune system. Aims: The present study aimed to design and synthesize a chimeric VLP vaccine of the phage Qbeta (Qβ) coat protein presenting the universal epitope of the coronavirus. Methods: The RNA phage Qβ coat protein was designed and synthesized, denoted as Qbeta. The CoV epitope, a universal epitope of coronavirus, was inserted into the C-terminal of Qbeta using genetic recombination, which was designated as Qbeta-CoV. The N-terminal of Qbeta-CoV was successively inserted into the TEV restriction site using mCherry red fluorescent label and modified affinity-purified histidine label 6xHE, which was denoted as HE-Qbeta-CoV. Isopropyl β-D-1-thiogalactopyranoside (IPTG) assessment revealed the expression of Qbeta, Qbeta-CoV, and HE-Qbeta-CoV in the BL21 (DE3) cells. The fusion protein was purified by salting out using ammonium sulfate and affinity chromatography. The morphology of particles was observed using electron microscopy. The female BALB/C mice were immunized intraperitoneally with the Qbeta-CoV and HE-Qbeta-CoV chimeric VLPs vaccines. Their sera were collected for the detection of antibody level and antibody titer using ELISA. The serum is used for the neutralization test of the three viruses of MHV, PEDV, and PDCoV. Results: The results revealed that the fusion proteins Qbeta, Qbeta-CoV, and HE-Qbeta-CoV could all obtain successful expression. Particles with high purity were obtained after purification; the chimeric particles of Qbeta-CoV and HE-Qbeta-CoV were found to be similar to Qbeta particles in morphology and formed chimeric VLPs. In addition, two chimeric VLP vaccines induced specific antibody responses in mice, and the antibodies showed certain neutralizing activity. Conclusion: The successful construction of the chimeric VLPs of the phage Qβ coat protein presenting the universal epitope of coronavirus provides a vaccine form with potential clinical applications for the treatment of coronavirus disease.

Sequence Analysis of Plum pox virus Strain C Isolates from Russia Revealed Prevalence of the D96E Mutation in the Universal Epitope and Interstrain Recombination Events

The understanding of genetic diversity, geographic distribution, and antigenic properties of Plum pox virus (PPV) is a prerequisite to improve control of sharka, the most detrimental viral disease of stone fruit crops worldwide. Forty new PPV strain C isolates were detected in sour cherry (Prunus cerasus) from three geographically distant (700–1100 km) regions of European Russia. Analysis of their 3’-terminal genomic sequences showed that nineteen isolates (47.5%) bear the D96E mutation in the universal epitope of the coat protein. Almost all of them cannot be detected by the monoclonal antibody 5B in triple antibody sandwich enzyme-linked immunosorbent assayand Western blot analysis that may potentially compromise serological PPV detection in cherries. Full-length genomes of seven PPV-C isolates were determined employing next-generation sequencing. Using the Recombination Detection Program (RDP4), the recombination event covering the region from (Cter)P1 to the middle of the HcPro gene was predicted in all the available PPV-C complete genomes. The isolates Tat-4, belonging to the strain CV, and RU-17sc (PPV-CR) were inferred as major and minor parents, respectively, suggesting possible pathways of evolution of the cherry-adapted strains. Downy cherry (P. tomentosa) was identified as the natural PPV-C host for the first time.