Vaccine development through terminal deletions of an infectious bursal disease virus protein 2 precursor variant

VP2 is the primary host-protective immunogen of infectious bursal disease virus (IBDV), the agent that causes the highly contiguous infectious bursal disease (IBD). Previous studies have shown that a C-terminal his-tagged 452 amino acid residue VP2 precursor variant (VP2-452H) can form an immunogenic subviral particle (SVP). A set of his-tagged N- and C-terminal VP2-452 deleting mutants (designated as N5-452H, N10-452H, N20-452H, N40-452H, VP2-441H, VP2-437H, VP2-411H and VP2-399H) was expressed in insect cells to discover the role of both N- and C-termini on the assembly of SVP and to develop an efficient SVP-based vaccine. Among these mutants, the expression level of N5-452H was the highest. Results of ultracentrifugation and electron microscopy also indicated that mutants of N-terminal deletion N10-452H, N20-452H and N40-452H or C-terminal deletion VP2-411H and VP2-399H lost the capability to self-assemble SVP. The other mutants, N5-452H, VP2-441H and VP2-437H, formed SVP. Additionally, SVP formed by N5-452H could not only be single-step purified by immobilized metal-ion affinity chromatography (IMAC), but it could also induce a high titer of neutralizing activity to protect chicks from the infection of IBDV at a low dosage (0.2 μg), suggesting that SVP formed by N5-452H can be an alternative vaccine candidate for the prevention of IBD.