Expression, purification, and characterization of the infectious bursal disease virus-like particles produced by insect cells

The cDNA of the large genomic segment A (ORF A1) of infectious bursal disease virus (IBDV) strain P3009 was synthesized and cloned into the transfer vector pBlueBac4. Following cotransfection and plaque purification, a plaque-pure recombinant baculovirus, vIBDVJ6, was selected to express IBDV capsid proteins. When Sf9 cells were infected with vIBDVJ6, IBDV precursor protein (polypeptide of VP2-VR4-VP3) was expressed and proteolytically processed to give VP2, VP3, and VP4 proteins by a viral protease. These resulting recombinant proteins can self-assemble to form virus-like particles (VLPs). The shape and size of the negatively stained purified IBDV-like particles were demonstrated to be similar to those of the complete P3009 IBDV particles under direct electron microscopic observation. Furthermore, the purified particles were strongly recognized by an anti-VP2 monoclonal antibody as confirmed by an immune-gold labeling experiment. IBDV-like particles will offer a unique opportunity to create completely non-infectious viral vaccines for use in the vaccination of chickens. The immunologic response in chickens stimulated by IBDV-like particles is currently being evaluated.