Recombinant B87 and HLJ0504 VP2 Vaccines Protect Chickens Against Infectious Bursal Disease

Infectious bursal disease virus (IBDV) causes immunosuppression and bursal damage in chickens, and safer recombinant vaccines that provide durable protection are needed. This study compared the antigenicity, immunogenicity, protective efficacy, safety and antibody persistence of unpurified VP2 preparations and purified VP2 virus-like particles (VLPs) derived from the B87 and HLJ0504 IBDV strains. Recombinant VP2 proteins were expressed in Escherichia coli, purified and characterized, formulated with oil adjuvant and evaluated in specific-pathogen-free White Leghorn chickens. Both VP2 proteins retained antigenicity and assembled into relatively uniform VLPs of approximately 25 nm. Purified VLPs induced stronger antibody responses than corresponding unpurified preparations, with 10 µg producing the highest responses. In a virus neutralization assay, HLJ0504 VP2-based preparations induced the highest neutralizing-antibody titers. Following challenge with virulent IBDV BC6/85, 10 µg of HLJ0504 VLPs and unpurified HLJ0504 VP2 at an agar-gel precipitation titer of 1:10 each protected nine of 10 chickens, similar to a commercial inactivated vaccine, and preserved bursal architecture. No systemic or injection-site adverse reactions were detected and selected recombinant vaccines maintained elevated serum-antibody levels for 20 weeks. Thus, HLJ0504 VP2-based vaccines, particularly the VLPs formulation, are promising safe and protective candidates for controlling infectious bursal disease.