Enhancing the immunogenicity of a recombinant PEDV subunit vaccine: the role of lipoprotein signal peptide.

The spike (S) protein of Porcine Epidemic Diarrhea Virus (PEDV) is a major structural glycoprotein responsible for viral attachment and entry, making it a critical target for the development of subunit vaccines. Within the S1 domain, a well-characterized region spanning residues 499–799, commonly referred to as the core neutralizing epitope (COE) the equivalent of the CO-26 K domain, contains multiple predicted B-cell, T-cell, and virus-neutralizing epitopes, making it highly immunogenic. This study investigates whether the incorporation of a bacterial lipoprotein signal peptide into the COE domain can enhance its antigenicity and protective efficacy by inducing lipidation-mediated activation of Toll-like receptor 2 (TLR2). A truncated COE construct was engineered either with a signal peptide (SP-COE) or without one (COE), and evaluated through a combination of in-silico, in vitro, and in vivo analyses. In silico epitope prediction tools identified strong B-cell and T-cell epitope coverage within COE. Molecular docking revealed favorable interactions with immune receptors, and structural modeling demonstrated the construct’s stability. In vitro, HEK-Blue hTLR2 reporter cells revealed that SP-COE elicited significantly higher NF-κB activation compared to COE, confirming effective TLR2 engagement. In vivo, mice immunized with SP-COE displayed significantly elevated total IgG and virus-neutralizing antibody titers, enhanced cytokine responses (e.g., IFN-γ, IL-4), and a stronger CD4⁺ T-cell response relative to the COE group. These findings demonstrate that incorporating a lipoprotein signal peptide improves the immunogenicity and protective potential of the PEDV COE antigen, highlighting its utility as an intrinsic adjuvant in subunit vaccine design.