No abstract

The use of virus-vectored platforms has increasingly gained attention in vaccine development as a means for delivering antigenic genes of interest into target hosts. Here, we describe a single-cycle influenza virus-based SARS-CoV-2 vaccine designated as scPR8-RBD-M2. The vaccine utilizes the chimeric gene encoding 2A peptide-based bicistronic protein cassette of the SARS-CoV-2 receptor-binding domain (RBD) and influenza matrix 2 (M2) protein. The C-terminus of the RBD was designed to link with the cytoplasmic domain of the influenza virus hemagglutinin (HA) to anchor the RBD on the surface of producing cells and virus envelope. The chimeric RBD-M2 gene was incorporated in place of the HA open-reading frame (ORF) between the 3′ and 5′ UTR of HA gene for the virus rescue in MDCK cells stably expressing HA. The virus was also constructed with the disrupted M2 ORF in segment seven to ensure that M2 from the RBD-M2 was utilized. The chimeric gene was intact and strongly expressed in infected cells upon several passages, suggesting that the antigen was stably maintained in the vaccine candidate. Mice inoculated with scPR8-RBD-M2 via two alternative prime-boost regimens (intranasal-intranasal or intranasal-intramuscular routes) elicited robust mucosal and systemic humoral immune responses and cell-mediated immunity. Notably, we demonstrated that immunized mouse sera exhibited neutralizing activity against pseudotyped viruses bearing SARS-CoV-2 spikes from various variants, albeit with varying potency. Our study warrants further development of a replication-deficient influenza virus as a promising SARS-CoV-2 vaccine candidate.

No abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent for a swine disease affecting the pig industry worldwide. Infection with PRRSV leads to reproductive complications, respiratory illness, and weak immunity to secondary infections. To better control PRRSV infection, novel approaches for generating control measures are critically needed. Here, in vitro Gibson assembly (GA) of viral genomic cDNA fragments was tested for its use as a quick and simple method to recover infectious PRRSV in cell culture. GA involves the activities of T5-exonuclease, Phusion polymerase, and Taq ligase to join overlapping cDNA fragments in an isothermal condition. Four overlapping cDNA fragments covering the entire PRRSV genome and one vector fragment were used to create a plasmid capable of expressing the PRRSV genome. The assembled product was used to transfect a co-culture of 293T and MARC-145 cells. Supernatants from the transfected cells were then passaged onto MARC-145 cells to rescue infectious virus particles. Verification and characterization of the recovered virus confirmed that the GA protocol generated infectious PRRSV that had similar characteristics to the parental virus. This approach was then tested for the generation of a chimeric virus. By replacing one of the four genomic fragments with that of another virus strain, a chimeric virus was successfully recovered via GA. In conclusion, this study describes for the first time the use of GA as a simple, yet powerful tool for generating infectious PRRSV needed for studying PRRSV biology and developing novel vaccines.