Background/objective: Infectious bursal disease (IBD) is an acute and highly contagious immunosuppressive disease in chickens caused by infectious bursal disease virus (IBDV). In recent years, a novel variant IBDV (nVarIBDV) has emerged and spread widely, inducing severe immunosuppression and posing a substantial threat to the poultry industry. More importantly, owing to antigenic variations, nVarIBDV can escape the immune protection of the existing vaccines. Therefore, it is imperative to develop a new vaccine that is antigenically matched to nVarIBDV.

Methods: The major protective antigen gene VP2 of the representative nVarIBDV strain SHG19 was inserted into the eukaryotic expression plasmid pCAGGS to construct the recombinant plasmid pCASHGVP2. Subsequently, pCASHGVP2 was encapsulated in lipid nanoparticles (LNPs) to form pCASHGVP2-LNP nanoparticles. Finally, using the SPF chicken model, the immune efficacy of pCASHGVP2-LNP was preliminarily assessed by administering two vaccine doses (10 and 20 μg) and two immunization regimens (single or double immunization).

Results: Efficient VP2 protein expression from pCASHGVP2 was confirmed by in vitro transfection experiments. The prepared pCASHGVP2-LNP nanoparticles exhibited an optimal particle size distribution and acceptable polydispersity index, indicating a homogeneous formulation. Furthermore, animal experiments showed that the candidate DNA vaccine elicited specific neutralizing antibodies after double immunization and protected immunized chickens from disease induced by nVarIBDV challenge.

Conclusions: This study reports the first development of an LNP-encapsulated VP2 DNA vaccine (pCASHGVP2-LNP) against nVarIBDV, highlighting its potential application for the prevention of nVarIBDV.