ACTIVE CROSS-PROTECTION INDUCED BY A RECOMBINANT BACULOVIRUS EXPRESSING CHIMERIC INFECTIOUS BURSAL DISEASE VIRUS STRUCTURAL PROTEINS

The VP2 structural gene encoded in the large genomic segment A of the variant GLS strain of infectious bursal disease virus (IBDV) was modif ied to encode a neutralization epitope (B69), found only on classic st rains of IBDV. A chimeric cDNA clone of the large segment A, encoding VP3, VP4, and the modified variant IBDV VP2 structural proteins, was e xpressed in a recombinant baculovirus. The chimeric protein expressed was assessed with a panel of neutralizing monoclonal antibodies (MAbs) , and it contained not only all previously MAb-defined GLS variant str ain epitopes but also the B69 neutralization epitope found on classic IBDV strains. Complete active protection was afforded to specific-path ogen-free chickens by a subunit chimeric vaccine against virulent chal lenge with the classic IM and STC strains, as well as against the vari ant E/Del and GLS IBDV strains. Compared with a previously tested reco mbinant subunit vaccine, which incorporated unmodified baculovirus-exp ressed large-segment A GLS proteins, the recombinant chimeric subunit vaccine resulted in markedly improved active cross-protection against classic IBDV challenge.