The Cholera Toxin B Subunit (CTB) Fused to the Porcine Arterivirus Matrix M and GP5 Envelope Proteins Fails to Enhance the GP5-Specific Antibody Response in Pigs Immunized with Adenovectors

Abstract

The porcine reproductive and respiratory syndrome virus (PRRSV) is an arterivirus of the Arteriviridae family. As the current commercial vaccines are incompletely protective effective against PRRSV infection, we developed a vaccine strategy using replicating but non-disseminating adenovectors (rAdVs) expressing the PRRSV M matrix protein in fusion with the neutralizing major epitope-carrying GP5 envelope protein (Roques et al. in Vet Res 44:17, 2013). Although production of GP5-specific antibodies (Abs) was observed, no PRRSV-specific neutralizing Abs (NAbs) were induced in pigs given the rAdVs expressing M-GP5 or M-GP5m (GP5m being a mutant form of GP5). Nevertheless, partial protection was observed in the M-GP5m-rAdV-inoculated pigs experimentally infected with PRRSV. Here, we determined the impact of the cholera toxin B subunit (CTB, known for its adjuvant effect) in fusion with the C-terminus of M-GP5m on the Ab response to PRRSV. Three-week-old pigs were immunized twice both intramuscularly and intranasally at 3-week intervals with rAdV-expressing the green fluorescent protein (rAdV-GFP), rAdV-M-GP5m, or rAdV-M-GP5m-CTB. Pigs immunized with rAdV-M-GP5m showed a high level of serum GP5-specific Abs (as determined by an indirect ELISA). In contrast, CTB in fusion with M-GP5m had an unexpected severe negative impact on GP5-specific Ab production. PRRSV-specific NAbs could not be detected in any pigs of all groups.

Combined Subcutaneous-Intranasal Immunization With Epitope-Based Antigens Elicits Binding and Neutralizing Antibody Responses in Serum and Mucosae Against PRRSV-2 and SARS-CoV-2

“…Tandem repeats of linear B-cell epitopes might augment BCR-crosslinking, B-cell endocytosis, and presentation to CD4 + helper T-cells ( 78 , 79 ). To enhance antibody production, we inserted two MHC-II restricted epitopes in 3BT that could improve CD4 + T-cell help to B cells: T-cell epitope 2, a previously characterized epitope found in the endodomain of GP5 ( 52 ), and Pan DR T helper epitope (PADRE), a universal synthetic epitope which, although designed to bind HLA-DR molecules in humans ( 80 ), it also potentiates humoral responses in pigs ( 81 , 82 ). In this way, our 3BT epitope-based antigen was constituted similarly to a conjugate protein-protein vaccine against the non-immunodominant epitope B of PRRSV-2 ( Supplementary Figure 1A ).…”

Development of a Ferritin Protein Nanoparticle Vaccine with PRRSV GP5 Protein

“…While existing vaccines have shown some effectiveness, there remains a need to develop a safer and more efficient vaccine. Genetically engineered subunit vaccines have garnered significant attention due to their safety profile and ease of production [ 11 , 12 ].…”