A novel albumin-based nanoparticle vaccine including the globular knob domain of the egg drop syndrome virus fiber protein for egg drop syndrome: Immunogenicity and preliminary structural analyses.

Egg drop syndrome (EDS), caused by the avian adenovirus known as EDS virus (EDSV), is a viral disease characterized by reduced egg production and abnormal egg quality in laying hens, resulting in substantial economic losses. While conventional vaccines can have some safety issues, the subunit vaccines circumvent these concerns. The globular knob domain of the EDSV fiber protein (EDSVFP) harbors critical neutralizing epitopes, making it an ideal vaccine target. In this study, chicken serum albumin nanoparticles (CSA-NPs) were employed as a delivery vehicle. The coding sequence for the knob domain and part of the shaft region of the EDSVFP was codon-optimized, cloned into the pET-28a vector, and expressed in Escherichia coli. The recombinant fiber protein (RFP) was purified, and the nanostructure was constructed by conjugating the purified RFP to CSA-NPs (CSA-NPs-RFP). Some structural features of the CSA-NPs and CSA-NPs-RFP were studied using dynamic light scattering and spectroscopic techniques. Immunogenicity was then evaluated by vaccinating laying hens and measuring antibody titers at 4- and 8-weeks post-vaccination using enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition tests. We found that the RFP achieved a high soluble expression yield of 127 mg/L after purification; nanoparticles were successfully prepared and exhibited favorable structural stability; and the CSA-NPs-RFP elicited significantly higher antibody titers compared to non-conjugated antigen formulations. Challenge experiments confirmed solid protection against viral infection for at least eight weeks post-immunization. These findings suggest that CSA-NPs-RFP could be a promising option for a subunit vaccine against EDS, considering its structural stability, immunogenicity, and protective effects.